Modulation of PKCd tyrosine phosphorylation and activity in salivary and PC-12 cells by Src kinases

Benes, Cyril, and Stephen P. Soltoff. Modulation of PKCd tyrosine phosphorylation and activity in salivary and PC-12 cells by Src kinases. Am J Physiol Cell Physiol 280: C1498–C1510, 2001.—Protein kinase C (PKC) d becomes tyrosine phosphorylated in rat parotid acinar cells exposed to muscarinic and substance P receptor agonists, which initiate fluid secretion in this salivary cell. Here we examine the signaling components of PKCd tyrosine phosphorylation and effects of phosphorylation on PKCd activity. Carbacholand substance P-promoted increases in PKCd tyrosine phosphorylation were blocked by inhibiting phospholipase C (PLC) but not by blocking intracellular Ca21 concentration elevation, suggesting that diacylglycerol, rather than D-myo-inositol 1,4,5-trisphosphate production, positively modulated this phosphorylation. Stimuli-dependent increases in PKCd activity in parotid and PC-12 cells were blocked in vivo by inhibitors of Src tyrosine kinases. Dephosphorylation of tyrosine residues by PTP1B, a protein tyrosine phosphatase, reduced the enhanced PKCd activity. Lipid cofactors modified the tyrosine phosphorylation-dependent PKCd activation. Two PKCd regulatory sites (Thr-505 and Ser-662) were constitutively phosphorylated in unstimulated parotid cells, and these phosphorylations were not altered by stimuli that increased PKCd tyrosine phosphorylation. These results demonstrate that PKCd activity is positively modulated by tyrosine phosphorylation in parotid and PC-12 cells and suggest that PLC-dependent effects of secretagogues on salivary cells involve Src-related kinases.