ENTRY OF OPAA(-2 CELLS REQUIRES CONCERTED ACTION OF GLYCOSAMINOGLYCANS, FIBRONECTIN AND INTEGRIN RECEPTORS() GONOCOCCI INTO HEP)

Heparan sulphate proteoglycans are increasingly implicated as eukaryot ic cell surface receptors for bacterial pathogens. Here, we report tha t Neisseria gonorrhoeae adheres to proteoglycan receptors on HEp-2 epi thelial cells but that internalization of the bacterium by this cell t ype requires the serum glycoprotein fibronectin. Fibronectin was shown to bind specifically to gonococci producing the OpaA adhesin, Binding assays with fibronectin fragments located the bacterial binding site near the N-terminal end of the molecule. However, none of the tested f ibronectin fragments supported gonococcal entry into the eukaryotic ce lls; a 120 kDa fragment carrying the cell adhesion domain with the ami no acid sequence RGD even inhibited the fibronectin-mediated uptake of MS11-OpaA. This inhibition could be mimicked by an RGD-containing hex apeptide and by alpha 5 beta 1 integrin-specific antibodies, suggestin g that interaction of the central region of fibronectin with integrin receptors facilitated bacterial uptake. Fibronectin was unable to prom ote gonococcal entry into HEp-2 cells that had been treated with the e nzyme heparinase ill, which degrades the glycosaminoglycan side-chains of proteoglycan receptors. On the basis of these results, we propose a novel cellular uptake pathway for bacteria, which involves the bindi ng of the pathogen to glycosaminoglycans that, in turn, act as co-rece ptors facilitating fibronectin-mediated bacterial uptake through integ rin receptors. in this scenario, fibronectin would act as a molecular bridge linking the Opa-proteoglycan complex with host cell integrin re ceptors.