The 5'-flanking region of the ovine follicle-stimulating hormone-beta gene contains six progesterone response elements: three proximal elements are sufficient to increase transcription in the presence of progesterone

Characterization of sea bass FSHβ 5' flanking region: transcriptional control by 17β-estradiol

The sea bass follicle-stimulating hormone 5' flanking region (sbFSHβ 5' FR) was cloned and characterized in order to study the molecular mechanisms underlying transcriptional regulation of the sbFSHβ gene. Analysis of the ~3.5 kb of this region revealed the presence of several putative cis-acting elements, including steroid hormone response elements, cAMP response elements, pituitary-specific transcription factor response elements, activator protein-1 response elements and TATA sequence. Deleted constructs containing ~3.5 kb of the sbFSHβ 5' FR fused to a luciferase reporter gene were transiently transfected into human embryonic kidney (HEK 293) and mouse mature gonadotrope (LβT2) cell lines. The sbFSHβ 5' FR was efficiently expressed under basal conditions in LβT2 but not in HEK 293, pointing to both positive and negative regulatory elements. In order to elucidate the estrogen-mediated sbFSHβ transcriptional activity, in vitro treatments with 17β-estradiol were carried out on primary cultures of pituitary cells and LβT2 cells transiently expressing luciferase under the control of sbFSHβ 5' FR. Overall, these results demonstrate that 17β-estradiol inhibits sbFSHβ gene expression directly at the level of the pituitary. However, it was also shown that estrogen did not induce changes of the sbFSH promoter-directed luciferase activity, suggesting that sbFSHβ 5'FR (~3.5 kb) activity is cell type dependent and its estrogen regulation could require cis-acting elements located upstream of the promoter region, which is characterized in this article.

A human FSHB promoter SNP associated with low FSH levels in men impairs LHX3 binding and basal FSHB transcription

FSH production is important for human gametogenesis. In addition to inactivating mutations in the FSHB gene, which result in infertility in both sexes, a G/T single-nucleotide polymorphism (SNP) at -211 relative to the transcription start site of the 5' untranslated region of FSHB has been reported to be associated with reduced serum FSH levels in men. In this study, we sought to identify the potential mechanism by which the -211 SNP reduces FSH levels. Although the SNP resides in a putative hormone response element, we showed that, unlike the murine gene, human FSHB was not induced by androgens or progestins in gonadotropes. On the other hand, we found that the LHX3 homeodomain transcription factor bound to an 11-bp element in the human FSHB promoter that includes the -211 nucleotide. Furthermore, we also demonstrated that LHX3 bound with greater affinity to the wild-type human FSHB promoter compared with the -211 G/T mutation and that LHX3 binding was more effectively competed with excess wild-type oligonucleotide than with the SNP. Finally, we showed that FSHB transcription was decreased in gonadotrope cells with the -211 G/T mutation compared with the wild-type FSHB promoter. Altogether, our results suggest that decreased serum FSH levels in men with the SNP likely result from reduced LHX3 binding and induction of FSHB transcription.

FOXL2 is involved in the synergy between activin and progestins on the follicle-stimulating hormone β-subunit promoter

Differential regulation of gonadotropin hormone production in the pituitary is critical for fertility. Activin and progesterone signaling in gonadotrope cells is important for Fshb gene expression. Previously, we reported that synergy between activin and progestins required the binding of SMAD proteins and the progesterone receptor (PR) to the murine Fshb promoter. In this study, we demonstrate that the FOXL2 transcription factor is also necessary for the full synergistic response between activin and progestins. We show that this synergy occurs in a species-specific manner and that multiple elements in the Fshb promoter that bind forkhead box L2 (FOXL2), SMA/mothers against decapentaplegic homologs (SMAD), and PR are required. Furthermore, we demonstrate that FOXL2 can physically interact with PR and SMAD3. Thus, it is likely that protein-protein interactions among FOXL2, SMAD, and PR recruited to the Fshb promoter play a key role in facilitating Fshb transcription before the secondary FSH surge in rodents.

Genetically determined dosage of follicle-stimulating hormone (FSH) affects male reproductive parameters

CONTEXT

The detailed role of FSH in contributing to male testicular function and fertility has been debated. We have previously identified the association between the T-allele of the FSHB promoter polymorphism (rs10835638; G/T, -211 bp from the mRNA start) and significantly reduced male serum FSH.

OBJECTIVE

In the current study, the T-allele carriers of the FSHB -211 G/T single nucleotide polymorphism represented a natural model for documenting downstream phenotypic consequences of insufficient FSH action.

DESIGN AND SUBJECTS

We genotyped rs10835638 in the population-based Baltic cohort of young men (n = 1054; GG carriers, n = 796; GT carriers, n = 244; TT carriers, n = 14) recruited by Andrology Centres in Tartu, Estonia; Riga, Latvia; and Kaunas, Lithuania. Marker-trait association testing was performed using linear regression (additive, recessive models) adjusted by age, body mass index, smoking, and recruitment center.

