Purpose: It has been shown that a lymphatic differentiation master gene, prox1, also plays an essential role in fetal hepatocyte migration. Its expression is detected in embryonic hepatoblasts and in adult hepatocytes. Hepatoma cells are similar to embryonic hepatoblasts to a certain extent because they both proliferate and invade the surrounding tissue. To address the possibility that Prox1 may be involved in the tumorigenesis of hepatocellular carcinoma (HCC), human clinical samples were

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... zed. Experimental Design: To screen prox1 as a potential tumor suppressor gene, its expression was analyzed in HCC cell lines and in human HCC tissues. Its growth-conferring abilities were assessed by transiently overexpressing Prox1in HCC cell lines and by knocking down its expression by RNA interference. Results: We found that there was a significant correlation between Prox1 expression and the differentiation scores of the tumors. Subsequently, we also showed that low expression of Prox1 in tumors was closely associated with a poor prognosis.The specific knockdown of Prox1by RNA interference strongly accelerated in vitro cell growth, whereas the overexpression of Prox1greatly suppressed the growth. Conclusions: Our results suggest that Prox1is involved in the differentiation and progression of HCC, and thus it may be a candidate for the development of novel diagnostic and therapeutic strategies for HCC.