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.
Ahn
Dae-ho
DH
Gastrointestinal Research Laboratory, Veterans' Affairs Medical Center, San Francisco, California 94121, USA.
Crawley
Suzanne C
SC
Hokari
Ryota
R
Kato
Shingo
S
Yang
Stacey C
SC
Li
Jian-Dong
JD
Kim
Young S
YS
D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008156:Luciferases / Q000378:metabolism; D055262:Mucin-2; D009077:Mucins / Q000096:biosynthesis / Q000235:genetics*; D016328:NF-kappa B / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014158:Transcription, Genetic / Q000187:drug effects*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects; D000097782:NF-kappaB-Inducing Kinase
D048031:JNK Mitogen-Activated Protein Kinases; D008156:Luciferases; D055262:Mucin-2; D009077:Mucins; D016328:NF-kappa B; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D000097782:NF-kappaB-Inducing Kinase; C524625:MUC2 protein, human; C494918:AKT1 protein, human