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Selenium binding protein 1 (SELENBP1) has been known to be reduced in various types cancer, and epigenetic change is shown to be likely to account for the reduction of <i>SELNEBP1</i> expression. With cDNA microarray comparative analysis, we found that SELENBP1 is markedly decreased in hepatitis B virus-X (HBx)-expressing cells. To clarify the effect of HBx on <i>SELENBP1</i> expression, we compared the expression levels of <i>SELENBP1</i> mRNA and protein by semi-quantitative RT-PCR, Northern blot, and Western blot. As expected, <i>SELENBP1</i> expression was shown to be reduced in cells expressing HBx, and reporter gene analysis showed that the <i>SELENBP1</i> promoter is repressed by HBx. In addition, the stepwise deletion of 5′ flanking promoter sequences resulted in a gradual decrease in basal promoter activity and inhibition of <i>SELENBP1</i> expression by HBx. Moreover, immunohistochemistry on tissue microarrays containing 60 pairs of human liver tissue showed decreased intensity of SELENBP1 in tumor tissues as compared with their matched non-tumor liver tissues. Taken together, our findings suggest that inhibition of <i>SELENBP1</i> expression by HBx might act as one of the causes in the development of hepatocellular carcinoma caused by HBV infection.