Targeting of intracellular signals by cAMP/PKA

Abstract

A Kinase Anchor Proteins (AKAPs) bind and concentrate PKAII isoforms at several sites within mammalian cells. Little is known about the conservation of this mechanism of targeting signals carried by cAMP in lower organisms. A cDNA for a novel AKAP (designated DAKAP550) was isolated by expression screening and characterized. The DAKAP550 gene is located in the 4F1,2 region of the X chromosome. The anchor protein contains more than 2000 amino acids. The RII binding region was mapped to a segment of 100 amino acid residues which contains two repeats that resemble RII binding domains of mammalian AKAPs. Anti-DAKAP550 antibodies complex a soluble protein that is abundant in the adult head (nervous system). Immunostaining of embryos revealed that DAKAP550 is located principally in brain and the ventral nerve cord during early development.;Cyclic AMP induces corticosteroid production, differential gene transcription and cell cycle arrest in adrenal cortex-derived Y1 cells. These responses follow a striking, cAMP-controlled alteration in Y1 cell morphology: the conversion of flat, firmly adherent Y1 epithelial cells into rounded, highly-refractile cells with short processes. Little is known about intracellular structures, effector proteins and mechanisms that link activated PKA to the transformation in cell shape. I observed that cAMP causes the rapid ({dollar}<{dollar}2 min) and selective tyrosine dephosphorylation of the focal adhesion protein paxillin. Dephospho-paxillin translocates from focal adhesions to the cytoplasm as stress fibers vanish and F-actin accumulates in membrane ruffles and cytoplasmic aggregates. Pervanadate, a potent inhibitor of protein tyrosine phosphatases (PTPs), abrogates all effects of cAMP. Thus, PTP activity is involved in transducing an elevation in cAMP into the rearrangement of the actin cytoskeleton. Conversely, genistein-sensitive protein tyrosine kinase activity is essential for reversing effects of cAMP. Moreover, the cAMP/PKA induced alteration in cell morphology can be mimicked by microinjection of a recombinant PTP The results suggest that a cAMP-mediated signaling pathway engages in a novel form of "cross-talk". It intersects with and modulates an integrin-regulated pathway, which transmits signals between the cytoskeleton and extracellular matrix via tyrosine phosphorylation/dephosphorylation.