Luteinizing Hormone Β-subunit Gene Research Articles

AMP-activated protein kinase activation reduces the transcriptional activity of the murine luteinizing hormone β-subunit gene.

Malnutrition is one of the factors that induces reproductive disorders. However, the underlying biological processes are unclear. AMP-activated protein kinase (AMPK) is an enzyme that plays crucial role as a cellular energy sensor. In the present study, we examined the effects of AMPK activation on the transcription of the murine gonadotropin subunit genes Cga, Lhb, and Fshb, and the gonadotropin-releasing hormone receptor Gnrh-r. Real-time PCR and transcription assay using LβT2 cells demonstrated that 5-amino-imidazole carboxamide riboside (AICAR), a cell-permeable AMP analog, repressed the expression of Lhb. Next, we examined deletion mutants of the upstream region of Lhb and found that the upstream regulatory region of Lhb (–2527 to –2198 b) was responsible for the repression by AICAR. Furthermore, putative transcription factors (SP1, STAT5a, and TEF) that might mediate transcriptional control of the Lhb repression induced by AICAR were identified. In addition, it was confirmed that both AICAR and a competitive inhibitor of glucose metabolism, 2-deoxy-D-glucose, induced AMPK phosphorylation in LβT2 cells. Therefore, the upstream region of Lhb is one of the target sites for glucoprivation inducing AMPK activation. In addition, AMPK plays a role in repressing Lhb expression through the distal –2527 to –2198 b region.

Response to comment on “Hypogonadotrophic hypogonadism due to a mutation in the luteinizing hormone β-subunit gene”

Response to comment on “Hypogonadotrophic hypogonadism due to a mutation in the luteinizing hormone β-subunit gene”

Comment on "Hypogonadotrophic hypogonadism due to a mutation in the luteinizing hormone β-subunit gene".

Comment on "Hypogonadotrophic hypogonadism due to a mutation in the luteinizing hormone β-subunit gene".

Hypogonadism in a Patient with Two Novel Mutations of the Luteinizing Hormone β-Subunit Gene Expressed in a Compound Heterozygous Form

LH gene mutations are rare; only four mutations have been described. The affected individuals are hypogonadal. We describe the clinical features of a 31-yr-old man who presented with delayed puberty and azoospermia and was found to have hypogonadism associated with an absence of circulating LH. The patient had a 12-bp deletion in exon 2 in the LH β-subunit gene and a mutation of the 5' splice site IVS2+1G→T in the same gene present in a compound heterozygous state. The first mutation predicts a deletion of four leucines of the hydrophobic core of the signal peptide. The second mutation disrupts the splicing of mRNA, generating a gross abnormality in the processing. The patient's heterozygous parents were clinically normal. The phenotype of a 16-yr-old sister of the proband, carrying the same mutations, was characterized by normal pubertal development and oligomenorrhea. This report unravels two novel mutations of the LH gene critical for synthesis and activity of the LH molecule. The insight gained from the study is that normal pubertal maturation in women can occur in a state of LH deficiency, whereas LH is essential for maturation of Leydig cells and thus steroidogenesis, puberty, and spermatogenesis in man. These mutations should be considered in girls and boys with selective deficiency of LH.

Role of luteinizing hormone β-subunit gene variants among South Indian women with polycystic ovary syndrome

Abnormal luteinizing hormone (LH) secretion and action are known to affect ovarian steroidogenesis and thus playing a crucial role in manifestation of polycystic ovary syndrome (PCOS). This study is first of its kind to study association of LH β-subunit gene variants with PCOS among South-Indian women. 250 PCOS cases and 299 controls were recruited for the study. All the exons of LH β gene were screened. Allele and genotype frequencies of the SNPs were compared between the cases and controls. We identified seven SNPs in the LH β gene; one SNP in exon 3 (rs#1056917) exhibited significant difference in the allele frequency between the PCOS cases and controls (p=0.015). Although, the LH β variants that are found to be more frequent among PCOS cases are silent in nature and not of any functional significance, they might influence other significant functional polymorphisms in the hypothalamic–pituitary–gonadal axis which needs to be explored.

