Abstract 4108: BH3 only Bcl-2 family member BNIP3 repressed expression of death receptor 5 (DR5) in glioblastoma cells: Implications for regulation of the tumor necrosis factor related apoptosis inducing ligand (TRAIL) cell death pathway

Abstract

Abstract Glioblastoma multiforme (GBM) is the most aggressive form of brain cancer. The median survival for patients with GBM is less than 15 months, even with treatment such as surgery, radiation and chemotherapy with temozolomide. Resistance to the standard treatment regimes represents a serious clinical challenge. GBM tumors contain extensive regions of necrosis, indicative of hypoxia. BNIP-3 (Bcl-2 nineteen kilodalton interacting protein) is a BH-3 only, pro-cell death member of the Bcl-2 family. BNIP-3 is up-regulated in hypoxia and leads to a non-classical programmed cell death through the mitochondria. In the majority of glioblastoma multiforme tumors, BNIP3 is localized to the nucleus and does not induce cell death. Our group has shown that when located in the nucleus, BNIP3 binds to DNA including the promoters of cell death genes such as AIF (apoptosis inducing factor). Herein, we found that BNIP3 bound to the promoter region of death receptor 5 (DR5). DR5 binds to the tumor necrosis factor related apoptosis inducing ligand (TRAIL) leading to induction of apoptosis. TRAIL is currently in phase 2 clinical trials for a wide variety of tumor types but glioblastoma tumors are resistant to TRAIL induced apoptosis. Our data showed that binding of BNIP3 to the promoter of DR5 prevented its expression and led to resistance to TRAIL induced cell death in glioma cells. Furthermore, when a BNIP3 construct was transiently over-expressed in the nucleus, DR5 mRNA and protein levels were reduced; also when BNip3 was knocked down using shRNA, DR5 message and protein levels increased. In BNIP3 knockout mice, we demonstrated that increased DR5 levels were increased in primary astrocytes compared to wild type controls as detected by western blot and immunofluorescence. We also showed similar results in brain sections from BNIP3 knockout mice. In paraffin embedded GBM tumors, we found that tumors that had BNIP3 in the nucleus had decreased levels of DR5, whereas tumors without BNIP3 in the nucleus had higher levels of DR5. Taken together, this represents a novel mechanism for regulation of DR5 expression, contributing to TRAIL resistance in GBM tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4108. doi:10.1158/1538-7445.AM2011-4108