Explore the vast range of titles available.

NF-κB (nuclear factor-κB) is a collective name for inducible dimeric transcription factors composed of members of the Rel family of DNA-binding proteins that recognize a common sequence motif. NF-κB is found in essentially all cell types and is involved in activation of an exceptionally large number of genes in response to infections, inflammation, and other stressful situations requiring rapid reprogramming of gene expression. NF-κB is normally sequestered in the cytoplasm of nonstimulated cells and consequently must be translocated into the nucleus to function. The subcellular location of NF-κB is controlled by a family of inhibitory proteins, IκBs, which bind NF-κB and mask its nuclear localization signal, thereby preventing nuclear uptake. Exposure of cells to a variety of extracellular stimuli leads to the rapid phosphorylation, ubiquitination, and ultimately proteolytic degradation of IκB, which frees NF-κB to translocate to the nucleus where it regulates gene transcription. NF-κB activation represents a paradigm for controlling the function of a regulatory protein via ubiquitination-dependent proteolysis, as an integral part of a phosphorylationbased signaling cascade. Recently, considerable progress has been made in understanding the details of the signaling pathways that regulate NF-κB activity, particularly those responding to the proinflammatory cytokines tumor necrosis factor-α and interleukin-1. The multisubunit IκB kinase (IKK) responsible for inducible IκB phosphorylation is the point of convergence for most NF-κB–activating stimuli. IKK contains two catalytic subunits, IKKα and IKKβ, both of which are able to correctly phosphorylate IκB. Gene knockout studies have shed light on the very different physiological functions of IKKα and IKKβ. After phosphorylation, the IKK phosphoacceptor sites on IκB serve as an essential part of a specific recognition site for E3RS IκB/β-TrCP , an SCF-type E3 ubiquitin ligase, thereby explaining how IKK controls IκB ubiquitination and degradation. A variety of other signaling events, including phosphorylation of NF-κB, hyperphosphorylation of IKK, induction of IκB synthesis, and the processing of NF-κB precursors, provide additional mechanisms that modulate the level and duration of NF-κB activity.

The I-κB-Kinase (IKK) complex represents a central signaling nexus in the TNF-dependent activation of the pro-inflammatory NF-κB pathway. However, recent studies suggested that the distinct IKK subunits (IKKα, IKKβ, and NEMO) might withhold additional NF-κB-independent functions in inflammation and cancer. Here, we generated mice lacking all three IKK subunits in liver parenchymal cells (LPC) (IKKα/β/NEMOLPC-KO) and compared their phenotype with mice lacking both catalytic subunits (IKKα/βLPC-KO), allowing to functionally dissect putative I-κB-Kinase-independent functions of the regulatory subunit NEMO. We show that the additional deletion of NEMO rescues IKKα/βLPC-KO mice from lethal cholestasis and biliary ductopenia by triggering LPC apoptosis and inducing a strong compensatory proliferation of LPC including cholangiocytes. Beyond this beneficial effect, we show that increased hepatocyte cell-death and compensatory proliferation inhibit the activation of LPC-necroptosis but trigger spontaneous hepatocarcinogenesis in IKKα/β/NEMOLPC-KO mice. Collectively, our data show that free NEMO molecules unbound to the catalytic IKK subunits control LPC programmed cell death pathways and proliferation, cholestasis and hepatocarcinogenesis independently of an IKK-related function. These findings support the idea of different functional levels at which NEMO controls inflammation and cancer in the liver.

Class IIa histone deacetylases (HDAC) have been shown to drive innate immune cell-mediated inflammation in the peripheral system, but their roles in cerebral inflammatory responses remain largely unknown. Here, we elucidate that HDAC7 is selectively elevated in lipopolysaccharide (LPS)-challenged astrocytes both in vivo and in vitro. We identify that HDAC7 binds to the inhibitory kappa B kinase (IKK) to promote IKKα and IKKβ deacetylation and subsequent activation, leading to the activation of nuclear factor κB (NF-κB). Astrocyte-specific overexpression of HDAC7 results in NF-κB activation, pro-inflammatory gene upregulation and anxiety-like behaviors in mice, while downregulating HDAC7 reserves LPS-induced NF-κB activation and inflammatory responses. Furthermore, pharmacological inhibition of HDAC7 by a class IIa HDAC inhibitor attenuates LPS-induced NF-κB activation, inflammatory responses and anxiety-like behaviors both in vivo and in vitro. Together, our data reveal a novel mechanism of HDAC7 in astrocyte-mediated inflammation and suggest that targeting HDAC7 could be a potential therapeutic strategy for the treatment of anxiety and other inflammation-related diseases.

