ENTEROINVASIVE BACTERIA DIRECTLY ACTIVATE EXPRESSION OF INOS AND NO PRODUCTION IN HUMAN COLON EPITHELIAL-CELLS

In these studies, we investigated whether bacterial infection of human colon epithelial cells is a sufficient stimulus to upregulate epithel ial cell expression of inducible nitric oxide synthase (iNOS) and nitr ic oxide (NO) production. Human colon epithelial cells (Caco-2 and HT- 29) rapidly upregulated iNOS mRNA and protein expression and NO produc tion after infection with enteroinvasive Escherichia coli, Salmonella dublin, or Shigella flexneri but not after infection with noninvasive E. coli or an invasion-deficient mutant of S. dublin. Bacterial infect ion in the absence of added cytokines was as potent or more potent a s timulus of iNOS expression and NO production as stimulation of cells w ith combinations of cytokines known to strongly upregulate this epithe lial cell response. Enteroinvasive E. coli increased epithelial NO pro duction to a greater extent than S. dublin, although S. dublin was a s tronger stimulus of epithelial cell interleukin-8 (IL-8) production. A fter enteroinvasive E. coli infection of polarized epithelial cell mon olayers, nitrite, a stable NO end product, was released predominately into the apical compartment early after infection, whereas IL-8 was re leased in parallel into the basolateral compartment. These studies sug gest NO and/or its redox products are an important component of the in testinal epithelial cell response to microbial infection.