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Regulation of the Anti-apoptotic Protein Ku70 and the Implications for Bax-Mediated Apoptosis

Gama, Vivian
http://rave.ohiolink.edu/etdc/view?acc_num=case1221831227

Abstract Details

2008, Doctor of Philosophy, Case Western Reserve University, Pharmacology.
Ku70 plays an important role in maintaining genomic integrity and cellular viability by repairing DNA damage and inhibiting Bax-mediated cell death. Apoptotic stresses decrease cellular Ku70 levels, which then trigger Bax-mediated apoptosis. This work demonstrates that Ku70 levels are controlled in part by the post-translational modification known as ubiquitination. Furthermore, ubiquitin-dependent degradation of Ku70 is increased by genotoxic stresses, a factor contributing to Bax activation. These results support the notion of an additional role of Ku70 in the cytosol, which is regulated by critical proteins involved in cell survival. The identification of the E3 ubiquitin ligase regulating Ku70 levels was critical to understanding how the cell may modulate Ku70 function as a Bax inhibitor. We demonstrated that the human double minute-2 (Hdm2) serves as a ubiquitin ligase for Ku70 both in vitro and in vivo. Moreover our data suggests that the localization of Hdm2 is critical for its activity towards Ku70. It was previously demonstrated that growth factors, through the activation of Akt, induce Hdm2 nuclear localization. Moreover, Akt is known to protect cells from different apoptotic stimuli. We investigated whether Akt-dependent phosphorylation of Hdm2 had any effect on Ku70 levels. We found that vascular endothelial growth factor (VEGF) treatment inhibited etoposide-induced Ku70 degradation in human umbilical vein endothelia cells (HUVECs) through the stimulation of the nuclear translocation of Hdm2, leaving Ku70-bound to Bax free from degradation. Constitutively active Akt, but not the dominant negative Akt, efficiently inhibited Ku70 degradation. A mutant of Hdm2 resistant to Akt phosphorylation was able to down-regulate Ku70 but not p53 in HUVECs, suggesting a differential mechanism of regulation for these two substrates in endothelial cells. Furthermore, Ku70 knockdown diminished the anti-apoptotic activity of Akt. Our results suggest that Akt inhibits Bax-mediated apoptosis, at least in part, by maintaining Ku70 levels through the induction of Hdm2 nuclear translocation. Hdm2-dependent Ku70 ubiquitination may provide a rheostat system controlling cell survival by measuring the balance between survival kinase and DNA damage response signals. Understanding these interactions will allow rationalizing strategies to modulate cell survival, aiming to the development of new and more effective therapeutic tools.
John Mieyal, PhD (Committee Chair)
Shigemi Matsuyama, PhD (Committee Member)
Clark Distelhorst, MD (Committee Member)
Yu-Chung Yang, PhD (Committee Member)
KU70; BAX; Hdm2; Ku80; APOPTOSIS; Ku70 levels; PROTEIN

Recommended Citations

Citations

  • Gama, V. (2008). Regulation of the Anti-apoptotic Protein Ku70 and the Implications for Bax-Mediated Apoptosis [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1221831227

    APA Style (7th edition)

  • Gama, Vivian. Regulation of the Anti-apoptotic Protein Ku70 and the Implications for Bax-Mediated Apoptosis. 2008. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1221831227.

    MLA Style (8th edition)

  • Gama, Vivian. "Regulation of the Anti-apoptotic Protein Ku70 and the Implications for Bax-Mediated Apoptosis." Doctoral dissertation, Case Western Reserve University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1221831227

    Chicago Manual of Style (17th edition)

case1221831227
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© 2008, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.