Growth arrest in A549 cells during hyperoxic stress is associated with decreased cyclin B1 and increased p21(Wafl/Cipl/Sdil) levels

Exposure to high concentrations of oxygen has previously been shown to caus e growth arrest in A549 cells, a distal lung epithelial cell line. We found that when A549 cells were exposed to 95% oxygen they underwent substantial growth inhibition. This was associated with induction of p21(Waf1/Cip1/Sdi 1) protein and a decrease in cyclin B1 protein. Flow cytometry revealed tha t A549 cells exposed to hyperoxia had a significant decrease in the percent age of cells in G(1) and a modest but significant increase in the percentag e of cells in S phase and G(2)/M, consistent with cells entering S phase. A 549 cells ill room air and hyperoxia were then treated with nocodazole, a m itotic inhibitor. Room air A549 cells treated with nocodazole showed a mark ed increase in G(2)/M consistent with mitotic arrest. In contrast, hyperoxi c treated cells had a modest but significant decrease in G(1) but only a mi nimal increase in G(2)/M consistent with partial G(1)/S arrest and growth i nhibition in S phase. To further investigate the role of p21(Waf1/Cip1/Sdi1 ) as a checkpoint regulator during hyperoxic growth inhibition, HCT116 cell s with wild-type and null p21(Waf1/Cip1/Sdi1) were exposed to hyperoxia. Bo th wild-type p21(+/+) cells and null p21(-/-) cells underwent growth inhibi tion when exposed to hyperoxia. At 48 h the hyperoxic treated HCT116 p21(+/ +) had a similar cell cycle distribution as the hyperoxic treated HCT116 p2 1(-/-) cells, suggesting that p21(Waf1/Cip1/Sdi1) may not be essential for growth arrest during hyperoxia. These findings suggest that hyperoxia cause s partial growth arrest at different phases of the cell cycle but primarily in S phase, that hyperoxic growth arrest is associated with a decrease in cyclin B1 protein and that p21 induction may not be essential for hyperoxic growth arrest. (C) 2001 Elsevier Science B.V. All rights reserved.