Akt1 intramitochondrial cycling is a crucial step in the redox modulation of cell cycle progression

Abstract

Akt is a serine/threonine kinase involved in cell proliferation, apoptosis, and glucose metabolism. Akt is differentially activated by growth factors and oxidative stress by sequential phosphorylation of Ser473 by mTORC2 and Thr308 by PDK1. On these bases, we investigated the mechanistic connection of H2O2 yield, mitochondrial activation of Akt1 and cell cycle progression in NIH/3T3 cell line with confocal microscopy, in vivo imaging, and directed mutagenesis. We demonstrate that modulation by H2O2 entails the entrance of cytosolic P-Akt1 Ser473 to mitochondria, where it is further phosphorylated at Thr308 by constitutive PDK1. Phosphorylation of Thr308 in mitochondria determines Akt1 passage to nuclei and triggers genomic post-translational mechanisms for cell proliferation. At high H2O2, Akt1-PDK1 association is disrupted and P-Akt1 Ser473 accumulates in mitochondria in detriment to nuclear translocation; accordingly, Akt1 T308A is retained in mitochondria. Low Akt1 activity increases cytochrome c release to cytosol leading to apoptosis. As assessed by mass spectra, differential H2O2 effects on Akt1-PDK interaction depend on the selective oxidation of Cys310 to sulfenic or cysteic acids. These results indicate that Akt1 intramitochondrial-cycling is central for redox modulation of cell fate.