Abstract 228: Tumor suppressor functions of BNIP3 and mitophagy in pancreatic ductal adenocarcinoma

Abstract

Abstract The role of mitochondrial dysfunction in cancer is an emerging research field fuelled by the growing realization that mitochondrial dynamics are subject to oncogenic control, with mitochondrial biogenesis and mitophagy in particular modulated directly or indirectly by key oncogenes (c-Myc, B-Raf, K-ras) and tumor suppressors (p53, pRB). Work from our lab has focused on understanding how defects in mitophagy influence tumorigenesis with a particular focus on how BNIP3 loss during tumor progression influences disease outcome. BNIP3 functions as a dimer at the outer mitochondrial membrane to target mitochondria for degradation at the autophagolysosome through its interaction with processed LC3 at nascent phagophores. BNIP3 is a transcriptional target of HIF-1, E2F and FoxO3A transcription factors and is induced by activated Ras and suppressed by the RB and p53 tumor suppressors. Various studies have shown BNIP3 expression to be induced at early stages of human cancers and then lost as cancers progress to malignancy. In particular, epigenetic silencing of BNIP3 in human pancreas cancer has been correlated with reduced median survival. However, the mechanisms by which loss of BNIP3 may be contributing to cancer progression are not well delineated and a better understanding of how BNIP3-dependent mitophagy modulates pancreatic cancer in particular could provide new insight to the development of this deadly disease. We set out to examine how loss of BNIP3 affects the progression of pancreatic ductal adenocarcinoma using human cell lines and genetically engineered mouse models. We show that loss of BNip3 markedly accelerates tumor initiation and progression to invasive PDAC in the Pdx1-Cre;LSL-KRasG12D mouse model with metastases to the liver and lungs evident in BNip3 null mice but not in age-matched wild-type mice. Supporting a role for BNIP3 in suppressing pancreatic tumorigenesis, we also showed that re-expression of exogenous BNIP3 in Miapaca-2 cells (in which endogenous BNIP3 is silenced) resulted in reduced growth while knockdown of BNIP3 in CFPAC1 cells (that express BNIP3) promotes cell growth. Work described here examines the underlying mechanisms explaining these tumor suppressor functions of BNIP3 in pancreatic ductal adenocarcinoma. Citation Format: Aparajita H. Chourasia, Maya Z. Springer, Kay F. Macleod. Tumor suppressor functions of BNIP3 and mitophagy in pancreatic ductal adenocarcinoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 228.