TNF and irritable bowel syndrome: Abbreviations: ATF-2, activating transcription factor-2; DSS, dextran sulfate sodium; IBD, inflammatory bowel disease; IL-1β, interleukin-1β; LPS, lipopolysaccharide; MAPK, mitogen-activated protein kinase; MLC, myosin light chain; MLCK, myosin light chain kinase; NF-κB, nuclear factor-kappa B; TAK1, transforming growth factor beta-activated kinase 1; TNF-α, tumor necrosis factor-α; ZO-1, zonula occludens-1.