Bimp1, a MAGUK family member linking protein kinase C activation to Bcl10-mediated NF-kappaB induction.

Bcl10 and MALT1, products of distinct chromosomal translocations in mucosa-associated lymphoid tissue lymphoma, cooperate in activating NF-kappaB. Mice lacking Bcl10 demonstrate severe immunodeficiency associated with failure of lymphocytes to activate nuclear factor kappaB (NF-kappaB) in response to antigen receptor stimulation and protein kinase C activation. We characterize Bimp1, a new signaling protein that binds Bcl10 and activates NF-kappaB. Bimp1-mediated NF-kappaB activation requires Bcl10 and IkappaB kinases, indicating that Bimp1 acts upstream of these mediators. Bimp1, Bcl10, and MALT1 form a ternary complex, with Bcl10 bridging the Bimp1/MALT1 interaction. A dominant negative Bimp1 mutant inhibits NF-kappaB activation by anti-CD3 ligation, phorbol ester, and protein kinase C expression. These results suggest that Bimp1 links surface receptor stimulation and protein kinase C activation to Bcl10/MALT1, thus leading to NF-kappaB induction.