Xanthohumol prevents dextran sulfate sodium-induced colitis via inhibition of IKKβ/NF-κB signaling in mice.
ABSTRACT: Xanthohumol (XN), a prenylated chalcone isolated from the hop plant, has been reported to exhibit multiple biological functions including anti-inflammation. However, the pharmacological function of XN on colitis remains unknown. In this study, we investigated the anti-inflammatory effect of synthesized XN and molecular mechanism on dextran sulfate sodium (DSS)-induced experimental colitis. XN attenuated the colitis symptoms along with the prevention of colonic lesions after DSS challenge. XN inhibited the production of pro-inflammatory cytokines, oxidative stress and cyclooxygenase-2 expression in DSS-treated mice. Moreover, XN inhibited the phosphorylation of IκBα, the nuclear translocation of NF-κB subunits and the transcriptional activity of NF-κB in vivo and in vitro. In contrast to XN, isoXN showed much less effects on the kinase activity of IKKβ and IκBα phosphorylation induced by XN in this study, suggesting that an electrophilic carbon center present in XN is critical for the anti-inflammation in colitis, especially inhibition of IKKβ/NF-κB signaling pathway. Consistently, our docking analysis revealed that XN could bind to the active site, presumably at the Cys99 of IKKβ. Taken together, these findings demonstrate a new function of XN to inhibit IKKβ/NF-κB signaling, suggesting XN could be the potential therapeutic agent for the prevention of colitis.
Project description:I kappa B kinase β (IKKβ) is one of the primary targets to regulate canonical NF-κB activity. The misregulation of NF-κB is associated with various diseases, including chronic inflammation and cancers. Most of the known IKKβ inhibitors target its active form and suffer from poor selectivity. In the present study, we aim to design inhibitors that can bind to the IKKβ inactive form and block its activation. We identified a potential allosteric site between the kinase domain (KD) and ubiquitin-like domain (ULD) of human IKKβ and used it to virtually screen a chemical library for allosteric inhibitors. Among the 133 compounds tested, 16 inhibited NF-κB activity by over 50% at 50 μM in a reporter gene assay. Further quantitative measurements and cytotoxicity study gave one compound 124 (3,4-dichloro-2-ethoxy-N-(2,2,6,6-tetramethylpiperidin-4-yl)benzenesulfonamide) which specifically targets the IKKβ inactive form. In cells, 124 inhibited IκBα phosphorylation and NF-κB transcriptional activity for the reporter gene with an IC50 of 35 μM by decreasing the phosphorylation level of Ser177/181 on IKKβ and blocking its activation upon TNFα stimulation. Molecular dynamics simulations demonstrated that 124 binds to the pocket between KD and ULD in the inactive conformation of IKKβ rather than the active conformation. As the first allosteric inhibitor that prevents IKKβ activation, 124 provides a good starting point for further inhibitor discovery and a probe for IKKβ enzyme cycle and regulatory mechanism study.
Project description:<label>CONTEXT</label>Alzheimer's disease (AD) is the most common form of dementia affecting the aged population and neuroinflammation is one of the most observed AD pathologies. NF-κB is the central regulator of inflammation and inhibitor κB kinase (IKK) is the converging point in NF-κB activation. Celastrol is a natural triterpene used as a treatment for inflammatory conditions.<label>OBJECTIVE</label>This study determines the neuroprotective and inhibitory effect of celastrol on amyloid beta1-42 (Aβ1-42) induced cytotoxicity and IKKβ activity, respectively.<label>MATERIALS AND METHODS</label>Retinoic acid differentiated IMR-32 cells were treated with celastrol (1 μM) before treatment with Aβ1-42 (IC30 10 μM) for 24 h. The cytotoxicity and IKK phosphorylation were measured by MTT and western blotting analysis, respectively. We screened 36 celastrol analogues for the IKKβ inhibition by molecular docking and evaluated their drug like properties to delineate the neuroprotective effects.<label>RESULTS</label>Celastrol (1 μM) inhibited Aβ1-42 (10 μM) induced IκBα phosphorylation and protected IMR-32 cells from cell death. Celastrol and 25 analogues showed strong binding affinity with IKKβ as evidenced by strong hydrogen-bonding interactions with critical active site residues. All the 25 analogues displayed strong anti-inflammatory properties but only 11 analogues showed drug-likeness. Collectively, molecule 15 has highest binding affinity, CNS activity and more drug likeness than parent compound celastrol.<label>DISCUSSION AND CONCLUSION</label>The decreased expression of pIκBα in celastrol pretreated cells affirms the functional representation of inhibited IKKβ activity in these cells. The neuroprotective potentials of celastrol and its analogues may be related to IKK inhibition.
