Targeting of the Yersinia pestis YopM protein into HeLa cells and intracellular trafficking to the nucleus

The YopM virulence protein of Yersinia pestis has been described as binding human alpha-thrombin and inhibiting thrombin-induced platelet aggregation in vitro. However, recent studies have shown that a YopM-CyaA fusion protei n could be targeted vectorially into eukaryotic cells through the Yersinia type III secretion system. In this study, our objective was to characterize YopM's fate in more detail. We followed YopM in the culture medium and ins ide infected HeLa cells. We confirmed that the native YopM is targeted into HeLa cells, where it is insensitive to exogenous trypsin. The bacteria mus t be surface located to target YopM, and YopB and YopD are necessary, where as the LcrE protein (called also YopN) makes this process more efficient. I mmunofluorescence localization revealed that YopM, in contrast to YopE, is not only targeted to the cytoplasm but also trafficks to the cell's nucleus by means of a vesicle-associated pathway that is strongly inhibited by bre feldin A, perturbed by monensin or bafilomycin Al and dependent upon microt ubules (decreased by colchicine and nocodazole). These findings revealed a novel interaction of Yersinia pestis with its eukaryotic host.