CD81 represses NF-?B in HCV-expressing hepatoma cells

The tetraspanin CD81 is one of the main entry receptors for Hepatitis C virus, which is a major causative agent to develop liver cirrhosis and hepatocellular carcinoma (HCC). Here, we identify CD81 as one of few surface proteins that are downregulated in HCV expressing hepatoma cells, discovering a functional role of CD81 beyond mediating HCV entry. CD81 was downregulated at the mRNA level in hepatoma cells that replicate HCV. Kinetics of HCV protein expression were increased in CD81-knockout cells and accompanied by enhanced cellular growth. Furthermore, loss of CD81 compensated for inhibition of pro-survival TBK1-signaling in HCV expressing cells. Analysis of functional phenotypes that could be associated with pro-survival signaling revealed that CD81 is a negative regulator of NF-{kappa}B. Interaction of the NF-{kappa}B subunits p50 and p65 was increased in cells lacking CD81. Similarly, we witnessed an overall increase in the total levels of phosphorylated and cellular p65 upon CD81-knockout. Finally, translocation of p65 in CD81-negative hepatoma cells was markedly induced upon stimulation with TNF or PMA. Altogether, CD81 emerges as aregulator of pro-survival NF-{kappa}B signaling. Considering the important and established role of NF-{kappa}B for HCV replication and tumorigenesis, the downregulation of CD81 by HCV and the associated increase in NF-{kappa}B signaling might serve as viral mechanism to maintain persistent infection, ultimately causing chronic inflammation and HCC. HighlightsO_LICD81 is downregulated and transcriptionally silenced upon HCV genome replication C_LIO_LILoss of CD81 is associated with increased cell growth and HCV expression C_LIO_LICD81 suppresses NF-{kappa}B signaling. C_LIO_LICD81 interferes with p65 activation and nuclear translocation C_LI