Involvement of hepatoma-derived growth factor in the growth inhibition of hepatocellular carcinoma cells by vitamin K2

Vitamin K-2 has been reported to suppress the growth of human hepatocellular carcinoma (HCC) in vitro and hepatocarcinogenesis in hepatitis C virus (HCV)-related cirrhosis in vivo. Hepatoma-derived growth factor (HDGF) is a unique nuclear targeting growth factor that is highly expressed in HCC cells and is a possible prognostic factor for patients with HCC. We investigated the regulation of HDGF expression by vitamin K-2. Three HCC-derived cell lines, HepG2, HuH-7, and SK-Hep-1, were used. Cell number was determined with the MTT assay. The expression levels of HDGF mRNA and protein were measured by the real-time reverse transcriptase-polymerase chain reaction (PCR) method and ELISA and Western blot analysis, respectively. The HDGF promoter activity was measured by a dual luciferase-reporter assay. Vitamin K-2 suppressed the growth of the three HCC cell lines in a dose-dependent manner. Vitamin K-2 significantly suppressed the expression of the HDGF protein and mRNA in three cell lines. By a luciferase assay, vitamin K-2 significantly suppressed the promoter activity of the HDGF protein. Based on some luciferase-reporter plasmids containing truncated promoter regions, the possible responsive site of vitamin K-2 seems to reside in the region -1 to -150 bp of the HDGF gene. These findings suggested that regulation of the HDGF gene expression is one of the crucial mechanisms of vitamin K-2-induced cell growth suppression for HCC.