PKCα Binds G3BP2 and Regulates Stress Granule Formation Following Cellular Stress

Protein kinase C (PKC) isoforms regulate a number of processes crucial for the fate of a cell. In this study we identify previously unrecognized interaction partners of PKC alpha and a novel role for PKC alpha in the regulation of stress granule formation during cellular stress. Three RNA-binding proteins, cytoplasmic poly(A)(+) binding protein (PABPC1), IGF-II mRNA binding protein 3 (IGF2BP3), and RasGAP binding protein 2 (G3BP2) all co-precipitate with PKC alpha. RNase treatment abolished the association with IGF2BP3 and PABPC1 whereas the PKC alpha-G3BP2 interaction was largely resistant to this. Furthermore, interactions between recombinant PKC alpha and G3BP2 indicated that the interaction is direct and PKC alpha can phosphorylate G3BP2 in vitro. The binding is mediated via the regulatory domain of PKC alpha and the C-terminal RNA-binding domain of G3BP2. Both proteins relocate to and co-localize in stress granules, but not to P-bodies, when cells are subjected to stress. Heat shock-induced stress granule assembly and phosphorylation of eIF2 alpha are suppressed following downregulation of PKC alpha by siRNA. In conclusion this study identifies novel interaction partners of PKC alpha and a novel role for PKC alpha in regulation of stress granules.