Development and characterization of in vitro self-assembled recombinant human follicle stimulating hormone originated from goat mammary epithelial cells

Follicle stimulating hormone (FSH), composed of FSHα and FSHβ subunits, is essential for female follicle development and male spermatogenesis. The recombinant human FSH (rhFSH) products on the market are mainly generated from mammalian cells and are expensive. Large animal mammary gland bioreactors are urgently needed to produce large amounts of rhFSH. However, there are currently no effective methods to prepare rhFSH by large animals mainly due to the fact that excessive accumulation of FSH might cause many adverse effects in animals. We herein report the development and characterization of functional self-assembled rhFSH produced in goat mammary epithelial cells (GMECs). FSHα and FSHβ stably expressed in Chinese hamster ovary (CHO) cell lines were secreted into culture medium and well glycosylated. Importantly, FSHα and FSHβ expressed apart were able to assemble into functional FSH. We next inserted human FSHα or FSHβ gene separately into goat β-Lactoglobulin locus in GMECs by CRISPR/Cas9. Inactive FSHα and FSHβ subunits expressed from GMECs assembled into rhFSH as analyzed by His-tag pull down assay. Functional assessment of rhFSH by cAMP induction assay, mouse ovulation induction and rat ovarian weight gain experiments showed that the bioactivity of self-assembled rhFSH expressed by GMECs was comparable to that of Gonal-F both in vitro and in vivo. Our study demonstrated that FSHα and FSHβ can be separately expressed and assembled into functional rhFSH, and provided the basis for future preparing FSH by goat mammary gland bioreactor with less health problems on the producing animals.

Effect of phytoestrogens on basal and GnRH-induced gonadotropin secretion

Plant-derived estrogens (phytoestrogens, PEs), like endogenous estrogens, affect a diverse array of tissues, including the bone, uterus, mammary gland, and components of the neural and cardiovascular systems. We hypothesized that PEs act directly at pituitary loci to attenuate basal FSH secretion and increase gonadotrope sensitivity to GnRH. To examine the effect of PEs on basal secretion and total production of FSH, ovine pituitary cells were incubated with PEs for 48 h. Conditioned media and cell extract were collected and assayed for FSH. Estradiol (E₂) and some PEs significantly decreased basal secretion of FSH. The most potent PEs in this regard were coumestrol (CM), zearalenone (ZR), and genistein (GN). The specificity of PE-induced suppression of basal FSH was indicated by the absence of suppression in cells coincubated with PEs and an estrogen receptor (ER) blocker (ICI 182 780; ICI). Secretion of LH during stimulation by a GnRH agonist (GnRH-A) was used as a measure of gonadotrope responsiveness. Incubation of cells for 12 h with E₂, CM, ZR, GN, or daidzein (DZ) enhanced the magnitude and sensitivity of LH secretion during subsequent exposure to graded levels of a GnRH-A. The E₂- and PE-dependent augmentation of gonadotrope responsiveness was nearly fully blocked during coincubation with ICI. Collectively, these data demonstrate that selected PEs (CM, ZR, and GN), like E₂, decrease basal secretion of FSH, reduce total FSH production, and enhance GnRH-A-induced LH secretion in a manner that is dependent on the ER.

Detailed analysis of formation of chicken pituitary primordium in early embryonic development

The primordium of the mammalian adenohypophysis derived from Rathke's pouch (RP) is known to be formed by oral ectoderm invagination. However, in the early phase of pituitary development, the detailed process by which the oral ectoderm develops into the adenohypophysis remains largely unknown. Using high-resolution non-radiolabeled in situ hybridization and the BrdU and TUNEL methods, we have examined the detailed expression pattern of factors involved in the formation of RP of chicken and the changes in the mitotic and apoptotic cell regions in RP. In the chicken embryo, Sonic hedgehog (Shh) mRNA was initially expressed in the stomodeal plate but not in the oral ectoderm. After prospective diencephalon had detached from the oral ectoderm, another Shh-expressing region appeared in the most rostral part of the recess. LIM homeobox gene 3 (Lhx3) mRNA first appeared in the anterior area of Rathke's recess, and expression then spread to the caudal region. alphaGSU mRNA-expressing cells were observed at both ends of the Lhx3-expressing region, and thereafter the expression area moved to the posterior region. Furthermore, a close overlap was found between the proliferating region and Lhx3 mRNA-expressing area, and TUNEL-positive cells appeared in Seessel's pouch derived from the foregut. Thus, the primordium of the pituitary gland corresponding to the Lhx3-expressing region is surrounded by the Shh-expressing region, which appears in two steps, and the mass growth and invagination of RP of chicken result from the coordination of the dorsal extension of the anterior region and the ventral extension of the posterior region of RP.

Increased food intake stimulates GnRH-I, glycoprotein hormone alpha-subunit and follistatin mRNAs, and ovarian follicular numbers in laying broiler breeder hens

The aim of this study, in 36 week-old laying broiler breeder hens, was to establish the effects on reproductive neuroendocrine gene expression of reinstating ad libitum food intake after moderate food restriction from 2 weeks of age. Seven days of ad libitum feeding increased the number of large pre-ovulatory ovarian follicles and gonadotropin releasing hormone-I (GnRH-I), glycoprotein hormone alpha-subunit and follistatin mRNAs. Plasma luteinizing hormone (LH) was also increased while plasma follicle-stimulating hormone (FSH) was reduced. There were no associated changes in gonadotropin inhibitory hormone (GnIH), LHbeta or FSHbeta mRNAs. The mechanism underlying the increased expression of alpha-subunit and follistatin mRNAs was investigated in vitro by incubating pituitary fragments with pulses of GnRH-I. This treatment increased alpha-subunit and follistatin mRNAs but did not affect gonadotropin beta-subunit mRNAs. It is concluded that lifting food restriction in laying hens increases GnRH-I gene transcription or mRNA stability which may be a consequence, or cause of increased GnRH-I release. This, in turn, increases glycoprotein hormone alpha-subunit and follistatin mRNAs, resulting in increased plasma LH and decreased plasma FSH, respectively.

Production of recombinant orange-spotted grouper (Epinephelus coioides) luteinizing hormone in insect cells by the baculovirus expression system and its biological effect

The cDNA sequence encoding orange-spotted grouper lhb (LHbeta) and cga (GTHalpha) subunits were cocloned into baculovirus transfer vectors and expressed in insect Sf9 cells. The results showed that two bands of 15.6 kDa and 11.4 kDa could be detected by SDS-PAGE and a band of 30 kDa could be detected by native PAGE. The recombinant grouper Lh (rgLh) could stimulate the secretion of testosterone (T) and estradiol-17beta (E2) from the gonad in a static incubation system in a time-dependent, but not a dose-dependent, manner. Using in vivo bioassay, the mRNA levels of two aromatases (cyp19a1a [P450aromA] and cyp19a1b [P450aromB]), gnrh (GnRH), lhb, and cga in the pituitary, gonad, and hypothalamus were determined in different groups of orange-spotted groupers treated respectively with rgLh, human chorionic gonadotropin (hCG), and a culture medium of insect cells transformed with an expression vector without lhb and cga subunits. The mRNA levels of cyp19a1a and cyp19a1b rose dramatically after injecting rgLh intraperitoneally, which was consistent with the secretion of sex steroid hormones. Interestingly, the mRNA levels of gnrh dropped in the pituitary, hypothalamus, and gonad, and the mRNA levels of lhb and cga in the pituitary of the experimental group expressed at a higher level than that of the hCG group. These results are in accord with the long positive feedback loop of Lh on gonad sex steroid hormones and the short negative feedback loop of Lh on gnrh mRNA levels. These results indicate that the rgLh is successfully expressed by the baculovirus-insect expression system and that the rgLh has biological activity.

A Pituitary cell type coexpressing messenger ribonucleic acid of proopiomelanocortin and the glycoprotein hormone alpha-subunit in neonatal rat and chicken: rapid decline with age and reappearance in vitro under regulatory pressure of corticotropin-releasing hormone in the rat

Promiscuous hormone mRNA expression in the pituitary remains poorly understood. We examined by means of RT-PCR and immunostaining whether glycoprotein hormone alpha-subunit (alphaGSU) could be coexpressed with proopiomelanocortin (POMC) in vivo and under pressure of CRH in vitro. Cells coexpressing alphaGSU and POMC mRNA amounted to 2.6% of the cells in ex vivo rat pituitary at birth [postnatal d 1 (P1)], fell to much lower level at P14, and were undetectable in adulthood. In cultured pituitary aggregates of P14 rats, alphaGSU/POMC cells remained scarce but represented up to 6.6% after chronic treatment with CRH but not leukemia inhibitory factor. CRH was less effective in aggregates from P1 and adult rats. The total alphaGSU population ex vivo at P1 was two times smaller than at P14, but in culture it expanded 2.5 times, concomitantly with a reciprocal change in POMC cell abundance. Tpit transcripts were detected in POMC-only and alphaGSU/POMC cells but not in alphaGSU-only cells. Cells coexpressing alphaGSU and POMC mRNA were relatively abundant in P14 chicken pituitary and aggregate cultures, but occurrence was not affected by CRH. Immunostaining showed alphaGSU and POMC colocalization in sporadic cells in intact rat pituitary and CRH-treated cultures at P1 but not at P14 and adult age. The data demonstrate the occurrence of cells coexpressing alphaGSU and POMC in rat and chicken pituitary. The developmental dynamics of this cell population and its response to CRH in vitro in the rat suggest a relationship of these cells with the embryonic branching of the POMC and alphaGSU cell lineages and their mutually opposite developmental course during early postnatal life.

