Abstract #3280: INrf2/Nrf2 control of Drug-Induced Apoptosis

INrf2:Nrf2 serve as sensor of chemical and radiation induced oxidative and electrophilic stress. Nrf2 is a nuclear transcription factor that regulates expression and coordinated induction of a battery of defensive genes including detoxifying enzymes and antioxidant genes. This induction is a mechanism of critical importance in neutralizing the stressors and providing cellular protection leading to cell survival. Nrf2 degrades predominantly within the cytoplasm of the cells by the interaction of actin-bound cytosolic protein, INrf2 (inhibitor of Nrf2) or Keap1 (Kelch-like ECH-associated protein 1). INrf2 functions as a substrate adaptor protein for a Cul3-Rbx1-dependent E3 ubiquitin ligase complex to ubiquitinate and degrade Nrf2 thus maintaining a steady-state levels of Nrf2. In the present study, we investigated the role of INrf2/Nrf2 on drug-induced apoptosis. Over expression of INrf2 increased and Nrf2 decreased Etoposide-induced apoptosis in tetracycline inducible human kidney carcinoma HEK293 cells. Immunoprecipitation assays revealed that INrf2 interacted with Nrf2 and also with PGAM5/Bcl-XL complex through interaction with PGAM5. Over expression of INrf2 led to ubiquitination and degradation of Nrf2 and down regulation of anti-apoptotic Bcl2 gene expression. Over expression of INrf2 also led to degradation of PGAM5/Bcl-XL complex. The down regulation of Bcl2 and degradation of Bcl-XL led to increase in Bax and apoptosis. Over expression of Nrf2 or treatment of cells with antioxidant led to increased nuclear localization of Nrf2 and resistance to Etoposide-mediated apoptosis. This is through Nrf2 activation of Bcl2 and Bcl-XL gene expression. Increase in Bcl2 and Bcl-XL led to decrease in Bax and reduced apoptosis. Deletion mapping and transfection assays identified the antioxidant response element (ARE) that mediated Nrf2 induction of Bcl2 and Bcl-XL. These results led to conclusion that INrf2 increases and Nrf2 decreases drug-induced apoptosis by manipulating Bcl-XL degradation and expression of Bcl2 and Bcl-XL.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 3280.