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

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

Author information

1
From the Department of Natural and Life Sciences, Open University of Israel, University Road 1, 4353701 Ranana, Israel and.
2
the Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv 69977801, Tel Aviv, Israel.
3
From the Department of Natural and Life Sciences, Open University of Israel, University Road 1, 4353701 Ranana, Israel and ronitwe@openu.ac.il.

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

PMID:
29632066
PMCID:
PMC5971458
DOI:
10.1074/jbc.RA118.002270
[Indexed for MEDLINE]
Free PMC Article

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