Metabolic utilization of exogenous pyruvate by mutant p53 (R175H) human melanoma cells promotes survival under glucose depletion.

Dominant-negative (DN) p53 mutations in the tumor suppressor p53 gene partly contribute to human cancer progression by inactivating the remaining wild type allele. Since tumor cells face glucose and growth factor shortage when growing distant from sites of vascularization, we used genetically-matched human C8161 melanoma harbouring wt p53 or a tumor-associated (DN) mutant p53 (R175H), to investigate whether this mutation influences survival under metabolic stress. Metabolic restriction (18 hours in glucose-free medium plus 2% serum) induced apoptosis-associated PARP cleavage in wt p53 melanoma, even when supplemented with 2.77 mM pyruvate or lactate. Mutant p53 melanoma were resistant to a comparable metabolic restriction, only showing PARP fragmentation when glucose depletion was accompanied by treatment with diphenylene iodonium (DPI), a NADPH oxidase inhibitor of superoxide (O2*-) generation. DPI-mediated apoptosis in mutant p53 cells was counteracted by 2.77 mM glucose or pyruvate, but not by lactate supplementation. Metabolic utilization and survival under glucose depletion was increased by pyruvate in mutant p53 (R175H) cells. Our results show for the first time that melanoma cells harbouring a p53 (R175H) mutation increase: a) survival under glucose depletion, counteracted by NADPH-oxidase modulators like DPI; b) resistance to DPI when supplemented with exogenous pyruvate.