IKK Complex Research Articles

H-RN, a novel antiangiogenic peptide derived from hepatocyte growth factor inhibits inflammation in vitro and in vivo through PI3K/AKT/IKK/NF-κB signal pathway

H-RN, a novel antiangiogenic peptide derived from the kringle 1 domain of hepatocyte growth factor (HGF), consists of the sequence RNPRGEEGGPW (molecular weight: 1254.34Da). Emerging evidence indicates that HGF and the kringle domain exhibit anti-inflammatory effects in inflammatory diseases. In the present study, we assessed the anti-inflammatory effect of H-RN in models of experimental ocular inflammation, including endotoxin-induced uveitis (EIU) and experimental autoimmune uveitis (EAU). The results demonstrated that intravitreal treatment of H-RN concentration-dependently suppressed clinical manifestation, inhibited ocular inflammatory cytokine production and improved histopathologic scores. Moreover, H-RN attenuated the LPS-induced mRNA and protein expression of tumor necrosis factor (TNF)-α and interleukin (IL)-6 in RAW 264.7 cells and inhibited cell chemotactic migration toward LPS. We also demonstrated that H-RN suppressed TNF-α-induced adhesion molecule expression in HUVECs, including ICAM-1, VCAM-1 and E-selectin, which contributed to its suppressive effect on adherence of U937 cells to endothelial cells. We also demonstrated the possible anti-inflammation mechanism of H-RN. Western blot and immunofluorescence staining analyses revealed that H-RN significantly suppressed LPS-induced phosphorylation of nuclear factor (NF)-κB-p65 at Ser276. Based on examination of upstream pathways, we found that H-RN inhibited PI3K-p85 and AKTSer473 phosphorylation, which may result in the attenuation of LPS-induced IKK complex activation and IκB degradation. Thus, our studies suggest that the 11-amino-acid peptide H-RN exhibits anti-inflammatory effects in vitro and in vivo and may represent a promising candidate for ocular inflammatory diseases.

Hepatitis B Virus Polymerase Suppresses NF-κB Signaling by Inhibiting the Activity of IKKs via Interaction with Hsp90β

Nuclear factor-κB (NF-κB) plays a central role in the regulation of diverse biological processes, including immune responses, development, cell growth, and cell survival. To establish persistent infection, many viruses have evolved strategies to evade the host’s antiviral immune defenses. In the case of hepatitis B virus (HBV), which can cause chronic infection in the liver, immune evasion strategies used by the virus are not fully understood. It has recently been reported that the polymerase of HBV (Pol) inhibits interferon-β (IFN-β) activity by disrupting the interaction between IKKε and the DDX3. In the current study, we found that HBV Pol suppressed NF-κB signaling, which can also contribute to IFN-β production. HBV Pol did not alter the level of NF-κB expression, but it prevented NF-κB subunits involved in both the canonical and non-canonical NF-κB pathways from entering the nucleus. Further experiments demonstrated that HBV Pol preferentially suppressed the activity of the IκB kinase (IKK) complex by disrupting the association of IKK/NEMO with Cdc37/Hsp90, which is critical for the assembly of the IKK complex and recruitment of the IKK complex to the tumor necrosis factor type 1 receptor (TNF-R1). Furthermore, we found that HBV Pol inhibited the NF-κB-mediated transcription of target genes. Taken together, it is suggested that HBV Pol could counteract host innate immune responses by interfering with two distinct signaling pathways required for IFN-β activation. Our studies therefore shed light on a potential therapeutic target for persistent infection with HBV.

