title: Combining ATR suppression with oncogenic Ras synergistically increases genomic instability, causing synthetic lethality or tumorigenesis in a dosage-dependent manner.
abstract: Previous studies indicate that oncogenic stress activates the ATR-Chk1 pathway. Here, we show that ATR-Chk1 pathway engagement is essential for limiting genomic instability following oncogenic Ras transformation. ATR pathway inhibition in combination with oncogenic Ras expression synergistically increased genomic instability, as quantified by chromatid breaks, sister chromatid exchanges, and H2AX phosphorylation. This level of instability was significantly greater than that observed following ATR suppression in untransformed control cells. In addition, consistent with a deficiency in long-term genome maintenance, hypomorphic ATR pathway reduction to 16% of normal levels was synthetic lethal with oncogenic Ras expression in cultured cells. Notably, elevated genomic instability and synthetic lethality following suppression of ATR were not due to accelerated cycling rates in Ras-transformed cells, indicating that these synergistic effects were generated on a per-cell-cycle basis. In contrast to the synthetic lethal effects of hypomorphic ATR suppression, subtle reduction of ATR expression (haploinsufficiency) in combination with endogenous levels of K-ras(G12D) expression elevated the incidence of lung adenocarcinoma, spindle cell sarcoma, and thymic lymphoma in p53 heterozygous mice. K-ras(G12D)-induced tumorigenesis in ATR(+/-)p53(+/-) mice was associated with intrachromosomal deletions and loss of wild-type p53. These findings indicate that synergistic increases in genomic instability following ATR reduction in oncogenic Ras-transformed cells can produce 2 distinct biological outcomes: synthetic lethality upon significant suppression of ATR expression and tumor promotion in the context of ATR haploinsufficiency. These results highlight the importance of the ATR pathway both as a barrier to malignant progression and as a potential target for cancer treatment.
authors.affiliation: Abramson Family Cancer Research Institute and Department of Cancer Biology, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Oren
authors.initials: O
authors.lastname: Gilad
authors.forename: Barzin Y
authors.initials: BY
authors.lastname: Nabet
authors.forename: Ryan L
authors.initials: RL
authors.lastname: Ragland
authors.forename: David W
authors.initials: DW
authors.lastname: Schoppy
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Smith
authors.forename: Amy C
authors.initials: AC
authors.lastname: Durham
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Brown
mesh_terms: D000818:Animals; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology; D064007:Ataxia Telangiectasia Mutated Proteins; D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D002478:Cells, Cultured; D000071877:Checkpoint Kinase 1; D004305:Dose-Response Relationship, Drug; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D011905:Genes, ras / Q000235:genetics*; D042822:Genomic Instability; D008297:Male; D051379:Mice; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D041681:NIH 3T3 Cells; D009374:Neoplasms, Experimental / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism; D034622:RNA Interference; D011995:Recombination, Genetic / Q000187:drug effects; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013629:Tamoxifen / Q000494:pharmacology; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
chemical_list: D018931:Antineoplastic Agents, Hormonal; D018797:Cell Cycle Proteins; D016159:Tumor Suppressor Protein p53; D013629:Tamoxifen; D011494:Protein Kinases; C576897:Atr protein, mouse; D064007:Ataxia Telangiectasia Mutated Proteins; D000071877:Checkpoint Kinase 1; C000605869:Chek1 protein, mouse; D017346:Protein Serine-Threonine Kinases