Modulation of Gonadotropin-Releasing Hormone-Induced Extracellular Signal-Regulated Kinase Activation by Dual-Specificity Protein Phosphatase 1 in LβT2 Gonadotropes

As the regulator of pituitary reproductive hormone synthesis, the hypothalamic neuropeptide GnRH is the central regulator of reproduction. A hallmark of GnRH action is the differential control of gene expression in pituitary gonadotropes through varied pulsatile stimulation. Among other signaling events, GnRH activation of the ERK family of MAPKs plays a significant role in the transcriptional regulation of the luteinizing hormone β-subunit gene and regulation of cap-dependent translation. We evaluated the ERK response to different GnRH pulse amplitudes in the gonadotrope cell line LβT2. We found that low-amplitude stimulation with GnRH invokes a rapid and transient ERK activation, whereas high-amplitude stimulation invokes a prolonged activation specifically in the cytoplasm fraction of LβT2 cells. Nuclear and cytoplasmic targets of ERK, Ets-like gene 1, and eukaryotic initiation factor 4E, respectively, are similarly activated. Feedback control of ERK activation occurs mainly through the dual-specificity protein phosphatases (DUSPs). DUSP1 is localized to the nucleus in LβT2 cells but DUSP4, another member implicated in GnRH feedback, exists in both the nucleus and cytoplasm. Manipulation of nuclear DUSP activity through overexpression or knockdown of Dusp1 modulates the ERK response to low and high GnRH pulse amplitudes and activation of the Lhb promoter. Dusp1 overexpression abolishes sustained ERK activation and inhibits Lhb promoter activity induced by high amplitude pulses. Conversely, Dusp1 knockdown enhances ERK activation by low-amplitude stimulation and increases stimulation of Lhb promoter activity. We conclude that DUSP1 feedback activity modulates ERK activation and the transcriptional response to GnRH.

Luteinizing hormone β-subunit gene ( LHβ) polymorphism in infertility and endometriosis-associated infertility

Objective To establish the frequency of LHβ G1502A polymorphism in infertile women with endometriosis, infertile women without endometriosis and a control group. Study design Case–control study including 110 infertile women with endometriosis, 84 infertile women without endometriosis and a control group consisting 209 healthy fertile women recruited from the ABC School of Medicine. The LHβ G1502A polymorphism was studied by RPLP-PCR (restriction fragment length polymorphism-polymerase chain reaction). Results Genotypes GG, GA and AA of the LHβ G1502A polymorphism presented frequencies of 54.6%, 31.8% and 13.6%, respectively, in the women with endometriosis ( p = 0.0398); of 52.4%, 38.1% and 9.5% ( p = 0.0123), respectively, in the infertile women without endometriosis; and of 68.9%, 21.5% and 9.6%, respectively, in the control group. In patients with minimal/mild endometriosis and moderate/severe endometriosis, the GG, GA and AA genotype frequencies were, respectively, 47.3%, 36.4% and 16.3% ( p = 0.0118); and 61.8%, 27.3% and 10.9% ( p = 0.5975). Considering the alleles, allele G was present in 70.5% of the patients with endometriosis, 71.4%% of the infertile women without endometriosis and in 79.7% of the controls, whereas allele A was present in 29.5%, 28.6% and 20.3%, respectively, in the infertile women with endometriosis ( p = 0.0121), infertile women without endometriosis ( p = 0.0409) and controls. Alleles G and A presented frequencies of 65.5% and 34.5% and 75.5% and 24.5%, respectively, in minimal/mild endometriosis ( p = 0.0026) and moderate/severe endometriosis ( p = 0.4062). Conclusion The data suggest that LHβ G1502A polymorphism may be involved in the predisposition to infertility and minimal/mild endometriosis-associated infertility, although endometriosis might be only a coincidental finding along with infertility.

Distinct Mechanisms Involving Diverse Histone Deacetylases Repress Expression of the Two Gonadotropin β-Subunit Genes in Immature Gonadotropes, and Their Actions Are Overcome by Gonadotropin-Releasing Hormone

The gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are produced in the embryonic pituitary in response to delivery of the hypothalamic gonadotropin releasing hormone (GnRH). GnRH has a pivotal role in reestablishing gonadotropin levels at puberty in primates, and for many species with extended reproductive cycles, these are reinitiated in response to central nervous system-induced GnRH release. Thus, a clear role is evident for GnRH in overcoming repression of these genes. Although the mechanisms through which GnRH actively stimulates LH and FSH beta-subunit (FSHbeta) gene transcription have been described in some detail, there is currently no information on how GnRH overcomes repression in order to terminate reproductively inactive stages. We show here that GnRH overcomes histone deacetylase (HDAC)-mediated repression of the gonadotropin beta-subunit genes in immature gonadotropes. The repressive factors associated with each of these genes comprise distinct sets of HDACs and corepressors which allow for differentially regulated derepression of these two genes, produced in the same cell by the same regulatory hormone. We find that GnRH activation of calcium/calmodulin-dependent protein kinase I (CaMKI) plays a crucial role in the derepression of the FSHbeta gene involving phosphorylation of several class IIa HDACs associated with both the FSHbeta and Nur77 genes, and we propose a model for the mechanisms involved. In contrast, derepression of the LH beta-subunit gene is not CaMK dependent. This demonstration of HDAC-mediated repression of these genes could explain the temporal shut-down of reproductive function at certain periods of the life cycle, which can easily be reversed by the actions of the hypothalamic regulatory hormone.

