AP-2 (activating protein 2) and Sp1 (selective promoter factor 1) regulatory elements play distinct roles in the control of basal activity and cyclic adenosine 3',5'-monophosphate responsiveness of the human chorionic gonadotropin-beta promoter.
The CG beta-subunit gene (CGbeta) arose evolutionarily from the LH beta-subunit gene (LHbeta) through gene duplication. Although the promoter sequences of the CGbeta and human (h) hLHbeta genes are greater than 90% homologous, their expression patterns are distinct. LHbeta is expressed in pituitary gonadotrope cells and CGbeta is expressed in placental trophoblast cells. The placental specific and cAMP-inducible region within the CGbeta promoter has been mapped to a complex enhancer element spanning 118 bp (-318 to -200). Transcription factor-binding sites within this enhancer have been partially characterized and include multiple binding sites for AP-2 (activating protein 2) and Sp1 (selective promoter factor 1), which activate basal and cAMP-induced expression. In this study, we performed a detailed analysis of the recognition sites for these transcription factors and examined the functional roles of these elements in the control of CGbeta expression. An upstream Sp1/AP-2 binding site (-318 to -279) preferentially binds Sp1, which occludes AP-2 binding to an adjacent site. In contrast, both Sp1 and AP-2 bind concurrently to a downstream composite Sp1/AP-2 element (-220 to -188). Functionally, mutations in any of the Sp1 or AP-2 binding sites cause a progressive decrease in basal CGbeta expression. However, cAMP stimulation of the CGbeta promoter is reduced by AP-2 mutations, whereas Sp1 mutations enhance cAMP activation. We conclude that multiple AP-2 and Sp1 elements are required to maintain basal CGbeta promoter activity, but these factors have opposing effects on cAMP regulation, which is mediated primarily by AP-2.
Johnson
W
W
Division of Endocrinology, Metabolism and Molecular Medicine, Northwestern University Medical School, Chicago, Illinois 60611, USA.
Jameson
J L
JL
D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line / Q000187:drug effects; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000235:genetics* / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism* / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D020218:Response Elements / Q000187:drug effects; D017422:Sequence Analysis, DNA; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D050656:Transcription Factor AP-2; D014157:Transcription Factors / Q000378:metabolism*
D018997:Chorionic Gonadotropin, beta Subunit, Human; D004268:DNA-Binding Proteins; D016329:Sp1 Transcription Factor; D050656:Transcription Factor AP-2; D014157:Transcription Factors; D000242:Cyclic AMP