Isolation and characterization of the human chorionic gonadotropin beta subunit (CG beta) gene cluster: regulation of transcriptionally active CG beta gene by cyclic AMP.

Long-term regulation of mammalian steroid hormone synthesis occurs principally by transcriptional regulation of the gene for the rate-limiting cholesterol side-chain cleavage enzyme P450scc. Adrenal steroidogenesis is regulated primarily by two hormones: adrenocorticotropin, which works via cyclic AMP (cAMP) and protein kinase A, and angiotensin H, which works via Ca2+ and protein kinase C. Forskolin and 8-bromo-cAMP stimulated, while prolonged treatment with a phorbol ester (12-O-tetradecanoylphorbol-13-acetate [TPA]) and a calcium ionophore (A23187) additively suppressed accumulation of endogenous P450scc mRNA in transformed murine adrenal Yl cells. In Yl cells transfected with 2,327 base pairs of the human P450scc promoter fused to the bacterial gene for chloramphenicol acetyltransferase (CAT), forskolin increased CAT activity 900% while combined TPA plus A23187 reduced CAT activity to 15% of the control level. Forskolin induced the P450scc promoter as rapidly as a promoter containing two cAMP-responsive elements fused to a simian virus 40 promoter, a system known to respond directly to cAMP. Basal expression was increased by sequences between -89 and -152 and was increased further by sequences between -605 and -2327. This upstream region also conferred inducibility by cAMP. TPA plus A23187 transiently increased CAT activity before repressing it, reflecting the complex actions of angiotensin II in vivo. Repression by prolonged treatment with TPA plus A23187 was mediated by multiple elements between -89 and -343. Induction of CAT activity by forskolin was not diminished by treatment with TPA plus A23187, nor were the regions of the promoter responsible for regulation by the two pathways coisolated. Thus, the human gene for P450scc is repressed by TPA plus A23187 by mechanisms and sequences independent of those that mediate induction by cAMP.Steroid hormones, which work by controlling transcription of specific genes, are critical regulators of physiological processes (5). The first, rate-limiting, and hormonally regulated step in the generation of steroid hormones is conversion of cholesterol to pregnenolone by the cholesterol sidechain cleavage enzyme P450scc. This mitochondrial cytochrome P450 enzyme receives electrons from NADPH via two protein intermediates, a flavoprotein, adrenodoxin reductase, and an iron-sulfur protein, adrenodoxin. By using these electrons, P450scc catalyzes three sequential reactions-22 hydroxylation, 20 hydroxylation, and C20,22 bond cleavage-apparently at a single active site (reviewed in reference 39). As side-chain cleavage is the rate-limiting step in steroidogenesis (51), it is important to understand both the hormonal regulation and tissue-specific expression of this gene.The developmental patterns of expression and hormonal regulation of P450scc are specific to each steroidogenic tissue. Increased steroidogenesis and accumulation of P450scc mRNA are stimulated by adrenocorticotropin in the human adrenal zonae fasciculata and reticularis, by luteinizing hormone and follicle-s...

show abstract

“…SB). To test this, (7,29,30,40). Temporal regulation of the human P450scc promoter by cAMP was even more rapid than that of the hCGa CRE (Fig.…”

Section: Methodsmentioning

confidence: 99%

Human P450scc gene transcription is induced by cyclic AMP and repressed by 12-O-tetradecanoylphorbol-13-acetate and A23187 through independent cis elements.

Moore¹,

Brentano²,

Miller³

1990

Mol. Cell. Biol.

View full text Add to dashboard Cite

show abstract

“…The promoter activity of hCG␤5 was stimulated by 8-bromo-cAMP in human JEG-3 placental cells but not hamster BHK fibroblast or INR1-G9 islet cells (26). It was later reported that the activating protein 2 (AP2) transcription factors TFAP2A and TFAP2C bind to GC-rich DNA sequences in the cAMP-responsive region the of hCG␤5 promoter (27)(28)(29)(30).…”

mentioning

confidence: 99%

A Positive Feedback Loop between Glial Cells Missing 1 and Human Chorionic Gonadotropin (hCG) Regulates Placental hCGβ Expression and Cell Differentiation

