title: Intracellular signaling pathways involved in Gas6-Axl-mediated survival of endothelial cells.
abstract: Gas6 is a gamma-carboxylated ligand for the receptor tyrosine kinase Axl. Gas6-Axl interactions can rescue endothelial cells from apoptosis, and this study examined the intracellular signaling mechanisms responsible for this phenomenon. Using flow cytometry, we first confirmed that Gas6 can abrogate apoptosis induced by serum starvation of primary cultures of human umbilical vein endothelial cells (HUVECs). This effect is mediated through phosphorylation of the serine-threonine kinase Akt, with maximal phosphorylation observed after 4 h of treatment with 100 ng/ml Gas6. Inhibition of Akt phosphorylation and abrogation of gas6-mediated survival of HUVECs by wortmannin implicated phosphatidylinositol 3-kinase as the mediator of Akt phosphorylation. Dominant negative Akt constructs largely abrogated the protective effect of Gas6 on HUVECs, underscoring the importance of Akt activation in Gas6-mediated survival. Several downstream regulators of this survival pathway were identified in HUVECs, namely, NF-kappaB as well as the antiapoptotic and proapoptotic proteins Bcl-2 and caspase 3, respectively. We showed that NF-kappaB is phosphorylated early after Gas6 treatment as evidenced by doublet formation on Western blotting. As well, the level of Bcl-2 protein increased, supporting the notion that the Bcl-2 antiapoptotic pathway is stimulated. The levels of expression of the caspase 3 activation products p12 and p20 decreased with Gas6 treatment, consistent with a reduction in proapoptotic caspase 3 activation. Taken together, these experiments provide new information about the mechanism underlying Gas6 protection from apoptosis in primary endothelial cell cultures.
authors.affiliation: Lady Davis Institute for Medical Research and Division of Hematology, Sir Mortimer B. Davis-Jewish General Hospital, McGill University, Montreal, Quebec, Canada.
authors.forename: Ines
authors.initials: I
authors.lastname: Hasanbasic
authors.forename: Jessica
authors.initials: J
authors.lastname: Cuerquis
authors.forename: Brian
authors.initials: B
authors.lastname: Varnum
authors.forename: Mark D
authors.initials: MD
authors.lastname: Blostein
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D053148:Caspase 3; D020169:Caspases / Q000502:physiology; D002470:Cell Survival / Q000502:physiology; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000166:cytology / Q000502:physiology*; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000494:pharmacology / Q000502:physiology*; D007425:Intracellular Membranes / Q000378:metabolism*; D016328:NF-kappa B / Q000502:physiology; D015513:Oncogene Proteins / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D000094963:Axl Receptor Tyrosine Kinase; D000099255:Growth Arrest-Specific Protein 6
chemical_list: D053148:Caspase 3; D020169:Caspases; D016895:Culture Media, Serum-Free; D036341:Intercellular Signaling Peptides and Proteins; D016328:NF-kappa B; D015513:Oncogene Proteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2; D020794:Receptor Protein-Tyrosine Kinases; D000094963:Axl Receptor Tyrosine Kinase; D000099255:Growth Arrest-Specific Protein 6; C494918:AKT1 protein, human; C505407:CASP3 protein, human; C000722289:AXL protein, human