Expression significance and functional characterization of homeoprotein Six1 in hepatocellular carcinoma

Abstract

Homeoprotein Six1 plays an important role on regulation of metastasis in human cancers. The aim of this study was to unravel the role of Six1 in hepatocellular carcinoma (HCC) through clinical and experimental studies. Seventy-two pairs of RNA and 103 pairs of protein from tumor and adjacent nontumor liver tissues of HCC patients after hepatectomy were examined. About 85% and 60% of HCC tumor tissues overexpressed Six1 mRNA and protein, respectively, compared with nontumor liver tissues. No Six1 protein was detected in nontumor liver tissues of HCC patients and normal liver tissues. Increased Six1 protein expression in HCC patients was significantly correlated with pathologic tumor-node-metastasis (pTNM) stage, venous infiltration and poor overall survival. Short hairpin RNA interference approach was used to suppress the expression of Six1 in a metastatic HCC cell line MHCC97L. In vitro functional assays demonstrated that suppression of Six1 expression significantly suppressed the growth rate and proliferation ability of MHCC97L, and markedly decreased its motility and invasiveness. Data from xenograft tumorigenesis model demonstrated that in vivo growth rate of subcutaneous xenograft of MHCC97L was inhibited after suppression of Six1 expression. Experimental and spontaneous metastasis models indicated that suppression of Six1 noticeably reduced the pulmonary metastatic potential of MHCC97L. Our data suggested that Six1 is frequently overexpressed in HCC patients and elevated Six1 protein in HCC patients may be an indication of advanced stage and poor overall survival after hepatectomy. Suppression of Six1 leading to reduction of metastatic ability of metastatic cells implies its potential therapeutic application on treatment of HCC metastasis.