RESULTS

Serum hormones directly correlated with the T-allele dosage of rs10835638 included FSH (additive model, P = 1.11 × 10(-6); T-allele effect, -0.41 IU/liter), inhibin-B (P = 2.16 × 10(-3); T-allele effect, -14.67 pg/ml), and total testosterone (P = 9.30 × 10(-3); T-allele effect, -1.46 nmol/liter). Parameters altered only among TT homozygotes were reduced testicular volume (recessive model, P = 1.19 × 10(-4); TT genotype effect, -9.47 ml) and increased serum LH (P = 2.25 × 10(-2); TT genotype effect, 1.07 IU/liter). The carrier status of rs10835638 alternative genotypes did not affect sperm motility and morphology, calculated free testosterone, serum SHBG, and estradiol concentrations.

CONCLUSION

We showed for the first time that genetically determined low FSH may have wider downstream effects on the male reproductive system, including impaired testes development, altered testicular hormone levels (inhibin-B, total testosterone, LH), and affected male reproductive potential.

Genomics and genetics of gonadotropin beta-subunit genes: Unique FSHB and duplicated LHB/CGB loci

The follicle stimulating hormone (FSH), luteinizing hormone (LH) and chorionic gonadotropin (HCG) play a critical role in human reproduction. Despite the common evolutionary ancestry and functional relatedness of the gonadotropin hormone beta (GtHB) genes, the single-copy FSHB (at 11p13) and the multi-copy LHB/CGB genes (at 19q13.32) exhibit locus-specific differences regarding their genomic context, evolution, genetic variation and expressional profile. FSHB represents a conservative vertebrate gene with a unique function and it is located in a structurally stable gene-poor region. In contrast, the primate-specific LHB/CGB gene cluster is located in a gene-rich genomic context and demonstrates an example of evolutionary young and unstable genomic region. The gene cluster is shaped by a constant balance between selection that acts on specific functions of the loci and frequent gene conversion events among duplicons. As the transcription of the GtHB genes is rate-limiting in the assembly of respective hormones, the genomic and genetic context of the FSHB and the LHB/CGB genes largely affects the profile of the hormone production.

Hormones in synergy: regulation of the pituitary gonadotropin genes

The precise interplay of hormonal influences that governs gonadotropin hormone production by the pituitary includes endocrine, paracrine and autocrine actions of hypothalamic gonadotropin-releasing hormone (GnRH), activin and steroids. However, most studies of hormonal regulation of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in the pituitary gonadotrope have been limited to analyses of the isolated actions of individual hormones. LHbeta and FSHbeta subunits have distinct patterns of expression during the menstrual/estrous cycle as a result of the integration of activin, GnRH, and steroid hormone action. In this review, we focus on studies that delineate the interplay among these hormones in the regulation of LHbeta and FSHbeta gene expression in gonadotrope cells and discuss how signaling cross-talk contributes to differential expression. We also discuss how recent technological advances will help identify additional factors involved in the differential hormonal regulation of LH and FSH.

Increased Prevalance of the -211 T allele of follicle stimulating hormone (FSH) beta subunit promoter polymorphism and lower serum FSH in infertile men

CONTEXT

The human FSHB promoter polymorphism (rs10835638; -211 G/T) has been associated with serum FSH in a cohort of young Estonian men. The minor allele carriers had reduced serum FSH (15.7% in GT heterozygotes; 40% in TT homozygotes) compared with GG homozygotes.

OBJECTIVE

Because FSH is essential for normal spermatogenesis and fertility, we speculated that abnormalities in FSH action could contribute to male infertility. We sought to study whether genetically inherited constitutively reduced FSH levels may affect male reproduction and replicate the association between rs10835638 and serum FSH among infertile male patients.

DESIGN

Genotyping of rs10835638 in a cohort of infertile men (n = 1029; Andrology Center of the Tartu University Clinics, Estonia), including idiopathic infertility cases (IIFC; n = 750).

PATIENTS

Patients included male partners (sperm concentration <20 x 10(6)/ml) of infertile couples failing to conceive a child for 12 months or longer.

RESULTS

A significant excess of TT homozygotes (1.1 vs. 2.4%) as well as GT heterozygotes (22.4 vs. 25.1%) was detected among infertile men compared with the young male cohort (chi(2) test, P < 0.05). The T allele of rs10835638 was associated with reduced serum FSH (analysis of covariance; full cohort: P = 1.20 x 10(-6), F = 13.8; IIFC: P = 7.70 x 10(-7), F = 14.3) as well as with low FSH to LH ratio (full cohort: P = 1.52 x 10(-11), F = 25.6; IIFC: P = 3.25 x 10(-9), F = 20.4). The median serum FSH levels differed between the GG and TT carriers by 48.5%. All IIFC with TT genotype exhibited low (<1.8) FSH to LH ratio.

CONCLUSIONS

In perspective, this genetic marker may have clinical significance in molecular diagnostics of male reproductive success and a potential to identify positive responders to FSH treatment.