Project description:Nuclear Factor kappa B (NF-κB) is a transcription factor involved in the regulation of cell signaling responses and is a key regulator of cellular processes involved in the immune response, differentiation, cell proliferation, and apoptosis. The constitutive activation of NF-κB contributes to multiple cellular outcomes and pathophysiological conditions such as rheumatoid arthritis, asthma, inflammatory bowel disease, AIDS and cancer. Thus there lies a huge therapeutic potential beneath inhibition of NF-κB signalling pathway for reducing these chronic ailments. Withania somnifera, a reputed herb in ayurvedic medicine, comprises a large number of steroidal lactones known as withanolides which show plethora of pharmacological activities like anti- inflammatory, antitumor, antibacterial, antioxidant, anticonvulsive, and immunosuppressive. Though a few studies have been reported depicting the effect of WA (withaferin A) on suppression of NF-κB activation, the mechanism behind this is still eluding the researchers. The study conducted here is an attempt to explore NF-κB signalling pathway modulating capability of Withania somnifera's major constituent WA and to elucidate its possible mode of action using molecular docking and molecular dynamics simulations studies.Formation of active IKK (IκB kinase) complex comprising NEMO (NF-κB Essential Modulator) and IKKβ subunits is one of the essential steps for NF-κB signalling pathway, non-assembly of which can lead to prevention of the above mentioned vulnerable disorders. As observed from our semi-flexible docking analysis, WA forms strong intermolecular interactions with the NEMO chains thus building steric as well as thermodynamic barriers to the incoming IKKβ subunits, which in turn pave way to naive complex formation capability of NEMO with IKKβ. Docking of WA into active NEMO/IKKβ complex using flexible docking in which key residues of the complex were kept flexible also suggest the disruption of the active complex. Thus the molecular docking analysis of WA into NEMO and active NEMO/IKKβ complex conducted in this study provides significant evidence in support of the proposed mechanism of NF-κB activation suppression by inhibition or disruption of active NEMO/IKKβ complex formation being accounted by non-assembly of the catalytically active NEMO/IKKβ complex. Results from the molecular dynamics simulations in water show that the trajectories of the native protein and the protein complexed with WA are stable over a considerably long time period of 2.6 ns.NF-κB is one of the most attractive topics in current biological, biochemical, and pharmacological research, and in the recent years the number of studies focusing on its inhibition/regulation has increased manifolds. Small ligands (both natural and synthetic) are gaining particular attention in this context. Our computational analysis provided a rationalization of the ability of naturally occurring withaferin A to alter the NF-κB signalling pathway along with its proposed mode of inhibition of the pathway. The absence of active IKK multisubunit complex would prevent degradation of IκB proteins, as the IκB proteins would not get phosphorylated by IKK. This would ultimately lead to non-release of NF-κB and its further translocation to the nucleus thus arresting its nefarious acts. Conclusively our results strongly suggest that withaferin A is a potent anticancer agent as ascertained by its potent NF-κB modulating capability. Moreover the present MD simulations made clear the dynamic structural stability of NEMO/IKKβ in complex with the drug WA, together with the inhibitory mechanism.
Project description:Vaccinia virus protein A49 inhibits NF-κB activation by molecular mimicry and has a motif near the N terminus that is conserved in IκBα, β-catenin, HIV Vpu, and some other proteins. This motif contains two serines, and for IκBα and β-catenin, phosphorylation of these serines enables recognition by the E3 ubiquitin ligase β-TrCP. Binding of IκBα and β-catenin by β-TrCP causes their ubiquitylation and thereafter proteasome-mediated degradation. In contrast, HIV Vpu and VACV A49 are not degraded. This paper shows that A49 is phosphorylated at serine 7 but not serine 12 and that this is necessary and sufficient for binding β-TrCP and antagonism of NF-κB. Phosphorylation of A49 S7 occurs when NF-κB signaling is activated by addition of IL-1β or overexpression of TRAF6 or IKKβ, the kinase needed for IκBα phosphorylation. Thus, A49 shows beautiful biological regulation, for it becomes an NF-κB antagonist upon activation of NF-κB signaling. The virulence of viruses expressing mutant A49 proteins or lacking A49 (vΔA49) was tested. vΔA49 was attenuated compared with WT, but viruses expressing A49 that cannot bind β-TrCP or bind β-TrCP constitutively had intermediate virulence. So A49 promotes virulence by inhibiting NF-κB activation and by another mechanism independent of S7 phosphorylation and NF-κB antagonism. Last, a virus lacking A49 was more immunogenic than the WT virus.
