AUTOPHOSPHORYLATION OF DICTYOSTELIUM MYOSIN-II HEAVY CHAIN-SPECIFIC PROTEIN-KINASE-C IS REQUIRED FOR ITS ACTIVATION AND MEMBRANE DISSOCIATION

Myosin II heavy chain (MHC) specific protein kinase C (MHC-PKC) isolat ed from the ameba, Dictyostelium discoideum, regulates myosin II assem bly and localization in response to the chemoattractant cAMP. cAMP sti mulation of Dictyostelium cells leads to translocation of MHC-PKC from the cytosol to the membrane fraction, as well as causing an increase in both MHC-PKC phosphorylation and its kinase activity. MHC-PKC under goes autophosphorylation with each mole of kinase incorporating about 20 mol of phosphate. The MHC-PKC autophosphorylation sites are thought to be located within a domain at the COOH-terminal region of MHC-PKC that contains a cluster of 21 serine and threonine residues. Here we r eport that deletion of this domain abolished the ability of the enzyme to undergo autophosphorylation in vitro. Furthermore, after this dele tion, cAMP dependent autophosphorylation of MHC-PKC as well as cAMP-de pendent increases in kinase activity and subcellular localization were also abolished. These results provide evidence for the role of autoph osphorylation in the regulation of MHC-PKC and indicate that this MHC- PKC autophosphorylation is required for the kinase activation in respo nse to cAMP and for subcellular localization.