REGULATION OF CYTOSKELETON ORGANIZATION AND PAXILLIN DEPHOSPHORYLATION BY CAMP - STUDIES ON MURINE Y1 ADRENAL-CELLS

Cyclic AMP induces corticosteroid production, differential gene transc ription, and cell cycle arrest in adrenal cortex-derived Y1 cells. The se responses follow a cAMP-controlled transformation in Y1 cell morpho logy: the conversion of flat epithelial cells into rounded, highly ref ractile cells with short processes. Little is known about effector pro teins and mechanisms that link activated protein kinase A to the alter ation in cell shape, We now report that cAMP causes rapid (less than o r equal to 1 min) and selective tyrosine dephosphorylation of paxillin , a focal adhesion protein. Paxillin is maximally dephosphorylated bef ore other physiological effects of cAMP are detected in Y1 cells. Deph osphopaxillin translocates from focal adhesions to the cytoplasm as st ress fibers vanish and F-actin accumulates in membrane ruffles and cyt oplasmic aggregates. Remnants of focal adhesion complexes dissociate f rom the cell cortex and coalesce into large structures that contain ag gregated F-actin. Pervanadate, an inhibitor of protein-tyrosine phosph atases, abrogates all effects of cAMP. Conversely, genistein-sensitive protein-tyrosine kinase activity is essential for establishing epithe lial morphology and reversing effects of cAMP in Y1 cells. Thus, cAMP/ protein kinase A (PKA) actions are initially targeted to focal adhesio ns and cortical actin cytoskeleton; paxillin is an early and unexpecte d downstream target in a PKA-mediated signaling pathway, and protein-t yrosine phosphatase activity provides an essential link between PKA. a ctivation and the control of cell shape.