The subcellular distribution of methionine sulfoxide reductase A in mouse and human tissues.

Among all known repair enzymes, methionine sulfoxide reductase A (MsrA) plays a key role in protecting against oxidative stress and its damaging effects. The enzyme is ubiquitously expressed in eukaryotic cells and different splice variants of the MsrA gene have been shown to permit the specific prevalence of the protein in different cell organelles. Here, we present novel insights in the intracellular localization of MsrA in selected samples from mouse and human tissue. Using immunocytochemical techniques at both the light and electron microscopic levels, we show incidence of MsrA in human oral mucosa cells, predominantly in the cell nucleus. In addition, the enzyme has been localized in mitochondria of mouse liver and kidney cells, in the cytoplasm of retina cells, and in the endoplasmic reticulum of glandular cells. Overall, the results indicate a correlation between the generation of reactive oxygen species (ROS) and the expression level of MsrA in subcellular compartments of the tissues examined.