ATR Suppresses Endogenous DNA Damage and Allows Completion of Homologous Recombination Repair

Abstract

DNA replication fork stalling or collapse that arises from endogenous damage poses a serious threat to genome stability, but cells invoke an intricate signaling cascade referred to as the DNA damage response (DDR) to prevent such damage. The gene product ataxia telangiectasia and Rad3-related (ATR) responds primarily to replication stress by regulating cell cycle checkpoint control, yet it’s role in DNA repair, particularly homologous recombination (HR), remains unclear. This is of particular interest since HR is one way in which replication restart can occur in the presence of a stalled or collapsed fork. Hypomorphic mutations in human ATR cause the rare autosomal-recessive disease Seckel syndrome, and complete loss of Atr in mice leads to embryonic lethality. We recently adapted the in vivo murine pink-eyed unstable (pun) assay for measuring HR frequency to be able to investigate the role of essential genes on HR using a conditional Cre/loxP system. Our system allows for the unique opportunity to test the effect of ATR loss on HR in somatic cells under physiological conditions. Using this system, we provide evidence that retinal pigment epithelium (RPE) cells lacking ATR have decreased density with abnormal morphology, a decreased frequency of HR and an increased level of chromosomal damage.

Targeting radioresistant breast cancer cells by single agent CHK1 inhibitor via enhancing replication stress

“…Using the established system, an increased frequency of HR in MCF-7/C6 and MDA-MB-231 FIR cells was observed, compared to their own parental cells (Figure 6A). The increased HR in RBCC co-related with the increased expression of ATR/CHK1/BRCA1/CtIP since these proteins are important for HR activity [20, 21, 52, 53]. The increased HR activity was not caused by the alteration of the cell cycle because identical cell cycle profiles were observed in radioresistant cells and their corresponding parental cells (Figure 6B).…”

DNA Damage as a Driver for Growth Delay: Chromosome Instability Syndromes with Intrauterine Growth Retardation

“…ATRIP is required for ATR localization to the ssDNA regions and hence for ATR activation [ 25 , 27 ]. Major functions of ATR are activation of cell cycle check point arrest, stabilization of stalled replication forks, and promotion of replication fork restart, which is achieved through its ability to phosphorylate a wide range of substrates that include p53 and H2AX [ 27 , 29 ].…”

“…Cellular phenotype of ATR deficient cells is characterized by decreased phosphorylation of ATR-dependent substrates as well as an impaired G2/M checkpoint arrest. These cells are characterized by markers that signal unrepaired DSBs, like the presence of γ H2AX, chromosomal breakage, [ 26 , 29 , 30 ] and micronuclei formation. This cellular phenotype may be originated by a failure to recover from replication stalling, which generates DSBs that are normally repaired by HR when they occur during S/G2.…”

Targeting lung cancer through inhibition of checkpoint kinases

“…The role of ATR in HR repair is less clear. However, ATR may support HR repair through control of the S phase checkpoint allowing time for repair, and through phosphorylation of Chk1 or other factors such as BRCA1 ( Brown et al, 2014 ).…”