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Helenalin Analogues Targeting NF-?B p65: Thiol Reactivity and Cellular Potency Studies of Varied Electrophiles.

ABSTRACT: Helenalin is a pseudoguaianolide natural product that targets Cys38 within the DNA binding domain of NF-?B transcription factor p65 (RelA). Helenalin contains two Michael acceptors that covalently modify cysteines: a ?-methylene-?-butyrolactone and a cyclopentenone. We recently reported two simplified helenalin analogues that mimic the biological activity of helenalin and contain both electrophilic moieties. To determine the individual contributions of the Michael acceptors toward NF-?B inhibition, we synthesized a small library of helenalin-based analogues containing various combinations of ?-methylene-?-butyrolactones and cyclopentenones. The kinetics of thiol addition to a subset of the analogues was measured to determine the relative thiol reactivities of the embedded electrophiles. Additionally, the cellular NF-?B inhibitory activities of the analogues were determined to elucidate the contributions of each Michael acceptor to biological potency. Our studies suggest the ?-methylene-?-butyrolactone contributes most significantly to the NF-?B inhibition of our simplified helenalin analogues.

SUBMITTER: Widen JC

PROVIDER: S-EPMC5894512 | biostudies-literature | 2018 Feb

REPOSITORIES: biostudies-literature

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Helenalin Analogues Targeting NF-κB p65: Thiol Reactivity and Cellular Potency Studies of Varied Electrophiles.

Widen John C JC Kempema Aaron M AM Baur Jordan W JW Skopec Hannah M HM Edwards Jacob T JT Brown Tenley J TJ Brown Dennis A DA Meece Frederick A FA Harki Daniel A DA

ChemMedChem 20180119 4

Helenalin is a pseudoguaianolide natural product that targets Cys38 within the DNA binding domain of NF-κB transcription factor p65 (RelA). Helenalin contains two Michael acceptors that covalently modify cysteines: a α-methylene-γ-butyrolactone and a cyclopentenone. We recently reported two simplified helenalin analogues that mimic the biological activity of helenalin and contain both electrophilic moieties. To determine the individual contributions of the Michael acceptors toward NF-κB inhibiti ...[more]

PMID: 29349898

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Project description:BackgroundThe NF-κB family of transcription factors and associated signalling pathways are abundant and ubiquitous in human immune responses. Activation of NF-κB transcription factors by viral pathogen-associated molecular patterns, such as viral RNA and DNA, is fundamental to anti-viral innate immune defences and pro-inflammatory cytokine production that steers adaptive immune responses. Diverse non-viral stimuli, such as lipopolysaccharide and cytokines, also activate NF-κB and the same anti-pathogen gene networks. Viruses adapted to human cells often encode multiple proteins targeting the NF-κB pathway to mitigate the anti-viral effects of NF-κB-dependent host immunity.ResultsIn this study we have demonstrated using a variety of assays, in a number of different cell types including primary cells, that plasmid-encoded or virus-delivered simian immunodeficiency virus (SIV) accessory protein Vpx is a broad antagonist of NF-κB signalling active against diverse innate NF-κB agonists. Using targeted Vpx mutagenesis, we showed that this novel Vpx phenotype is independent of known Vpx cofactor DCAF1 and other cellular binding partners, including SAMHD1, STING and the HUSH complex. We found that Vpx co-immunoprecipitated with canonical NF-κB transcription factor p65, but not NF-κB family members p50 or p100, preventing nuclear translocation of p65. We found that broad antagonism of NF-κB activation by Vpx was conserved across distantly related lentiviruses as well as for Vpr from SIV Mona monkey (SIVmon), which has Vpx-like SAMHD1-degradation activity.ConclusionsWe have discovered a novel mechanism by which lentiviruses antagonise NF-κB activation by targeting p65. These findings extend our knowledge of how lentiviruses manipulate universal regulators of immunity to avoid the anti-viral sequelae of pro-inflammatory gene expression stimulated by both viral and extra-viral agonists. Importantly our findings are also relevant to the gene therapy field where virus-like particle associated Vpx is routinely used to enhance vector transduction through antagonism of SAMHD1, and perhaps also through manipulation of NF-κB.