Project description:Existing data suggest that NF-kappaB signaling is a key regulator of cancer-induced skeletal muscle wasting. However, identification of the components of this signaling pathway and of the NF-κB transcription factors that regulate wasting is far from complete. In muscles of C26 tumor bearing mice, overexpression of d.n. IKKβ blocked muscle wasting by 69%, the IκBα-super repressor blocked wasting by 41%. In contrast, overexpression of d.n. IKKα or d.n. NIK did not block C26-induced wasting. Surprisingly, overexpression of d.n. p65 or d.n. c-Rel did not significantly block muscle wasting. Genome-wide mRNA expression arrays showed upregulation of many genes previously implicated in muscle atrophy. To test if these upregulated genes were direct targets of NF-κB transcription factors, we compared genome-wide p65 or p50 binding to DNA in control and cachectic muscle using ChIP-sequencing. Bioinformatic analysis of ChIP-seq data from control and C26 muscles showed increased p65 and p50 binding to a few regulatory and structural genes but only two of these genes were upregulated with atrophy. The p65 and p50 ChIP-seq data are consistent with our finding of no significant change in protein binding to an NF-κB oligo in a gel shift assay. Taken together, these data support the idea that although inhibition of IκBα, and particularly IKKβ, blocks cancer-induced wasting, the alternative NF-κB signaling pathway is not required. In addition, the downstream NF-κB transcription factors do not regulate the transcriptional changes. These data are consistent with the growing body of literature showing that there are NF-κB-independent substrates of IKKβ and IκBα that regulate physiological processes. To compare gene expression changes in atrophied muscles from C26 tumor bearing mice, gastrocnemius/plantaris muscles were harvested from 4 C26 tumor-bearing mice, and 3 control non tumor-bearing mice. Total RNA were isolated and pooled (2-3 muslces in the same group per RNA sample ) to make equal amount of total RNA per sample. Three pooled total RNA samples from healthy control muscles and 3 pooled total RNA from muscles of C26 tumor bearing mice were labelled and hybridized on 6 Mouse Affyemtrix Gene 1.0 ST arrays. Two-side t-tests and multiple test corrections were performed to identify differentially expressed genes due to C26 tumor bearing induced cachexia.
Project description:Human bocavirus (HBoV), a parvovirus, is a single-stranded DNA etiologic agent causing lower respiratory tract infections in young children worldwide. Nuclear factor kappa B (NF-κB) transcription factors play crucial roles in clearance of invading viruses through activation of many physiological processes. Previous investigation showed that HBoV infection could significantly upregulate the level of TNF-α which is a strong NF-κB stimulator. Here we investigated whether HBoV proteins modulate TNF-α-mediated activation of the NF-κB signaling pathway. We showed that HBoV NS1 and NS1-70 proteins blocked NF-κB activation in response to TNF-α. Overexpression of TNF receptor-associated factor 2 (TRAF2)-, IκB kinase alpha (IKKα)-, IκB kinase beta (IKKβ)-, constitutively active mutant of IKKβ (IKKβ SS/EE)-, or p65-induced NF-κB activation was inhibited by NS1 and NS1-70. Furthermore, NS1 and NS1-70 didn't interfere with TNF-α-mediated IκBα phosphorylation and degradation, nor p65 nuclear translocation. Coimmunoprecipitation assays confirmed the interaction of both NS1 and NS1-70 with p65. Of note, NS1 but not NS1-70 inhibited TNF-α-mediated p65 phosphorylation at ser536. Our findings together indicate that HBoV NS1 and NS1-70 inhibit NF-κB activation. This is the first time that HBoV has been shown to inhibit NF-κB activation, revealing a potential immune-evasion mechanism that is likely important for HBoV pathogenesis.
Project description:The DNA sensing pathway triggers innate immune responses against DNA virus infection, and NF-κB signaling plays a critical role in establishing innate immunity. We report here that the herpes simplex virus 1 (HSV-1) ubiquitin-specific protease (UL36USP), which is a deubiquitinase (DUB), antagonizes NF-κB activation, depending on its DUB activity. In this study, ectopically expressed UL36USP blocked promoter activation of beta interferon (IFN-β) and NF-κB induced by cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING). UL36USP restricted NF-κB activation mediated by overexpression of STING, TANK-binding kinase 1, IκB kinase α (IKKα), and IKKβ, but not p65. UL36USP was also shown to inhibit IFN-stimulatory DNA-induced IFN-β and NF-κB activation under conditions of HSV-1 infection. Furthermore, UL36USP was demonstrated to deubiquitinate IκBα and restrict its degradation and, finally, abrogate NF-κB activation. More importantly, the recombinant HSV-1 lacking UL36USP DUB activity, denoted as C40A mutant HSV-1, failed to cleave polyubiquitin chains on IκBα. For the first time, UL36USP was shown to dampen NF-κB activation in the DNA sensing signal pathway to evade host antiviral innate immunity.IMPORTANCE It has been reported that double-stranded-DNA-mediated NF-κB activation is critical for host antiviral responses. Viruses have established various strategies to evade the innate immune system. The N terminus of the HSV-1 UL36 gene-encoded protein contains the DUB domain and is conserved across all herpesviruses. This study demonstrates that UL36USP abrogates NF-κB activation by cleaving polyubiquitin chains from IκBα and therefore restricts proteasome-dependent degradation of IκBα and that DUB activity is indispensable for this process. This study expands our understanding of the mechanisms utilized by HSV-1 to evade the host antiviral innate immune defense induced by NF-κB signaling.
