title: Deletion of the Met tyrosine kinase in liver progenitor oval cells increases sensitivity to apoptosis in vitro.
abstract: The hepatocyte growth factor (HGF)/Met signaling system is essential for liver development, homeostasis, and function. In this study, we took advantage of a liver-specific, Met-conditional knockout mouse generated in our laboratory to address the molecular mechanisms of HGF/Met signaling in adult liver progenitor cell (oval cell) biology. For this purpose, we isolated oval cells from 3,5-diethoxycarbonyl-1,4-dihydro-collidine-treated Met(flx/flx) mice and established oval cell-derived cell lines that carried either functional (Met(flx/flx)) or a nonfunctional (Met(-/-)) met gene using virus-mediated Cre-loxP recombination. Oval cells lacking Met tyrosine kinase activity displayed neither Met phosphorylation nor activation of downstream targets and were refractory to HGF stimulation. Although Met(-/-) and Met(flx/flx) cells proliferated at similar rates under 10% serum, Met-deficient cells demonstrated decreased cell viability and were more prone to apoptosis when challenged with either serum starvation or the pro-apoptotic cytokine transforming growth factor-beta. Treatment with HGF reduced transforming growth factor-beta-mediated cell death in Met(flx/flx) but not Met(-/-) cells. Importantly, Met(flx/flx) and Met(-/-) cells both constitutively expressed hgf, and conditioned medium from serum-starved oval cells exhibited anti-apoptotic activity in Met(flx/flx) cells. Furthermore, serum-starved Met(flx/flx) cells showed persistent activation of the Met tyrosine kinase, suggesting HGF/Met autocrine regulation. In conclusion, these data reveal a critical, functional role for Met in oval cell survival through an autocrine mechanism.
authors.affiliation: Department Bioquímica y Biología Molecular II, Facultad de Farmacia, Universidad Complutense de Madrid, Plaza de Ramón y Cajal S/N, 28040-Madrid, Spain.
authors.forename: Gaelle
authors.initials: G
authors.lastname: del Castillo
authors.forename: Valentina M
authors.initials: VM
authors.lastname: Factor
authors.forename: Margarita
authors.initials: M
authors.lastname: Fernández
authors.forename: Alberto
authors.initials: A
authors.lastname: Alvarez-Barrientos
authors.forename: Isabel
authors.initials: I
authors.lastname: Fabregat
authors.forename: Snorri S
authors.initials: SS
authors.lastname: Thorgeirsson
authors.forename: Aránzazu
authors.initials: A
authors.lastname: Sánchez
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002470:Cell Survival / Q000502:physiology; D003997:Dicarbethoxydihydrocollidine; D017228:Hepatocyte Growth Factor / Q000502:physiology*; D022781:Hepatocytes / Q000502:physiology*; D007202:Indicators and Reagents; D051379:Mice; D019859:Proto-Oncogene Proteins c-met / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction; D013234:Stem Cells / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000502:physiology
chemical_list: D007202:Indicators and Reagents; D016212:Transforming Growth Factor beta; D003997:Dicarbethoxydihydrocollidine; D017228:Hepatocyte Growth Factor; D019859:Proto-Oncogene Proteins c-met