Disease relevance of ATR

• While NBS shares overlapping characteristics with ataxia telangiectasia, it also has features overlapping with ATR-Seckel (ATR: ataxia-telangiectasia and Rad3-related protein) syndrome, a subclass of Seckel syndrome mutated in ATR [1].
• We have uncovered novel phenotypes caused by MRN deficiency that support a functional link between this complex, ATR and Smc1, including hypersensitivity to UV exposure, a defective UV responsive intra-S phase checkpoint and a specific pattern of genomic instability [2].
• In the present study, we demonstrate that HIV-1 infection of primary, human CD4(+) lymphocytes causes G(2) arrest in a Vpr-dependent manner and that this response requires ATR, as shown by RNA interference [3].
• Here we show that infection with an adenovirus lacking the E4 region also induces a cellular DNA damage response, with activation of ATM and ATR [4].
• Moreover, induction of ATR(ki) produced a 10-fold increase in chromosomal aberrations, further emphasizing the vital role for ATR in genetic stability [5].

Psychiatry related information on ATR

• Seckel syndrome (SCKL) is a rare, genetically heterogeneous disorder, with dysmorphic facial appearance, growth retardation, microcephaly, mental retardation, variable chromosomal instability, and hematological disorders [6].

High impact information on ATR

• Although it is known that MSCI and MSUC are both dependent on histone H2A.X phosphorylation mediated by the kinase ATR, and cause repressive H3 Lys9 dimethylation, the mechanisms underlying silencing are largely unidentified [7].
• Paradoxically, telomere function depends on checkpoint proteins such as ATM and ATR, but a molecular model explaining this seemingly contradictory relationship has been missing so far [8].
• They report that a physical interaction between ATR and a distinct domain of TopBP1 greatly enhances ATR kinase activity [9].
• The nuclear protein kinase ATR is a key regulator of genome integrity that functions at checkpoints for damaged or incompletely replicated DNA [9].
• First, the ATR-dependent machinery is recruited to telomeres before telomere replication is completed, likely in response to single-stranded DNA resulting from replication fork stalling [8].

Chemical compound and disease context of ATR

• Taken together, these data suggest that the effect(s) of caffeine on HIV-1 transduction is mediated at least partly by the inhibition of the ATR pathway but is not dependent on the caffeine-mediated inhibition of cell cycle checkpoints [10].

Biological context of ATR

• These findings demonstrate that ATR/ATM-dependent phosphorylation of hRad17 is a critical early event during checkpoint signalling in DNA-damaged cells [11].
• The dramatic relocalization of ATR in response to DNA damage points to a possible mechanism for its ability to enhance the phosphorylation of substrates in response to DNA damage [12].
• Thus, MCPH1 also has an ATR-independent role in maintaining inhibitory Cdk1 phosphorylation, which prevents premature entry into mitosis [13].
• These results suggest that tCdc6 proteins act as dominant-negative inhibitors of replication initiation and that they disrupt chromatin structure and/or induce DNA damage, leading to the activation of ATM/ATR kinase activation and p53-Bax-mediated apoptosis [14].
• MSH2 and ATR form a signaling module and regulate two branches of the damage response to DNA methylation [15].

Anatomical context of ATR

• NBS cell lines show a similar defect in ATR phosphorylation of Chk1, c-jun and p-53 in response to UV irradiation- and hydroxyurea (HU)-induced replication stalling [1].
• Cleavage of Cdc6 by caspase-3 promotes ATM/ATR kinase-mediated apoptosis of HeLa cells [14].
• Pretreatment of normal and AT fibroblasts with caffeine or UCN-01, inhibitors of ATR (AT mutated and Rad3 related) and Chk1, respectively, abolished the S checkpoint response to UVC [16].
• The event leading to ATR activation in CD4(+) lymphocytes is the accumulation of replication protein A in nuclear foci, an indication that Vpr likely induces stalling of replication forks [3].
• Three overlapping clones isolated from a Jurkat T-cell cDNA library revealed a 7.9-kb open reading frame encoding a protein that we have named FRP1 (FRAP-related protein) with 2644 amino acids and a predicted molecular mass of 301 kDa [17].

