Inactivation of thyrotropin-releasing hormone (TRH) by the hormonally regulated TRH-degrading ectoenzyme

O’Donnell

L, McLachlan

Robertson

DM:

motes the conversion between

NG,

ministered

pro-

sis in intact

RI, Wreford

1994.

Testosterone

cycle. Endocrinology

135:2608-

YT,

NG,

graphic

AK:

localization

1978.

Autoradio-

DM: 1990. Quantitative

of specifically

‘251-labeled follicle stimulating spermatogonia

pophysectomized

bound

hormone

on

of the rat testis. Endocrinol-

Parvinen

M: 1982. Regulation

Pescovitz

of the seminif-

Endocr

Rev 3:404417.

OH, Srivastava

matogenesis.

Trends

control

Endocrin

PR,

of sperMetab

5:

126-131. Persson

1990. Expression receptors ulated

C, Soder 0, et al.:

of p-nerve growth

mRNA in Sertoli

by testosterone.

factor

cells is downregScience

247:704-

of an-

Endocrinology

J: 1988. Follicle

and androgens

the concentration

Endocrinology

stim-

increase

of the androgen

cells.

receptor 122: 154 l-

hormone primate

W, Prins

G, Musto

Quian CA: 1994. Androgen in rat testis:

androgen

Endocrinology Weinbauer

NA, Suarez-

receptor

distri-

new implications

regulation

effect

on

size, and serum

antagonist-treated (Macaca

for

of spermatogenesis.

Endocrinol-

ogy 129:1831-1839. Yoshinaga 1991.

K, Nishikawa Role

of c-kit

matogenesis pression

S, Ogawa M, et al.: expression

in mouse

identification

of sper-

as a specific

and function.

site of c-kit ex-

Development

113:

NG, de Kretser

DM:

689-699. Zhengwei

Y, Wreford

1990. A quantitative

study of spermatogenrat testis. Biol Reprod

43~629-635. Zirkin BR, Santulli

R, Awoniyi CA, Ewing LL:

1989. Maintenance

of advanced

spermato-

genie cells in the adult rat testis:

134:2307-2316.

tive relationship

GF, Behre HM, Fingscheidt

nonhuman

fascicularis).

esis in the developing

Vornberger

U, Ni-

eschlag E: 1991. Human follicle stimulating

707.

a stimulatory testicular

spermatogenesis:

1550.

bution

H, Ayer-Le Lierre

hormone

in Sertoli

CH, Breyer

Monts BA: 1994. Paracrine

cytological

in intact and hy-

stages.

G, Cailleau

ulating

erous epithelium.

de

127:1215-1223. Verhoeven

ogy 103:1944-1951.

DM,

rats: identification

drogen-dependent

exerts

spermatogenesis,

inhibin levels in the gonadotropin-releasing

Robertson

studies of spermatogenesis

J, Christensen

rats.

125:1000-1010.

Wreford

Kretser

2614. Orth

Sun

hormone

on spermatogene-

and hypophysectomized

Endocrinology

of round spermatids

stages VII and VIII of the rat sper-

matogenic

testosterone

tion within

to testosterone

the testis.

quantitaconcentra-

Endocrinology

124:

3043-3049.

TEM

Raj HGM, Dym M: 1976. The effects of selective withdrawal genesis

of FSH or LH on spermato-

in the immature

rat. Biol Reprod

14:489-494. Rea MA, Marshall

GR, Weinbauer

schlag E: 1986. Testosterone tuitary

GF, Nie-

maintains

pi-

and serum FSH and spermatogene-

sis in gonadotropin-releasing tagonist-suppressed

rats.

hormone

an-

J Endocrol

108:

101-103. Russell

LD, Corbin

TJ, Borg

LR, Graso P, Bartke human pable

follicle

KE, de Franca

A: 1993. Recombinant

stimulating

of exerting

hormone

is ca-

effect

in the

a biologic

adult hypophysectomized

of degenerating

Endocrinology

133:2062-2070.