An important property of NEMO, the core element of the IKK complex involved in NF‐κB activation, resides in its ability to specifically recognize poly‐ubiquitin chains. A small domain called NOA/UBAN has been suggested to be responsible for this property. We recently demonstrated that the C‐terminal Zinc Finger (ZF) of NEMO is also able to bind ubiquitin. We show here by ZF swapping and mutagenesis that this represents its only function. While neither NOA nor ZF shows any preference for K63‐linked chains, we demonstrate that together they form a bipartite high‐affinity K63‐specific ubiquitin‐binding domain. A similar domain can be found in two other proteins, Optineurin and ABIN2, and can be freely exchanged with that of NEMO without interfering with its activity. This suggests that the main function of the C‐terminal half of NEMO is to specifically bind K63‐linked poly‐ubiquitin chains. We also demonstrate that the recently described binding of NEMO to linear poly‐ubiquitin chains is dependent on the NOA alone and does not require the presence of the ZF.

IκB kinases (IKKs) play critical roles in innate immunity through signal-induced activation of the key transcription factors nuclear factor-κB (NF-κB) and interferon regulatory factors (IRFs). However, studies of invertebrate IKK functions remain scarce. In this study, we performed phylogenetic analysis of IKKs and IKK-related kinases encoded in the Pacific oyster genome. We then cloned and characterized the oyster α β gene. We found that oyster IKKα/β-2, a homolog of human IKKα/IKKβ, responded to challenge with lipopolysaccharide (LPS), peptidoglycan (PGN), and polyinosinic-polycytidylic acid [poly(I:C)]. As a versatile immune molecule, IKKα/β-2 activated the promoters of κ α, and β, as well as IFN-stimulated response element (ISRE)-containing promoters, initiating an antibacterial or antiviral immune state in mammalian cells. Importantly, together with the cloned oyster IKKα/β-1, we investigated the signal transduction pathways mediated by these two IKKα/β proteins. Our results showed that IKKα/β-1 and IKKα/β-2 could interact with the oyster TNF receptor-associated factor 6 (TRAF6) and that IKKα/β-2 could also bind to the oyster myeloid differentiation factor 88 (MyD88) protein directly, suggesting that oyster IKKα/βs participate in both RIG-I-like receptor (RLR) and Toll-like receptor (TLR) signaling for the reception of upstream immune signals. The fact that IKKα/β-1 and IKKα/β-2 formed homodimers by interacting with themselves and heterodimers by interacting with each other, along with the fact that both oyster IKKα/β proteins interacted with NEMO protein, indicates that oyster IKKα/βs and the scaffold protein NEMO form an IKK complex, which may be a key step in phosphorylating IκB proteins and activating NF-κB. Moreover, we found that oyster IKKα/βs could interact with IRF8, and this may be related to the IKK-mediated activation of ISRE promotors and their involvement in the oyster \"interferon (IFN)-like\" antiviral pathway. Moreover, the expression of oyster IKKα/β-1 and IKKα/β-2 may induce the phosphorylation of IκB proteins to activate NF-κB. These results reveal the immune function of oyster IKKα/β-2 and establish the existence of mollusk TLR and RLR signaling mediated by IKKα/β proteins for the first time. Our findings should be helpful in deciphering the immune mechanisms of invertebrates and understanding the development of the vertebrate innate immunity network.

Hypoxia is a feature of the microenvironment of a growing tumor. The transcription factor NFκB is activated in hypoxia, an event that has significant implications for tumor progression. Here, we demonstrate that hypoxia activates NFκB through a pathway involving activation of IκB kinase-β (IKKβ) leading to phosphorylation-dependent degradation of IκBα and liberation of NFκB. Furthermore, through increasing the pool and/or activation potential of IKKβ, hypoxia amplifies cellular sensitivity to stimulation with TNFα. Within its activation loop, IKKβ contains an evolutionarily conserved LxxLAP consensus motif for hydroxylation by prolyl hydroxylases (PHDs). Mimicking hypoxia by treatment of cells with siRNA against PHD-1 or PHD-2 or the pan-prolyl hydroxylase inhibitor DMOG results in NFκB activation. Conversely, overexpression of PHD-1 decreases cytokine-stimulated NFκB reporter activity, further suggesting a repressive role for PHD-1 in controlling the activity of NFκB. Hypoxia increases both the expression and activity of IKKβ, and site-directed mutagenesis of the proline residue (P191A) of the putative IKKβ hydroxylation site results in a loss of hypoxic inducibility. Thus, we hypothesize that hypoxia releases repression of NFκB activity through decreased PHD-dependent hydroxylation of IKKβ, an event that may contribute to tumor development and progression through amplification of tumorigenic signaling pathways. IKK

