Pro-opiomelanocortin (POMC) is encoded by a single copy gene. POMC gene transcription occurs in several tissues, notably in the pituitary anterior and intermediate lobes and in the hypothalamus. A POMC-like mRNA is also made in the gonads. In the male, the mRNA is found in Leydig cells, the same cells which contain immunoreactive POMC peptides. Gonadal POMC mRNA is much shorter than its counterpart in pituitary, and in fact lacks part of the sequence which encodes the amino-terminal glycopeptide. These data suggest that gonadal POMC gene transcription initiates at a different site in the gene than does the pituitary transcript, and gives rise to a structurally different protein. This finding raises questions about hormonal regulation of POMC gene expression in the gonads. In particular, what are the effects of glucocorticoids on Leydig cell POMC gene activity? These steroid hormones are potent inhibitors of both transcription of the gene and secretion of the peptides in the anterio pituitary. Because Leydig cells seem to have functional glucocorticoid receptors, a comparison of the steroid hormones action on the POMC gene in Leydig and pituitary cells provides a natural model for further defining molecular mechanisms involved in steroid hormone action. In doing so it may give new insight into biochemical links between the stress response and reproductive systems, as well as expand our knowledge of a substance (the steroid hormone) which is one of the most widely used pharmacological agents. Moreover, while there is much known about interactions between the glucocorticoid-receptor complex and DNA sequences in and around genes whose expression is stimulated by the hormone, little is known about steroid-hormone inhibition of gene activity. Therefore, the present study should provide new insights into this mode of hormone action. The proposed studies will use cloned DNA probes in POMC mRNA quantitation studies and in structural analysis of the POMC gene, both in chromatin and in a purified state in the presence of the glucocorticoid-receptor complex. Studies will also examine the structure of Leydig cell POMC protein. In addition, they will determine whether secretion is regulated by agents which affect POMC peptide secretion in other tissues and/or agents which regulate secretion of other substances from Leydig cells.
