title: Axl activates autocrine transforming growth factor-β signaling in hepatocellular carcinoma.
abstract: In hepatocellular carcinoma (HCC), intrahepatic metastasis frequently correlates with epithelial to mesenchymal transition (EMT) of malignant hepatocytes. Several mechanisms have been identified to be essentially involved in hepatocellular EMT, among them transforming growth factor (TGF)-β signaling. Here we show the up-regulation and activation of the receptor tyrosine kinase Axl in EMT-transformed hepatoma cells. Knockdown of Axl expression resulted in abrogation of invasive and transendothelial migratory abilities of mesenchymal HCC cells in vitro and Axl overexpression-induced metastatic colonization of epithelial hepatoma cells in vivo. Importantly, Axl knockdown severely impaired resistance to TGF-β-mediated growth inhibition. Analysis of the Axl interactome revealed binding of Axl to 14-3-3ζ, which is essentially required for Axl-mediated cell invasion, transendothelial migration, and resistance against TGF-β. Axl/14-3-3ζ signaling caused phosphorylation of Smad3 linker region (Smad3L) at Ser213, resulting in the up-regulation of tumor-progressive TGF-β target genes such as PAI1, MMP9, and Snail as well as augmented TGF-β1 secretion in mesenchymal HCC cells. Accordingly, high Axl expression in HCC patient samples correlated with elevated vessel invasion of HCC cells, higher risk of tumor recurrence after liver transplantation, strong phosphorylation of Smad3L, and lower survival. In addition, elevated expression of both Axl and 14-3-3ζ showed strongly reduced survival of HCC patients.
  
  
  CONCLUSIONS
  Our data suggest that Axl/14-3-3ζ signaling is central for TGF-β-mediated HCC progression and a promising target for HCC therapy.
authors.affiliation: Department of Medicine I, Division: Institute of Cancer Research, Comprehensive Cancer Center, Medical University of Vienna, Vienna, Austria.
authors.forename: Patrick
authors.initials: P
authors.lastname: Reichl
authors.forename: Mirko
authors.initials: M
authors.lastname: Dengler
authors.forename: Franziska
authors.initials: F
authors.lastname: van Zijl
authors.forename: Heidemarie
authors.initials: H
authors.lastname: Huber
authors.forename: Gerhard
authors.initials: G
authors.lastname: Führlinger
authors.forename: Christian
authors.initials: C
authors.lastname: Reichel
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Sieghart
authors.forename: Markus
authors.initials: M
authors.lastname: Peck-Radosavljevic
authors.forename: Markus
authors.initials: M
authors.lastname: Grubinger
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Mikulits
mesh_terms: D048948:14-3-3 Proteins / Q000502:physiology; D019898:Autocrine Communication; D006528:Carcinoma, Hepatocellular / Q000401:mortality / Q000473:pathology*; D002465:Cell Movement; D058750:Epithelial-Mesenchymal Transition; D005260:Female; D006801:Humans; D008113:Liver Neoplasms / Q000401:mortality / Q000473:pathology*; D008297:Male; D009361:Neoplasm Invasiveness; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000502:physiology*; D000094963:Axl Receptor Tyrosine Kinase
chemical_list: D048948:14-3-3 Proteins; D011518:Proto-Oncogene Proteins; D016212:Transforming Growth Factor beta; C572235:YWHAZ protein, human; D019869:Phosphatidylinositol 3-Kinases; D020794:Receptor Protein-Tyrosine Kinases; D000094963:Axl Receptor Tyrosine Kinase; C000722289:AXL protein, human