Stimulation of B7-H1 in Hepatocarcinoma Cells by Hepatitis B virus X Antigen

Abstract

The cross-talk between the hepatitis B virus X protein (HBx) and B7-H1 in hepatocarcinoma (HCC) is unclear. This study analyzed the potential relationships between HBx and B7-H1 in hepatocarcinogenesis. One of human HCC cell lines, HepG2 cells, was transfected to stably express HBx protein (HBx⁺-HepG2). The transcription of B7-H1 mRNA was increased significantly in these cells compared to cells transfected with control vector (HBx^--HepG2), as confirmed by a comparative genome-wide microarray analysis (Capitalbio) and real time quantitative PCR (qPCR). Flow cytometry and western-blot further demonstrated that B7-H1 protein synthesis was enhanced in HBx⁺-HepG2 cells. Site-directed mutagenesis of promoter constructs revealed that the transcription factor (NF)-κB binding site between 128 and 137 bp upstream of B7-H1 gene transcriptional start site is primarily responsible for HBx‐mediated B7-H1 expression. Co-culture experiments with HBx⁺-HepG2/T cells showed that the number of apoptotic T cells increased profoundly, and this effect could be partially prevented when a neutralizing mAb against B7-H1 was added to the culture, demonstrating that B7-H1 signaling can promote T cell apoptosis. Our results suggest that the expression of B7-H1 in hepatocarcimona cells can be initiated by HBx antigen, thus inducing T cell apoptosis and finally potentially facilitates the genesis of HCC.

Keywords:

• HBx
• HepG2 cells
• B7-H1
• NF-κB
• T cell apoptosis

ACKNOWLEDGMENTS

This work was supported by grants from the National Key Basic Research Program of China (Nos. 2007CB512401 and 2007CB512805), and National Natural Science Foundation of China (NSFC Nos. 30571700, 30600546, 30700855, 30800982, 30901347 and 30930086).

Declaration of Interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.