CARMA3 deficiency abrogates G protein-coupled receptor-induced NF-κB activation

G protein-coupled receptors (GPCRs) play pivotal roles in regulating various cellular functions. Although many GPCRs induce NF-kappa B activation, the molecular mechanism of GPCR-induced NF-kappa B activation remains largely unknown. CARMA3 (CARD and MAGUK domain-containing protein 3) is a scaffold molecule with unknown biological functions. By generating CARMA3 knockout mice using the gene targeting approach, here we show CARMA3 is required for GPCR-induced NF-kappa B activation. Mechanistically, we found that CARMA3 deficiency impairs GPCR-induced kappa B kinase (IKK) activation, although it does not affect GPCR-induced IKK alpha/beta phosphorylation, indicating that inducible phosphorylation of IKK alpha/beta alone is not sufficient to induce its kinase activity. We also found that CARMA3 is physically associated with NEMO/IKK gamma, and induces polyubiquitination of an unknown protein(s) that associates with NEMO, likely by linking NEMO to TRAF6. Consistently, we found TRAF6 deficiency also abrogates GPCR-induced NF-kappa B activation. Together, our results provide the genetic evidence that CARMA3 is required for GPCR-induced NF-kappa B activation.