R, Sprando

LL, Zirkin

BR:

spermatogenesis

terone

C: 1992. Testos-

and spermatogenesis:

of stage-specific,

Endo-

S, Millar M, Kerr JB,

PTK, McKinnell

teins secreted

can

in the hy-

testosterone?

RM, Maddocks

Saunders

CA, Ewing

adult rat testis with exog-

enously administered crinology 126:95-101.

identification

androgen-regulated

pro-

by adult rat seminiferous

tu-

bules. J Androl 13:172-184. Skinner

MK,

McLachlan

1989. Stimulation cretion P-Mod-S.

RI, Bremner

of Sertoli

by the testicular

WJ:

cell inhibin

paracrine

se-

factor

monkeys.

a 4.5-year Fertil

study

Steril

TEM Vol. 6, No. 3, 1995

in male

The peptidergic signal substance TRH is inactivated by the TRHdegrading enzyme, a peptidase that exhibits a high degree of substrate specificity and other unusual characteristics. The tissue-specific regulation of the adenohypophyseal enzyme by estradiol and thyroid hormones suggests that it may serve an integrative function in modulating the response of adenohypophyseal target cells to TRH and thus pituitary hormone secretion. The high enzymatic activity of neuronal cells indicates that centrally this peptidase also might act as a terminator of neural TRH signals. (Trends Endocrinol Metab 1995;6: 101-l 0.5) TRH

(pyroGlu-His-Pro-NH,),

hypothalamic

the

neuropeptide elucidated,

secretion

of TSH

vitro

[for

reviews,

and

Schally

first

hormone stimulates

to the

and PFU. in viva and in see Guillemin

(1978)].

Under

(1978) certain,

rhesus

40: 1 lo- 117.

Sun YT, Irby DC, Robertson DM: 1989. The effects

Karl Bauer

be structurally

Mol Cell Endocrinol66:239-249.

Srinath BR, Wickings EJ, Witting C, Nieschlag E: 1983. Active immunization with follicle stimulating hormone for fertility control:

Regulator of TRH Signals?

cells.

To what extent

be maintained

pophysectomized

Sharpe

germ

RL, Awoniyi 1990.

A Potentid

rat by reducing

the numbers Santulli

Inactivation of ThyrotropinReleasing Hormone (TRH) by the Hormonally Regulated TRHDegrading Ectoenzyme

DM, de Kretser

of exogenously

01995,

ad-

mainly

pathologic,

ample,

acromegaly,

thyroidism) TRH

or in some also

stimulatory review In

Karl Bauer is at the Max-Planck-Institut fur experimentelle Endokrinologie, D-30603 Hannover, Germany.

has

ioral

been

effect

see Harvey addition

functions,

TRH

changes

effects

Elsevier Science Inc., 1043-2760/95/$9.50 SSDI 1043-2760(94)00216-Q

in

conditions

the

animal

reported

ex-

hypomodels,

to exert

on GH secretion

a

[for

(1990)].

to- these elicits and

(for

liver cirrhosis,

neuroendocrine a variety

of behav-

neuropharmacologic

central

nervous

system

101

(CNS), suggesting that it may be involved in various forms of cellular communication and may act as a putative neuromodulator or even as a neurotransmitter (Griffiths 1985, Horita 1986). This interpretation is supported by numerous biochemical studies and by the observation that TRH and TRH receptors are widely distributed in extrahypothalamic brain areas throughout the central nervous system (CNS) as well as in the gastrointestinal tract [for reviews, see Sharif (1989) and Jackson et al. (199O)l. Because biologically highly active substances are potentially extremely toxic, we should expect that for TRH there are very efficient degradation and/or elimination systems, ensuring the rapid inactivation of this signal peptide after its release. Rapid inactivation of TRH by blood and tissue enzymes has been demonstrated in vitro by various investigators [for an excellent review on the catabolism of TRH, see O’Cuinn et al. (199O)l. The biochemical data currently available strongly suggest that the biologic inactivation of TRH after its release is catalyzed by two closely related enzymes, the membrane-bound TRHdegrading enzyme and the TRHdegrading serum enzyme.

??

