Conversion of TNFα from antiproliferative to proliferative ligand in mouse intestinal epithelial cells by regulating mitogen-activated protein kinase

The mechanisms regulating the balance between intestinal epithelial cell proliferation and differentiation are essential to maintaining an intact mucosal barrier. Mitogen-activated protein (MAP) kinases appear to be key transducers of extracellular signals in these pathways. The goal of this study was to investigate the regulation of MAP kinase by tumor necrosis factor iv (TNF alpha) and epidermal growth factor (EGF) in intestinal epithelial cells. The young adult mouse colon cell line was studied for TNF alpha and/or EGF regulation of MAP kinase in the presence or absence of the MAP kinase kinase (MEK1) inhibitor PD 98059. Proliferation was determined by hemocytometry, and activated MAP kinase was identified by Western blot analysis, in vitro kinase assay, and confocal laser immunofluorescent microscopy. TNFa stimulated sustained nuclear MAP kinase activity, while EGF stimulated transient cytoplasmic MAP kinase activity. Changing TNF alpha's sustained MAP kinase activation to transient converted TNF alpha from an anti-proliferative to a proliferative ligand. These findings demonstrate that both TNF alpha and EGF activate MAP kinase in intestinal epithelial cells. The kinetics and subcellular distribution of this enzyme activity may be pivotal in the transduction of divergent cellular responses in the intestinal epithelium with implications for altered proliferative signals in inflammatory bowel, disease. (C) 1999 Academic Press.