Cytosolic-DNA-Mediated, STING-Dependent Proinflammatory Gene Induction Necessitates Canonical NF-κB Activation through TBK1

STING (stimulator of interferon genes) is known to control the induction of innate immune genes in response to the recognition of cytosolic DNA species, including the genomes of viruses such as herpes simplex virus 1 (HSV-1). However, while STING is essential for protection of the host against numerous DNA pathogens, sustained STING activity can lead to lethal inflammatory disease. It is known that STING utilizes interferon regulatory factor 3 (IRF3) and nuclear factor κB (NF-κB) pathways to exert its effects, although the signal transduction mechanisms remain to be clarified fully. Here we demonstrate that in addition to the activation of these pathways, potent induction of the Jun N-terminal protein kinase/stress-activated protein kinase (JNK/SAPK) pathway was similarly observed in response to STING activation by double-stranded DNA (dsDNA). Furthermore, TANK-binding kinase 1 (TBK1) associated with STING was found to facilitate dsDNA-mediated canonical activation of NF-κB as well as IRF3 to promote proinflammatory gene transcription. The triggering of NF-κB function was noted to require TRAF6 activation. Our findings detail a novel dsDNA-mediated NF-κB activation pathway facilitated through a STING-TRAF6-TBK1 axis and suggest a target for therapeutic intervention to plausibly stimulate antiviral activity or, alternatively, avert dsDNA-mediated inflammatory disease. The IKK complex, which is composed of two catalytic subunits, IKKα and IKKβ, has been suggested to be essential for the activation of canonical NF-κB signaling in response to various stimuli, including cytokines (e.g., interleukin-1α [IL-1α] and tumor necrosis factor alpha [TNF-α]), Toll-like receptor (TLR) ligands (e.g., lipopolysaccharide [LPS]), and dsRNAs derived from viruses, or a synthetic analog. STING has been identified as a critical signaling molecule required for the detection of cytosolic dsDNAs derived from pathogens and viruses. However, little is known about how cytosolic dsDNA triggers NF-κB signaling. In the present study, we demonstrate that TBK1, identified as an IKK-related kinase, may predominantly control the activation of NF-κB in response to dsDNA signaling via STING through the IKKαβ activation loop. Thus, our results establish TBK1 as a downstream kinase controlling dsDNA-mediated IRF3 and NF-κB signaling dependent on STING.

The Role of IKKβ in Venezuelan Equine Encephalitis Virus Infection

Venezuelan equine encephalitis virus (VEEV) belongs to the genus Alphavirus, family Togaviridae. VEEV infection is characterized by extensive inflammation and studies from other laboratories implicated an involvement of the NF-κB cascade in the in vivo pathology. Initial studies indicated that at early time points of VEEV infection, the NF-κB complex was activated in cells infected with the TC-83 strain of VEEV. One upstream kinase that contributes to the phosphorylation of p65 is the IKKβ component of the IKK complex. Our previous studies with Rift valley fever virus, which exhibited early activation of the NF-κB cascade in infected cells, had indicated that the IKKβ component underwent macromolecular reorganization to form a novel low molecular weight form unique to infected cells. This prompted us to investigate if the IKK complex undergoes a comparable macromolecular reorganization in VEEV infection. Size-fractionated VEEV infected cell extracts indicated a macromolecular reorganization of IKKβ in VEEV infected cells that resulted in formation of lower molecular weight complexes. Well-documented inhibitors of IKKβ function, BAY-11-7082, BAY-11-7085 and IKK2 compound IV, were employed to determine whether IKKβ function was required for the production of infectious progeny virus. A decrease in infectious viral particles and viral RNA copies was observed with inhibitor treatment in the attenuated and virulent strains of VEEV infection. In order to further validate the requirement of IKKβ for VEEV replication, we over-expressed IKKβ in cells and observed an increase in viral titers. In contrast, studies carried out using IKKβ−/− cells demonstrated a decrease in VEEV replication. In vivo studies demonstrated that inhibitor treatment of TC-83 infected mice increased their survival. Finally, proteomics studies have revealed that IKKβ may interact with the viral protein nsP3. In conclusion, our studies have revealed that the host IKKβ protein may be critically involved in VEEV replication.