Expression and purification of feline thyrotropin (fTSH): immunological detection and bioactivity of heterodimeric and yoked glycoproteins

The goal of this study was to express and purify recombinant feline TSH as a possible immunoassay standard or pharmaceutical agent. Previously cloned feline common glycoprotein alpha (CGA) and beta subunits were ligated into the mammalian expression vector pEAK10. The feline CGA-FLAG and beta subunits were cloned separately into the pEAK10 expression vector, and transiently co-transfected into PEAK cells. Similarly, previously cloned and sequenced yoked (single chain) fTSH (yfTSH) and the CGA-FLAG sequences were ligated into the same vector, and stable cell lines selected by puromycin resistance. Expression levels of at least 1 microg/ml were achieved for both heterodimeric and yoked fTSH forms. The glycoproteins were purified in one step using anti-FLAG immunoaffinity column chromatography to high purity. The molecular weights of feline CGA-FLAG subunit, beta subunit and yfTSH were 20.4, 17, and 45 kDa, respectively. Both heterodimeric and yoked glycoproteins were recognized with approximately 40% detection by both a commercial canine TSH immunoassay and an in-house canine TSH ELISA. The yoked glycoprotein exhibited parallelism with the heterodimeric form in the in-house ELISA, supporting their possible use as immunoassay standards. In bioactivity assays, the heterodimeric and yoked forms of fTSH were 12.5 and 3.4% as potent as pituitary source bovine TSH at displacing (125)I-bTSH and 45 and 24% as potent in stimulating adenylate cyclase activity in human TSH receptor-expressing JP09 cells. However, in addition to reduced receptor binding affinity, the recombinant glycohormones produced a reduced maximal effect at maximal concentration (E(max)) suggesting the possibility of the recombinant glycohormone constructs acting as partial agonists at the human TSH receptor.

Evaluation of Histological and Molecular Endpoints for Enhanced Detection of Thyroid System Disruption in Xenopus laevis Tadpoles

Amphibian metamorphosis represents a promising model for the identification of thyroid system-disrupting chemicals due to the pivotal role played by thyroid hormones for the initiation and regulation of metamorphosis. An important aspect of bioassay development is the identification and evaluation of sensitive and diagnostic endpoints. In this study, several morphological, histological, and molecular endpoints were evaluated for their utility to detect alterations in thyroid system function after exposure of stage 51 Xenopus laevis tadpoles to various concentrations (1.0, 2.5, 10, 25, and 50 mg/l) of the anti-thyroidal compound ethylenethiourea (ETU). Analysis of developmental stages on exposure day 20 and monitoring of time to fore limb emergence (FLE) revealed retardation and complete arrest of tadpole development at 25 mg/l and 50 mg/l ETU, respectively. Development was not affected by 1.0, 2.5, and 10 mg/l ETU. Histological alterations in the thyroid gland were observed in FLE-displaying tadpoles after exposure to 2.5, 10, and 25 mg/l ETU, as well as in developmentally arrested tadpoles exposed to 50 mg/l ETU. Prevalence and severity of histological changes increased in a concentration-dependent manner. Semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) showed increased mRNA expression of the alpha- and beta-subunits of thyroid-stimulating hormone (TSHalpha, TSHbeta) in pituitary tissue of tadpoles exposed to 25 and 50 mg/l ETU. Results demonstrate the successful detection of anti-thyroidal effects of ETU in Xenopus laevis tadpoles using various endpoints and highlight the particular sensitivity of thyroid gland histology to detect thyroid system disruption in tadpoles.

Transcriptional activity of the 5' upstream region of the porcine glycoprotein hormone alpha subunit gene

Gene expression of the porcine glycoprotein hormone alpha subunit (p-alphaGSU) was examined in LbetaT2 cells, which were established from the anterior pituitary lobe of the immortalized transgenic mouse and produce alphaGSU, and in CHO cells cloned from Chinese hamster ovaries. Expression of the reporter gene fused with p-alphaGSU gene upstream in LbetaT2 cells showed that the distal regions -540/-240 and -798/-541 are important for the activation of gene expression. In contrast, the transcriptional activity of the distal region of p-alphaGSU gene was repressed in CHO cells. The region -540/-240 contains an adequate enhancer, called pituitary glycoprotein hormone basal element, whereas the region -798/-541 has no distinguished element. Transfection of the expression vector containing cDNA of a pan-pituitary activator, Ptx1, whose putative binding sites are present scatted in the distal region of the p-alphaGSU gene, revealed unexpectedly that this factor significantly suppressed the expression of p-alphaGSU gene in LbetaT2 cells, indicating that Ptx1 is unrelated to the upregulation in the region -798/-541. Thus, this study demonstrated for the first time that the distal region -798/-541of the p-alphaGSU gene is indispensable for prominent expression of this gene in which an as yet unidentified factor may participate.

[Relationship between imbalanced synthesis of human chorionic gonadotropin alpha and beta subunits and pregnancy-induced hypertension]

OBJECTIVE

To study the relationship between imbalanced synthesis of human chorionic gonadotropin (hCG) alpha and beta subunits and the pathology of pregnancy-induced hypertension (PIH).

METHODS

Total hCG, free alphahCG and betahCG were measured in serum samples collected from 60 cases of PIH and 30 normal gravid women by radioimmunoassay. The ratio of total hCG/betahCG, betahCG/FalphahCG, (FalphahCG+betahCG)/betahCG were calculated. Immunohistochemical staining was performed in 13 placenta from each group.

RESULTS

In PIH group the levels of FalphahCG, total hCG and betahCG were significantly higher than those of normal group (FalphahCG: 528 +/-421 IU/L compared with 222 +/-129 IU/L; betahCG: 39396 +/-6412 IU/L compared with 24265 +/-5575 IU/L; total hCG: 66597 +/-9294 IU/L compared with 36078 +/-4767 IU/L, all P<0.001). The betahCG/FalphahCG ratio in PIH was lower than that of normal group (91.23 +/-53.38 Compared with 119.4 +/-80.1, P<0.05); (FalphahCG+betahCG)/betahCG ratio and total hCG/betahCG ratio in two groups were (1.022 +/-0.026 compared with 1.015 +/-0.011; 1.802 +/-0.339 compared with 1.807 +/-0.258, respectively P>0.05). The immunohistochemical intensity of betahCG and FalphahCG in syncytiotrophoblast was significantly increased in 13 PIH compared with the control.

CONCLUSION

These data suggested that the imbalanced synthesis of hCG alpha and beta subunits may cause hypertension.

Diurnal rhythms of common ?-subunit mRNA expression in the pars tuberalis of hamsters and chickens

To clarify whether the common alpha-subunit of glycoprotein hormones is involved in photic signal transduction, alpha-subunit mRNA levels in the pars tuberalis (PT) of both hamsters and chickens were estimated at different time points of the day/night cycle by laser capture microdissection (LCM) and real-time quantitative polymerase chain reaction (PCR). Distinct diurnal rhythms were found for alpha-subunit mRNA expression in both species. In the hamster PT, alpha-subunit mRNA levels gradually increased during the dark phase; the diurnal peak was found at time (ZT) 21. The lowest value was obtained at ZT 5 during the day. In the chicken PT, alpha-subunit mRNA levels were maintained at a low constant level at night between ZT 13 and 21. Thus, alpha-subunit mRNA expression in the PT depends on the light-dark cycle and may be controlled by the pineal hormone melatonin. The effect of various photoperiods on the hamster PT was examined by real-time PCR, immunohistochemistry, and electron microscopy. In hamsters kept under short photoperiod (L/D=8 h:16 h) or complete darkness, a dramatic decrease of alpha-subunit mRNA level was induced, and the PT-specific cells accumulated glycogen-like particles and enlarged secretory granules. Under long photoperiods (L/D=16 h:8 h), however, the alpha-subunit mRNA level was elevated and the PT-specific cells exhibited highly active features, i.e., piles of lamellar cisternae of rough endoplasmic reticulum and well-developed Golgi complexes. The alpha-subunit synthesized by the PT-specific cells may therefore participate in the circadian and seasonal regulation of endocrine activities.

Differential regulation of gonadotropins and glycoprotein hormone alpha-subunit by IGF-I in anterior pituitary cells from male rats

IGF-I has been demonstrated to stimulate basal and GnRH-induced gonadotropin release. IGF-I also elicites alpha-subunit secretion in human pituitary tumor cells. The aims of this study were to evaluate both the effect of IGF-I on gonadotropin LH-beta and FSH-beta mRNA levels and glycoprotein alpha-subunit gene expression in cultured rat anterior pituitary cells. The exposure of pituitary cells to recombinant human IGF-I (rhlGF-I; 2 microg/ml) for 72 h markedly stimulated basal LH and FSH release whereas their mRNA levels remained unmodified. IGF-I elicited a-subunit release from pituitary cells (p < 0.01) and augmented its mRNA levels. Exposure to IGF-I consistently reduced GH release from pituitary cells. This study shows that the gonadotropin-releasing effects of IGF-I are not paralleled by changes in their mRNAs whereas IGF-I stimulates not only alpha-subunit release but also its mRNA levels. This study provides the first observation of alpha-subunit regulation by IGF-I in normal pituitary cells, where a differential regulation between release and synthesis for gonadotropin a-and 1-subunits is also shown.

