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Wnt/β-Catenin Signaling Contributes to Activation of Normal and Tumorigenic Liver Progenitor Cells

¹ International Cooperation Laboratory on Signal Transduction, Eastern Hepatobiliary Surgery Institute, Second Military Medical University; and ² National Laboratory for Oncogene and Related Genes, Cancer Institute of Shanghai Jiao Tong University, Shanghai, China

Requests for reprints: Hongyang Wang, International Cooperation Laboratory on Signal Transduction, Eastern Hepatobiliary Surgery Institute, Second Military Medical University, Shanghai 200438, P.R. China. Phone: 86-21-2507-0856; Fax: 86-21-6556-6851; E-mail: hywangk{at}vip.sina.com.

Key Words: Wnt • β-catenin • hepatic progenitor cells • hepatocellular carcinoma • chemotherapy

Adult hepatic progenitor (oval) cells are facultative stem cells in liver, which participate in a range of human liver diseases, including hepatocellular carcinoma (HCC). However, the molecular pathways regulating the expansion and differentiation of these cells are poorly understood. We show that active Wnt/β-catenin signaling occurs preferentially within the oval cell population, and forced expression of constitutively active β-catenin mutant promotes expansion of the oval cell population in the regenerated liver. More importantly, we identify a subpopulation of less differentiated progenitor-like cells in HCC cell lines and primary HCC tissues, which are defined by expression of the hepatic progenitor marker OV6 and endowed with endogenously active Wnt/β-catenin signaling. These OV6⁺ HCC cells possess a greater ability to form tumor in vivo and show a substantial resistance to standard chemotherapy compared with OV6^– tumor cells. The fraction of tumor cells expressing OV6 is enriched after Wnt pathway activation, whereas inhibition of β-catenin signaling leads to a decrease in the proportion of OV6⁺ cells. In addition, the chemoresistance of OV6⁺ HCC progenitor-like cells can be reversed by lentivirus-delivered stable expression of microRNA targeting β-catenin. These results highlight the importance of the Wnt/β-catenin pathway in activation and expansion of oval cells in normal rodent models and human HCCs. OV6⁺ tumor cells may represent the cellular population that confers HCC chemoresistance, and therapies targeted to the Wnt/β-catenin signaling may provide a specific method to disrupt this resistance mechanism to improve overall tumor control with chemotherapy. [Cancer Res 2008;68(11):4287–95]

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