Membrane-bound protein kinase A inhibits smooth muscle cell proliferation in vitro and in vivo by amplifying cAMP-protein kinase A signals.

cAMP-dependent protein kinase is anchored to discrete cellular compartments by a family of proteins, the A-kinase anchor proteins (AKAPs). We have investigated in vivo and in vitro the biological effects of the expression of a prototypic member of the family, AKAP75, on smooth muscle cells. In vitro expression of AKAP75 in smooth muscle cells stimulated cAMP-induced transcription, increased the levels of the cyclin-dependent kinase-2 inhibitor p27(kip1), and reduced cell proliferation. In vivo expression of exogenous AKAP75 in common carotid arteries, subjected to balloon injury, significantly increased the levels of p27(kip1) and inhibited neointimal hyperplasia. Both the effects in smooth muscle cells in vitro and in carotid arteries in vivo were specifically dependent on the amplification of cAMP-dependent protein kinase (PKA) signals by membrane-bound PKA, as indicated by selective loss of the AKAP75 biological effects in mutants defective in the PKA anchor domain or by suppression of AKAP effects by the PKA-specific protein kinase inhibitor. These data indicate that AKAP proteins selectively amplify cAMP-PKA signaling in vitro and in vivo and suggest a possible target for the inhibition of the neointimal hyperplasia after vascular injury.