- Email: [email protected]
The CIS Family: Negative Regulators of JAK–STAT Signaling
Cytokine + Growth Factor Reviews Vol[ 8\ No[ 2:3\ pp[ 086Ð193\ 0887 Þ 0887 Elsevier Science Ltd[ All rights reserved
PII] S0248Ð5090"87#99908Ð6
Printed in Great Britain 0248!5090:87 ,08[99¦9[99
MINI REVIEW
The CIS Family: Negative Regulators of JAK–STAT Signaling
Akihiko Yoshimura* A family of cytokine!inducible SH1 proteins "CISs# has recently been identi_ed and the members are growing in number[ In this family\ the central SH1 domain and approximately 39 amino acids at the C!terminus "CIS homology domain^ CH domain# are well conserved\ while the N!terminal region shares little similarity and varies in length[ Most CISs appear to be induced by several cytokines and at least three of them "CIS0\ CIS2 and JAB# negatively regulate cytokine signal transduction[ Forced expression of CIS0 inhibits STAT4 activation by binding of CIS0 to cytokine receptors\ and CIS2 and JAB directly bind to the kinase domain of JAKs\ thereby inhibiting kinase activity[ Therefore\ these CIS family members seem to be present in a classical negative feedback loop of cytokine signaling[ They may also play a role in the mutual suppression of cytokine actions frequently found in immune and in~ammatory responses[ Precise molecular mechanisms of the signal inhibition and their physiological functions will be addressed in the near future[ The CH domain is also found in several interesting genes containing WD!39 repeats\ SPRY domains\ ankyrin repeats\ and GTPases[ However\ the function of the CH domain remains to be determined[ Þ 0887 Elsevier Science Ltd[ All rights reserved[
Key words] Cytokine = JAK = STAT = SH1 domain = regulation[
Growth and di}erentiation of immune and hemato! poietic cells are controlled by multiple cytokines includ! ing interleukins "ILs# and colony stimulating factors[ Although lacking catalytic domains\ growth and di}er! entiation of immune and hematopoietic cells are con! trolled by multiple cytokines including interleukins "ILs# and colony stimulating factors[ Although lacking cata! lytic domains\ members of the cytokine receptor super! family mediate the ligand!dependent activation of protein tyrosine phosphorylation through their association and activation of protein tyrosine phosphorylation through their association and activation of members of the Janus kinase "JAK# family of protein tyrosine kinases ð0\ 1Ł[ Cytokines induce homo!dimerization and activation of their cognate receptors\ resulting in the activation of associated JAK kinases "JAK0\ JAK1\ JAK2 and Tyk1#[ The activated JAKs phosphorylate the receptor cyto! plasmic domains which create docking sites for SH1! containing signaling proteins[ Members of the signal
Institute of Life Science\ Kurume University\ Aikawamachi 1321!2 Kurume 728!9750\ Japan[ Tel[] ¦70 831 26 5202^ fax^ ¦70 831 20 4101^ e!mail^ yosimuraÝIsi[kurume!u[ac[jp
transducers and activators of the transcription "STATs# family are among the substrates for tyrosine phos! phorylation ð2\ 3Ł[ Although this pathway was found initially to be activated by interferons "IFNs#\ it is now known that a large number of cytokines\ growth factors\ and hormonal factors activate JAK and:or STAT proteins[ Various cytokines induce the tyrosine phos! phorylation and activation of one or more of the seven STAT family members[ The role of various STATs in the biological responses to cytokines has been assessed through the analysis of receptor mutations which disrupt STAT activation\ and more recently by disrupting genes in mice[ For example\ mice in which the genes for STAT0\ STAT3 and STAT5 are disrupted are viable but lack functions that are mediated by IFNs\ interleukin 01 "IL! 01# or IL!3\ respectively ð4Ð8Ł[ this suggests that these STATs perform very speci_c functions in immune responses[ In contrast\ two highly related STAT4a and STAT4b are activated by members of the various cyto! kines\ including growth hormone "GH#\ prolactin "PRL#\ erythropoietin "EPO#\ IL!1\ IL!2\ granulocyte!mac! rophage!colony stimulating factor "GM!CSF#\ and thrombopoietin "TPO#[ Phenotypes of STAT4a and STAT4b single gene knockout mice as well as double
086
087
A[ Yoshimura
knockout mice revealed an important role of STAT4s in PRL and GH signaling as well as in IL!1 dependent T! cell functions ð09Ð02Ł[ REGULATION OF JAK/STAT SIGNALING Over the years\ the majority of investigations on cyto! kines have focused on the mechanisms by which they exert their actions[ However\ it is clear that the actions of cytokines are limited in both magnitude and duration\ making it important to understand the mechanisms by which their actions are negatively controlled[ Moreover\ the down!modulation of one cytokine action by several factors including another cytokine is often found in important physiological circumstances[ For example\ Th0 and Th1 cytokines suppress each other ð03Ł[ cAMP\ calcium ionophore\ and GM!CSF have been shown to inhibit JAK0ÐSTAT0 or STAT2 pathways ð04Ł\ although the molecular basis of such modulation has not been well characterized[ Degradation of STATs and receptors should be involved in regulation of signaling ð05\ 06Ł[ Naturally occurring dominant negative variants of STAT4 have also been reported ð07\ 08Ł[ Tyrosine phos! phatases containing SH1 domain also regulate cytokine signaling\ both positively and negatively[ One of them\ SHP!0 "HCP#\ has shown to be a negative regulator of JAK kinases and implicated in familial erythrocytosis "familial polycythemia# inherited as an autosomal domi! nant trait ð19Ł[ In this disease\ the disruption of SHP!0 binding sites of the EPO receptor resulted in prolonged activation "phosphorylation# of JAK1 ð10Ł[ Recently\ a new family of cytokine!inducible SH1 proteins "CISs# that\ in turn\ inhibit the cytokine action has been observed with keen interest[ Some of the members have been shown to be involved in negative regulation of cyto! kine signals\ especially JAKs and STATs[ CIS; PROTOTYPE OF CYTOKINE-INDUCED SH2 PROTEINS The _rst member of this family was denoted as CIS "now called CIS0#\ for cytokine!induced SH1 containing protein ð11\ 12Ł[ CIS0 was cloned originally as an immedi! ate early gene that was induced by IL!1\ IL!2\ and EPO[ CIS0 was found to be associated with the tyrosine phos! phorylated EPO receptor and the ILs!2 receptor b chain following stimulation with EPO or IL!2\ respectively ð11Ł[ Recently\ we also found that CIS0 binds to the PRL receptor and IL1 receptor b chain "Doppeler et al[\ and Javad Aman et al[] manuscript in preparation#[ From a functional perspective\ it was noted that the forced expression of CIS0 could partially suppress IL!2!induced proliferation\ although the mechanism of action for CIS0 was unclear ð11Ł[ One possibility is that CIS0 is an adaptor protein "between cytokine receptors and other molecules involved in growth inhibition# based on the presence of an SH1 domain in the central portion of the molecule and both N! and C!terminal regions that are rich in proline and leucines\ residues that can be involved in
mediating protein!protein interactions[ Alternatively\ it was also suggested that CIS0 might function by directly blocking phosphotyrosine motifs on receptors\ pre! venting their coupling to stimulatory signaling pathways ð11Ł[ Finally\ given that CIS0 was observed to have a relatively short half life\ the third potential role that was suggested was that CIS0 might be a scavenger of tyrosine phosphorylated proteins\ targeting them for degradation as well ð11Ł[ We have recently found that CIS0 is ubiqui! tinated ð35Ł[ Thus\ it is quite interesting if CIS0 is involved in ubiquitin:proteasome dependent degradation of the activated cytokine receptors[ The CIS0 promoter contains two pairs of tandem TTCNNNGAA motifs that are putative binding sites for STAT4\ and a CIS0 promoter reporter construct showed increase in activity by EPO in cells transfected with EPOR and STAT4 ð13Ł[ The essential role of STAT4 in CIS expression was con_rmed by the observation that CIS0 expression did not occur in ovaries in STAT4a:STATb! double knockout "KO# mice ð02Ł[ In addition to the pro! duction of CIS0 being regulated by the JAK!STAT4 pathway\ it was interesting that CIS0 could negatively modulate STAT4 activation ð13Ł^ the forced expression of CIS0 partially suppressed STAT4 activation in 182 and BA:F2 cells[ Thus\ CIS0 seems to act as a negative feedback regulator for the JAKÐSTAT4 