FSHB promoter polymorphism within evolutionary conserved element is associated with serum FSH level in men

BACKGROUND

No polymorphisms affecting serum FSH levels have been described in the human FSHB gene. We have identified a potential regulatory single nucleotide polymorphism (SNP, rs10835638; G/T) 211 bp upstream from the FSHB mRNA transcription start-site, located within a highly conserved region among placental mammals. We aimed to determine the correlation of carrier status of rs10835638 alternative alleles with serum FSH level in men, and testicular and hormonal parameters.

METHODS

A quantitative genetic association study using a cohort of healthy men (n = 554; age 19.2 ± 1.7 years) visiting the Centre of Andrology, Tartu University Hospital, Estonia.

RESULTS

Rs10835638 (allele frequencies: G 87.6%, T 12.4%) was significantly associated with serum FSH level (analysis of variance: F = 13.0, P = 0.0016, df = 1; regression testing for a linear trend: P = 0.0003). Subjects with the GG genotype exhibited higher FSH levels (3.37 ± 1.79 IU/l, n = 423) compared with heterozygotes (2.84 ± 1.54 IU/l, n = 125) (P = 0.0005), the group of T-allele carriers (GT+TT, 2.78 ± 1.51 IU/l, n = 131) (P = 0.0005) and TT-homozygotes (2.02 ± 0.81 IU/L, n = 6) (P = 0.031). Rs10835638 was also associated with significant (P < 0.05) reduction in free testosterone index and testes volume, but increased semen volume, sex hormone-binding globulin, serum testosterone and estradiol. LH and inhibin-B levels did not differ significantly between groups.

CONCLUSIONS

The identification of a regulatory SNP in FSHB promoter paves the way to study the effect of constitutively low FSH on male health and fertility. As FSH contributes to follicular development and sex steroid production in women, the role of this FSHB variant in female reproductive success is still to be addressed.

The regulation of FSHbeta transcription by gonadal steroids: testosterone and estradiol modulation of the activin intracellular signaling pathway

Recent reports suggest that androgens increase FSHbeta transcription directly via the androgen receptor and by modulating activin signaling. Estrogens may also regulate FSHbeta transcription in part through the activin system. Activin signaling can be regulated extracellularly via activin, inhibin, or follistatin (FS) or intracellularly via the Smad proteins. We determined the effects of androgen and estrogen on FSHbeta primary transcript (PT) concentrations in male and female rats, and we correlated those changes with pituitary: activin betaB mRNA, FS mRNA, the mRNAs for Smads2, -3, -4, and -7, and the phosphorylation (p) status of Smad2 and -3 proteins. In males, testosterone (T) increased FSHbeta PT two- to threefold between 3 and 24 h and was correlated with reduced FS mRNA, transient increases in Smad2, -4, and -7 mRNAs, and a six- to 10-fold increase in pSmad2, and activin betaB mRNA was unchanged. In females, T also increased FSHbeta PT twofold and pSmad2 threefold but had no effect on activin betaB, FS, or the Smad mRNAs. Androgen also increased Smad2 phosphorylation in gonadotrope-derived alphaT3 cells. In contrast, estradiol had no effect on FSHbeta PT but transiently increased activin betaB mRNA and suppressed FS mRNA before increasing FS mRNA at 24 h and increased Smads2, -3, and -7 mRNAs and pSmad2 threefold. In conclusion, T acts on the pituitary to increase FSHbeta PT in both sexes and modulates FS mRNA, Smad mRNAs, and/or Smad2 phosphorylation. These findings suggest that T regulates FSHbeta transcription, in part, through modulation of various components of the activin-signaling system.

Activin and glucocorticoids synergistically activate follicle-stimulating hormone beta-subunit gene expression in the immortalized LbetaT2 gonadotrope cell line

FSH is produced by the pituitary gonadotrope to regulate gametogenesis. Production of the beta-subunit of FSH is the rate-limiting step in FSH synthesis, and a number of peptide and steroid hormones within the reproductive axis have been found to regulate transcription of the FSH beta-subunit gene. Although both activin and glucocorticoids are notable regulators of FSHbeta by themselves, we find that cotreatment results in a synergistic interaction on the mouse FSHbeta promoter at the level of the gonadotrope using transient transfection of a reporter gene into the LbetaT2 immortalized gonadotrope-derived cell line. This synergistic interaction is specific to FSHbeta, because only additive effects of these two hormones are observed on LH beta-subunit, GnRH receptor, and mouse mammary tumor virus gene expression. Components of both activin and glucocorticoid signaling are found to be necessary for synergy, and there are specific cis elements on the mouse FSHbeta promoter that contribute to the synergistic response as well. We also identify novel activin-responsive regions in the mouse FSHbeta promoter and find that the -120 site can bind Smad2/3 in vitro. In addition, the glucocorticoid receptor and Smad3 are sufficient to confer a striking synergy with glucocorticoids on the mouse FSHbeta promoter. Our studies provide the first evidence of a synergistic interaction between activin and glucocorticoids within the gonadotrope cell and demonstrate that this synergy can occur directly at the level of the mouse FSHbeta promoter.

