Escherichia coli expressing a Neisseria gonorrhoeae opacity-associated outer membrane protein invade human cervical and endometrial epithelial cell lines.

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Abstract
Members of the opacity-associated (Opa) outer membrane protein family of Neisseria gonorrhoeae have been proposed to mediate adherence to and invasion of cultured human epithelial cells. We transformed Escherichia coli with a plasmid containing a gonococcal opa gene fused in-frame to the leader sequence of the beta-lactamase gene as described by Palmer et al. [Palmer, L., Brooks, G. F. & Falkow, S. (1989) Mol. Microbiol. 3, 663-671]. These transformed E. coli [E. coli (opa)] expressed the heat-modifiable opa gene product (the Opa protein) in their outer membrane and adhered to and invaded ME-180 human endocervical epithelial cells. In a 2-h adherence assay, an average of 26.7 E. coli (opa) adhered per ME-180 cell, whereas the control E. coli carrying only the expression vector (pKT279) did not adhere at all (less than 0.15 bacterium per cell). We investigated the ability of the adherent E. coli (opa) to invade ME-180 epithelial cells by using a gentamicin selection assay. We recovered up to 1 x 10(6) gentamicin-resistant bacteria per monolayer when ME-180 cells were infected with E. coli (opa) compared to less than 10 bacteria when the epithelial cells were infected with the same number of control E. coli (pKT279). The kinetics and level of invasion by E. coli (opa) were similar to invasion by Opa+ N. gonorrhoeae. Maximum invasion occurred 4 h after infection with 4 x 10(7) bacteria. Transmission electron microscopy studies confirmed that E. coli (opa) invaded ME-180 cells. In comparative studies, the number of E. coli (opa) that invaded HEC-1-B human endometrial epithelial cells was about an order of magnitude less than the number that invaded ME-180 cells, and E. coli (opa) did not invade Chang human conjunctival epithelial cells at all. The observations that early (less than 4 h) invasion by E. coli (opa) was dramatically inhibited, in a dose-responsive manner, by the actin-disrupting reagent cytochalasin D but later invasion (8-24 h) was not suggest that invasion mediated by Opa proteins may occur by two mechanisms, only one of which is dependent upon microfilament function. Transmission electron microscopy also revealed that infected epithelial cells had a dramatically increased amount of cytoplasmic fibrillar material surrounding the nucleus. The function and genesis of this material remain unclear. These studies indicate that at least one gonococcal Opa protein is an invasin.