pathway[ The negative e}ect of CIS0 on STAT4 was con_rmed by the recent observation of CIS0!transgenic mice "Matsumoto et al[ manuscript in preparation#[ The female transgenic mice did not produce enough milk\ so that they could not feed their pups\ implicating defects in PRL:STAT4 signaling[ The mice also exhibited growth retardation as well as defects of IL1 response in T cells\ which were similarly observed in STAT4a\ or STAT4b\ or double KO mice "Matsumoto et al[^ manuscript in preparation#[ Therefore\ it is now clear that CIS0 is a negative regulator of STAT4\ at least when it is overexpressed[ The precise molecular mechanisms of the inhibition need to be addressed[ FINDING OF THE SECOND CIS MOLECULE; JAB/SOCS-1 /SS-1 Three groups have independently cloned the second CIS family member by entirely di}erent experimental approaches[ Starr et al[ "0886# cloned Suppressor of Cyto! kine Signaling!0 "SOCS!0# as an inhibitor of IL5 induced di}erentiation and growth arrest of murine monocytic leukemia cell line M0 ð14Ł^ Endo et al[ "0886# cloned the same protein as a JAK!binding protein "JAB# that could interact with the catalytic "JH0# domain of JAK1 ð15Ł^ and Naka et al[ "0886# identi_ed it using an antibody that recognizes a common sequence of SH1 domain of STATs and that it was not a STAT protein but instead was STAT!induced STAT inhibitor!0 "SSI!0# ð16Ł[ Collec! tively\ JAB:SOCS!0:SSI!0 is a potent inhibitor of IL5 signaling\ including IL5 induced tyrosine phos! phorylation of gp 029 and STAT2[ Interestingly\ JAB
Regulation of JAK:STAT signaling
can interact with not only JAK1 but also with JAK0 and is an inhibitor of JAK catalytic activity[ When it is overexpressed\ JAB can inhibit any signaling utilizing JAKs\ such at STAT4 activation by EPO\ STAT2 acti! vation by leukemia inhibitory factor "LIF# or IL5\ and c! fos induction by IL!1[ However\ since JAB did not inhibit _broblast growth factor "FGF# signaling\ although it binds to the FGF receptor\ it seems to be speci_c to JAK tyrosine kinases ð17Ł[ Ohya et al[ also cloned the same gene "called TIP!2# by two!hybrid screening using Tec kinase domain as bait ð18Ł[ JAB was found to suppress Tec kinase activity[ However\ this e}ect was negligible compared with JAKs[ Again\ it is notable that binding does not always mean inhibition[ THE CIS FAMILY By the data base search\ Masuhara et al[ "0886# reported _ve additional CIS family members "CIS1Ð5# ð17Ł[ Hilton and co!workers "0887# also identi_ed one additional member "SOCS!6:CIS6^ partial cDNA# ð29Ł[ A partial cDNA of CIS4 was also cloned by Takenawa|s group as a binding protein for the SH2 domains of Nck\ Ash "Grb1#\ and phospholipase!C "PLC#g ð20Ł[ This gene was expressed mainly in the brain[ Other CIS family members are expressed in hematopoietic and lymphoid tissues such as bone marrow\ spleen\ and thymus\ and their expression is induced by a subset of cytokines in some hematopoietic cells ð17Ł[ Thus\ it is reasonable that this family is called CIS family[ Notably\ CIS2 is shown to be induced by growth hormone and leptin ð20\ 21Ł\ and is also induced by tumor necrosis factor "TNF# and IL0\ which do not normally use JAK:STATs ð14Ł[ CIS2 is also expressed in the murine pituitary in vivo and pituitary CIS2 mRNA was stimulated 8!fold and 5!fold by the injection of LIF or interleukin!0 b respectively ð22Ł[ Figure 0 shows the alignment of the predicted amino acid sequences of human CIS family members "CISs#[ While the N!terminal regions share little sequence simi! larity\ all seven contain an SH1 domain and a conserved C!terminal region that we designate as the CH "CIS! homology# domain[ The consensus motif in the CH domain is LXXPXXRX4SLQHLCRXXIX5Ð8 IXXLPLPXXLXDYLXXYXY:F "X^ any amino acid#\ although the entire length of the C!terminal region varies[ The SH1 domain exhibits 12Ð47) identity among CISs[ Relatively high identity was seen between CIS0 and CIS1 "about 49)#\ CIS3 and CIS4 "about 47)#\ and JAB and CIS2 "about 39)#[ The _rst three amino acids of the SH1 domain of JAB and CIS2 are FYW\ whereas those of other CISs are WYW\ suggesting that the _rst residue\ F may be important for binding of JAB and CIS2 to JAK kinases "see below#[ The −4 and −0 positions of the SH1 domain are _xed as L and G respectively[ Inter! estingly\ SH1 domains of STATs also contain the same amino acids at these positions ð23Ł[ The N!terminal region of CIS0\ CIS1\ CIS2 and JAB is only 39Ð79 amino acids in length\ while CIS3\ CIS5 and CIS6 have quite a long N!terminal region "more than 249 amino acids#[
088
CH-DOMAIN CONTAINING PROTEINS Data base search also revealed that a similar CH domain is present in several proteins which contain ank! yrin!like repeats\ in the Ras!like GTPases and in proteins containing WD domain ð17Ł[ Hilton et al[ have identi_ed a further 05 proteins that contain this motif by using data base search ð29Ł[ They call CH domain asSOCS box[ These proteins fall into _ve classes based on the protein motifs found at the N!terminus of the CH domain[ In addition to four new CIS proteins "SOCS!3 to SOCS!6# containing an SH1 domain\ they describe four new fam! ilies of proteins that contain either WD!39 repeats "WSB! 0 and !1#\ SPRY domains "SSB!0 to !2#\ or ankyrin repeats "ASB!0 to !2# as well as G proteins[ Although the function of these protein families remains to be deter! mined\ CH domain may be involved in signal trans! duction because these domains in the N!terminal region are frequently found in signalling molecules[ NOMENCLATURE Since CIS0 was the _rst member of this family to be identi_ed\ and most of the family members are cytokine! inducible genes\ it is reasonable to refer to these proteins as the CIS family proteins[ SOCS\ JAB\ and SSI nomenclatures all have merit\ but the sooner the nomenclature can be agreed upon\ the greater will be the clarity for the scienti_c community to understand the multiple studies that are likely to be published related to this exciting family of molecules[ In Table 0\ di}erent names of each CIS member are listed[ BINDING OF CIS3 AND JAB TO JAK2 TYROSINE KINASE DOMAIN AND THEIR INHIBITORY EFFECT ON JAK SIGNALLING Among CIS family members\ only CIS2 and JAB can bind to JAK1!JH0 ð17\ 24Ł[ Binding was con_rmed by using two!hybrid analysis as well as co!precipitation assay in vivo and in vitro[ The interaction of JAK1!JH0 with JAB was stronger than that with CIS2[ CIS2 also bound to the tyrosine kinase domains of the FGF recep! tor and PYK1 in yeast[ Interestingly\ JAB bound to active c!kit tyrosine kinase domain\ while CIS2 did not[ In con! trast\ CIS2 bound to lck\ while JAB did not[ These _nd! ings indicate that JAB and CIS2 can directly interact with tyrosine kinases\ even though they have di}erent preferences[ By using a simple reporter gene assay system\ we found that JAB and CIS2 almost completely blocked cytokine! dependent STAT2 and STAT4 reporter gene activation ð17Ł[ CIS1 and CIS3 had no e}ect or rather enhanced the reporter gene activation[ However\ CIS2 and JAB did not e}ect FGF! or PDGF!induced c!fos promoter activation\ suggesting that the e}ect of CIS2 and JAB is quite speci_c to JAK tyrosine kinases ð17Ł[ In stable cell lines\ CIS2 and JAB also can inhibit JAK!STAT pathway\ even though these two seem to
199
A[ Yoshimura
Figure 0[ Amino acid sequence alignment of the seven human CIS family genes[ Black boxes indicate positions at which at least four amino acids are identical\ and gray boxes indicate those at which three amino acids are identical[ Only partial amino acid sequences are available for CIS4:NAP3[ CIS6 was not included here[
have di}erent activities[ The forced expression of CIS2 and JAB in M0 leukemia cells prevented IL5! or LIF! induced growth arrest and di}erentiation[ However\ unlike JAB\ CIS2 did not inhibit IFNg!induced growth arrest\ suggesting a di}erence in cytokine speci_city between CIS2 and JAB[ While JAB inhibited IL5!induced STAT2 activation rapidly and profoundly\ CIS2 inhibited STAT2 activation with slower kinetics than
JAB\ and allowed rapid c!fos induction and partial FcgRI expression in response to IL5[ In JAB transformants\ IFNg induced!STAT0 activation was almost completely suppressed\ while it was not a}ected in CIS2 trans! formants[ These di}erent e}ects of JAB and CIS2 on cytokine response in M0 cells could be explained by di}erent inhibitory e}ects of JAB and CIS2 "see below#[ Minamoto et al[ reported that the overexpression of SS0!