Androgens, progestins, and glucocorticoids induce follicle-stimulating hormone beta-subunit gene expression at the level of the gonadotrope

FSH is produced by the pituitary gonadotrope to regulate gametogenesis. Steroid hormones, including androgens, progestins, and glucocorticoids, have all been shown to stimulate expression of the FSHbeta subunit in primary pituitary cells and rodent models. Understanding the molecular mechanisms of steroid induction of FSHbeta has been difficult due to the heterogeneity of the anterior pituitary. Immortalized LbetaT2 cells are a model of a mature gonadotrope cell and express the endogenous steroid receptor for each of the three hormones. Transient transfection of each receptor, along with ligand treatment, stimulates the mouse FSHbeta promoter, but induction is severely diminished using receptors that lack the ability to bind DNA, indicating that induction is likely through direct DNA binding. All three steroid hormones act within the first 500 bp of the FSHbeta promoter where six putative hormone response elements exist. The -381 site is critical for FSHbeta induction by all three steroid hormones, whereas the -197 and -139 sites contribute to maximal induction. Interestingly, the -273 and -230 sites are also necessary for androgen and progestin induction of FSHbeta, but not for glucocorticoid induction. Additionally, we find that all three receptors bind the endogenous FSHbeta promoter, in vivo, and specifically bind the -381 site in vitro, suggesting that the binding of the receptors to this element is critical for the induction of FSHbeta by these 3-keto steroid hormones. Our data indicate that androgens, glucocorticoids, and progestins act via their receptors to directly activate FSHbeta gene expression in the pituitary gonadotrope.

Effects of changing gonadotropin-releasing hormone pulse frequency and estrogen treatment on levels of estradiol receptor-alpha and induction of Fos and phosphorylated cyclic adenosine monophosphate response element binding protein in pituitary gonadotropes: studies in hypothalamo-pituitary disconnected ewes

Estrogen receptor-alpha (ER alpha) levels in gonadotropes are increased during the follicular phase of the ovine estrous cycle, a time of increased frequency of pulsatile secretion of GnRH and elevated plasma estrogen levels. In the present study, our first aim was to determine which of these factors causes the rise in the number of gonadotropes with ER alpha. Ovariectomized hypothalamo-pituitary disconnected ewes (n = 4-6) received the following treatments: 1) no treatment, 2) injection (im) of 50 microg estradiol benzoate (EB), 3) pulses (300 ng iv) of GnRH every 3 h, 4) GnRH treatment as in group 3 and EB treatment as in group 2, 5) increased frequency of GnRH pulses commencing 20 h before termination, and 6) GnRH treatment as in group 5 with EB treatment. These treatments had predictable effects on plasma LH levels. The number of gonadotropes in which ER alpha was present (by immunohistochemistry) was increased by either GnRH treatment or EB injection, but combined treatment had the greatest effect. Immunohistochemistry was also performed to detect phosphorylated cAMP response element binding protein (pCREB) and Fos protein in gonadotropes. The number of gonadotropes with Fos and with pCREB was increased only in group 6. We conclude that either estrogen or GnRH can up-regulate ER alpha in pituitary gonadotropes. On the other hand, during the period of positive feedback action of estrogen, the appearance of pCREB and Fos in gonadotropes requires the combined action of estrogen and increased frequency of GnRH input. This suggests convergence of signaling for GnRH and estrogen.

Pituitary transcription factor Prop-1 stimulates porcine follicle-stimulating hormone beta subunit gene expression

Molecular cloning of the transcription factor that modulates the expression of porcine follicle-stimulating hormone beta subunit (FSHbeta) gene was performed by the yeast one-hybrid cloning system using the -852/-746 upstream region (Fd2) as a bait sequence. We eventually cloned a pituitary transcription factor, Prop-1, which has been identified as an upstream transcription factor of Pit-1 gene. Binding ability of Prop-1 to the bait sequence was confirmed using recombinant Prop-1, and the binding property was investigated by DNase I footprinting, revealing that Prop-1 certainly bound to the large AT-rich region throughout the Fd2. Co-transfection of Prop-1 expression vector together with a reporter gene fused with Fd2 in CHO cells demonstrated an attractive stimulation of reporter gene expression. Immunohistochemistry of adult porcine pituitary confirmed the colocalization of the Prop-1 and FSHbeta subunit. This study is the first to report that Prop-1 participates in the regulation of FSHbeta gene. The present finding will provide new insights into the development of pituitary cell lineage and combined pituitary hormone deficiency (CPHD), since why the defect of Prop-1 causes CPHD including gonadotropins (FSH and LH) has yet to be clarified.

