ATR: an essential regulator of genome integrity

Abstract

PrefaceGenome maintenance is a constant problem in all cells and a coordinated response to DNA damage is required to maintain cellular viability and prevent disease. The ATR and ATM protein kinases are master regulators of the DNA damage response, signaling to control cell cycle transitions, DNA replication, DNA repair, and apoptosis. Recent studies have provided insights into the mechanisms controlling ATR activation, helped to explain the overlapping but non-redundant activities of ATR and ATM in DNA damage signaling, and clarified the critical functions of ATR in maintaining genome integrity. IntroductionAll cells have elaborate mechanisms to maintain their genomes. DNA can be damaged during replication, by reactive metabolic byproducts as well as environmental mutagens. Responding to and repairing DNA damage is critical for cell viability and disease prevention.The DNA damage response (DDR) is a signal transduction pathway that coordinates cell cycle transitions, DNA replication, DNA repair and apoptosis. The major regulators of the DDR are the phosphoinositide 3-kinase related protein kinases (PIKKs), including ataxia-telangiectasia mutated (ATM) and ATM and Rad3 related (ATR). ATM and ATR share many biochemical and functional similarities. Both are large kinases with significant sequence homology and a strong preference to phosphorylate serine or threonine residues that are followed by glutamine. Both target an overlapping set of substrates that promote cell cycle arrest and DNA repair. However, ATR is essential for the viability of replicating human and mouse cells, whereas ATM is not 1-3 . ATM functions in response to rare occurrences of double strand breaks. By contrast, ATR is activated during every S-phase to regulate the firing of replication origins, the repair of damaged replication forks and to prevent the premature onset of mitosis 4, 5 (Fig. 1).Mutations in ATM predispose carriers to cancer and are found in approximately 0.5-1% of the population 6, 7 . People with mutations in both alleles of ATM suffer from the neurodegenerative and cancer predisposition disorder ataxia-telangiectasia 8 . Mutations in ATR are rare and probably only compatible with viability when heterozygous or hypomorphic. While the only clear link between ATR gene mutation and disease is in a few patients with the rare Seckel syndrome (characterized by growth retardation and microcephaly) 9 , disruptions in the ATR pathway do cause genomic instability, and ATR is activated by most cancer chemotherapies. Furthermore, ATR signaling is a promising target for cancer drug development 10, 11 . This review will focus on ATR signaling in the DNA damage response, and compare and contrast it with the more specialized role of ATM. NIH Public Access Mechanisms of ATR ActivationThe broad functions and physiological importance of ATR derive in large part from recognizing the signals that lead to its activation versus that of ATM. Thus, we will address the mechanism of activation in some detail. Recognizing DNA damageAlthough ATR is activ...

The natural anticancer compound rocaglamide selectively inhibits the G1-S-phase transition in cancer cells through the ATM/ATR-mediated Chk1/2 cell cycle checkpoints

“…22,37 Although we observed a time-and dose-dependent increase in gH2AX levels in Roc-A treated Jurkat cells (Fig. 5a), Roc-A does not induce massive DNA DSBs as compared with doxorubicin, an anticancer drug known to cause DNA DSBs (Fig.…”

“…ATM and ATR are reported to be generally activated in response to DNA damage. 1,22 Therefore, we checked the levels of the DSBs biomarker gH2AX in Roc-A-treated Jurkat cells by Western blot analysis. Indeed, we observed a doseand time-dependent increase of gH2AX levels in Jurkat cells after Roc-A treatment (Fig.…”

Palmitoylation-dependent activation of MC1R prevents melanomagenesis

“…Since ATR is a central effector of the UVB-response 23,24 we asked if ATR-mediated phosphorylation of ZDHHC13 promoted MC1R palmitoylation following UV exposure. HPMs expressing HA-ZDHHC13 were irradiated with UVB and after anti-HA immunoprecipitation phosphorylation of ZDHHC13 was detected by with specific phospho-S/T-Q antibody.…”

Protein monoubiquitylation: targets and diverse functions

“…At sites of DNA damage, the PCNA‐like complex 9‐1‐1 (RAD9‐HUS1‐RAD1) is loaded by another clamp loader complex (comprising RAD17 and RFC2 to RFC5) to initiate the DNA damage response (Cimprich & Cortez 2008). The shared clamp loader proteins RFC2 and RFC4 are monoubiquitylated on chromatin by RAD18 in response to DNA damage (Tomida et al .…”