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 epithelia l cells by interacting with a complement-regulatory protein, decay-accelera ting factor. This model of bacterial internalization, with a well-character ized bacterial ligand and host receptor, provides a unique opportunity to i nvestigate the early stages of invasion. We used immunofluorescence stainin g techniques to examine the distribution of receptor and cytoskeletal prote ins in HeLa cells infected with E. coli recombinant strains that expressed Dr family of adhesins: Dr, Dr-II, F1845, AFA-I, and AFA-III, A major rearra ngement of decay-accelerating factor was found at the adherence sites of re combinant strains expressing Dr, Dr-II, and F1845 adhesins, The changes in the distribution of receptor were significantly smaller on HeLa cells infec ted with E. coli bearing AFA-I or AFA-III afimbrial adhesins. Receptor aggr egation was associated with the redistribution of cytoskeleton-associated p roteins such as actin, alpha-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 bea ds to HeLa cells. Using scanning and transmission electronmicroscopic techn iques, we have shown that beads coated with Dr fimbriae, as opposed to bead s coated with bovine serum albumin, were enwrapped by cellular microvilli a nd ultimately internalized into HeLa cells. This indicates that interaction of Dr fimbriae with decay-accelerating factor is associated with redistrib ution of receptor and is sufficient to promote bacterial internalization.