Impairments in enzyme activity and biosynthesis of brush border-associatedhydrolases in human intestinal Caco-2/TC7 cells infected by members of theAfa/Dr family of diffusely adhering Escherichia coli

Wild-type diffusely adhering Escherichia coli (DAEC) harbouring afimbrial a dhesin (Afa) or fimbrial Dr and F1845 adhesins (Afa/Dr DAEC) apically infec ting the human intestinal epithelial cells promote injuries in the brush bo rder of the cells, We report here that infection by Afa/Dr DAEC wild-type s trains 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 (DP P IV). Blockers of the transduction signal molecules, previously found to b e active against the Afa/Dr DAEC-induced cytoskeleton injury, were inactive against the Afa/Dr-induced decrease in sucrase enzyme activity, In paralle l, Afa/Dr DAEC infection promotes the blockade of the biosynthesis of St an d DPP IV without affection enzyme stability. The observation that no change s occurred in mRNA levels of SI and DPP IV upon infection suggested that th e decrease in biosynthesis probably resulted from a decrease in the transla tion rate. When the cells were infected with recombinant E. coli strains ex pressing homologous adhesins of the wild-type strains, neither a decrease i n sucrase and DPP IV enzyme activities nor an inhibition of enzyme biosynth esis were observed. in conclusion, taken together, these data give new insi ghts into the mechanisms by which the wild-type Afa/Dr DAEC strains induce functional injuries in polarized fully differentiated human intestinal cell s, 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 pa thogenicity.