Hepatitis B virus X protein upregulates expression of calpain small subunit 1 via nuclear factor-kappaB/p65 in hepatoma cells.

Hepatitis B virus (HBV) infection is closely correlated with the development of hepatocellular carcinoma (HCC), in which hepatitis B virus X protein (HBx) plays crucial roles. HBx is believed to be a multifunctional oncoprotein. It has been reported that the calpain small subunit 1 (Capn4) is upregulated in the HCC tissues and involved in the metastasis of HCC. Therefore, we suppose that HBx may promote hepatoma cell migration through Capn4. In the present study, we investigated the effect of HBx on regulating Capn4 expression in human HCC cells. Our data showed that HBx could increase promoter activity of Capn4 and upregulate the expression of Capn4 at the levels of mRNA and protein in human hepatoma HepG2 (or H7402) cells using luciferase reporter gene assay, real-time quantitative RT-PCR assay and Western blot analysis. While, the RNA interference targeting HBx mRNA was able to abolish the upregulation. Interestingly, we found that the inhibition of nuclear factor-kappaB (NF-kappaB) mediated by siRNA targeting NF-kappaB/p65 mRNA or PDTC (an inhibitor of NF-kappaB) could attenuate the upregulation of Capn4. While, HBx failed to increase the promoter activity of Capn4 in hepatoma cells when the putative NF-kappaB binding site of the Capn4 promoter was mutant, suggesting that NF-kappaB is involved in the activation of Capn4 mediated by HBx. In function, wound healing assay showed that HBx could significantly enhance the migration ability of HepG2 cells through upregulating Capn4. Thus, we conclude that HBx upregulate Capn4 through NF-kappaB/p65 to promote migration of hepatoma cells. (c) 2010 Wiley-Liss, Inc.