Comparative transcriptional and translational analysis of heme oxygenase expression in response to sulfur mustard

Sulfur mustard (SM) is a potent alkylating agent which reacts with nucleophilic groups on DNA, RNA and proteins. It is capable of inducing cellular toxicity and oxidative stress via production of reactive oxygen species (ROS) and reactive nitrogen species (RNS). The accumulation of high amounts of the reactive species causes harmful effects such as DNA damage, lipid peroxidation, protein oxidation, inflammation and apoptosis. Although SM (also known as mustard gas) and its derivatives are rapidly removed from the body, long-term damages are much more serious than the short-term effects and may be correlated with the subsequent changes occurred on the genome. In order to defend against oxidative properties of this toxic molecule, cells trigger several anti-oxidant pathways through up-regulating the corresponding genes. Enzymes like heme oxygenase-1, superoxide dismutase and glutathione-S-transferase are the examples of such genes. These enzymes produce anti-oxidant substances that are able to scavenge the reactive species, alleviate their noxious effects and protect the cells. Following SM gas exposure, gene transcription (mRNA levels) of these enzymes are ramped up to help detoxify the cells. Yet, some studies have reported that the up-regulated transcription does not necessarily translate into higher protein expression levels. The exact reason why this phenomenon happens is not clear. Creation of mutations in the genome sequence may lead to protein structure changes. Phosphorylation or other post-translational alterations of proteins upon SM exposure are also considered as possible causes. In addition, alterations in some microRNAs responsible for regulating post-translation events may inhibit the expression of the anti-oxidant proteins in the poisoned cells at translational level.