Purified pili and porin from Neisseria quickly mobilize calcium (Ca2+) stores in monocytes and epithelial cells, ultimately influencing host cell viability as well as bacterial intracellular survival. Here, we examined the Ca2+ transients induced in human epithelial cells during infection by live, piliated N. gonorrhoeae. Porin induced an influx of Ca2+ from the extracellular medium less than 60 s post infection. The porin-induced transient is followed by a pilus-induced release of Ca2+ from intracellular stores. The timing of these events is similar to that observed using purified proteins. Interestingly, the porin-induced Ca2+ flux is required for the pilus-induced transient, indicating that the pilus-induced Ca2+ release is, itself, Ca2+ dependent. Several lines of evidence indicate that porin is present on pili. Moreover, pilus retraction strongly influences the porin- and pilus-induced Ca2+ fluxes. These and other results strongly suggest that the pilus and porin cooperate to modulate calcium signalling in epithelial cells, and propose a model to explain how N. gonorrhoeae triggers Ca2+ transients in the initial stages of pilus-mediated attachment.
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