Gonococcal phospholipase d modulates the expression and function of complement receptor 3 in primary cervical epithelial cells.

CR3-mediated endocytosis is a primary mechanism by which Neisseria gonorrhoeae elicits membrane ruffling and cellular invasion of the cervical epithelia. Our data indicate that, upon infection of cervical epithelia, N. gonorrhoeae specifically releases proteins, including a phospholipase D (PLD) homolog, which facilitate membrane ruffling. To elucidate the function of gonococcal PLD in infection of the cervical epithelia, we constructed an N. gonorrhoeae PLD mutant. By comparative association and/or invasion assays, we demonstrated that PLD mutant gonococci are impaired in their ability to adhere to and to invade primary cervical cells. This defect can be rescued by the addition of supernatants obtained from wild-type-infected cell monolayers but not by exogenously added Streptomyces PLD. The decreased level of total cell association (i.e., adherence and invasion) observed for mutant gonococci is, in part, attributed to the inability of these bacteria to recruit CR3 to the cervical cell surface with extended infection. Using electron microscopy, we demonstrate that gonococcal PLD may be necessary to potentiate membrane ruffling and clustering of gonococci on the cervical cell surface. These data may be indicative of the inability of PLD mutant gonococci to recruit CR3 to the cervical cell surface. Alternatively, in the absence of gonococcal PLD, signal transduction events required for CR3 clustering may not be activated. Collectively, our data indicate that PLD augments CR3-mediated gonococcus invasion of and survival within cervical epithelia. Neisseria gonorrhoeae is a strict human pathogen, which causes the sexually transmitted disease gonorrhea. This organism possesses multiple mechanisms by which it is able to colonize its sole human host and which are dependent upon the particular microenvironment of the infection site. In this respect, the gonococcus senses its particular microenvironment and adjusts its mode of pathogenicity accordingly. Several gonococcal constituents are implicated to play a role in its pathogenicity, including lipooligosaccharide (LOS), porin, pilus, and the opacity-associated outer membrane proteins. Invasion of male urethral epithelial cells is mediated by LOS, the terminal galactose of which serves as a ligand for the asialoglycoprotein receptor (ASGP-R) (15). An intimate association between the gonococcal and host cell membranes precedes clathrin-dependent endocytosis (15). In contrast, complement (C) receptor type 3 (CR3)-mediated endocytosis is a primary mechanism by which N. gonorrhoeae invades primary human cervical epithelial cells (8). This process is dependent upon the cooperative binding of (gonococcus-bound, host-derived) iC3b, gonococcal porin, and gonococcal pilus to the I domain of CR3 (7, 9). Engagement of CR3 results in membrane ruffling (8) and internalization of gonococci in macropinosomes (10). Our studies show that ruffling induced by gonococci during cervical cell infection is delayed from the onset of infection by 60 to 90 min (10). The onset of ruffling can be accelerated to 30 min by the addition of filtered, preconditioned (i.e., derived from a previous infection) medium. This prompted a search for factors which might be responsible for expediting the cytoskeletal changes induced by gonococcal infection. Here we describe the identification of gonococcal phospholipase D (PLD), which is specifically released upon infection of cervical epithelia. We further demonstrate a role for gonococcal PLD in membrane ruffling, CR3 recruitment to the cervical cell surface, and, consequently, in gonococcal invasion of the cervical epithelia. We propose that this secreted protein is a novel neisserial virulence factor, capable of modulating effector functions within host cells.