IL-13 Suppresses TNF-Induced Activation of Nuclear Factor-κB, Activation Protein-1, and Apoptosis

IL-13 is known to suppress the production of inflammatory cytokines such as TNF. Whether IL-13 also modulates the biologic effects of TNF is not known. In the present report we examined the effect of IL-13 on TNF-induced activation of nuclear transcription factors NF-κB and activation protein-1 (AP-1) and apoptosis. Pretreatment of cells with IL-13 blocked TNF-induced NF-κB activation, nuclear translocation of p65 subunit, and degradation of IκBα. IL-13 also inhibited NF-κB activation by LPS, okadaic acid, H2O2, and ceramide. TNF-induced NF-κB-dependent gene transcription was also blocked by IL-13. TNF-induced activation of another nuclear transcription factor, AP-1, was suppressed by IL-13. The activation of N-terminal c-Jun kinase and mitogen-activated protein kinase kinase, implicated in the regulation of AP-1 and NF-κB, was also down-regulated by IL-13. TNF-mediated cytotoxicity and activation of caspase-3 were abolished by IL-13. The inhibitory effects of IL-13 on TNF were sensitive to H-7, neomycin, and wortmannin, suggesting that the pathway consisting of protein kinase C, phosphatidylinositol 3-kinase, and phospholipase C must be involved in IL-13 signaling. Thus, overall, these results demonstrate that IL-13 is a potent inhibitor of TNF-mediated activation of NF-κB, AP-1, and apoptosis, which may contribute to its previously described immunosuppressive and anti-inflammatory effects.