Regulation of JAK:STAT signaling
190
Table 0[ List of CIS family members
CIS0 JAB CIS1 CIS2 CIS3 CIS4 CIS5 CIS6
Other name
Amino acid length
Inductiona
Targetb
CIS SOCS!0\ SSI!0 SOCS!1\ SSI!2 SOCS!2\ SSI!2 SOCS!5 SOCS!6\ NAP3 SOCS!4 SOCS!3
146 100 086 114 424 ×374 425 ×410
Yes^ STAT4 Yes^ STAT 0\ 2 Yes Yes^ STAT0\ 2 Yes < Yes <
Receptors JAKs < JAKs < < < <
a Induction of mRNA by various cytokines in some hematopoietic cells[ STATs possibly involved in induction are also indicated[ b Apparent tyrosine phosphorylated proteins that bind to each CIS[ < means not done or not identi_ed[
1 "CIS1# also conferred resistance to IL5 on M0 cells ð25Ł[ However\ we and other groups have obtained opposite results ð17] Hilton et al[ personal communicationsŁ[ Tyrosine phosphorylation of JAKs in response to cyto! kines in M0 cells is not very evident\ probably because of very low content of JAKs or receptors[ We\ therefore\ created stable JAB transformants from NIH2T2 cells\ and these transformants were defective in IFNg and IFNb signaling[ IFNg!induced activation of JAK0 and JAK1 as well as IFNb!induced activation of JAK0 and Tyk1 were clearly detected in NIH2T2 cells[ In contrast\ the tyrosine phosphorylation of JAK0\ JAK1 and Tyk1 was largely impaired in JAB transformants[ This is the _rst example showing that JAB can directly inhibit JAKs in stable cell lines[ FGF induced tyrosine phos! phorylation and activation of the FGF receptor normally\ suggesting that the inhibition of tyrosine kinase activity in JAB transformants was speci_c to JAKs[ Thus\ the IFN!unresponsiveness of JAB transformants can be explained by the inhibition of activation for JAKs by JAB[ To prove that JAB and CIS2 inhibit JAK tyrosine kinase activity\ we used the transient expression in 182 cells[ We used GST!JH0 instead of full length JAK1\ because GST!JH0 was quite active by simple over! expression and GST!JH0 can be puri_ed easily with immobilized GSH[ CIS2 and JAB bound to GST!JH0 in 182 cells[ However\ the binding of CIS2 to GST!JH0 was much weaker than that of JAB[ Tyrosine phos! phorylation of cellular proteins by GST!JH0 was blocked by co!expression of JAB and CIS2 in a dose!dependent manner[ However\ the inhibition of tyrosine phos! phorylation required a higher level of CIS2 than JAB expression\ suggesting that JAB can more e.ciently bind to and inhibit JAK kinases than CIS2[ Thus\ both JAB and CIS2 can inhibit JAK tyrosine kinase activity\ even though JAB is a stronger inhibitor than CIS2[ This could account for the di}erent e}ect of CIS2 and JAB to IFN! and IL5! response of M0 cells[ Probably\ IFNs can acti! vate JAKs more strongly than IL5 or LIF in M0 cells[ JAB is strong enough to inhibit both IFN! and IL5! induced JAK activity\ whereas CIS2 can prevent IL5
or LIF!signaling but not IFN signaling because CIS2 possessed a lower inhibitory e}ect[ PHYSIOLOGICAL FUNCTION OF JAB AND CIS3 Since CIS0\ CIS2\ and JAB are induced by cytokines\ and negatively regulate cytokine signals\ these genes act in a classic negative loop for cytokine signal transduction "Figure 1#[ The genes could also be involved in cross!talk among cytokine signals[ CISs induced by one cytokine can modulate the intensity of other cytokine signals[ For example\ GM!CSF inhibits IL5! or IFNg!dependent STATs activation ð04Ł[ This inhibition requires new RNA and protein synthesis^ thus\ CIS family members are good candidates for the factors that contribute to the inhibition[ CIS2 may also act as a negative feedback regulator of the cytokine!mediated neuro!immuno!endocrine inter! face[ Bjorbaek et al[ "0887# found that peripheral leptin administration to ob:ob\ but not db:db mice\ rapidly induced CIS2 mRNA in the hypothalamus\ but had no e}ect on CIS0\ JAB\ or CIS1 ð21Ł[ In mammalian cell lines\ CIS2\ but not CIS0 or CIS1\ blocked leptin!induced signal transduction[ Expression of CIS2 mRNA in the arcuate and dorsomedial hypothalamic nuclei is increased in Ay:a mice\ a model of leptin!resistant murine obesity[ CIS2 may be a leptin!inducible inhibitor of leptin signaling\ and a potential mediator of leptin resistance in obesity[ Auernhammer et al[ "0887# also found that the injection of LIF or IL0b increased CIS2 mRNA in the pituitary and in AtT!19 cells\ and the stable over! expression of CIS2 inhibits basal and LIF!stimulated ACTH section ð22Ł[ As far as we ascertained\ IFNg is the most potent inducer of JAB in a wide variety of cell lines[ IFNb has no inducible e}ect[ The promoter region of JAB contains a potential GAS motif ð27Ł\ suggesting the involvement of STAT0 in the induction of JAB by IFNg[ Previously\ JAB was reported to be induced by IL5 in mouse liver and M0 cells\ suggesting that JAB is a negative feedback regulator of IL5:STAT2[ However\ results generated by us and others suggest that IL5 or LIF induces the
) 191
A[ Yoshimura
Figure 1[ The action of CIS family members[ CIS0 is induced by STAT4\ then binds to the receptor\ thereby inhibiting activation of STAT4 as well as some SH1 proteins "SH1!X# that also bind to the receptor[ CIS2 and JAB are strongly induced by IFNg\ so STAT0 may be involved in induction[ They directly bind to JAKs\ thereby inhibiting signaling[ After induction\ CIS2 and JAB may inhibit other cytokine signaling rather than IFNg[
expression of JAB much less e.ciently than IFNg[ JAB could be a negative feedback regulator of IFNg:STAT0 rather than IL5:STAT2[ IFNg is known as an inhibitory cytokine\ and to sup! press many cytokine action or cellular responses[ For example\ IL3!induced IgE synthesis and germline tran! scription were suppressed in the presence of IFNg in B cells ð28Ł[ JAB could be a part of the mechanism for the antagonistic e}ect of IFNg on the other cytokines[ JAB is also most abundantly expressed in the thymus ð14Ł\ which suggests a regulatory role for JAB in cytokine actions in T cells[ IFNg has been shown to play an impor! tant role in immune responses\ including the development of Th0 cells ð39Ł[ IFNg!treated Th0 cells become resistant to growth inhibition by IFNs\ which has been explained by loss of the IFNg receptor b chain ð30Ł[ However\ such loss of the receptor may need a long term of incubation of cells with IFNg[ Induction of JAB may partly explain the early down!regulation of IFNg!responsiveness in Th0 cells[ We also found that the JAB expression is very high in CTLL1 cells[ It also has been shown that exogenously expressed EPO receptor and G!CSF receptor are not functional in this cell line ð31\ 32Ł[ Since the molecular basis of such a selective inhibition of particular cytokine receptor signaling has not been elucidated\ JAB could be a good candidate for the factor which is involved in this cytokine unresponsiveness in CTLL1[ Although EPO does not induce tyrosine phosphorylation of JAK1 in CTLL1 cells expressing exogenous EPO receptor ð33Ł\ the reason why CTLL1 can still respond to IL1 is not clear
CMYK Page 191
at present[ JAB may have a lower a.nity to JAK2 than to JA0 and JA1\ thereby allowing the activation of IL1 signaling but not EPO or G!CSF signaling[ Our recent study suggests disregulated overexpression of JAB can confer IFN!resistance on cells[ JAB could be a mechanism for IFN!resistance with a dominant pheno! type because the resistance appeared on the constitutive expression[ Indeed\ two!independently isolated IFN! resistant clones expressed elevated levels of JAB[ IFN! resistance with a recessive phenotype has been well described[ Mutations in the receptors\ JAKs and STATs have been found in IFN!resistant mutants ð34Ł[ Reduced activation of JAKs by JAB overexpression could also be\ at least in part\ a mechanism for the IFN!resistance with a dominant phenotype[ It is clinically important to address whether JAB is involved in the interferon!resistance frequently found in patients with chronic myelogenous leukemia or those carrying hepatitis type C virus[ CONCLUSION We characterized three of the CIS family members^ CIS0\ JAB and CIS2[ CIS0 is induced via STAT4\ then binds to the activated receptor\ thereby somehow inhibit! ing STAT4 activity[ JAB and CIS2 are induced by several cytokines "probably STAT0 or STAT2 is involved in this induction#\ then bind to JAK kinases directly\ thereby inhibiting kinase activity[ Although little is known about other CIS family members\ studies have just been started[ Understanding the precise inhibitory mechanism of JAKs and STATs by CISs is very important for developing
)
Regulation of JAK:STAT signaling
