The expression of biliary/progenitor markers by hepatocellular carcinoma (HCC) is often associated with poor prognosis and stem cell-like behaviors of tumor cells. Hepatocellular adenomas (HCA) also often express biliary/progenitor markers and frequently act as precursor lesions for HCC. However, the cell of origin of HCA and HCC that expresses these markers still remains unclear. Therefore, to evaluate if mature hepatocytes give rise to HCA and HCC tumors, and to understand the molecular pathways involved in tumorigenesis, we lineage-labeled hepatocytes by injecting adeno-associated virus (AAV) containing thyroxine-binding globulin (TBG) promoter driven-Cre into RosaYFP mice. Yellow fluorescent protein (YFP) was present in more than 96% of hepatocytes before exposure to carcinogens. We treated AAV-TBG-Cre;RosaYFP mice with diethylnitrosamine (DEN) followed by multiple injections of carbon tetrachloride (CCl4) to induce carcinogenesis and fibrosis, and found that HCA and HCC nodules were YFP+ lineage-labeled and also positive for osteopontin (Opn), SRY (sex determining region Y)-box 9 (Sox9), and epithelial cell adhesion molecule (EpCAM), and enriched for transcripts of biliary/progenitor markers such as Prom1, Cd44, and Dlk1. Next, we performed the converse experiment and lineage-labeled Foxl1-positive hepatic progenitor cells simultaneously with exposure to carcinogens. None of the tumor nodules expressed YFP, indicating that Foxl1-expressing cells are not the cell of origin for hepatotoxin-induced liver tumors. We confirmed that HCA and HCC cells are derived from mature hepatocytes and not from Foxl1-Cre-marked cells in a second model of toxin-induced hepatic neoplasia, using DEN and 3,3’,5,5’-tetrachloro-1,4-bis(pyridyloxy)benzene (TCPOBOP). Conclusion Our results indicate that hepatocytes are the cell of origin of HCA and HCC in DEN/CCl4 and DEN/TCPOBOP-induced liver tumors.
Protein tyrosine phosphatase of liver regeneration-1 (Prl-1) is an immediate-early gene that is significantly induced during liver regeneration. Several in vitro studies have suggested that Prl-1 is important for the regulation of cell cycle progression. To evaluate its function in liver regeneration, we ablated the Prl-1 gene specifically in mouse hepatocytes using the Cre-loxP system. Prl-1 mutant mice (Prl-1(loxP/loxP);AlfpCre) appeared normal and fertile. Liver size and metabolic function in Prl-1 mutants were comparable to controls, indicating that Prl-1 is dispensable for liver development, postnatal growth, and hepatocyte differentiation. Mutant mice demonstrated a delay in DNA synthesis after 70% partial hepatectomy, although ultimate liver mass restoration was not affected. At 40 h posthepatectomy, reduced protein levels of the cell cycle regulators cyclin E, cyclin A2, cyclin B1, and cyclin-dependent kinase 1 were observed in Prl-1 mutant liver. Investigation of the major signaling pathways involved in liver regeneration demonstrated that phosphorylation of protein kinase B (AKT) and signal transducer and activator of transcription (STAT) 3 were significantly reduced at 40 h posthepatectomy in Prl-1 mutants. Taken together, this study provides evidence that Prl-1 is required for proper timing of liver regeneration after partial hepatectomy. Prl-1 promotes G1/S progression via modulating expression of several cell cycle regulators through activation of the AKT and STAT3 signaling pathway.
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