Bone Marrow-Specific Knock-In of a Non-Activatable Ikkα Kinase Mutant Influences Haematopoiesis but Not Atherosclerosis in Apoe-Deficient Mice

BackgroundThe Ikkα kinase, a subunit of the NF-κB-activating IKK complex, has emerged as an important regulator of inflammatory gene expression. However, the role of Ikkα-mediated phosphorylation in haematopoiesis and atherogenesis remains unexplored. In this study, we investigated the effect of a bone marrow (BM)-specific activation-resistant Ikkα mutant knock-in on haematopoiesis and atherosclerosis in mice.Methods and Results Apolipoprotein E (Apoe)-deficient mice were transplanted with BM carrying an activation-resistant Ikkα gene (IkkαAA/AAApoe−/−) or with Ikkα+/+Apoe−/− BM as control and were fed a high-cholesterol diet for 8 or 13 weeks. Interestingly, haematopoietic profiling by flow cytometry revealed a significant decrease in B-cells, regulatory T-cells and effector memory T-cells in IkkαAA/AAApoe−/− BM-chimeras, whereas the naive T-cell population was increased. Surprisingly, no differences were observed in the size, stage or cellular composition of atherosclerotic lesions in the aorta and aortic root of IkkαAA/AAApoe−/− vs Ikkα+/+Apoe−/− BM-transplanted mice, as shown by histological and immunofluorescent stainings. Necrotic core sizes, apoptosis, and intracellular lipid deposits in aortic root lesions were unaltered. In vitro, BM-derived macrophages from IkkαAA/AAApoe−/− vs Ikkα+/+Apoe−/− mice did not show significant differences in the uptake of oxidized low-density lipoproteins (oxLDL), and, with the exception of Il-12, the secretion of inflammatory proteins in conditions of Tnf-α or oxLDL stimulation was not significantly altered. Furthermore, serum levels of inflammatory proteins as measured with a cytokine bead array were comparable.ConclusionOur data reveal an important and previously unrecognized role of haematopoietic Ikkα kinase activation in the homeostasis of B-cells and regulatory T-cells. However, transplantation of IkkαAA mutant BM did not affect atherosclerosis in Apoe−/− mice. This suggests that the diverse functions of Ikkα in haematopoietic cells may counterbalance each other or may not be strong enough to influence atherogenesis, and reveals that targeting haematopoietic Ikkα kinase activity alone does not represent a therapeutic approach.

Copper is a potent inhibitor of both the canonical and non-canonical NFκB pathways

Copper is an essential trace element that plays key roles in many metabolic processes. Homeostatic regulation of intracellular copper is normally tightly controlled, but deregulated copper levels are found in numerous metabolic and neurodegenerative diseases, as well as in a range of neoplasms. There are conflicting reports regarding the exact role of copper in the regulation of NFκB-responsive genes, specifically whether copper leads to increased activation of the NFκB pathways, or downregulation. Here we show that increased intracellular levels of copper, using the ionophore clioquinol, leads to a potent inhibition of NFκB pathways, induced by multiple distinct stimuli. Addition of copper to cells inhibits ubiquitin-mediated degradation of IκBα by preventing its phoshorylation by the upstream IKK complex. Intriguingly, copper-dependent inhibition of NFκB can be reversed by the addition of the reducing agent, N-acetylcysteine (NAC). These results suggest that the oxidative properties of excess copper prevent NFκB activation by blocking IκBα destruction, and that NFκB activity should be assessed in diseases associated with copper excess.

MEKK3 and TAK1 synergize to activate IKK complex in Helicobacter pylori infection

Helicobacter pylori colonises the gastric epithelial cells of half of the world's population and represents a risk factor for gastric adenocarcinoma. In gastric epithelial cells H. pylori induces the immediate early response transcription factor nuclear factor of kappa light polypeptide gene enhancer in B-cells (NF-κB) and the innate immune response. We show that H. pylori induces in a type IV secretion system-dependent (T4SS) and cytotoxin associated gene A protein (CagA)-independent manner a transient activation of the inhibitor of NF-κB (IκBα) kinase (IKK)-complex. IKKα and IKKβ expression stabilises the regulatory IKK complex subunit NF-κB essential modulator (NEMO). We provide evidence for an intimate mutual control of the IKK complex by mitogen-activated protein kinase kinase kinase 3 (MEKK3) and transforming growth factor β activated kinase 1 (TAK1). TAK1 interacts transiently with the E3 ubiquitin ligase tumor necrosis factor receptor-associated factor 6 (TRAF6). Protein modifications in the TAK1 molecule, e.g. TAK1 autophosphorylation and K63-linked ubiquitinylation, administer NF-κB signalling including transient recruitment of the IKK-complex. Overall, our data uncover H. pylori-induced interactions and protein modifications of the IKK complex, and its upstream regulatory factors involved in NF-κB activation.