drugs or methods to speci_cally inhibit cytokine signaling as well as other tyrosine kinases[ In addition to the need to further understand their mechanism"s# of action\ it remains unclear to what degree these proteins have over! lapping vs distinctive functions[ REFERENCES 0[ O|Shea JJ\ STATs\ cytokine signal transduction\ and immunoregulation] are we there yet< Immunity 0886\ 6\ 0Ð 00[ 1[ Ihle\ JN[ Cytokine receptor signaling[ Nature 0884\ 266\ 480Ð483[ 2[ Darnell JE Jr[ STATs and Gene Regulation[ Science 0886\ 166\ 0529Ð0524[ 3[ Ihle JN[ STATs] Signal transducers and activators of tran! scription[ Cell 0885\ 73\ 220Ð223[ 4[ Durbin JE\ Hackenmiller R\ Simon MC\ Levy DE[ Tar! geted disruption of the mouse Stat0 gene results in compro! mised innate immunity to viral disease[ Cell 0885\ 73\ 332Ð 349[ 5[ Meraz MA\ White JM\ Sheehan KC\ Bach EA\ Rodig SJ\ Dighe AS\ Kaplan DH\ Riley JK\ Greenlund AC\ Campbell D\ Carver!Moore K\ DuBois RN\ Clark R\ Aguet M\ Schreiber RD[ Targeted disruption of the Stat0 gene in mice reveals unexpected physiologic speci_city in the JAK!STAT signaling pathway[ Cell 0885\ 73\ 320Ð331[ 6[ Kaplan MH\ Sun YL\ Hoey T\ Grusby MJ[ Impaired IL! 01 responses and enhanced development of Th1 cells in Stat3!de_cient mice[ Nature 0885\ 271\ 063Ð066[ 7[ Shimoda K\ van Deursen J\ Sangster MY\ Sarawar SR\ Carson RT\ Tripp RA\ Chu C\ Quelle FW\ Nosaka T\ Vignali DA\ Doherty PC\ Grosveld G\ Paul WE\ Ihle JN[ Lack of Il!3 induced TH1 response and IgE class switching in mice with disrupted Stat5 gene[ Nature 0885\ 279\ 529Ð 522[ 8[ Takeda K\ Tanaka T\ Shi W\ Matsumoto M\ Minami M\ Kashiwamura S\ Nakanishi K\ Yoshida N\ Kishimoto T\ Akira S[ Essential role of Stat5 in IL!3 signaling[ Nature 0885\ 279\ 516Ð529[ 09[ Udy GB\ Towers RP\ Snell RG\ Wilkins RJ\ Park SH\ Ram PA\ Waxman DJ\ Davey HW[ Requirement of STAT4b for sexual dimorphism of body growth rates and liver gene expression[ Proc Natl Acad Sci U[S[A[ 0886\ 83\ 6128Ð6133[ 00[ Liu X\ Robinson GW\ Wagner KU\ Garrett L\ Wynshaw! Boris A\ Hennighausen L[ Stat4a is mandatory for adult mammary gland development and lactogenesis[ Genes Dev 0886\ 00\ 068Ð075[ 01[ Nakajima H\ Liu XW\ Wynshaw!Boris A\ Rosenthal LA\ Imada K\ Finbloom DS\ Hennighausen L\ Leonard WJ[ An indirect e}ect of Stat4a in IL!1!induced proliferation] a critical role for Stat4a in IL!1!mediated IL!1 receptor alpha chain induction[ Immunity 0886\ 6\ 580Ð690[ 02[ Teglund S\ McKay C\ Schuetz E\ van Deursen JM\ Stravopodis D\ Wang D\ Brown M\ Bodner S\ Grosveld G\ Ihle JN[ Stat4a and Stat4b proteins have essential and nonessential\ or redundant\ roles in cytokine responses[ Cell 0887\ 82\ 730Ð749[ 03[ Rook GA\ Hernandez!Pando R\ Lightman SL[ Hormones\ peripherally activated prohormones and regulation of the Th0:Th1 balance[ Immunol Today 0883\ 04\ 290Ð292[ 04[ Sengupta TK\ Schmitt EM\ Ivashkiv LB[ Inhibition of cytokines and JAK!STAT activation by distinct signaling pathways[ Proc Natl Acad Sci U[S[A[ 0885\ 82\ 8388Ð8493[ 05[ Kim TK\ Maniatis T[ Regulation of interferon!gamma! activated STAT0 by the ubiquitin!proteasome pathway[ Science 0885\ 162\ 0606Ð0608[ 06[ Strous GJ\ van Kerkhof P\ Govers R\ Ciechanover A\ Schwartz AL[ The ubiquitin conjugation system is required
07[ 08[ 19[
10[
11[
12[
13[
14[
15[
16[
17[
18[
29[
20[
21[ 22[
192
for ligand!induced endocytosis and degradation of the growth hormone receptor[ EMBO J 0885\ 04\ 2795Ð2701[ Wang D\ Stravopodis D\ Teglund S\ Kitazawa J\ Ihle JN[ Naturally occurring dominant negative variants of Stat4[ Mol Cell Biol 0885\ 05\ 5030Ð5037[ Azam M\ Lee C\ Strehlow I\ Schindler C[ Functionally distinct isoforms of STAT4 are generated by protein pro! cessing[ Immunity 0886\ 5\ 580Ð690[ Kralovics R\ Indrak K\ Stopka T\ Berman BW\ Prchal JF\ Prchal JT[ Two new EPO receptor mutations] truncated EPO receptors are most frequently associated with primary familial and congenital polycythemias[ Blood 0886\ 89\ 1946Ð1950[ Klingmuller U\ Lorenz U\ Cantley LC\ Neel BG\ Lodish HF[ Speci_c recruitment of SH!PTP0 to the erythropoietin receptor causes inactivation of JAK1 and termination of proliferative signals[ Cell 0884\ 79\ 618Ð627[ Yoshimura A\ Ohkubo T\ Kiguchi T\ Jenkins NA\ Gilbert DJ\ Copeland NG\ Hara T\ Miyajima A[ A novel cytokine! inducible gene CIS encodes an SH1!containing protein that binds to tyrosine!physphorylated interleukin 2 and ery! thropoietin receptors[ EMBO J 0884\ 03\ 1705Ð1715[ Uchida K\ Yoshimura A\ Inazawa J\ Yanagisawa K\ Osada H\ Masuda A\ Saito T\ Takahashi T\ Miyajima A\ Takahashi T[ Molecular cloning of CISH\ chromosome assignment to 2p10[2\ and analysis of expression in fetal and adult tissues[ Cyto`enet Cell Genet 0886\ 67\ 198Ð101[ Matsumoto A\ Masuhara M\ Mitsui K\ Yokouchi M\ Ohtsubo M\ Misawa H\ Miyajima A\ Yoshimura A[ CIS\ a cytokine inducible SH1 protein\ is a target of the JAK! STAT4 pathway and modulates STAT4 activation[ Blood 0886\ 78\ 2037Ð2043[ Starr R\ Willson TA\ Viney EM\ Murray LJ\ Rayner JR\ Jenkins BJ\ Gonda TJ\ Alexander WS\ Metcalf D\ Nicola NA\ Hilton DJ[ A family of cytokine!inducible inhibitors of signalling[ Nature 0886\ 276\ 806Ð810[ Endo TA\ Masuhara M\ Yokouchi M\ Suzuki R\ Sakamoto H\ Mitsui K\ Matsumoto A\ Tanimura S\ Ohtsubo M\ Misawa H\ Miyazaki T\ Leonor N\ Taniguchi T\ Fujita T\ Kanakura Y\ Komiya S\ Yoshimura A[ A new protein containing an SH1 domain that inhibits JAK kinases[ Nat! ure 0886\ 276\ 810Ð813[ Naka T\ Narazaki M\ Hirata M\ Matsumoto T\ Minamoto S\ Aono A\ Nishimoto N\ Kajita T\ Taga T\ Yoshizaki K\ Akira S\ Kishimoto T[ Structure and function of a new STAT!induced STAT inhibitor[ Nature 0886\ 276\ 813Ð818[ Masuhara M\ Sakamoto H\ Matsumoto A\ Suzuki R\ Yasukawa H\ Mutsui K\ Wakioka T\ Tanimura S\ Sasaki A\ Misawa H\ Yokouchi M\ Ohtsubo M\ Yoshimura A[ Cloning and Characterization of Novel CIS Family Genes[ Biochem Biophys Res Commun 0886\ 128\ 328Ð335[ Ohya Ki\ Kajigaya S\ Yamashita Y\ Myazato A\ Hatake K\ Miura Y\ Ikeda U\ Shimada K\ Ozawa K\ Mano H[ SOCS!0:JAB:SS0!0 can bind to and suppress Tec protein! tyrosine kinase[ J Biol Chem 0886\ 161\ 16\067Ð16\071[ Hilton DJ\ Richardson RT\ Alexander WS\ Viney EM\ Willson TA\ Sprigg NS\ Starr R\ Nicholson SE\ Metcalf D\ Nicola NA[ Twenty proteins containing a C!terminal SOCS box form _ve structural classes[ Proc Natl Acad Sci U[S[A[ 0887\ 84\ 003Ð008[ Matuoka K\ Miki H\ Takahashi K\ Takenawa T[ A novel ligand for an SH2 domain of the adaptor protein Nck bears an SH1 domain and nuclear signaling motifs[ Biochem Biophys Res Commun 0886\ 128\ 377Ð381[ Bjorbaek C\ Elquist JK\ Frantz JD\ Shoelson SE\ Flier JS[ Identi_cation of SOCS!2 as a potential mediator of central leptin resistance[ Mol Cell 0887\ 3\ 508Ð514[ Auernhammer CJ\ Chesnokova V\ Bousquet C\ Melmed S[ Pituitary corticotroph SOCS!2] novel intracellular regu! lation of leukemia!inhibitory factor!mediated proopio!
193
23[
24[
25[
26[
27[
28[
A[ Yoshimura melanocortin gene expression and adrenocorticotropin secretion[ Mol Endocrinol 0887\ 01\ 843Ð850[ Chen X\ Vinkemeier U\ Zhao Y\ Jeruzalmi D\ Darnell JE Jr\ Kuriyan J[ Crystal structure of a tyrosine phos! phorylated STAT!0 dimer bound to DNA[ Cell 0887\ 82\ 716Ð728[ Suzuki R\ Sakamoto H\ Yawukawa H\ Masuhara M\ Wakioka T\ Sasaki A\ Yuge K\ Yokouchi M\ Komiya S\ Inoue A\ Yoshimura A[ CIS2 and JAB have di}erent regu! latory roles in interleukin!5 mediated di}erentiation and STAT2 activation in M0 leukemia cells[ Onco`ene\ in press[ Minamoto S\ Ikegame K\ Ueno K\ Narazaki M\ Naka T\ Yamamoto H\ Matsumoto T\ Saito H\ Hosoe S\ Kishimoto T[ Cloning and functional analysis of new members of STAT induced STAT inhibitor "SSI# family] SSI!0 and SSI! 2[ Biochem Biophys Res Commun 0886\ 126\ 68Ð72[ Sakamoto H\ Yasukawa H\ Masuhara M\ Tanimura S\ Sasaki A\ Yuge K\ Ohtsubo M\ Ohtsuka S\ Fujita T\ Ohta T\ Furukawa Y\ Iwase S\ Yamada H\ Yoshimura A[ A Janus kinase inhibitor\ JAB\ is an interferon!g inducible gene and confers resistance to interferon[ Blood 0887\ 81\ 0557Ð0565[ Schluter G\ Celik A\ Obata R\ Schlicker M\ Ho}erbert S\ Schlung A\ Adham IM\ Engel W[ Sequence analysis of the conserved protamine gene cluster shows that it contains a fourth expressed gene[ Mol Reprod Devel 0885\ 32\ 0Ð5[ Xu L\ Rothman P[ IFN!g represses o germline transcription and subsequently down!regulates switch recombination to epsilon[ Int Immunol 0883\ 5\ 404Ð410[