Hypophyseal gene expression profiles of FSH-beta, LH-beta, and glycoprotein hormone-alpha subunits in Ictalurus punctatus throughout a reproductive cycle

A determination of the seasonal changes in the expression of the genes encoding the subunits of gonadotropic hormones is an important first step in the understanding of the molecular control of the onset of puberty and the reproductive cycle in fish. In this study, the abundance of transcripts encoding the glycoprotein hormone alpha (GpH-alpha), follicle-stimulating hormone beta (FSH-beta), and luteinizing hormone beta (LH-beta) subunits in pituitaries of female channel catfish were systematically tracked throughout an annual reproductive cycle. All three genes showed a concurrent elevation coinciding with the onset of ovarian recrudescence but then each showed a second elevation at different times of the ovarian cycle. In addition to the initial peak at recrudescence, the expression of FSH-beta and GpH-alpha gene peaked again during mid- and late-vitellogenic growth, respectively. The LH-beta gene expression remained low during the phases of regression and vitellogenic growth but was moderately elevated (7-fold) at the onset of ovarian recrudescence and dramatically elevated (36-fold) just prior to spawning (June-July) when the FSH-beta levels were at their lowest. The expression patterns of FSH-beta and LH-beta are remarkably similar to the ovarian expression of their respective receptors.

Absence of pituitary adenylate cyclase-activating polypeptide-stimulated transcription of the human glycoprotein alpha-subunit gene in LbetaT2 gonadotrophs reveals disrupted cAMP-mediated gene transcription

Hormone regulation of anterior pituitary expression of the common glycoprotein hormone alpha-subunit (alphaGSU) is mediated by multiple response elements residing in the first -435 bp of the human promoter. In rat pituitary cells and mouse alphaT3-1 precursor gonadotrophs, the human alphaGSU promoter is strongly responsive to activators of the adenylyl cyclase/cAMP pathway, such as the hypothalamic releasing hormone, pituitary adenylate cyclase-activating polypeptide (PACAP) and forskolin (an adenylyl cyclase activator). However, the role of PACAP and cAMP in regulating alphaGSU transcription in the more differentiated LbetaT2 gonadotroph is unclear. Here, we investigate the regulation of the human alphaGSU promoter by PACAP and forskolin in LbetaT2 and alphaT3-1 gonadotrophs. PACAP failed to stimulate alphaGSU promoter activity or cAMP production in LbetaT2 cells, in marked contrast to alphaT3-1 cells. LbetaT2 gonadotrophs expressed extremely low levels of any PACAP type 1 receptors (PAC(1)-R) isoform by RT-PCR and lacked PAC(1)-R by radioligand binding. Forskolin stimulated the alphaGSU promoter in LbetaT2 cells, but by less than 30% of the response seen in alphaT3-1 gonadotrophs. This blunted cAMP transcriptional effect was not due to different levels of cAMP generation, or altered expression of the cAMP target proteins CREB, Akt, CBP or ICER. However, only LbetaT2 cells showed detectable expression of the protein kinase A type IIalpha regulatory subunit. Binding of activating transcription factor-2 and phosphorylated CREB to the consensus CRE was observed in both LbetaT2 and alphaT3-1 gonadotrophs, yet forskolin failed to stimulate either CRE- or CREB-mediated transcription in LbetaT2 cells. Collectively, these data demonstrate the lack of functional PACAP receptors in LbetaT2 gonadotrophs, and a pronounced attenuation in the responsiveness of this differentiated gonadotroph cell line to cAMP stimulus.

Production of biologically active tethered ovine FSHbetaalpha by the methylotrophic yeast Pichia pastoris

The pituitary-derived glycoprotein hormone FSH plays a central role in controlling vertebrate gonadal function. In female mammals the maturation of ovarian follicles is critically dependent upon stimulation by FSH. Moreover, injection of exogenous FSH is used extensively to stimulate increased numbers of follicles to ovulate. Structurally FSH is a heterodimeric glycoprotein composed of two non-covalently associated polypeptide subunits. The tertiary structures of both the alpha- and beta-subunits are constrained by intramolecular disulphide bonds and are post-translationally modified with two N-linked carbohydrate moieties, the structure of which appears to modulate in vivo biological activity. Here we report the expression of ovine FSH (oFSH) as a biologically active single-chain polypeptide using the methylotrophic yeast Pichia pastoris. Sequences encoding the mature oFSH alpha- and beta-proteins were fused to form a gene encoding a fusion protein with the C-terminus of the beta-chain joined to the N-terminus of the alpha-chain, with the chains separated by a two amino acid linker sequence. This fusion gene was itself fused to two alternative Pichia leader sequences (mating factor alpha and acid phosphatase) and transformed into the Pichia strains GS115 and SMD1168. The recombinant fusion protein (oFSHbetaalpha) was expressed at approximately 0.1 microg/ml in 'shake-flask' cultures. The Pichia-expressed tethered protein was biologically active in an in vitro bioassay, had a molecular mass of 28 kDa, as determined by SDS-PAGE, and bound the bovine FSH receptor with a binding profile similar to that of native oFSH.

Trans-differentiation of prostatic stromal cells leads to decreased glycoprotein hormone alpha production

Age-related development of benign prostatic hyperplasia is an important health issue in developed countries. The histopathogenetic hallmark of this disease is the increase in relative and absolute numbers of smooth muscle cells (SMC). Glycoprotein hormone alpha-subunit (GPHalpha) is expressed in the human prostate, and, because of its structural similarities to other cystine knot growth factors, it has been considered to have growth regulatory functions of its own. Primary cell cultures allowing for selective cultivation of prostatic epithelial cells, fibroblasts, and SMC were established. Directed trans-differentiation and cellular homogeneity was pursued by confocal scanning laser microscopy with cell type-specific markers. GPHalpha production by these cells was assessed by immunofluorimetric assays. Its predominant source was young fibroblasts, whereas replicative senescent fibroblasts, SMC, and control fibroblasts from foreskin did not produce significant amounts. Functionally, GPHalpha reduced growth of stromal cells at concentrations of 10 and 100 nmol/liter as shown by cell viability assays. It is concluded that histogenetic reorganization over the adult lifetime, guided by endocrine factors like steroid hormones together with senescence of fibroblasts, leads to a decreased production of growth inhibitors, such as GPHalpha, favoring proliferation and the development of benign prostatic hyperplasia.

Effect of pinealectomy on the photoperiod-dependent changes of the specific secretory cells and alpha-subunit mRNA level in the chicken pars tuberalis

The effect of pinealectomy on the synthesis of the common alpha-subunit of glycoprotein hormones by the specific secretory cells of the pars tuberalis (PT-specific cells) was examined in male chicks. Expression of melatonin receptor (Mel(1c)) mRNA was demonstrated in the chick pars tuberalis by reverse transcription-polymerase chain reaction analysis. Northern blot analyses revealed that, after pinealectomy, common alpha-subunit mRNA levels were increased in the pars tuberalis of chicks kept under normal lighting (L:D=12 h:12 h), indicating that melatonin inhibits the synthesis of the alpha-subunit of PT-specific cells. Furthermore, alpha-subunit mRNA levels in the pars tuberalis were shown to display similar photoperiod-dependent changes in pinealectomized chicks as in intact animals. Levels of alpha-subunit mRNA in the pars tuberalis were decreased in both pinealectomized and control chicks kept under continuous light (L:D=24 h:0), whereas the levels were enhanced in pinealectomized chicks kept under extended darkness (L:D=1 h:23 h) and under normal lighting. Thus, pinealectomy did not affect the inhibition or stimulation of the alpha-subunit synthesis in the chicken pars tuberalis elicited by continuous light or extended darkness, respectively. Quantitative electron-microscopic analyses showed that, after exposure to continuous light for 30 days, many PT-specific cells were filled with enlarged secretory granules in both pinealectomized and control chicks. Exposure to extended darkness for 30 days caused an increase in the cytoplasmic and nuclear areas of the PT-specific cells. Secretory granules were however larger in pinealectomized than in intact control chicks. These results suggest that the activity of PT-specific cells is mainly regulated by photoperiod.

A novel Ala(-3)Thr mutation in the signal peptide of human luteinizing hormone beta-subunit: potentiation of the inositol phosphate signalling pathway and attenuation of the adenylate cyclase pathway by recombinant variant hormone

Upon screening for polymorphisms in the human luteinizing hormone beta-subunit (LH beta) gene, we discovered a novel mutation in the LH beta signal peptide with functional consequences for signal transduction in mouse Leydig tumour cells (mLTC-1). This G(52)A point mutation in exon 2 of the LH beta gene, detected in heterozygous form in several normal DNA samples, caused an Ala(-3)Thr amino acid substitution. Recombinant forms of wild-type (WT) and Ala(-3)Thr variant (V) LH were produced in human embryonic kidney (HEK) 293 cells and purified. The immunoreactivities of the recombinant LH were determined by immunofluorometric assays and in-vitro bioactivities in mLTC-1 cells were assessed by using cAMP, progesterone and inositol trisphosphate (IP(3)), and activation of mitogen-activated protein kinase (MAPK) as end-points. Whereas both LH forms stimulated progesterone production and MAPK in similar fashion, WT-LH was more potent in stimulating cAMP, and V-LH was more potent in stimulating IP(3) generation. Both LH forms bound to LH receptors with similar affinities. No evidence was found for influence of the signal peptide mutation on efficacy of alpha- and beta-subunit dimerization. Sequencing of the recombinant V-LH beta protein also revealed that the mutation did not interfere with signal peptide cleavage. In summary, the present findings indicate that the Ala(-3)Thr mutation in the LH beta-subunit signal peptide has functional consequences, in the form of dissociation of stimulatory potency for different signal transduction pathways in vitro.

