Membrane association of estrogen receptor α and β influences 17β-estradiol-mediated cancer cell proliferation

s t e r o i d s 7 3 ( 2 0 0 8 ) 853–858

available at www.sciencedirect.com

journal homepage: www.elsevier.com/locate/steroids

Membrane association of estrogen receptor ␣ and ␤ influences 17␤-estradiol-mediated cancer cell proliferation Maria Marino a,∗ , Paolo Ascenzi a,b a b

Department of Biology, University “Roma Tre”, Viale G. Marconi 446, I-00146 Roma, Italy Interdepartmental Laboratory for Electron Microscopy, University ‘Roma Tre’, Via della Vasca Navale 79, I-00146 Roma, Italy

a r t i c l e

i n f o

Published on line 14 December 2007

a b s t r a c t S-Palmitoylation is a widespread post-translational modification of integral and/or peripheral proteins occurring in all eukaryotic cells. The family of S-palmitoylated proteins is large

Keywords:

and diverse and recently, estrogen receptor isoforms (ER␣ and ER␤) belonging to the nuclear

Estrogen receptor ␣

receptor superfamily have been added to the palmitoylproteoma. S-Palmitoylation allows

Estrogen receptor ␤

ER␣ and ER␤ localization at the plasma membrane, where they associate with caveolin-1.

Estrogen receptor palmitoylation

Upon 17␤-estradiol (E2) stimulation, ER␣ dissociates from caveolin-1 allowing the activation

17␤-Estradiol

of rapid signals relevant for cell proliferation. In contrast to ER␣, E2 increases ER␤ associa-

Rapid signals

tion with caveolin-1 and activates p38 kinase and the downstream pro-apoptotic cascade

Cancer cell proliferation

(i.e., caspase-3 activation and PARP cleavage). These data highlight the physiological role of palmitoylation in modulating the ER␣ and ER␤ localization at the plasma membrane and the regulation of different E2-induced non-genomic functions relevant for controlling cell proliferation. © 2007 Elsevier Inc. All rights reserved.

1.

Introduction

Fatty acid addition is a widespread post-translational modification of integral and/or peripheral proteins occurring in all eukaryotic cells [1]. Proteins can be modified by fatty acid addition in several different ways. Co-translational modification with myristate (C14:0) (Fig. 1) occurs at the N-terminal Gly residue after its appearance following the cleavage of the initiator amino acid Met, this modification is known as N-myristoylation. Palmitoylation refers to the linkage of palmitate (C16:0) to Cys residues (Fig. 1). When palmitate is added to the N-terminal Cys residue, a thioester intermediate occurs followed by a rearrangement to a more stable amide linkage, this modification is known as Npalmitoylation. More frequently, palmitate is attached to a non-N-terminal Cys residue through a thioester linkage, leading to S-palmitoylation [1,2].

∗

Corresponding author. Tel.: +39 06 55176345; fax: +39 06 55176321. E-mail address: [email protected] (M. Marino). 0039-128X/$ – see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.steroids.2007.12.003

N-Palmitoylation results, like other lipid addition (e.g., N-myristoylation and S-prenylation), as a permanent modification, whereas S-palmitoylated proteins could encounter different destinies. Proteins can be permanently modified with palmitate or palmitate can be hydrolysed from the protein, as this is an essential step in the protein degradative process [1,2]. However, for many proteins, cycles of palmitoylation and de-palmitoylation occur throughout their lifetime rendering, thus, palmitoylation unique among lipid modifications in that it is the only reversible lipid modification of proteins [1–4]. Palmitoylation exerts diverse effects on the protein structure and function. Indeed, the attachment of this long chain fatty acid increases protein hydrophobicity and thereby facilitates membrane association. Palmitoylation promotes protein targeting to membrane microdomains (e.g., lipid rafts and caveolae) that are enriched in cholesterol and saturated fatty acid chains, allowing the lipid molecules to pack tightly

854

s t e r o i d s 7 3 ( 2 0 0 8 ) 853–858

Fig. 2 – Amino acid sequence alignment of human ER␣ and ER␤. GenBank accession codes are ER␣, NP 000116; and ER␤, NP 001428. The amino acid sequence alignment was obtained with Clustal [50]. The diamond, the circle, and the horizontal line indicate the palmitoylable Cys residue, the hydrophilic positively charged Lys residue, and the hydrophobic patch, respectively. For details, see [11].

