Impairments in enzyme activity and biosynthesis of brush border‐associated hydrolases in human intestinal Caco‐2/TC7 cells infected by members of the Afa/Dr family of diffusely adhering Escherichia coli

Wild‐type diffusely adhering Escherichia coli (DAEC) harbouring afimbrial adhesin (Afa) or fimbrial Dr and F1845 adhesins (Afa/Dr DAEC) apically infecting the human intestinal epithelial cells promote injuries in the brush border of the cells. We report here that infection by Afa/Dr DAEC wild‐type strains C1845 and IH11128 in polarized human fully differentiated Caco‐2/TC7 cells dramatically impaired the enzyme activity of functional brush border‐associated proteins sucrase‐isomaltase (SI) and dipeptidylpeptidase IV (DPP IV). Blockers of the transduction signal molecules, previously found to be active against the Afa/Dr DAEC‐induced cytoskeleton injury, were inactive against the Afa/Dr‐induced decrease in sucrase enzyme activity. In parallel, Afa/Dr DAEC infection promotes the blockade of the biosynthesis of SI and DPP IV without affection enzyme stability. The observation that no changes occurred in mRNA levels of SI and DPP IV upon infection suggested that the decrease in biosynthesis probably resulted from a decrease in the translation rate. When the cells were infected with recombinant E. coli strains expressing homologous adhesins of the wild‐type strains, neither a decrease in sucrase and DPP IV enzyme activities nor an inhibition of enzyme biosynthesis were observed. In conclusion, taken together, these data give new insights into the mechanisms by which the wild‐type Afa/Dr DAEC strains induce functional injuries in polarized fully differentiated human intestinal cells. Moreover, the results revealed that other pathogenic factor(s) distinct from the Afa/Dr adhesins may play(s) a crucial role in this mechanism of pathogenicity.