ACTIVATION OF PROTEIN-KINASE-C BY COEXISTING DIACYLGLYCEROL-ENRICHED AND DIACYLGLYCEROL-POOR LIPID DOMAINS

TO test the hypothesis that activation of protein kinase C (PKC) is re lated to the interface between coexisting diacylglycerol- (DAG-) enric hed and DAG-poor phases, the thermotropic phase behavior of the ternar y mixtures dimyristoylphosphatidylcholine (DMPC)/dimyristoylphosphatid ylserine (DMPS)/ dioleoylglycerol (DO), DMPC/DMPS/1 -palmitoyl-2-oleoy lglycerol (PO), and DMPC/DMPS/dimyristoylglycerol (DM) was analyzed an d compared with the ability of the lipid mixtures to support PKC activ ity. Differential scanning calorimetry (DSC) was used to monitor the g el-to-liquid crystalline phase transition as a function of the mole fr action of DO ((chi DO)), PO ((chi PO)), or DM ((chi DM)) in DMPC/DMPS (1:1) multilamellar vesicles (MLVs) and of (chi DO) in large unilamell ar vesicles (LUVs), The addition of DAG at low mole fractions gave ris e to the appearance of two or more overlapping transitions. The phase boundaries of the ternary mixtures deduced from the partial phase diag rams were (chi DO) = similar to 0.10 and similar to 0.3 for DMPC/ DMPS /DO, (chi PO) = similar to 0.05 and similar to 0.4 for DMPC/DMPS/PO, a nd (chi DM) = similar to 0.025 and similar to 0.5-0.6 for DMPC/ DMPS/D M. Above these mole fractions of DAG, the transitions again became ver y sharp. The ability of the lipid mixtures to support activity of PKC alpha and PKC eta was examined below and above the gel-to-liquid cryst alline phase transition. In the gel phase, PKC activity went through a maximum as a function of increasing mole fraction of each DAG and was restricted to lipid compositions in which coexisting phases were obse rved. Maximal activity decreased with increasing saturation of the DAG . In the fluid state, maximal PKC activity was shifted to higher DO mo le fractions and the peak was much broader, Collectively, these data s upport a role for both the presence and nature of interface between co mpositionally distinct domains in activation of PKC.