NF-kappaB inducing kinase activates NF-kappaB transcriptional activity independently of IkappaB kinase gamma through a p38 MAPK-dependent RelA phosphorylation pathway.
Molecular and biochemical analysis indicates that nuclear transcription factor kappaB (NF-kappaB)-inducing kinase (NIK) mediates IKK activation and NF-kappaB transcriptional activity. However, gene deletion studies suggest that NIK triggers gene expression without affecting IkappaBalpha degradation and NF-kappaB DNA binding activity. In order to investigate the role of NIK in NF-kappaB transcriptional activity, we used mouse embryonic fibroblasts (MEF) derived from wild-type (wt) and IkappaB kinase gamma (IKKgamma) gene deficient (IKKgamma(-/-)) mice. We report that although TNF-induced NF-kappaB transcriptional activity is abolished in IKKgamma(-/-) cells, adenoviral gene delivery of NIK (Ad5NIK) still enhanced transcriptional activity and IL-6 mRNA accumulation. Moreover, NIK targets the transactivation function of NF-kappaB through stimulation of the transactivation domain (TAD) of RelA (S536) in IKKgamma(-/-) cells. Interestingly, Ad5NIK, but not TNF, induces RelA S536 and p38 mitogen-activated protein kinase (MAPK) phosphorylation in IKKgamma(-/-) cells. Functional analysis demonstrated that Ad5NIK-induced NF-kappaB transcriptional activity, IL-6 mRNA expression and RelA phosphorylation are inhibited by the p38 inhibitor SB203580, suggesting a role for this MAPK in NIK signaling to NF-kappaB. These data demonstrate for the first time the presence of an IKKgamma-independent NIK/p38 MAPK-dependent signaling pathway that activates NF-kappaB and induces pro-inflammatory gene expression through RelA phosphorylation.
Jijon
H
H
Center for Gastrointestinal Biology and Disease, Division of Gastroenterology and Hepatology, Department of Medicine, University of North Carolina, CB 7032, 7341B Medical Biomolecular Research Building, Chapel Hill, NC 27599-7080, USA.
Allard
B
B
Jobin
C
C
D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D017353:Gene Deletion; D051550:I-kappa B Kinase; D015850:Interleukin-6 / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout / Q000235:genetics; D016296:Mutagenesis; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D012333:RNA, Messenger / Q000378:metabolism; D051996:Transcription Factor RelA; D015533:Transcriptional Activation; D014162:Transfection; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000097782:NF-kappaB-Inducing Kinase
D051550:I-kappa B Kinase; D015850:Interleukin-6; D016328:NF-kappa B; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger; D051996:Transcription Factor RelA; D048051:p38 Mitogen-Activated Protein Kinases; D000097782:NF-kappaB-Inducing Kinase; C496564:Chuk protein, mouse; C496562:Ikbkb protein, mouse; C496566:Ikbke protein, mouse