Prohibitin Inhibits Tumor Necrosis Factor alpha-induced Nuclear Factor-kappa B Nuclear Translocation via the Novel Mechanism of Decreasing Importin α3 Expression

Expression of prohibitin 1 (PHB), a multifunctional protein in the cell, is decreased during inflammatory bowel disease (IBD). Little is known regarding the regulation and role of PHB during intestinal inflammation. We examined the effect of tumor necrosis factor alpha (TNF-alpha), a cytokine that plays a central role in the pathogenesis of IBD, on PHB expression and the effect of sustained PHB expression on TNF-alpha activation of nuclear factor-kappa B (NF-kappa B) and epithelial barrier dysfunction, two hallmarks of intestinal inflammation. We show that TNF-alpha decreased PHB protein and mRNA abundance in intestinal epithelial cells in vitro and in colon mucosa in vivo. Sustained expression of prohibitin in intestinal epithelial cells in vitro and in vivo (prohibitin transgenic mice, PHB TG) resulted in a marked decrease in TNF-alpha-induced nuclear translocation of the NF-kappa B protein p65, NF-kappa B/DNA binding, and NF-kappa B-mediated transcriptional activation despite robust I kappa B-alpha phosphorylation and degradation and increased cytosolic p65. Cells overexpressing PHB were protected from TNF-alpha-induced increased epithelial permeability. Expression of importin alpha 3, a protein involved in p50/p65 nuclear import, was decreased in cells overexpressing PHB and in colon mucosa of PHB TG mice. Restoration of importin alpha 3 levels sustained NF-kappa B activation by TNF-alpha during PHB transfection. These results suggest that PHB inhibits NF-kappa B nuclear translocation via a novel mechanism involving alteration of importin alpha 3 levels. TNF-alpha decreases PHB expression in intestinal epithelial cells and restoration of PHB expression in these cells can protect against the deleterious effects of TNF-alpha and NF-kappa B on barrier function.