title: Dual and opposing roles of ERK in regulating G(1) and S-G(2)/M delays in A549 cells caused by hyperoxia.
abstract: This study explores the role of ERK activation in regulating G(1) and S-G(2)/M delays during hyperoxia. We demonstrate here that exposing A549 human alveolar type 2 adenocarcinoma cells to hyperoxia (95% O(2)) for 0.5-24 h time-dependently increases phospho-ERK, phospho-p53(Ser15), p53, and p21(CIP1) protein levels. Decreasing phospho-ERK with the pharmacological inhibitors, PD98059 and U0126, markedly suppresses hyperoxia-stimulated phospho-p53(Ser15), p53, and p21(CIP1), and also restores the hyperoxia-reduced kinase activities of cyclin D1/E1-Cdks. Our results suggest that ERK activation during hyperoxia contributes to the p53/p21-mediated G(1) checkpoint. However, inhibition of ERK signaling during hyperoxia further delays S-phase entry and progression. Hyperoxia induces significant expression of cyclin A/B1 and translocation of cyclin A into nuclei while marginally decreasing cyclin A/B1-Cdks kinase activities, which may be related to nuclear association with p21. Interestingly, inhibition of ERK signaling markedly suppresses the elevation of cyclin A/B1 proteins and cyclin A/B1-Cdks kinase activities during hyperoxia. Taken together, the results presented here suggest that hyperoxia-activated ERK acts upstream of p53 and p21 to suppress G(1)-Cdk activities; however, it is also required for induction of cyclin A/B1 and maintenance of cyclin A/B1-Cdk activities that oppose delays in S-phase entry and progression.
authors.affiliation: Molecular Carcinogenesis Laboratory, Department of Life Sciences, Institute of Biotechnology, National Tsing Hua University, Hsinchu 300, Taiwan.
authors.forename: Jen-Chung
authors.initials: JC
authors.lastname: Ko
authors.forename: Yi-Ting
authors.initials: YT
authors.lastname: Wang
authors.forename: Jia-Ling
authors.initials: JL
authors.lastname: Yang
mesh_terms: D000230:Adenocarcinoma / Q000473:pathology; D015153:Blotting, Western; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D004789:Enzyme Activation; D005434:Flow Cytometry; D019084:Fluorescent Antibody Technique, Indirect; D016193:G1 Phase; D016195:G2 Phase; D006801:Humans; D018496:Hyperoxia / Q000503:physiopathology*; D008175:Lung Neoplasms / Q000473:pathology; D018613:Microscopy, Confocal; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008954:Models, Biological; D011233:Precipitin Tests; D016196:S Phase; D016159:Tumor Suppressor Protein p53 / Q000235:genetics
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D016159:Tumor Suppressor Protein p53; D018844:Cyclin-Dependent Kinases; D020928:Mitogen-Activated Protein Kinases