TOR complex 2 in fission yeast is required for chromatin-mediated gene silencing and assembly of heterochromatic domains at subtelomeres

J Biol Chem. 2018 May 25;293(21):8138-8150. doi: 10.1074/jbc.RA118.002270. Epub 2018 Apr 9.

Abstract

The conserved serine/threonine protein kinase target of rapamycin (TOR) is a major regulator of eukaryotic cellular and organismal growth and a valuable target for drug therapy. TOR forms the core of two evolutionary conserved complexes, TOR complex 1 (TORC1) and TORC2. In the fission yeast Schizosaccharomyces pombe, TORC2 responds to glucose levels and, by activating the protein kinase Gad8 (an orthologue of human AKT), is required for well-regulated cell cycle progression, starvation responses, and cell survival. Here, we report that TORC2-Gad8 is also required for gene silencing and the formation of heterochromatin at the S. pombe mating-type locus and at subtelomeric regions. Deletion of TORC2-Gad8 resulted in loss of the heterochromatic modification of histone 3 lysine 9 dimethylation (H3K9me2) and an increase in euchromatic modifications, including histone 3 lysine 4 trimethylation (H3K4me3) and histone 4 lysine 16 acetylation (H4K16Ac). Accumulation of RNA polymerase II (Pol II) at subtelomeric genes in TORC2-Gad8 mutant cells indicated a defect in silencing at the transcriptional level. Moreover, a concurrent decrease in histone 4 lysine 20 dimethylation (H4K20me2) suggested elevated histone turnover. Loss of gene silencing in cells lacking TORC2-Gad8 is partially suppressed by loss of the anti-silencer Epe1 and fully suppressed by loss of the Pol II-associated Paf1 complex, two chromatin regulators that have been implicated in heterochromatin stability and spreading. Taken together, our findings suggest that TORC2-Gad8 signaling contributes to epigenetic stability at subtelomeric regions and the mating-type locus in S. pombe.

Keywords: Akt PKB; Epe1; Paf1 complex; Schizosaccharomyces pombe; TORC2; gene expression; gene silencing; heterochromatin; mating-type locus; subtelomeres.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Chromatin / genetics*
  • Chromatin / metabolism
  • Gene Silencing*
  • Heterochromatin / genetics*
  • Heterochromatin / metabolism
  • Histones / genetics
  • Histones / metabolism
  • Mechanistic Target of Rapamycin Complex 2 / genetics*
  • Mechanistic Target of Rapamycin Complex 2 / metabolism
  • Multiprotein Complexes / genetics
  • Multiprotein Complexes / metabolism
  • Phosphorylation
  • Protein-Serine-Threonine Kinases / genetics*
  • Protein-Serine-Threonine Kinases / metabolism
  • Schizosaccharomyces / genetics*
  • Schizosaccharomyces / growth & development
  • Schizosaccharomyces / metabolism
  • Schizosaccharomyces pombe Proteins / genetics*
  • Schizosaccharomyces pombe Proteins / metabolism
  • Telomere / genetics*
  • Telomere / metabolism

Substances

  • Chromatin
  • Heterochromatin
  • Histones
  • Multiprotein Complexes
  • Schizosaccharomyces pombe Proteins
  • Gad8 protein, S pombe
  • Mechanistic Target of Rapamycin Complex 2
  • Protein-Serine-Threonine Kinases