Characteristics of the TRH-Degrading Serum Enzyme and the Membrane-Bound TRH-Degrading Enzyme

Initial studies with rat and porcine serum demonstrated that the catabolism of TRH is initiated by an enzyme that cleaves the pyroGlu-His bond (Taylor and Dixon 1978, Bauer and Nowak 1979). Of special biologic interest was the observation that this enzyme not only exhibits unusual enzyme-chemical characteristics but also an extraordinarily high degree of substrate specificity (Bauer et al. 1981). Further studies with membrane preparations (O’Connor and O’Cuinn 1984, Horsthemke et al. 1984, Garat et al. 1985, Elmore et al. 1990) and partially purified enzyme preparations (O’Connor and O’Cuinn 1985, Wilk and Wilk 1989) then demonstrated that the membrane-bound enzyme exhibits the same unusual enzyme-chemical characteristics as the serum enzyme and, most

102

01995,

importantly, possesses identical properties with respect to substrate specificity. Both of these enzymes only hydrolyze TRH and none of the other naturally occurring neuropeptides tested so far. A high degree of substrate specificity is uncommon for most peptidases. Normally, we would rather expect that a standard set of general proteolytic enzymes furnishes a highly efficient inactivation system for an unlimited number of peptidergic communication factors, provided the peptidases are localized as ectoenzymes at specific target sites. The specificity of their anatomic and cellular localization most likely determines their biologic functions (Bauer and Horsthemke 1983, Turner et al. 1985). TRH seems to be one of the rare exceptions to this rule. ??

Cellular and Subcellular Localization

For the enzymatic inactivation of the peptidergic signal, the minimal condition is that the enzyme be localized on the plasma membrane with its active site oriented toward the extracellular space. Subcellular fractionation studies first showed that the particulate TRHdegrading enzyme is located in synaptosomal (O’Connor and O’Cuinn 1984, Torres et al. 1986, Elmore et al. 1990) and adenohypophyseal (Horsthemke et al. 1984) plasma membranes. Further studies with murine brain cells in primary culture and reaggregate cell cultures of rat anterior pituitaries (Bauer 1987b, Bauer et al. 1990, Cruz et al. 1991) then demonstrated that TRH added to the culture medium is not taken up by these cells but is rapidly degraded by neuronal cells and, interestingly enough, not by glial cells. Low but significant TRH-degrading activities were observed on the pituitary aggregates. Cell fractionation studies with dispersed pituitary cells demonstrated a close correlation between enzyme activity and the distribution of lactotrophic cells, regardless of the animal models used and the fractionation techniques employed, thus indicating that the enzyme is preferentially associated with lactotrophic cells (Bauer et al. 1990). ??

Purification

and Cloning

After solubilization by limited proteolysis under very mild conditions, we suc-

Elsevler Science Inc., 1043-2760/95/$9.50

ceeded recently in purifying the TRHdegrading ectoenzyme from rat and pig brain (about 200,000-fold) to electrophoretic homogeneity. Whereas SDSPAGE analysis revealed a single band with a molecular mass of 116 kD, a molecular mass of 230 kD was estimated by gel filtration, suggesting that the enzyme consists of two identical subunits, a feature not uncommon for other peptidases. As is also not uncommon for a cell surface protein, the enzyme was identified as a glycoprotein (Bauer 1994). After chemical and enzymatic fragmentation of the purified materials, the sequences of several peptides could be elucidated. This information provided the basis for screening cDNA libraries from rat brain and pituitaries, and finally we succeeded in isolating a cDNA that encodes the entire enzyme (Schauder et al. 1994). The analysis of the deduced amino acid sequence was consistent with the identification of the enzyme as a glycosylated, membraneanchored Zn*+ metallopeptidase (see Figure l), and upon transfection in mammalian cells a functionally active enzyme could be expressed, displaying the characteristics of the TRH-degrading ectoenzyme.

??

