Akt is required for Axl-Gas6 signaling to protect cells from E1A-mediated apoptosis.
Adenovirus type 5 E1A protein (E1A) associates with anti-tumor activities by reversing the transformed phenotype, inhibiting metastasis, and inducing apoptosis. We have previously identified that E1A suppresses the expression of Axl, a transforming tyrosine kinase and that Axl-Gas6 receptor-ligand interaction prevents E1A transfectants from apoptosis induced by serum deprivation. To determine how the Axl-Gas6 interaction prevents E1A-mediated apoptosis, we analysed the expression of anti-apoptotic molecules and found that the activated form of Akt was suppressed in the E1A transfectant ip 1-E1A and that Gas6 was able to activate Akt in ip 1-E1A cells reexpressing Axl (ip 1-E1A-Axl). To determine whether activated Akt is required to prevent E1A-mediated apoptosis, ip 1-E1A-Axl cells were treated with the phosphatidylinositol-3'-OH kinase inhibitor wortmannin or transfected with a dominant negative Akt mutant. In both cases, Gas6 no longer protected the cells from serum deprivation-induced apoptosis. Thus, we conclude that activated Akt is required for Axl-Gas6 signaling to prevent E1A-mediated apoptosis induced by serum deprivation. Downstream molecules of Akt, including NF-kappaB, Fas ligand, and BAD were examined, among which phosphorylation of BAD by Axl-Gas6 signaling is associated with the anti-apoptotic activity of Akt in our study.
Lee
Wei-Ping
WP
Department of Molecular and Cellular Oncology and Breast Cancer Research Program, The University of Texas M.D. Anderson Cancer Center, Houston, Texas, TX 77030, USA.
Wen
Yong
Y
Varnum
Brian
B
Hung
Mien-Chie
MC
D017500:Adenovirus E1A Proteins / Q000378:metabolism*; D000730:Androstadienes / Q000494:pharmacology; D017209:Apoptosis; D015153:Blotting, Western; D016895:Culture Media, Serum-Free; D005260:Female; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D016328:NF-kappa B / Q000378:metabolism; D015513:Oncogene Proteins / Q000378:metabolism*; D010051:Ovarian Neoplasms / Q000378:metabolism / Q000473:pathology / Q000821:virology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011506:Proteins / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection; D014407:Tumor Cells, Cultured; D000077191:Wortmannin; D000094963:Axl Receptor Tyrosine Kinase; D000099255:Growth Arrest-Specific Protein 6
D017500:Adenovirus E1A Proteins; D000730:Androstadienes; D016895:Culture Media, Serum-Free; D036341:Intercellular Signaling Peptides and Proteins; D016328:NF-kappa B; D015513:Oncogene Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011506:Proteins; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D020794:Receptor Protein-Tyrosine Kinases; D000077191:Wortmannin; D000094963:Axl Receptor Tyrosine Kinase; D000099255:Growth Arrest-Specific Protein 6; C494918:AKT1 protein, human; C000722289:AXL protein, human