Abstract 3994: Recruitment of p53 to Mitochondrial VDAC1 Triggers Autophagy of Ventricular Myocytes During Metabolic Stress
Autophagy is an evolutionary conserved process that allows cells’ to recycle their macromolecular constituents during times of cellular stress. Autophagy has been detected in several cardiac pathologies including ischemia-reperfusion, hypoxia and the myocardial infarct border zone. Though little is known of the cellular factors that govern autophagy recent evidence has implicated the mitochondrion as a central underlying feature. In this report we show that metabolic stress imposed by nutrient deprivation or hypoxia triggers p53 gene expression and p53 protein stabilization by HIF-1. During nutrient deprivation or hypoxia p53 is actively recruited to mitochondrial outer membrane where it provokes mitochondrial defects consistent with the loss of membrane potential, permeability transition pore opening (MPTP). Localization of p53 to mitochondrial membranes increased the conversion of the autophagy marker LC3BII to LC3BI with a corresponding 7 fold increase (p<0.05) in autophagosome formation as indicated by punctate LC3-GFP staining. Cell fractionation experiments revealed p53 localized to the mitochondrial compartment and associated with the outer mitochondrial membrane protein VDAC1 but not VDAC2 or VDAC3 in a manner dependent on the BH3 only protein Bnip3. Interestingly, adenovirus mediated delivery of siRNA directed against Bnip3 or a carboxyl terminal domain mutant of Bnip3 defective for mitochondrial targeting, independently suppressed mitochondrial p53- VDAC 1 interactions in ventricular myocytes. Notably, autophagy induced by p53 was also abrogated in cells rendered defective for Bnip3 or VDAC1. To our knowledge our data provide the first direct evidence that stabilization of p53 by HIF-1 during metabolic stress provokes mitochondrial defects and autophagy in ventricular myocytes. We further show that recruitment of p53 to mitochondrial VDAC 1 is dependent upon Bnip3 and crucial for induction of autophagy. Our data highlights a novel relationship between the tumor suppressor function of p53 and Bnip3 that may explain how cells, by actively undergoing autophagy avert apoptosis during times of cellular stress.