Hormonal Regulation of the TRH-Degrading Enzyme

As an interesting question, one might ask whether peptidases exhibiting such unusual characteristics might serve very specialized and perhaps even regulatory functions. The mandatory prerequisite for a regulatory function necessarily implies that the activity of such enzymes be controlled in turn by some other mechanisms. For TRH one would obviously first ask whether the TRH-degrading ectoenzyme is regulated by thyroid hormones. Regulation

by Thyroid Hormones

In vivo studies first demonstrated that the activity of the adenohypophyseal TRH-degrading ectoenzyme is stringently controlled by thyroid hormones (Bauer 1987a, Ponce et al. 1988, Suen and Wilk 1989). When animals were rendered hypothyroid by treatment with the goitrogenic agent propylthiouracil (PTU), the activity of the adenohypophyseal enzyme decreased within a few

SSDI 1043-2760(94)00216-Q

TEM Vol. 6, No. 3, 1995

EXTRACELLULAR SPACE

CYTOPLASM

HP

tt

to

t

I I I

Zn*+ I\

T

t ttt T

T

I_CO,H

I I Arg Tyr

1

His-&u-Xaa-Xaa-His

consensussequence Figure 1. Structure of the TRH-degrading ectoenzyme. According to the deduced amino acid sequence the protein consists of 1025 amino acids with a molecular mass of 117,302 D. It contains a short, presumably cytoplasmic, region at its amino terminus with a potential phosphorylation site that could be important for the inactivation and the high turnover of the enzyme. This region is followed by a stretch of 24 hydrophobic amino acids with characteristics of the transmembrane-spanning regions of integral membrane proteins. The large, most likely extracellular, domain contains 12 potential N-glycosylation sites, a consensus sequence for tyrosine sulfation and, most importantly, the consensus sequence of the zinc-dependent metallopeptidase family-namely the HEXXH motif with a second glutamic acid separated by 18 amino acids. In agreement with the active site studies (O’Connor and O’Cuinn 1987, Czekay and Bauer 1993), a tyrosine and arginine residue is also found in the expected conserved distance to the HEXkH sequence. -

days. Conversely, when euthyroid animals received a single injection of triiodothyronine (T,), the enzyme activity rapidly increased after a lag phase of 4-6 h, reaching maximal levels within 24 h and returning to basal values within physiologically meaningful time periods of 96 h. The short lag phase indicated that the onset of hormone expression is preceeded by the induction of protein synthesis (most likely as the result of T,induced gene transcription). The rapid decline of the enzyme activity after stimulation indicates a high turnover of the enzyme. In contrast to the adenohypophyseal enzyme, neither the activity nor the mRNA levels of the TRH-degrading brain ectoenzyme were affected by the thyroid status of the animals (Bauer 1987a, Emerson and Wu 1987, Ponce et al. 1988). The same is true for the membrane-bound enzymes from all other tissues that contain detectable activities of this enzyme, namely spinal cord, posterior pituitary, retina, lung, and liver. The activities of these enzymes were not affected even when the animals received multiple injections of T3 at pharmacologic concentrations (50 pg TX/100 g body weight). Under these conditions,

TEM Vol.6,No. 3, 1995

01995,

however, significant changes in the activity of the TRH-degrading serum enzyme were noticed (Bauer 1976, White et al. 1976, DuPont et al. 1976, Emerson and Wu 1987). Compared to the membrane-bound adenohypophyseal enzyme, the TRHdegrading serum enzyme responded sluggishly to the thyroid status of the animals. The activity in serum decreased slowly over several weeks when PTU was added to the animals’ drinking water and increased after a prolonged lag phase of 24 h when injections of thyroid hormones were given daily. Nevertheless, a considerable difference (five-fold) in the enzymatic activity became evident between hypothyroid and hyperthyroid animals, and also a significant genderdependent difference could already be noticed during these experiments (Bauer 1976). Regulation by Estradiol

Because serum of euthyroid female rats showed only 85% of the enzymatic activity of euthyroid males, we addressed the question whether the activities of the membrane-bound TRH-degrading enzymes might also be regulated by steroid hormones. A direct comparison of the

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ScienceInc.,

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enzymatic activities between different tissues of male and female rats revealed that there were no significant differences, with one exception: the anterior pituitaries (Bauer 1988). The enzymatic activity of the adenohypophyseal enzyme of normal male rats was three times higher than that of normal female rats. After ovariectomy, the activity rapidly increased within a few days, reaching the values of male rats within 3 weeks and decreased again when the ovariectomized rats were treated with estradiol benzoate (Bauer 1988). The activity of the adenohypophyseal enzyme of normal male rats was decreased by injections of estradiol benzoate.

