Increasing evidence suggests that the presence of endotoxemia is of substantial clinical relevance to patients with cirrhosis, but it is unclear whether and how gut-derived LPS amplifies the tumorigenic response of the liver. We found that the circulating levels of LPS were elevated in animal models of carcinogen-induced hepatocarcinogenesis. Reduction of LPS using antibiotics regimen in rats or genetic ablation of its receptor Toll-like receptor 4 (TLR4) in mice prevented excessive tumor growth and multiplicity. Additional investigation revealed that TLR4 ablation sensitizes the liver to carcinogen-induced toxicity via blocking NF-jB activation and sensitizing the liver to reactive oxygen species (ROS)-induced toxicity, but lessens inflammation-mediated compensatory proliferation. Reconstitution of TLR4-expressing myeloid cells in TLR4-deficient mice restored diethylnitrosamine (DEN)-induced hepatic inflammation and proliferation, indicating a paracrine mechanism of LPS in tumor promotion. Meanwhile, deletion of gut-derived endotoxin suppressed DENinduced cytokine production and compensatory proliferation, whereas in vivo LPS prechallenge promotes hepatocyte proliferation. Conclusion: Our data indicate that sustained LPS accumulation represents a pathological mediator of inflammation-associated hepatocellular carcinoma (HCC) and manipulation of the gut flora to prevent pathogenic bacterial translocation and endotoxin absorption may favorably influence liver function in patients with cirrhosis who are at risk of developing HCC. (HEPATOLOGY 2010;52:1322-1333

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/B-catenin signaling occurs preferentially within the oval cell population, and forced expression of constitutively active B-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/B-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 À tumor cells. The fraction of tumor cells expressing OV6 is enriched after Wnt pathway activation, whereas inhibition of B-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 micro-RNA targeting B-catenin. These results highlight the importance of the Wnt/B-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/B-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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