TNF-alpha activates MUC2 transcription via NF-kappaB but inhibits via JNK activation

The molecular mechanisms responsible for TNF- alpha-mediated MUC2 intestinal mucin up- regulation in HM3 colon adenocarcinoma cells were analyzed using promoter- reporter assays of the 5'- flanking region of the MUC2 gene. Chemical inhibitors, mutant reporter constructs, and EMSA confirmed I- kappaB/ NF- kappaB pathway involvement. Wortmannin, LY294002 and dominant negative Akt, as well as dominant negative NF- kappaB- inducing kinase ( NIK) inhibited MUC2 reporter transcription, indicating that both phosphatidylinositol- 3- OH kinase ( PI3K)/ Akt signaling pathway and NIK pathways mediate the effects of TNF- alpha. Wortmannin inhibited NF- kappaB binding and transcriptional activity without inhibiting NF-kappaB translocation to the nucleus, indicating that PI3K/ Akt signaling activates NF- kappaB transcriptional activity directly. Our results demonstrate that TNF-alpha up- regulates MUC2 in human colon epithelial cells via several signaling pathways, involving both NIK and PI3K/ Akt, which converge at the common IKK/ I- kappaB/ NF- kappaB pathway. TNF- alpha activated JNK, but JNK inhibitor SP600125 and dominant negative cJun consistently activated transcription, revealing a negative role for this signaling pathway. Thus TNF- alpha causes a net up- regulation of MUC2 gene expression in cultured colon cancer cells because NF- kappaB transcriptional activation of this gene is able to counter- balance the suppressive effects of the JNK pathway. However, the existence of this inhibitory JNK pathways suggests a mechanism whereby - in the absence of NF- kappaB activation TNF- alpha production during inflammation in vivo could actually inhibit MUC2 production, giving rise to the defective mucosal protection which characterizes inflammatory bowel disease. Copyright (C) 2005 S. Karger AG, Basel.