Fig. 1 – Fatty acylation of proteins. S-Palmitoylcysteine (upper panel) is formed by the reversible addition of the 16-carbon lipid, palmitate, to the thiol group of a Cys residue. When this addition occurs at the N-terminal Cys residue, there is a chemical rearrangement that results in the attachment of the palmitate through a stable amide linkage, a process known as N-palmitoylation (middle panel). The 14-carbon lipid, myristate, can also be attached to N-terminal Gly residues (N-myristoylation) (bottom panel).

together and form a “liquid ordered” phase. This enhances protein/protein and protein/lipid interactions which appear relevant for efficient signal transduction. Palmitoylation also influences intracellular protein trafficking and protein activity [3–7]. Palmitoylation is a widespread modification found almost exclusively in membrane proteins. The family of proteins modified with thioester-linked palmitate is large and diverse. It includes transmembrane-spanning proteins and soluble proteins such as ion channels, neurotransmitter receptors, heterotrimeric guanine nucleotide-binding protein (G-protein)-coupled receptors, and integrins. In addition, hormone receptor signalling relies on protein palmitoylation at many levels, including palmitoylated co-receptors, Src family kinases, and adaptor or scaffolding proteins. The localization and signalling capacities of Ras and G-proteins are modulated by dynamic protein palmitoylation [1,5]. Recently, estrogen receptor (ER) isoforms belonging to the nuclear receptor superfamily have been added to the palmitoylproteoma [8]. Here, we review the role of ER␣ and ER␤ S-palmitoylation on 17␤-estradiol (E2)-induced non-genomic functions committed to the control of cell proliferation.

2.

ERs are palmitoylated proteins

Although dozens of palmitoylproteins have been described, few strong predictors of whether a protein will be a sub-

strate for palmitoylation have emerged. In fact, palmitoylated proteins have no clear consensus sequence(s) for this posttranslational modification although protein palmitoylation is thought to be an enzymatic reaction, mediated by a palmitoyltransferase(s) (PAT). The common denominator for most palmitoylated proteins is a membrane targeting sequence encompassing the target Cys, it consists of positively charged residue(s) and lipid anchors or transmembrane domains [9]. Based on multiple sequence alignment, we postulated that the amino acid sequence encompassing the solvent-exposed Cys447 and Cys399 residues present in the ligand-binding domain (LBD) of ER␣ and ER␤, respectively, are the unique which follow this requirement. In fact, an hydrophobic patch (Leu zipper-like) and an hydrophilic positively charged Lys residue are present close to the S-palmitoylable Cys447 and Cys339 residues of ER␣ and ER␤, respectively (Fig. 2) [10]. Remarkably, this sequence appears to occur also in other hormone receptors, representing a general rule for Spalmitoylation of this class of proteins [11]. The experimental evidence that ERs are palmitoylated proteins derived later from experiments performed with labeled palmitate [12,13]. In cervix carcinoma cells (HeLa cells) transiently transfected with ER␣ or ER␤ expression vectors, both receptors undergo S-palmitoylation. Remarkably, palmitate incorporation in both ERs is not a spontaneous reaction, being catalyzed by PAT. In fact, low levels of S-palmitoylated ER␣ or ER␤ were found in cells pre-treated with the PAT inhibitor 2-bromo-hexadecanoic acid (2-Br) [12,13]. The half time for PAT catalyzed incorporation of palmitate in ER␣- and ER␤transfected HeLa cells is ∼7 min and ∼60 min, respectively. This suggests that ER␤ is a poorer substrate than ER␣ for PAT [13].

