Inhibition of p38alpha unveils an AMPK-FoxO3A axis linking autophagy to cancer-specific metabolism.

Autophagy is an essential process for the maintenance of cellular and metabolic homeostasis. Indeed, it is required for the recovery of ATP-generating substrates in cells subjected to different types of stress insults. Thus, the activity of the autophagic machinery strongly depends on the metabolic status of the cell.(1) It has been proposed that this principle applies not only to normal, but also to cancer cells,(2) despite the profound differences in their metabolism. Cancer cells predominantly produce ATP through the constitutive activation of aerobic glycolysis, a process that generally relies on the stabilization and activation of the transcription factor HIF1alpha, which regulates the expression of glycolytic genes.(3) We recently showed that p38alpha is required to sustain the expression of HIF1alpha target genes, and that its inhibition causes a rapid drop in ATP levels in colorectal cancer cells (CRCs). This acute energy need triggers AMPK-dependent nuclear accumulation of FoxO3A and subsequent activation of its transcriptional program, leading to sequential induction of autophagy, cell cycle arrest and cell death. In vivo, pharmacological blockade of p38alpha has both a cytostatic and cytotoxic effect on colorectal neoplasms, associated with nuclear enrichment of FoxO3A and expression of its target genes p21 and PTEN.(4) Our data suggest that CRCs impaired in their glycolytic metabolism trigger autophagy as a reversible recovery mechanism and undergo cell cycle arrest; however, the persistence of the stress insults inevitably leads to cell death.