Abstract 3797: Wildtype p53 upregulation induces contrasting bioenergetic and metabolic responses in malignant and non-malignant mammary epithelial cells (2011)

Abstract In addition to its well established genome stabilizing and tumor suppressing role, p53 can also modulate cell metabolism and mitochondrial function. Small molecule MDM2 antagonists like nutlin-3 or MI-63 (Ascenta) are therapeutic prototypes that rapidly increase wildtype (wt) p53 levels in mammalian cells inducing apoptosis in cancer cells and growth arrest or senescence in non-malignant cells. We employed MI-63 (10 uM × 24h) to induce a near 10-fold increase in p53wt protein expression and compare its mitochondrial bioenergetic and metabolic consequences in malignant (MCF7) and non-malignant (MCF10A) human mammary epithelial cells, whose fates are differentially affected by MI-63. We utilized chromatin immunopreciptation-DNA sequencing (ChIP-seq; Illumina 3G sequencer) and expression microarrays (Affymetrix U133Av2) to identify genome-wide direct and indirect p53 target genes potentially affecting MCF7 mitochondrial structure and function. Within 24h of p53wt upregulation, 1903 genes were differentially expressed including 539 of the 2239 differentially bound direct p53 gene targets, leaving 1364 differentially expressed indirect p53 target genes. While p53 binding was not detected in the mitochondrial genome, GO analysis identified genes associated with the mitochondrial matrix (3 up, 28 down) and genes associated with the outer mitochondrial membrane (7 up, 10 down) as significantly enriched among the p53 regulated nuclear targets (EASE = 0.003, FDR p = 0.03 and EASE = 0.002, FDR p = 0.02 respectively). Real-time, kinetic measurement (Seahorse XF) of oxygen consumption rates (OCR) and extracellular acidification rates (ECAR) was performed in adherent cultures of MCF7 and MCF10A cells after comparable 24 h MI-63 induction of p53wt. In contrast to the apparent inhibitory effect of p53wt induction on MCF7 transcription of mitochondrial matrix genes, basal and spare mitochondrial respiratory capacity were stimulated ∼2-fold. This p53wt induced increase in ATP supply and OCR was caused by slightly higher OXPHOS and maximal recruitment of glycolysis, assessed by ECAR and simulated by cell supplementation with pyruvate. Unlike this metabolic and bioenergetic response in the malignant MCF7 cells, p53wt upregulation in the non-malignant MCF10A cells not only failed to stimulate OCR and ECAR but significantly depressed glycolysis. While it is generally thought that the metabolic function of p53wt is to favor energy production by mitochondrial OXPHOS and resist the shift to glycolysis that is characteristically seen in cancer cells, our findings suggest that malignant and non-malignant epithelial cells may have different metabolic and bioenergetic responses to upregulated p53wt. Further studies are needed to determine if these different p53wt responses contribute to the different cell fate responses induced by MDM2 antagonists like MI-63. 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 3797. doi:10.1158/1538-7445.AM2011-3797