3. ER␣ and ER␤ palmitoylation is a ligand-dependent process Palmitoylation must be considered more than a simple way of membrane association of otherwise soluble proteins. In fact, cycles of palmitoylation and de-palmitoylation affect protein activation allowing their movement(s) within membrane subdomains. De-palmitoylation of the endothelial nitric oxide synthase increases in response to cell treatment with the activator bradykinin [14]. Moreover, de-palmitoylation has a

s t e r o i d s 7 3 ( 2 0 0 8 ) 853–858

subtle effect on membrane distribution of G-proteins affecting their partitioning within membrane sub-domains [1]. Ligand (e.g., E2) binding modulates ER␣ and ER␤ palmitoylation [13,15]. E2 binding to ER␣ and ER␤ decreases the ER palmitoylation rate (t1/2 ∼ 30 min) and induces structural modification(s) impairing PAT recognition (i.e., ER palmitoylation) [13,15]. Note that, upon E2 binding, the Cys447 residue of ER␣ is not yet able to react with iodoacetic acid, a Cysreacting reagent [16]. This is in agreement with the solvent inaccessibility of Cys447 in the ER␣- and ER␤-ligand adducts (see [17]). Furthermore, E2 affects the localization of the stably integrated membrane targeted ER (MT-ER) in breast cancer cell lines [18]. MT-ER is myristoylated at the N-terminus and palmitoylated at the C-terminus. In the absence of E2, MT-ER is localized primarily to the cell membrane with some cytoplasmic localization. After E2 treatment, the localization of MT-ER at the plasma membrane decreases showing a punctuate pattern with localization in the cytoplasm [18]. ER␣ and ER␤ bind a wide variety of compounds with remarkable structural and functional diversity. Partialagonists (e.g., flavonoids, 4-hydroxytamoxifen, and raloxifene) and antagonists (e.g., ICI 164,384) bind to LBD with a geometry reminiscent that of natural agonists (i.e., E2). However, their large side chain substituents are not accommodated within the confines of the binding cavity, this results in multiple ligand-dependent conformationals of ER␣ and ER␤ [17] which, in turn, affects ER␣ and ER␤ palmitoylation status. Remarkably, the flavonoid naringenin (Nar, 5,7,4 trihydroxyflavanone), a weak ER␣ antagonist [19], induces a faster ER␣ de-palmitoylation than E2 (t1/2 ∼ 8 min and ∼30 min, respectively) (Marino, unpublished results). These data raise the possibility that different ligands, which induce different conformational changes in ER␣ and ER␤, could differently affect receptor palmitoylation status.

4. Palmitoylation impacts on ER␣ and ER␤ association to membrane proteins Current evidence indicates that the small population of ER␣ and ER␤ localized at the plasma membrane exists within caveolar rafts, interacting with specific membrane proteins [10,20–22]. ER␣ can further associate with specialized proteins including the modulator of the non-genomic activity of estrogen receptor (MNAR) (also named proline-, glutamic acid-, and leucine-rich protein-1; PELP1), Shc, epidermal growth factor (EGF) and insulin-like growth factor-1 (IGF-1) receptors, and striatin [23–29]. Shc and striatin have been reported to interact with the A/B domain of ER␣ [30], while MNAR acts as an adapter coupling ER to Src [28]. Although E2-induced ER␣ and ER␤ de-palmitoylation displays similar kinetics (t1/2 ∼ 30 min), the E2 stimulation promotes different ER/protein recognition. Palmitoylation enables ER␣ to reside at the plasma membrane and to interact with caveolin-1. Upon E2 binding, ER␣ undergoes slow de-palmitoylation and dissociates from caveolin-1, facilitating ER␣ movement to other membrane micro-domains [15]. Thus, ER␣ could be re-located by docking to other partner proteins (i.e., Shc/IGF-1 receptor and Src/p85) [31,32]. E2-stimulation of HeLa cells transfected with the un-palmitoylable ER␣

