SUMMARY Cancers are distributed unevenly across the body, but the importance of cell intrinsic factors such as stem cell function in determining organ cancer risk is unknown. Therefore, we used Cre-recombination of conditional lineage tracing, oncogene and tumour suppressor alleles to define populations of stem and non-stem cells in mouse organs, and test their life-long susceptibility to tumourigenesis. We show that tumour incidence is determined by the life-long generative capacity of mutated cells. This relationship held true in the presence of multiple genotypes and regardless of developmental stage, strongly supporting the notion that stem cells dictate organ cancer risk. Using the liver as a model system, we further show that damage-induced activation of stem cell function markedly increases cancer risk. Therefore, we propose that a combination of stem cell mutagenesis and extrinsic factors that enhance the proliferation of these cell populations, creates a ‘perfect storm’ that ultimately determines organ cancer risk.

Fibroblast Growth Factor (FGF)-10 promotes the proliferation and survival of murine hepatoblasts during early stages of hepatogenesis through a Wnt-β-catenin dependent pathway. To determine the mechanism by which this occurs, we expanded primary culture of hepatoblasts enriched for progenitor markers CD133 and CD49f from embryonic day (E) 12.5 fetal liver and an established tumor initiating stem cell line from Mat1a−/− livers in media conditioned with recombinant (r) FGF10 or rFGF7. FGF Receptor (R) activation resulted in the downstream activation of MAPK, PI3K-AKT, and β-catenin pathways, as well as cellular proliferation. Additionally, increased levels of nuclear β-catenin phosphorylated at Serine-552 in cultured primary hepatoblasts, Mat1a−/− cells, and also in ex vivo embryonic liver explants indicate AKT-dependent activation of β-catenin downstream of FGFR activation; conversely, the addition of AKT inhibitor Ly294002 completely abrogated β-catenin activation. FGFR activation-induced cell proliferation and survival were also inhibited by the compound ICG-001, a small molecule inhibitor of β-catenin-CREB Binding Protein (CBP) in hepatoblasts, further indicating a CBP-dependent regulatory mechanism of β-catenin activity. Conclusion: FGF signaling regulates the proliferation and survival of embryonic and transformed progenitor cells in part through AKT-mediated activation of β-catenin and downstream interaction with the transcriptional co-activator CBP.

Biliary atresia (BA), the most common cause of end-stage liver disease and the leading indication for pediatric liver transplantation, is associated with intrahepatic ductular reactions within regions of rapidly expanding periportal biliary fibrosis. While the extent of such biliary fibrosis is a negative predictor of long-term transplant-free survival, the cellular phenotypes involved in the fibrosis are not well established. Using a Rhesus rotavirus (RRV)-induced mouse model of BA, we demonstrate significant expansion of a cell population expressing the putative stem/progenitor cell marker PROMININ-1 (PROM1) adjacent to ductular reactions within regions of periportal fibrosis. PROM1positive (pos) cells express Collagen-1α1. Subsets of PROM1pos cells co-express progenitor cell marker CD49f, epithelial marker E-CADHERIN, biliary marker CYTOKERATIN-19, and mesenchymal markers VIMENTIN and α-SMOOTH MUSCLE ACTIN. Expansion of the PROM1pos cell population is associated with activation of Fibroblast Growth Factor (FGF) and Transforming Growth Factor-β (TGFβ) signaling. In vitro co-treatment of PROM1-expressing Mat1a−/− hepatic progenitor cells with recombinant human FGF10 and TGFβ1 promotes morphologic transformation toward a myofibroblastic cell phenotype with increased expression of myofibroblastic genes Collagen-1α1, Fibronectin, and α–Smooth muscle actin. Infants with BA demonstrate similar expansion of periportal PROM1pos cells with activated SMAD3 signaling in association with increased hepatic expression of FGF10, FGFR1, and FGFR2 as well as mesenchymal genes SLUG and SNAIL. Infants with perinatal subtype of BA have higher tissue levels of PROM1 expression than those with embryonic subtype. Conclusion Expansion of collagen-producing PROM1pos cells within the regions of periportal fibrosis is associated with activated FGF and TGFβ pathways in both experimental and human BA. PROM1pos cells may, therefore, play an important role in the biliary fibrosis of BA.

Background & Aims Fibroblast Growth Factors (FGFs) promote the proliferation and survival of hepatic progenitor cells (HPCs) via AKT-dependent β-catenin activation. Moreover, the emergence of hepatocytes expressing the HPC marker A6 during 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-induced liver injury is mediated partly by FGF and β-catenin signaling. Herein, we investigate the role of FGF signaling and AKT-mediated β-catenin activation in acute DDC liver injury. Methods Transgenic mice were fed DDC chow for 14 days concurrent with either Fgf10 over-expression or inhibition of FGF signaling via expression of soluble dominant-negative FGF Receptor (R)-2IIIb. Results After 14 days of DDC treatment, there was an increase in periportal cells expressing FGFR1, FGFR2, and AKT-activated phospho-Serine 552 (pSer552) β-CATENIN in association with up-regulation of genes encoding FGFR2IIIb ligands, Fgf7, Fgf10, and Fgf22. In response to Fgf10 over-expression, there was an increase in the number of pSer552-β-CATENIN(positive)+ive periportal cells as well as cells co-positive for A6 and hepatocyte marker, Hepatocyte Nuclear Factor-4α (HNF4α). A similar expansion of A6+ive cells was observed after Fgf10 over-expression with regular chow and after partial hepatectomy during ethanol toxicity. Inhibition of FGF signaling increased the periportal A6+iveHNF4α+ive cell population while reducing centrolobular A6+ive HNF4α+ive cells. AKT inhibition with Wortmannin attenuated FGF10-mediated A6+iveHNF4α+ive cell expansion. In vitro analyses using FGF10 treated HepG2 cells demonstrated AKT-mediated β-CATENIN activation but not enhanced cell migration. Conclusion During acute DDC treatment, FGF signaling promotes the expansion of A6-expressing liver cells partly via AKT-dependent activation of β-CATENIN expansion of A6+ive periportal cells and possibly by reprogramming of centrolobular hepatocytes.