The long-term objective of this project is to understand the various intracellular factors contributing to the regulation of steroid hormone synthesis. Steroid hormones are ubiquitous, life-sustaining regulatory chemicals that can be grouped into three broad categories: mineralocorticoids regulate renal sodium retention and blood pressure; glucocorticoids regulate carbohydrate metabolism and various cellular processes; sex steroids are required for reproduction. Much is already known about the circulating hormones that stimulate the adrenals and gonads to secrete steroid hormones, but little is known about the intracellular mechanisms by which these hormones work. Understanding these mechanism is important for understanding the various disorders of steroid hormone synthesis and for developing therapies specific to each step in steroidogenesis. Our initial work will focus on two steps in the synthesis of steroid hormones from cholesterol. First, the rate-limiting quantitative regulatory step is the conversation of cholesterol to prenenolone by the cholesterol side chain cleavage enzyme, P450scc. This mitochondrial enzyme requires two electron-transport factors: a flavoprotein termed adrenodoxin reductase and an iron/sulfur protein termed adrenodoxin. Second, the qualitative regulatory enzyme is P450c17, which has both 17alpha-hydroxylase and 17,20 lyase activities. Lack of either activity directs human adrenal steroid precursors to mineralocorticoid synthesis; presence of 17alpha-hydroxylase activity without 17,20 lyase activity directs steroids to glucocorticoid synthesis; presence of both activities results in the synthesis of sex steroids. We have already cloned genes and/or cDNAs for P450scc, P450c17, adrenodoxin, and adrenodoxin reductase. The amounts of these enzymes that are produced, and consequently the amount and type of steroids produced, depends largely on the regulation of the transcription of these genes and possibly also the regulation of the stability of their mRNAs. By putting the cloned genes into cultured cells by both transient and stable transfections, we can determine how these genes are regulated by stimulatory hormones and cell- specific factors. We will identify the DNA sequences in these genes that confer such hormonal inducibility and tissue-specific expression. We will also examine specific sequences in these genes that may influence the stability of their mRNA products. Successful completion of this work will permit us to begin to understand how adrenals and gonads use the same genes and enzymes to produce different steroids under independent physiologic control.
Showing the most recent 10 out of 70 publications
