Role of decay-accelerating factor domains and anchorage in internalization of Dr-fimbriated Escherichia coli

Dr-fimbriated Escherichia coli capable of invading epithelial cells recognizes human decay-accelerating factor (DAF) as its cellular receptor. The role of extracellular domains and the glycosylphosphatidylinositol anchor of DAF in the process of internalization of Dr(+) E. coli was characterized in a cell-cell interaction model. Binding of Dr(+) E. coli to the short consensus repeat 3 domain of DAF expressed by Chinese hamster ovary cells was critical for internalization to occur. Deletion of short consensus repeat 3 domain or replacement of Ser(165) by Leu in this domain, or the use of a monoclonal antibody to this region abolished internalization. Replacing the glycosylphosphatidylinositol anchor of DAF with the transmembrane anchor of membrane cofactor protein or HLA-B44 resulted in abolition or reduction of internalization respectively. Cells expressing glycosylphosphatidylinositol-anchored DAF but not the transmembrane-anchored DAF internalized Dr(+) E. coli through a glycolipid pathway, since the former cells were more sensitive to inhibition by methyl-beta-cyclodextrin, a sterol-chelating agent. Electron microscopic studies revealed that the intracellular vacuoles containing the internalized Dr(+) E. coli were morphologically distinct between the anchor variants of DAF. The cells expressing glycosylphosphatidylinositol-anchored DAF contained a single bacterium in tight-fitting vacuoles, while the cells expressing transmembrane-anchored DAF contained multiple (two or three) bacteria in spacious phagosomes. This finding suggests that distinct postendocytic events operate in the cells expressing anchor variants of DAF. We provide direct evidence for the DAF-mediated internalization of Dr(+) E. coli and demonstrate the significance of the glycosylphosphatidylinositol anchor, which determines the ability and efficiency of the internalization event.