CHEMOATTRACTANT-MEDIATED INCREASES IN CGMP INDUCE CHANGES IN DICTYOSTELIUM MYOSIN-II HEAVY CHAIN-SPECIFIC PROTEIN-KINASE-C ACTIVITIES

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 (Abu-Elne el et al. 1996. J. Biol. Chem. 271:977-954), Recent studies have indic ated that cAMP-induced cGMP accumulation plays a role in the regulatio n of myosin II phosphorylation and localization (Liu, G., and P. Newel l, 1991. J. Cell. Sci. 98: 483-490). This report describes the roles o f cAMP and cGMP in the regulation of MHC-PKC membrane association, pho sphorylation, and activity (hereafter termed MHC-PKC activities). cAMP stimulation of Dictyostelium cells resulted in translocation of MHC-P KC from the cytosol to the membrane fraction, as well as increasing in MHC-PKC phosphorylation and in its kinase activity. We present eviden ce that MHC is phosphorylated by MHC-PKC in the cell cortex which lead s to myosin II dissociation from the cytoskeleton. Use of Dictyosteliu m mutants that exhibit aberrant cAMP-induced increases in cGMP accumul ation revealed that MHC-PKC activities are regulated by cGMP, Dictyost elium streamer F mutant (stmF), which produces a prolonged peak of cGM P accumulation upon cAMP stimulation, exhibits prolonged increases in MHC-PKC activities. In contrast, Dictyostelium KI-10 mutant that lacks the normal cAMP-induced cGMP response, or KI-4 mutant that shows near ly normal cAMP-induced cGMP response but has aberrant cGMP binding act ivity, show no changes in MHC-PKC activities, We provide evidence that cGMP may affect MHC-PKC activities via the activation of cGMP-depende nt protein kinase which, in turn, phosphorylates MHC-PKC, The results presented here indicate that cAMP-induced cGMP accumulation regulates myosin II phosphorylation and localization via the regulation of MHC-P KC.