Project description:The NF-κB signaling pathway is central to the innate and adaptive immune responses. Upon their detection of pathogen-associated molecular patterns, Toll-like receptors on the cell surface initiate signal transduction and activate the NF-κB pathway, leading to the production of a wide array of inflammatory cytokines, in attempt to eradicate the invaders. As a countermeasure, pathogens have evolved ways to subvert and manipulate this system to their advantage. Enteropathogenic and enterohemorrhagic Escherichia coli (EPEC and EHEC) are closely related bacteria responsible for major food-borne diseases worldwide. Via a needle-like protein complex called the type three secretion system (T3SS), these pathogens deliver virulence factors directly to host cells and modify cellular functions, including by suppressing the inflammatory response. Using gain- and loss-of-function screenings, we identified two bacterial effectors, NleC and NleE, that down-regulate the NF-κB signal upon being injected into a host cell via the T3SS. A recent report showed that NleE inhibits NF-κB activation, although an NleE-deficient pathogen was still immune-suppressive, indicating that other anti-inflammatory effectors are involved. In agreement, our present results showed that NleC was also required to inhibit inflammation. We found that NleC is a zinc protease that disrupts NF-κB activation by the direct cleavage of NF-κB's p65 subunit in the cytoplasm, thereby decreasing the available p65 and reducing the total nuclear entry of active p65. More importantly, we showed that a mutant EPEC/EHEC lacking both NleC and NleE (ΔnleC ΔnleE) caused greater inflammatory response than bacteria carrying ΔnleC or ΔnleE alone. This effect was similar to that of a T3SS-defective mutant. In conclusion, we found that NleC is an anti-inflammatory bacterial zinc protease, and that the cooperative function of NleE and NleC disrupts the NF-κB pathway and accounts for most of the immune suppression caused by EHEC/EPEC.

Project description:Cysteine is unique among all protein-coding amino acids owing to its intrinsically high nucleophilicity. The cysteinyl thiol group can be covalently modified by both a broad range of redox mechanisms and various electrophiles derived from exogenous or endogenous sources. Measuring proteomic cysteines response to redox perturbation or electrophiles is critical for understanding the underlying mechanisms involved. Activity-based protein profiling (ABPP) based on thiol-reactive probes has been the method of choice for such analyses. We therefore adapted this approach and developed a new chemoproteomic platform, termed as QTRP (Quantitative Thiol Reactivity Profiling), that relies on the ability of a commercially available thiol-reactive probe IPM to covalently label, enrich, and quantify the reactive cysteinome in cells and tissues. Here, we provide a detailed and updated workflow of QTRP that includes procedures for (i) labeling of the reactive cysteinome from cell or tissue samples (e.g. control vs treatment) with IPM, (ii) processing the protein samples into tryptic peptides and tagging the probe-modified peptides with isotopically labeled azido-biotin reagents containing a photo-cleavable linker via click chemistry reaction, (iii) capturing biotin-conjugated peptides with streptavidin beads, (iv) identifying and quantifying the photo-released peptides by mass spectrometry (MS)-based shotgun proteomics, (v) interpreting MS data by a streamlined informatic pipeline using a proteomics software, pFind 3, and an automatic post-processing algorithm. We also outline here how to use QTRP for measuring the changes on proteomic cysteines upon redox perturbation and for identifying targeted cysteine sites of thiol-reactive electrophiles. We anticipate that this protocol should find broad applications in both redox/chemical biology and drug discovery. The protocol for sample preparation takes 3 days, whereas MS measurements and data analyses require 75 min and <30 min, respectively, per sample.

Dataset Information

Helenalin Analogues Targeting NF-?B p65: Thiol Reactivity and Cellular Potency Studies of Varied Electrophiles.

Publications

Helenalin Analogues Targeting NF-κB p65: Thiol Reactivity and Cellular Potency Studies of Varied Electrophiles.

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