KGF FACILITATES REPAIR OF RADIATION-INDUCED DNA-DAMAGE IN ALVEOLAR EPITHELIAL-CELLS

Administration of exogenous keratinocyte growth factor (KGF) prevents or attenuates several forms of oxidant-mediated lung injury. Because D NA damage in epithelial cells is a component of radiation pneumotoxici ty, we determined whether KGF ameliorated DNA strand breaks in irradia ted A549 cells. Cells were exposed to Cs-137 gamma rays, and DNA damag e was measured by alkaline unwinding and ethidium bromide fluorescence after a 30-min recovery period. Radiation induced a dose-dependent in crease in DNA strand breaks. The percentage of double-stranded DNA aft er exposure to 30 Gy increased from 44.6 +/- 3.5% in untreated control cells to 61.6 +/- 5.0% in cells cultured with 100 ng/ml KGF for 24 h (P < 0.05). No reduction in DNA damage occurred when the cells were cu ltured with KGF but maintained at 0 degrees C during and after irradia tion. The sparing effect of KGF on radiation-induced DNA damage was bl ocked by aphidicolin, an inhibitor of DNA polymerases-alpha, -delta, a nd -epsilon and by butylphenyl dGTP, which blocks DNA polymerase-alpha strongly and polymerases-delta and -epsilon less effectively. However , dideoxythymidine triphosphate, a specific inhibitor of DNA polymeras e-beta, did not abrogate the KGF effect. Thus KGF increases DNA repair capacity in irradiated pulmonary epithelial cells, an effect mediated at least in part by DNA polymerases-alpha, -delta, and -epsilon. Enha ncement of DNA repair capability after cell damage may be one mechanis m by which KGF is able to ameliorate oxidant-mediated alveolar epithel ial injury.