Estrogen activates the high-density lipoprotein receptor gene via binding to estrogen response elements and interaction with sterol regulatory element binding protein-1A.

The effects of E2 on the high-density lipoprotein receptor (HDL-R) scavenger receptor class B type I (SR-BI) gene were examined. Four putative estrogen response element half-site motifs (ERE(1/2)) (-2176, -1726, -1622, and -1211, designated ERE(1/2)-1, 2, 3, and 4, respectively) were identified in the HDL-R SR-BI promoter. Transfection studies and mutation analysis demonstrated that E2 significantly increased HDL-R SR-BI promoter activity and that mutating ERE(1/2)-1, 2, and 4 resulted in a loss of E2 responsiveness. Both ER alpha and ER beta formed specific complexes with ERE(1/2)-1, 2, and 4 but did not bind ERE(1/2)-3 in vitro. Interestingly, ERE(1/2)-3 was the motif shown not to be important for E2-activation of the HDL-R SR-BI promoter in the mutational analysis studies. The influence of SREBP-1a (sterol regulatory element binding protein-1a) on E2 regulation of the HDL-R SR-BI gene was also examined. SREBP-1a was able to bind directly to the ERE(1/2) motifs and enhanced ER binding when both ER subtypes were present. ER alpha and beta also bound to a sterol response element motif, but they did not enhance SREBP-1a binding. Cotransfection studies demonstrated that the presence of the three factors, ER alpha, ER beta, and SREBP-1a, enhanced the overall luciferase activity produced from the HDL-R SR-BI promoter construct in the presence of only one of the factors. Interaction of SREBP-1a with both ERs was demonstrated using a mammalian two-hybrid assay. The data confirmed that E2 through the ERs can positively regulate the HDL-R SR-BI through binding and activation of three ERE(1/2) motifs and identified SREBP-1a as a potential coactivator of the E2-ER-dependent effects on the HDL-R SR-BI gene.

Transcriptional repression of the rat steroidogenic acute regulatory (StAR) protein gene by the AP-1 family member c-Fos.

PGF2alpha, working via protein kinase C, may inhibit transcription of the StAR gene through negative regulatory factors. Administration of PGF2alpha increased c-Fos mRNA with a corresponding reduction in StAR mRNA. A search of the rat StAR promoter revealed three putative AP-1 elements at bp positions -85, -187 and -1561, which demonstrated specific binding of c-Fos by mobility shift assays. Co-transfection of c-Fos with the p-1862 StAR promoter caused a reduction in luciferase activity in the presence or absence of cAMP. Mutation of all three AP-1 sites in the p-1862 StAR promoter abolished c-Fos repression. Mutation of the proximal AP-1 site in the p-1862 StAR promoter reduced SF-1 mediated induction. This study is the first to demonstrate that c-Fos represses StAR gene transcription and adds to the current knowledge on the complex relationship that exists between SF-1 and c-Fos in the regulation of StAR activity.

Repression of the steroidogenic acute regulatory gene by the multifunctional transcription factor Yin Yang 1.

The transport of cholesterol to the inner mitochondrial membrane by the steroidogenic acute regulatory (StAR) protein is a critical step in steroidogenesis. The current study was designed to examine whether the multifunctional transcription factor Yin Yang 1 (YY1) was able to repress activation of the StAR gene. YY1 bound to three putative YY1-binding sites in the rat StAR promoter. Cotransfection of the StAR promoter linked to a luciferase reporter gene and YY1 in the presence or absence of sterol regulatory element binding protein-1a (SREBP-1a) resulted in transcriptional repression. YY1 was found to colocalize in the nucleus with SREPB-1a. YY1 inhibited SREBP-1a/nuclear factor Y (NF-Y) enhancement of StAR activation and YY1 decreased SREBP-1a binding to a sterol regulatory element in the presence or absence of NF-Y. YY1 also decreased NF-Y binding to a nonconsensus NF-Y-binding motif in the StAR promoter. These studies provide novel information on the mechanisms of YY1-mediated repression of the StAR gene.