TAK1 adaptor proteins, TAB2 and TAB3, link the signalosome to B-cell receptor-induced IKK activation.

Transforming growth factor-β-activated kinase (TAK)1-binding proteins (TAB) activate nuclear factor-κB by linking TAK1 to signaling molecules. We investigated the mechanisms underlying B-cell receptor (BCR) signaling in TAB2- and TAB3-deficient and TAB3 domain deletion mutant DT40 B cell lines. Loss of TAB2 and TAB3 abolished BCR-induced inhibitor of κB kinase (IKK) activation and TAK1 binding to caspase recruitment domain membrane-associated guanylate kinase protein (CARMA)1. Deletion of TAB3, coupling of ubiquitin conjugation to ER degradation, coiled-coil, and zinc finger domains blocked IKK activation and association with CARMA1. Thus, TAB2 and TAB3 connect signaling molecules that activate IKK in BCR signaling.