Sterol regulatory element binding protein-1a regulation of the steroidogenic acute regulatory protein gene.
The binding of tropic hormones to their specific receptors in steroidogenic cells stimulates the cAMP second-messenger system in the presence of steroidogenic factor-1 (SF-1) to increase expression of steroidogenic acute regulatory (StAR) protein, facilitating the transfer of cholesterol to the inner mitochondrial membrane. The increased use of cholesterol in steroidogenesis triggers activation of sterol- sensitive genes through a second regulatory pathway involving the binding of sterol regulatory element (SRE)-binding proteins (SREBP) to SREs located in the promoter regions of these genes. A search of the rat StAR promoter revealed five potential SRE sites, which demonstrated specific binding with recombinant SREBP-1a. Overexpression of SREBP-1a, -1c or -2 in HTB-9 cells cotransfected with the rat StAR promoter resulted in an increase in promoter-driven luciferase activity. In addition, SREBP-1a was able to activate the StAR promoter through an E-box but only in a promoter construct lacking SREs. SREBPs are known to be weak transcriptional activators and require the presence of additional coactivators like Sp1 and nuclear factor-Y (NF-Y) to elicit maximum activation. Electrophoretic mobility shift assays demonstrated that Sp1, SF-1, and NF-Y enhanced SREBP-1a binding to SREs in the StAR promoter. There was a 4-fold increase in StAR promoter luciferase reporter gene expression when HTB-9 cells were cotransfected with expression vectors for SREBP-1a and NF-Y. In addition, the combined action of SREBP-1a and SF-1 increased both basal (1.6-fold) and cAMP-induced (3.5-fold) activation of the rat StAR promoter. Although Sp1 enhanced SREBP-1a binding to an SRE, Sp1 was not able to increase StAR promoter activity in the presence of SREBP-1a. These results suggest that SREBP-induced regulation of the rat StAR gene is responsive to selective combinations of transcriptional cofactors that could necessitate the convergence of multiple regulatory pathways to enhance gene transcription.
Department of Obstetrics and Gynecology and Molecular Biology and Biochemistry, University of South Florida, College of Medicine, Tampa, Florida 33606, USA.
W K
WK
Shea-Eaton
M J
MJ
Trinidad
D
D
Lopez
A
A
Nackley
M P
MP
McLean
D000818:Animals; D001665:Binding Sites; D023081:CCAAT-Binding Factor / Q000096:biosynthesis / Q000235:genetics; D022762:CCAAT-Enhancer-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D004586:Electrophoresis; D005786:Gene Expression Regulation / Q000235:genetics; D018257:Helix-Loop-Helix Motifs / Q000235:genetics; D008156:Luciferases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D010750:Phosphoproteins / Q000096:biosynthesis* / Q000235:genetics; D011401:Promoter Regions, Genetic; D051381:Rats; D011994:Recombinant Proteins / Q000032:analysis / Q000096:biosynthesis; D054339:Steroidogenic Factor 1; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics; D014162:Transfection; D000098682:Steroidogenic Acute Regulatory Protein
D023081:CCAAT-Binding Factor; D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D010750:Phosphoproteins; D011994:Recombinant Proteins; C497389:Srebf1 protein, rat; D054339:Steroidogenic Factor 1; D051780:Sterol Regulatory Element Binding Protein 1; D014157:Transcription Factors; C402244:nuclear factor Y; D000098682:Steroidogenic Acute Regulatory Protein; C515060:steroidogenic factor 1, rat; D008156:Luciferases