Expression, purification, and characterization of protein kinase C-epsilon

Of the recently described members of the protein kinase C (PKC) family (-delta, -epsilon, -zeta), no detailed properties of the purified enzymes have been presented. Here we describe the expression of PKC-epsilon in insect cells using a baculovirus vector. The recombinant enzyme has been purified to homogeneity by sequential chromatography on DEAE-cellulose, serine-Sepharose, Mono Q, and Superose 12; the protein shows a molecular mass of 90 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. PKC-epsilon is dependent upon phospholipid and diacylglycerol (or phorbol esters) for activity and displays a pattern of specificity for these effectors similar to other PKC isotypes. Similarly, inhibition of PKC-epsilon by staurosporine and H-7 parallels inhibition of other PKC isotypes. However, unlike PKC-alpha, -beta, and -gamma, PKC-epsilon shows no dependence upon Ca2+. Furthermore, the substrate specificity of PKC-epsilon is quite different from other characterized PKCs. The importance of functional diversity within the PKC family is discussed.