The long-range goal of this project is to provide a detailed understanding of the biochemistry and regulation of hepatic cytochrome P45O (CYP) enzymes that oxidatively metabolize steroid hormones, cholesterol and other endogenous lipophilic compounds, using the rat as a model system. The proposed project period focuses on pituitary control of sex-specific steroid hydroxylase P450 enzymes, with special emphasis on the cellular and molecular mechanism(s) by which serum growth hormone (GH) and its sex- dependent ultradian secretory pattern differentially regulate the expression of male-specific and female-specific steroid hydroxylase P45Os in rat liver. The female-specific steroid sulfate l5beta-hydroxylase CYP 2C12 and the male-specific testosterone 2alpha/16alpha-hydroxylase CYP 2C11 genes will be studied as prototypic examples of GH-regulated liver P450 genes. The major objectives of this project are to: (1) identify functional GH response elements within the 5'-flank of CYP 2C12 that mediate the transcriptional activation of this gene by continuous GH; (2) clone a cDNA that encodes the GH-regulated transcription factor that binds to these GH response elements and then (3) elucidate the mechanisms by which continuous GH activates this liver transcription factor; (4) identify the mechanisms by which activation of the plasma membrane-bound GH receptor leads to induction of CYP 2C12 gene expression; (5) employ both in vitro and in vivo approaches to identify the mechanisms by which continuous GH suppresses CYP 2C11 transcription, as well as the mechanisms by which intermittent GH stimulates CYP 2C11 gene expression. These studies will lead to a basic understanding, at the cellular and molecular level, of the primary mechanisms whereby pituitary hormones regulate the expression of a family of enzymes that controls a wide range of metabolic reactions in liver, including reactions that play a central role in steroid hormone metabolism, cholesterol degradation, drug biotransformation and carcinogen activation.
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