ABSTRACT
SCOPE: Many phytochemicals with beneficial pharmacological properties contain electrophilic sites, e.g. α,ß-unsaturated carbonyl (enone) groups. There is increasing evidence that many biological effects of electrophilic compounds depend on covalent conjugation to reactive protein thiols. For example, the reaction of electrophiles with cysteinyl residues of the sensor protein Keap1 activates the cell-protective Nrf2 response. Thus it is of interest to identify more generally the proteins to which small molecule electrophiles bind covalently. METHODS AND RESULTS: Here we use a Click chemistry approach to identify target proteins of the chemopreventive phytochemical xanthohumol (XN), an enone-containing chalcone from hops (Humulus lupulus L.). Using an alkynylated analog of XN (XN-alkyne), we purified covalent protein-electrophile conjugates from cell lysates. We confirm the previously described conjugation of XN to Keap1. One of the newly identified candidate target proteins is glucose-6-phosphate dehydrogenase (G6PDH). We confirm that XN attenuates intracellular G6PDH activity at low micromolar concentrations. CONCLUSION: We find support for the notion that XN modulates multiple pathways and processes by covalent modification of proteins with reactive cysteines.
Subject(s)
Click Chemistry/methods , Flavonoids/chemistry , Flavonoids/metabolism , Propiophenones/chemistry , Propiophenones/metabolism , Proteins/metabolism , Alkynes/chemistry , Alkynes/metabolism , Cysteamine/chemistry , Flavonoids/pharmacology , Glucosephosphate Dehydrogenase/antagonists & inhibitors , Glucosephosphate Dehydrogenase/chemistry , Glucosephosphate Dehydrogenase/metabolism , Humans , Kelch-Like ECH-Associated Protein 1/chemistry , Kelch-Like ECH-Associated Protein 1/metabolism , Magnetic Resonance Spectroscopy , Molecular Weight , Propiophenones/pharmacology , Proteins/chemistry , Solubility , Spectrometry, Mass, Electrospray Ionization , Sulfhydryl Compounds/chemistryABSTRACT
Inflammatory signaling pathways orchestrate the cellular response to infection and injury. These pathways are known to be modulated by compounds that alkylate cysteinyl thiols. One class of phytochemicals with strong thiol alkylating activity is the chalcones. In this study we tested fourteen chalcone derivatives, α-X-substituted 2',3,4,4'-tetramethoxychalcones (α-X-TMCs, X = H, F, Cl, Br, I, CN, Me, p-NO2-C6H4, Ph, p-OMe-C6H4, NO2, CF3, COOEt, COOH), for their ability to modulate inflammatory responses, as monitored by their influence on heme oxygenase-1 (HO-1) activity, inducible nitric oxide synthase (iNOS) activity, and cytokine expression levels. We confirmed that the transcriptional activity of Nrf2 was activated by α-X-TMCs while for NF-κB it was inhibited. For most α-X-TMCs, anti-inflammatory activity was positively correlated with thiol alkylating activity, i.e. stronger electrophiles (X = CF3, Br and Cl) being more potent. Notably, this correlation did not hold true for the strongest electrophiles (X = CN and NO2) which were found to be ineffective as anti-inflammatory compounds. These results emphasize the idea that chemical fine-tuning of electrophilicity is needed to achieve and optimize desired therapeutic effects.
Subject(s)
Anti-Inflammatory Agents/chemistry , Chalcones/chemistry , Inflammation/metabolism , Animals , Cysteamine/chemistry , Cytokines/metabolism , Enzyme-Linked Immunosorbent Assay , Glutathione/chemistry , HeLa Cells , Heme Oxygenase-1/metabolism , Humans , Interleukin-6/metabolism , Interleukin-8/metabolism , Lipopolysaccharides/chemistry , Macrophages/metabolism , Mice , NF-E2-Related Factor 2/metabolism , NF-kappa B/metabolism , Nitric Oxide Synthase Type II/metabolism , Photochemical Processes , Sulfhydryl Compounds/chemistry , Transcription, GeneticABSTRACT
The peptide hormone hepcidin regulates mammalian iron homeostasis by blocking ferroportin-mediated iron export from macrophages and the duodenum. During inflammation, hepcidin is strongly induced by interleukin 6, eventually leading to the anemia of chronic disease. Here we show that hepatoma cells and primary hepatocytes strongly up-regulate hepcidin when exposed to low concentrations of H(2)O(2) (0.3-6 µM), concentrations that are comparable with levels of H(2)O(2) released by inflammatory cells. In contrast, bolus treatment of H(2)O(2) has no effect at low concentrations and even suppresses hepcidin at concentrations of >50 µM. H(2)O(2) treatment synergistically stimulates hepcidin promoter activity in combination with recombinant interleukin-6 or bone morphogenetic protein-6 and in a manner that requires a functional STAT3-responsive element. The H(2)O(2)-mediated hepcidin induction requires STAT3 phosphorylation and is effectively blocked by siRNA-mediated STAT3 silencing, overexpression of SOCS3 (suppressor of cytokine signaling 3), and antioxidants such as N-acetylcysteine. Glycoprotein 130 (gp130) is required for H(2)O(2) responsiveness, and Janus kinase 1 (JAK1) is required for adequate basal signaling, whereas Janus kinase 2 (JAK2) is dispensable upstream of STAT3. Importantly, hepcidin levels are also increased by intracellular H(2)O(2) released from the respiratory chain in the presence of rotenone or antimycin A. Our results suggest a novel mechanism of hepcidin regulation by nanomolar levels of sustained H(2)O(2). Thus, similar to cytokines, H(2)O(2) provides an important regulatory link between inflammation and iron metabolism.
