Research updateABINs: A20 binding inhibitors of NF-κB and apoptosis signaling
Graphical abstract
Introduction
Nuclear factor-κB (NF-κB) dependent gene expression plays a key role in development and immunity. The NF-κB family of transcription factors consists of five members: p50/p105, p52/p100, c-Rel, RelA (p65) and RelB, forming several homo- and heterodimers. In resting cells, NF-κB is kept inactive in the cytoplasm by binding to inhibitor of κB (IκB) proteins. In the classical NF-κB pathway, which is activated by tumor necrosis factor (TNF), interleukin-1 (IL-1), Toll-like receptors (TLRs) and other innate immune stimuli, receptor triggering stimulates an IκB kinase (IKK) complex consisting of the regulatory protein NEMO, also known as IKKγ, and the kinases IKKα and IKKβ. IKKβ mediates the phosphorylation of IκBα, followed by its K48-linked polyubiquitination and degradation by the proteasome. Free NF-κB then translocates to the nucleus where it can bind to κB elements in the promoters of responsive genes [1], [2]. Importantly, unrestrained NF-κB activation is associated with several autoimmune diseases and sepsis [3]. Several proteins therefore negatively regulate NF-κB activation by affecting specific protein–protein interactions or posttranslational modifications of NF-κB signaling proteins [4]. The expression of many of these negative regulators is itself regulated by NF-κB and thus imposes a negative feedback mechanism. One of these negative feedback NF-κB inhibitors is the ubiquitin-editing protein A20, also known as tumor necrosis factor alpha induced protein 3 (TNFAIP3) [5]. Remarkably, in some cells A20 also exerts anti-apoptotic activities. A20 deficient mice die shortly after birth due to massive inflammation and tissue damage in multiple organs. Moreover, A20 deficient murine embryonic fibroblasts are hypersensitive to TNF-induced apoptosis and show prolonged IKK activity and IκBα phosphorylation, leading to sustained NF-κB activation and enhanced cytokine production [6]. Mechanistically, A20 was shown to exert its NF-κB inhibitory function in TNF signaling by acting as a dual ubiquitin-editing protein on RIP1 [7]. The latter is normally K63-polyubiquitinated, which in contrast to K48-polyubiquitination does not trigger proteasome-mediated degradation but enables the binding of RIP1 to specific downstream signaling proteins such as the IKK adaptor protein NEMO that contains an ubiquitin-binding domain (UBD). The N-terminal de-ubiquitinating domain of A20 mediates the removal of K63-polyubiquitin chains from RIP1, whereas the C-terminal zinc finger domain catalyzes RIP1 K48-polyubiquitination, thereby targeting RIP1 for proteasomal degradation [7]. Similarly, A20 has been shown to inhibit lipopolysaccharide (LPS)-induced NF-κB activation by de-ubiquitinating K63-polyubiquitinated TRAF6 [8], but A20-mediated K48-ubiquitination of TRAF6 has not yet been reported.
Section snippets
Identification of ABINs
Yeast two-hybrid screening of a mouse fibroblast L929r2 cDNA library with A20 as bait originally led to the identification of A20-binding inhibitor of NF-κB (ABIN)-1 and ABIN-2 [9]. A TBLASTN search in the non-redundant and expressed sequence tag database identified ABIN-3 as another related protein [10]. Based on their identification in other independent studies, several alternative names have been given to ABINs: ABIN-1/TNIP-1/NAF1/VAN, ABIN-2/TNIP-2/FLIP1, ABIN-3/TNIP-3/LIND (see below).
ABIN-1
The human ABIN-1 gene is situated on chromosome 5q32–33.1 and consists of 18 exons. The first exon remains untranslated, whereas exons 2 till 18 contain the coding sequence. Cloning of the ABIN-1 cDNA revealed the existence of two isoforms of 72 kDa, ABIN-1α and ABIN-1β, which only differ in their C-terminus. Genomic structure analysis indicated that ABIN-1α and ABIN-1β are produced by alternative splicing, with ABIN-1β mRNA being synthesized when an alternative splice acceptor site within exon
ABIN-1
Several functions have been suggested for ABIN-1, mostly depending on the identity and function of its protein interaction partners. As already mentioned before, all ABINs bind to the ubiquitin-editing protein A20, which is known for its NF-κB inhibiting and anti-apoptotic activities. Similar to A20, ABIN-1 overexpression in HEK293T cells inhibits TNF-, IL-1-, and LPS-induced NF-κB activation [9]. Moreover, RNA interference of A20 also impairs the NF-κB inhibitory effect of ABIN-1
ABINs in disease
Given the central role of NF-κB in several inflammatory diseases, NF-κB inhibition has been proposed as a novel therapeutic strategy. Using a murine model of allergen-induced asthma, we demonstrated that adenovirus-mediated delivery of ABIN-1 to the lung results in considerable inhibition of allergen-induced NF-κB activity and eosinophil infiltration [67]. Furthermore, ABIN-1 decreases allergen-specific immunoglobulin E levels in the serum, as well as the levels of eotaxin, IL-1, IL-4, IL-5,
Conclusion and perspectives
From the above-mentioned findings it is clear that ABINs fulfill important roles in the regulation of immunity and normal tissue homeostasis. Much information is still based on results obtained by overexpression of specific ABINs but data from ABIN deficient mice have recently become available [47], [53]. These illustrate that each ABIN family member has specific non-redundant functions but that their originally described NF-κB inhibitory function might be redundant. The generation and analysis
Acknowledgements
Research in the authors lab is supported by grants from the ‘Interuniversitaire Attractiepolen’ (IAP6/18), the FWO-Vlaanderen (grant 3G010505), the ‘Foundation against Cancer’, the ‘Emmanuel van der Schueren Foundation’ and the ‘Geconcerteerde Onderzoeksacties’ (GOA grant 01G06B6) of the Ghent University. L.V. and K.V. hold a BOF postdoctoral fellowship from the Ghent University and a predoctoral fellowship from the IWT, respectively.