The SUMOylation machinery is dispensable for Tax-induced NF-kB activation

The HTLV-1 Tax protein is a good example of the diversity and functional importance of post-translational modifications. Indeed, Tax is phosphorylated, acetylated, conjugated to at least K48- and K63-linked poly-ubiquitin chains as well as to SUMO-1 and SUMO-2/3 molecules. In previous studies, we and others proposed that these modifications regulate both the intracellular distribution of Tax and its ability to activate the NF-kB pathway. In particular, Tax SUMOylation was associated to the formation of Tax nuclear bodies believed to represent transcriptionally active structures. However, our recent finding that a Tax mutant intrinsically weakly SUMOylated remains able to fully activate a NF-kB promoter challenged the importance of SUMOylation and/or nuclear body formation in the NF-kB activity of Tax. In this study, we further explored the role of Tax SUMOylation by targeting Ubc9, the unique E2 SUMO conjugating enzyme. We found that either a catalytically inactive form of Ubc9 (Ubc9-C93S) or Ubc9 siRNA totally blocks Tax conjugation to endogenous SUMO-1 or SUMO-2/3, showing that as expected, Tax SUMOylation is under the control of the catalytic activity of Ubc9. We next observed that this absence of Tax SUMOylation prevents neither the activation of the cytoplasmic IKK complex nor the activation of a NF-kB promoter. Finally, we also observed that surprisingly, the ability of Tax to form nuclear body was also not affected by overexpression of Ubc9-C93S. These data provide the direct demonstration that Tax SUMOylation and nuclear body formation are dispensable for Tax-induced NF-kB activation.

Low levels of HTLV-2 Tax conjugation to ubiquitin and SUMO do not impede Tax-mediated activation of NF-κB

Constitutive activation of NF-κB by HTLV-1 Tax is a key event in the process of T lymphocyte immortalization and leukemogenesis. Tax1 is post-translationally modified by both ubiquitin and SUMO. These modifications were originally thought to be required for Tax1-mediated NF-κB activation by allowing recruitment of IKK-γ/NEMO together with Tax1 in Golgi-associated cytoplasmic domains, followed by activation of the IKK complex and RelA/p65 nuclear translocation. Although HTLV-2 Tax also activates the canonical NF-κB pathway, the requirement of post-translational modifications had not been investigated so far. We therefore compared the ubiquitination, SUMOylation, and acetylation patterns of Tax2 and Tax1. We first show that in contrast to Tax1, Tax2 conjugation to endogenous ubiquitin and SUMO is barely detectable while both Tax2 and Tax1 are acetylated. Consistent with these observations, overexpression of the E2 ubiquitin-conjugating enzyme Ubc13 does not affect Tax2 conjugation to ubiquitin and Tax2-mediated NF-κB activation. We further identify the domains surrounding Tax1 lysine residues K4-10 and K6-10 as critical determinants of Tax conjugation to ubiquitin and SUMO, respectively. We finally demonstrate that a non-ubiquitinable, non-SUMOylable, and non-acetylable Tax2 mutant retains a significant ability to activate transcription from a NF-κB-dependent promoter after partial activation of the IKK complex and induction of RelA/p65 nuclear translocation. Taken together, these results thus indicate that Tax2 does not share Tax1 requirements toward ubiquitination and SUMOylation for efficient NF-κB activation and highlight key distinctions between both viral proteins. These results will be discussed in the light of the recent findings from other labs.

Detection of NF-κB pathway activation in T helper cells.

