title: Biochemical evidence for deficient DNA repair leading to enhanced G2 chromatid radiosensitivity and susceptibility to cancer.
abstract: Human tumor cells and cells from cancer-prone individuals, compared with those from normal individuals, show a significantly higher incidence of chromatid breaks and gaps seen in metaphase cells immediately after G2 X irradiation. Previous studies with DNA repair-deficient mutants and DNA repair inhibitors strongly indicate that the enhancement results from a G2 deficiency(ies) in DNA repair. We report here biochemical evidence for a DNA repair deficiency that correlates with the cytogenetic studies. In the alkaline elution technique, after a pulse label with radioactive thymidine in the presence of 3-acetylaminobenzamide (a G2-phase blocker) and X irradiation, DNA from tumor or cancer-prone cells elutes more rapidly during the postirradiation period than that from normal cells. These results indicate that the DNA of tumor and cancer-prone cells either repairs more slowly or acquires more breaks than that of normal cells; breaks can accumulate during incomplete or deficient repair processes. The kinetic difference between normal and tumor or cancer-prone cells in DNA strand-break repair reaches a maximum within 2 h, and this maximum corresponds to the kinetic difference in chromatid aberration incidence following X irradiation reported previously. These findings support the concept that cells showing enhanced G2 chromatid radiosensitivity are deficient in DNA repair. The findings could also lead to a biochemical assay for cancer susceptibility.
mesh_terms: D002460:Cell Line; D002842:Chromatids / Q000528:radiation effects*; D002869:Chromosome Aberrations; D004260:DNA Repair; D004273:DNA, Neoplasm / Q000528:radiation effects*; D004198:Disease Susceptibility; D006801:Humans; D066298:In Vitro Techniques; D007399:Interphase / Q000528:radiation effects; D009369:Neoplasms / Q000235:genetics*; D011831:Radiation Genetics; D011836:Radiation Tolerance
chemical_list: D004273:DNA, Neoplasm