Abstract: 4

C/EBP AND SF-1 COOPERATE TO REGULATE THE StAR PROMOTER.

AJ Reinhart¹ , SC Williams¹ , DM Stocco^{1 *}
Dept. of Cell Biology and Biochemistry, Texas Tech Univ Health Sciences Center, Lubbock, Texas ¹

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 cAMP, leading to increased StAR mRNA levels within 30 min. The precise molecular mechanism underlying such regulation is unknown. We have examined the StAR promoter for putative transcription factor binding sites which may regulate transcription in a developmental and/or hormone-induced context. We identified two 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 analysis indicated that C/EBP bound with high affinity to C1 and with low affinity to C2. Functional analysis of these sites 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. Interestingly, 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 non-steroidogenic cell line. Furthermore, we have found that SF-1 and C/EBP physically associate in vitro, and that co-activators may be involved in C/EBP/SF-1 mediated StAR transcription in vivo. These data indicate that C/EBP is involved in the transcriptional regulation of the StAR gene, and may function in concert with SF-1 and co-activators to play an important role in developmental and hormone-responsive regulation of steroidogenesis. (Supported by NIH grant #HD17481)

    This abstract is being presented on Saturday, July 31 at 2:15 PM at Todd 116.