Project description:Gamabufotalin (CS-6), a major bufadienolide of Chansu, has been used for cancer therapy due to its desirable metabolic stability and less adverse effect. However, the underlying mechanism of CS-6 involved in anti-tumor activity remains poorly understood.The biological functions of gamabufotalin (CS-6) were investigated by migration, colony formation and apoptosis assays in NSCLC cells. The nuclear localization and interaction between transcriptional co-activator p300 and NF-κB p50/p65 and their binding to COX-2 promoter were analyzed after treatment with CS-6. Molecular docking study was used to simulate the interaction of CS-6 with IKKβ. The in vivo anti-tumor efficacy of CS-6 was also analyzed in xenografts nude mice. Western blot was used to detect the protein expression level.Gamabufotalin (CS-6) strongly suppressed COX-2 expression by inhibiting the phosphorylation of IKKβ via targeting the ATP-binding site, thereby abrogating NF-κB binding and p300 recruitment to COX-2 promoter. In addition, CS-6 induced apoptosis by activating the cytochrome c and caspase-dependent apoptotic pathway. Moreover, CS-6 markedly down-regulated the protein levels of COX-2 and phosphorylated p65 NF-κB in tumor tissues of the xenograft mice, and inhibited tumor weight and size.Our study provides pharmacological evidence that CS-6 exhibits potential use in the treatment of COX-2-mediated diseases such as lung cancer.
Project description:Post-translational modifications of RelA play an important role in regulation of NF-κB activation. We previously demonstrated that in malignant hematopoietic cells, histone deacetylase inhibitors (HDACIs) induced RelA hyperacetylation and NF-κB activation, attenuating lethality. We now present evidence that IκB kinase (IKK) β-mediated RelA Ser-536 phosphorylation plays a significant functional role in promoting RelA acetylation, inducing NF-κB activation, and limiting HDACI lethality in human multiple myeloma (MM) cells. Immunoblot profiling revealed that although basal RelA phosphorylation varied in MM cells, Ser-536 phosphorylation correlated with IKK activity. Exposure to the pan-HDACIs vorinostat or LBH-589 induced phosphorylation of IKKα/β (Ser-180/Ser-181) and RelA (Ser-536) in MM cells, including cells expressing an IκBα "super-repressor," accompanied by increased RelA nuclear translocation, acetylation, DNA binding, and transactivation activity. These events were substantially blocked by either pan-IKK or IKKβ-selective inhibitors, resulting in marked apoptosis. Consistent with these events, inhibitory peptides targeting either the NF-κB essential modulator (NEMO) binding domain for IKK complex formation or RelA phosphorylation sites also significantly increased HDACI lethality. Moreover, IKKβ knockdown by shRNA prevented Ser-536 phosphorylation and significantly enhanced HDACI susceptibility. Finally, introduction of a nonphosphorylatable RelA mutant S536A, which failed to undergo acetylation in response to HDACIs, impaired NF-κB activation and increased cell death. These findings indicate that HDACIs induce Ser-536 phosphorylation of the NF-κB subunit RelA through an IKKβ-dependent mechanism, an action that is functionally involved in activation of the cytoprotective NF-κB signaling cascade primarily through facilitation of RelA acetylation rather than nuclear translocation.
Project description:The NF-κB essential modulator (NEMO) is the master regulator of NF-κB signaling, controlling the immune and nervous systems. NEMO affects the activity of IκB kinase-β (IKKβ), which relieves the inhibition of the NF-κB transcriptional regulation machinery. Despite major effort, there is only a very sparse, phenomenological understanding of how NEMO regulates IKKβ and shows specificity in its large range of molecular interactions. We explore the key molecular interactions of NEMO using a molecular biophysics approach, incorporating rapid-mixing stopped-flow, high-pressure, and CD spectroscopies. Our study demonstrates that NEMO has a significant degree of native structural disorder and that molecular flexibility and ligand-induced conformational change are at the heart of the molecular interactions of NEMO. We found that long chain length, unanchored, linear polyubiquitin drives NEMO activity, enhancing the affinity of NEMO for IKKβ and the kinase substrate IκBα and promoting membrane association. We present evidence that unanchored polyubiquitin achieves this regulation by inducing NEMO conformational change by an allosteric mechanism. We combine our quantitative findings to give a detailed molecular mechanistic model for the activity of NEMO, providing insight into the molecular mechanism of NEMO activity with broad implications for the biological role of free polyubiquitin.