Genetic interactions between BLM and DNA ligase IV in human cells.
BLM has been implicated in DNA double-strand break (DSB) repair, but its precise role remains obscure. To explore this, we generated BLM(-/-) and BLM(-/-)LIG4(-/-) cells from the human pre-B cell line Nalm-6. BLM(-/-) cells exhibited retarded growth, increased mutation rates, and hypersensitivity to agents that block replication fork progression. Interestingly, these phenotypes were significantly suppressed by deletion of LIG4, suggesting that nonhomologous end-joining (NHEJ) is unfavorable for integrity and survival of cells lacking BLM. We propose that the absence of BLM leads to accumulation of replication-associated, one-ended DSBs, which are deleterious to cells and lead to genomic instability when repaired by NHEJ. In addition, the NHEJ pathway per se was marginally affected by BLM deficiency, as evidenced by x-ray sensitivity and I-SceI-based DSB repair assays. More intriguingly, however, these experiments revealed the presence of an alternative, DNA ligase IV-independent end-joining pathway, which was significantly affected by the loss of BLM. Collectively, our results provide the first evidence for genetic interactions between BLM and NHEJ in human cells.
So
Sairei
S
Kihara Institute for Biological Research, Graduate School of Integrated Science, Yokohama City University, Maioka-cho 641-12, Totsuka-ku, Yokohama 244-0813, Japan.
Adachi
Noritaka
N
Lieber
Michael R
MR
Koyama
Hideki
H
D000251:Adenosine Triphosphatases / Q000235:genetics* / Q000502:physiology; D001402:B-Lymphocytes / Q000378:metabolism; D001483:Base Sequence; D015153:Blotting, Western; D002460:Cell Line; D049109:Cell Proliferation; D002469:Cell Separation; D002470:Cell Survival; D004249:DNA Damage; D004265:DNA Helicases / Q000235:genetics* / Q000502:physiology; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000235:genetics* / Q000502:physiology; D004260:DNA Repair; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D005434:Flow Cytometry; D017353:Gene Deletion; D005822:Genetic Vectors; D006801:Humans; D008954:Models, Biological; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D053484:RecQ Helicases; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012854:Sister Chromatid Exchange; D013866:Thioguanine / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection; D014965:X-Rays
D018076:DNA, Complementary; C000607893:LIG4 protein, human; D000251:Adenosine Triphosphatases; C097151:Bloom syndrome protein; D004265:DNA Helicases; D053484:RecQ Helicases; D011088:DNA Ligases; D000072481:DNA Ligase ATP; D013866:Thioguanine