Over-expression of methionine sulfoxide reductase A in the endoplasmic reticulum increases resistance to oxidative and ER stresses.

ABSTRACT

MsrA and MsrB catalyze the reduction of methionine-S-sulfoxide and methionine-R-sulfoxide, respectively, to methionine in different cellular compartments of mammalian cells. One of the three MsrBs, MsrB3, is an endoplasmic reticulum (ER)-type enzyme critical for stress resistance including oxidative and ER stresses. However, there is no evidence for the presence of an ER-type MsrA or the ER localization of MsrA. In this work, we developed an ER-targeted recombinant MsrA construct and investigated the potential effects of methionine-S-sulfoxide reduction in the ER on stress resistance. The ER-targeted MsrA construct contained the N-terminal ER-targeting signal peptide of human MsrB3A (MSPRRSLPRPLSLCLSLCLCLCLAAALGSAQ) and the C-terminal ER-retention signal sequence (KAEL). The over-expression of ER-targeted MsrA significantly increased cellular resistance to H2O2-induced oxidative stress. The ER-targeted MsrA over-expression also significantly enhanced resistance to dithiothreitol-induced ER stress; however, it had no positive effects on the resistance to ER stresses induced by tunicamycin and thapsigargin. Collectively, our data suggest that methionine-S-sulfoxide reduction in the ER compartment plays a protective role against oxidative and ER stresses.