TNFα- and IKKβ-mediated TANK/I-TRAF phosphorylation: implications for interaction with NEMO/IKKγ and NF-κB activation

Abstract

Pro-inflammatory cytokines trigger signalling cascades leading to NF-kappaB (nuclear factor-kappaB)-dependent gene expression through IKK [IkappaB (inhibitory kappaB) kinase]-dependent phosphorylation and subsequent degradation of the IkappaB proteins and via induced phosphorylation of p65. These signalling pathways rely on sequentially activated kinases which are assembled by essential and non-enzymatic scaffold proteins into functional complexes. Here, we show that the pro-inflammatory cytokine TNFalpha (tumour necrosis factor alpha) promotes TANK [TRAF (TNF receptor-associated factor) family member associated NF-kappaB activator] recruitment to the IKK complex via a newly characterized C-terminal zinc finger. Moreover, we show that TANK is phosphorylated by IKKbeta upon TNFalpha stimulation and that this modification negatively regulates TANK binding to NEMO (NF-kappaB essential modulator). Interestingly, reduced TANK expression by RNA interference attenuates TNFalpha-mediated induction of a subset of NF-kappaB target genes through decreased p65 transactivation potential. Therefore the scaffold protein TANK is required for the cellular response to TNFalpha by connecting upstream signalling molecules to the IKKs and p65, and its subsequent IKKbeta-mediated phosphorylation may be a mechanism to terminate the TANK-dependent wave of NF-kappaB activation.

A CD40 Kozak sequence polymorphism and susceptibility to antibody-mediated autoimmune conditions: the role of CD40 tissue-specific expression

“…Even though the signaling pathways of activation of CD40 in thyrocytes have not yet been examined, these can be postulated based on data from studies of activation of necrosis factor kappa B (NFkB) by transforming growth factor-beta (TGF-b) in Graves' thyrocytes, 49 as well as of CD40 signaling in other cell types. [50][51][52][53][54][55][56][57][58][59] According to our intrinsic hypothesis, CD40 ligand more readily activates CD40, overexpressed on the surface of thyrocytes in individuals harboring the CC genotype. Once activated, CD40 receptors multimerize, recruiting TNF-receptor associated factors (TRAFs) to their cytoplasmic tails.…”

“…Downstream of the initial receptor ligation, TRAFs recruit and activate kinases such as inhibitor of k-B (IkB) kinase (IKK), leading to activation of NFkB pathway. NFkB is able to turn on transcription of a number of genes including cytokines, chemokines and adhesion molecules, which could augment thyroidal inflammation [50][51][52][53][54][55][56][57][58][59] (Figure 4b). Moreover, activation of the CD40 pathway has been shown to activate anti-apoptotic pathways in several non-lympho- The intrinsic thyroidal CD40 model.…”

Lipopolysaccharide-mediated Interferon Regulatory Factor Activation Involves TBK1-IKKϵ-dependent Lys63-linked Polyubiquitination and Phosphorylation of TANK/I-TRAF

“…Human FLAG-TANK and truncation mutants of TANK were previously described, as were FLAG-TANK ⌬IKK⑀, FLAG-TANK⌬ZnF, FLAG-IKK⑀, and the wild type and kinase-dead IKK⑀-Myc constructs (18,37). The ISRE reporter plasmid was kindly provided by Dr. R. Beyaert (Department for Molecular Biomedical Research, Unit of Molecular Signal Transduction in Inflammation, VIB-Ghent University, Belgium).…”

Are the IKKs and IKK-related kinases TBK1 and IKK-ɛ similarly activated?

“…Later, its role in the NF-kB-activating pathways was supported by its binding to NEMO [57]. However, the role for TANK in the IKK-dependent NF-kB signaling cascades remains controversial because TANK-depleted, knockdown cells do not show any defect in TNF-a-or LPSmediated IKK activation [21,58]. Nevertheless, these observations do not rule out the possibility that TANK might connect upstream kinases such as TBK1 and IKK-e, thereby promoting IKK-independent phosphorylation of the NF-kB proteins p65 [59,60], c-Rel [61] or p52 [62] in response to as yet poorly characterized signals.…”