MEF2 Cooperates With Forskolin/cAMP and GATA4 to Regulate Star Gene Expression in Mouse MA-10 Leydig Cells

In Leydig cells, steroidogenic acute regulatory protein (STAR) participates in cholesterol shuttling from the outer to the inner mitochondrial membrane, the rate-limiting step in steroidogenesis. Steroid hormone biosynthesis and steroidogenic gene expression are regulated by LH, which activates various signaling pathways and transcription factors, including cAMP/Ca(2+)/CAMK (Ca(2+)/calmodulin-dependent kinase)-myocyte enhancer factor 2 (MEF2). The 4 MEF2 transcription factors are essential regulators of cell differentiation and organogenesis in numerous tissues. Recently, MEF2 was identified in Sertoli and Leydig cells of the testis. Here, we report that MEF2 regulates steroidogenesis in mouse MA-10 Leydig cells by acting on the Star gene. In MA-10 cells depleted of MEF2 using siRNAs (small interfering RNAs), STAR protein levels, Star mRNA levels, and promoter activity were significantly decreased. On its own, MEF2 did not activate the mouse Star promoter but was found to cooperate with forskolin/cAMP. By chromatin immunoprecipitation and DNA precipitation assays, we confirmed MEF2 binding to a consensus element located at -232 bp of the Star promoter. Mutation or deletion of the MEF2 element reduced but did not abrogate the MEF2/cAMP cooperation, indicating that MEF2 cooperates with other DNA-bound transcription factor(s). We identified GATA4 (GATA binding protein 4) as a partner for MEF2 in Leydig cells, because mutation of the GATA element abrogated the MEF2/cAMP cooperation on a reporter lacking a MEF2 element. MEF2 and GATA4 interact as revealed by coimmunoprecipitation, and MEF2 and GATA4 transcriptionally cooperate on the Star promoter. Altogether, our results define MEF2 as a novel regulator of steroidogenesis and Star transcription in Leydig cells and identify GATA4 as a key partner for MEF2-mediated action.