855

Cys447Ala mutant does not increase ER␣ association to MNAR or c-Src, impairing ER␣ ability to activate downstream kinases (Marino, personal communication). Correspondingly, the rapid Nar-induced ER␣ de-palmitoylation (t1/2 ∼ 8 min) induces the dissociation of the ER␣-caveolin-1 complex and impairs receptor association with adaptors and/or signaling proteins (i.e., MNAR and c-Src) (Marino, personal communication). The intact A/B domain and the Tyr537 residue present in the E domain are both required for ER␣ interaction with Src in the MNAR-ER␣-Src complex [23,28]. No association between ER␤, MNAR, and Src was observed before and after E2 stimulation [13]. On the other hand, E2 induces ER␤ de-palmitoylation and increases ER␤ level and its association with caveolin-1 [13]. As a whole these data raise the intriguing possibility that the short A/B domain of ER␤ could facilitate the E2-induced association between ER␤ and caveolin-1, impairing its association with MNAR and Src. However, E2 increases the association of ER␤ to a cytosolic kinase, p38 kinase, a member of the mitogen-activated protein kinase (MAPK) family, inducing p38 activation [13].

5. Palmitoylation is necessary for E2-induced effects The mechanism(s) by which E2 exerts proliferative effects is assumed to be exclusively mediated by rapid membranestarting actions [33–39]. E2 treatment of mammary-derived MCF-7 cells triggers the association of ER␣ to Src and p85, the regulatory subunit of PI3K, leading to DNA synthesis [36]. In hepatoma cell line (HepG2), multiple and parallel membranestarting pathways are rapidly activated by E2 binding to ER␣ [33,38,39]. The blockade of phospholipase C/protein kinase C (PLC/PKC), extracellular regulated kinase/MAPK (ERK/MAPK), and phosphoinositide 3 kinase/AKT (PI3K/AKT) pathways completely prevents the E2-induced DNA synthesis [38,39]. ERK/MAPK and PI3K/AKT pathways, rapidly activated by the ER␣–E2 complex, also have a critical role in E2 action as a survival agent. In fact, these pathways enhance the expression of the anti-apoptotic protein Bcl-2, block the activation of the p38 kinase, reduce the pro-apoptotic caspase-3 activation, and promote G1-to-S phase transition via the enhancement of the cyclin D1 expression [12,38,39]. S-Palmitoylation is a prerequisite of these E2-induced rapid events. In fact, the un-palmitoylable ER␣ Cys447Ala mutant or PAT inhibition do not support the E2-induced proliferative signaling via the ERK/MAPK and PI3K/AKT pathways in ER␣ containing HeLa and HepG2 cells [15]. Similar results have been recently reported in other tumor cell lines [40]. What is the contribution of ER␤ to E2-induced cell proliferation? ER␤ appears to act as a dominant regulator of E2 signaling. When co-expressed with ER␣, ER␤ causes a reduction of the ER␣-mediated transcriptional activation and the repression of ER␣-mediated effects, including cell proliferation [41,42]. Consistent with this notion, E2 increases proliferation of ER␣-expressing MCF-7 cells [42]. On the other hand, ER␤ inhibits the E2-induced proliferation in transfected MCF-7 cells and prevents tumor formation in a mouse xenograft model in response to E2 [43]. These findings seem to

856

s t e r o i d s 7 3 ( 2 0 0 8 ) 853–858

Fig. 3 – Schematic model illustrating the localization at and maintenance to the plasma membrane of ER␣ and ER␤. Under steady-state condition (upper panel, left), ER␣ is palmitoylated (black triangle) and localized at the plasma membrane associated to caveolin-1 (cav1). Upon E2 stimulation (upper panel, right) ER␣ is de-palmitoylated allowing its association to signaling proteins to trigger cell functions. Palmitoylated ER␤ (bottom panel, left) resides at the plasma membrane associated to caveolin-1 (cav1) and p38. Upon E2 stimulation (bottom panel, right) ER␤ undergoes de-palmitoylation, this increases ER␤ association to cav1, p38, and membrane. This association impairs the ER␤ re-allocation at the plasma membrane and its association with other signaling proteins. However, ER␤ association to p38 increases the kinase activity triggering cell functions. ERK, extracellular regulated kinase; G-prot, guanine nucleotide-binding protein; MNAR, modulator of non-genomic activity of ER; p85␣, ␣-subunit of phosphatidylinositol 3 kinase. For details, see text.

