Different accumulation of activated extracellular signal-regulated kinases(ERK 1/2) and role in cell-cycle alterations by epidermal growth factor, hydrogen peroxide, or asbestos in pulmonary epithelial cells

The extracellular signal-regulated kinase (ERK) pathway is induced by cytok ines and oxidative stress. In this study we examined the patterns of locali zation of phosphorylated ERK proteins in relationship to subsequent phenoty pic: responses by the mitogenic agent epidermal growth factor (EGF) (5 ng/ mi); hydrogen peroxide (H2O2) (100 to 300 muM), an inducer of apoptosis; an d crocidolite asbestos (5 mug/cm(2) dish) in a nontransformed murine alveol ar type II epithelial cell line (C10), Laser scanning cytometry and flow cy tometry were used to determine: (1) whether expression of phosphorylated ER Ks was cell cycle-related; and (2) whether cell-cycle alterations by agents could be modified after addition of the mitogen-activated protein kinase/E RK kinase (MEK) 1 inhibitor PD98059, In contrast to other stimuli which ind uced transient increases in phosphorylated ERKs, asbestos caused fiber-asso ciated localization of phosphorylated ERKs that were elevated from 1 to 24 h (P less than or equal to 0.05), and striking apoptosis followed by increa sed numbers of cells in the S phase at 72 h. In both control and asbestos-e xposed cells, the percentage of phosphorylated ERK-positive cells was great est in cells in the C-2/M and 5 phases of the cell cycle. All stimuli cause d increased proportions of cells in C-2/M at 24 h that were inhibited by PD 98059 (30 muM). Increases in G(2)/M cells by H2O2 and asbestos also were de creased at 48 h by the MEK-1 inhibitor. In addition, PD98059 abrogated elev ations in S-phase cells by EGF and H2O2 at 24 h and by asbestos at 72 h. Ou r results suggest that ERKs mediate cell-cycle alterations during the devel opment of epithelial cell apoptosis or proliferation by diverse ERK stimuli .