A20/TNFAIP3 inhibits NF-κB activation induced by the Kaposi's sarcoma-associated herpesvirus vFLIP oncoprotein

Kaposi's sarcoma-associated herpesvirus (KSHV) K13/vFLIP (viral Flice-inhibitory protein) induces transcription of numerous genes through NF-kappa B activation, including pro-inflammatory cytokines, which contribute to the pathogenesis of Kaposi's sarcoma (KS). In this study, we report that KSHV vFLIP induces the expression of the NF-kappa B regulatory proteins A20, ABIN-1 and ABIN-3 (A20-binding NF-kappa B inhibitors) in primary human endothelial cells, and that KS spindle cells express A20 in KS tissue. In reporter assays, A20 strongly impaired vFLIP-induced NF-kappa B activation in 293T cells, but ABIN-1 and ABIN-3 did not. Mutational analysis established that the C-terminal domain (residues 427-790) is critical for A20 modulation of NF-kappa B, but the ubiquitin-editing OTU (ovarian tumor) domain is not. In functional assays, A20 inhibited vFLIP-induced expression of the chemokine IP-10, reduced vFLIP-induced cell proliferation and increased IKK1 protein levels. Thus, we demonstrate that A20 negatively regulates NF-kappa B activation directly induced by KSHV vFLIP. By attenuating excessive and prolonged vFLIP-induced NF-kappa B activation that could be harmful to KSHV-infected cells, A20 likely has an important role in the pathogenesis of KSHV-associated diseases, in which vFLIP is expressed. Oncogene (2013) 32, 1223-1232; doi:10.1038/onc.2012.145; published online 23 April 2012