be linked to the ER␤ repressive effect on ER␣-induced indirect gene transcription by binding to other transcription factors (e.g., AP-1 and Sp1) [42]. However, in ER␤ transfected HeLa cells E2 has been reported to rapidly induce a persistent membrane-initiated activation of p38 without any interference on survival proliferative pathways [12]. ER-dependent caspase-3 activation and poly(ADP-ribose)polymerase (PARP) cleavage are some of the downstream events triggered by E2-induced p38 activation in ER␤ containing colon cancer cells (DLD1) [13]. Accordingly, E2 induces the cleavage of the caspase-3 proform, resulting in the production of the protease active subunit. In turn, the active enzyme catalyzes the inactivation of PARP [13]. These findings indicate that the plasma membrane localized ER␤ is important for anti-proliferative effects of E2 [12]. Furthermore, the rapid and prolonged E2-induced p38 activation is also fundamental both for the rapid increase of ER␤ mRNA translation and for the slow ER␤ gene transcription [44]. The consequence is the E2-induced increase of ER␤ levels, in DLD1 cells which further increases the E2 protective effect against the cancer cell growth [13,45]. Indeed, p38 inhibition impairs the increase of the ER␤ levels and prevents the E2-induced DLD-1 cell number reduction [44]. These results reinforce the interpretation of a role for ER␤ levels as a negative regulator of colon tumor growth [13,44 and literature cited therein]. Even though the membrane localization of ER␣ and ER␤ and the associated non-genomic actions are an area of active research, nuclear actions of membrane ERs has not received much attention [26,46]. Note that ER␣ and ER␤ palmitoylation is required for E2-induced gene transcription [15]. In fact, in

HeLa cells co-transfected with the estrogen responsive element (ERE) containing complement 3 (pC3) promoter or with the ERE-devoid cyclin D1 (pD1) promoter constructs and ER␣ expression vector, the E2 treatment induces the increase of pC3 and pD1 promoter activities, respectively [13]. On the other hand, in ER␤-transfected HeLa cells, E2 induces the increase of the pC3 promoter activity only [13]. Notably, the pre-treatment of ER␣ or ER␤-transfected HeLa cells with 2Br reduces the E2-mediated pC3 promoter activity [13]. As expected, ER␣ palmitoylation has a powerful effect on the E2induced cyclin D1 promoter activity which is totally impaired by treatment with 2-Br, whereas ER␤ was unable to mediate cyclin D1 promoter activity, both in the presence or absence of 2-Br [13]. Thus, E2-induced rapid signaling could affect the nuclear activities of ER␣ and ER␤. Both rapid and genomic pathways synergize each other to provide plasticity for cell response to sex steroids.

6.

Conclusion and perspectives

The mechanism(s) underling the mitogenic role played by E2 in different target tissues are now better understood based on the studies reported by different laboratories, including our own. These studies designate a strict relationship between the E2-induced non-genomic functions and cell proliferation. The non-genomic functions are thought to require plasma membrane ER␣ and ER␤ which are dependent on S-palmitoylation. S-Palmitoylation localizes ER␣ and ER␤ at the plasma membrane directing several and distinct E2 effects on cell proliferation (Fig. 3). The molecular mechanism(s) which rapidly

