SF-1 (steroidogenic factor-1) and C/EBP beta (CCAAT/enhancer binding protein-beta) cooperate to regulate the murine StAR (steroidogenic acute regulatory) promoter.
The steroidogenic acute regulatory (StAR) protein mediates the rate-limiting step of steroidogenesis, which is the transfer of cholesterol to the inner mitochondrial membrane. In steroidogenic tissues, StAR expression is acutely regulated by trophic hormones through a cAMP second messenger pathway, leading to increased StAR mRNA levels within 30 min, reaching maximal levels after 4-6 h of stimulation. The molecular mechanisms underlying such regulation remain unknown. We have examined the StAR promoter for putative transcription factor-binding sites that may regulate transcription in a developmental and/or hormone-induced context. Through sequence analysis, deoxyribonuclease I (DNAse I) footprinting and electrophoretic mobility shift assays (EMSAs), we have identified two putative CCAAT/enhancer binding protein (C/EBP) DNA elements at -113 (C1) and -87 (C2) in the mouse StAR promoter. Characterization of these sites by EMSA indicated that C/EBP beta bound with high affinity to C1 and C2 was a low-affinity C/EBP site. Functional analysis of these sites in the murine StAR promoter showed that mutation of one or both of these binding sites decreases both basal and (Bu)2cAMP-stimulated StAR promoter activity in MA-10 Leydig tumor cells, without affecting the fold activation [(Bu)2cAMP-stimulated/basal] of the promoter. Furthermore, we have demonstrated that these two C/EBP binding sites are required for steroidogenic factor-1 (SF-1)-dependent transactivation of the StAR promoter in a nonsteroidogenic cell line. These data indicate that in addition to SF-1, C/EBP beta is involved in the transcriptional regulation of the StAR gene and may play an important role in developmental and hormone-responsive regulation of steroidogenesis.
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D022762:CCAAT-Enhancer-Binding Proteins; D019556:COS Cells / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051717:Fushi Tarazu Transcription Factors; D018398:Homeodomain Proteins; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D018160:Receptors, Cytoplasmic and Nuclear; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D020218:Response Elements; D054339:Steroidogenic Factor 1; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D000098682:Steroidogenic Acute Regulatory Protein