Convergence of SIRT1 and ATR signaling to modulate replication origin dormancy

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. Overall design: Nascent strands were purified with the lambda exonuclease methods from HCT116 cells. Chromatin from HCT116 cells was subjected to ChIP-Seq with antibody directed against pT530-SIRT1, pS108-MCM2, pS40/41, pS53 and pS139-MCM2.