Genetic defects in SAPK signalling, chromatin regulation, vesicle transport and CoA-related lipid metabolism are rescued by rapamycin in fission yeast

Abstract

Rapamycin inhibits TOR (target of rapamycin) kinase, and is being used clinically to treat various diseases ranging from cancers to fibrodysplasia ossificans progressiva. To understand rapamycin mechanisms of action more comprehensively, 1014 temperature-sensitive (ts) fission yeast (Schizosaccharomyces pombe) mutants were screened in order to isolate strains in which the ts phenotype was rescued by rapamycin. Rapamycin-rescued 45 strains, among which 12 genes responsible for temperature sensitivity were identified. These genes are involved in stress-activated protein kinase (SAPK) signalling, chromatin regulation, vesicle transport, and CoA- and mevalonate-related lipid metabolism. Subsequent metabolome analyses revealed that rapamycin upregulated stress-responsive metabolites, while it downregulated purine biosynthesis intermediates and nucleotide derivatives. Rapamycin alleviated abnormalities in cell growth and cell division caused by sty1 mutants (Δsty1) of SAPK. Notably, in Δsty1, rapamycin reduced greater than 75% of overproduced metabolites (greater than 2× WT), like purine biosynthesis intermediates and nucleotide derivatives, to WT levels. This suggests that these compounds may be the points at which the SAPK/TOR balance regulates continuous cell proliferation. Rapamycin might be therapeutically useful for specific defects of these gene functions.

The fission yeast Greatwall–Endosulfine pathway is required for proper quiescence/G0 phase entry and maintenance

“…Upon nitrogen deprivation, ∆mug134 cells showed phenotypes similar to that of ∆cek1∆ppk18 and ∆cek1∆ppk18∆ppk31 cells: ∆mug134 cells divided less than twice, possessed 2C DNA content and were unable to maintain long‐term viability (Figure f–i). These results are consistent with previous results (Sajiki, Tahara, Villar‐Briones et al, ) and suggest that Mug134 is indispensable for entry into the G 0 phase and in sustaining long‐term viability as in the case of Gwl‐like kinases.…”

“…In metazoa, Gwl kinase phosphorylates α‐endosulfine/ARPP‐19 (Ensa), and phosphorylated Ensa directly binds to and inhibits PP2A B55 (Gharbi‐Ayachi et al, ; Mochida et al, ). Recently, Sajiki, Tahara, Villar‐Briones et al ()) isolated S. pombe Mug134, an ortholog of Ensa, and identified it as a protein required for G 0 phase induction by nitrogen starvation. As the S. pombe Gwl‐like kinases, Ppk18 and Cek1, have been shown to be involved in regulating the G 0 phase entry and maintenance, we analyzed the phenotypes of mug134 ‐deficient cells in −N condition.…”

“…Mutants of Sty1/Spc1 and Wis1, which are homologues of mitogen-activated protein kinase (MAPK) and MAPKK, respectively, are defective in proper entry into the G 0 phase. These mutants are unable to cease cell growth, arrest with 1C DNA and sustain viability after nitrogen withdrawal (Sajiki et al, 2009;Sajiki, Tahara, Villar-Briones et al, 2018). TORC2 and Gad8, a downstream effector kinase of TORC2, were also reported to be required for cells to arrest with 1C DNA under −N and sexual differentiation (Ikeda, Morigasaki, Tatebe, Tamanoi, & Shiozaki, 2008;Martin et al, 2017;Matsuo, Kubo, Watanabe, & Yamamoto, 2003).…”

S-Adenosylmethionine Synthetase Is Required for Cell Growth, Maintenance of G0 Phase, and Termination of Quiescence in Fission Yeast

“…Another possibility is that rapamycin, perhaps through TOR kinase, alters methyltransferase activity to give priority to methylation reactions essential to growth. We also identified 12 other groups of ts mutants that were rescued by rapamycin (Sajiki et al., 2018); thus, perhaps Sam1 with some methyltransferases, composes an additional group. According to the report proposing that rapamycin re-balances TOR activity with the activities of identified gene products (Sajiki et al., 2018), the balance between TOR kinase and Sam1 appears important for cell proliferation, and severe impairment of the balance blocks cell growth.…”

“…We also identified 12 other groups of ts mutants that were rescued by rapamycin (Sajiki et al., 2018); thus, perhaps Sam1 with some methyltransferases, composes an additional group. According to the report proposing that rapamycin re-balances TOR activity with the activities of identified gene products (Sajiki et al., 2018), the balance between TOR kinase and Sam1 appears important for cell proliferation, and severe impairment of the balance blocks cell growth. The detailed mechanism of this rapamycin-induced rescue should be the subject of further investigation.…”