Caffeine Stabilises Fission Yeast Wee1 in a Rad24-Dependent Manner but Attenuates Its Expression in Response to DNA Damage

Abstract

The widely consumed neuroactive compound caffeine has generated much interest due to its ability to override the DNA damage and replication checkpoints. Previously Rad3 and its homologues was thought to be the target of caffeine’s inhibitory activity. Later findings indicate that the Target of Rapamycin Complex 1 (TORC1) is the preferred target of caffeine. Effective Cdc2 inhibition requires both the activation of the Wee1 kinase and inhibition of the Cdc25 phosphatase. The TORC1, DNA damage, and environmental stress response pathways all converge on Cdc25 and Wee1. We previously demonstrated that caffeine overrides DNA damage checkpoints by modulating Cdc25 stability. The effect of caffeine on cell cycle progression resembles that of TORC1 inhibition. Furthermore, caffeine activates the Sty1 regulated environmental stress response. Caffeine may thus modulate multiple signalling pathways that regulate Cdc25 and Wee1 levels, localisation and activity. Here we show that the activity of caffeine stabilises both Cdc25 and Wee1. The stabilising effect of caffeine and genotoxic agents on Wee1 was dependent on the Rad24 chaperone. Interestingly, caffeine inhibited the accumulation of Wee1 in response to DNA damage. Caffeine may modulate cell cycle progression through increased Cdc25 activity and Wee1 repression following DNA damage via TORC1 inhibition, as TORC1 inhibition increased DNA damage sensitivity.

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

“…As previously reported, both caffeine (10 mM) and torin1 (5 µM) override the cell cycle arrest induced by 5 µg/ mL phleomycin in wild type S. pombe cells (Figure 1A) [8]. These observations suggest that caffeine overrides DNA damage checkpoint signalling via inhibition of TORC1 activity [8]. As direct inhibition of TORC1 activity with torin1 is more effective than exposure to caffeine, the latter may exert an indirect inhibitory effect on the kinase complex.…”

“…As PP2A Pab1 regulates Cdc25 and Wee1 activity, TORC1 regulates the timing of cell division via modulation of Cdc2 activity in response to nutritional and environmental cues [16,45,46]. Direct TORC1 inhibition with torin1 mimics the effects of caffeine on cells exposed to phleomycin [8].…”

“…More recent studies indicate that caffeine inhibits TORC1 signalling in yeast and mammalian cells. Indeed, TORC1 inhibition in S. pombe is sufficient to override DNA damage checkpoint signalling [8,15]. It remains unclear, if caffeine directly inhibits TORC1 by acting as a low intensity ATP competitor or indirectly via the S. pombe AMP-Activated Protein Kinase(AMPK) Ssp2 [24,25].…”

Smurf1 Suppression Enhances Temozolomide Chemosensitivity in Glioblastoma by Facilitating PTEN Nuclear Translocation

“…Moreover, Akt shuttles between nuclear and cytoplasmic compartments and thereby carries a nuclear signal (via phosphorylation) back out to the cytoplasm (inside-out signaling) to phosphorylate its downstream targets. Inhibition of mTORC1 signaling enhances DNA damage sensitivity [ 66 ]. Thus, DNA-damage-induced Akt activation expedites crosstalk between DNA repair/genome stability and cell growth/survival pathways [ 67 ].…”

Crosstalk between the mTOR and DNA Damage Response Pathways in Fission Yeast

“…Conversely, inappropriate TORC1 inhibition under genotoxic conditions would advance cells into mitosis with unrepaired DNA, leading to a loss of viability. This is indeed the case, as both caffeine and torin1 enhance DNA damage sensitivity in S. pombe [ 96 ]. Furthermore, caffeine appears to indirectly regulate the activity of both Cdc25 and Wee1.…”