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

Abstract

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 ‘dormant’ 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 replication fork elongation. 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.

Dynamics of replication origin over-activation

“…As shown in Fig. 6c, density plots comparing replication origin utilization in SIRT1 proficient and deficient samples clearly demonstrate that the SIRT1-deficient sample exhibited a higher level of replication origin utilization as reported 8 . In contrast, the MLN4924treated samples did not exhibit a similar bias ( Fig.…”

“…On each chromosome, replication starts at distinct regions termed replication origins, which initiate replication sequentially during S phase. DNA synthesis initiates at replication origins once the helicases incorporated into pre-replication complexes are activated, forming active replication forks 4,7,8 . As the helicases are activated, the pre-replication complex proteins responsible for recruiting helicases to chromatin are degraded, preventing the further recruitment of helicases to the genomic regions already undergoing duplication 9-12 . In metazoans, pre-replication complexes are bound to chromatin in excess, but chromosome duplication initiates only at a fraction of the many potential origins.…”

“…As the helicases are activated, the pre-replication complex proteins responsible for recruiting helicases to chromatin are degraded, preventing the further recruitment of helicases to the genomic regions already undergoing duplication 9-12 . In metazoans, pre-replication complexes are bound to chromatin in excess, but chromosome duplication initiates only at a fraction of the many potential origins. The selection of active origins among the excess of pre-replication complex binding sites is often tissue-specific 8 and preferentially associates with specific chromatin modifications 8,13 . The excess potential origins ("dormant origins"), which are bound by pre-replication complexes but do not initiate replication during normal mitotic growth, can be activated under distinct conditions that slow or stall replication fork elongation (replication stress 1 ).…”

“…This observation suggests that the recruitment of pre-replication complexes to flexible or consistently dormant origins might serve as a redundancy to ensure the prevention of incomplete genome duplication. The flexible choice of replication origins could also preserve genome integrity by coordinating replication with transcription and chromatin assembly on the shared chromatin template 8 .…”

Nicotinamide increases the sensitivity of chronic myeloid leukemia cells to doxorubicin via the inhibition of SIRT1

“…6,7 Studies have demonstrated that some histone deacetylase inhibitors can eliminate quiescent leukemic stem cells and reduce drug resistance in CML. [10][11][12][13] Sirtuin 1 (SIRT1), a member of the sirtuin family modulates several processes such as DNA repairing, cell cycle, metabolism, aging, and cell survival under stress conditions. [10][11][12][13] Sirtuin 1 (SIRT1), a member of the sirtuin family modulates several processes such as DNA repairing, cell cycle, metabolism, aging, and cell survival under stress conditions.…”