Clinical application of the methods to detect enzyme activities of proteins involved in repair of DNA double strand breaks

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The presence of genomic instability in cells is known to play an important role in the multistage carcinogenesis of various organs. The DNA double strand breaks (DSBs) repair pathway has been implicated in maintaining genomic integrity via suppression of chromosomal rearrangements. DNA-dependent protein kinase (DNA-PK) has an important role in DNA DSBs repair. The purpose of this study was to determine how DNA-PK activity varies among untreated cancer patients and cancer-free normal healthy volunteers and how this affects cancer risk. DNA-PK activities of peripheral blood lymphocytes (PBL) in normal volunteers were 15.84 ± 4.87 pmol and those of cancer patients were 12.28 ± 5.10 pmol. There was the significant difference between them (p=0.012). Age and smoking had no association with DNA-PK activity A relationship between DNA-PK acitvity and chromosome aberration in PBL was shown to exist. The frequency of excess fragment increased as the DNA-PK activity decreased.NBS1, a protein essential for DNA double strand break repair, re-localizes into subnuclear structures upon the induction of DNA damage by ionizing radiation, forming ionizing radiation-induced foci (IRIF). We compared NBS1 IRIF in PBL taken from 46 sporadic breast cancer patients and 30 cancer-free healthy volunteers. The number of persistent NBS1 IRIF per nucleus at 24 hours after irradiation in invasive cancer patients was significantly higher than in normal healthy volunteers. The frequency of spontaneous chromosome aberration increased as the number of persistent NBS1 IRIF increased, indicating that number of persistent NBS1 IRIF might be associated with chromosome instability. There was also an inverse correlation between NBS1 IRIF number and the activity of DNA-PK, which plays an important role in the non-homologous end-joining pathway (NHEJ), another mechanism of DNA DSB repair, indicating close interrelationship between HR and NHEJ in DNA DSB repair mechanism.