Chemoattractant-mediated Increases in cGMP Induce Changes in Dictyostelium Myosin II Heavy Chain-specific Protein Kinase C Activities

Myosin II heavy chain (MHC)-specific pro- tein kinase C (MHC-PKC) isolated from the ameba, Dictyostelium discoideum, regulates myosin II assembly and localization in response to the chemoattractant cAMP (Abu-Elneel et al. 1996. J. Biol. Chem. 271:977- 984). Recent studies have indicated that cAMP-induced cGMP accumulation plays a role in the regulation of myosin II phosphorylation and localization (Liu, G., and P. Newell. 1991. J. Cell. Sci. 98: 483-490). This re- port describes the roles of cAMP and cGMP in the reg- ulation of MHC-PKC membrane association, phospho- rylation, and activity (hereafter termed MHC-PKC activities), cAMP stimulation of Dictyostelium cells re- sulted in translocation of MHC-PKC from the cytosol to the membrane fraction, as well as increasing in MHC-PKC phosphorylation and in its kinase activity. We present evidence that MHC is phosphorylated by MHC-PKC in the cell cortex which leads to myosin II dissociation from the cytoskeleton. Use of Dictyostel- ium mutants that exhibit aberrant cAMP-induced in- creases in cGMP accumulation revealed that MHC- PKC activities are regulated by cGMP. Dictyostelium streamer F mutant (stmF), which produces a prolonged peak of cGMP accumulation upon cAMP stimulation, exhibits prolonged increases in MHC-PKC activities. In contrast, Dictyostelium KI-10 mutant that lacks the nor- mal cAMP-induced cGMP response, or KI-4 mutant that shows nearly normal cAMP-induced cGMP re- sponse but has aberrant cGMP binding activity, show no changes in MHC-PKC activities. We provide evi- dence that cGMP may affect MHC-PKC activities via the activation of cGMP-dependent protein kinase which, in turn, phosphorylates MHC-PKC. The results presented here indicate that cAMP-induced cGMP ac- cumulation regulates myosin II phosphorylation and lo- calization via the regulation of MHC-PKC.