Effects of Gas6 and hydrogen peroxide in Axl ubiquitination and downregulation.
The receptor tyrosine kinase Axl has been shown to be activated by its ligand Gas6 and by oxidative stress in the form of hydrogen peroxide. However, the regulatory mechanisms controlling the levels of Axl upon Gas6 binding or oxidative stress have not been elucidated. This report demonstrates that Gas6-induced downregulation of Axl is blocked by inhibitors of endocytosis and lysosomal degradation, but not by inhibitors of proteosomal activity. Furthermore, it is shown that binding of Axl to Gas6 induces the phosphorylation and ubiquitination of Axl and the interaction of Axl with the ubiquitin ligase c-Cbl. Importantly, hydrogen peroxide induces Axl tyrosine phosphorylation but not its ubiquitination, determining the inhibition of Axl downregulation. These results suggest that as shown for other receptor tyrosine kinases, ubiquitination of Axl is needed to ensure its proper degradation in the lysosome, and that oxidative stress may inhibit Axl ubiquitination and downregulation.
Valverde
Paloma
P
Tufts University, Boston, MA 02111, USA. paloma.valverde@tufts.edu
D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism* / Q000494:pharmacology*; D015513:Oncogene Proteins / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D025801:Ubiquitin / Q000378:metabolism*; D000094963:Axl Receptor Tyrosine Kinase; D000099255:Growth Arrest-Specific Protein 6
D006861:Hydrogen Peroxide; D036341:Intercellular Signaling Peptides and Proteins; D015513:Oncogene Proteins; D011518:Proto-Oncogene Proteins; D020794:Receptor Protein-Tyrosine Kinases; D025801:Ubiquitin; D000094963:Axl Receptor Tyrosine Kinase; D000099255:Growth Arrest-Specific Protein 6; C000722289:AXL protein, human