Activin regulation of the follicle-stimulating hormone beta-subunit gene involves Smads and the TALE homeodomain proteins Pbx1 and Prep1

FSH is critical for normal reproductive function in both males and females. Activin, a member of the TGFbeta family of growth factors, is an important regulator of FSH expression, but little is known about the molecular mechanisms through which it acts. We used transient transfections into the immortalized gonadotrope cell line LbetaT2 to identify three regions (at -973/-962, -167, and -134) of the ovine FSH beta-subunit gene that are required for full activin response. All three regions contain homology to consensus binding sites for Smad proteins, the intracellular mediators of TGFbeta family signaling. Mutation of the distal site reduces activin responsiveness, whereas mutation of either proximal site profoundly disrupts activin regulation of the FSHbeta gene. These sites specifically bind LbetaT2 nuclear proteins in EMSAs, and the -973/-962 site binds Smad4 protein. Interestingly, the protein complex binding to the -134 site contains Smad4 in association with the homeodomain proteins Pbx1 and Prep1. Using glutathione S-transferase interaction assays, we demonstrate that Pbx1 and Prep1 interact with Smads 2 and 3 as well. The two proximal activin response elements are well conserved across species, and Pbx1 and Prep1 proteins bind to the mouse gene in vivo. Furthermore, mutation of either proximal site abrogates activin responsiveness of a mouse FSHbeta reporter gene as well, confirming their functional conservation. Our studies provide a basis for understanding activin regulation of FSHbeta gene expression and identify Pbx1 and Prep1 as Smad partners and novel mediators of activin action.

Androgen regulates follicle-stimulating hormone beta gene expression in an activin-dependent manner in immortalized gonadotropes

Little is known about the molecular mechanisms of androgen regulation of the FSHbeta gene; however, studies suggest that it consists of a complex feedback loop that involves multiple mechanisms acting at both the level of the hypothalamus and the pituitary. In the present study, we address androgen regulation of the FSHbeta gene in immortalized gonadotrope cells and investigate the roles of activin and GnRH in androgen action. Using transient transfection assays in the FSHbeta-expressing mouse gonadotrope cell line, LbetaT2, we demonstrate that androgens stimulate expression of an ovine FSHbeta reporter gene in a dose-dependent manner. Mutation of either of two conserved androgen response elements at -245/-231 and -153/-139 within the proximal region of the ovine FSHbeta gene promoter abolishes this stimulation, and androgen receptor binds directly to the -244 ARE in vitro. Androgen induction of the FSHbeta reporter gene is also dependent upon the activin autocrine loop present in the LbetaT2 cells, as well as an activin-response element at -138/-124 of the FSHbeta gene. However, activin regulation of other genes remains unaffected by androgens. In addition, androgens stimulate expression of a mouse GnRH receptor reporter gene, and thus may indirectly augment the response of the FSHbeta gene to GnRH. Taken together, these data demonstrate that, in mouse gonadotropes, androgens act directly on the ovine FSHbeta gene to stimulate expression by a mechanism that is dependent upon activin, as well as acting indirectly, potentially through a second mechanism that may be dependent upon induction of GnRH receptor.

Demonstration of progesterone receptor-mediated gonadotrophin suppression in the human male

OBJECTIVE

Synthetic gestogens in combination with testosterone have potential as a male hormonal contraceptive, predominantly acting by augmenting suppression of gonadotrophin secretion. Little is known, however, of the effects of gestogens in the male. Gestogens have affinity for both androgen and progesterone receptors but the relative contribution of action at these two receptors in gonadotrophin suppression remains unclear. In this study the effects of progesterone, with no significant androgen-receptor affinity are compared to desogestrel, a synthetic gestogen with relatively low affinity for the androgen receptor, on gonadotrophin secretion in normal men.

DESIGN

Subjects received either 50 mg progesterone intramuscularly (i.m.) or 300 micro g desogestrel orally daily for 7 days. Frequent blood sampling over 12 h was undertaken before and after drug administration. GnRH [100 micro g intravenously (i.v.)] was administered 2 h before the end of the frequent sampling period.

SUBJECTS

Twenty healthy men were randomly allocated to the two treatment groups.

RESULTS

Both progesterone and desogestrel administration resulted in decreases in the concentration of both LH and FSH secretion, as well as testosterone. Analysis of the pulsatile nature of LH secretion indicated that both treatments reduced LH pulse amplitude, and that progesterone reduced LH pulse frequency. Progesterone, but not desogestrel, treatment also reduced the increase in LH secretion in response to GnRH.

CONCLUSIONS

The effects of progesterone were at least as marked as those of a maximally effective dose of desogestrel. As progesterone has negligible affinity for the androgen receptor, these results are compatible with the suppressive effects of synthetic 19-norgestogens on gonadotrophin secretion in the male being mediated via the progesterone receptor, with its androgenicity contributing minimally to gonadotrophin suppression.

Isolated follicle-stimulating hormone (FSH) deficiency in a young man with normal virilization who did not have mutations in the FSHbeta gene

OBJECTIVE

To determine the cause of isolated FSH deficiency in a young infertile man.

DESIGN

Case report.

SETTING

Clinical and genetic studies in an academic research environment.