Upon activation of CD4+ T helper cells the transcription factor complex NF-κB becomes activated and its subunits are able to translocate to the nucleus. There, the dimerized proteins regulate the transcription of for example cytokine and pro-survival genes. This process is of central importance for a proper function of T helper cells as its loss causes severe immunodeficiency, whereas its deregulation can contribute to lymphomagenesis or autoimmunity. In this protocol we describe four methods to investigate NF-κB activation in T helper cells by testing (1) the assembly of the Carma1-Malt1-Bcl10 complex by co-immunoprecipitation, (2) the activation of the IKK complex and the degradation of IκBα by western blot analysis, (3) the degradation of IκBα by intracellular flow cytometry, and (4) the nuclear translocation and DNA binding activity of NF-κB by nonradioactive electrophoretic mobility shift assay (EMSA).

The IκB kinase complex in NF ‐κB regulation and beyond

The IκB kinase (IKK) complex is the signal integration hub for NF-κB activation. Composed of two serine-threonine kinases (IKKα and IKKβ) and the regulatory subunit NEMO (also known as IKKγ), the IKK complex integrates signals from all NF-κB activating stimuli to catalyze the phosphorylation of various IκB and NF-κB proteins, as well as of other substrates. Since the discovery of the IKK complex components about 15years ago, tremendous progress has been made in the understanding of the IKK architecture and its integration into signaling networks. In addition to the control of NF-κB, IKK subunits mediate the crosstalk with other pathways, thereby extending the complexity of their biological function. This review summarizes recent advances in IKK biology and focuses on emerging aspects of IKK structure, regulation and function.

HTLV-1 Tax deregulates autophagy by recruiting autophagic molecules into lipid raft microdomains.

The retroviral oncoprotein Tax from Human T cell leukemia virus type 1 (HTLV-1), an etiological factor that causes adult T cell leukemia and lymphoma, plays a crucial role in initiating T lymphocyte transformation by inducing oncogenic signaling activation. We here report that Tax is a determining factor for dysregulation of autophagy in HTLV-1-transformed T cells and Tax-immortalized CD4 memory T cells. Tax facilitated autophagic process by activating IκB kinase complex, which subsequently recruited an autophagy molecular complex containing Beclin1 and Bif-1 to the lipid raft microdomains. Tax engaged a crosstalk between IκB kinase complex and autophagic molecule complex by directly interacting with both complexes, promoting assembly of LC3+ autophagosomes. Moreover, expression of lipid raft-targeted Bif-1 or Beclin1 was sufficient to induce formation of LC3+ autophagosomes, suggesting that Tax recruitment of autophagic molecules to lipid rafts is a dominant strategy to deregulate autophagy in the context of HTLV-1 transformation of T cells. Furthermore, depletion of autophagy molecules such as Beclin1 and PI3 kinase class III resulted in impaired growth of HTLV-1-transformed T cells, indicating a critical role of Tax-deregulated autophagy in promoting survival and transformation of virally infected T cells.

Evasion of Antiviral Immunity through Sequestering of TBK1/IKKε/IRF3 into Viral Inclusion Bodies

Cells are equipped with pattern recognition receptors (PRRs) such as the Toll-like and RIG-I-like receptors that mount innate defenses against viruses. However, viruses have evolved multiple strategies to evade or thwart host antiviral responses. Viral inclusion bodies (IBs), which are accumulated aggregates of viral proteins, are commonly formed during the replication of some viruses in infected cells, but their role in viral immune evasion has rarely been explored. Severe fever with thrombocytopenia syndrome (SFTS) is an emerging febrile illness caused by a novel phlebovirus in the Bunyaviridae. The SFTS viral nonstructural protein NSs can suppress host beta interferon (IFN-β) responses. NSs can form IBs in infected and transfected cells. Through interaction with tank-binding kinase 1 (TBK1), viral NSs was able to sequester the IKK complex, including IKKε and IRF3, into IBs, although NSs did not interact with IKKε or IRF3 directly. When cells were infected with influenza A virus, IRF3 was phosphorylated and active phosphorylated IRF3 (p-IRF3) was translocated into the nucleus. In the presence of NSs, IRF3 could still be phosphorylated, but p-IRF3 was trapped in cytoplasmic IBs, resulting in reduced IFN-β induction and enhanced viral replication. Sequestration of the IKK complex and active IRF3 into viral IBs through the interaction of NSs and TBK1 is a novel mechanism for viral evasion of innate immunity.