??

Implication

of the

TRH-Degrading Ectoenzyme Within Neuroendocrine Mechanisms

Control

The stringent regulation of the adenohypophyseal TRH-degrading ectoenzyme by peripheral hormones strongly suggests that within neuroendocrine control mechanisms, this enzyme could represent an additional element, affecting the intensity of the hypothalamic stimulus and/or the duration of action of the signaling molecule. Thus, in addition to the well-known neuroendocrine control mechanisms, this enzyme could also influence the response of TRH-target cells to the hypothalamic TRH signal, consequently influencing adenohypophyseal hormone secretion. As already known, peripheral hormones strongly influence the synthesis and secretion of adenohypophyseal hormones either directly via

SSDI 1043-2760(94)00216-Q

103

the classic feedback regulatory systems or by indirect mechanisms. Furthermore, peripheral hormones also strongly affect the transduction of hypothalamic signals at adenohypophyseal target sites by altering the responsiveness of these cells to the signaling molecule via the mechanisms regulating the number of the corresponding receptors on the anterior pituitary cells. [For recent reviews on the regulation of TRH receptors, see Hinkle (1989) and Gershengorn (1993)]. As an attempt to put the TRH-degrading ectoenzyme into perspective within these regulatory systems, we evaluated the changes in adenohypophyseal transcript levels after manipulating the hormonal conditions of the experimental animals (Schomburg et al. 1993a and b). After a single injection of T, into euthyroid rats, we observed a very rapid increase in the mRNA levels of the TRHdegrading ectoenzyme and concomitantly a rapid decrease in the transcript levels of the TRH-receptor within 2-4 h. With regard to the TSHP-mRNA levels, we observed a rapid reduction in the length of the TSHP transcripts already 4 h after injecting T, and subsequently a slow decline in the TSHP-mRNA levels. These data are consistent with the known effects of T, on the regulation of TSH biosynthesis via TSHP gene transcription [for review, see Chin et al. (1993)] and the TX-induced decrease in the stability of TSHP-mRNA, which seems to be directly related to the shortening of the TSHP poly(A) tail (Krane et al. 1991). However, our extended time course demonstrated that the nadir of TSHP-mRNA levels with extremely low transcript concentrations was reached surprisingly late, 48 h after the hormonal stimulus. Conversely, after induction of hypothyroid conditions by PTU treatment, the mRNA levels of the enzyme decreased very rapidly and considerably, whereas those of the TRHreceptor and TSHP increased only moderately (two- to three-fold) within several days. After a single injection of estradiol, the mRNA levels of the enzyme rapidly and dramatically decreased within 2-4 h, whereas the TRH receptor transcript concentrations increased moderately, as expected from the studies reported in the literature both on the regulation of TRH binding sites (DeLean et al. 1977) and TRH receptor transcripts (Kimura

104

et al. 1994). In contrast, a single injection of estradiol (0.5 pg/lOO g body weight) neither significantly affected the mRNA levels of TSHP nor the PRL transcript concentrations. The kinetic data thus suggest that the effect of T, and estradiol on the mRNA levels of the adenohypophyseal hormones TSH and PRL follows the acute regulation of the TRH receptor transcript concentrations and of the mRNA levels of the TRH-degrading ectoenzyme. The early events apparently take place primarily at the signal-receiving site by mechanisms regulating (a) the number of TRH receptors and (b) the activity of the TRH-degrading ectoenzyme, which seem to operate in a mirror image to each other at specific TRH target sites of the anterior pituitary cells. To us it appears an attractive concept that the TRH-degrading ectoenzyme might contribute an important control element to balance the secretion of hypophyseal hormones according to the hormonal condition of the body (Figure 2). This mechanism might especially be important for the modulation of PRL secretion, which is not regulated by peripheral hormones via the classic feedback systems. Thus, it is tempting to postulate as a working hypothesis that PRL secretion might be modulated by an alternative “feedback mechanism” through the integrative function of the hormonally regulated TRH-degrading ectoenzyme. Of course, extensive studies are yet required to verify this working hypothesis and to explore the biologic function of this enzyme within the fascinating machinery that orchestrates the harmonious balance of an organism.