s t e r o i d s 7 3 ( 2 0 0 8 ) 853–858

follows E2 entry in ER␤-containing cells further sustains the tumor suppressor function played by this ER isoform. Although ER␣ undergoes palmitoylation, the outcome effects in cell physiology are opposite to those reported for ER␤. Thus, the expression of each ER isoform and/or their co-expression in the cells could account for the different E2-dependent modulation of cell proliferation (Fig. 3). Considering that all classes of steroid hormones possess receptors able to generate rapid responses [18,47,48], a new area of investigation focusing the role played by chemical modification(s) on steroid receptor activity and localization could be open. Intriguingly, several members of the steroid hormone receptor family, displaying an amino acid sequence highly homologous to that encompassing the Cys447 and Cys399 residues of ER␣ and ER␤, respectively, could undergo S-palmitoylation [11]. Recently, mutational analysis of this sequence present in the LBD of the progesterone receptor and of the androgen receptor confirmed that S-palmitoylation mediates rapid signalling [49]. These studies will aid the development of specific agonist and antagonists with wellcharacterized effects able to modify discrete E2-induced cellular functions.

Acknowledgments The authors wish to thank past and present members of their laboratories who contributed to the ideas presented here through data and discussions. This work was supported by grants from the Ministry of University and Research of Italy (PRIN-COFIN 2006 to M.M.).

references

[1] Smotrys JE, Linder ME. Palmitoylation of intracellular signaling proteins: regulation and function. Annu Rev Biochem 2004;73:559–87. [2] Linder ME, Deschenes RJ. Palmitoylation: policing protein stability and traffic. Nat Rev Mol Cell Biol 2007;8:74–84. [3] Dietrich LE, Ungermann C. On the mechanism of protein palmitoylation. EMBO Rep 2004;5:1053–7. ˜ FM, Vogler ¨ [4] Escriba´ PV, Wedegaertner PB, Goni O. Lipid–protein interactions in GPCR-associated signaling. Biochim Biophys Acta 2007;1768:836–52. [5] Resh MD. Palmitoylation of ligands, receptors, and intracellular signaling molecules. Sci STKE 2006;2006:re14. [6] Resh MD. Use of analogs and inhibitors to study the functional significance of protein palmitoylation. Methods 2006;40:191–7. [7] Nadolski MJ, Linder ME. Protein lipidation. FEBS J 2007;274:5202–10. [8] Acconcia F, Ascenzi P, Fabozzi G, Visca P, Marino M. S-Palmitoylation modulates human estrogen receptor-␣ functions. Biochem Biophys Res Commun 2004;316:878–83. [9] Bijlmakers MJ, Marsh M. The on-off story of protein palmitoylation. Trends Cell Biol 2003;13:32–42. [10] Acconcia F, Bocedi A, Ascenzi P, Marino M. Does palmitoylation target estrogen receptors to plasma membrane caveolae? IUBMB Life 2003;55:33–5. [11] Marino M, Ascenzi P. Steroid hormone rapid signaling: the pivotal role of S-palmitoylation. IUBMB Life 2006;58:716–9. [12] Acconcia F, Totta P, Ogawa S, Cardillo I, Inoue S, Leone S, et al. Survival versus apoptotic 17␤-estradiol effect: role of ER␣

[13]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26] [27]

[28]

[29]

[30]