Proline-Rich Tyrosine Kinase 2 Mediates Gonadotropin-Releasing Hormone Signaling to a Specific Extracellularly Regulated Kinase-Sensitive Transcriptional Locus in the Luteinizing Hormone β-Subunit Gene

G protein-coupled receptor regulation of gene transcription primarily occurs through the phosphorylation of transcription factors by MAPKs. This requires transduction of an activating signal via scaffold proteins that can ultimately determine the outcome by binding signaling kinases and adapter proteins with effects on the target transcription factor and locus of activation. By investigating these mechanisms, we have elucidated how pituitary gonadotrope cells decode an input GnRH signal into coherent transcriptional output from the LH beta-subunit gene promoter. We show that GnRH activates c-Src and multiple members of the MAPK family, c-Jun NH2-terminal kinase 1/2, p38MAPK, and ERK1/2. Using dominant-negative point mutations and chemical inhibitors, we identified that calcium-dependent proline-rich tyrosine kinase 2 specifically acts as a scaffold for a focal adhesion/cytoskeleton-dependent complex comprised of c-Src, Grb2, and mSos that translocates an ERK-activating signal to the nucleus. The locus of action of ERK was specifically mapped to early growth response-1 (Egr-1) DNA binding sites within the LH beta-subunit gene proximal promoter, which was also activated by p38MAPK, but not c-Jun NH2-terminal kinase 1/2. Egr-1 was confirmed as the transcription factor target of ERK and p38MAPK by blockade of protein expression, transcriptional activity, and DNA binding. We have identified a novel GnRH-activated proline-rich tyrosine kinase 2-dependent ERK-mediated signal transduction pathway that specifically regulates Egr-1 activation of the LH beta-subunit proximal gene promoter, and thus provide insight into the molecular mechanisms required for differential regulation of gonadotropin gene expression.

Analyses of the cDNA and genomic DNA sequences encoding the luteinizing hormone β-subunit precursor protein in the rabbit

To examine the molecular basis for efficient induction of superovulation in the rabbit, we determined the cDNA sequences of the luteinizing hormone β-subunit (LHB) from Japanese White (JW), New Zealand White (NZW), and Dutch-Belted (Dutch) rabbits, and we compared these LHB sequences with those of other mammals. Using 5′- and 3′-rapid amplification of cDNA ends (RACE) with pituitary cDNA libraries, we found that the LHB cDNAs of all three breeds are the same length (523 bp from the 5′-end to the polyA site) and have putative AATAAA polyadenylation signal sequences at nucleotides 504 to 509. Northern blot analysis indicated that the ∼600-nt mRNA encoding JW LHB is slightly longer than the LHB mRNAs of the other two breeds. The NZW and Dutch rabbit LHB coding sequences are 426 bp long, and their G + C contents are higher (>73%) than those of other mammalian LHBs (<70%). The predicted 141-amino-acid sequences of the JW and NZW LHB proteins are identical, and the Dutch LHB and JW/NZW sequences differ at only two residues. The exon–intron configuration of the NZW LHB gene (three exons and two introns) is similar to that of other mammalian LHB genes, and the sequences of NZW rabbit and other mammalian LHB promoter regions are highly conserved. Phylogenetic analysis of the deduced amino acid sequences of the three rabbit LHB proteins indicated that the rabbit occupies a phylogenetic position between rodents and domestic animals, and is far from humans. The results suggest that LH prepared from rodents or domestic animals, if available, would be a better inducer for superovulation in rabbits than human LH/CG.