Cheong

Wang

Chuang

et al. 2016

Molecular and Cellular Biology

View full text Add to dashboard Cite

e Human chorionic gonadotropin (hCG) is composed of a common ␣ subunit and a placenta-specific ␤ subunit. Importantly, hCG is highly expressed in the differentiated and multinucleated syncytiotrophoblast, which is formed via trophoblast cell fusion and stimulated by cyclic AMP (cAMP). Although the ubiquitous activating protein 2 (AP2) transcription factors TFAP2A and TFAP2C may regulate hCG␤ expression, it remains unclear how cAMP stimulates placenta-specific hCG␤ gene expression and trophoblastic differentiation. Here we demonstrated that the placental transcription factor glial cells missing 1 (GCM1) binds to a highly conserved promoter region in all six hCG␤ paralogues by chromatin immunoprecipitation-on-chip (ChIPchip) analyses. We further showed that cAMP stimulates GCM1 and the CBP coactivator to activate the hCG␤ promoter through a GCM1-binding site (GBS1), which also constitutes a previously identified AP2 site. Given that TFAP2C may compete with GCM1 for GBS1, cAMP enhances the association between the hCG␤ promoter and GCM1 but not TFAP2C. Indeed, the hCGcAMP-protein kinase A (PKA) signaling pathway also stimulates Ser269 and Ser275 phosphorylation of GCM1, which recruits CBP to mediate GCM1 acetylation and stabilization. Consequently, hCG stimulates the expression of GCM1 target genes, including the fusogenic protein syncytin-1, to promote placental cell fusion. Our study reveals a positive feedback loop between GCM1 and hCG regulating placental hCG␤ expression and cell differentiation. Successful pregnancy requires a variety of hormones, growth factors, and cytokines to regulate uterine decidualization, embryo implantation, and pregnancy maintenance. For instance, progesterone and estrogen steroid hormones from the ovary prepare the uterine endometrium for embryo implantation. Human chorionic gonadotropin (hCG) is a critical hormone for pregnancy maintenance in humans. hCG is a glycoprotein hormone comprising ␣ and ␤ subunits. The hCG␣ subunit is shared with other glycoprotein hormones, including thyroid-stimulating hormone, follicle-stimulating hormone, and luteinizing hormone (LH), whereas the hCG␤ subunit is specifically expressed in placenta and is unique to hCG. While hCG␣ is encoded by a single gene on chromosome 6, hCG␤ can be encoded by a gene cluster of six (hCG␤1, -2, -3, -5, -7, and -8) paralogues on chromosome 19 (1). Recent studies have suggested that the expression of hCG␤5 and -8 may account for the majority of hCG␤ transcripts given that all hCG␤ paralogues share high sequence homology in their promoter regions (2, 3).hCG expression can be detected in early 6-to 8-cell embryos, and this may serve as an embryonic signal for the rendering of appropriate maternal physiology for pregnancy (1). After implantation, the serum hCG level increases dramatically as pregnancy proceeds, reaching its peak at 9 or 10 weeks of gestation, and then decreases and remains at ϳ20% of the peak value until term (4). One of the crucial hCG functions is to stimulate progesterone synthesis from the corpus luteu...

show abstract

“…5). This proposed genesis and structure of white rhino LH loci contrasts with the primate LH -CG gene cluster-locus wherein the repeated members of the gene family are tandemly linked (Talmadge et al 1983, Policastro et al 1983, Graham et al 1987, Jameson & Lindell 1988, having evolved by a different replicative process involving unequal crossing over of adjacent DNA regions (Stark & Wahl 1995).…”

Section: Discussionmentioning

confidence: 99%

Duplication of the southern white rhinoceros (Ceratotherium simum simum) luteinizing hormone beta subunit gene

Lund

Sherman²

1998

Journal of Molecular Endocrinology

View full text Add to dashboard Cite

Luteotropic glycoprotein hormones (LGH) include luteinizing hormone (LH) and chorionic gonadotropin (CG). The order Primates is the only phylogenetic clad known to exhibit more than one LGH subunit gene per haploid genome. In the present study, we report the discovery of a second case of LGH gene replication, in the white (w) rhinoceros (r or rhino). The presence of more than one gene was strongly suggested by a complex banding pattern observed on Southern blots of DNA prepared from two unrelated white rhinos. The existence of two LGH genes per haploid genome was estimated by genomic equivalence assay. However, genomic restriction-site mapping studies, together with other findings, suggested that the replicates are probably not tandemly arranged as occurs in primates. A simple band pattern was observed in Southern blots of four other perissodactyl species, indicating that a single-copy LH gene is the consensus condition. Two distinct white rhino LH genomic clones (wrLH 1 and wrLH 2) were isolated. The nucleotide sequence of wrLH 1 was identical with that of wrLH 2, except that the latter lacked the consensus mammalian LGH second intron. Sequences of the TATA-containing proximal 5 -flanking regions of the two genes were homologous to at least 57 relative to the site of pituitary transcriptional initiation. We conclude that wrLH 1 is the extant form of the ancestral perissodactyl LH gene, whereas wrLH 2 is a randomly integrated cDNA element (processed gene) reverse transcribed from a partially spliced ancestral wrLH 1 mRNA. That wrLH 2 was heritable demonstrates that wrLH 1 was transcribed in gametes or early conceptus cells contributing to the germline at some point in time since the divergence of white rhinos from other members of the family Rhinocerotidae. Furthermore, because homologous proximal (pituitary) promoter sequence is present in wrLH 2, it can be concluded that the wrLH 1 mRNA template from which wrLH 2 is derived was transcribed from a secondary promoter located upstream of the consensus TATA-regulated pituitary promoter.

show abstract

Isolation and characterization of the human chorionic gonadotropin beta subunit (CG beta) gene cluster: regulation of transcriptionally active CG beta gene by cyclic AMP.

Cited by 54 publications

References 41 publications

Human P450scc gene transcription is induced by cyclic AMP and repressed by 12-O-tetradecanoylphorbol-13-acetate and A23187 through independent cis elements.

Human P450scc gene transcription is induced by cyclic AMP and repressed by 12-O-tetradecanoylphorbol-13-acetate and A23187 through independent cis elements.

A Positive Feedback Loop between Glial Cells Missing 1 and Human Chorionic Gonadotropin (hCG) Regulates Placental hCGβ Expression and Cell Differentiation

Duplication of the southern white rhinoceros (Ceratotherium simum simum) luteinizing hormone beta subunit gene

Contact Info

Product

Resources

About