NF‐κB is a critical target of signaling downstream of the T cell receptor (TCR) complex, but how TCR signaling activates NF‐κB is poorly understood. We have developed an expression cloning strategy that can identify catalytic and noncatalytic molecules that participate in different pathways of NF‐κB 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‐κB activation by αCD3/αCD28 cross‐linking and PMA/ionomycin treatment, but not by TNFα or dsRNA. CARD11 is not required for TCR‐mediated induction of NFAT or AP‐1. CARD11 functions upstream of the IκB‐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 factor‐ specific activation of NF‐κB by the TCR complex and establish a role for a MAGUK family member in antigen receptor signaling
