Multiple PKCdelta tyrosine residues are required for PKCdelta-dependent activation of involucrin expression--a key role of PKCdelta-Y311.

Protein kinase C-delta (PKCdelta) is a key regulator of human involucrin (hINV) gene expression and is regulated by tyrosine phosphorylation. However, a comprehensive analysis of the requirement for individual PKCdelta tyrosine residues is lacking. We show that multiple tyrosine residues influence the ability of PKCdelta to increase hINV gene expression. Mutation of individual PKCdelta tyrosine residues 52, 64, 155, 187, or 565 does not reduce the ability of PKCdelta to increase hINV promoter activity; however, simultaneous mutation of these five tyrosines markedly reduces activity. Moreover, restoration of any one of these residues results in nearly full activity restoration. It is significant that phosphorylation of PKCdelta-Y(311) is reduced in the five-tyrosine mutant and that mutation of Y(311) results in reduced PKCdelta activity comparable to that observed in the five-tyrosine mutant. Restoration of any one of the tyrosine residues in the five-tyrosine mutant restores Y(311) phosphorylation and biological activity. In addition, reduced phosphorylation of endogenous PKCdelta-Y(311) is associated with reduced biological activity. These findings indicate that PKCdelta activity requires Y(311) and a second tyrosine residue; however, any one of the several tyrosine residues can serve in the secondary role.