gene transcription and translation, as well as epigenetic mechanisms such as DNA methylation or acetylation. miRNAs comprise a highly conserved 18�C22 bp RNA family that bind to mRNA and either block transcription or promote mRNA degradation and thus represent a unique mechanism for controlling gene expression. It has been proposed that miRNAs regulate the expression of many mammalian genes. Therefore it is likely that miRNAs regulate AZD-8055 several genes involved in the cellular response to potentially lethal stressors. While it seems likely that there is a mechanistic connection between miRNAs and the response to cellular stress, there have been few studies to date demonstrating this in mammalian cells. In plants it has been shown that changes in miRNA expression appear to be important in tolerance to stresses resulting from changes in environmental conditions including nutrient and water availability, acidity, and temperature. In normal human cells, it has been shown that miRNAs can alter p53 activity, and it is now widely reported that miRNA expression is altered in several benign and malignant diseases. Changes in miRNA expression also occur under conditions of hypoxia, and are localized to stress response elements in cells subjected to various stressors. Therefore, it seems logical that miRNAs may play a role in the preprogrammed intracellular response to exogenous cytotoxic agents that induce oxidative stress. Ionizing radiation is an important modality used in the treatment of malignancy and is one example of an agent that induces oxidative genotoxic stress. Ionizing radiation causes severe cellular damage and stress both directly, by energetic disruption of DNA integrity, and indirectly, as a result of the formation of intracellular free 1421373-65-0 chemical information radicals. A small number of studies have shown an effect of radiation on miRNA expression patterns both in vitro and in vivo. Two studies have shown that radiation sensitivity can be altered by upregulating the expression of a single miRNA species. However, the mechanism underlying the effect of radiation on specific miRNA expression remains to be elucidated. In this study, we show that alterations in miRNA expression due to ionizing radiation are also produced in res