Molecular insights into replication‐associated genome instabilities caused by CST deficiency

Abstract

The RPA‐like ssDNA binding protein complex CTC1/STN1/TEN1 (CST) has recently been implicated in promoting genome stability under replications stress. Deficiency in CST genes cause the Coats plus syndrome, a complex genetic disorder affecting multiple systems including brain, retina, bone, gastrointestine, and other parts of the body. Yet the precise role of CST in countering replications stress is unclear. Recently we have reported that CST is enriched at GC‐rich and repetitive fragile sequences genome‐wide in response to hydroxyurea (HU)‐induced replication stress (Chastain et al, 2016, Cell Rep 16, 1300–1314). CST deficiency leads to spontaneous chromosome breakage and high‐level chromosome fragmentation that can be further exacerbated by replication stress. Mechanistically, we have found that upon fork stalling, CST proteins form distinct nuclear foci that colocalize with RAD51. Furthermore, replication stress induces physical association between CST with RAD51 in an ATR‐dependent and DNA‐independent manner. Strikingly, CST deficiency diminishes HU‐induced RAD51 foci formation and reduces RAD51 recruitment to GC‐rich fragile sequences. Collectively, our findings establish that CST promotes RAD51 recruitment to GC‐rich repetitive sequences in response to replication stress to facilitate replication restart, thereby providing insights into the mechanism underlying genome stability maintenance. In the present research, we characterize eleven reported disease‐causing CTC1 missense mutations in maintaining genome stability. Our results show that these mutations induce spontaneous chromosome breakage that leads to global genome instabilities. These mutations abolish or reduce CST interaction with RAD51, disrupt RAD51 foci formation, and/or diminish binding to GC‐rich genomic fragile sites under replication stress. Furthermore, CTC1 mutations limit cell proliferation under unchallenged condition and significantly reduce clonal viability under replication stress. Our findings thus provide molecular evidence linking replication‐associated genomic defects with Coats plus disease pathology.Support or Funding InformationResearch is supported by NIH R01GM112864.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.