Raf-1 and B-Raf promote protein kinase C θ interaction with BAD

PKCθ regulates the proliferation, survival and differentiation of T-cells. Here we show that PKCθ interacts with Raf-1 and B-Raf kinases. Raf-1 enhanced the kinase activity of associated PKCθ, while PKCθ reduced the catalytic activity of associated Raf-1. In contrast, B-Raf binding did not affect PKCθ kinase activity, and PKCθ did not change B-Raf activity. Coexpression of mutationally activated Raf-1 in cells enhanced the phosphorylation of T538 in the PKCθ activation loop. PKCθ and Raf cooperated in terms of binding to BAD, a pro-apoptotic Bcl-2 family protein that is inactivated by phosphorylation. While neither Raf-1 nor B-Raf could phosphorylate BAD, they enhanced the ability of PKCθ to interact with BAD and to phosphorylate BAD in vitro and in vivo, suggesting a new role for Raf proteins in T-cells by targeting PKCθ to interact with and phosphorylate BAD.