The transcriptosomal response of human A549 lung cells to a hydrogen peroxide-generating system: relationship to DNA damage, cell cycle arrest, and caspase activation.

Intracellular oxidative stress is a dynamic situation characterized by the accumulation of reactive oxygen metabolites, such as hydrogen peroxide. This is traditionally associated with both macromolecular damage and adaptive changes in gene expression, aimed at preventing cellular demise. However, the overall extent of such genetic changes is not well characterized. Here we present a comprehensive analysis of altered mRNA profiles in human A549 type II lung epithelial cells in response to hydrogen peroxide, at concentrations failing to induce necrotic toxicity. The results of an Affymetrix-based screen of the steady-state levels of mRNAs for several thousand genes revealed a complex pattern of transcriptional and/or posttranscriptional response to oxidative stress, which can be functionally related to both the oxidation and repair of damaged DNA, the induction and permanency of cell cycle arrest, and caspase-3 activation. Many of the genetic events can be related to activation of the p53/p21 pathway, but many other novel inductions and suppressions were detected, revealing the intricacy of the response. The data also disclosed a potential interaction between hydrogen peroxide treatment and increased sensitivity to cell killing by TRAIL, which could be functionally confirmed at the level of induction of caspase-3 activity.

Protein S-glutathionylation correlates to selective stress gene expression and cytoprotection.

During situations of oxidative stress phenotypic adaptation to altered redox state is achieved by changes in expression of selected genes. The mechanisms regulating this may involve reversible S-glutathionylation of cellular proteins. In this study we compared and contrasted changes in gene expression patterns in human type II lung epithelial A549 cells and human endothelial ECV304 cells in correlation to glutathione oxidation and the formation of glutathione-protein mixed disulphides, after exposure to subtoxic levels of hydrogen peroxide, formed in the medium by addition of glucose oxidase, or the thiol oxidant diamide. Both the number of specific mRNAs and their levels of induction were grossly correlated to the degree of S-glutathionylation of cellular protein. Thus, diamide induced the expression of a variety of protein and DNA chaperones and transcriptional regulators, particularly in ECV304 cells. On the other hand, the peroxide failed to induce many of these species, in association with only minimal disturbances to glutathione homeostasis. The induction of the chaperone responses at the level of mRNA was clearly shown to translate into a more resistant morphological phenotype in response to both heat shock and oxidative stress induced by the DNA-damaging pro-oxidant potassium bromate.