The long term objective of this project is a thorough understanding of how steroid hormone synthesis is regulated in a developmental and tissue-specific fashion, and how dysregulation may result in reproductive disorders such as polycystic ovarian syndrome (PCOS). The genes for steroidogenic enzymes are transcriptionally regulated at several levels: developmentally, tissue specifically, and hormonally. This regulation shares common features but also differs among the various genes for the steroidogenic enzymes and among various mammals. We will focus on the gene encoding P450c17 (17alpha hydroxylase/17,2 lyase) as it is the key branch point in steroidogenesis, it has been implicated in the etiology of PCOS, and it may be involved in early development of nervous and reproductive systems. Its expression in the human adrenal is required for the synthesis of 17 hydroxy C21 steroids (e.g. cortisol) and for synthesis of C19 sex steroids in the gonads and brain. In the nervous system, expression of P450c17 also results in DHEA synthesis, a potent neuromodulators. We have been using the rodent as our model system for studying the transcriptional regulation of this gene, and have identified cis-acting DNA elements and several novel trans-acting nuclear factors. One of these transcription factors, SET, had been identified from a chromosomal translocation in a patient with acute undifferentiated leukemia, but its role as a transcription factor way unknown. We shall now determine the mechanism of SET action by identifying its DNA binding, transactivation, and potential dimerization domains, and identifying co-factors that may interact with SET to participate in its transactivating functions. AS SET is abundantly expressed and regulates P450c17 expression in the developing gonad and nervous system, we will determine if these co-factors are tissue- specifically expressed, and/or if they modify other known functions of SET. Our studies localizing cis-active elements in the rat P450c17 gene have identified a region bound by a factor that we call StF-IT-2, that interacts with the orphan nuclear receptor SF-1 in a novel way, to regulate P450c17 transcription. We will characterize that interaction, and purify, characterize and clone the cDNA for StF-IT-2. Successful completion of these studies will give us a better understanding of how the gonadal and nervous systems initiate steroidogenesis, the mechanism of action of a new class of transcription factor, novel mechanisms by which SF-1 regulates gene expression, and will identify another transcription factor that may participate in a unique aspect of P450c17 expression.