Decay-accelerating factor and cytoskeleton redistribution pattern in HeLa cells infected with recombinant Escherichia coli strains expressing Dr family of adhesins

Escherichia coli strains expressing Dr fimbriae are able to enter epithelial cells by interacting with a complement-regulatory protein, decay- accelerating factor. This model of bacterial internalization, with a well- characterized bacterial ligand and host receptor, provides a unique opportunity to investigate the early stages of invasion. We used immunofluorescence staining techniques to examine the distribution of receptor and cytoskeletal proteins in HeLa cells infected with E. coli recombinant strains that expressed Dr family of adhesins: Dr, Dr-H, F1845, AFA-I, and AFA-III. A major rearrangement of decay-accelerating factor was found at the adherence sites of recombinant strains expressing Dr, Dr-II, and F1845 adhesins. The changes in the distribution of receptor were significantly smaller on HeLa cells infected with E. coli bearing AFA-I or AFA-III afimbrial adhesins. Receptor aggregation was associated with the redistribution of cytoskeleton-associated proteins such as actin, α-actinin, ezrin, and occasionally tropomyosin. Purified Dr fimbriae coated on polystyrene beads were capable of triggering clustering of receptor and accumulating actin at the adhesion sites of beads to HeLa cells. Using scanning and transmission electron microscopic techniques, we have shown that beads coated with Dr fimbriae, as opposed to beads coated with bovine serum albumin, were enwrapped by cellular microvilli and ultimately internalized into HeLa cells. This indicates that interaction of Dr fimbriae with decay- accelerating factor is associated with redistribution of receptor and is sufficient to promote bacterial internalization.