Pituitary homeobox 1 (Pitx1) stimulates rat LHβ gene expression via two functional DNA-regulatory regions

Luteinizing hormone (LH) plays a central role in the reproductive axis, stimulating both gonadal steroid biosynthesis and the development of mature gametes. Over the past decade, significant progress has been made in characterizing the transcription factors and associated DNA-regulatory sites which mediate expression of the LH beta-subunit gene (LHbeta). One of these factors, pituitary homeobox 1 (Pitx1), has been shown to stimulate LHbeta gene promoter activity, both alone and in synergy with the orphan nuclear receptor, steroidogenic factor-1 (SF-1), and the early growth response gene 1 (Egr-1). Prior reports have attributed the Pitx1 response to a cis-element located at position -101 in the rat LHbeta gene promoter. While investigating the role of Pitx1 in regulating rat LHbeta gene expression, we observed a small, but significant, residual Pitx1 response despite mutation or deletion of this site. In the studies presented here, we identify the presence of a second functional Pitx1 region spanning positions -73 to -52 in the rat LHbeta gene promoter. Based on electrophoretic mobility shift assay, Pitx1 binds to both the initially described 5'Pitx1 site as well as this putative 3'Pitx1 region. In transient transfection analysis, mutation of the LHbeta-3'Pitx1 site significantly blunted Pitx1 responsiveness, with elimination of the Pitx1 response in a construct containing mutations in both Pitx1 cis-elements. We also analyzed the importance of each of these Pitx1 sites for providing functional synergy with SF-1 and with Egr-1. We observed a markedly decreased synergistic response with mutation of the 5'Pitx1 site with further loss following mutation of the 3'Pitx1 site. In contrast, functional interaction between Pitx1 and Egr-1 persisted with mutation of both Pitx1 regions. We conclude that Pitx1 stimulates the rat LHbeta gene promoter via two Pitx1 DNA-regulatory regions. These results further our understanding of the molecular mechanisms that regulate expression of this critical reproductive gene promoter.

Activin Regulates Luteinizing Hormone β-Subunit Gene Expression through Smad-Binding and Homeobox Elements

LH beta-subunit (LHbeta), which is essential for ovulation and reproductive fitness, is synthesized specifically in pituitary gonadotropes. In this study, we show that LHbeta gene expression is induced by activin in mouse primary pituitary cells if the cells are treated within 24 h after dispersion in culture. Furthermore, male mice deficient in Smad3, and therefore in activin signaling, have lower expression of both LHbeta and FSHbeta mRNAs compared with their wild-type littermates. Using the LbetaT2 immortalized mouse gonadotrope cell line that endogenously expresses LH, we identify specific elements in the regulatory region of the rat LHbeta gene necessary for its induction by activin. Activin responsiveness is conferred by a promoter-proximal region located -121/-86 from the transcriptional start site. Maximal LHbeta induction by activin requires a homeobox element (HB) and a 5'-early growth response (Egr) site found in this region of the promoter. Juxtaposed to the HB are three Smad-binding elements (SBEs), which are essential for LHbeta induction. Interestingly, two of the SBEs are also critical for basal expression of the LHbeta gene. We demonstrate that Smad proteins are necessary and sufficient for activin induction of the LHbeta gene. Furthermore, Smad proteins can bind one of the identified SBEs. In addition to binding this SBE, Smad proteins interact with pituitary homeobox 1 (Ptx-1) and orthodenticle homeobox 1 (Otx-1), which can bind the HB located close to the Smad-binding site. Thus, activin induction of LHbeta gene expression requires a combination of several transcription factors, both basal and activin induced, as well as cooperation between multiple DNA elements.

Genetic analysis of three polymorphic sites of the luteinizing hormone β-subunit gene in infertile Korean men with nonobstructive azoospermia

Objective To investigate the genetic background of nonobstructive male factor infertility. Design Clinical and controlled study. Patient(s) Ninety-five nonobstructive male infertile patients (75 with azoospermia, 18 with oligoasthenoteratozoospermia, and two with oligozoospermia) and 200 healthy fertile control men. Intervention(s) Patients were investigated for genetic background including karyotype, Yq chromosome deletion, and three polymorphisms of the LH β-subunit gene (Trp8Arg, Ile15Thr, and Gly102Ser). Main outcome measure(s) To determine three polymorphisms of the LH β-subunit gene. Result(s) An abnormal karyotype was found in 11 of the 75 patients with azoospermia and one of the 18 patients with oligoasthenoteratozoospermia. Eleven (12%) had one or more deleted sites at 13 loci on Yq. The Gly102Ser variant of the LH β-subunit gene was not detected at all. The frequency of double Trp8Arg and Ile15Thr heterozygotes was similar between the fertile (14.5%, n = 200) and infertile (12.6%, n = 95) groups, with the exception of one homozygous mutation (Arg8 and Thr15) from patient with azoospermia. Conclusion(s) Three variants of the LH β-subunit gene (Trp8Arg, Ile15Thr, and Gly102Ser) may not be associated with male factor infertility. We found one homozygous Arg8 and Thr15 mutation in a patient with azoospermia with normal hormone levels (FSH, LH, PRL, T), a normal karyotype, and no Yq microdeletions.