Epidermal growth factor regulation of equine glycoprotein hormone alpha subunit expression in trophoblast cells

Primates and equids are the only species known to express the placental glycoprotein hormone, chorionic gonadotropin (CG), a heterodimeric glycoprotein composed of an alpha subunit linked to a hormone-specific beta subunit. The regulatory mechanisms involved in the induction of equine glycoprotein alpha subunit gene expression have not been identified. Epidermal growth factor (EGF) receptor is known to transduce signals that alter a number of different cellular functions (cell proliferation, differentiation, hormone secretion, and gene regulation). In the present study, we investigated the regulation of the equine alpha subunit gene by EGF in trophoblasts. We found that 2800 base pairs of 5' flanking sequence from the equine alpha subunit promoter is sufficient for basal expression in human choriocarcinoma cells. Epidermal growth factor and phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC), increased transcriptional activity of the equine alpha subunit promoter (-2800/+21). These responses were blocked by pretreatment with bisindolylmaleimide-I, an inhibitor of PKC, suggesting an involvement of this pathway downstream of EGF. In addition, PD98059, an inhibitor of the extracellular signal-regulated kinase (ERK) pathway, completely blocked activation of the equine alpha promoter by PMA, suggesting that mitogen-activated protein kinase (MAPK) cascade was involved downstream of the PKC pathway. In conclusion, the EGF/PKC/MAPK pathway regulates equine glycoprotein alpha subunit gene expression through a distinct regulatory region (-2300 to -1900) in trophoblasts, while essential elements for basal expression appear to exist within the -2800 to -1900 region of the promoter.

Defect of syncytiotrophoblast formation and human chorionic gonadotropin expression in Down's syndrome

The syncytiotrophoblast (ST) is a major component of the human placenta as it is involved in feto-maternal exchanges and the secretion of pregnancy-specific hormones. We have studied the formation and function of the ST in normal and trisomy 21 (T21)-affected placenta using the in vitro model of cytotrophoblast differentiation into ST. Cytotrophoblast cells were isolated from first trimester, second trimester and term placentae. In vitro cytotrophoblast cells isolated from normal placenta fused to form the ST. This was associated with an increase in the transcript levels and the secretion of human chorionic gonadotropin (hCG). However, the secretion of hCG decreased through pregnancy. In T21-affected placentae, we observed a defect (or a delay) in ST formation and a dramatic decrease in the synthesis and secretion of this hormone compared with cultured cells isolated from control age-matched placentae. These results were confirmed by a significant (P < 0.05) decrease in transcript levels of alpha and beta subunits of hCG in total homogenates of T21-affected placentae compared with controls. These results suggest a decrease in functional mass of ST in T21 placenta, and therefore a decrease in production of placental pregnancy-specific polypeptide hormones.

Identification of CGA as a novel estrogen receptor-responsive gene in breast cancer: an outstanding candidate marker to predict the response to endocrine therapy

The estrogen receptor (ER) status of breast tumors is used to identify patients who may respond to endocrine agents such as tamoxifen. However, ER status alone is not perfectly predictive, and there is a pressing need for more reliable markers of endocrine responsiveness. Here, we identified the well-known CGA gene (coding for the alpha subunit of glycoprotein hormones) as a new ERalpha-responsive gene in human breast cancer cells. We used a real-time quantitative reverse transcription-PCR assay to quantify CGA mRNA copy numbers in a large series of breast tumors. CGA overexpression (> 10 SD above the mean for normal breast tissues) was observed in 44 of 131 (33.6%) breast tumor RNAs, ranging from 20 to 16,500 times the level in normal breast tissues; the highest levels of CGA gene expression were close to those observed in placenta. Significant links were observed between CGA gene overexpression and Scarff-Bloom-Richardson histopathological grade I+II (P = 0.015), and progesterone (P = 0.0009) and estrogen (P < 10(-7)) receptor positivity, which suggested that CGA is a marker of low tumor aggressiveness. We observed CGA mRNA overexpression in 44 of 90 (48.9%) ERalpha-positive tumors and in none of the 41 ERalpha-negative tumors. Immunohistochemical studies demonstrated that human chorionic gonadotropin alpha protein was strictly limited to ERalpha-positive tumor cells. Overexpression of the CGA gene was not accompanied by overexpression of the CGB gene. Our results also suggest that CGA could be a more reliable marker than PS2 and PR for ERalpha functionality and, thus, for endocrine responsiveness. Moreover, the CGA marker has the added value of dichotomizing ERalpha-positive patients into two subgroups of similar size. Specific antibodies directed to secreted human chorionic gonadotropin alpha protein are commercially available, thus facilitating the future application of this marker to the clinical management of breast cancer.

Early maturity in the male striped bass, Morone saxatilis: follicle-stimulating hormone and luteinizing hormone gene expression and their regulation by gonadotropin-releasing hormone analogue and testosterone

Striped bass are seasonal breeding fish, spawning once a year during the spring. All 3-yr-old males are sexually mature; however, 60-64% of the fish mature earlier as 1- or 2-yr-old animals. The endocrine basis underlying early maturity in 2-yr-old males was studied at the molecular level by monitoring changes in pituitary beta FSH and beta LH mRNA levels by ribonuclease protection assay, and correlating these changes to stages of testicular development. In maturing males, the mRNA levels of beta FSH were elevated during early spermatogenesis, whereas beta LH mRNA levels peaked during spermiation. The appearance of spermatozoa in the testis was associated with a decrease in beta FSH mRNA and a rise in beta LH mRNA abundance. Immature males had lower levels of beta LH mRNA than maturing males, but there were no differences in beta FSH mRNA levels between immature and maturing males. The regulation of gonadotropin gene expression in 2-yr-old males was studied by the chronic administration of GnRH analogue (GnRHa) and testosterone (T), with or without pimozide (P) supplementation. In immature males, the combination of T and GnRHa stimulated a three- to fivefold increase in beta FSH and beta LH mRNA levels, but the same treatment had no effect on gonadotropin gene expression in maturing males. In addition, the coadministration of P to immature males suppressed the stimulatory effect of GnRHa and T on beta FSH and beta LH mRNA levels, suggesting that dopamine may have a novel role in regulating gonadotropin gene expression.

Selective expression of trophoblastic hormones by lung carcinoma: neurendocrine tumors exclusively produce human chorionic gonadotropin alpha-subunit (hCGalpha)

Recent findings suggest that glycoprotein- and protein hormones act as local auto/paracrine growth/differentiation factors in normal and malignant tissue. An imbalanced or even selective production of human chorionic gonadotropin-alpha (hCGalpha) by neuroendocrine tumors in various organs has been reported. In this context, the ectopic production of trophoblastic hormones by lung carcinoma has not been investigated systemically. Because the determination of serum levels of hCGalpha are flawed by a number of factors, we designed an immunohistochemical study to precisely assess the comprehensive paraneoplastic auto-/paracrine hormone production by lung carcinoma of various histological types. To this end, 90 patients with primary lung neoplasms (40 neuroendocrine tumors, 29 adenocarcinomas, 20 squamous cell carcinomas, and 1 adenosquamous carcinoma) were analyzed by our well characterized monoclonal antibodies (mabs) against the glycoprotein hormones hCG, and its derivatives hCGalpha, hCGbeta, hCGbeta core-fragment (hCGbetacf), luteinizing hormone (LH, LHbeta), follicle-stimulating hormone (FSH, FSHbeta), and the protein hormones placental lactogen (PL) and growth hormone (GH). Overall, trophoblastic hormone immunoreactivity was found in 31% (28/90) of all lung carcinomas, regardless of histological differentiation. Detailed analysis showed 23% (21/90) hCGalpha-, 7% (6/90) hCGbeta, and 2% (2/90) hCGbetacf-positive cases. The tumors produced neither the intact heterodimer hCG, nor the other placental protein hormones PL-A/B and GH-V, or the hCG-related pituitary gonadotropins FSH/FSHbeta and LH/LHbeta. With regard to histological differentiation, it appeared that neuroendocrine tumors exclusively produced free hCGalpha in a distinct expression pattern depending on histological tumor grade. Thirty-eight percent (15/40) of all neuroendocrine neoplasms were hCGalpha-positive, and marker positivity increased with more mature, highly differentiated tumors (20% of small cell neuroendocrine carcinomas versus 90% of atypical and typical carcinoids). This is in striking contrast not only to trophoblastic malignancies and testicular germ cell tumors, but also to nontrophoblastic tumors, such as gynecological and urothelial malignancies, 60% of which produce hCGbeta and where marker positivity correlates with poor histological tumor differentiation. In conclusion, free hCGalpha, but not hCGbeta, is a useful marker for neuroendocrine differentiation in primary lung tumors. The fact that it is preferentially produced by the differentiated tumor types (carcinoids) points to a putative biological function in these tissues. The few hCGbeta-positive NSCLC must not be confounded with primary mediastinal choriocarcinoma.

Expression of the pituitary transcription factor Ptx-1, but not that of the trans-activating factor prop-1, is reduced in human corticotroph adenomas and is associated with decreased alpha-subunit secretion

We have studied the expression of the pituitary transcription factors Ptx-1 and Prop-1 in a series of 34 pituitary adenomas fully characterized for in vitro hormone secretion and histological staining. In studies involving mammalian cell lines, the pituitary transcription factor Ptx-1 has been shown to be a pituitary hormone panactivator, whereas more recent studies have shown that it plays an important role in alpha-subunit gene expression. Its expression has not been examined previously in human pituitary adenomas characterized by in vitro hormone secretory profiles. Of the 34 pituitary adenomas studied, Ptx-1 expression was reduced by more than 50% compared to that of the housekeeping gene human glyceraldehyde-3-phosphate dehydrogenase in the 6 corticotroph adenomas, which also had significantly reduced alpha-subunit production (all 6 tumors secreting < or =0.5 ng/24 h). Mutations of the pituitary transcription factor Prop-1, which is responsible for the syndrome of Ames dwarfism in mice, are being increasingly recognized as a cause of combined pituitary hormone deficiency in humans, although ACTH deficiency has been described only once. Prop-1 expression was detected in all 34 pituitary adenomas, including 6 corticotroph adenomas and 5 gonadotroph adenomas. The expression of Prop-1 has not been described previously in these cell phenotypes.

