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K‐252a Induces Tyrosine Phosphorylation of the Focal Adhesion Kinase and Neurite Outgrowth in Human Neuroblastoma SH‐SY5Y Cells

Abstract: The protein kinase inhibitor K‐252a has been shown to promote cholinergic activity in cultures of rat spinal cord and neuronal survival in chick dorsal root ganglion cultures. To determine the mechanism by which K‐252a acts as a neurotrophic factor, we examined the effects of this molecule on a human neuroblastoma cell line, SH‐SY5Y. K‐252a induced neurite outgrowth in a dose‐dependent manner. Coincident with neurite outgrowth was the early tyrosine phosphorylation of 125‐ and 140‐kDa proteins. The phosphorylation events were independent of protein kinase C inhibition because down‐regulation of protein kinase C by long‐term treatment with phorbol ester did not prevent K‐252a‐induced tyrosine phosphorylation. Similarly, the protein kinase C inhibitors H7, GF‐109203X, and calphostin C did not induce the phosphorylation. We have identified one of the phosphosubstrates as the pp125 focal adhesion protein tyrosine kinase (Fak). Induction of phosphorylation coincided with increased Fak activity and appeared to be independent of ligand/integrin interaction. The induction of Fak phosphorylation by K‐252a was also observed in LA‐N‐5 cells and primary cultures of rat embryonic striatal cells but not in PC12 cells. The protein kinase C‐independent induction of tyrosine phosphorylation and the identification of Fak as a substrate of K‐252a‐induced tyrosine kinase activity suggest that this compound mediates neurotrophic effects through a novel signaling pathway.