An ATR- and Chk1-dependent S checkpoint inhibits replicon initiation following UVC-induced DNA damage.
Inhibition of replicon initiation is a stereotypic DNA damage response mediated through S checkpoint mechanisms not yet fully understood. Studies were undertaken to elucidate the function of checkpoint proteins in the inhibition of replicon initiation following irradiation with 254 nm UV light (UVC) of diploid human fibroblasts immortalized by the ectopic expression of telomerase. Velocity sedimentation analysis of nascent DNA molecules revealed a 50% inhibition of replicon initiation when normal human fibroblasts were treated with a low dose of UVC (1 J/m(2)). Ataxia telangiectasia (AT), Nijmegen breakage syndrome (NBS), and AT-like disorder fibroblasts, which lack an S checkpoint response when exposed to ionizing radiation, responded normally when exposed to UVC and inhibited replicon initiation. 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. 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. Taken together, these data suggest that the UVC-induced S checkpoint response of inhibition of replicon initiation is mediated by ATR signaling through Chk-1 and is independent of ATM, Nbs1, and Mre11.
Heffernan
Timothy P
TP
Department of Pathology and Laboratory Medicine, Center for Environmental Health and Susceptibility, and Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
Simpson
Dennis A
DA
Frank
Alexandra R
AR
Heinloth
Alexandra N
AN
Paules
Richard S
RS
Cordeiro-Stone
Marila
M
Kaufmann
William K
WK
D064007:Ataxia Telangiectasia Mutated Proteins; D002110:Caffeine / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D000071877:Checkpoint Kinase 1; D004247:DNA / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects*; D004249:DNA Damage; D004260:DNA Repair; D004261:DNA Replication; D004268:DNA-Binding Proteins; D004318:Doxycycline / Q000378:metabolism; D004706:Endodeoxyribonucleases / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation; D005090:Exodeoxyribonucleases / Q000235:genetics / Q000378:metabolism; D005347:Fibroblasts / Q000502:physiology / Q000528:radiation effects; D018816:Genes, cdc; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D012093:Replicon / Q000235:genetics*; D016196:S Phase / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins; D015398:Signal Transduction / Q000502:physiology*; D019098:Telomerase / Q000378:metabolism; D025521:Tumor Suppressor Proteins; D014466:Ultraviolet Rays
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C112156:NBN protein, human; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins; D025521:Tumor Suppressor Proteins; D002110:Caffeine; D004247:DNA; D011494:Protein Kinases; C576324:ATM protein, human; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases; D019098:Telomerase; D004706:Endodeoxyribonucleases; D005090:Exodeoxyribonucleases; C094191:MRE11 protein, S cerevisiae; D004318:Doxycycline