Stimulator of interferon genes (STING) is crucial for the innate immune to defend against pathogenic infections. Our previous study showed that a STING homolog from Litopenaeus vannamei (LvSTING) was involved in antibacterial response via regulating antimicrobial peptides (AMPs). Nevertheless, how LvSTING induces AMPs expression to inhibit bacterial infection remains unknown. Herein, we revealed that the existence of a STING–IKKβ–Relish–AMPs axis in shrimp that was essential for opposing to Vibrio parahaemolyticus invasion. We observed that LvRelish was essential for host defense against V. parahaemolyticus infection via inducing several AMPs, such as LvALF1, LvCRU1, LvLYZ1 and LvPEN4. Knockdown of LvSTING or LvIKKβ in vivo led to the attenuated phosphorylation and diminished nuclear translocation of LvRelish, as well as the impaired expression levels of LvRelish-regulated AMPs. Accordingly, shrimps with knockdown of LvSTING or LvIKKβ or both were vulnerable to V. parahaemolyticus infection. Finally, LvSTING could recruit LvRelish and LvIKKβ to form a complex, which synergistically induced the promoter activity of several AMPs in vitro . Taken together, our results demonstrated that the shrimp STING–IKKβ–Relish–AMPs axis played a critical role in the defense against bacterial infection, and provided some insights into the development of disease prevention strategies in shrimp culture.

At least eight types of ubiquitin chain exist, and individual linkages affect distinct cellular processes. The only distinguishing feature of differently linked ubiquitin chains is their structure, as polymers of the same unit are chemically identical. Here, we have crystallized Lys 63‐linked and linear ubiquitin dimers, revealing that both adopt equivalent open conformations, forming no contacts between ubiquitin molecules and thereby differing significantly from Lys 48‐linked ubiquitin chains. We also examined the specificity of various deubiquitinases (DUBs) and ubiquitin‐binding domains (UBDs). All analysed DUBs, except CYLD, cleave linear chains less efficiently compared with other chain types, or not at all. Likewise, UBDs can show chain specificity, and are able to select distinct linkages from a ubiquitin chain mixture. We found that the UBAN (ubiquitin binding in ABIN and NEMO) motif of NEMO (NF‐κB essential modifier) binds to linear chains exclusively, whereas the NZF (Npl4 zinc finger) domain of TAB2 (TAK1 binding protein 2) is Lys 63 specific. Our results highlight remarkable specificity determinants within the ubiquitin system.

As a multifunctional scavenger receptor, stabilin‐1 (STAB1) has been identified to induce chronic inflammation and promote cancer progression. Although in silico studies from multiple data sets showed that STAB1 might facilitate the progression of acute myeloid leukemia (AML) and drug resistance, the real impacts of STAB1 expression on AML patients and the detailed mechanisms remain unclear. Herein, we found that a higher expression of STAB1 is associated with a worse prognosis in AML patients. Subsequent in vitro experiments demonstrated that STAB1 knockdown suppressed proliferation and promoted apoptosis through regulating the IKK/NF‐κB pathway in human AML cell lines HEL and NB4. In addition, in vivo studies showed that STAB1 silencing prolonged survival, reduced proliferation, and inhibited aggressiveness of AML cells in xenograft mouse models. Moreover, we investigated the impact of STAB1 expression in AML cells on macrophage differentiation and found that co‐culture of macrophages with conditioned medium from STAB1‐knockdown AML cells reduced M2 polarization of macrophages. Taken together, our study suggests that STAB1 promotes growth and aggressiveness of AML cells through activating the IKK/NF‐κB pathway while also regulating M2 macrophage polarization within the chronic inflammatory environment. Therefore, targeting STAB1 could be a potential therapeutic strategy for treating AML. In this study, we explored the effects of silenced STAB1 expression in AML cells on the polarization of M2‐like macrophages, as well as the involvement of nuclear factor‐kappa B (NF‐κB) signaling pathways in the pro‐oncogenic roles of STAB1. By investigating the expression pattern of STAB1 along with its regulatory mechanisms in AML patients, we aimed to shed new light on potential novel strategies for improving the efficacy of AML treatments.

Doxorubicin (DOX) is an effective chemotherapeutic drug, but its use can lead to cardiomyopathy, which is the leading cause of mortality among cancer patients. Macrophages play a role in DOX-induced cardiomyopathy (DCM), but the mechanisms undlerlying this relationship remain unclear. This study aimed to investigate how IKKα regulates macrophage activation and contributes to DCM in a mouse model. Specifically, the role of macrophage IKKα was evaluated in macrophage-specific IKKα knockout mice that received DOX injections. The findings revealed increased expression of IKKα in heart tissues after DOX administration. In mice lacking macrophage IKKα, myocardial injury, ventricular remodeling, inflammation, and proinflammatory macrophage activation worsened in response to DOX administration. Bone marrow transplant studies confirmed that IKKα deficiency exacerbated cardiac dysfunction. Macrophage IKKα knockout also led to mitochondrial damage and metabolic dysfunction in macrophages, thereby resulting in increased cardiomyocyte injury and oxidative stress. Single-cell sequencing analysis revealed that IKKα directly binds to STAT3, leading to the activation of STAT3 phosphorylation at S727. Interestingly, the inhibition of STAT3-S727 phosphorylation suppressed both DCM and cardiomyocyte injury. In conclusion, the IKKα-STAT3-S727 signaling pathway was found to play a crucial role in DOX-induced cardiomyopathy. Targeting this pathway could be a promising therapeutic strategy for treating DOX-related heart failure.