Deletion of the Met tyrosine kinase in liver progenitor oval cells increases sensitivity to apoptosis in vitro.
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.
del Castillo
Gaelle
G
Department Bioquímica y Biología Molecular II, Facultad de Farmacia, Universidad Complutense de Madrid, Plaza de Ramón y Cajal S/N, 28040-Madrid, Spain.
Factor
Valentina M
VM
Fernández
Margarita
M
Alvarez-Barrientos
Alberto
A
Fabregat
Isabel
I
Thorgeirsson
Snorri S
SS
Sánchez
Aránzazu
A
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
D007202:Indicators and Reagents; D016212:Transforming Growth Factor beta; D003997:Dicarbethoxydihydrocollidine; D017228:Hepatocyte Growth Factor; D019859:Proto-Oncogene Proteins c-met