Syndecan-1 and syndecan-4 can mediate the invasion of OpaHSPG-expressing Neisseria gonorrhoeae into epithelial cells.

Neisseria gonorrhoeae (Ngo) expressing the outer membrane protein OpaHSPG can adhere to and invade epithelial cells via binding to heparan sulphate proteoglycan (HSPG) receptors. In this study, we have investigated the role of syndecan-1 and syndecan-4, two members of the HSPG family, in the uptake of Ngo by epithelial cells. When overexpressed in HeLa cells, both syndecans co-localize with adherent Ngo on the host cell surface. This overexpression of syndecan-1 and syndecan-4 leads to a three- and sevenfold increase in Ngo invasion respectively. In contrast, transfection with the syndecan-1 and syndecan-4 mutant constructs lacking the intracellular domain results in an abrogation of the invasion process, characteristic of a dominant-negative mode of action. A concomitant loss of the capacity to mediate Ngo uptake was also observed with syndecan-4 mutant constructs carrying lesions in the dimerization motif necessary for the binding of protein kinase C (PKC) and phosphatidylinositol 4,5-bisphosphate (PIP2), and mutants that are deficient in a C-terminal EFYA amino acid motif responsible for binding to syntenin or CASK. We conclude that syndecan-1 and syndecan-4 can both mediate Ngo uptake into epithelial cells, and that their intracellular domains play a crucial role in this process, perhaps by mediating signal transduction or anchorage to the cytoskeleton.

Ligation of cell surface heparan sulfate proteoglycans by antibody-coated beads stimulates phagocytic uptake into epithelial cells: a model for cellular invasion by Neisseria gonorrhoeae.

Binding of a particular opacity outer membrane protein (Opa) of Neisseria gonorrhoeae to cell surface heparan sulfate proteoglycans (HSPGs) of epithelial cells results in tight bacterial adherence; however, the role of this ligand-receptor interaction in triggering the subsequent bacterial internalization step is uncertain. Here we have used latex beads coated with HSPG-ligating antibodies as an in vitro model to study the role of HSPGs in gonococcal uptake into epithelial cells. Beads and gonococci showed the same cell line-specified adherence patterns and increase in phagocytic uptake mediated by serum or purified vitronectin (Vn). Heparitinase digestion as well as antibody competition experiments indicate that a critical level of HSPG ligation is necessary and sufficient to trigger phagocytic uptake into epithelial cells. Vn was found to specifically enhance HSPG-dependent phagocytic uptake while phagocytosis resulting from the ligation of other cell surface receptors was unaffected in the presence of Vn. Pharmacological studies with PKC inhibitors suggest a role for PKC in phagocytic uptake of HSPG-ligating beads. The use of drugs impairing cytoskeletal functions indicates that HSPG-dependent phagocytosis requires actin polymerization by a process distinct from receptor-mediated endocytosis.