The Shigella type three secretion system effector OspF invades host nucleus by binding host importin α1.

Shigella type III effector OspF, a nuclear translocation protein, has been showed to have an essential role in Shigella flexneri infection and virulence; OspF increases inflammation and induces bacterial invasion by down-regulating MAPK kinases pathway. Nevertheless, the exact mechanisms underlying its nuclear translocation and signaling remain unclear. In the following study, we constructed series of OspF truncated mutants to identify the OspF nuclear localization signals which mapped to the amino acids 209-239. Moreover, we found that this sequence was essential to bind the canonical nuclear import adaptor importin α1. Additionally, the 209-239 residues deletion mutant could not bind the importin α1. Consistent with this observation, our results revealed that OspF can inhibit the MAPK signals in the nucleus. Moreover, OspF translocate to the nucleus through Ran-GTPase and importin α1-dependent manner. These results can provide new avenues for depicting the biological functions of OspF during Shigella infection.