Association of protein kinase Cμ with type II phosphatidylinositol 4- kinase and type I phosphatidylinositol-4-phosphate 5-kinase

Protein kinase Cμ (PKCμ), also named protein kinase D, is an unusual member of the PKC family that has a putative transmembrane domain and pleckstrin homology domain. This enzyme has a substrate specificity distinct from other PKC isoforms (Nishikawa, K., Toker, A., Johannes, F. J., Songyang, Z., and Cantley, L. C. (1997) J. Biol. Chem. 272, 952-960), and its mechanism of regulation is not yet clear. Here we show that PKCμ forms a complex in vivo with a phosphatidylinositol 4-kinase and a phosphatidylinositol-4- phosphate 5-kinase. A region of PKCμ between the amino-terminal transmembrane domain and the pleckstrin homology domain is shown to be involved in the association with the lipid kinases. Interestingly, a kinase- dead point mutant of PKCμ failed to associate with either lipid kinase activity, indicating that autophosphorylation may be required to expose the lipid kinase interaction domain. Furthermore, the subcellular distribution of the PKCμ-associated lipid kinases to the particulate fraction depends on the presence of the amino-terminal region of PKCμ including the predicted transmembrane region. These results suggest a novel model in which the noncatalytic region of PKCμ acts as a scaffold for assembly of enzymes involved in phosphoinositide synthesis at specific membrane locations.