Growth arrest in A549 cells during hyperoxic stress is associated with decreased cyclin B1 and increased p21(Waf1/Cip1/Sdi1) levels.
Exposure to high concentrations of oxygen has previously been shown to cause 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/Sdi1) protein and a decrease in cyclin B1 protein. Flow cytometry revealed that A549 cells exposed to hyperoxia had a significant decrease in the percentage of cells in G(1) and a modest but significant increase in the percentage of cells in S phase and G(2)/M, consistent with cells entering S phase. A549 cells in room air and hyperoxia were then treated with nocodazole, a mitotic inhibitor. Room air A549 cells treated with nocodazole showed a marked increase in G(2)/M consistent with mitotic arrest. In contrast, hyperoxic treated cells had a modest but significant decrease in G(1) but only a minimal increase in G(2)/M consistent with partial G(1)/S arrest and growth inhibition in S phase. To further investigate the role of p21(Waf1/Cip1/Sdi1) as a checkpoint regulator during hyperoxic growth inhibition, HCT116 cells with wild-type and null p21(Waf1/Cip1/Sdi1) were exposed to hyperoxia. Both wild-type p21(+/+) cells and null p21(-/-) cells underwent growth inhibition when exposed to hyperoxia. At 48 h the hyperoxic treated HCT116 p21(+/+) had a similar cell cycle distribution as the hyperoxic treated HCT116 p21(-/-) cells, suggesting that p21(Waf1/Cip1/Sdi1) may not be essential for growth arrest during hyperoxia. These findings suggest that hyperoxia causes 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.
McGrath-Morrow
S A
SA
Department of Pediatrics, Eudowood Division of Pediatric Respiratory Sciences, Johns Hopkins Medical Institutions, Baltimore, MD 21205, USA. smorrow@jhmi.edu
Stahl
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J
D000818:Animals; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000378:metabolism; D002460:Cell Line; D019926:Cyclin B / Q000032:analysis / Q000378:metabolism*; D056744:Cyclin B1; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000032:analysis / Q000378:metabolism*; D005434:Flow Cytometry; D006801:Humans; D018496:Hyperoxia; D015739:Nocodazole / Q000494:pharmacology; D018384:Oxidative Stress; D018809:Proliferating Cell Nuclear Antigen / Q000032:analysis; D016196:S Phase; D013997:Time Factors
C534699:CCNB1 protein, human; C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D019926:Cyclin B; D056744:Cyclin B1; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D018809:Proliferating Cell Nuclear Antigen; D015739:Nocodazole