PATIENT(S)

A 19-year-old man with normal virilization, azoospermia, and isolated FSH deficiency.

INTERVENTION(S)

Pituitary and gonadal functions were evaluated at baseline and after repeated GnRH stimulation. FSH was tested with both immunological and biological methods. The FSHbeta gene was sequenced in the patient and in a series of 50 controls.

MAIN OUTCOME MEASURE(S)

Clinical, endocrine, and genetic characterization of an infertile patient with isolated FSH deficiency.

RESULT(S)

LH and T secretions were normal. No interference in FSH measurement was detected, and serum FSH concentrations were very low and completely unresponsive to repeated GnRH stimulation. No circulating FSH-like bioactivity was detected by means of rat Sertoli cell bioassay. Other pituitary functions were unaffected, and no lesions were seen at pituitary nuclear magnetic resonance (NMR). Inhibin B and activin levels were normal, but a progressive decrease of activin concentrations was seen during GnRH stimulation. The coding sequence of the FSHbeta gene was normal, but the patient was homozygous for a novel G/T substitution in the promoter region within a P response element. This substitution was present in heterozygosity in eight out of 50 controls and in homozygosity in one man with normal FSH levels.

CONCLUSION(S)

We report an infertile male with isolated FSH deficiency but no evidence of mutations in the FSHbeta gene. The G/T substitution in the FSHbeta promoter represents a novel silent polymorphism, indicating that other defects in factors involved in FSH-specific expression should be taken into account.

Pituitary homeobox 1 activates the rat FSHbeta (rFSHbeta) gene through both direct and indirect interactions with the rFSHbeta gene promoter

Molecular mechanisms underlying gonadotrope-specific and hormonal regulation of FSHbeta gene expression remain largely unknown. We have studied the role of pituitary homeobox 1 (Ptx1), a transcription factor important for regulation of many pituitary-specific genes, in the regulation of rat FSHbeta (rFSHbeta) gene transcription. We demonstrate that Ptx1 activates the rFSHbeta gene promoter both basally and in synergy with GnRH. The effect of Ptx1 was localized to -140/-50, a region also important for basal activity of the promoter. Two putative Ptx1 binding sites (P1 and P2) homologous to consensus Ptx1 binding elements were identified in this region. We demonstrate specific binding of Ptx1 to the P2 but not to the P1 site. Furthermore, functional studies indicate that the P2 but not the P1 site mediates activation of the promoter by Ptx1. Residual activation of the promoter by Ptx1 was observed independent of the P2 site. However, no additional Ptx1 binding sites were identified in this region, indicating that the residual activation observed is likely independent of direct Ptx1 binding to the promoter. These results identify a functional Ptx1 binding site in the rFSHbeta gene promoter and suggest the presence of an additional activating pathway that is independent of direct binding of Ptx1 to the promoter.

Transcriptional activation of the ovine follicle-stimulating hormone-beta gene by gonadotropin-releasing hormone involves multiple signal transduction pathways

GnRH regulates gonadotrope cells through GnRH receptor activation of the PKC-, MAPK-, and calcium-activated signaling cascades. Due to the paucity of homologous model systems expressing FSHbeta, little is known about the specific mechanisms involved in transcriptional regulation of this gene by GnRH. Previous studies from our laboratory demonstrated that the gonadotrope-derived LbetaT2 cell line expresses FSHbeta mRNA. In the present study we characterized the mechanisms involved in GnRH regulation of the FSHbeta promoter using this cell model. Using transfection assays, we show that GnRH regulation of the ovine FSHbeta promoter involves at least two elements, present between -4152/-2878 and -2550/-1089 bp, in association with one or several elements within the proximal region of the promoter. Surprisingly, the two activating protein-1 sites previously shown to be involved in the FSHbeta response to GnRH in heterologous cells do not play a role in GnRH responsiveness in the gonadotrope cell model. Here we demonstrate that calcium influx itself is not sufficient to confer the response, but it is necessary for both 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and GnRH induction of the FSHbeta gene. Moreover, we show that GnRH regulation of FSHbeta gene expression is mediated by PKC and establish the presence of multiple PKC isozymes in LbetaT2 cells. Interestingly, GnRH and TPA induce activity of the FSHbeta promoter through different, although possibly overlapping, pools of PKC isoforms. This is further supported by the use of a MAPK inhibitor, which abolishes the induction of FSHbeta by GnRH, but not by TPA. In conclusion, we have demonstrated that calcium, PKC, and MAPK signaling systems are all involved in the induction of FSHbeta gene expression by GnRH in the LbetaT2 mouse gonadotrope cell model.