Mutations and polymorphisms in gonadotropin genes

Mutations in gonadotropin genes are extremely rare. Only one case of inactivating human luteinizing hormone (LH) β mutation exists in the literature, a male with absence of Leydig cells, lack of spontaneous puberty and infertility. A total of four cases of inactivating mutation of the follicle-stimulating hormone β (FSHβ) gene (two female and two male) are known. The phenotype of the women was primary amenorrhea and absence of follicular maturation, the men were azoospermic. In addition, a common genetic variant (v) of LH was recently discovered. It is caused by two point mutations in the LH β-subunit gene, resulting in amino acid alterations: Trp 8→Arg and Ile 15→Thr. In addition, the latter change introduces an extra glycosylation signal for oligosaccharide attachment to Asn 13. The v-LHβ allele has a carrier frequency ranging from 0 to >50% in various populations. The variant LH molecule has increased intrinsic bioactivity in vitro, but decreased circulatory half-life in vivo, and the v-LHβ promoter is about 50% more active in cell line transfections than that of wild-type (wt) LH. These differences in LH synthesis and action in individuals homo- or heterozygous for the v-LH allele are reflected by altered disposition to pathologies of pituitary–gonadal function, such as delayed puberty, polycystic ovarian syndrome and infertility.

Steroidogenic Factor-1 and Early Growth Response Protein 1 Act through Two Composite DNA Binding Sites to Regulate Luteinizing Hormone β-Subunit Gene Expression

Recent in vivo and in vitro studies have implicated the orphan nuclear receptor, steroidogenic factor-1 (SF-1), and the early growth response protein 1 (Egr-1) in the transcriptional regulation of the luteinizing hormone beta-subunit (LHbeta) gene. We have previously demonstrated the ability of SF-1 to bind to and transactivate the rat LHbeta gene promoter acting at a consensus gonadotrope-specific element (GSE) located at position -127. We have now identified a second functional GSE site at position -59. In addition, based on electrophoretic mobility shift assay, in vitro translated Egr-1 is shown to bind to two putative Egr-1 binding sites (positions -112 and -50), which appear to be paired with the identified GSE sites. By transient transfection assay in pituitary-derived GH3 cells, it was seen that Egr-1 increases promoter activity of region -207/+5 of the rat LHbeta gene promoter through action at both Egr-1 sites. Furthermore, LHbeta gene promoter activity is markedly augmented in the presence of both factors together relative to activity in the presence of SF-1 or Egr-1 alone (150-fold versus 14-fold and 12-fold, respectively). These data define two composite SF-1-Egr-1 response-elements in the proximal LHbeta gene promoter and suggest that SF-1 and Egr-1 act synergistically to increase expression of the LHbeta gene in the gonadotrope.

Identification of cis-acting deoxyribonucleic acid elements that mediate gonadotropin-releasing hormone stimulation of the rat luteinizing hormone beta-subunit gene.

GnRH plays a critical role in reproductive development and function by regulating the biosynthesis and secretion of the pituitary gonadotropins, LH and FSH. Although it is known that GnRH induces gonadotropin subunit gene transcription, the mechanism by which this occurs has not been elucidated. Studies have been hindered by the lack of available cell lines that express the LH and FSH subunit genes and respond to GnRH. We have transfected the rat pituitary GH3 cell line with the rat GnRH receptor complementary DNA. These cells, when cotransfected with regulatory regions of the LH or FSH subunit genes fused to a luciferase reporter gene, respond to GnRH with an increase in promoter activity comparable to that seen in primary rat pituitary cells. In this study, we have used this cell model to identify cis-acting elements of the LHbeta gene that mediate stimulation by GnRH. Analysis of a series of 5'-deletion and internal deletion constructs has revealed two regions of the rat LHbeta gene promoter involved in mediating the response to GnRH, region A (-490/-352) and region B (-207/-82). Fusion of region A upstream of a heterologous minimal promoter linked to the luciferase gene conferred GnRH responsiveness to the promoter, whereas region B did not. However, the presence of both regions A and B conferred a greater GnRH response than region A alone. Electrophoretic mobility shift assay revealed the presence of a protein(s) binding to region A using GH3 as well as alphaT3-1 nuclear extracts. Thus, region A (-490/-352) confers GnRH responsiveness to the LHbeta subunit gene and binds to a protein(s) present in pituitary cell lines. DNA sequences in region B (-207/-82) also contribute to GnRH responsiveness. The identification of putative GnRH response elements in the rat LHbeta gene promoter will aid in elucidation of the mechanisms of regulation of gene expression by GnRH.