Outer Membrane Vesicles Mediate the Secretion and Nuclear Trafficking of a Bacterial Nucleomodulin

Nucleomodulins are a family of bacterial virulence proteins that traffic to the nucleus of host cells to disrupt nuclear processes and, in some cases, promote carcinogenesis. The mechanisms by which nucleomodulins are secreted and injected into host cells are not entirely clear. We hypothesised that bacterial extracellular vesicles (EVs), also known as outer membrane vesicles, may represent a novel mechanism for nucleomodulin delivery to host cells. To address this, we studied the role of EVs in the secretion of Helicobacter pylori tumour necrosis factor-α-inducing protein (Tipα), a protein that was reported to undergo nuclear trafficking and to promote carcinogenesis. Importantly, we showed that most Tipα present in H. pylori culture supernatants is associated with EVs and, moreover, is encapsulated within these particles in its biologically active dimeric form. Confocal microscopy and cell fractionation studies demonstrated that EVs carry Tipα to the nuclear compartment of host cells and can bind host DNA. EVs from isogenic tipA mutants induced greater pro-inflammatory cytokine responses in host cells than EVs from wild-type bacteria; however, this effect was dependent on the EV isolation method. We propose that EVs represent a new mechanism by which bacteria secrete and deliver nucleomodulins to their target cells, resulting in altered immune responses and possibly carcinogenesis.