The pilus and porin of Neisseria gonorrhoeae cooperatively induce Ca2+ transients in infected epithelial cells

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Abstract
Purified pili and porin from Neisseria quickly mobilize calcium (Ca(2+)) stores in monocytes and epithelial cells, ultimately influencing host cell viability as well as bacterial intracellular survival. Here, we examined the Ca(2+) transients induced in human epithelial cells during infection by live, piliated N. gonorrhoeae. Porin induced an influx of Ca(2+) from the extracellular medium less than 60 s post infection. The porin-induced transient is followed by a pilus-induced release of Ca(2+) from intracellular stores. The timing of these events is similar to that observed using purified proteins. Interestingly, the porin-induced Ca(2+) flux is required for the pilus-induced transient, indicating that the pilus-induced Ca(2+) release is, itself, Ca(2+) dependent. Several lines of evidence indicate that porin is present on pili. Moreover, pilus retraction strongly influences the porin- and pilus-induced Ca(2+) 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 Ca(2+) transients in the initial stages of pilus-mediated attachment.