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

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.