Figure 1.

Nickel treatment induces down-regulation of HR, but not NHEJ, protein expression and activity in human cancer cell lines and non-tumorigenic human lung cells. (A) Western blot analysis of HR and NHEJ proteins in human cancer cell lines treated with 0, 100, 250 or 500 μM NiCl₂ for 48 h. Quantitation of band density is presented in Supplementary Figure S1 and uncropped blots are available in Supplementary Figures S7 and S8. (B) Western blot analysis of HR and NHEJ proteins in BEAS-2B cells treated with 0, 100 or 250 μM NiCl₂ or hypoxia (1% O₂) for 48 h. Quantitation of band density is presented in Supplementary Figure S1 and uncropped blots are available in Supplementary Figure S9. (C) Relative HR activity determined by reactivation of the HR luciferase plasmid reporter in A549 and BEAS-2B cells pretreated with 250 μM NiCl₂ for 48 h or BEAS-2B cells pretreated with 1% O₂ for 48 h. HR repair is normalized to mock-treated control cells. (D) Relative NHEJ activity determined by reactivation of the NHEJ luciferase plasmid reporter in A549 and BEAS-2B treated as in panel C. NHEJ repair is normalized to mock-treated control cells. In panels C and D, statistical analyses by one-sample t-test were performed comparing relative repair values to a hypothetical value of 1. Columns, mean of 3 independent experiments; error bars, SEM; **significant at P < 0.01; *significant at P < 0.05; # significant at P < 0.1; ns, not significant.