Overexpression of BH3-Only Protein BNIP3 Leads to Enhanced Tumor Growth

Abstract

BCL-2/E1B-19 kDa-interacting protein 3 (BNIP3) is a BH3-only mitochondrial protein. Expression of BNIP3 is strongly stimulated by hypoxia. Up-regulation of BNIP3 has been detected in several human carcinomas including carcinomas of the lung and breast. The significance of BNIP3 overexpression in these cancers is not known. To determine whether BNIP3 plays a role in tumor growth, we generated A549 lung carcinoma cells that overexpressed BNIP3 and examined their ability to form tumors in the mouse xenograft model. All cell lines that overexpressed BNIP3 formed larger tumors compared to the parental or vector-transformed A549 cells. Breast carcinoma cell lines that overexpressed BNIP3 also induced tumors in athymic mice in the absence of hormone administration, while the parental cell line did not. Stable shRNA-mediated knockdown of endogenous BNIP3 severely impaired the tumorigenic activity of A549 cells. The tumor growth-enhancing activity was reduced by deletion of the BH3 domain of BNIP3. Expression of a dominant-negative mutant of BNIP3 lacking the C-terminal transmembrane domain also inhibited the tumorigenic potential of A549 cells. These results suggest that BNIP3 plays a fundamental role in the development of certain solid tumors such as the lung and breast carcinomas.

Phosphorylation of the BNIP3 C-Terminus Inhibits Mitochondrial Damage and Cell Death without Blocking Autophagy

“…Notably, a significant increase in cell death was observed in hypoxic control cells (no exogenous BNIP3), reflecting expression of endogenous BNIP3 during hypoxia [ 36 , 38 ]. As expected, co-expression of endogenous WT BNIP3 with exogenous ΔTM BNIP3 prevented hypoxia-induced cell death due to the known action of ΔTM BNIP3 as a dominant negative form of BNIP3 [ 33 , 36 ]. Interestingly, cells expressing 6D BNIP3 were protected from the effect of endogenous BNIP3, suggesting that this phosphomimetic BNIP3 mutant blocks the cytotoxic effects of WT BNIP3 in a manner similar to dominant negative ΔTM BNIP3 ( Fig 5D ).…”

“…Treatment of cells with 8-Bromo-cAMP increased the amount of BNIP3 detected with this antibody, indicating increased phosphorylation of T188 in response to elevated cAMP ( Fig 1A ). An increase in T188 phosphorylation of endogenous BNIP3 was also observed upon elevation of cAMP in A549, MDA-MB-231, and AU565 cells, all of which are solid tumor cancer cell lines that express endogenous BNIP3 ( Fig 1A ) [ 33 , 34 ]. Furthermore, tandem mass spectrometry of His-tagged BNIP3 purified from HEK 293 cells pretreated with 8-Bromo-cAMP identified multiple C-terminal BNIP3 phosphopeptides, each containing four phosphate groups (Fig 1B and 1C ).…”

“…This is particularly the case in oncology, where it is observed that in some cancers, such as pancreatic, gastric, and colorectal cancers, BNIP3 expression is suppressed or silenced by DNA methylation [ 54 , 55 ], suggesting that the cells have blocked BNIP3 expression to evade cell death. In other cases, including endometrial, breast, and lung cancers, high BNIP3 expression is associated with poorer prognosis and a more aggressive phenotype [ 33 , 56 – 58 ].…”

A Membrane-Type-1 Matrix Metalloproteinase (MT1-MMP) – Discoidin Domain Receptor 1 Axis Regulates Collagen-Induced Apoptosis in Breast Cancer Cells

“…Finally, BNIP3 ( S12 Fig. ) was associated with protective autophagy, cell survival [ 76 , 77 ] and enhanced tumour growth [ 78 ].…”

Dysregulation of autophagy in human follicular lymphoma is independent of overexpression of BCL-2

“…Only one gene, BNIP3, showed significantly decreased expression in both FL and DLBCL B-cells. BNIP3 is a hypoxia-dependent autophagy inducer and its expression is suppressed in many types of cancer [ 28 ] but overexpressed in lung and breast carcinomas [ 29 ]. Gene expression patterns in both FL and DLBCL were not associated with Ann Arbor stage or international prognostic index (IPI) scores (data not shown).…”