HCG concentration and receptor gene expression in placental tissue from trisomy 18 and 21

Trisomy 21 is associated with high maternal serum concentrations of intact human chorionic gonadotrophin alpha(HCG) and free beta-HCG whereas these concentrations are markedly decreased in trisomy 18. In this study, we investigated the effect of trisomy 21 and 18 on endogenous HCG concentrations and luteinizing hormone (LH)/HCG receptor expression in placental villous tissue in eight trisomy 21, six trisomy 18 and 42 chromosomally normal samples, collected at 12-16 weeks gestation. The tissue concentrations of intact HCG, free alpha-HCG and free beta-HCG subunits were measured using solid-phase two-site immunoradiometric assay. LH/HCG receptor expression was evaluated with immunohistochemistry and in-situ hybridization. Villous tissue in trisomy 21 contained higher beta-HCG concentrations than the controls (P < 0.05). In trisomy 18 cases, the beta-HCG concentration was lower than in the control group (P < 0.01). Both immunocytochemistry and in-situ hybridization demonstrated a more intense staining of the trophoblast in cases of trisomy 21 and 18, compared with controls with the strongest signal in cases of trisomy 18 (P < 0.01). We concluded that in trisomy 21 the high tissue HCG concentration and expression of LH/HCG receptor in the trophoblast may reflect the relative immaturity of the trophoblastic tissue whereas in trisomy 18, the very low concentration of endogenous HCG, associated with an over-expression of LH/HCG receptor in the trophoblast, is probably secondary to the poor differentiation of the cytotrophoblast.

Mechanisms that mediate negative regulation of the thyroid-stimulating hormone alpha gene by the thyroid hormone receptor

A group of transcriptional cofactors for nuclear hormone receptors, referred to as corepressors (CoRs) and coactivators (CoAs), has been shown to induce transcriptional silencing and hormone-induced activation, respectively, of genes that contain positive hormone response elements. Transcriptional silencing by CoRs involves the recruitment of histone deacetylases (HDACs), whereas ligand-dependent activation is associated with the recruitment of CoAs, which possess or recruit histone acetyltransferases (HATs). In a reciprocal manner, negatively regulated genes are stimulated by nuclear receptors in the absence of ligand and are repressed in response to ligand binding to receptors. We show here that negative regulation of the thyroid-stimulating hormone alpha (TSHalpha) promoter by the thyroid hormone receptor (TR) involves a novel mechanism in which the recruitment of CoRs by TR is associated with transcriptional stimulation and histone acetylation. Expression of excess HDAC reverses the stimulation mediated by the TR.CoR complex, consistent with a pivotal role for acetylation in this event. Addition of the ligand, 3,5,3'-triiodothyronine (T3), induces transcriptional repression of the TSHalpha promoter and is associated with the loss of histone acetylation. T3-dependent repression is blocked by phosphorylation of cAMP response element binding protein, or by inhibition of HDAC, indicating that receptor action is subverted by maneuvers that stimulate histone acetylation of the target gene. We propose that negative regulation of a subset of genes by TR involves the active exchange of CoRs and CoAs with intrinsic promoter regulatory elements that normally strongly induce histone acetylation and transcriptional activation.

Sodium butyrate-mediated induction of the glycoprotein hormone alpha-subunit gene: requirement for continued protein synthesis, identification of a butyrate-responsive element, and inhibition of promoter activation by 2-deoxyglucose

Production of the glycoprotein hormone alpha-subunit (GPH alpha) was enhanced by sodium butyrate (Btr) in HeLa cells. Induction of the HeLa alpha-subunit gene by Btr was inhibited by the simultaneous addition of cycloheximide (CHX), indicating a requirement for continued protein synthesis. Transient expression assays using plasmids containing the GPH alpha gene promoter fused to the chloramphenicol acetyltransferase (CAT) reporter gene demonstrated that the GPH alpha promoter is inducible by Btr in HeLa cells, and this induction could be prevented by 2-deoxyglucose (dGlc). CAT production driven by the SV-40 early promoter, the cytochrome P-450-IA1 promoter, and the Rous sarcoma virus long terminal repeat was also enhanced by Btr, but the augmented synthesis was not inhibited by the addition of dGlc, demonstrating that the effect is restricted only to some promoters. CAT synthesis could be induced by Btr when the GPH alpha promoter extended upstream to position -169 (relative to the transcription start site at +1) but not when the promoter terminated at -150, classifying the DNA between these termini as a Btr-responsive element (BRE). This region overlaps the composite trophoblast-specific enhancer. Inactivation of enhancer subdomains by site-directed mutagenesis confirmed the deletion analysis and ranked their response to Btr as CRE < TSE < URE < alpha ACT. Electrophoretic mobility shift analysis failed to detect any significant difference among several enhancer binding proteins in nuclear extracts from untreated and Btr-treated cells. Together, these results suggest that Btr-mediated induction of the alpha-subunit gene in HeLa cells is manifest either through the synthesis of a new transcription factor(s), which is inhibited by CHX but required for increased transcription from the GPH alpha gene promoter, or through the activity of existing factors that may require glycosylation or phosphorylation by a modification system that is inducible by Btr and inhibited by dGlc and CHX. These results further suggest that the factor is not an enhancer-binding protein or that Btr increases its transactivation potential without altering its DNA-binding activity.

The Australian brushtail possum (Trichosurus vulpecula) gonadotrophin alpha-subunit: analysis of cDNA sequence and pattern of expression

A cDNA sequence from the gonadotrophin alpha-subunit mRNA of Australian brushtail possum (Trichosurus vulpecula) has been determined and analysed. Comparison with seven eutherian mammalian gonadotrophin alpha-subunit gene sequences revealed an average of 82.6% homology between the coding region nucleotide sequences and 88.8% identity between the predicted amino acid sequences. The predicted possum gonadotrophin alpha-subunit protein has ten evolutionarily conserved cysteine residues, two potential N-linked glycosylation sites and a putative enzyme recognition sequence which it has been suggested is required for sulphation of carbohydrate moieties. Comparison of the possum gonadotrophin alpha-subunit 3' untranslated region (UTR) sequence with the 3' UTRs of eutherian alpha-subunit transcripts revealed sequence homology. In particular, an 18 nucleotide imperfect palindromic sequence present in the possum 3' UTR, with the potential to form a hairpin loop, was found to be evolutionarily conserved and present in five out of seven eutherian alpha-subunit 3' UTR sequences. In situ hybridization localized the transcripts to a sub-population of anterior pituitary cells presumed to be gonadotrophs and thyrotrophs. In summary, these results indicate considerable conservation of the structure and function of the gonadotrophin alpha-subunit protein since the divergence of the marsupial and eutherian mammalian lineages.

Cell-specific expression of the mouse glycoprotein hormone alpha-subunit gene requires multiple interacting DNA elements in transgenic mice and cultured cells

The glycoprotein hormone alpha-subunit gene is expressed and differentially regulated in pituitary gonadotropes and thyrotropes. Previous gene expression studies suggested that cell specificity may be regulated by distinct DNA elements. We have identified an enhancer region between -4.6 and -3.7 kb that is critical for high level expression in both gonadotrope and thyrotrope cells of transgenic mice. Fusion of the enhancer to -341/+43 mouse alpha-subunit promoter results in appropriate pituitary cell specificity and transgene expression levels that are similar to levels observed with the intact -4.6 kb/+43 construct. Deletion of sequences between -341 and -297 resuited in a loss of high level expression and cell specificity, exhibited by ectopic transgene activation in GH-, ACTH-, and PRL-producing pituitary cells as well as in other peripheral tissues. Consistent with these results, transient cell transfection studies demonstrated that the enhancer stimulated activity of a -341/+43 alpha-promoter in both alphaTSH and alphaT3 cells, but it did not enhance alpha-promoter activity significantly in CV-1 cells. Removal of sequences between -341 and -297 allowed the enhancer to function in heterologous cells. Loss of high level expression and cell specificity may be due to loss of sequences required for binding of the LIM homeoproteins or the alpha-basal element 1. These data demonstrate that the enhancer requires participation by both proximal and distal sequences for high level expression and suggests that sequences from -341 to -297 are critical for restricting expression to the anterior pituitary.

Silencing of the gene for the alpha-subunit of human chorionic gonadotropin by the embryonic transcription factor Oct-3/4

CG is required for maintenance of the corpus luteum during pregnancy in higher primates. As CG is a heterodimeric molecule, some form of coordinated control must be maintained over the transcription of its two subunit genes. We recently found that expression of human CG beta-subunit (hCGbeta) in JAr human choriocarcinoma cells was almost completely silenced by the embryonic transcription factor Oct-3/4, which bound to a unique ACAATAATCA octameric sequence in the hCGbeta gene promoter. Here we report that Oct-3/4 is also a potent inhibitor of hCG alpha-subunit (hCGalpha) expression in JAr cells. Oct-3/4 reduced human GH reporter expression from the -170 hCGalpha promoter in either the presence or absence of cAMP by about 70% in transient cotransfection assays, but had no effect on expression from either the -148 hCGalpha or the -99 hCGalpha promoter. Unexpectedly, no Oct-3/ 4-binding site was identified within the -170 to -148 region of the hCGalpha promoter, although one was found around position -115 by both methylation interference footprinting and electrophoretic mobility shift assays. Site-directed mutagenesis of this binding site destroyed the affinity of the promoter for Oct-3/4, but did not affect repression of the promoter. Therefore, inhibition of hCGalpha gene transcription by Oct-3/4 appears not to involve direct binding of this factor to the site responsible for silencing. When stably transfected into JAr cells, Oct-3/4 reduced the amounts of both endogenous hCGalpha mRNA and protein by 70-80%. Oct-3/4 is therefore capable of silencing both hCGalpha and hCGbeta gene expression. We suggest that as the trophoblast begins to form, reduction of Oct-3/4 expression permits the coordinated onset of transcription from the hCGalpha and hCGbeta genes.

