SIGNALING & FUNCTION OF THE SGK STEROID INDUCIBLE KINASE

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DESCRIPTION: A dynamic balance of steroid receptor signaling and cellular phosphorylation cascades coordinately control cell growth at key steps where these signal transduction pathways converge. Conceivably, the stringent regulation of such points of convergence confer responsiveness to anti-proliferative signals in normal cells, and may regulate the uncontrolled proliferation of transformed cells if appropriately induced or activated. Glucocorticoids, one class of steroid hormones, can strongly inhibit the in vivo and in vitro growth of Con8 rat mammary tumor cells, which are derived from a hormone responsive rat mammary adenocarcinoma. To identify the steroid regulated mediators of this growth arrest, subtractive cloning of glucocorticoid responsive genes from a mammary tumor cell cDNA library uncovered a novel serine/threonine protein kinase, sgk, that is transcriptionally regulated by glucocorticoids and serum. The existence of sgk suggests a new pathway of cross-talk between steroid hormones and cellular phosphorylation cascades. Analysis of sgk structure/function relationships by in vitro mutagenesis will be carried out to determine the role of specific protein coding domains in transphosphorylation, substrate specificity and as targets of cellular phosphorylation cascades. The role of sgk in the glucocorticoid growth suppression response in cultured cells and in mammary cell derived tumors will be examined by analyzing vectors encoding the wild type, mutant or anti-sense forms of this protein kinase gene. Finally, interactive cloning strategies, such as the yeast two hybrid system, will be employed to identify the sgk binding proteins uncovered by co-immunoprecipitation and their functional characterization carried out to elucidate the sgk intracellular signal transduction pathway. Thus, the overall goal is to define the precise functional relationships between the steroid regulated signaling mediated by sgk and the glucocorticoid growth arrest of mammary tumor cells.