Transcriptional regulation of the ovine follicle-stimulating hormone-beta gene by activin and gonadotropin-releasing hormone (GnRH): involvement of two proximal activator protein-1 sites for GnRH stimulation

Previous studies from our laboratory demonstrated that a transgene consisting of the promoter for the ovine FSH beta-subunit gene and a luciferase reporter (wt-oFSHbetaLuc) was expressed and regulated like the FSHbeta gene in vivo and in vitro. In the present study pituitary cultures were prepared from these transgenic mice as well as mice carrying mutated oFSHbetaLuc lacking two functional activator protein-1 (AP-1) sites at -120 and -83 bp (mut-oFSHbetaLuc). These AP-1 sites were reported necessary for induction of oFSHbetaLuc by GnRH in a HeLa cell system. To examine the importance of the two AP-1 sites in mediating GnRH and activin effects in primary gonadotropes, pituitary cultures derived from transgenic mice were pretreated with follistatin to remove activin or activin-like factors present in the cultures. Follistatin lowered luciferase expression in cultures carrying both wt-oFSHbetaLuc and mut-oFSHbetaLuc transgenes by 74-86%, and subsequent addition of activin induced luciferase expression of both wt- and mut-transgenes by 4- to 14-fold within 4 h, suggesting that these AP-1 sites are not involved in activin stimulation of FSHbeta gene transcription. When GnRH was added along with activin, the wt-oFSHbetaLuc transgene was induced 200% compared with activin alone, but this effect was not observed with the mut-oFSHbetaLuc transgene. These data confirmed the HeLa cell studies showing that GnRH signals through two AP-1 sites to increase oFSHbeta transcription in gonadotropes. However, as the mutation of both AP-1 sites had no apparent effect on the expression and regulation of the transgene in vivo (basal, castration, GnRH down-regulation, cycle stage, and GnRH immunoneutralization), it appears that these AP-1 sites have little influence over the major effect of GnRH observed in vivo. These data also showed that activin plays a major role in transcriptional regulation of the FSHbeta gene, and the oFSHbeta promoter contains the activin response element(s) that is as yet undefined.

The promoter for the ovine follicle-stimulating hormone-beta gene (FSHbeta) confers FSHbeta-like expression on luciferase in transgenic mice: regulatory studies in vivo and in vitro

Transgenic mice harboring the ovine FSHbeta (oFSHbeta) promoter plus first intron (from -4741 to +759 bp) linked to a luciferase reporter gene (oFSHbetaLuc) were generated to determine whether this promoter can direct tissue-specific expression in vivo and serve as a model for studying hormonal regulation of the FSHbeta gene. Of six lines of transgenic mice analyzed, luciferase was detected uniquely in the pituitaries of five of them. Pituitary luciferase activity was decreased 51-99% by chronic GnRH treatment (Lupron depot). Orchidectomy caused a 2- to 8-fold increase, and ovariectomy caused a 2- to 27-fold increase in pituitary luciferase activity. Furthermore, pituitary luciferase expression was consistently higher on estrus than on diestrus (3- to 20-fold). These data strongly suggested that the transgene was expressed specifically in pituitary gonadotropes and regulated in the same way as the endogenous mouse FSHbeta gene. Using primary pituitary cell cultures prepared from these transgenic mice, basal luciferase expression was maximal on day 3 and then decreased by day 6 of culture, a pattern reflected by endogenous mouse FSH secretion. In these pituitary cultures, basal oFSHbetaLuc expression was decreased 61-82% by follistatin or 59-79% by inhibin. Similarly, mouse FSH secretion was decreased 71% by follistatin or 65% by inhibin. Progesterone inhibited oFSHbetaLuc expression by 44-51%, but it had no effect on endogenous mouse FSH secretion. Estradiol lowered FSH secretion by 21%, but did not decrease oFSHbetaLuc expression significantly. In conclusion, these data demonstrated the ability of the oFSHbeta promoter to direct expression of a reporter gene specifically to pituitary gonadotropes in transgenic mice. Studying oFSHbetaLuc expression in vivo and in cell cultures derived from pituitaries of these transgenic mice should prove useful for understanding many features of FSHbeta regulation.

Follistatin suppresses steroid-enhanced follicle-stimulating hormone release in vitro in rats

Previous in vitro and in vivo studies from our laboratory showed that progesterone (P(4)), corticosterone (B), and testosterone (T) increase intracellular content and release of FSH in the anterior pituitary. Activin (Act) and inhibin (Inh) are structurally related proteins with antagonistic actions, as Act stimulates and Inh inhibits FSH secretion from the anterior pituitary. Together with follistatin (FS), a protein that bioneutralizes Act, they form an autocrine-paracrine loop in the anterior pituitary that tightly regulates FSH secretion. The objective of the present study was to test the hypothesis that P(4), B, and T modulate this autocrine-paracrine loop to favor increased FSH secretion. If Act were to mediate steroid-induced FSH release, FS would be expected to block these effects. To test this interaction, cell cultures were prepared from anterior pituitaries of male and female rats, and treated with Act, B, P(4), or T in the absence or presence of FS. Act, B, P(4), and T increased FSH release; FS suppressed both basal and Act- and steroid-stimulated FSH release to approximately 50% below basal levels. Cell cultures from anterior pituitary of female rats were used to compare the interaction of incremental concentrations of FS on dose-related Act- and P(4)-stimulated FSH release. With increasing concentrations of Act, the FS-induced suppression of FSH release was attenuated and eventually abolished; in contrast, maximally stimulatory concentrations of P(4) did not fully overcome the FS-induced suppression of FSH release. The effects of P(4), B, and Act in the presence and absence of estradiol on steady-state mRNA levels of FSHbeta, Actbeta(B), and FS were determined in primary pituitary cell cultures from metestrous female rats by reverse transcription-polymerase chain reaction. Whereas Act, P(4), B increased FSHbeta mRNA levels, only Act raised the level of FS mRNA, and neither steroid increased Actbeta(B) mRNA. The results support the hypothesis that endogenous Act is a common mediator of the action of P(4), B, and T in the rat primary anterior pituitary cell culture. We conclude that the stimulation of FSH release and intracellular content in the gonadotroph by P(4), B, and T is mediated, in part, by Act and involves modulation of a tightly regulated Act/FS autocrine-paracrine loop.

