Co-culture supernatants from Vibrio vulnificus-infected INT-407 cells induce IL-8 production in intestinal epithelial cells: crucial role of V. vulnificus rtxE.

In a previous study, we reported that a gene mutation of repeat in toxin E (RtxE), a transporter of cytotoxic factors, resulted in a significant impairment of epithelial cell cytotoxicity in Vibrio vulnificus, and that the expression of the rtxE gene was induced by the exposure to the host cells. In this study, we evaluated and compared the effects of co-culture supernatants from V. vulnificus-infected INT-407 cells and either the V. vulnificus wild-type or rtxE mutant on the production of interleukin (IL)-8, a pro-inflammatory cytokine, as well as its underlying mechanisms in human intestinal epithelial cells. INT-407 cells were co-cultured with the wild-type V. vulnificus or the rtxE mutant strain to obtain the conditioned supernatants. IL-8 production and nuclear factor (NF)-κB activation from the INT-407 cells treated with each supernatant, were investigated. The co-culture supernatants from the rtxE mutant V. vulnificus-infected INT-407 cells significantly induced lower levels of IL-8 production and promoter activation, NF-κB DNA binding activity, and NF-κB minimal promoter activation in human intestinal epithelial cells, than those from the wild-type V. vulnificus-infected INT-407 cells. Importantly, the reduced IL-8 production and NF-κB activity of the V. vulnificus rtxE mutant, were restored by co-culture supernatants from the rtxE-complemented V. vulnificus. On the whole, these results show that the rtxE gene of V. vulnificus performs a critical role in the secretion of factors from bacteria and host cells, which are involved in IL-8 production via the NF-κB activation pathway in host cells.