CYTOSKELETAL AND PHOSPHOINOSITIDE REQUIREMENTS FOR MUSCARINIC RECEPTOR SIGNALING TO FOCAL ADHESION KINASE AND PAXILLIN

The mechanism whereby agonist occupancy of muscarinic cholinergic rece ptors elicits an increased tyrosine phosphorylation of focal adhesion kinase (FAK) and paxillin has been examined, Addition of oxotremorine- M to SH-SY5Y neuroblastoma cells resulted in rapid increases in the ph osphorylation of FAK (t(1/2) = 2 min) and paxillin that were independe nt of integrin-extracellular matrix interactions, cell attachment, and the production of phosphoinositide-derived second messengers, In cont rast, the increased tyrosine phosphorylations of FAK and paxillin were inhibited by inclusion of either cytochalasin D or mevastatin, agents that disrupt the cytoskeleton. Furthermore, phosphorylation of FAK an d paxillin could be prevented by addition of either wortmannin or LY-2 94002, under conditions in which the synthesis of phosphatidylinositol 4-phosphate was markedly attenuated. These results indicate that musc arinic receptor-mediated increases in the tyrosine phosphorylation of FAK and paxillin in SH-SY5Y neuroblastoma cells depend on both the mai ntenance of an actin cytoskeleton and the ability of these cells to sy nthesize phosphoinositides.