857

and ER␤ activated non-genomic signalling. J Cell Physiol 2005;203:193–201. Galluzzo P, Caiazza F, Moreno S, Marino M. Role of ER␤ palmitoylation in the inhibition of human colon cancer cell proliferation. Endocr Relat Cancer 2007;14:153– 67. Robinson LJ, Busconi L, Michel T. Agonist-modulated palmitoylation of endothelial nitric oxide synthase. J Biol Chem 1995;270:995–8. Acconcia F, Ascenzi P, Bocedi A, Spisni E, Tomasi V, Trentalance A, et al. Palmitoylation-dependent estrogen receptor ␣ membrane localization: regulation by 17␤-estradiol. Mol Biol Cell 2005;16:231–7. Hegy GB, Shackleton CH, Carlquist M, Bonn T, Engstrom O, Sjoholm P, et al. Carboxymethylation of the human estrogen receptor ligand-binding domain–estradiol complex: HPLC/ESMS peptide mapping shows that cysteine 447 does not react with iodoacetic acid. Steroids 1996;61: 367–73. Ascenzi P, Bocedi A, Marino M. Structure-function relationship of estrogen receptor ␣ and ␤: impact on human health. Mol Aspects Med 2006;27:299–402. Rai D, Frolova A, Frasor J, Carpenter AE, Katzenellenbogen BS. Distinctive actions of membrane targeted versus nuclear localized estrogen receptors in breast cancer cells. Mol Endo 2005;19:1606–17. Totta P, Acconcia F, Leone S, Cardillo I, Marino M. Mechanisms of naringenin-induced apoptotic cascade in cancer cells: involvement of estrogen receptor ␣ and ␤ signalling. IUBMB Life 2004;56:491–9. Chambliss KL, Shaul PW. Rapid activation of endothelial NO synthase by estrogen: evidence for a steroid receptor fast-action complex (SRFC) in caveolae. Steroids 2002;67:413–9. Chambliss KL, Yuhanna IS, Anderson RG, Mendelsohn ME, Shaul PW. ER␤ has nongenomic action in caveolae. Mol Endo 2002;16:938–46. Razandi M, Oh P, Pedram A, Schnitzer J, Levin ER. ERs associate with and regulate the production of caveolin: implications for signaling and cellular actions. Mol Endo 2002;16:100–15. Barletta F, Wong CW, McNally C, Komm BS, Katzenellenbogen B, Cheskis BJ. Characterization of the interactions of estrogen receptor and MNAR in the activation of cSrc. Mol Endo 2004;18:1096–108. Zhang Z, Kumar R, Santen RJ, Song RXD. The role of adapter protein Shc in estrogen non-genomic action. Steroids 2004;69:523–9. Acconcia F, Kumar R. Signaling regulation of genomic and nongenomic functions of estrogen receptors. Cancer Lett 2005;238:1–14. Levin ER. Integration of the extra-nuclear and nuclear actions of estrogen. Mol Endo 2005;19:1951–9. Song RXD, Zhang Z, Santen RJ. Estrogen rapid action via protein complex formation involving ER␣ and Src. Trends Endocrinol Metab 2005;16:347–53. Greger JG, Guo Y, Henderson R, Ross JF, Cheskis BJ. Characterization of MNAR expression. Steroids 2006;71:317–22. Rayala SK, Hollander P, Balasenthil S, Molli PR, Bean AJ, Vadlamudi RK, et al. Hepatocyte growth factor-regulated tyrosine kinase substrate (HRS) interacts with PELP1 and activates MAPK. J Biol Chem 2006;281: 4395–403. Lu Q, Pallas DC, Surks HK, Baur WE, Mendelsohn ME, Karas RH. Striatin assembles a membrane signaling complex necessary for rapid, nongenomic activation of endothelial NO synthase by estrogen receptor ␣. Proc Natl Acad Sci USA 2004;101:17126–31.

