Synthesis of cytochrome c oxidase 2: a p53-dependent metabolic regulator that promotes respiratory function and protects glioma and colon cancer cells from hypoxia-induced cell death

Abstract

P53 has an important role in the processing of starvation signals. P53-dependent molecular mediators of the Warburg effect reduce glucose consumption and promote mitochondrial function. We therefore hypothesized that the retention of wild-type p53 characteristic of primary glioblastomas limits metabolic demands induced by deregulated signal transduction in the presence of hypoxia and nutrient depletion. Here we report that short hairpin RNA-mediated gene suppression of wild-type p53 or ectopic expression of mutant temperature-sensitive dominant-negative p53 V135A increased glucose consumption and lactate production, decreased oxygen consumption and enhanced hypoxia-induced cell death in p53 wild-type human glioblastoma cells. Similarly, genetic knockout of p53 in HCT116 colon carcinoma cells resulted in reduced respiration and hypersensitivity towards hypoxia-induced cell death. Further, wild-type p53 gene silencing reduced the expression of synthesis of cytochrome c oxidase 2 (SCO2), an effector necessary for respiratory chain function. An SCO2 transgene reverted the metabolic phenotype and restored resistance towards hypoxia in p53-depleted and p53 mutant glioma cells in a rotenonesensitive manner, demonstrating that this effect was dependent on intact oxidative phosphorylation. Supplementation with methyl-pyruvate, a mitochondrial substrate, rescued p53 wild-type but not p53 mutant cells from hypoxic cell death, demonstrating a p53-mediated selective aptitude to metabolize mitochondrial substrates. Further, SCO2 gene silencing in p53 wild-type glioma cells sensitized these cells towards hypoxia. Finally, lentiviral gene suppression of SCO2 significantly enhanced tumor necrosis in a subcutaneous HCT116 xenograft tumor model, compatible with impaired energy metabolism in these cells. These findings demonstrate that glioma and colon cancer cells with p53 wild-type status can skew the Warburg effect and thereby reduce their vulnerability towards tumor hypoxia in an SCO2-dependent manner. Targeting SCO2 may therefore represent a valuable strategy to enhance sensitivity towards hypoxia and may complement strategies targeting glucose metabolism.

Tp53-induced Glycolysis and Apoptosis Regulator (TIGAR) Protects Glioma Cells from Starvation-induced Cell Death by Up-regulating Respiration and Improving Cellular Redox Homeostasis

“…Cell Death Analysis-Cell death was assessed by propidium iodide (PI)-FACS (31). Experiments were performed in triplicates and are presented as mean Ϯ S.D.…”

“…Oxygen Consumption-Oxygen concentration in the medium was measured using the ABL-80 FLEX blood gas analyzer (Radiometer, Willich, Germany) as described previously (31).…”

“…glucose, is also severely impaired in some regions of solid tumors (28 -30). We recently showed that WT p53 can limit glucose demands under tumor microenvironment conditions by inducing expression of synthesis of cytochrome c oxidase 2 (SCO2), ultimately promoting cellular survival (31). Resistance mechanisms toward these hypoxic and nutrientstarved conditions are considered to be important for the survival of tumor cells within a solid tumor and for the resistance to radiotherapy, surgery, and targeted therapy (32).…”

ERGO: A pilot study of ketogenic diet in recurrent glioblastoma

“…A significant decrease of ATP levels accompanied by unaltered glucose concentrations in the tumor tissue of bevacizumab-treated mice could indicate that glucose levels in the tumor are insufficient to sustain ATP production. One reason might be a lack of oxygen leading to less efficient ATP generation by suppressed oxidative phosporylation and therefore increased glucose needs (5,7,38). Microdialysis analyses have shown a correlation between systemic glucose concentrations and glucose levels within the glioma tissue (11).…”

“…There is also evidence of increased glycolysis in glioblastoma. First, malignant gliomas are characterized by activation of growth factor receptor/PI3 kinase/Akt signaling (2) leading to increased reliance on glycolysis (3) and by loss of p53 wild-type activity which can result in reduced expression of synthesis of cytochrome C oxidase 2 (SCO2), necessary for the proper assembly and function of the mitochondrial respiratory chain (4,5), and of tp53-induced glycolysis and apoptosis regular (TIGAR), which suppresses glycolysis (6,7). Second, hypoxia typically present in malignant glioma is expected to stimulate accumulation of HIF-1α and subsequent expression of genes involved in glucose metabolism and in the suppression of oxidative phosphorylation (8,9).…”