Torin1 mediated TOR kinase inhibition reduces Wee1 levels and advances mitotic commitment in fission yeast and HeLa cells

Abstract

The Target Of Rapamycin TOR kinase regulates cell growth and division. Rapamycin only inhibits a subset of TOR activities. Here we show that in contrast to the mild impact of rapamycin on cell division, blocking the catalytic site of TOR with the Torin1 inhibitor completely arrests growth without cell death in S.pombe. A mutation of the Tor2 TORC1 glycine residue (G2040D) that lies adjacent to the key Torin interacting tryptophan provides Torin1 resistance, confirming Torin1's specificity for TOR. Using this mutation we show that Torin1 advanced mitotic onset before inducing growth arrest. In contrast to TOR inhibition with Rapamycin, regulation by either Wee1 or Cdc25 was sufficient for this Torin1 induced advanced mitosis. Torin1 promoted a Polo and Cdr2 kinase controlled drop in Wee1 levels. Experiments in human cell lines re-capitulated these yeast observations; mTOR was inhibited by Torin1, Wee1 levels declined and mitotic commitment was advanced in HeLa cells. Thus, the regulation of the mitotic inhibitor Wee1 by TOR signalling is a conserved mechanism that helps to couple cell cycle and growth controls.