RACK1 modulates NF-κB activation by interfering with the interaction between TRAF2 and the IKK complex

The transcription factor NF-κB plays a pivotal role in innate immunity in response to a variety of stimuli, and the coordinated regulation of this pathway determines the proper host responses to extracellular signals. In this study, we identified RACK1 as a novel negative regulator of NF-κB signaling, NF-κB-mediated cytokine induction and inflammatory reactions. RACK1 physically associates with the IKK complex in a TNF-triggered manner. This interaction interferes with the recruitment of the IKK complex to TRAF2, which is a critical step for IKK phosphorylation and subsequent activation triggered by TNF. By modulating the interaction between TRAF2 and IKK, RACK1 regulates the levels of NF-κB activation in response to different intensities of stimuli. Our findings suggest that RACK1 plays an important role in controlling the sensitivity of TNF-triggered NF-κB signaling by regulating IKK activation and provide new insight into the negative regulation of inflammatory reactions.

Silencing of the cell cycle checkpoint gene 14‐3‐3σ in basal cell carcinomas correlates with reduced expression of IKK‐α

14-3-3σ is down-regulated in a large proportion of basal cell carcinomas (BCC). IkappaB kinase α (IKK-α), one of the two catalytic subunits of the IKK complex involved in NF-kappaB-activation, also functions as a modulator of epidermal development and differentiation. Down-regulation of IKK-α causes hyperplasia and promotes skin cancer. IKK-α has been found to regulate the expression of 14-3-3σ by shielding its promoter from hypermethylation and thereby preventing its silencing in mouse keratinocytes. To evaluate the potential role of IKK-α in the silencing of 14-3-3σ in basal cell carcinoma. Expression of 14-3-3σ and IKK-α was studied by immunohistochemistry in 33 sporadic BCCs and 26 BCCs from patients with basal cell nevus syndrome (BCNS). Marked reduction or absence of 14-3-3σ was found in 24 (92%) BCCs from BCNS patients, and in 29 (88%) sporadic BCCs. Marked reduction or absence of IKK-α was found in 22 (85%) BCCs from patients with BCNS, and in 27 (82%) sporadic BCCs. Expression levels for 14-3-3σ and IKK-α correlated positively in 92% of BCCs from BCNS patients, and in 85% of sporadic BCCs. Our findings suggest that down-regulation of IKK-α is required for 14-3-3σ promoter methylation and silencing in the pathogenesis of BCC. Besides, our observation that 14-3-3σ silencing is also frequently found in BCC from patients with BCNS suggests a possible link between the sonic hedgehog/patched and 14-3-3σ/IKK-α pathways.

Dysfunctional NF-κB and brain myelin formation

Dysfunctional NF-κB and brain myelin formation

Molecular control of the NEMO family of ubiquitin-binding proteins

Research over the past decade has revealed how NF-κB essential modulator (NEMO; also known as IKKγ) regulates the IKKα-IKKβ signalling axis in the innate immune system. The discovery that NEMO is a polyubiquitin-binding protein and that the IKK complex is modulated by other protein kinases that are themselves controlled by polyubiquitin chains has provided a deeper molecular understanding of the non-degradative roles of ubiquitylation. New mechanistic insights of NEMO and related polyubiquitin-binding proteins have become a paradigm for how the interplay between phosphorylation and ubiquitylation controls cell signalling networks in health and disease.

