The liver contains a population of small bipotential facultative progenitor cells that reconstitute liver function when mature hepatocytes or cholangiocytes are unable to proliferate. Mesenchymal markers, including members of the forkhead transcription factor gene family, have been detected in hepatic progenitor cells. The winged helix transcription factor Foxl1 localizes to mesenchymal cells in the intestine; however, its expression in the liver has not been reported. We found that Foxl1 is expressed in rare cells in the normal liver but is dramatically induced in the livers of mice that have undergone bile duct ligation or were fed a 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-containing or choline-deficient, ethionine-supplemented diet. In addition, we employed genetic lineage tracing using a Foxl1-Cre transgenic mouse crossed with the Rosa26R lacZ reporter line to demonstrate that

Hepatocellular carcinoma (HCC) is the major form of primary liver cancer which accounts for more than half million deaths annually worldwide. While the incidence of HCC is still on the rise, options of treatment are limited and the overall survival rate is poor. The acquisition of cancer drug resistance remains one of the key hurdles to successful treatment. Clearly, a thorough understanding of the underlying mechanisms is needed for new strategies to design novel treatments and/or to improve the current therapies. In the present study, we examined the expression of cancer stem cell (CSC) marker CD133, the activation of insulin-like growth factor 1 receptor (IGF-1R) signaling, and the nuclear translocation of IGF-1R in HCC Mahlavu cells under the treatment of gefitinib, a cancer drug that inhibits epidermal growth factor receptor (EGFR) pathway. Our results demonstrated that Mahlavu cells exhibited strong gefitinib resistance and the CD133 expression level was dramatically increased (from 3.88% to 32%) after drug treatment. In addition, the gefitinib treated cells displayed increased levels of phosphorylation in IGF-1R and Akt, indicating the intensified activation of this cancer-associated signaling pathway. Moreover, we revealed that IGF-1R underwent nuclear translocation in gefitinib treated cells using confocal microscopy. The IGF-1R nuclear translocation was enhanced under gefitinib treatment and appeared in a dose-dependent manner. Our findings suggest that increased IGF-1R nuclear translocation after gefitinib treatment may contribute to the drug resistance and IGF1-R activation, which might also associate with the upregulation of CD133 expression.

Cholangiocyte proliferation is one of the hallmarks of the response to cholestatic injury. We previously reported that the winged helix transcription factor Foxl1 is dramatically induced in cholangiocytes following bile duct ligation. In this study, we investigated the function of Foxl1 in the bile duct ligation model of cholestatic liver injury in Foxl1 À/À and control mice. We found that Foxl1 À/À livers exhibit an increase in parenchymal necrosis, significantly impaired cholangiocyte and hepatocyte proliferation, and failure to expand bile ductular mass. Wnt3a and Wnt7b expression was decreased in the livers of Foxl1 À/À mice along with reduced expression of the b-catenin target gene Cyclin D1 in Foxl1 À/À cholangiocytes. These results show that Foxl1 promotes liver repair after bile-duct-ligation-induced liver injury through activation of the canonical wnt/b-catenin pathway.

G protein coupled receptor kinase 2 (GRK2) plays a central role in the regulation of a variety of important signaling pathways. Alternation of GRK2 protein level and activity casts profound effects on cell physiological functions and causes diseases such as heart failure, rheumatoid arthritis, and obesity. We have previously reported that overexpression of GRK2 has an inhibitory role in cancer cell growth. To further examine the role of GRK2 in cancer, in this study, we investigated the effects of reduced protein level of GRK2 on insulin-like growth factor 1 receptor (IGF-1R) signaling pathway in human hepatocellular carcinoma (HCC) HepG2 cells. We created a GRK2 knockdown cell line using a lentiviral vector mediated expression of GRK2 specific short hairpin RNA (shRNA). Under IGF-1 stimulation, HepG2 cells with reduced level of GRK2 showed elevated total IGF-1R protein expression as well as tyrosine phosphorylation of receptor. In addition, HepG2 cells with reduced level of GRK2 also demonstrated increased tyrosine phosphorylation of IRS1 at the residue 612 and increased phosphorylation of Akt, indicating a stronger activation of IGF-1R signaling pathway. However, HepG2 cells with reduced level of GRK2 did not display any growth advantage in culture as compared with the scramble control cells. We further detected that reduced level of GRK2 induced a small cell cycle arrest at G2/M phase by enhancing the expression of cyclin A, B1, and E. Our results indicate that GRK2 has contrasting roles on HepG2 cell growth by negatively regulating the IGF-1R signaling pathway and cyclins' expression.

Hepatocellular carcinoma (HCC) is one of the deadliest forms of human liver cancer and does not respond well to conventional therapies. Novel effective treatments are urgently in need. G-protein-coupled kinase 2 (GRK2) is unique serine/threonine kinase that involves in many signaling pathways and regulates various essential cellular processes. Altered levels of GRK2 have been linked with several human diseases including cancer. In this study, we investigated a novel approach for HCC treatment by inducing overexpression of GRK2 in human HCC cells. We found that overexpression of GRK2 through recombinant adenovirus transduction inhibits the growth of human HCC cells. BrdU incorporation assay showed that the growth inhibition caused by elevated GRK2 level was due to reduced cell proliferation but not apoptosis. To examine the anti-proliferative function of increased GRK2 level, we performed cell cycle analysis using propidium iodide staining. We found that the proliferation suppression was associated with G2/M phase cell cycle arrest by the wild-type GRK2 but not its kinase-dead K220R mutant. Furthermore, increased levels of wild-type GRK2 induced upregulation of phosphor-Ser15 p53 and cyclin B1 in a dose-dependent manner. Our data indicate that the anti-proliferative function of elevated GRK2 is associated with delayed cell cycle progression and is GRK2 kinase activity-dependent. Enforced expression of GRK2 in human HCC by molecular delivery may offer a potential therapeutic approach for the treatment of human liver cancer.