The Csk homologous kinase associates with TrkA receptors and is involved in neurite outgrowth of PC12 cells

Csk homologous kinase (CHK), a member of the Csk regulatory tyrosine kinase family, is expressed primarily in brain and hematopoietic cells. The role of CHK in the nervous system is as yet unknown. Using PC12 cells as a model system of neuronal cells, we show that CHK participates in signaling media ted by TrkA receptors, CHK was found to be associated with tyrosine phospho rylated TrkA receptors in PC12 cells upon stimulation with NGF. Binding ass ays and far Western blotting analysis, using glutathione S-transferase fusi on proteins containing the Src homology 2 (SH2) and SH3 domains of CHK, dem onstrate that the SH2 domain of CHK binds directly to the tyrosine-phosphor ylated TrkA receptors. Site-directed mutagenesis of TrkA cDNA, as well as p hosphopeptide inhibition of the in vitro interaction of the CHK-SH2 domain or native CHK with TrkA receptors, indicated that the residue Tyr-785 on Tr kA is required for its binding to the CHK-SH2 domain upon NGF stimulation. In addition, overexpression of CHK resulted in enhanced activation of the m itogen-activated protein kinase pathway upon NGF stimulation, and microinje ction of anti-CHK antibodies, but not anti-Csk antibodies, inhibited neurit e outgrowth of PC12 cells in response to NGF. Thus, CHK is a novel signalin g molecule that participates in TrkA signaling, associates directly with Tr kA receptors upon NGF stimulation, and is involved in neurite outgrowth of PC12 cells in response to NGF.