Activation of the canonical IKK complex by K63/M1-linked hybrid ubiquitin chains

Polyubiquitin (pUb) chains formed between the C terminus of ubiquitin and lysine 63 (K63) or methionine 1 (M1) of another ubiquitin have been implicated in the activation of the canonical IκB kinase (IKK) complex. Here, we demonstrate that nearly all of the M1-pUb chains formed in response to interleukin-1, or the Toll-Like Receptors 1/2 agonist Pam3CSK4, are covalently attached to K63-pUb chains either directly as K63-pUb/M1-pUb hybrids or indirectly by attachment to the same protein. Interleukin-1 receptor (IL-1R)-associated kinase (IRAK) 1 is modified first by K63-pUb chains to which M1-pUb linkages are added subsequently, and myeloid differentiation primary response gene 88 (MyD88) and IRAK4 are also modified by both K63-pUb and M1-pUb chains. We show that the heme-oxidized IRP2 ubiquitin ligase 1 interacting protein (HOIP) component of the linear ubiquitin assembly complex catalyzes the formation of M1-pUb chains in response to interleukin-1, that the formation of K63-pUb chains is a prerequisite for the formation of M1-pUb chains, and that HOIP interacts with K63-pUb but not M1-pUb linkages. These findings identify K63-Ub oligomers as a major substrate of HOIP in cells where the MyD88-dependent signaling network is activated. The TGF-beta-activated kinase 1 (TAK1)-binding protein (TAB) 2 and TAB3 components of the TAK1 complex and the NFκB Essential Modifier (NEMO) component of the canonical IKK complex bind to K63-pUb chains and M1-pUb chains, respectively. The formation of K63/M1-pUb hybrids may therefore provide an elegant mechanism for colocalizing both complexes to the same pUb chain, facilitating the TAK1-catalyzed activation of IKKα and IKKβ. Our study may help to resolve the debate about the relative importance of K63-pUb and M1-pUb chains in activating the canonical IKK complex.

IκB kinase complex (IKK) triggers detachment-induced autophagy in mammary epithelial cells independently of the PI3K-AKT-MTORC1 pathway

Adherent cells require proper integrin-mediated extracellular matrix (ECM) engagement for growth and survival; normal cells deprived of proper ECM contact undergo anoikis. At the same time, autophagy is induced as a survival pathway in both fibroblasts and epithelial cells upon ECM detachment. Here, we further define the intracellular signals that mediate detachment-induced autophagy and uncover an important role for the IκB kinase (IKK) complex in the induction of autophagy in mammary epithelial cells (MECs) deprived of ECM contact. Whereas the PI3K-AKT-MTORC1 pathway activation potently inhibits autophagy in ECM-detached fibroblasts, enforced activation of this pathway is not sufficient to suppress detachment-induced autophagy in MECs. Instead, inhibition of IKK, as well as its upstream regulator, MAP3K7/TAK1, significantly attenuates detachment-induced autophagy in MECs. Furthermore, function-blocking experiments corroborate that both IKK activation and autophagy induction result from decreased ITGA3-ITGB1 (α3β1 integrin) function. Finally, we demonstrate that pharmacological IKK inhibition enhances anoikis and accelerates luminal apoptosis during acinar morphogenesis in three-dimensional culture. Based on these results, we propose that the IKK complex functions as a key mediator of detachment-induced autophagy and anoikis resistance in epithelial cells.

Defective immune responses in mice lacking LUBAC-mediated linear ubiquitination in B cells

The linear ubiquitin chain assembly complex (LUBAC) plays a crucial role in activating the canonical NF-κB pathway, which is important for B-cell development and function. Here, we describe a mouse model (B-HOIP(Δlinear)) in which the linear polyubiquitination activity of LUBAC is specifically ablated in B cells. Canonical NF-κB and ERK activation, mediated by the tumour necrosis factor (TNF) receptor superfamily receptors CD40 and TACI, was impaired in B cells from B-HOIP(Δlinear) mice due to defective activation of the IKK complex; however, B-cell receptor (BCR)-mediated activation of the NF-κB and ERK pathways was unaffected. B-HOIP(Δlinear) mice show impaired B1-cell development and defective antibody responses to thymus-dependent and thymus-independent II antigens. Taken together, these data suggest that LUBAC-mediated linear polyubiquitination is essential for B-cell development and activation, possibly via canonical NF-κB and ERK activation induced by the TNF receptor superfamily, but not by the BCR.