39[ Wang ZE\ Reiner SL\ Zheng S\ Dalton DK\ Locksley RM[ CD3¦ e}ector cells default to the Th1 pathway in inter! feron gamma!de_cient mice infected with Leishmania major[ J Exp Med 0883\ 068\ 0256Ð0260[ 30[ Pernis A\ Gupta S\ Gollob KJ\ Garfein E\ Co}man RL\ Schindler C\ Rothman P[ Lack of interferon gamma recep! tor beta chain and the prevention of interferon gamma signaling in TH0 cells[ Science 0884\ 158\ 134Ð136[ 31[ Fukunaga R\ Ishizaka!Ikeda E\ Pan CX\ Seto Y\ Nagata S[ Functional domains of the granulocyte colony!stimulating factor receptor[ EMBO J 0880\ 09\ 1744Ð1754[ 32[ Yamamura Y\ Kageyama Y\ Matuzaki T\ Noda M\ Ikawa Y[ Dinstict downstream signaling mechanism between ery! thropoietin receptor and interleukin!1 receptor[ EMBO J 0881\ 00\ 3898Ð3804[ 33[ Wakao H\ Harada N\ Kitamura T\ Mui AL!F\ Miyajima A[ Interleukin 1 "IL1# and erythropoietin "EPO# activate STAT4:MGF via distinct pathways[ EMBO J 0884\ 03\ 1416Ð1424[ 34[ Darnell JE Jr\ Kerr IM\ Stark GR[ JakÐSTAT pathways and transcriptional activation in response to IFNs and other extracellular signaling proteins[ Science 0883\ 153\ 0304Ð0310[ 35[ Verdier F\ Chretien S\ Muller O\ Varlet P\ Yoshimura A\ Gisselbrecht S\ Lacombe C\ Mayeux P[ Proteasomes regu! late erythropoietin receptor and STAT4 activation] possible involvement of the ubiquitinated CIS protein[ J Biol Chem\ in press[
PII] S0248Ð5090"87#99908Ð6
Printed in Great Britain 0248!5090:87 ,08[99¦9[99
MINI REVIEW
The CIS Family: Negative Regulators of JAK–STAT Signaling
Akihiko Yoshimura* A family of cytokine!inducible SH1 proteins "CISs# has recently been identi_ed and the members are growing in number[ In this family\ the central SH1 domain and approximately 39 amino acids at the C!terminus "CIS homology domain^ CH domain# are well conserved\ while the N!terminal region shares little similarity and varies in length[ Most CISs appear to be induced by several cytokines and at least three of them "CIS0\ CIS2 and JAB# negatively regulate cytokine signal transduction[ Forced expression of CIS0 inhibits STAT4 activation by binding of CIS0 to cytokine receptors\ and CIS2 and JAB directly bind to the kinase domain of JAKs\ thereby inhibiting kinase activity[ Therefore\ these CIS family members seem to be present in a classical negative feedback loop of cytokine signaling[ They may also play a role in the mutual suppression of cytokine actions frequently found in immune and in~ammatory responses[ Precise molecular mechanisms of the signal inhibition and their physiological functions will be addressed in the near future[ The CH domain is also found in several interesting genes containing WD!39 repeats\ SPRY domains\ ankyrin repeats\ and GTPases[ However\ the function of the CH domain remains to be determined[ Þ 0887 Elsevier Science Ltd[ All rights reserved[
Key words] Cytokine = JAK = STAT = SH1 domain = regulation[
Growth and di}erentiation of immune and hemato! poietic cells are controlled by multiple cytokines includ! ing interleukins "ILs# and colony stimulating factors[ Although lacking catalytic domains\ growth and di}er! entiation of immune and hematopoietic cells are con! trolled by multiple cytokines including interleukins "ILs# and colony stimulating factors[ Although lacking cata! lytic domains\ members of the cytokine receptor super! family mediate the ligand!dependent activation of protein tyrosine phosphorylation through their association and activation of protein tyrosine phosphorylation through their association and activation of members of the Janus kinase "JAK# family of protein tyrosine kinases ð0\ 1Ł[ Cytokines induce homo!dimerization and activation of their cognate receptors\ resulting in the activation of associated JAK kinases "JAK0\ JAK1\ JAK2 and Tyk1#[ The activated JAKs phosphorylate the receptor cyto! plasmic domains which create docking sites for SH1! containing signaling proteins[ Members of the signal
Institute of Life Science\ Kurume University\ Aikawamachi 1321!2 Kurume 728!9750\ Japan[ Tel[] ¦70 831 26 5202^ fax^ ¦70 831 20 4101^ e!mail^ yosimuraÝIsi[kurume!u[ac[jp
transducers and activators of the transcription "STATs# family are among the substrates for tyrosine phos! phorylation ð2\ 3Ł[ Although this pathway was found initially to be activated by interferons "IFNs#\ it is now known that a large number of cytokines\ growth factors\ and hormonal factors activate JAK and:or STAT proteins[ Various cytokines induce the tyrosine phos! phorylation and activation of one or more of the seven STAT family members[ The role of various STATs in the biological responses to cytokines has been assessed through the analysis of receptor mutations which disrupt STAT activation\ and more recently by disrupting genes in mice[ For example\ mice in which the genes for STAT0\ STAT3 and STAT5 are disrupted are viable but lack functions that are mediated by IFNs\ interleukin 01 "IL! 01# or IL!3\ respectively ð4Ð8Ł[ this suggests that these STATs perform very speci_c functions in immune responses[ In contrast\ two highly related STAT4a and STAT4b are activated by members of the various cyto! kines\ including growth hormone "GH#\ prolactin "PRL#\ erythropoietin "EPO#\ IL!1\ IL!2\ granulocyte!mac! rophage!colony stimulating factor "GM!CSF#\ and thrombopoietin "TPO#[ Phenotypes of STAT4a and STAT4b single gene knockout mice as well as double
086
087
A[ Yoshimura
knockout mice revealed an important role of STAT4s in PRL and GH signaling as well as in IL!1 dependent T! cell functions ð09Ð02Ł[ REGULATION OF JAK/STAT SIGNALING Over the years\ the majority of investigations on cyto! kines have focused on the mechanisms by which they exert their actions[ However\ it is clear that the actions of cytokines are limited in both magnitude and duration\ making it important to understand the mechanisms by which their actions are negatively controlled[ Moreover\ the down!modulation of one cytokine action by several factors including another cytokine is often found in important physiological circumstances[ For example\ Th0 and Th1 cytokines suppress each other ð03Ł[ cAMP\ calcium ionophore\ and GM!CSF have been shown to inhibit JAK0ÐSTAT0 or STAT2 pathways ð04Ł\ although the molecular basis of such modulation has not been well characterized[ Degradation of STATs and receptors should be involved in regulation of signaling ð05\ 06Ł[ Naturally occurring dominant negative variants of STAT4 have also been reported ð07\ 08Ł[ Tyrosine phos! phatases containing SH1 domain also regulate cytokine signaling\ both positively and negatively[ One of them\ SHP!0 "HCP#\ has shown to be a negative regulator of JAK kinases and implicated in familial erythrocytosis "familial polycythemia# inherited as an autosomal domi! nant trait ð19Ł[ In this disease\ the disruption of SHP!0 binding sites of the EPO receptor resulted in prolonged activation "phosphorylation# of JAK1 ð10Ł[ Recently\ a new family of cytokine!inducible SH1 proteins "CISs# that\ in turn\ inhibit the cytokine action has been observed with keen interest[ Some of the members have been shown to be involved in negative regulation of cyto! kine signals\ especially JAKs and STATs[ CIS; PROTOTYPE OF CYTOKINE-INDUCED SH2 PROTEINS The _rst member of this family was denoted as CIS "now called CIS0#\ for cytokine!induced SH1 containing protein ð11\ 12Ł[ CIS0 was cloned originally as an immedi! ate early gene that was induced by IL!1\ IL!2\ and EPO[ CIS0 was found to be associated with the tyrosine phos! phorylated EPO receptor and the ILs!2 receptor b chain following stimulation with EPO or IL!2\ respectively ð11Ł[ Recently\ we also found that CIS0 binds to the PRL receptor and IL1 receptor b chain "Doppeler et al[\ and Javad Aman et al[] manuscript in preparation#[ From a functional perspective\ it was noted that the forced expression of CIS0 could partially suppress IL!2!induced proliferation\ although the mechanism of action for CIS0 was unclear ð11Ł[ One possibility is that CIS0 is an adaptor protein "between cytokine receptors and other molecules involved in growth inhibition# based on the presence of an SH1 domain in the central portion of the molecule and both N! and C!terminal regions that are rich in proline and leucines\ residues that can be involved in
