The AMPK-TORC1 signalling axis regulates caffeine-mediated DNA damage checkpoint override and cell cycle effects in fission yeast

Abstract

AbstractCaffeine is among the most widely consumed neuroactive compounds in the world. It induces DNA damage checkpoint signalling override and enhances sensitivity to DNA damaging agents. However, the precise underlying mechanisms have remained elusive. The Ataxia Telangiectasia Mutated (ATM) orthologue Rad3 has been proposed as the cellular target of caffeine. Nevertheless, recent studies suggest that the Target of Rapamycin Complex 1 (TORC1) might be the main target. In the fission yeastSchizosaccharomyces pombe(S. pombe), caffeine mimics the effects of activating the Sty1-regulated stress response and the AMP-Activated Protein Kinase (AMPK) homologue Ssp1-Ssp2 pathways on cell cycle progression. Direct inhibition of TORC1 with the ATP-competitive inhibitor torin1, is sufficient to override DNA damage checkpoint signalling. It is, therefore, plausible, that caffeine modulates cell cycle kinetics by indirectly suppressing TORC1 through activation of Ssp2. Deletion ofssp1andssp2suppresses the effects of caffeine on cell cycle progression. In contrast, direct inhibition of TORC1 enhances DNA damage sensitivity in these mutants. These observations suggest that caffeine overrides DNA damage signalling, in part, via the indirect inhibition of TORC1 through Ssp2 activation. The AMPK-mTORC1 signalling axis plays an important role in aging and disease and presents a potential target for chemo- and radio-sensitization. Our results provide a clear understanding of the mechanism of how caffeine modulates cell cycle progression in the context of Ssp1-AMPKαSsp2-TORC1 signalling activities and can potentially aid in the development of novel dietary regimens, therapeutics, and chemo-sensitizing agents.