858

s t e r o i d s 7 3 ( 2 0 0 8 ) 853–858

[31] Migliaccio A, Castoria G, Di Domenico M, de Falco A, Bilancio A, Auricchio F. Src is an initial target of sex steroid hormone action. Ann NY Acad Sci 2002;963:185–90. [32] Song RXD, Barnes CJ, Zhang Z, Bao Y, Kumar R, Santen RJ. The role of Shc and insulin-like growth factor 1 receptor in mediating the translocation of estrogen receptor ␣ to the plasma membrane. Proc Natl Acad Sci USA 2004;101:2076–81. [33] Marino M, Pallottini V, Trentalance A. Estrogens cause rapid activation of IP3-PKC-␣ signal transduction pathway in HEPG2 cells. Biochem Biophys Res Commun 1998;245:254–8. [34] Castoria G, Barone MV, Di Domenico M, Bilancio A, Ametrano D, Migliaccio A, et al. Non-trascriptional action of oestradiol and progestin triggers DNA synthesis. EMBO J 1999;18:2500–10. [35] Lobenhofer EK, Huper G, Iglehart JD, Marks JR. Inhibition of mitogen-activated protein kinase and phosphatidylinositol 3-kinase activity in MCF-7 cells prevents estrogen-induced mitogenesis. Cell Growth Differ 2000;11:99–110. [36] Castoria G, Migliaccio A, Bilancio A, Di Domenico M, de Falco A, Lombardi M, et al. PI3-kinase in concert with Src promotes the S-phase entry of oestradiol-stimulated MCF-7 cells. EMBO J 2001;20:6050–9. [37] Marino M, Distefano E, Pallottini V, Caporali S, Ceracchi G, Trentalance A. ␤-Estradiol stimulation of DNA synthesis requires different PKC isoforms in HepG2 and MCF7 cells. J Cell Physiol 2001;188:170–7. [38] Marino M, Acconcia F, Bresciani F, Weisz A, Trentalance A. Distinct nongenomic signal transduction pathways controlled by 17␤-estradiol regulate DNA synthesis and cyclin D1 gene transcription in HepG2 cells. Mol Biol Cell 2002;13:3720–9. [39] Marino M, Acconcia F, Trentalance A. Biphasic estradiol induced AKT-phosphorylation is modulated by PTEN via MAP kinase in HepG2 cells. Mol Biol Cell 2003;14:2583–91. ´ [40] Pietras RJ, Marquez DC, Chen H-W, Tsai E, Weinberg O, Fishbein M. Estrogen and growth factor receptor interactions

[41]

[42] [43]

[44]

[45]

[46]

[47]

[48]

[49]

[50]

in human breast and non-small cell lung cancer cells. Steroids 2005;70:372–81. Ogawa S, Inoue S, Watanabe T, Hiroi H, Orimo A, Hosoi T, et al. The complete primary structure of human estrogen receptor ␤ (hER␤) and its heterodimerization with ER␣ in vivo and in vitro. Biochem Biophys Res Commun 1998;243:122–6. Matthews J, Gustafsson JA. Estrogen signaling: a subtle balance between ER␣ and ER␤. Mol Interv 2003;3:281–92. Paruthiyil S, Parmar H, Kerekatte V, Cunha GR, Firestone GL, Leitman DC. Estrogen receptor ␤ inhibits human breast cancer cell proliferation and tumor formation by causing a G2 cell cycle arrest. Cancer Res 2004;64:423–8. Caiazza F, Galluzzo P, Lorenzetti S, Marino M. 17␤-Estradiol induces ER␤ up-regulation via p38/MAPK activation in colon cancer cells. Biochem Biophys Res Commun 2007;359:102–7. Marino M, Ascenzi P, Acconcia F. S-Palmitoylation modulates estrogen receptor ␣ localization and functions. Steroids 2006;71:298–303. Zhang D, Trudeau VL. Integration of membrane and nuclear estrogen receptor signaling. Comp Biochem Physiol A Mol Integr Physiol 2006;144:306–15. Losel RM, Falkenstein E, Feuring M, Schultz A, Tillmann HC, Rossol-Haseroth K, et al. Nongenomic steroid action: controversies, questions, and answers. Physiol Rev 2003;83:965–1016. Norman AW, Mizwicki MT, Norman DP. Steroid-hormone rapid actions, membrane receptors and a conformational ensemble model. Nat Rev Drug Discov 2004;3:27–41. Pedram A, Razandi M, Sainson RC, Kim JK, Hughes CC, Levin ER. A conserved mechanism for steroid receptor translocation to the plasma membrane. J Biol Chem 2007;282:22278–88. Thompson JD, Higgins DG, Gibson TJ, Clustal W. Improving the sensitivity of progressive multiple sequence alignment through sequence weighting, position-specific gap penalties and weight matrix choice. Nucl Acids Res 1994;22:4673–80.