Isolation and characterization of bypass mutant alleles of Gad8, the AGC kinase downstream of TORC2

Target of rapamycin (TOR) is an evolutionary conserved serine/threonine kinase that coordinates cell growth and proliferation in response to environmental changes and stress. The fission yeast Schizosaccharomyces pombe contains two TOR kinases; Tor2 mainly acts as the catalytic subunit of TORC1, while Tor1 mainly acts as the catalytic subunit of TORC2. Most studies have dealt with TOR complex 1 (TORC1), which is the target of the anticancer drug, rapamycin. The cellular functions of TORC2 are less well understood. This is partly due to the fact that- in contrast to TORC1, there are no specific inhibitors of TORC2. Accumulating data revealed that most of the cellular functions of S. pombe TORC2 are mediated via the phosphorylation and activation of the AGC kinase Gad8. In our study, we isolated mutant alleles of Gad8, which bypass the need for phosphorylation by Tor1 and suppress most of the defective phenotypes of Δtor1 mutant cells. Using these mutant alleles of Gad8 we are planning to screen for small molecules that inhibit wild type, but not gad8-bypass mutant strains. Such screens are expected to reveal TORC2- specific inhibitors. Deregulation of mTOR, as part of TORC2, is linked to cancer. Therefore investigation of bypass mutant allele of Gad8 can help us to better understand the role of TORC2 in cancer.