Expression and cellular localization of inhibin alpha-subunit mRNA in equine fetal gonads

The expression of inhibin alpha-subunit mRNA in equine fetal gonads during pregnancy (Days 90 to 300) was examined by means of Northern blot analysis. In all samples examined, a single species of transcript was detected at the size of 1.5 kb. A digoxigenin-labeled antisense cRNA probe specific to equine inhibin alpha-subunit was synthesized and in situ hybridization analysis to locate the inhibin alpha-subunit mRNA positive cells was performed using frozen tissue sections of equine fetal ovary (day 150 of pregnancy) and equine fetal testis (day 180 of pregnancy). In the fetal ovary, positive cells were seen throughout the interstitial area but did not show any particular localization. In the fetal testis, on the other hand, the antisense cRNA hybridized almost exclusively to the interstitial cells surrounding developing seminiferous cords and Sertoli cells within the cords. Positive signals were also detected in a limited number of the interstitial cells located away from the cords. These results suggest that in equine fetal gonads, inhibin and/or inhibin alpha-subunit related molecules such as the monomeric form are produced and these molecules may have a paracrine/autocrine role within the gonads.

Expression of alpha and beta genes of human chorionic gonadotropin in lung cancer

To confirm the ectopic production of human chorionic gonadotropin (hCG) in lung cancer, we attempted to detect the presence of mRNA transcripts of the alpha and beta genes for hCG in lung cancer tissues obtained from surgical operations. Although we were able to show the presence of hCG beta mRNA transcripts in lung cancer tissue by Northern blot, the sensitivity of the assay was too low for a precise analysis of hCG beta mRNA transcripts in most lung cancers. Using reverse transcription PCR (RT-PCR) and Southern blot analysis, however, various amounts of mRNA transcripts of hCG beta genes 3, 5, 7 and 8 were demonstrated in 9 of the 14 lung cancer tissues examined, while no mRNA transcripts were detectable in 12 normal lung tissues from the same patients. Our results are consistent with a clear difference in serum and urinary hCG beta levels observed between normal subjects and lung cancer patients. The expression of the hCG alpha gene, however, was detected in normal lung tissues more frequently than in lung cancer tissues using RT-PCR Southern blot. Our results strongly suggest the production of hCG beta as being part of the phenotype of malignantly transformed lung cells and further strengthen its superior specificity over intact hCG or hCG alpha as a tumor marker for lung cancers.

Correlation in HeLa cells of anchorage-independent growth and synthesis of the glycoprotein hormone alpha-subunit

In addition to its normal synthesis in pituitary and placenta for production of the four glycoprotein hormones (GPH), the free alpha-subunit is produced by a variety of tumors and tumor-derived cell lines. It has long been used clinically as a tumor marker, but the question remains as to whether ectopic production of GPH alpha represents the random and chance activation of the hormone gene during cancer development or whether GPH alpha may contribute directly or indirectly to the biology of the tumor. One characteristic of tumorigenic cells in culture is their ability to proliferate in an anchorage-independent way. Data are presented in the following paper to show that the cloning efficiency of HeLa cervical carcinoma cells in soft agar is directly correlated with their production of the GPH alpha-subunit. HeLa variants that differ over 400-fold in their production of GPH alpha similarly exhibited a marked difference in their ability to form colonies in 0.3% noble agar. When HeLa SR3 cells (a variant that produces GPH alpha at high levels) was stably transfected with a vector producing the antisense strand of GPH alpha cDNA, the synthesis of the GPH alpha-subunit was reduced in these cells as was their cloning efficiency in soft agar. Similarly, when HeLa A5F cells (a variant producing little or no GPH alpha) were stably transfected with an alpha-subunit expression vector, the production of GPH alpha was increased significantly in concert with an increased ability to form colonies in 0.3% noble agar. Somatic cell hybrids between HeLa SR3 and HeLa A5F exhibited intermediate levels of GPH alpha gene expression and colony formation in soft agar compared to the parental strains. These data suggest that some parameters of the tumorigenic phenotype, such as anchorage-independent growth, are responsive to, or are dependent upon, the production of free alpha-subunit.

The function of retinoid X receptors on negative thyroid hormone response elements

Retinoid X receptors (RXRs) form heterodimers with thyroid hormone receptors (TRs). RXRs increase DNA binding affinity of TRs and T3-mediated transactivation on positive T3 response elements (TREs). However, the role of RXRs on negative TREs, and the relation of RXRs to the dominant negative effect of mutant TRs, are not defined. To clarify the function of RXRs on negative TREs, we performed transient cotransfection studies using the rat glycoprotein hormone alpha promoter fused to luciferase gene (alphaLuc), and human TRH promoter fused to luciferase gene (TRH-Luc) as reporters. We found that the JEG-3 cell-alphaLuc system was very sensitive to TR regulation. Using TRbeta1 wild-type (WT) expression vector, 6.2 ng/well (170 ng/10 cm dish), and 0.2 ng/well (11 ng/10 cm dish) caused maximal, and half maximal, inhibition of Luc activities in the presence of 1 nM T3. A T3 dose dependent inhibition study was also performed. From these studies, we determined that the appropriate conditions in which to study alphaLuc transactivation, in a linear portion of the dose response curve, was using 0.8 ng/well TRbeta1 expression vector and 0.1 nM T3. Under these conditions, TRbeta1 mutant R316H (GH), but not G345R (Mf), showed a weak dominant negative effect at a 1:1 ratio in the presence of 0.1 nM T3 although neither mutant had detectable T3 binding affinity. Moreover this dominant negative effect of R316H on the alphaLuc reporter was enhanced in the presence of RXRgamma. Mutant G345R showed a stronger dominant negative effect than did R316H when using a double palindromic TRE fused to herpes simplex thymidine kinase-Luc reporter as a positive TRE. These results conform to the clinical features of R316H which is associated with apparent pituitary resistance of thyroid hormone (PRTH). Mutant R316H also showed a weak dominant negative effect with TRH-Luc at a 1:1 ratio in the absence or presence of RXRgamma. However RXRgamma did not enhance the dominant negative effect as it did using alphaLuc reporter gene. Electrophoretic gel mobility shift assay (EMSA) showed that RXR alpha augmented the DNA binding affinity of wild type and R316H TRs as heterodimers on the previously reported negative TREs of glycoprotein hormone alpha promoter, suggesting that RXR does not produce its response by removing TRs from these TREs. RXR alpha augmented DNA binding affinity of TRbeta1WT, and R316H showed a weaker heterodimer band than did the wild type in EMSA. Using the TRH-Luc reporter, basal activity was increased by wild type TRbeta1. However a TRbeta1 DNA binding domain mutant, (C127S) which can not bind to DNA, did not increase the basal activity. This indicates that DNA binding of the TR is required for increasing basal activity of TRH promoter. These results indicate that (1) RXR-TR heterodimers play a role in basal transactivation and T3 suppression of negatively regulated genes, and (2) RXRs increase the dominant negative effect of some mutant TRs on specific negative TREs. (3) This effect occurs without removing TRs from the TRE. (4) The differential dominant negative effect of mutant R316H (negative TRE > positive TRE) may explain, at least in part, the presentation of R316H as PRTH. (5) Augmentation of basal activity by wild type TRs on a negative TRE requires DNA binding.

Immunodetection of glycoprotein hormone subunits in nonfunctioning and glycoprotein hormone-secreting pituitary adenomas

While it is established that nonfunctioning pituitary adenomas (NFPA) produce a spectrum of glycoprotein hormones, the ability of glycoprotein hormone-secreting adenomas to synthesize hormones other than those in vivo hypersecreted has been poorly investigated so far. In this study the immunolocalization of the beta-subunits of LH, FSH, CG and TSH and the common alpha-subunit was investigated in 10 NFPA, 3 gonadotropin-secreting adenomas (Gn-omas, 1 LH-oma, 1 FSH-oma and 1 LH/FSH-oma) and 3 TSH-secreting adenomas (TSH-omas) using an immunohistochemical technique with specific antibodies to glycoprotein subunits. The percentage of positive cells was determined observing at least 5 photograph fields containing about 50 cells. Nine of the 10 NFPA were positive for FSH beta with a high percent of positive cells (> or =30%), 6 for LH beta and 5 for TSH beta with a lower number of labelled cells (from 5 to 30%). Of the 8 NFPA tested, 5 showed a marked positivity for CG beta. In Gn-omas, tumors were positive for the gonadotropin that was in vivo hypersecreted (10-60% positive cells) and negative for either TSH beta or CG beta. Similarly, in TSH-omas TSH beta was detected in a variable proportion of cells (10-30%) with no immunoreactivity for either LH beta or FSH beta or CG beta. This study indicates that the coexpression of FSH beta, LH beta, CG beta and TSH beta molecules is characteristic of NFPA since Gn-omas were negative for CG beta and TSH beta and TSH-omas were negative for FSH beta, LH beta and CG beta. Moreover, the biological events that make NFPA 'silent' glycoprotein hormone-secreting adenomas remain unclear since the positivity for gonadotropins and TSH showed by NFPA was similar to that observed in Gn-omas and TSH-omas, respectively.