1

TSH / PRL

ihvoid Figure2. Postulated effects of peripheral hormones on the regulation of TRH-responsive target cells of the anterior pituitary. Thyroid hormones and estradiol strongly affect not only the synthesis and secretion of the pituitary hormones TSH and PRL, but also influence the number of TRH receptors and thus the responsiveness of TRH target cells of the anterior pituitary. In addition, the transmission of TRH signals might be controlled by the hormonally regulated TRH-degrading ectoenzyme, conceivably influencing the response of TRH-target cells by affecting the intensity of the hypothalamic stimulus and/or the duration of action of the signaling molecule. The very rapid and stringent hormonal regulation of the enzymatic activity, in mirror image to the number of TRH receptors, indicates that both mechanisms cooperate at the signal receiving site of TRH target cells, reinforcing the control of adenohypophyseal hormone secretion.

References Bauer K: 1976. Regulation

??

Acknowledgments

The author thanks Dr. P.W. Jungblut for obliging help and continuous support, Lutz Schomburg and all co-workers for helpful discussion and enthusiastic collaboration, Valerie Ashe for linguistic help and for typing the manuscript, Drs. S. Lee, W.W. Chin, M.C. Gershengorn, and R.A. Maurer for kindly providing the respective plasmids used in this study, and Jacob Tesdorpf for the graphic work. This work was supported by a grant from the Deutsche Forschungsgemeinschaft.

thyrotropin-releasing hormones.

of degradation

hormone

of

by thyroid

Nature 259:591-593.

Bauer K: 1987a. Adenohypophysial tion of thyrotropin-releasing ulated by thyroid

degrada-

hormone

reg-

Nature

330:

hormones.

375-377. Bauer

K: 1987b.

inactivation

Degradation

and biological

of thyrotropin-releasing

mone and other neuropeptides. SM, Weiner

RI, eds. Integrative

hor-

In McCann Neuroen-

docrinology: Molecular, Cellular, and Clinical Aspects. Basel, Karger, pp 102-l 14. Bauer K: 1988. Degradation and biological inactivation of thyrotropin-releasing hormone (TRH): regulation of the membranebound TRH-degrading

01995, Elsevier Science Inc., 1043-2760/95/$9.50SSDI 1043-2760(94)00216-Q

enzyme from rat an-

TEA4 Vol. 6, No. 3, 1995

terior

pituitary

hormones.

by estrogens

Biochimie

and thyroid

Bauer K: 1994. Purification

and characteriza-

ectoenzyme.

brain.

Em J Biochem

224:

387-396. Batter

B: 1983.

Degradation

of neuropeptides.

In Koch

eds. Biochemical

and Clinical

Neuropeptides.

G, Richter

D,

Aspects

New York, Academic

of

Press,

pp 195-210. a thyroliberin-degrading catalyzing

serum

the hydrolysis

of a serum

Bauer K, Carmeliet

H: 198 1. Spec-

peptidase-hydrolyzing

in primary

P, Schulz

cultures

cells.

1993. Thyroid gene

local-

thyrotro-

of neuronal,

hormone

regulation

expression.

aminopeptidase

DS: Prog

thyrotropin-releasing

II in primary brain.

cul-

J Neurochem of the

hormone-degrading

hormone

and thyroid

Bio-

receptor

hormones.

hor-

hormone-releasing

1989.

factor.

A, Carino

cology

TRH

receptors.

MA, Lai H: 1986. Pharma-

of thyrotropin-releasing

Annu Rev Pharmacol Coninck

hormone.

Toxic01 26:31 l-332.

