Interaction of PKCbeta with CARMA1 mediates B cell receptor-induced NF-kappaB activation

The function and development of B cells depend on pre-B cell receptor (pre-BCR) and B cell receptor (BCR). Engagement of pre-BCR or BCR triggers concerted phosphorylation and activation of kinases, adaptor proteins and effectors. These signaling events ultimately lead to activation of multiple transcription factors including NF-kappaB (NF-κB). We hypothesized the signaling molecules are functionally interconnected in a large signaling complex (or signalosome).; In this dissertation, studies in Chapter 2 examined the membrane-proximal events that take place during B cell receptor engagement. Our data demonstrate that membrane microdomain-lipid rafts are the major functional compartments for both human pre-B cell and B cell receptors activation. Engagement of pre-BCR or BCR leads to recruitment of multiple signaling molecules to the raft fractions, generating raft-associated signaling signalosomes.; The signaling events in BCR signalosome lead to activation of IκB kinase (IKK) and NF-κB which are essential for B cell survival and activation. Our data in Chapter 3 demonstrate that PKCβ plays a fundamental role in these events. Our data also show that the IKK complex is recruited into raft microdomains upon B cell activation. This recruitment is abrogated in PKCβ deficient B cells.; In Chapter 4,I evaluated the hypothesis that the MAGUK family protein CARMA1 may provide a mechanism to couple BCR signaling to NF-κB activation. Our data indicate that CARMA1 is required for BCR-induced IKK and NF-κB activation. A significant potion of CARMA1 is constitutively associated with lipid rafts, and BCR crosslinking significantly enhances this association. BCR signaling also induced serine phosphorylation of CARMA1. Inhibition of PKC activity blocked both CARMA1 phosphorylation and recruitment to lipid rafts. The results also reveal the association of PKCβ with CARMA1 in activated B cells. Together, these findings support a model whereby BCR-induced NF-κB activation is modulated via interaction of PKCβ and the CARMA1/Bc110 complex.