Calcium and glycoprotein hormone alpha-subunit gene expression and secretion in alpha T3-1 gonadotropes

GnRH stimulates both transcription and secretion of the alpha-subunit in pituitary cells, but the precise role of the calcium- signaling mechanisms mediating these actions are unclear. We have examined the role of calcium using alpha T3-1 gonadotropes transfected with alpha-promoter constructs linked to a luciferase reporter gene and concomitant measurement of alpha-subunit secretion. The calcium channel agonist, BayK8644 (1 microM) significantly stimulated alpha-subunit transcription (4.9-fold, P < 0.05) but to a lesser extent than either GnRH (100 nM, 20.7-fold, P < 0.001) or phorbol-12-myristate-13-acetate (TPA, 100 nM, 8.7-fold, P < 0.05). The transcriptional response to a combination of BayK8644 and TPA was approximately additive. Despite stimulating alpha-subunit gene expression, BayK8644 had no effect on alpha-subunit secretion at 24 h, and co-addition of BayK8644 and TPA did not produce any further stimulation of alpha-subunit secretion (3.0-fold, P < 0.001) compared with TPA alone (3.2-fold, P < 0.001). Pretreatment of alpha T3-1 cells with the calcium channel blocker, nifedipine (1 microM for 5 min), essentially blocked GnRH-stimulated alpha-promoter activity without affecting GnRH-stimulated alpha-subunit release. In contrast, thapsigargin pretreatment (1 microM for 5 min), which depletes intracellular calcium stores, significantly reduced basal and GnRH-stimulated secretion without affecting the ability of GnRH to increase alpha-promoter activity. Incubation of alpha T3-1 cells in calcium-depleted media showed that the transcriptional response was dependent on extracellular calcium concentration, with maximum stimulation by GnRH seen at a calcium concentration of 1.7 mM. Deletion analysis indicated that sequences between -420 and -244 bp were involved in mediating the response to BayK8644. Constructs containing only upstream alpha-promoter sequences from -517 to -98 bp, fused to the heterologous thymidine kinase promoter, exhibited loss of responsiveness to BayK8644 below -298 bp. These upstream elements were also found to be important for basal expression of the alpha-promoter and for mediating the response to TPA but were distinct from GnRH responsiveness of the human promoter in alpha T3-1 cells. These studies suggest differential regulation of GnRH-stimulated alpha-subunit gene transcription and secretion by extracellular calcium influx and intracellular calcium mobilization. The transcriptional response to extracellular calcium influx is mediated through two or more elements between -420 and -244 bp, which are also involved in basal and TPA-stimulated expression of the alpha-subunit promoter.

Specification of pituitary cell lineages by the LIM homeobox gene Lhx3

During pituitary organogenesis, the progressive differentiation of distinct pituitary-specific cell lineages from a common primordium involves a series of developmental decisions and inductive interactions. Targeted gene disruption in mice showed that Lhx3, a LIM homeobox gene expressed in the pituitary throughout development, is essential for differentiation and proliferation of pituitary cell lineages. In mice homozygous for the Lhx3 mutation, Rathke's pouch formed but failed to grow and differentiate; such mice lacked both the anterior and intermediate lobes of the pituitary. The determination of all pituitary cell lineages, except the corticotrophs, was affected, suggesting that a distinct, Lhx3-independent ontogenetic pathway exists for the initial specification of this lineage.

Steroid and pulsatile gonadotropin-releasing hormone (GnRH) regulation of luteinizing hormone and GnRH receptor in a novel gonadotrope cell line

Properties of a pituitary gonadotrope include the capacity to regulate gonadotropin synthesis and secretion in response to a GnRH signal. Progress in identifying the steps involved in these processes has been impeded by the lack of a homogeneous in vitro model of gonadotropes. This paper presents functional characterization of a L beta T2 gonadotrope cell line generated by tumorigenesis in transgenic mice carrying the rat LH beta-subunit regulatory region linked to the SV40 T-antigen oncogene. This cell line expresses LH beta, alpha-subunit, and GnRH-receptor (GnRH-R) mRNAs (though not FSH beta), responds to glucocorticoid treatment with a reversible dampening of proliferation, and responds to pulsatile, concentration-dependent GnRH administration with LH secretion. L beta T2 cells presented with four GnRH pulses (10 nM, 90-min interpulse interval) on each of 4 days respond with incremental increases in LH secretion on successive days. This increase was greatest (15-fold) in the presence of estradiol and dexamethasone. Part of the enhanced responsiveness is apparently due to an increase in GnRH-R; pulsatile GnRH treatment alone as well as steroid treatment alone led to an increase in GnRH-R mRNA levels. When secretion was stimulated on day 4 with 54 mM [K+] pulses, bypassing the GnRH-R, the LH-secretory response indicated that the GnRH pulse history as well as estradiol and dexamethasone have actions on L beta T2-secretory capacity distinct from changes in the GnRH-R. This increase can be explained in part by the marked up-regulation of LH beta, but not alpha-subunit, mRNA observed in GnRH-pulsed cells. In summary, L beta T2 clonal gonadotropes exhibit functional characteristics consistent with those of normal pituitary gonadotropes such as LH secretion via a regulated pathway and changes in GnRH-R and LH beta gene expression in response to signaling by GnRH and steroid hormones and therefore should be a useful tool for dissecting the cellular and molecular events involved in these fundamental gonadotrope properties.

Testosterone inhibits the basal and gonadotropin-releasing hormone-stimulated synthesis and release of newly synthesized alpha- and lutropin (LH) beta-subunit but not release of stored LH in cultured rat pituitary cells

To further explore the mechanism of steroid feedback in male, the effects of testosterone (T) and gonadotropin-releasing hormone (GnRH) on the rates of alpha- and lutropin (LH)beta-chain synthesis, neosynthesized subunits and radioimmunoassayable LH release into the medium were studied in the cultures of anterior pituitary cells from orchiectomized and intact rats. Polypeptides were [35S]methionine-labeled, immunoprecipitated separately in the medium and cells, then after SDS-PAGE precisely quantified. The total (medium + cells) radioactivity incorporated in the absence of GnRH into alpha- and LH beta-subunit was increased in orchiectomized rat cells vs. intact rat cells. GnRH stimulated the synthesis of both subunits, whether cells were from normal or castrated rat. T suppressed basal and GnRH-enhanced synthesis of both subunits in castrated rat cells. The values became closed to those observed in the normal rat cells. Also release of neosynthesized subunits from castrated rat cells into the culture medium was inhibited by T. In contrast, T did not change the basal and GnRH-induced radioimmunoassayed LH release. These results show that T can inhibit directly, at the pituitary level, alpha- and LH beta-subunit synthesis and neosynthesized but not stored LH release. They could explain, at least in part, no correlation between modifications of GnRH and LH secretion observed in vivo in response to T replacement.

Cloning and analysis of the cDNA for the common alpha-subunit of the donkey pituitary glycoprotein hormones

Reverse transcription-PCR was used to clone the coding region of the donkey (Equus asinus) glycoprotein hormone alpha-subunit transcript from pituitary gland RNA. The donkey alpha-subunit sequence demonstrated considerable identity with the horse (97% at the nucleotide level), confirming the very close evolutionary linkage between these two species. The predicted amino acid sequence revealed that the donkey alpha-subunit has the same unusual C-terminus as the horse alpha-subunit, when compared with all other mammalian alpha-subunits, including a Tyr-His transposition between positions 87 and 93 and Ile instead of Ser as the C-terminal residue. Since recent evidence indicates important involvement of this region of the alpha-subunit in receptor binding, these findings provide a possible partial explanation for the unique biological properties of the equine gonadotrophins.

Different composite regulatory elements direct expression of the human alpha subunit gene to pituitary and placenta

To identify elements of the human alpha subunit gene necessary for cell-specific expression, we generated an array of block mutations spanning approximately 400 base pairs (bp) of promoter proximal region and examined them using transient transfection analysis in pituitary (alpha T3) and placental (BeWo) cell lines. Comparison of promoter activity in the two cell types revealed both common and unique elements required for transcription in pituitary and placenta. Two strong elements, the cyclic AMP response element (CRE) and the upstream regulatory element (URE), regulate expression of the alpha subunit gene in BeWo cells. In contrast, promoter activity in alpha T3 cells requires an array of weaker elements. These include the CREs, the URE, as well as two previously described elements, pituitary glycoprotein hormone basal element (PGBE) and gonadotrope-specific element (GSE), and two new elements we designated as the alpha basal elements 1 and 2 (alpha BE1 and alpha BE2). These new elements reside between -316 and -302 bp (alpha BE1) and -296 and -285 bp (alpha BE2) of the human alpha subunit promoter and bind distinct proteins designated alpha BP1 and alpha BP2, respectively. Southwestern blot analysis revealed that alpha BE1 specifically binds 54- and 56-kDa proteins. Additional studies disclosed several potential interactions between proteins that bind the CRE and proteins that occupy PGBE, alpha BE1, and alpha BE2, suggesting that gonadotrope-specific expression occurs through a unique composite regulatory element that includes components of the placenta-specific enhancer.

Targeted disruption of the pituitary glycoprotein hormone alpha-subunit produces hypogonadal and hypothyroid mice

Pituitary thyrotropin (TSH) and gonadotropins (LH and FSH) are thought to be critical for thyroid and gonadal development and function. Each of these pituitary hormones is a heterodimer composed of a common alpha-subunit and unique beta-subunit, and heterodimerization is required for function. No mutations in the alpha-subunit or any of the beta-subunit genes have been reported in mice. To assess directly the functional role of TSH, LH, and FSH in thyroid and gonadal development, we created a disruption of the alpha-subunit gene by homologous recombination. The homozygous mutant animals were hypogonadal and exhibited profound hypothyroidism resulting in dwarfism. Thyroid development was arrested in late gestation, but GnRH neuron migration, development of secondary sex organs, and fetal and neonatal gonadal development were normal. This establishes the importance of thyrotropin in ontogeny and reveals that fetal pituitary gonadotropins are not required for sexual differentiation or genital development in male or female fetuses. The pituitary cells that produce TSH beta-subunit exhibited dramatic hypertrophy and hyperplasia as a result of the lack of thyroid function. This proliferation response occurred at the expense of somatotrope and lactotrope cells, consistent with a derivation of these three cell types from a common precursor.

