The ORF2 glycoprotein of hepatitis E virus inhibits cellular NF-κB activity by blocking ubiquitination mediated proteasomal degradation of IκBα in human hepatoma cells

Background: Nuclear factor kappa B (NF-kappa B) is a key transcription factor that plays a crucial role in host survival during infection by pathogens. Therefore, it has been a priority of many pathogens to manipulate the cellular NF-kappa B activity in order to create a favorable environment for their survival inside the host. Results: We observed that heterologous expression of the open reading frame 2 (ORF2) protein in human hepatoma cells led to stabilization of the cellular I kappa B alpha (I kappa B alpha) pool, with a concomitant reduction in the nuclear localization of the p65 subunit of NF-kappa B and inhibition of NF-kappa B activity. Although basal or TPA induced phosphorylation of I kappa Ba was not altered, its ubiquitination was markedly reduced in ORF2 expressing cells. Further analysis revealed that ORF2 protein could directly associate with the F-box protein, beta transducin repeat containing protein (beta TRCP) and ORF2 over expression resulted in reduced association of I beta B alpha with the SKP1 and CUL1 components of the SCF beta TRCP complex. Chromatin immunoprecipitation (ChIP) assay of the proximal promoter regions of MHC-I heavy chain and IL-8 genes using p65 antibody and LPS stimulated ORF2 expressing cell extract revealed decreased association of p65 with the above regions, indicating that ORF2 inhibited p65 binding at endogenous promoters. Conclusions: In this report we suggest a mechanism by which ORF2 protein of HEV may inhibit host cell NF-kappa B activity during the course of a viral infection.