title: Dissecting cellular responses to irradiation via targeted disruptions of the ATM-CHK1-PP2A circuit.
abstract: Exposure of proliferating cells to genotoxic stresses activates a cascade of signaling events termed the DNA damage response (DDR). The DDR preserves genetic stability by detecting DNA lesions, activating cell cycle checkpoints and promoting DNA damage repair. The phosphoinositide 3-kinase-related kinases (PIKKs) ataxia telangiectasia-mutated (ATM), ATM and Rad 3-related kinase (ATR) and DNA-dependent protein kinase (DNA-PK) are crucial for sensing lesions and signal transduction. The checkpoint kinase 1 (CHK1) is a traditional ATR target involved in DDR and normal cell cycle progression and represents a pharmacological target for anticancer regimens. This study employed cell lines stably depleted for CHK1, ATM or both for dissecting cross-talk and compensatory effects on G(2)/M checkpoint in response to ionizing radiation (IR). We show that a 90% depletion of CHK1 renders cells radiosensitive without abrogating their IR-mediated G(2)/M checkpoint arrest. ATM phosphorylation is enhanced in CHK1-deficient cells compared with their wild-type counterparts. This correlates with lower nuclear abundance of the PP2A catalytic subunit in CHK1-depleted cells. Stable depletion of CHK1 in an ATM-deficient background showed only a 50% reduction from wild-type CHK1 protein expression levels and resulted in an additive attenuation of the G(2)/M checkpoint response compared with the individual knockdowns. ATM inhibition and 90% CHK1 depletion abrogated the early G(2)/M checkpoint and precluded the cells from mounting an efficient compensatory response to IR at later time points. Our data indicates that dual targeting of ATM and CHK1 functionalities disrupts the compensatory response to DNA damage and could be exploited for developing efficient anti-neoplastic treatments.
authors: Environmental Stress and Cancer Group, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC, USA.
authors: Stela S
authors: SS
authors: Palii
authors: Yuxia
authors: Y
authors: Cui
authors: Cynthia L
authors: CL
authors: Innes
authors: Richard S
authors: RS
authors: Paules
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D000071877:Checkpoint Kinase 1; D004249:DNA Damage / Q000528:radiation effects; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D059565:G2 Phase Cell Cycle Checkpoints / Q000528:radiation effects; D057809:HEK293 Cells; D006801:Humans; D059566:M Phase Cell Cycle Checkpoints / Q000528:radiation effects; D010766:Phosphorylation; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D054648:Protein Phosphatase 2 / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D011839:Radiation, Ionizing; D015398:Signal Transduction; D025521:Tumor Suppressor Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D034741:RNA, Small Interfering; D025521:Tumor Suppressor Proteins; D011494:Protein Kinases; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases; D054648:Protein Phosphatase 2
keywords: DNA damage; ataxia telangiectasia mutated; checkpoint kinase-1; feedback regulation; phosphatase