The activation of NF-κB by receptors in the tumor necrosis factor (TNF) receptor and Toll/interleukin-1 (IL-1) receptor families requires the TRAF family of adaptor proteins. Receptor oligomerization causes the recruitment of TRAFs to the receptor complex, followed by the activation of a kinase cascade that results in the phosphorylation of IκB. TANK is a TRAFbinding protein that can inhibit the binding of TRAFs to receptor tails and can also inhibit NF-κB activation by these receptors. However, TANK also displays the ability to stimulate TRAF-mediated NF-κB activation. In this report, we investigate the mechanism of the stimulatory activity of TANK. We find that TANK interacts with TBK1 (TANK-binding kinase 1), a novel IKK-related kinase that can activate NF-κB in a kinasedependent manner. TBK1, TANK and TRAF2 can form a ternary complex, and complex formation appears to be required for TBK1 activity. Kinase-inactive TBK1 inhibits TANK-mediated NF-κB activation but does not block the activation mediated by TNF-α, IL-1 or CD40. The TBK1-TANK-TRAF2 signaling complex functions upstream of NIK and the IKK complex and represents an alternative to the receptor signaling complex for TRAF-mediated activation of NF-κB.

PKC isoforms and CARMA1 play crucial roles in immunoreceptor-dependent NF-kappaB activation. We tested whether PKC-dependent phosphorylation of CARMA1 directly regulates this signaling cascade. B cell antigen receptor (BCR) engagement led to the progressive recruitment of CARMA1 into lipid rafts and to the association of CARMA1 with, and phosphorylation by, PKCbeta. Furthermore, PKCbeta interacted with the serine-rich CARMA1 linker, and both PKCbeta and PKCtheta phosphorylated identical serine residues (S564, S649, and S657) within this linker. Mutation of two of these sites ablated the functional activity of CARMA1. In contrast, deletion of the linker resulted in constitutive, receptor- and PKC-independent NF-kappaB activation. Together, our data support a model whereby CARMA1 phosphorylation controls NF-kappaB activation by triggering a shift from an inactive to an active CARMA1 conformer. This PKC-dependent switch regulates accessibility of the CARD and CC domains and controls assembly and full activation of the membrane-associated IkappaB kinase (IKK) signalosome.

NF-kappaB is a transcription factor that is critical for innate and adaptive immunity. Recently, a noncanonical pathway for NF-kappaB activation has emerged. Four recent papers provide physiological roles for this pathway and expand our understanding of lymphoid development and organogenesis with potential applications in the treatment of autoimmune disease.

NF-kB is a critical target of signaling downstream of the T cell receptor (TCR) complex, but how TCR signaling activates NF-kB is poorly understood. We have developed an expression cloning strategy that can identify catalytic and noncatalytic molecules that participate in different pathways of NF-kB activation. Screening of a mouse thymus cDNA library yielded CARD11, a membrane-associated guanylate kinase (MAGUK) family member containing CARD, PDZ, SH3 and GUK domains. Using a CARD-deleted variant of CARD11 and RNA interference (RNAi), we demonstrate that CARD11 mediates NF-kB activation by aCD3/aCD28 cross-linking and PMA/ionomycin treatment, but not by TNFa or dsRNA. CARD11 is not required for TCR-mediated induction of NFAT or AP-1. CARD11 functions upstream of the IkB-kinase (IKK) complex and cooperates with Bcl10 in a CARD domain-dependent manner. RNAi-rescue experiments suggest that the CARD, coiled-coil, SH3 and GUK domains of CARD11 are critical for its signaling function. These results implicate CARD11 in factorspeci®c activation of NF-kB by the TCR complex and establish a role for a MAGUK family member in antigen receptor signaling.