Studies are proposed to identify and characterize cellular mechanims through which polypeptide hormones and cyclic nucleotides regulate cell growth and differentiated function. Clonal functional bovine adrenal cortical and Y-1 cells will be used to study growth regulation by ACTH, FGF, cAMP and cGMP. Synchronized cell populations will be used to determine the stages of the cell growth cycle at which ACTH induced growth arrest occurs and to quantitate effects of ACTH and cAMP on associated biochemical events. The ACTH and cAMP growth arrested Y-1 cell will be used as a model of cellular hypertrophy to quantitate effects of ACTH and cAMP on the steroidogenic pathway. Since the effects of cAMP and cGMP are initiated through control of specific cyclic nucleotide-dependent protein kinases, these will be further characterized. An antibody generated against the cAMP receptor protein will be tested for cross reactivity with the cGMP receptor protein; the two receptors will also be compared in a mutant cell lacking cAMP receptor-protein kinase activity. The antibody to the cAMP receptor will be used in a radioimmunoassay for quantitation of cAMP receptor protein. Substrates subject to phosphorylation by the two cyclic nucleotide-dependent protein kinase systems will be sought. Regulation of ACTH and FGF receptors will be studied and related to observed effects on cell growth and differentiated function. Autoregulation and regulation by the opposite polypeptide will be studied and mechanisms involved will be explored. The mechanisms through which hormones and cyclic nucleotides induce the synthesis of prolactin and growth hormone will be studied in GH3 cells which synthesize large quantities of these proteins differentially in response to several hormones. The cellular levels of mRNA for these two peptides will be quantitated under varying hormonal conditions by translation in a cell free protein synthesizing system and by RNA-DNA hybridization. These studies are designed to distinguish between transcriptional and post-transcriptional regulation by a membrane active peptide TRF and by cAMP. The structure of the pre-hormone portion of prolactin will be determined and its function in the synthesis and secretion of prolactin explored. Models of post-transcriptional regulation of protein biosynthesis will be tested.