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.
Liu
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Department of Biological Sciences, University of Missouri, Columbia 65211, USA.
Leaman
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Villalta
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Roberts
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RM
D001483:Base Sequence; D001665:Binding Sites; D002822:Choriocarcinoma / Q000473:pathology; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000096:biosynthesis / Q000235:genetics; D016384:Consensus Sequence; D018983:DNA Footprinting; D004268:DNA-Binding Proteins / Q000494:pharmacology* / Q000502:physiology; D005260:Female; D005326:Fetal Proteins / Q000494:pharmacology*; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D015292:Glycoprotein Hormones, alpha Subunit / Q000096:biosynthesis / Q000235:genetics*; D018398:Homeodomain Proteins / Q000494:pharmacology* / Q000502:physiology; D051863:Host Cell Factor C1; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics; D050811:Octamer Transcription Factor-1; D050813:Octamer Transcription Factor-2; D050814:Octamer Transcription Factor-3; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology; D014157:Transcription Factors / Q000494:pharmacology* / Q000502:physiology; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000187:drug effects; D014594:Uterine Neoplasms / Q000473:pathology
D018997:Chorionic Gonadotropin, beta Subunit, Human; D004268:DNA-Binding Proteins; D005326:Fetal Proteins; D015292:Glycoprotein Hormones, alpha Subunit; C497692:HCFC1 protein, human; D018398:Homeodomain Proteins; D051863:Host Cell Factor C1; D009363:Neoplasm Proteins; D050811:Octamer Transcription Factor-1; D050813:Octamer Transcription Factor-2; D050814:Octamer Transcription Factor-3; C494165:POU2F1 protein, human; C058435:POU2F2 protein, human; C494173:POU5F1 protein, human; D012097:Repressor Proteins; D014157:Transcription Factors