B, Leblanc

P, Kordon

S, Wattiaux

Subcellular

C, Watti-

R, Bauer

distribution

K:

of particle-

capable

of hydro-

lyzing gonadotropin, thyroliberin, enkephalin, and substance P. Eur J Biochem 139: 315-320. IMD, Lechan RM, Lee SL: 1990. TRH

bution crinol

biosynthesis,

anatomic

and processing.

Front

distri-

Neuroendo-

11:267-312. N, Arai K, Sahara

Y, Suzuki H: 1994.

transcriptionally

scriptionally

and posttran-

upregulates

thyrotropin-

releasing bonucleic

hormone receptor messenger riacid in rat pituitary cells. Endo-

crinology

1341432-440.

Krane IM, Spindle roid hormone

ER, Chin WW: 1991. Thydecreases

P-subunit

messenger

L, Dussault on

by rat and human

plasma.

Clin

(Oxf) 5323-328.

the stability

and

of rat thyrotropin

EC,

O’Connor

B,

hydrolyzing pyroglutamate ase from guinea-pig brain.

aminopeptidNeuropeptides

specificity

hydrolyzing

pyroglutamate

Thyroid

status

influences rat serum but not brain TRH pyroglutamyl aminopeptidase activities. En120:1215-1217. J, Charli JL, Joseph-Bravo

01995,

by enzymes of brain tissue. J Neu54:1-13.

G, Charli JL, Pasten

studies

Schally

AV: 1978.

regulation 202:18-28. Schauder

Aspects

B, Schomburg Cloning

ectoenzyme releasing

of hypothalamic

of the pituitary

K: 1994.

Neuroendo-

gland.

Science

L, Kijhrle

J, Bauer

of a cDNA encoding

that

degrades

hormone.

an

thyrotropin-

Proc Nat1 Acad Sci USA

Schomburg

L, Schauder

K: 1993a.

The

degrading

ectoenzyme

on a narrow

of guineaof

pyroglutamate brain. Eur

B, O’Cuinn G: 1987. Active site on a narrow specificity thyami-

nopeptidase purified from synaptosomal membrane of guinea-pig brain. J Neurothem 48676-680.

Elsevier Science Inc., 1043-2760/95/$9.50

level of the TRHof rat hypophyseal

and hypothalamic

tissue are differently

ulated by thyroid

hormones

rochem

[abst].

L, Schauder

K: 1993b. Thyroid

B, Czekay G, Bauer

hormones

modulate

mRNA levels of the TRH-receptor TRH-degrading cells [abst]. l):B23. Sharif

reg-

J Neu-

61(Suppl):41A.

Schomburg

ectoenzyme

in pituitary

NA: 1989. Quantitative

gions of different

the

and the

Neuroendocrinology

phy of TRH receptors

58(Suppl

autoradiogra-

in discrete

mammalian

brain re-

species.

Ann

NY Acad Sci 553:147-175. Suen CS, Wilk S: 1989. Regulation tropin-releasing triiodothyronine.

J Neurochem

Taylor WL, Dixon JE: serum

releasing

en-

by L-3,5,3’52:884-888.

1978. Characterization

of a pyroglutamate rat

of thyro-

hormone-degrading

zymes in rat brain and pituitary

aminopeptidase

that

degrades

hormone.

from

thyrotropin-

J Biol Chem 253:6934-

6940. H, Charli

thyrotropin

J-L,

Gonzalez-Noriega

A,

P: 1986. Subcel-

of the enzymes degrading

releasing

in rat brain.

Turner

AJ, Matsas

there

specificity

pyroglutamate

B, Czekay G, Bauer

mRNA

hormone

and metab-

Neurochem

Int 9:103-

110.

144:271-278.

membrane

roliberin-hydrolyzing

JA, Aceves C, Jo-

activity by thyroid hormones. crinology 48:2 11-2 13.

olism

B, O’Cuinn G: 1985. Purification

synaptosomal

O’Connor studies

of

aminopeptid-

membranes

Eur J Biochem

and kinetic

hor-

hormone-releasing

Vargas MA, Joseph-Bravo

thyroliberin-

aminopeptidase from guinea-pig J Biochem 150:47-52.

