Ku70/80 gene expression and DNA-dependent protein kinase (DNA-PK) activitydo not correlate with double-strand break (dsb) repair capacity and cellular radiosensitivity in normal human fibroblasts

The expression of the Ku70 and Ku80 genes as well as the activity of the DN A-dependent protein kinase (DNA-PK) were studied in 11 normal human fibrobl ast lines. The proteins studied are known to be part of a double-strand bre ak (dsb) repair complex involved in nonhomologous recombination, as was dem onstrated for the radiosensitive rodent mutant cell lines of the complement ation groups 5-7. The 11 fibroblast lines used in this study represent a ty pical spectrum of normal human radiosensitivity with the surviving fraction measured for a dose of 3.5 Gy, SF3.5Gy, ranging from 0.03 to 0.28. These d ifferences in cell survival were previously shown to correlate with the num ber of non-repaired dsbs. We found that the mRNA signal intensities of both Ku70 and Ku80 genes were fairly similar for the 11 cell lines investigated . In addition, the DNA-PK activity determined by the pulldown assay was fai rly constant in these fibroblast lines. Despite the correlation between cel l survival and dsb repair capacity, there was no correlation between dsb re pair capacity and DNA-PK activity in the tested normal human fibroblast lin es. Obviously, in this respect, other proteins/pathways appear to be more r elevant.