ERK activation protects against DNA damage and apoptosis in hyperoxic rat AEC2.

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Abstract
The survival of type 2 alveolar epithelial cells (AEC2) in the lung after hyperoxic injury is regulated by signals from the cellular environment. Keratinocyte growth factor and Matrigel can ameliorate the hallmarks of apoptosis seen in hyperoxic AEC2 after 24-h culture on plastic [S. Buckley, L. Barsky, B. Driscoll, K. Weinberg, K. D. Anderson, and D. Warburton. Am. J. Physiol. 274 (Lung Cell. Mol. Physiol. 18): L714-L720, 1998]. We used the same model of in vivo short-term hyperoxia to characterize the protective effects of substrate attachment. Culture of hyperoxic AEC2 on various biological adhesion substrates showed reduced DNA end labeling in cells grown on all biological substrates compared with growth on plastic. In contrast, the synthetic substrate poly-D-lysine conferred no protection. Hyperoxic AEC2 cultured on laminin showed an increased ratio of expression of Bcl-2 to interleukin-1beta-converting enzyme compared with culture on plastic. Laminin also partially restored hyperoxia-depleted glutathione levels and conferred improved optimal mitochondrial viability as measured by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Conversely, attachment to the nonphysiological substrate poly-D-lysine afforded no such protection, suggesting that protection against hyperoxia-induced damage may be associated with integrin signaling. Increased activation of extracellular signal-regulated kinase (ERK), as detected by increased ERK tyrosine phosphorylation, was seen in hyperoxic AEC2 as soon as the cells started to attach to laminin and was sustained after 24 h of culture in contrast to that in control AEC2. To confirm that protection against DNA strand breakage and apoptosis was being conferred by ERK activation, the cells were also plated in the presence of 50 microM PD-98059, an inhibitor of the ERK-activating mitogen-activating kinase. Culture for 24 h with PD-98059 abolished the protective effect of laminin. We speculate that after hyperoxic lung injury, signals through the basement membrane confer specific protection against oxygen-induced DNA strand breakage and apoptosis through an ERK activation-dependent pathway.

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