Diethyl sulfate-induced cell cycle arrest and apoptosis in human bronchial epithelial 16HBE cells

In this study, we investigated the effects of diethyl sulfate (DES) on cell proliferation, cell cycle progression and apoptosis in human bronchial epithelial 16HBE cells. Cells were treated with various doses of DES (0, 0.5, 1.0, 2.0, 4.0 or 8.0mM) for 12, 24 or 36h. Cell proliferation and apoptosis were determined by MTT assay and flow cytometer, respectively. The results showed that DES inhibited cell proliferation in a dose- and time-dependent manner, and induced significant apoptosis in 16HBE cells. Apoptosis related proteins measurement results revealed that DES-induced apoptosis was concurrent with the increasing of Bax and cleavage fragment caspase-3 and the decreasing of Bcl-2 and full length procaspase-3. When cells were incubated with 2.0mM of DES for several time intervals, S and G2/M phase accumulation was observed. Further analysis indicated that both DES-induced G1/S transition acceleration and S arrest resulted in S phase accumulation, and that DES-induced G2/M arrest resulted in G2/M phase accumulation. Western blotting results demonstrated that after DES treatment p-chk1 (Ser345) and p-chk2 (Thr68) levels decreased in G1 cells, and increased in S and G2/M cells. In addition, the increasing of chk1 and chk2 were also induced by DES treatment. With the increase in the dose of DES, p53 levels first increased (0.5-4.0mM) and then decreased (8.0mM). Down-regulation of p53 by RNA interference increased 4.0mM of DES-induced apoptosis but did not affect 2.0mM DES-induced cell cycle arrest. In conclusion, DES inhibits 16HBE cells proliferation in a dose- and time-dependent behavior. Within the sublethal dose, DES induces S and G2/M arrest through activating DNA damage checkpoints. Within the lethal dose, DES induces apoptosis through evoking apoptosis programs. p53 might play an important role in the transition between evoking cell cycle arrest/pro-survival and apoptosis programs upon DES exposure.