Associations of ATR with chemical compounds

• They are also impaired in ubiquitination of FANCD2 after HU treatment, which is ATR dependent [1].
• These data support a model in which MSH2 and ATR function upstream to regulate two branches of the response pathway to DNA damage caused by MNNG [15].
• Here, we show that thymidine, which slows the progression of replication forks by depleting cellular pools of dCTP, induces a novel DNA damage response that, uniquely, depends on both ATM and ATR [18].
• Together, these results suggest a relationship between BLM, ATR, and the RMN complex in the response to replication arrest, proposing a role for BLM protein and RMN complex in the resolution of stalled replication forks [19].
• Expression of a kinase-inactive allele of ATR (ATRkd) in human fibroblasts causes increased sensitivity to ionizing radiation (IR), cis-platinum and methyl methanesulfonate, but only slight UV radiation sensitivity [20].

Physical interactions of ATR

• These results demonstrate that the Mre11 complex can function as a damage sensor upstream of ATM/ATR signaling in mammalian cells [4].
• PP5 forms a complex with ATR in a genotoxic stress-inducible manner [21].
• ATR couples FANCD2 monoubiquitination to the DNA-damage response [22].
• In response to hydroxyurea, UV or aphidicolin, Claspin is phosphorylated in the Chk1-binding domain and its protein levels are increased in an ATR-dependent manner [23].

Enzymatic interactions of ATR

• ATR phosphorylates BRCA1 on six Ser/Thr residues, including Ser 1423, in vitro [12].
• Rad17 binds to chromatin prior to damage and is phosphorylated by ATR on chromatin after damage but Rad17's phosphorylation is not required for Rad9 loading onto chromatin [24].
• Here, we show that WRN is phosphorylated through an ATR/ATM dependent pathway in response to replication blockage [25].
• While ATR phosphorylates the N-terminus of RPA70, Chk1 preferentially phosphorylates RPA's major ssDNA binding domain [26].
• In response to genotoxic stress, Chk1 is phosphorylated on serines 317 (S317) and 345 (S345) by the ataxia-telangiectasia-related (ATR) protein kinase [27].
• Nbs1 is phosphorylated by ATR at Ser-343 when replication forks are stalled, and this phosphorylation event is also important for down-regulating DNA replication following UV treatment [28].

Co-localisations of ATR

• We show that TopBP1 tightly colocalizes with ATR in distinct nuclear subcompartments generated by DNA damage [29].

Regulatory relationships of ATR

• ATM regulates ATR chromatin loading in response to DNA double-strand breaks [30].
• Moreover, overexpression of kinase-inactive ATR in U2OS cells severely attenuated UVC-induced Chk1 phosphorylation and reversed the UVC-induced inhibition of replicon initiation, as did overexpression of kinase-inactive Chk1 [16].
• ATR knock-down with siRNA suppressed CPT-induced RPA2 hyperphosphorylation and focus formation [31].
• In response to DNA damage, ATM/ATR-dependent checkpoint pathways inhibit Plk1 activity [32].
• Furthermore, Xenopus egg extracts containing a version of TopBP1 with an inactivating point mutation in the ATR-activating domain are defective in checkpoint regulation [33].
• Our results suggest that HCLK2 functions in the same pathway as TopBP1 but that the two proteins regulate different steps in ATR activation [34].

Other interactions of ATR

• Functional interactions between BRCA1 and the checkpoint kinase ATR during genotoxic stress [12].
• We show that Nbs1 also facilitates ATR-dependent phosphorylation [1].
• These observations rule out ATR and implicate both ATM and DNA-PK in RPA2 phosphorylation after exposure to IR [35].
• Molecular association between ATR and two components of the nucleosome remodeling and deacetylating complex, HDAC2 and CHD4 [36].
• However, activation of the G2/M checkpoint in response to IR escapes this accepted paradigm because it is dependent on both ATM and ATR but independent of Chk2 [30].
• Cellular complementation experiments demonstrate that TopBP1-mediated ATR activation is required for checkpoint signaling and cellular viability [37].

Analytical, diagnostic and therapeutic context of ATR

• Using fluorescence in situ hybridization and a full-length cDNA FRP1 clone, the FRP1 gene has been mapped to the chromosomal locus 3q22-q24 [17].
• Monoallelic ATR gene targeting in MLH1-deficient HCT 116 colon carcinoma cells resulted in hypersensitivity to genotoxic stress accompanied by dramatic increases in fragile site instability, and chromosomal amplifications and rearrangements [38].
• Mutants of Chk1 containing alanine in place of serines 317 and 345 were poorly activated in response to replication blocks or genotoxic stress in vivo, were poorly phosphorylated by ATR in vitro, and were not found in faster-eluting fractions by gel filtration [39].
• Its role as a signal transducer in cell cycle checkpoint is well established, but it is currently unclear whether ATR functions as a damage sensor as well [40].
• Here we have purified the ATR protein and investigated its interaction with DNA by using biochemical analysis and electron microscopy [40].

References