Figure 6. Model of the Role of Pilus Retraction in Promoting a Cytoprotective Environment during Gonococcal Infection of an Epithelial Cell.

(1) Initial contact between the bacterium and host cell activates low levels of MAPK, and transcription of infection-induced genes. This level of signaling may or may not be able to protect the cell from apoptosis; thus, the host cell “teeters” on the edge of life and death.

(2) As the infection proceeds, microcolonies of gonococci are formed, and more pili are locally available to retract.

(3) Pilus retraction amplifies MAPK activation, which in turn enhances the transcription of mechanical stress–induced genes.

(4) Pilus retraction may also stimulate other pathways that mediate gene expression and survival signaling. Overall signaling events tip the balance in favor of cell survival.