mediating protein!protein interactions[ Alternatively\ it was also suggested that CIS0 might function by directly blocking phosphotyrosine motifs on receptors\ pre! venting their coupling to stimulatory signaling pathways ð11Ł[ Finally\ given that CIS0 was observed to have a relatively short half life\ the third potential role that was suggested was that CIS0 might be a scavenger of tyrosine phosphorylated proteins\ targeting them for degradation as well ð11Ł[ We have recently found that CIS0 is ubiqui! tinated ð35Ł[ Thus\ it is quite interesting if CIS0 is involved in ubiquitin:proteasome dependent degradation of the activated cytokine receptors[ The CIS0 promoter contains two pairs of tandem TTCNNNGAA motifs that are putative binding sites for STAT4\ and a CIS0 promoter reporter construct showed increase in activity by EPO in cells transfected with EPOR and STAT4 ð13Ł[ The essential role of STAT4 in CIS expression was con_rmed by the observation that CIS0 expression did not occur in ovaries in STAT4a:STATb! double knockout "KO# mice ð02Ł[ In addition to the pro! duction of CIS0 being regulated by the JAK!STAT4 pathway\ it was interesting that CIS0 could negatively modulate STAT4 activation ð13Ł^ the forced expression of CIS0 partially suppressed STAT4 activation in 182 and BA:F2 cells[ Thus\ CIS0 seems to act as a negative feedback regulator for the JAKÐSTAT4 pathway[ The negative e}ect of CIS0 on STAT4 was con_rmed by the recent observation of CIS0!transgenic mice "Matsumoto et al[ manuscript in preparation#[ The female transgenic mice did not produce enough milk\ so that they could not feed their pups\ implicating defects in PRL:STAT4 signaling[ The mice also exhibited growth retardation as well as defects of IL1 response in T cells\ which were similarly observed in STAT4a\ or STAT4b\ or double KO mice "Matsumoto et al[^ manuscript in preparation#[ Therefore\ it is now clear that CIS0 is a negative regulator of STAT4\ at least when it is overexpressed[ The precise molecular mechanisms of the inhibition need to be addressed[ FINDING OF THE SECOND CIS MOLECULE; JAB/SOCS-1 /SS-1 Three groups have independently cloned the second CIS family member by entirely di}erent experimental approaches[ Starr et al[ "0886# cloned Suppressor of Cyto! kine Signaling!0 "SOCS!0# as an inhibitor of IL5 induced di}erentiation and growth arrest of murine monocytic leukemia cell line M0 ð14Ł^ Endo et al[ "0886# cloned the same protein as a JAK!binding protein "JAB# that could interact with the catalytic "JH0# domain of JAK1 ð15Ł^ and Naka et al[ "0886# identi_ed it using an antibody that recognizes a common sequence of SH1 domain of STATs and that it was not a STAT protein but instead was STAT!induced STAT inhibitor!0 "SSI!0# ð16Ł[ Collec! tively\ JAB:SOCS!0:SSI!0 is a potent inhibitor of IL5 signaling\ including IL5 induced tyrosine phos! phorylation of gp 029 and STAT2[ Interestingly\ JAB
Regulation of JAK:STAT signaling
can interact with not only JAK1 but also with JAK0 and is an inhibitor of JAK catalytic activity[ When it is overexpressed\ JAB can inhibit any signaling utilizing JAKs\ such at STAT4 activation by EPO\ STAT2 acti! vation by leukemia inhibitory factor "LIF# or IL5\ and c! fos induction by IL!1[ However\ since JAB did not inhibit _broblast growth factor "FGF# signaling\ although it binds to the FGF receptor\ it seems to be speci_c to JAK tyrosine kinases ð17Ł[ Ohya et al[ also cloned the same gene "called TIP!2# by two!hybrid screening using Tec kinase domain as bait ð18Ł[ JAB was found to suppress Tec kinase activity[ However\ this e}ect was negligible compared with JAKs[ Again\ it is notable that binding does not always mean inhibition[ THE CIS FAMILY By the data base search\ Masuhara et al[ "0886# reported _ve additional CIS family members "CIS1Ð5# ð17Ł[ Hilton and co!workers "0887# also identi_ed one additional member "SOCS!6:CIS6^ partial cDNA# ð29Ł[ A partial cDNA of CIS4 was also cloned by Takenawa|s group as a binding protein for the SH2 domains of Nck\ Ash "Grb1#\ and phospholipase!C "PLC#g ð20Ł[ This gene was expressed mainly in the brain[ Other CIS family members are expressed in hematopoietic and lymphoid tissues such as bone marrow\ spleen\ and thymus\ and their expression is induced by a subset of cytokines in some hematopoietic cells ð17Ł[ Thus\ it is reasonable that this family is called CIS family[ Notably\ CIS2 is shown to be induced by growth hormone and leptin ð20\ 21Ł\ and is also induced by tumor necrosis factor "TNF# and IL0\ which do not normally use JAK:STATs ð14Ł[ CIS2 is also expressed in the murine pituitary in vivo and pituitary CIS2 mRNA was stimulated 8!fold and 5!fold by the injection of LIF or interleukin!0 b respectively ð22Ł[ Figure 0 shows the alignment of the predicted amino acid sequences of human CIS family members "CISs#[ While the N!terminal regions share little sequence simi! larity\ all seven contain an SH1 domain and a conserved C!terminal region that we designate as the CH "CIS! homology# domain[ The consensus motif in the CH domain is LXXPXXRX4SLQHLCRXXIX5Ð8 IXXLPLPXXLXDYLXXYXY:F "X^ any amino acid#\ although the entire length of the C!terminal region varies[ The SH1 domain exhibits 12Ð47) identity among CISs[ Relatively high identity was seen between CIS0 and CIS1 "about 49)#\ CIS3 and CIS4 "about 47)#\ and JAB and CIS2 "about 39)#[ The _rst three amino acids of the SH1 domain of JAB and CIS2 are FYW\ whereas those of other CISs are WYW\ suggesting that the _rst residue\ F may be important for binding of JAB and CIS2 to JAK kinases "see below#[ The −4 and −0 positions of the SH1 domain are _xed as L and G respectively[ Inter! estingly\ SH1 domains of STATs also contain the same amino acids at these positions ð23Ł[ The N!terminal region of CIS0\ CIS1\ CIS2 and JAB is only 39Ð79 amino acids in length\ while CIS3\ CIS5 and CIS6 have quite a long N!terminal region "more than 249 amino acids#[
088
CH-DOMAIN CONTAINING PROTEINS Data base search also revealed that a similar CH domain is present in several proteins which contain ank! yrin!like repeats\ in the Ras!like GTPases and in proteins containing WD domain ð17Ł[ Hilton et al[ have identi_ed a further 05 proteins that contain this motif by using data base search ð29Ł[ They call CH domain asSOCS box[ These proteins fall into _ve classes based on the protein motifs found at the N!terminus of the CH domain[ In addition to four new CIS proteins "SOCS!3 to SOCS!6# containing an SH1 domain\ they describe four new fam! ilies of proteins that contain either WD!39 repeats "WSB! 0 and !1#\ SPRY domains "SSB!0 to !2#\ or ankyrin repeats "ASB!0 to !2# as well as G proteins[ Although the function of these protein families remains to be deter! mined\ CH domain may be involved in signal trans! duction because these domains in the N!terminal region are frequently found in signalling molecules[ NOMENCLATURE Since CIS0 was the _rst member of this family to be identi_ed\ and most of the family members are cytokine! inducible genes\ it is reasonable to refer to these proteins as the CIS family proteins[ SOCS\ JAB\ and SSI nomenclatures all have merit\ but the sooner the nomenclature can be agreed upon\ the greater will be the clarity for the scienti_c community to understand the multiple studies that are likely to be published related to this exciting family of molecules[ In Table 0\ di}erent names of each CIS member are listed[ BINDING OF CIS3 AND JAB TO JAK2 TYROSINE KINASE DOMAIN AND THEIR INHIBITORY EFFECT ON JAK SIGNALLING Among CIS family members\ only CIS2 and JAB can bind to JAK1!JH0 ð17\ 24Ł[ Binding was con_rmed by using two!hybrid analysis as well as co!precipitation assay in vivo and in vitro[ The interaction of JAK1!JH0 with JAB was stronger than that with CIS2[ CIS2 also bound to the tyrosine kinase domains of the FGF recep! tor and PYK1 in yeast[ Interestingly\ JAB bound to active c!kit tyrosine kinase domain\ while CIS2 did not[ In con! trast\ CIS2 bound to lck\ while JAB did not[ These _nd! ings indicate that JAB and CIS2 can directly interact with tyrosine kinases\ even though they have di}erent preferences[ By using a simple reporter gene assay system\ we found that JAB and CIS2 almost completely blocked cytokine! dependent STAT2 and STAT4 reporter gene activation ð17Ł[ CIS1 and CIS3 had no e}ect or rather enhanced the reporter gene activation[ However\ CIS2 and JAB did not e}ect FGF! or PDGF!induced c!fos promoter activation\ suggesting that the e}ect of CIS2 and JAB is quite speci_c to JAK tyrosine kinases ð17Ł[ In stable cell lines\ CIS2 and JAB also can inhibit JAK!STAT pathway\ even though these two seem to
199
A[ Yoshimura
Figure 0[ Amino acid sequence alignment of the seven human CIS family genes[ Black boxes indicate positions at which at least four amino acids are identical\ and gray boxes indicate those at which three amino acids are identical[ Only partial amino acid sequences are available for CIS4:NAP3[ CIS6 was not included here[
have di}erent activities[ The forced expression of CIS2 and JAB in M0 leukemia cells prevented IL5! or LIF! induced growth arrest and di}erentiation[ However\ unlike JAB\ CIS2 did not inhibit IFNg!induced growth arrest\ suggesting a di}erence in cytokine speci_city between CIS2 and JAB[ While JAB inhibited IL5!induced STAT2 activation rapidly and profoundly\ CIS2 inhibited STAT2 activation with slower kinetics than
JAB\ and allowed rapid c!fos induction and partial FcgRI expression in response to IL5[ In JAB transformants\ IFNg induced!STAT0 activation was almost completely suppressed\ while it was not a}ected in CIS2 trans! formants[ These di}erent e}ects of JAB and CIS2 on cytokine response in M0 cells could be explained by di}erent inhibitory e}ects of JAB and CIS2 "see below#[ Minamoto et al[ reported that the overexpression of SS0!
