XXXX x calmodulin prevents myristoylated @entity493 -rich kinase C substrate protein phosphorylation by protein kinase Cs in C6 @entity35 @entity11 cells.

@entity6106 @entity141 @entity4527 @entity28422 @entity11 @entity205 @entity1360 @entity865 @entity35 @entity864 @entity493
@entity1360 stimulated membrane-associated protein kinase Cs (PKCs) activity in C6 @entity35 @entity11 cells as much as the potent PKCs stimulator @entity864 ( @entity865 ). However, while @entity865 , as expected, powerfully stimulated the phosphorylation of the PKCs' 85-kDa myristoylated @entity493 -rich protein kinase C substrate ( @entity28422 ) protein, @entity1360 unexpectedly did not. Instead, @entity1360 reduced the basal @entity28422 phosphorylation. Pretreating the @entity11 cells with @entity1360 prevented @entity865 -stimulated PKCs from phosphorylating the @entity28422 protein. The stimulation of membrane PKCs activity and the prevention of @entity28422 phosphorylation by @entity1360 required external @entity141 because they were both abolished by adding 5 mM @entity4527 to the culture medium. Recently (Chakravarthy, B. R., Isaacs, R. J., Morley, P., Durkin, J. P., and Whitfield, J. F. (1995) J. Biol. Chem. 270, 1362-1368), we proposed that @entity141 x calmodulin complexes block @entity28422 phosphorylation by the activated PKCs in keratinocytes stimulated by raising the external @entity141 concentration. In the present experiments calmodulin prevented @entity28422 phosphorylation by @entity865 -stimulated PKCs in @entity11 cell lysates, and this blockade was lifted by a calmodulin antagonist, the calmodulin-binding domain peptide. But, physiologically more significant, pretreating intact @entity11 cells with a cell-permeable calmodulin antagonist, @entity6106 , prevented @entity1360 from blocking @entity28422 phosphorylation by PKCs in unstimulated and @entity865 -stimulated cells. The effect of @entity1360 on @entity28422 phosphorylation was not due to the stimulation of @entity141 x calmodulin-dependent phosphoprotein phosphatase, calcineurin, because @entity205 , a potent inhibitor of this phosphatase, did not stop @entity1360 from preventing @entity28422 phosphorylation. The ability of @entity1360 to prevent @entity865 -stimulated PKCs from phosphorylating @entity28422 depended on whether @entity1360 was added before, with, or after @entity865 . Maximum blockade occurred when @entity1360 was added before @entity865 but was less effective when added with or after @entity865 . These results indicate that @entity141 x calmodulin can profoundly affect PKCs' signaling at the substrate level.
