Methionine sulfoxide reductase A (MsrA) is a ubiquitous antioxidant repair enzyme which specifically reduces the oxidized methionine (Met-O) in proteins to methionine (Met). Previous studies have shown that lack of or overexpression of MsrA in cells affects the function of proteins and can lead to altered cellular processes. Interestingly, some pathogenic bacteria secrete and/or carry MsrA on their surface, suggesting some key roles for this enzyme in the modulation of host cellular processes. Therefore, we investigated how exogenously added MsrA affects the ability of the host cells in combating infection by using an in vitro Mycoplasma genitalium cytotoxicity model. HeLa cells pretreated with MsrA and infected with M. genitalium showed significantly lower necrosis (cytotoxicity) than untreated cells infected with M. genitalium. Intriguingly, necrotic cell death pathway specific real time RT-PCR revealed that M. genitalium infection upregulates the expression of the TNF gene in HeLa cells and that MsrA pretreatment of the cells downregulates its expression significantly. Consistent with this, enzyme linked immunosorbent assay (ELISA) results showed that HeLa cells pretreated with MsrA secreted reduced levels of TNF-α following M. genitalium infection. Also, our study demonstrates that MsrA treatment of cells affects the phosphorylation status of transcriptional regulators such as NF-кB, JNK and p53 that regulate different cytokines. Further, fluorescent microscopy showed the cellular uptake of exogenously added MsrA fused with red fluorescent protein (MsrA-RFP). Altogether, our results suggest that secreted MsrA may help pathogens to modulate host cellular processes.