Multiple binding sites for nuclear proteins of the anterior pituitary are located in the 5'-flanking region of the porcine follicle-stimulating hormone (FSH) beta-subunit gene

Gonadotropins, follicle-stimulating hormone (FSH), and luteinizing hormone (LH), are synthesized specifically in the gonadotropes of the anterior pituitary. The aim of this study was to investigate nuclear factors that bind specifically to the porcine FSH beta-subunit gene. We examined nuclear protein binding to 2.75 kilobase pairs (kbp) of DNA adjacent to the porcine FSH beta-subunit gene: about 2.32 kbp of upstream DNA and 0.43 kbp of downstream DNA. The upstream region contains only TATA box, CACCC element, and some imperfect sequences of cAMP-responsive element, activator protein-1 binding site, and activator protein-2 binding site. Gel mobility shift assay using nuclear proteins extracted from the porcine anterior pituitary revealed that the proteins bound to a limited region of DNA, 107 bp long (designated as Fd2), located about -800 bp upstream from the transcription initiation site. Competitive binding assays demonstrated that the protein binding was sequence specific; the addition of excess amounts of several putative regulatory sequences and plasmid (non-homologous) DNA fragments did not reduce the binding. Furthermore, all five subfragments of Fd2 were also bound by the pituitary nuclear proteins, showing that the entire region of Fd2 is involved in this interaction. Southwestern blotting demonstrated that at least seven protein species of 110, 98, 78, 63, 52, 42, and 35 kDa recognize Fd2. Nuclear proteins from several other porcine tissues were also able to bind to the Fd2 fragment but the gel shift patterns were different and the bindings were weak, although only the cerebellum showed a pattern of binding that was similar to that of the anterior pituitary. These data suggest that multiple proteins of the anterior pituitary recognize a specific region of the porcine FSH beta-subunit gene.

Two proximal activating protein-1-binding sites are sufficient to stimulate transcription of the ovine follicle-stimulating hormone-beta gene

FSH is an important regulator of mammalian gametogenesis and the female reproductive cycle. Although little is known about the transcriptional regulation of the beta-subunit (the rate-limiting subunit of FSH synthesis), sequence analysis of the ovine FSHbeta promoter has revealed a number of potential activating protein-1 (AP-1; Jun/Fos)-binding sites. To determine whether the gene encoding the beta-subunit of ovine FSH (oFSHbeta) is responsive to AP-1 transcriptional complexes, chimeric constructs containing deleted portions of the oFSHbeta promoter fused to a luciferase reporter were transiently transfected along with c-Jun and c-Fos expression constructs into JAR cells. Analysis of these deletion constructs revealed that the proximal promoter of oFSHbeta is highly stimulated by c-Jun and c-Fos proteins (typically 20-fold with a reporter construct containing oFSHbeta sequences from -215 to +759 bp). This stimulation was lost when a similar construct containing sequences from -84 to +759 bp was tested. Transcriptional start site analysis using reverse transcription-PCR verified that the transcriptional initiation of the -215-bp deletion construct, with or without cotransfected c-Jun/c-Fos, was the same as that observed in vivo. Computer analysis of oFSHbeta sequences from -215 to +1 bp identified four putative AP-1-like elements, located at -155, -120, -83, and -10 bp. Gel retardation experiments using oligonucleotides corresponding to the four putative AP-1-like sites revealed that only -120 and -83 sites in oFSHbeta bound AP-1 proteins in vitro. Site-directed mutagenesis of the -120 and -83 sites showed that each element was required for stimulation by c-Jun and c-Fos proteins as well as 12-O-tetradecanoyl phorbol-13-acetate in transient transfection assays. Finally, immunocytochemical dual labeling was used to show that more than 75% of all FSHbeta-containing cells in ovine pituitary sections from cycling ewes contained nuclear c-Jun, JunB, JunD, and Fos proteins. These data, taken together, show that oFSHbeta transcription can be stimulated by c-Jun and c-Fos proteins via two functionally linked AP-1-like sites in the oFSHbeta proximal promoter and that these sites are likely to be important regulators of FSH production in vivo.