The adaptor protein c-Cbl-associated protein (CAP) limits pro-inflammatory cytokine expression by inhibiting the NF-κB pathway

C-Cbl-associated protein (CAP), also known as Sorbin and SH3 domain-containing protein 1 (Sorbs1) or ponsin, an adaptor protein of the insulin-signalling pathway, mediates anti-viral and anti-cytotoxic protection in acute viral heart disease. In the present study we describe a novel protective immuno-modulatory function of CAP in inflammation. Among the three members of the Sorbs family of adapter molecules, which include CAP (Sorbs1), ArgBP2 (Sorbs2), and Vinexin (Sorbs3), CAP consistently down-regulated the expression of pro-inflammatory cytokines in mouse fibroblasts, cardiomyocytes, and myeloid-derived leukocytes, after Toll-like receptor (TLR) stimulation. Upon the same TLR stimulation, ArgBP2 partially down-regulated pro-inflammatory cytokine production in mouse fibroblasts and cardiomyocytes, while Vinexin rather promoted their production. Mechanistically, CAP limited pro-inflammatory cytokine expression by suppressing the phosphorylation of Inhibitor of kappa B (IκB) kinase (Iκκ)-α and Iκκ-β and their downstream NF-κB-dependent signalling pathway. Molecular affinity between CAP and Iκκ-α/ Iκκ-β was necessary to block the NF-κB pathway. The CAP-dependent inhibitory mechanism - in vivo exclusively IL-6 inhibition - was confirmed after collecting blood from mice with systemic inflammation induced by lipopolysaccharide (LPS) and in the heart tissue collected from mice infected with the cardiotropic Coxsackievirus B3 (CVB3). Taken together, CAP down-regulates pro-inflammatory cytokines by interfering with the normal function of the NF-κB pathway. The promotion of CAP production could support the development of new strategies aiming to limit excessive and detrimental activation of the immune system.