Activation of PKN, a Novel 120-kDa Protein Kinase with Leucine Zipper-like Sequences, by Unsaturated Fatty Acids and by Limited Proteolysis

PKN, a novel protein kinase with catalytic domain homologous to PKC family and unique amino terminal leucine zipper-like sequences, was purified partially from COS7 cells transfected with the cDNA construct encoding human PKN for enzymatic characterization of the enzyme. Using serine containing synthetic peptides based on PKC pseudosubstrate sites as the phosphate acceptors, kinase activities estimated from partially purified PKN were not stimulated by Ca2+/phosphatidylserine/diolein but were activated several-fold to several tens-fold by 40 μM unsaturated fatty acids, such as arachidonic acid, linoleic acid, and oleic acid. Autophosphorylation of the immunoprecipitates using anti-PKN antiserum was also stimulated by various unsaturated fatty acids. Limited proteolysis of PKN with trypsin induced an enhancement of the peptide kinase activity that was almost independent of arachidonic acid.