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Convergence of SIRT1 and ATR signaling to modulate replication origin dormancy

ABSTRACT: During routine genome duplication, many potential replication origins remain inactive, or dormant. Such origin dormancy is achieved, in part, by an interaction with the metabolic sensor SIRT1 deacetylase. We report here that dormant origins are a group of consistent, pre-determined genomic sequences that can be distinguished from baseline (i.e. ordinarily active) origins by their preferential association with MCM2, a component of the replicative helicase, phosphorylated on serine 108 (pS108-MCM2). pS108-MCM2 is a substrate of the ATR kinase, which is recruited to chromatin via an interaction with hyperacetylated TOPBP1 in cells undergoing replication stress or in cells devoid of SIRT1 deacetylase activity. In turn, S108-MCM2 phosphorylation enhances a second, DDK-dependent, S139-MCM2 phosphorylation, which triggers initiation of DNA replication at dormant origins. These observations suggest that replication origin dormancy and activation are regulated by distinct post-translational modifications on the MCM helicase that reflect a balance between SIRT1 activity and ATR signaling.

INSTRUMENT(S): Q Exactive HF

ORGANISM(S): Homo Sapiens (ncbitaxon:9606)

SUBMITTER: Mirit Aladjern

PROVIDER: MSV000088134 | MassIVE |

REPOSITORIES: MassIVE

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Convergence of SIRT1 and ATR signaling to modulate replication origin dormancy

Project description:During routine genome duplication, many potential replication origins remain inactive, or 'dormant'. Such origin dormancy is achieved, in part, by an interaction with the metabolic sensor SIRT1 deacetylase. We report here that dormant origins are a group of consistent, pre-determined genomic sequences that can be distinguished from baseline (i.e. ordinarily active) origins by their preferential association with MCM2, a component of the replicative helicase, phosphorylated on serine 108 (pS108-MCM2). pS108-MCM2 is a substrate of the ATR kinase, which is recruited to chromatin via an interaction with hyperacetylated TOPBP1 in cells undergoing replication stress or in cells devoid of SIRT1 deacetylase activity. In turn, S108-MCM2 phosphorylation enhances a second, DDK-dependent, S139-MCM2 phosphorylation, which triggers initiation of DNA replication at dormant origins. These observations suggest that replication origin dormancy and activation are regulated by distinct post-translational modifications on the MCM helicase that reflect a balance between SIRT1 activity and ATR signaling.

2022-05-09 | GSE184353 | GEO

Phosphorylated SIRT1 associates with replication origins to prevent excess replication initiation and preserve genomic stability

Project description:Chromatin structure affects DNA replication patterns, but the role of specific chromatin modifiers in regulating the replication process is yet unclear. We report that phosphorylation of the human SIRT1 deacetylase on Threonine 530 (T530-pSIRT1) modulates DNA synthesis. T530-pSIRT1 associates with replication origins and inhibits replication from a group of ÒdormantÓ potential replication origins, which initiate replication only when cells are subject to replication stress. Although both active and dormant origins bind T530-pSIRT1, active origins are distinguished from dormant origins by their unique association with an open chromatin mark, histone H3 methylated on lysine 4. SIRT1 phosphorylation also facilitates leading and lagging strand coordination. SIRT1 T530 phosphorylation is essential to prevent DNA breakage upon replication stress and cells harboring SIRT1 that cannot be phosphorylated exhibit a high prevalence of extrachromosomal elements, hallmarks of perturbed replication. These observations suggest that SIRT1 phosphorylation modulates the distribution of replication initiation events to insure genomic stability.

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H4S47 O-GlcNAcylation regulates the activation of mammalian replication origins

Project description:The transmission and maintenance of genetic information in eukaryotic cells rely on the faithful duplication of the entire genome. In each round of division, excessive replication origiNS are licensed, while only a fraction is activated to give rise to bi-directional replication forks travelling in the context of chromatin. However, it remaiNS elusive how eukaryotic replication origiNS are selectively activated. Here we demoNStrate that O-GlcNAc traNSferase (OGT) enhances replication initiation by catalysing H4S47 O-GlcNAcylation. Mutation of H4S47 impairs DBF4-dependent protein kinase (DDK) recruitment on chromatin, causing compromised phosphorylation of replicative helicase mini-chromosome maintenance (MCM) complex. Meanwhile, our short nascent-strand sequencing (SNS-seq) confirms the important role of H4S47 O-GlcNAcylation in origin activation. Together, H4S47 O-GlcNAcylation directs origin activation through facilitating MCM phosphorylation, and this may shed light on the spatial and temporal control of DNA replication by the dynamically changing chromatin environment.

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Post-licensing specification of eukaryotic replication origins by facilitated Mcm2-7 sliding along DNA

Project description:Eukaryotic genomes are replicated from many origin sites that are licensed by the loading of inactive double hexamers of the replicative DNA helicase, Mcm2-7. How eukaryotic origin positions are specified remains elusive. Here we show that, contrary to the bacterial paradigm, eukaryotic origins are not irrevocably defined by selection of the loading site for the replicative helicase, but can shift in position after helicase loading. Using purified proteins, we show that DNA translocases, including RNA polymerase, can push budding yeast Mcm2-7 double hexamers along DNA. Displaced Mcm2-7 double hexamers support DNA replication initiation distal to the loading site in vitro. In yeast cells that are defective for transcription termination, collisions with RNA polymerase induce a shift in origin positions that correlates with the direction of transcription. These results reveal a eukaryotic origin specification mechanism that departs from the classical replicon model, helping eukaryotic cells to negotiate transcription-replication conflict.

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Post-licensing specification of eukaryotic replication origins by facilitated Mcm2-7 sliding along DNA

2016-01-07 | E-GEOD-69065 | biostudies-arrayexpress

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Checkpoint-independent Regulation of Origin Firing by Mrc1 through Interaction with Hsk1 kinase

Project description:Mrc1 is a conserved checkpoint mediator protein that transduces replication-stress signal to downstream effector kinase. Loss of mrc1 checkpoint activity results in aberrant activation of late/dormant origins in the presence of hydroxyurea. Mrc1 was also suggested to regulate orders of early-origin firing in a checkpoint-independent manner, but its mechanism was unknown. Here we identify HBS (Hsk1 Bypass Segment) on Mrc1. ∆HBS does not suppress late/dormant origin firing in the presence of hydroxyurea but causes precocious and enhanced activation of weak early-firing origins during normal S-phase progression, and bypasses the requirement of Hsk1 for growth. This may be caused by disruption of intramolecular binding between HBS and NTHBS (N-terminal-Target-of-HBS). Hsk1 binds to Mrc1 through HBS and phosphorylates a segment adjacent to NTHBS, disrupting intramolecular interaction. We propose that Mrc1 exerts “brake” on initiation (through intra-molecular interaction) and this brake can be released (upon loss of intra-molecular interaction) by either Hsk1-mediated phosphorylation of Mrc1 or deletion of HBS (or phosphomimic mutation) which can bypass the function of Hsk1 for growth. The “brake” mechanism may explain the checkpoint-independent regulation of early origin firing in fission yeast.

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Project description:We have comprehensively explored the origin utilisation in Haloferax mediterranei. Here we report three active chromosomal origins by genome-wide replication profiling, and demonstrate that when these three origins are deleted, a dormant origin becomes activated.

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Project description:A potential origin that appears to stay dormant in its native host Haloferax volcanii lacking the main active origins becomes activated and competent for replication of the entire chromosome when integrated into the chromosome of the origin-deleted H. mediterranei. Measurement of replication dynamics (marker frequency analysis; MFA) for Haloferax mediterranei H13

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