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Akt is required for Axl-Gas6 signaling to protect cells from E1A-mediated apoptosis
Wei-Ping Lee1, Yong Wen, Brian Varnum
1Department of Molecular and Cellular Oncology and Breast Cancer Research Program, The University of Texas M.D. Anderson Cancer Center, Houston, Texas, TX 77030, USA.
Abstract:
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.
Insights
Adenovirus E1A protein has anti-tumor effects. The Axl-Gas6 pathway prevents E1A-induced apoptosis by activating Akt, a key survival molecule.
Area of Science:
- Oncology
- Molecular Biology
- Cell Signaling
Background:
- Adenovirus type 5 E1A protein (E1A) exhibits anti-tumor properties, including reversing transformation, inhibiting metastasis, and inducing apoptosis.
- E1A suppresses Axl tyrosine kinase expression, and the Axl-Gas6 interaction protects E1A-expressing cells from apoptosis.
Purpose of the Study:
- To elucidate the mechanism by which the Axl-Gas6 interaction prevents E1A-mediated apoptosis.
- To investigate the role of Akt signaling in mediating the anti-apoptotic effects of Axl-Gas6 in the context of E1A expression.
Main Methods:
- Analysis of anti-apoptotic molecule expression in E1A transfectants.
- Assessment of Akt activation by Gas6 in cells re-expressing Axl.
- Inhibition of Akt signaling using wortmannin or a dominant-negative Akt mutant to evaluate protection from apoptosis.
Main Results:
- Activated Akt was suppressed in E1A transfectants but could be activated by Gas6 in cells re-expressing Axl.
- Inhibition of Akt activation abrogated Gas6-mediated protection from serum deprivation-induced apoptosis.
- Phosphorylation of BAD by Axl-Gas6 signaling was linked to Akt's anti-apoptotic activity.
Conclusions:
- Activated Akt is essential for Axl-Gas6 signaling to confer resistance to E1A-mediated apoptosis.
- The Axl-Gas6-Akt pathway, involving downstream effectors like BAD, plays a critical role in cell survival during adenovirus infection.