Glycoprotein hormone alpha-subunit production and plurihormonality in human corticotroph tumours--an in vitro and immunohistochemical study

Glycoprotein hormone alpha-subunit (alpha SU) is a recognized product of clinically non-functioning, glycoprotein hormone-secreting and somatotroph adenomas but has not been studied systematically in corticotroph tumours. We have performed immunohistochemistry for alpha SU in a consecutive series of four corticotroph tumours causing Nelson's syndrome, three corticotroph macroadenomas, 12 corticotroph microadenomas and one adrenocorticotrophin-secreting bronchial carcinoid tumour. In addition we have assessed alpha SU secretion in vitro in corticotroph adenomas from two subjects with Cushing's disease and two subjects with Nelson's syndrome. Immunohistochemistry, performed after microwave treatment of sections to enhance antigen retrieval, demonstrated alpha SU positivity in 3/4 Nelson's tumours, 2/3 corticotroph macroadenomas, 7/12 microadenomas and one bronchial carcinoid. Eight of the 13 tumours positive for alpha SU were also immunostained after microwave pretreatment of sections for thyrotrophin (six positive), follicle-stimulating hormone (four positive), luteinizing hormone (three positive), beta-chorionic gonadotrophin (five positive), growth hormone (three positive) and prolactin (two positive) immunoreactivity. In vitro cell cultures of all four tumours studied secreted adrenocorticotrophin and three secreted alpha SU, with the variable presence of luteinizing hormone, follicle-stimulating hormone, thyrotrophin, growth hormone and prolactin, in basal culture. The alpha SU secretion was augmented by phorbol ester (160 +/- 15%, SEM, n = 3 wells; p < 0.01) and 8-bromo-cAMP (138 +/- 8%; p < 0.05) in one tumour. These data indicate that plurihormonality and, in particular, alpha SU elaboration and secretion by corticotroph tumours is more common than hitherto recognized. Possible mechanisms include abnormal or deregulated gene expression, autocrine or paracrine effects or a stem cell origin of tumour.(ABSTRACT TRUNCATED AT 250 WORDS)

Consequences of antisense human chorionic gonadotrophin-alpha subunit cDNA expression in human choriocarcinoma JAR cells

The biosynthesis of human chorionic gonadotrophin (hCG) is a hallmark endocrine function of human choriocarcinoma cells. The present study investigated the consequences of greatly diminishing this synthesis in JAR cells by stably transfecting them with pRSV-antisense hCG-alpha cDNA expression vector. The vector directs the synthesis of antisense hCG-alpha subunit mRNA which would then bind to sense hCG-alpha subunit mRNA, thus blocking its translation and consequently dimer hCG protein synthesis. The transfection with pRSV-antisense hCG-alpha cDNA resulted in a dramatic decrease in hCG secretion as compared with untransfected parental cells or those transfected with an empty vector used for the selection of clones. The decreased secretion was due to a decreased synthesis which in turn was due to a fall in steady-state hCG-alpha and -beta subunit mRNA levels. The decrease of hCG-beta subunit transcripts was unexpected and it was not due to contamination of antisense hCG-alpha cDNA construct with hCG-beta sequence. The transcription of hCG-alpha and -beta subunit genes was not altered in transfected cells suggesting that increased degradation was responsible for decreased steady-state hCG subunit mRNA levels. Despite the decreased hCG levels, the transfected cells maintained normal hCG receptor levels, responded to epidermal growth factor stimulation of hCG synthesis and secretion and grew at the same rate as the control parental cells and those transfected with an empty vector.

Role of the Pro-Leu-Arg motif in glycosylation of human gonadotropin alpha-subunit

CG, LH, FSH, and TSH are a family of heterodimeric glycoprotein hormones that contain a common alpha-subunit, but differ in their hormone-specific beta-subunit. Processing of the N-linked oligosaccharide of the glycoprotein family is both tissue and dimer specific. LH, TSH, and free alpha synthesized in pituitary bear oligosaccharide terminating with sulfate (SO4) and N-acetylgalactosamine (GalNAc), whereas the termination of oligosaccharide in CG synthesized in placenta and FSH is sialic acid and galactose (Gal). Using site-directed mutagenesis and gene transfer, we studied the role of the Pro-Leu-Arg motif, which has been shown to be a recognition marker of glycoprotein hormone-specific GalNAc transferase, in sulfation of N-linked oligosaccharide in alpha-subunit. The wild-type or mutated alpha gene was transfected into GH3 cells. Our data revealed that substitution of the Pro-Leu-Arg motif by Ala-Leu-Ala did not affect the sulfation of N-linked oligosaccharide, but generated the attachment of O-linked oligosaccharide. alpha-Subunit containing either of the two N-linked glycosylations is also sulfated. We conclude that in GH3 cells, the Pro-Leu-Arg motif plays no role in the sulfation of oligosaccharide in alpha-subunit, and both N-glycosylations are terminated with SO4.

Retardation of a surface protein chimera at the cis Golgi

Dipeptidyl peptidase IV (D4) and the alpha subunit of human chorionic gonadotrophin (alpha hcg) are plasma membrane and secretory proteins, respectively. In the course of studies to understand mechanisms involved in transport along the exocytotic pathway, the ectoplasmic domain of D4 was replaced by the mature polypeptide of alpha hcg, resulting in the membrane anchored chimera, D4 alpha hcg. Surprisingly, when transfected into Chinese hamster ovary (CHO) and Madin-Darby canine kidney (MDCK) cells, strong perinuclear Golgi staining was predominant, in addition to the expected surface staining. By following the biogenesis and transport of the molecule, it was established that newly synthesized D4 alpha hdg is eventually transported to the cell surface but only after a significant retardation in the Golgi apparatus. The compartment of retardation was identified as the early or cis Golgi, before the medial Golgi, where resistance to endoglycosidase (endo) H is conferred. As a result of the transport retardation of the chimera, we were able to document the appearance of an endo D sensitive intermediate, which is usually too transient to be apparent in normal cells. The retardation of this chimera in the cis Golgi complements our previous report in which the D4 molecule with its transmembrane domain replaced by that of aminopeptidase N resulted in retardation in the trans Golgi/trans Golgi network in MDCK and CHO cells [Low, S. H., Tang, B. L., Wong, S. H., & Hong, W. (1994) J. Biol. Chem. 269, 1985-1994).(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of the alpha-subunit of glycoprotein hormones in the pars tuberalis-specific glandular cells in rat, mouse and guinea-pig

The nature of the hormone(s) secreted by the pars tuberalis (PT) is still unknown. This pituitary lobe is mainly formed by specific glandular cells that differ in their ultrastructural features from the other adenohypophysial cell types. Data from the literature indicate the presence of thyroid-stimulating hormone immunoreactivity in the PT-specific cells of the rat and the Djungarian hamster but not of other species, including the mouse and guinea-pig. The PT also encloses variable numbers of pars distalis cells, essentially gonadotrophs that are mainly dispersed in its caudal area. We studied the expression of the glycoprotein hormone alpha-subunit in the PT of the rat, mouse and guinea-pig by in situ hybridization and immunocytochemistry. In situ hybridization, using an oligonucleotide probe complementary to rat cDNA sequence 196-237 revealed the expression of the alpha-subunit gene throughout the PT of the rat and the mouse; in the guinea-pig, the probe labelled no pituitary cells. Light- and electron-microscopic immunocytochemistry demonstrated alpha-subunit immunoreactivity in the secretory granules of the PT-specific cells in the three species examined. These cells did not react with a specific antibody against the beta-subunit of luteinizing hormone, an antibody that labelled scattered gonadotrophs. The present data suggest that hormone(s) produced by the PT-specific glandular cells are, at least partly, related to glycoprotein hormones.

Evidence that signalling pathways by which thyrotropin-releasing hormone and gonadotropin-releasing hormone act are both common and distinct

TRH and GnRH receptors are each coupled to G proteins of the Gq/11 family. Activation of each of these receptors by their respective ligands results in the stimulation of phospholipase C activity, leading to calcium mobilization and protein kinase C activation. Thus, the effects of TRH and GnRH may be mediated through the same intracellular signal transduction pathway. To compare responses to TRH and GnRH directly within one cell type, we have stably transfected the rat pituitary GH3 lactotrope cell line, which expresses the endogenous TRH receptor, with an expression vector containing rat GnRH receptor cDNA. Transfected cells specifically bound GnRH with high affinity and responded to GnRH stimulation with an increase in PRL mRNA levels, analogous to their response to TRH stimulation. Stably transfected GH3 cells, which were then transiently transfected with luciferase reporter constructs containing either the PRL or the glycoprotein hormone alpha-subunit promoter, responded to either GnRH or TRH stimulation with an increase in luciferase activity in a time- and dose-dependent fashion. The stimulatory effects of maximally effective concentrations of TRH and GnRH were additive on PRL, but not alpha-subunit, gene expression. These data, coupled with evidence of cross-desensitization of alpha-subunit, but not PRL, promoter activity stimulation by TRH and GnRH, suggest that there may be differences in the signal transduction pathways activated by TRH and GnRH receptors in the regulation of PRL and alpha-subunit gene expression.