TRAF3 controls activation of the canonical and alternative NFkappaB by the lymphotoxin beta receptor.
Components of lymphotoxin beta receptor (LTBR)-associated signaling complexes, including TRAF2, TRAF3, NIK, IKK1, and IKK2 have been shown to participate in the coupling of LTBR to NFkappaB. Here, we report that TRAF3 functions as a negative regulator of LTBR signaling via both canonical and non-canonical NFkappaB pathways by two distinct mechanisms. Analysis of NFkappaB signaling in cell lines with functionally intact NFkappaB pathway but lacking LTBR-mediated induction of NFkappaB target genes revealed an inverse association of cellular TRAF3 levels with LTBR-specific defect in canonical NFkappaB activation. Increased expression of TRAF3 correlated with its increased recruitment to LTBR-induced signaling complexes, decreased recruitment of TRAF2, and attenuated phosphorylation of IkappaB alpha and RelA. In contrast, activation of NFkappaB by TNF did not depend on TRAF3 levels. siRNA-mediated depletion of TRAF3 promoted recruitment of TRAF2 and IKK1 to activated LTBR, enabling LTBR-inducible canonical NFkappaB signaling and NFkappaB target gene expression. TRAF3 knock-down also increased mRNA and protein expression of several non-canonical NFkappaB components, including NFkappaB2/p100, RelB, and NIK, accompanied by processing of NFkappaB2/p100 into p52. These effects of TRAF3 depletion did not require LTBR signaling and were consistent with autonomous activation of the non-canonical NFkappaB pathway. Our data illustrate the function of TRAF3 as a dual-mode repressor of LTBR signaling that controls activation of canonical NFkappaB, and de-repression of the intrinsic activity of non-canonical NFkappaB. Modulation of cellular TRAF3 levels may thus contribute to regulation of NFkappaB-dependent gene expression by LTBR by affecting the balance of LTBR-dependent activation of canonical and non-canonical NFkappaB pathways.
Bista
Pradeep
P
Department of Immunology, Biogen Idec, Inc., Cambridge, Massachusetts 02142, USA.
Zeng
Weike
W
Ryan
Sarah
S
Bailly
Veronique
V
Browning
Jeffrey L
JL
Lukashev
Matvey E
ME
D045744:Cell Line, Tumor; D005786:Gene Expression Regulation / Q000502:physiology*; D055785:Gene Knockdown Techniques; D006801:Humans; D051550:I-kappa B Kinase / Q000235:genetics / Q000378:metabolism; D020672:I-kappa B Proteins / Q000235:genetics / Q000378:metabolism; D053259:Lymphotoxin beta Receptor / Q000235:genetics / Q000378:metabolism*; D052003:NF-kappa B p52 Subunit / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology*; D047992:TNF Receptor-Associated Factor 2 / Q000235:genetics / Q000378:metabolism; D048008:TNF Receptor-Associated Factor 3 / Q000235:genetics / Q000378:metabolism*; D051996:Transcription Factor RelA / Q000235:genetics / Q000378:metabolism*; D051841:Transcription Factor RelB / Q000235:genetics / Q000378:metabolism*; D000097782:NF-kappaB-Inducing Kinase
D051550:I-kappa B Kinase; D020672:I-kappa B Proteins; D053259:Lymphotoxin beta Receptor; D052003:NF-kappa B p52 Subunit; D017346:Protein Serine-Threonine Kinases; D034741:RNA, Small Interfering; D047992:TNF Receptor-Associated Factor 2; D048008:TNF Receptor-Associated Factor 3; D051996:Transcription Factor RelA; D051841:Transcription Factor RelB; D000097782:NF-kappaB-Inducing Kinase; C505697:LTBR protein, human; C498143:RELA protein, human; C497593:RELB protein, human; C090656:TRAF3 protein, human; C496559:CHUK protein, human