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Protein and Vesicle Trafficking, Cytoskeleton

Novel effect of NF-B activation: carbonylation and nitration injury to cytoskeleton and disruption of monolayer barrier in intestinal epithelium

Section of Gastroenterology and Nutrition, Department of Internal Medicine, Department of Pharmacology, and Department of Molecular Physiology, Rush University Medical Center, Chicago, Illinois 60612

Submitted 18 March 2004 ; accepted in final form 31 May 2004

Using monolayers of intestinal cells, we reported that upregulation of inducible nitric oxide synthase (iNOS) is required for oxidative injury and that activation of NF-B is key to cytoskeletal instability. In the present study, we hypothesized that NF-B activation is crucial to oxidant-induced iNOS upregulation and its injurious consequences: cytoskeletal oxidation and nitration and monolayer dysfunction. Wild-type (WT) cells were pretreated with inhibitors of NF-B, with or without exposure to oxidant (H₂O₂). Other cells were transfected with an IB mutant (an inhibitor of NF-B). Relative to WT cells exposed to vehicle, oxidant exposure caused increases in IB instability, NF-B subunit activation, iNOS-related activity (NO, oxidative stress, tubulin nitration), microtubule disassembly and instability (increased monomeric and decreased polymeric tubulin), and monolayer disruption. Monolayers pretreated with NF-B inhibitors (MG-132, lactacystin) were protected against oxidation, showing decreases in all measures of the NF-B iNOS NO pathway. Dominant mutant stabilization of IB to inactivate NF-B suppressed all measures of the iNOS/NO upregulation while protecting monolayers against oxidant insult. In these mutants, we found prevention of tubulin nitration and oxidation and enhancement of cytoskeletal and monolayer stability. We concluded that 1) NF-B is required for oxidant-induced iNOS upregulation and for the consequent nitration and oxidation of cytoskeleton; 2) NF-B activation causes cytoskeletal injury following upregulation of NO-driven processes; and 3) the molecular event underlying the destabilizing effects of NF-B appears to be increases in carbonylation and nitrotyrosination of the subunit components of cytoskeleton. The ability to promote NO overproduction and cytoskeletal nitration/oxidation is a novel mechanism not previously attributed to NF-B in cells.

tubulin cytoskeleton; microtubules; oxidation/nitration; inducible nitric oxide synthase/peroxynitrite; inflammatory bowel disease; Caco-2 cells; gut barrier; nuclear factor-B/IB

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