G6PD-mediated increase in de novo NADP+ biosynthesis promotes antioxidant defense and tumor metastasis

Abstract

Metastasizing cancer cells are able to withstand high levels of oxidative stress through mechanisms that are poorly understood. Here, we show that under various oxidative stress conditions, pancreatic cancer cells markedly expand NADPH and NADP+ pools. This expansion is due to up-regulation of glucose-6-phosphate dehydrogenase (G6PD), which stimulates the cytoplasmic nicotinamide adenine dinucleotide kinase (NADK1) to produce NADP+ while converting NADP+ to NADPH. G6PD is activated by the transcription factor TAp73, which is, in turn, regulated by two pathways. Nuclear factor–erythroid 2 p45-related factor-2 suppresses expression of the ubiquitin ligase PIRH2, stabilizing the TAp73 protein. Checkpoint kinases 1/2 and E2F1 induce expression of the TAp73 gene. Levels of G6PD and its upstream activators are elevated in metastatic pancreatic cancer. Knocking down G6PD impedes pancreatic cancer metastasis, whereas forced G6PD expression promotes it. These findings reveal an intracellular network that maintains redox homeostasis through G6PD-mediated increase in de novo NADP+ biosynthesis, which may be co-opted by tumor cells to enable metastasis.