15:31-36. CH, Wu CF: 1987.

a narrow

O’Connor

and luteinizing

lular distribution

ase in synaptosomal

M: 1990.

seph-Bravo P: 1988. Tissue-specific regulation of pyroglutamate aminopeptidase II

Torres

RNA. Mol Endocrinol

O’Connor B, O’Cuinn G: 1984. Localization

pig brain.

O’Cuinn G: 1990. Further characterization of the substrate specificity of a TRH-

Ponce

B, Elmore

of thyrotropin-releasing

91:9534-9538.

Pituitary

the poly(A) tract length

of thyrotropin-releasing

TEM Vol. 6, No. 3, 1995

Science

51469475.

F, Levasseur

Griffiths

the

125:345-358.

levels by

JH, Schally AV: 1976. Effect of thyroxine

Garat B, Miranda

of the neuron.

Endocri-

100: 1496-1504.

docrinology

Horita

Kimura

DeLean A, Ferland L, Drouin J, Kelly PA, Labrie F: 1977. Modulation of pituitary thyro-

Emerson

PM:

Estradiol

ectoenzyme as a metallopeptidase. them J 290:921-926.

MA,

in the brain:

Thyrotropin-releasing

a growth

J Endocrinol

prohormone:

of pyroglu-

Czekay G, Bauer K: 1993. Identification

Endocrinol

S: 1990.

Jackson

localization

tures of fetal mouse 56:1594-1601.

the inactivation

Harvey

1984.

of thy-

Recent

effects.

202:390402.

aux-De

J, Darling

and

10:225-235.

bound neutral peptidases

P: 199 1. Neuronal

A, Labrie

new endocrinology

glial, and

Cruz C, Charli J-L, Vargas MA, Joseph-Bravo

hormone

cloning

Ret Prog Horm

and central

R: 1978. Peptides

Horsthemke

Horm Res 48:393-414.

tropin-releasing

Guillemin

enzyme

Endocrinology

Chin WW, Carr FE, Burnside

nology

Thyrotropin-

Thyrotropin-releasing

endocrine

mone

hormone

receptor:

1985.

G, O’Connor

Degradation

rochem

Ann NY Acad Sci 553:176-187.

M, Baes M, De-

and cellular

hormone-degrading

adenohypophyseal 127:1224-1233.

estrogens

hormone:

Hinkle

118:173-176.

of the membrane-bound

pin-releasing

tamate

1993.

regulation of its expression. Res 48:341-363.

mone:

nef C: 1990. Regulation

rotropin

at

at the pyroglutamyl-histidine

bond. Eur J Biochem

ization

enzyme

bond. Eur J Bio-

Bauer K, Nowak P, Kleinkauf thyroliberin

of

of thyroliberin

the pyroglutamyl-histidine them 99:239-246.

Elmore

MC:

EC:

in rat

6:27-40.

hormone

Griffiths

degrading

hormone

Psychoneuroendocrinology

Bauer K, Nowak P: 1979. Characterization

DuPont

Gershengorn

O’Cuinn

of a membrane-bound

aminopeptidase

Neuropeptides

releasing

K, Horsthemke

ificity

Presence

thyroliberin-releasing

tion of the thyrotropin-releasing-hormonedegrading

P: 1985.

pyroglutamyl

70:69-74.

Biochem White

R, Kenny

AI: 1985.

neuropeptide-specific Pharmacol

N, Jeffcoate

KC: 1976.

34:1347-1356.

SL, Griffiths

Effect

Are

peptidases?

of thyroid

EC, Hooper status

on the

thyrotropin-releasing

hormone-degrading

activity

J Endocrinol

71:13-

Wilk S, Wilk EK: 1989. Pyroglutamyl

peptid-

of rat serum.

19. ase II, a thyrotropin-releasing degrading enzyme: purification ficity studies of the rabbit Neurochem Int 15:8 l-90.

SSDI 1043-2760(94)00216-Q

hormoneand speci-

brain

enzyme.

105