Regulation of JAK:STAT signaling
190
Table 0[ List of CIS family members
CIS0 JAB CIS1 CIS2 CIS3 CIS4 CIS5 CIS6
Other name
Amino acid length
Inductiona
Targetb
CIS SOCS!0\ SSI!0 SOCS!1\ SSI!2 SOCS!2\ SSI!2 SOCS!5 SOCS!6\ NAP3 SOCS!4 SOCS!3
146 100 086 114 424 ×374 425 ×410
Yes^ STAT4 Yes^ STAT 0\ 2 Yes Yes^ STAT0\ 2 Yes < Yes <
Receptors JAKs < JAKs < < < <
a Induction of mRNA by various cytokines in some hematopoietic cells[ STATs possibly involved in induction are also indicated[ b Apparent tyrosine phosphorylated proteins that bind to each CIS[ < means not done or not identi_ed[
1 "CIS1# also conferred resistance to IL5 on M0 cells ð25Ł[ However\ we and other groups have obtained opposite results ð17] Hilton et al[ personal communicationsŁ[ Tyrosine phosphorylation of JAKs in response to cyto! kines in M0 cells is not very evident\ probably because of very low content of JAKs or receptors[ We\ therefore\ created stable JAB transformants from NIH2T2 cells\ and these transformants were defective in IFNg and IFNb signaling[ IFNg!induced activation of JAK0 and JAK1 as well as IFNb!induced activation of JAK0 and Tyk1 were clearly detected in NIH2T2 cells[ In contrast\ the tyrosine phosphorylation of JAK0\ JAK1 and Tyk1 was largely impaired in JAB transformants[ This is the _rst example showing that JAB can directly inhibit JAKs in stable cell lines[ FGF induced tyrosine phos! phorylation and activation of the FGF receptor normally\ suggesting that the inhibition of tyrosine kinase activity in JAB transformants was speci_c to JAKs[ Thus\ the IFN!unresponsiveness of JAB transformants can be explained by the inhibition of activation for JAKs by JAB[ To prove that JAB and CIS2 inhibit JAK tyrosine kinase activity\ we used the transient expression in 182 cells[ We used GST!JH0 instead of full length JAK1\ because GST!JH0 was quite active by simple over! expression and GST!JH0 can be puri_ed easily with immobilized GSH[ CIS2 and JAB bound to GST!JH0 in 182 cells[ However\ the binding of CIS2 to GST!JH0 was much weaker than that of JAB[ Tyrosine phos! phorylation of cellular proteins by GST!JH0 was blocked by co!expression of JAB and CIS2 in a dose!dependent manner[ However\ the inhibition of tyrosine phos! phorylation required a higher level of CIS2 than JAB expression\ suggesting that JAB can more e.ciently bind to and inhibit JAK kinases than CIS2[ Thus\ both JAB and CIS2 can inhibit JAK tyrosine kinase activity\ even though JAB is a stronger inhibitor than CIS2[ This could account for the di}erent e}ect of CIS2 and JAB to IFN! and IL5! response of M0 cells[ Probably\ IFNs can acti! vate JAKs more strongly than IL5 or LIF in M0 cells[ JAB is strong enough to inhibit both IFN! and IL5! induced JAK activity\ whereas CIS2 can prevent IL5
or LIF!signaling but not IFN signaling because CIS2 possessed a lower inhibitory e}ect[ PHYSIOLOGICAL FUNCTION OF JAB AND CIS3 Since CIS0\ CIS2\ and JAB are induced by cytokines\ and negatively regulate cytokine signals\ these genes act in a classic negative loop for cytokine signal transduction "Figure 1#[ The genes could also be involved in cross!talk among cytokine signals[ CISs induced by one cytokine can modulate the intensity of other cytokine signals[ For example\ GM!CSF inhibits IL5! or IFNg!dependent STATs activation ð04Ł[ This inhibition requires new RNA and protein synthesis^ thus\ CIS family members are good candidates for the factors that contribute to the inhibition[ CIS2 may also act as a negative feedback regulator of the cytokine!mediated neuro!immuno!endocrine inter! face[ Bjorbaek et al[ "0887# found that peripheral leptin administration to ob:ob\ but not db:db mice\ rapidly induced CIS2 mRNA in the hypothalamus\ but had no e}ect on CIS0\ JAB\ or CIS1 ð21Ł[ In mammalian cell lines\ CIS2\ but not CIS0 or CIS1\ blocked leptin!induced signal transduction[ Expression of CIS2 mRNA in the arcuate and dorsomedial hypothalamic nuclei is increased in Ay:a mice\ a model of leptin!resistant murine obesity[ CIS2 may be a leptin!inducible inhibitor of leptin signaling\ and a potential mediator of leptin resistance in obesity[ Auernhammer et al[ "0887# also found that the injection of LIF or IL0b increased CIS2 mRNA in the pituitary and in AtT!19 cells\ and the stable over! expression of CIS2 inhibits basal and LIF!stimulated ACTH section ð22Ł[ As far as we ascertained\ IFNg is the most potent inducer of JAB in a wide variety of cell lines[ IFNb has no inducible e}ect[ The promoter region of JAB contains a potential GAS motif ð27Ł\ suggesting the involvement of STAT0 in the induction of JAB by IFNg[ Previously\ JAB was reported to be induced by IL5 in mouse liver and M0 cells\ suggesting that JAB is a negative feedback regulator of IL5:STAT2[ However\ results generated by us and others suggest that IL5 or LIF induces the
) 191
A[ Yoshimura
Figure 1[ The action of CIS family members[ CIS0 is induced by STAT4\ then binds to the receptor\ thereby inhibiting activation of STAT4 as well as some SH1 proteins "SH1!X# that also bind to the receptor[ CIS2 and JAB are strongly induced by IFNg\ so STAT0 may be involved in induction[ They directly bind to JAKs\ thereby inhibiting signaling[ After induction\ CIS2 and JAB may inhibit other cytokine signaling rather than IFNg[
expression of JAB much less e.ciently than IFNg[ JAB could be a negative feedback regulator of IFNg:STAT0 rather than IL5:STAT2[ IFNg is known as an inhibitory cytokine\ and to sup! press many cytokine action or cellular responses[ For example\ IL3!induced IgE synthesis and germline tran! scription were suppressed in the presence of IFNg in B cells ð28Ł[ JAB could be a part of the mechanism for the antagonistic e}ect of IFNg on the other cytokines[ JAB is also most abundantly expressed in the thymus ð14Ł\ which suggests a regulatory role for JAB in cytokine actions in T cells[ IFNg has been shown to play an impor! tant role in immune responses\ including the development of Th0 cells ð39Ł[ IFNg!treated Th0 cells become resistant to growth inhibition by IFNs\ which has been explained by loss of the IFNg receptor b chain ð30Ł[ However\ such loss of the receptor may need a long term of incubation of cells with IFNg[ Induction of JAB may partly explain the early down!regulation of IFNg!responsiveness in Th0 cells[ We also found that the JAB expression is very high in CTLL1 cells[ It also has been shown that exogenously expressed EPO receptor and G!CSF receptor are not functional in this cell line ð31\ 32Ł[ Since the molecular basis of such a selective inhibition of particular cytokine receptor signaling has not been elucidated\ JAB could be a good candidate for the factor which is involved in this cytokine unresponsiveness in CTLL1[ Although EPO does not induce tyrosine phosphorylation of JAK1 in CTLL1 cells expressing exogenous EPO receptor ð33Ł\ the reason why CTLL1 can still respond to IL1 is not clear
CMYK Page 191
at present[ JAB may have a lower a.nity to JAK2 than to JA0 and JA1\ thereby allowing the activation of IL1 signaling but not EPO or G!CSF signaling[ Our recent study suggests disregulated overexpression of JAB can confer IFN!resistance on cells[ JAB could be a mechanism for IFN!resistance with a dominant pheno! type because the resistance appeared on the constitutive expression[ Indeed\ two!independently isolated IFN! resistant clones expressed elevated levels of JAB[ IFN! resistance with a recessive phenotype has been well described[ Mutations in the receptors\ JAKs and STATs have been found in IFN!resistant mutants ð34Ł[ Reduced activation of JAKs by JAB overexpression could also be\ at least in part\ a mechanism for the IFN!resistance with a dominant phenotype[ It is clinically important to address whether JAB is involved in the interferon!resistance frequently found in patients with chronic myelogenous leukemia or those carrying hepatitis type C virus[ CONCLUSION We characterized three of the CIS family members^ CIS0\ JAB and CIS2[ CIS0 is induced via STAT4\ then binds to the activated receptor\ thereby somehow inhibit! ing STAT4 activity[ JAB and CIS2 are induced by several cytokines "probably STAT0 or STAT2 is involved in this induction#\ then bind to JAK kinases directly\ thereby inhibiting kinase activity[ Although little is known about other CIS family members\ studies have just been started[ Understanding the precise inhibitory mechanism of JAKs and STATs by CISs is very important for developing
)
Regulation of JAK:STAT signaling