References (74)
- et al.
A20 and A20-binding proteins as cellular inhibitors of nuclear factor-κB-dependent gene expression and apoptosis
Biochem Pharmacol
(2000) - et al.
LIND/ABIN-3 is a novel LPS-inducible inhibitor of NF-κB activation
J Biol Chem
(2007) - et al.
Structure–function analysis of the A20-binding inhibitor of NF-κB, ABIN-1
FEBS Lett
(2003) - et al.
Identification and cloning of a novel cellular protein Naf1, Nef-associated factor 1, that increases cell surface CD4 expression
FEBS Lett
(1999) - et al.
Identification of direct genomic targets downstream of the nuclear factor-κB transcription factor mediating tumor necrosis factor signaling
J Biol Chem
(2005) - et al.
Gene expression profiling in conjunction with physiological rescues of IKKα-null cells with wild-type or mutant IKKα reveals distinct classes of IKKα/NF-κB-dependent genes
J Biol Chem
(2005) - et al.
Identification of Naf1/ABIN-1 among TNF-α-induced expressed genes in human synoviocytes using oligonucleotide microarrays
FEBS Lett
(2003) - et al.
Transcriptional profiling of IKK2/NF-κB-and p38 MAP kinase-dependent gene expression in TNF-α-stimulated primary human endothelial cells
Blood
(2004) - et al.
ABIN-1 binds to NEMO/IKKγ and co-operates with A20 in inhibiting NF-κB
J Biol Chem
(2006) - et al.
Identification of a novel A20-binding inhibitor of nuclear factor-kappa B activation termed ABIN-2
J Biol Chem
(2001)
Overexpression of ABIN-2, a negative regulator of NF-κB, delays liver regeneration in the ABIN-2 transgenic mice
Biochem Biophys Res Commun
Identification of a novel mechanism of NF-kappaB inactivation by progesterone through progesterone receptors in Hec50co poorly differentiated endometrial cancer cells: induction of A20 and ABIN-2
Gynecol Oncol
Optineurin negatively regulates TNF alpha-induced NF-kappaB activation by competing with NEMO for ubiquitinated RIP
Curr Biol
A new ERK2 binding protein, Naf1, attenuates the EGF/ERK2 nuclear signaling
Biochem Biophys Res Commun
Naf1 alpha is phosphorylated in mitotic phase and required to protect cells against apoptosis
Biochem Biophys Res Commun
Live and let die: Nef functions beyond HIV replication
Immunity
Regulation of the NF-κB activation pathway by isolated domains of FIP3/IKKγ, a component of the IκB-α kinase complex
J Biol Chem
ABIN-2 protects endothelial cells from death and has a role in the antiapoptotic effect of angiopoeitin-1
Blood
NF-κB1/p105 regulates lipopolysaccharide-stimulated MAP kinase signaling by governing the stability and function of the Tpl2 kinase
Mol Cell
The A20-binding protein ABIN-2 exerts unexpected function in mediating transcriptional coactivation
FEBS Lett
Nuclear factor-kappaB plays a centrale role in tumour necrosis factor-mediated liver disease
Biochem Pharmacol
Tumor necrosis factor alpha prevents tumor necrosis factor receptor-mediated mouse hepatocyte apoptosis, but not fas-mediated apoptosis: role of nuclear factor-kappaB
Hepatology
Molecular tools to reestablish progestin control of endometrial cancer cell proliferation
Am J Obstet Gynecol
Introduction to NF-κB: players, pathways, perspectives
Oncogene
Transcriptional regulation via the NF-κB signaling module
Oncogene
Nuclear factor-κB: its role in health and disease
J Mol Med
Post-translational modifications regulating the activity and function of the nuclear factor kappa B pathway
Oncogene
Failure to regulate TNF-induced NF-κB and cell death responses in A20-deficient mice
Science
De-ubiquitination and ubiquitin ligase domains of A20 downregulate NF-κB signaling
Nature
The ubiquitin-modifying enzyme A20 is required for termination of Toll-like receptor responses
Nat Immunol
The zinc finger protein A20 inhibits TNF-induced NF-κB-dependent gene expression by interfering with an RIP-or TRAF2-mediated transactivation signal and directly binds to a novel NF-κB-inhibiting protein ABIN
J Cell Biol
Ubiquitin binding mediates the NF-κB inhibitory potential of ABIN proteins
Oncogene
High frequency of alternative splicing of human genes participating in the HIV-1 life cycle
J Acquir Immune Defic Syndr
Multiple splicing variants of Naf1/ABIN-1 transcripts and their alterations in hematopoietic tumors
Int J Mol Med
A human nuclear shuttling protein that interacts with human immunodeficiency virus type 1 matrix is packaged into virions
J Virol
Divergent gene regulation and growth effects by NF-κB in epithelial and mesenchymal cells of human skin
Oncogene
Identification of NF-κB-regulated genes induced by TNFα utilizing expression profiling and RNA interference
Oncogene
Cited by (144)
Establishment and characterization of a new activated B-cell-like DLBCL cell line, TMD12
2022, Experimental HematologyStructural and Biochemical Basis for Higher-Order Assembly between A20-Binding Inhibitor of NF-κB 1 (ABIN1) and M1-Linked Ubiquitins
2021, Journal of Molecular BiologyPrecision medicine in lupus nephritis: can biomarkers get us there?
2018, Translational Research