title: CD133+ liver cancer stem cells from methionine adenosyl transferase 1A-deficient mice demonstrate resistance to transforming growth factor (TGF)-beta-induced apoptosis.
abstract: Methionine adenosyltransferase (MAT) is an essential enzyme required for S-adenosylmethionine biosynthesis. Hepatic MAT activity falls during chronic liver injury, and mice lacking Mat1a develop spontaneous hepatocellular carcinoma by 18 months. We have previously demonstrated that CD133(+)CD45(-) oval cells isolated from 16-month-old Mat1a(-/-) mice represent a liver cancer stem cell population. The transforming growth factor beta (TGF-beta) pathway constitutes a central signaling network in proliferation, apoptosis, and tumorigenesis. In this study, we tested the response of tumorigenic liver stem cells to TGF-beta. CD133(+)CD45(-) oval cells were isolated from premalignant 16-month-old Mat1a(-/-) mice by flow cytometry and expanded as five clone lines derived from a single cell. All clone lines demonstrated expression of both hepatocyte and cholangiocyte markers and maintained a small population (0.5% to 2%) of CD133(+) cells in vitro, and three of five clone lines produced tumors. Although TGF-beta1 inhibited cell growth equally in CD133(-) and CD133(+) cells from each clone line, the CD133(+) population demonstrated significant resistance to TGF-beta-induced apoptosis compared with CD133(-) cells. Furthermore, CD133(+) cells demonstrated a substantial increase in mitogen-activated protein kinase (MAPK) pathway activation, as demonstrated by phosphorylated extracellular signal-regulated kinase levels before and after TGF-beta stimulation. MAPK inhibition using mitogen-activated protein kinase kinase 1 (MEK1) inhibitor PD98059 led to a significant increase in TGF-beta-induced apoptosis in CD133(+) cells. Conversely, a constitutively active form of MEK1 blocked the apoptotic effects of TGF-beta in CD133(-) cells.
  
  
  CONCLUSIONS
  CD133(+) liver cancer stem cells exhibit relative resistance to TGF-beta-induced apoptosis. One mechanism of resistance to TGF-beta-induced apoptosis in CD133(+) cancer stem cells is an activated mitogen-activated protein kinase/extracellular signal-regulated kinase pathway.
authors.affiliation: Department of Pediatrics, The Pennsylvania State University College of Medicine, Penn State Children's Hospital, Hershey, PA.
authors.forename: Wei
authors.initials: W
authors.lastname: Ding
authors.forename: Marialena
authors.initials: M
authors.lastname: Mouzaki
authors.forename: Hanning
authors.initials: H
authors.lastname: You
authors.forename: Joshua C
authors.initials: JC
authors.lastname: Laird
authors.forename: Jose
authors.initials: J
authors.lastname: Mato
authors.forename: Shelly C
authors.initials: SC
authors.lastname: Lu
authors.forename: C Bart
authors.initials: CB
authors.lastname: Rountree
mesh_terms: D000071916:AC133 Antigen; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism*; D017209:Apoptosis; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D049109:Cell Proliferation; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006023:Glycoproteins / Q000378:metabolism*; D008099:Liver / Q000473:pathology; D008113:Liver Neoplasms / Q000473:pathology; D008114:Liver Neoplasms, Experimental / Q000209:etiology*; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D020935:MAP Kinase Signaling System; D008716:Methionine Adenosyltransferase / Q000172:deficiency*; D051379:Mice; D018345:Mice, Knockout; D014411:Neoplastic Stem Cells / Q000502:physiology*; D010455:Peptides / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000502:physiology*; D014183:Transplantation, Heterologous
chemical_list: D000071916:AC133 Antigen; D015703:Antigens, CD; D018797:Cell Cycle Proteins; D006023:Glycoproteins; D010455:Peptides; C000606024:Prom1 protein, mouse; D016212:Transforming Growth Factor beta; C490703:Mat1a protein, mouse; D008716:Methionine Adenosyltransferase; D048049:Extracellular Signal-Regulated MAP Kinases; D048369:MAP Kinase Kinase 1