P53, CIP1, AND GADD153 EXPRESSION FOLLOWING TREATMENT OF A549 CELLS WITH NATURAL AND MAN-MADE VITREOUS FIBERS

DNA damage induced by chemicals and ionizing radiation is associated w i ih the expression of negative regulators of the cell cycle. The arre st of cells in G1 and G2 phases of the cell cycle provides time for DN A repair. Asbestos fibers are carcinogenic when inhaled by both humans and animals, however, the mechanism by which the fibers exert their e ffect is unknown. This work was undertaken to determine whether the ex pression of DNA damage-inducible genes differs between crocidolite, a fiber positive for lung tumors, and JM 100 glass microfiber, which is negative for lung tumors when inhaled by rats. Temporal and dose-relat ed expressions of p53, Cip1, and Gadd153 proteins were determined in c ultured A549 cells treated with either Union internationale Contre le Cancer crocidolite or JM 100 for 20 hr and cultured in fresh media. Im munolabeled cells were analyzed by flow cytometry, and the increased n umber of protein-expressing cells was determined by subtracting the ex pression in unexposed cells from exposed cells. Crocidolite induced th e expression of all three proteins with a maximum expression after app roximately 18 hr in fresh media. At a similar time point, JM 100 did n ot markedly induce the three proteins. Crocidolite also induced a dose -dependent increase in the number of cells in the G2 phase of the cell cycle. These results show that asbestos behaves like ionizing radiati on and genotoxic chemicals by inducing proteins associated with DNA da mage and cell-cycle arrest. The clear difference in response between c rocidolite and JM 100 may help elucidate the mechanism of action of to xic and nontoxic fibers.