RESUMO
Smc5/6, like cohesin and condensin, is a structural maintenance of chromosomes complex crucial for genome stability. Unlike cohesin and condensin, Smc5/6 carries an essential Nse2 subunit with SUMO E3 ligase activity. While screening for new DNA replication checkpoint mutants in fission yeast, we have identified two previously uncharacterized mutants in Smc5/6. Characterization of the mutants and a series of previously reported Smc5/6 mutants uncovered that sumoylation of the RecQ helicase Rqh1 by Nse2 facilitates the checkpoint signaling at the replication fork. We found that mutations that eliminate the sumoylation sites or the helicase activity of Rqh1 compromised the checkpoint signaling similar to a nse2 mutant lacking the ligase activity. Surprisingly, introducing a sumoylation site mutation to a helicase-inactive rqh1 mutant promoted cell survival under stress. These findings, together with other genetic data, support a mechanism that sumoylation of Rqh1 by Smc5/6-Nse2 recruits Rqh1 or modulates its helicase activity at the fork to facilitate the checkpoint signaling. Since the Smc5/6 complex, Rqh1, and the replication checkpoint are conserved in eukaryotes, a similar checkpoint mechanism may be operating in human cells.
Assuntos
Proteínas de Schizosaccharomyces pombe , Schizosaccharomyces , Proteínas Mutadas de Ataxia Telangiectasia/genética , Proteínas de Ciclo Celular/metabolismo , Quinase do Ponto de Checagem 2 , Proteínas Cromossômicas não Histona/genética , Cromossomos/metabolismo , Dano ao DNA , DNA Helicases/genética , Replicação do DNA , Humanos , Mutação/genética , RecQ Helicases/genética , Schizosaccharomyces/genética , Schizosaccharomyces/metabolismo , Proteínas de Schizosaccharomyces pombe/genética , Proteínas de Schizosaccharomyces pombe/metabolismo , SumoilaçãoRESUMO
DNA replication checkpoint is a cell signaling pathway that is activated in response to perturbed replication. Although it is crucial for maintaining genomic integrity and cell survival, the exact mechanism of the checkpoint signaling remains to be understood. Emerging evidence has shown that RecQ helicases, a large family of helicases that are conserved from bacteria to yeasts and humans, contribute to the replication checkpoint as sensors, adaptors, or regulation targets. Here, we highlight the multiple functions of RecQ helicases in the replication checkpoint in four model organisms and present additional evidence that fission yeast RecQ helicase Rqh1 may participate in the replication checkpoint as a sensor.
Assuntos
Pontos de Checagem do Ciclo Celular/genética , DNA Helicases/genética , Replicação do DNA/genética , RecQ Helicases/genética , Proteínas de Schizosaccharomyces pombe/genética , Humanos , Schizosaccharomyces/genética , Transdução de Sinais/genéticaRESUMO
Rad3 is the orthologue of ATR and the sensor kinase of the DNA replication checkpoint in Schizosaccharomyces pombe Under replication stress, it initiates checkpoint signaling at the forks necessary for maintaining genome stability and cell survival. To better understand the checkpoint initiation process, we have carried out a genetic screen in fission yeast by random mutation of the genome, looking for mutants defective in response to the replication stress induced by hydroxyurea. In addition to the previously reported mutant with a C-to-Y change at position 307 encoded by tel2 (tel2-C307Y mutant) (Y.-J. Xu, S. Khan, A. C. Didier, M. Wozniak, et al., Mol Cell Biol 39:e00175-19, 2019, https://doi.org/10.1128/MCB.00175-19), this screen has identified six mutations in rqh1 encoding a RecQ DNA helicase. Surprisingly, these rqh1 mutations, except for a start codon mutation, are all in the helicase domain, indicating that the helicase activity of Rqh1 plays an important role in the replication checkpoint. In support of this notion, integration of two helicase-inactive mutations or deletion of rqh1 generated a similar Rad3 signaling defect, and heterologous expression of human RECQ1, BLM, and RECQ4 restored the Rad3 signaling and partially rescued a rqh1 helicase mutant. Therefore, the replication checkpoint function of Rqh1 is highly conserved, and mutations in the helicase domain of these human enzymes may cause the checkpoint defect and contribute to the cancer predisposition syndromes.
Assuntos
Quinase do Ponto de Checagem 2/metabolismo , DNA Helicases/metabolismo , Replicação do DNA , DNA Fúngico/biossíntese , Proteínas de Schizosaccharomyces pombe/metabolismo , Pontos de Checagem do Ciclo Celular/efeitos dos fármacos , Proteínas de Ciclo Celular/metabolismo , Quinase do Ponto de Checagem 2/genética , DNA Helicases/genética , DNA Fúngico/genética , DNA Fúngico/metabolismo , Instabilidade Genômica , Hidroxiureia/farmacologia , Proteínas Quinases/metabolismo , RecQ Helicases/genética , RecQ Helicases/metabolismo , Schizosaccharomyces/metabolismo , Proteínas de Schizosaccharomyces pombe/genética , Transdução de Sinais/efeitos dos fármacosRESUMO
With roles in DNA repair, recombination, replication and transcription, members of the RecQ DNA helicase family maintain genome integrity from bacteria to mammals. Mutations in human RecQ helicases BLM, WRN and RecQL4 cause incurable disorders characterized by genome instability, increased cancer predisposition and premature adult-onset aging. Yeast cells lacking the RecQ helicase Sgs1 share many of the cellular defects of human cells lacking BLM, including hypersensitivity to DNA damaging agents and replication stress, shortened lifespan, genome instability and mitotic hyper-recombination, making them invaluable model systems for elucidating eukaryotic RecQ helicase function. Yeast and human RecQ helicases have common DNA substrates and domain structures and share similar physical interaction partners. Here, we review the major cellular functions of the yeast RecQ helicases Sgs1 of Saccharomyces cerevisiae and Rqh1 of Schizosaccharomyces pombe and provide an outlook on some of the outstanding questions in the field.