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PolySUMOylation restrains ubiquitination to protect fragile genomic loci during replication stress in fission yeast

ABSTRACT: Formation of polymeric SUMO chains, polySUMOylation, is an emerging regulator of genome stability beyond its role in proteasomal targeting. Using Schizosaccharomyces pombe, we show that cells devoid of SUMO chains experience elevated, spontaneous replication stress concentrated at rDNA, accompanied by excessive recruitment of the recombination factor Rad52, independently from PCNA-K164 ubiquitination signaling. PolySUMOylation promotes completion of replication following hydroxyurea-induced stress in the absence of recombination. Loss of SUMO chains leads to a global increase in ubiquitination and a shift in toward K63-linked ubiquitin chains. Proteomic analyses identify shared and distinct targets of Nse2 and Pli1 E3 SUMO ligases, suggesting Pli1 role at specific genomic loci such as rDNA. Chromatin mapping demonstrated enrichment of both ligases at rDNA, centromeres, telomeres, and other fragile genomic regions. We propose that sequential monoSUMOylation and Pli1-dependent SUMO chain formation occur on chromatin to limit excessive ubiquitination, which protects vulnerable genomic loci from replication-associated instability.

ORGANISM(S): Schizosaccharomyces pombe

PROVIDER: GSE329309 | GEO | 2026/04/29

REPOSITORIES: GEO

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Project description:Genomic instability associated with DNA replication stress is linked to cancer and genetic pathologies in humans. If not properly regulated, replication stress, such as fork stalling and collapse, can be induced at natural replication impediments present throughout the genome. The fork protection complex (FPC) is thought to play a critical role in stabilizing stalled replication forks at several known replication barriers including eukaryotic rDNA genes and the fission yeast mating-type locus. However, little is known about the role of the FPC at other natural impediments including telomeres. Telomeres are considered to be difficult to replicate due to the presence of repetitive GT-rich sequences and telomere-binding proteins. However, the regulatory mechanism that ensures telomere replication is not fully understood. Here, we report the role of the fission yeast Swi1/Timeless, a subunit of the FPC, in telomere replication. Loss of Swi1 causes telomere shortening in a telomerase-independent manner. Our epistasis analyses suggest that heterochromatin and telomere-binding proteins are not major impediments for telomere replication in the absence of Swi1. Instead, repetitive DNA sequences impair telomere integrity in swi1Î mutant cells, leading to the loss of repeat DNA. In the absence of Swi1, telomere shortening is accompanied with an increased recruitment of Rad52 recombinase and more frequent amplification of telomere/subtelomeres, reminiscent of tumor cells that utilize the alternative lengthening of telomeres pathway (ALT) to maintain telomeres. These results suggest that Swi1 ensures telomere replication by suppressing recombination and repeat instability at telomeres. Our studies may also be relevant in understanding the potential role of the FPC in regulation of telomere stability in cancer cells. Genome-wide distributions of Rad52 in wild type and in swi1 deletion in fission yeast The'SP1173_WT ChIP-seq' is an input sample (non-tagged data).

Project description:NguyenLK2011 - Ubiquitination dynamics in Ring1B-Bmi1 system This theoretical model investigates the dynamics of Ring1B/Bmi1 ubiquitination to identify bistable switch-like and oscillatory behaviour in the system. Michaelis-Menten (MM) equations are used to formulate the model. However, the authors show that the dynamics persist even for Mass-Action kinetics. This SBML file is the MM version of the model. This model is described in the article: Switches, excitable responses and oscillations in the Ring1B/Bmi1 ubiquitination system. Nguyen LK, Muñoz-García J, Maccario H, Ciechanover A, Kolch W, Kholodenko BN. PLoS Comput. Biol. 2011 Dec; 7(12): e1002317 Abstract: In an active, self-ubiquitinated state, the Ring1B ligase monoubiquitinates histone H2A playing a critical role in Polycomb-mediated gene silencing. Following ubiquitination by external ligases, Ring1B is targeted for proteosomal degradation. Using biochemical data and computational modeling, we show that the Ring1B ligase can exhibit abrupt switches, overshoot transitions and self-perpetuating oscillations between its distinct ubiquitination and activity states. These different Ring1B states display canonical or multiply branched, atypical polyubiquitin chains and involve association with the Polycomb-group protein Bmi1. Bistable switches and oscillations may lead to all-or-none histone H2A monoubiquitination rates and result in discrete periods of gene (in)activity. Switches, overshoots and oscillations in Ring1B catalytic activity and proteosomal degradation are controlled by the abundances of Bmi1 and Ring1B, and the activities and abundances of external ligases and deubiquitinases, such as E6-AP and USP7. This model is hosted on BioModels Database and identified by: BIOMD0000000622. To cite BioModels Database, please use: BioModels Database: An enhanced, curated and annotated resource for published quantitative kinetic models. To the extent possible under law, all copyright and related or neighbouring rights to this encoded model have been dedicated to the public domain worldwide. Please refer to CC0 Public Domain Dedication for more information.

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PolySUMOylation restrains ubiquitination to protect fragile genomic loci during replication stress in fission yeast

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