PKCβ regulates BCR-mediated IKK activation by facilitating the interaction between TAK1 and CARMA1

The B cell antigen receptor (BCR)-mediated activation of I kappa B kinase (IKK) and nuclear factor kappa B require protein kinase C (PKC)beta; however, the mechanism by which PKC beta regulates IKK is unclear. Here, we demonstrate that another protein kinase, TGF beta-activated kinase (TAK)1, is essential for IKK activation in response to BCR stimulation. TAK1 interacts with the phosphorylated CARMA1 ( also known as caspase recruitment domain [CARD] 11, Bimp3) and this interaction is mediated by PKC beta. IKK is also recruited to the CARMA1-Bcl10-mucosal-associated lymphoid tissue 1 adaptor complex in a PKC beta-dependent manner. Hence, our data suggest that phosphorylation of CARMA1, mediated by PKC beta, brings two key protein kinases, TAK1 and IKK, into close proximity, thereby allowing TAK1 to phosphorylate IKK.