Functional Elements within CARD11’S Inhibitory Domain Dictate Downstream Signaling to NF-Kappa B in Lymphocytes

Antigen (Ag) receptor engagement on lymphocytes triggers a signaling cascade that phosphorylates the scaffold protein CARD11 in its inhibitory domain (ID) and transforms it from a closed and inactive state into an open and active conformation. This conformational change results in disruption of intramolecular interactions, cofactor assembly, NF-κB activation and lymphocyte activation. To better understand how CARD11’s inhibitory domain regulates these functions, we performed a systematic analysis of the 231 residues that comprise the inhibitory domain. We discovered the inhibitory domain is made up of multiple operational elements that cooperatively control its overall function. Four independent and redundant repressive elements maintain CARD11 in the closed conformation and prevent Bcl10 association. A single, contiguous inducibility element controls the transition from the closed to open conformation. Furthermore, we identified two novel activating elements that demonstrated a greater potential for CARD11 hyperactivity than was previously thought. We found that lymphoma-associated mutations in CARD11 disrupted intramolecular binding to multiple repressive elements, allowing them to bypass the need for inhibitory domain phosphorylation. Overall, we uncovered a highly evolved mechanism of modulating CARD11’s inhibitory domain that precisely tunes NF-κB levels and lymphocyte function