drugs or methods to speci_cally inhibit cytokine signaling as well as other tyrosine kinases[ In addition to the need to further understand their mechanism"s# of action\ it remains unclear to what degree these proteins have over! lapping vs distinctive functions[ REFERENCES 0[ O|Shea JJ\ STATs\ cytokine signal transduction\ and immunoregulation] are we there yet< Immunity 0886\ 6\ 0Ð 00[ 1[ Ihle\ JN[ Cytokine receptor signaling[ Nature 0884\ 266\ 480Ð483[ 2[ Darnell JE Jr[ STATs and Gene Regulation[ Science 0886\ 166\ 0529Ð0524[ 3[ Ihle JN[ STATs] Signal transducers and activators of tran! scription[ Cell 0885\ 73\ 220Ð223[ 4[ Durbin JE\ Hackenmiller R\ Simon MC\ Levy DE[ Tar! geted disruption of the mouse Stat0 gene results in compro! mised innate immunity to viral disease[ Cell 0885\ 73\ 332Ð 349[ 5[ Meraz MA\ White JM\ Sheehan KC\ Bach EA\ Rodig SJ\ Dighe AS\ Kaplan DH\ Riley JK\ Greenlund AC\ Campbell D\ Carver!Moore K\ DuBois RN\ Clark R\ Aguet M\ Schreiber RD[ Targeted disruption of the Stat0 gene in mice reveals unexpected physiologic speci_city in the JAK!STAT signaling pathway[ Cell 0885\ 73\ 320Ð331[ 6[ Kaplan MH\ Sun YL\ Hoey T\ Grusby MJ[ Impaired IL! 01 responses and enhanced development of Th1 cells in Stat3!de_cient mice[ Nature 0885\ 271\ 063Ð066[ 7[ Shimoda K\ van Deursen J\ Sangster MY\ Sarawar SR\ Carson RT\ Tripp RA\ Chu C\ Quelle FW\ Nosaka T\ Vignali DA\ Doherty PC\ Grosveld G\ Paul WE\ Ihle JN[ Lack of Il!3 induced TH1 response and IgE class switching in mice with disrupted Stat5 gene[ Nature 0885\ 279\ 529Ð 522[ 8[ Takeda K\ Tanaka T\ Shi W\ Matsumoto M\ Minami M\ Kashiwamura S\ Nakanishi K\ Yoshida N\ Kishimoto T\ Akira S[ Essential role of Stat5 in IL!3 signaling[ Nature 0885\ 279\ 516Ð529[ 09[ Udy GB\ Towers RP\ Snell RG\ Wilkins RJ\ Park SH\ Ram PA\ Waxman DJ\ Davey HW[ Requirement of STAT4b for sexual dimorphism of body growth rates and liver gene expression[ Proc Natl Acad Sci U[S[A[ 0886\ 83\ 6128Ð6133[ 00[ Liu X\ Robinson GW\ Wagner KU\ Garrett L\ Wynshaw! Boris A\ Hennighausen L[ Stat4a is mandatory for adult mammary gland development and lactogenesis[ Genes Dev 0886\ 00\ 068Ð075[ 01[ Nakajima H\ Liu XW\ Wynshaw!Boris A\ Rosenthal LA\ Imada K\ Finbloom DS\ Hennighausen L\ Leonard WJ[ An indirect e}ect of Stat4a in IL!1!induced proliferation] a critical role for Stat4a in IL!1!mediated IL!1 receptor alpha chain induction[ Immunity 0886\ 6\ 580Ð690[ 02[ Teglund S\ McKay C\ Schuetz E\ van Deursen JM\ Stravopodis D\ Wang D\ Brown M\ Bodner S\ Grosveld G\ Ihle JN[ Stat4a and Stat4b proteins have essential and nonessential\ or redundant\ roles in cytokine responses[ Cell 0887\ 82\ 730Ð749[ 03[ Rook GA\ Hernandez!Pando R\ Lightman SL[ Hormones\ peripherally activated prohormones and regulation of the Th0:Th1 balance[ Immunol Today 0883\ 04\ 290Ð292[ 04[ Sengupta TK\ Schmitt EM\ Ivashkiv LB[ Inhibition of cytokines and JAK!STAT activation by distinct signaling pathways[ Proc Natl Acad Sci U[S[A[ 0885\ 82\ 8388Ð8493[ 05[ Kim TK\ Maniatis T[ Regulation of interferon!gamma! activated STAT0 by the ubiquitin!proteasome pathway[ Science 0885\ 162\ 0606Ð0608[ 06[ Strous GJ\ van Kerkhof P\ Govers R\ Ciechanover A\ Schwartz AL[ The ubiquitin conjugation system is required
07[ 08[ 19[
10[
11[
12[
13[
14[
15[
16[
17[
18[
29[
20[
21[ 22[
192
for ligand!induced endocytosis and degradation of the growth hormone receptor[ EMBO J 0885\ 04\ 2795Ð2701[ Wang D\ Stravopodis D\ Teglund S\ Kitazawa J\ Ihle JN[ Naturally occurring dominant negative variants of Stat4[ Mol Cell Biol 0885\ 05\ 5030Ð5037[ Azam M\ Lee C\ Strehlow I\ Schindler C[ Functionally distinct isoforms of STAT4 are generated by protein pro! cessing[ Immunity 0886\ 5\ 580Ð690[ Kralovics R\ Indrak K\ Stopka T\ Berman BW\ Prchal JF\ Prchal JT[ Two new EPO receptor mutations] truncated EPO receptors are most frequently associated with primary familial and congenital polycythemias[ Blood 0886\ 89\ 1946Ð1950[ Klingmuller U\ Lorenz U\ Cantley LC\ Neel BG\ Lodish HF[ Speci_c recruitment of SH!PTP0 to the erythropoietin receptor causes inactivation of JAK1 and termination of proliferative signals[ Cell 0884\ 79\ 618Ð627[ Yoshimura A\ Ohkubo T\ Kiguchi T\ Jenkins NA\ Gilbert DJ\ Copeland NG\ Hara T\ Miyajima A[ A novel cytokine! inducible gene CIS encodes an SH1!containing protein that binds to tyrosine!physphorylated interleukin 2 and ery! thropoietin receptors[ EMBO J 0884\ 03\ 1705Ð1715[ Uchida K\ Yoshimura A\ Inazawa J\ Yanagisawa K\ Osada H\ Masuda A\ Saito T\ Takahashi T\ Miyajima A\ Takahashi T[ Molecular cloning of CISH\ chromosome assignment to 2p10[2\ and analysis of expression in fetal and adult tissues[ Cyto`enet Cell Genet 0886\ 67\ 198Ð101[ Matsumoto A\ Masuhara M\ Mitsui K\ Yokouchi M\ Ohtsubo M\ Misawa H\ Miyajima A\ Yoshimura A[ CIS\ a cytokine inducible SH1 protein\ is a target of the JAK! STAT4 pathway and modulates STAT4 activation[ Blood 0886\ 78\ 2037Ð2043[ Starr R\ Willson TA\ Viney EM\ Murray LJ\ Rayner JR\ Jenkins BJ\ Gonda TJ\ Alexander WS\ Metcalf D\ Nicola NA\ Hilton DJ[ A family of cytokine!inducible inhibitors of signalling[ Nature 0886\ 276\ 806Ð810[ Endo TA\ Masuhara M\ Yokouchi M\ Suzuki R\ Sakamoto H\ Mitsui K\ Matsumoto A\ Tanimura S\ Ohtsubo M\ Misawa H\ Miyazaki T\ Leonor N\ Taniguchi T\ Fujita T\ Kanakura Y\ Komiya S\ Yoshimura A[ A new protein containing an SH1 domain that inhibits JAK kinases[ Nat! ure 0886\ 276\ 810Ð813[ Naka T\ Narazaki M\ Hirata M\ Matsumoto T\ Minamoto S\ Aono A\ Nishimoto N\ Kajita T\ Taga T\ Yoshizaki K\ Akira S\ Kishimoto T[ Structure and function of a new STAT!induced STAT inhibitor[ Nature 0886\ 276\ 813Ð818[ Masuhara M\ Sakamoto H\ Matsumoto A\ Suzuki R\ Yasukawa H\ Mutsui K\ Wakioka T\ Tanimura S\ Sasaki A\ Misawa H\ Yokouchi M\ Ohtsubo M\ Yoshimura A[ Cloning and Characterization of Novel CIS Family Genes[ Biochem Biophys Res Commun 0886\ 128\ 328Ð335[ Ohya Ki\ Kajigaya S\ Yamashita Y\ Myazato A\ Hatake K\ Miura Y\ Ikeda U\ Shimada K\ Ozawa K\ Mano H[ SOCS!0:JAB:SS0!0 can bind to and suppress Tec protein! tyrosine kinase[ J Biol Chem 0886\ 161\ 16\067Ð16\071[ Hilton DJ\ Richardson RT\ Alexander WS\ Viney EM\ Willson TA\ Sprigg NS\ Starr R\ Nicholson SE\ Metcalf D\ Nicola NA[ Twenty proteins containing a C!terminal SOCS box form _ve structural classes[ Proc Natl Acad Sci U[S[A[ 0887\ 84\ 003Ð008[ Matuoka K\ Miki H\ Takahashi K\ Takenawa T[ A novel ligand for an SH2 domain of the adaptor protein Nck bears an SH1 domain and nuclear signaling motifs[ Biochem Biophys Res Commun 0886\ 128\ 377Ð381[ Bjorbaek C\ Elquist JK\ Frantz JD\ Shoelson SE\ Flier JS[ Identi_cation of SOCS!2 as a potential mediator of central leptin resistance[ Mol Cell 0887\ 3\ 508Ð514[ Auernhammer CJ\ Chesnokova V\ Bousquet C\ Melmed S[ Pituitary corticotroph SOCS!2] novel intracellular regu! lation of leukemia!inhibitory factor!mediated proopio!
193
23[
24[
25[
26[
27[
28[
A[ Yoshimura melanocortin gene expression and adrenocorticotropin secretion[ Mol Endocrinol 0887\ 01\ 843Ð850[ Chen X\ Vinkemeier U\ Zhao Y\ Jeruzalmi D\ Darnell JE Jr\ Kuriyan J[ Crystal structure of a tyrosine phos! phorylated STAT!0 dimer bound to DNA[ Cell 0887\ 82\ 716Ð728[ Suzuki R\ Sakamoto H\ Yawukawa H\ Masuhara M\ Wakioka T\ Sasaki A\ Yuge K\ Yokouchi M\ Komiya S\ Inoue A\ Yoshimura A[ CIS2 and JAB have di}erent regu! latory roles in interleukin!5 mediated di}erentiation and STAT2 activation in M0 leukemia cells[ Onco`ene\ in press[ Minamoto S\ Ikegame K\ Ueno K\ Narazaki M\ Naka T\ Yamamoto H\ Matsumoto T\ Saito H\ Hosoe S\ Kishimoto T[ Cloning and functional analysis of new members of STAT induced STAT inhibitor "SSI# family] SSI!0 and SSI! 2[ Biochem Biophys Res Commun 0886\ 126\ 68Ð72[ Sakamoto H\ Yasukawa H\ Masuhara M\ Tanimura S\ Sasaki A\ Yuge K\ Ohtsubo M\ Ohtsuka S\ Fujita T\ Ohta T\ Furukawa Y\ Iwase S\ Yamada H\ Yoshimura A[ A Janus kinase inhibitor\ JAB\ is an interferon!g inducible gene and confers resistance to interferon[ Blood 0887\ 81\ 0557Ð0565[ Schluter G\ Celik A\ Obata R\ Schlicker M\ Ho}erbert S\ Schlung A\ Adham IM\ Engel W[ Sequence analysis of the conserved protamine gene cluster shows that it contains a fourth expressed gene[ Mol Reprod Devel 0885\ 32\ 0Ð5[ Xu L\ Rothman P[ IFN!g represses o germline transcription and subsequently down!regulates switch recombination to epsilon[ Int Immunol 0883\ 5\ 404Ð410[
39[ Wang ZE\ Reiner SL\ Zheng S\ Dalton DK\ Locksley RM[ CD3¦ e}ector cells default to the Th1 pathway in inter! feron gamma!de_cient mice infected with Leishmania major[ J Exp Med 0883\ 068\ 0256Ð0260[ 30[ Pernis A\ Gupta S\ Gollob KJ\ Garfein E\ Co}man RL\ Schindler C\ Rothman P[ Lack of interferon gamma recep! tor beta chain and the prevention of interferon gamma signaling in TH0 cells[ Science 0884\ 158\ 134Ð136[ 31[ Fukunaga R\ Ishizaka!Ikeda E\ Pan CX\ Seto Y\ Nagata S[ Functional domains of the granulocyte colony!stimulating factor receptor[ EMBO J 0880\ 09\ 1744Ð1754[ 32[ Yamamura Y\ Kageyama Y\ Matuzaki T\ Noda M\ Ikawa Y[ Dinstict downstream signaling mechanism between ery! thropoietin receptor and interleukin!1 receptor[ EMBO J 0881\ 00\ 3898Ð3804[ 33[ Wakao H\ Harada N\ Kitamura T\ Mui AL!F\ Miyajima A[ Interleukin 1 "IL1# and erythropoietin "EPO# activate STAT4:MGF via distinct pathways[ EMBO J 0884\ 03\ 1416Ð1424[ 34[ Darnell JE Jr\ Kerr IM\ Stark GR[ JakÐSTAT pathways and transcriptional activation in response to IFNs and other extracellular signaling proteins[ Science 0883\ 153\ 0304Ð0310[ 35[ Verdier F\ Chretien S\ Muller O\ Varlet P\ Yoshimura A\ Gisselbrecht S\ Lacombe C\ Mayeux P[ Proteasomes regu! late erythropoietin receptor and STAT4 activation] possible involvement of the ubiquitinated CIS protein[ J Biol Chem\ in press[