BNIP3 (Bcl-2 19 kDa Interacting Protein) Acts as Transcriptional Repressor of Apoptosis-Inducing Factor Expression Preventing Cell Death in Human Malignant Gliomas

Abstract

The Bcl-2 19 kDa interacting protein (BNIP3) is a pro-cell-death BH3-only member of the Bcl-2 family. We previously found that BNIP3 is localized to the nucleus in the majority of glioblastoma multiforme (GBM) tumors and fails to induce cell death. Herein, we have discovered that nuclear BNIP3 binds to the promoter of the apoptosis-inducing factor (AIF) gene and represses its expression. BNIP3 associates with PTB-associating splicing factor (PSF) and HDAC1 (histone deacetylase 1) contributing to transcriptional repression of the AIF gene. This BNIP3-mediated reduction in AIF expression leads to decreased temozolomide-induced apoptosis in glioma cells. Furthermore, nuclear BNIP3 expression in GBMs correlates with decreased AIF expression. Together, we have discovered a novel transcriptional repression function for BNIP3 causing reduced AIF expression and increased resistance to apoptosis. Thus, nuclear BNIP3 may confer a survival advantage to glioma cells and explain, in part, why BNIP3 is expressed at high levels in solid tumors, especially GBM.

BNIP3 is essential for mitochondrial bioenergetics during adipocyte remodelling in mice

“…Besides the increase in the amount of mitochondria, it was interesting to note that there was an increase in oxygen consumption and uncoupling, which suggests that BNIP3 enhances mitochondrial function in the adipocytes. The critical differences in the effect of BNIP3 in various tissues might be because of differences in the tissue-specific expression and function of PPARγ [32][33][34], PPARγ coregulators [35,36] and BNIP3-interacting proteins [37][38][39]. In fact, our preliminary experiments using C2C12 myotubes showed the increment in mtDNA copy number resulting from rosiglitazone exposure to be independent of BNIP3 (data not shown).…”

“…Also, different PPARγ co-regulators might enable BNIP3 to act in a tissue-specific manner [35,36]. Furthermore, from our bioinformatics analysis, we could find several mitochondria-related proteins that physically interact with BNIP3 [37][38][39] and are expressed differently depending on the type of tissue. These findings support our data showing a cell-context-dependent BNIP3 action and explain why the BNIP3-AMPK-PGC1 pathway acts differently in adipocytes in mitochondrial biogenesis.…”

Bcl-2 family member Mcl-1 expression is reduced under hypoxia by the E3 ligase FBW7 contributing to BNIP3 induced cell death in glioma cells

“…Since BNIP3 expression is elevated in GBM tumors, 21 the colocalization of Mcl-1 and BNIP3 in glioma cells, GBM tumors and xenografted tumors was investigated. In U373 cells, Mcl-1 and BNIP3 did not co-localize under normoxic conditions but under hypoxia Mcl-1 and BNIP3 were co-localized in a punctate pattern indicative of mitochondrial localization (Fig.…”

“…21 The cells were grown in Gibco DMEM/F-12CGlutaMAXTM-1 media (Life Technologies) supplemented with 100 units of penicillin per mL plus 100 mg of streptomycin per mL (Life Technologies) and 5% fetal bovine serum in a humidified 5% CO 2 , 37 C incubator. HEK293 cells were maintained in DMEM supplemented with 10% bovine calf serum and 100 units of penicillin per mL plus 100 mg of streptomycin per mL.…”

“…Mouse astrocytes were isolated as previously described. 21 Mice were obtained from Dr. Dorn, Washington University, St. Louis. Briefly, postnatal mice between P0 and P6 were sacrificed by decapitation.…”