The transcription factor Nrf2 (nuclear factor (erythroid-derived 2)-like 2) and the kinase AMPK (AMP-activated protein kinase) participate in the cellular adaptive response to redox or energy stress. Despite accumulating evidence for positive cooperativity between both proteins, information about direct post-translational modification of Nrf2 by AMPK in living cells is scarce. Here, MS-based analysis of immunoprecipitated Nrf2 revealed serine 374, 408 and 433 in human Nrf2 to be hyperphosphorylated as a function of activated AMPK. A direct phosphate-transfer by AMPK to those sites was indicated by in vitro kinase assays with recombinant proteins as well as interaction of AMPK and Nrf2 in cells, evident by co-immunoprecipitation. Mutation of serine 374, 408 and 433 to alanine did not markedly affect half-life, nuclear accumulation or induction of reporter gene expression upon Nrf2 activation with sulforaphane. However, some selected endogenous Nrf2 target genes responded with decreased induction when the identified phosphosites were mutated, whereas others remained unaffected. Notably, the genes susceptible to the mutation of the phosphorylation sites in Nrf2 consistently showed reduced induction in AMPKα1 −/−cells. Overall, our data reveal AMPK-triggered phosphorylation of Nrf2 at three serine residues, apparently determining the extent of transactivation of selected target genes.

Urolithin A inhibits growth of colon cancer cells alone and synergistically in combination with oxaliplatin. Those activities are markedly supported by activation of the p53/TIGAR axis and subsequent reduction of the cellular glycolytic potential by urolithin A.

Hyperproliferation of vascular smooth muscle cells (VSMCs) is critically involved in the onset of atherosclerosis and restenosis. Although caffeic acid phenethyl ester (CAPE, 1), one of the main constituents of honeybee propolis, has been shown to exert a beneficial effect in models of vascular injury in vivo, detailed mechanistic investigations in vascular cells are scarce. This study has examined the antiproliferative activity of 1 in platelet-derived growth factor (PDGF)-stimulated primary rat aortic VSMCs and aimed to shed light on underlying molecular mechanisms. Compound 1 inhibited the proliferation of VSMCs upon exposure to PDGF in a dose-dependent manner by interfering with cell cycle progression from the G0/1- to the S-phase. Enhanced phosphorylation of p38 mitogen-activated protein kinase (MAPK) as well as stabilization of hypoxia-inducible factor (HIF)-1α and subsequent induction of heme oxygenase-1 (HO-1) could be identified as molecular events contributing to the observed growth arrest in PDGF-activated VSMCs upon exposure to 1.

Cross-linking mass spectrometry is an increasingly used, powerful technique to study protein−protein interactions or to provide structural information. Due to substochiometric reaction efficiencies, crosslinked peptides are usually low abundance. This results in challenging data evaluation and the need for an effective enrichment. Here we describe an improved, easy to implement, one-step method to enrich azide-tagged, acidcleavable disuccinimidyl bis-sulfoxide (DSBSO) cross-linked peptides using dibenzocyclooctyne (DBCO) coupled Sepharose beads. We probed this method using recombinant Cas9 and E. coli ribosome. For Cas9, the number of detectable cross-links was increased from ∼100 before enrichment to 580 cross-links after enrichment. To mimic a cellular lysate, E. coli ribosome was spiked into a tryptic HEK background at a ratio of 1:2−1:100. The number of detectable unique cross-links was maintained high at ∼100. The estimated enrichment efficiency was improved by a factor of 4−5 (based on XL numbers) compared to enrichment via biotin and streptavidin. We were still able to detect cross-links from 0.25 μg cross-linked E. coli ribosomes in a background of 100 μg tryptic HEK peptides, indicating a high enrichment sensitivity. In contrast to conventional enrichment techniques, like SEC, the time needed for preparation and MS measurement is significantly reduced. This robust, fast, and selective enrichment method for azide-tagged linkers will contribute to mapping protein−protein interactions, investigating protein architectures in more depth, and helping to understand complex biological processes.

BackgroundMild but chronically elevated circulating unconjugated bilirubin is associated with reduced total and low‐density lipoprotein cholesterol concentration, which is associated with reduced cardiovascular disease risk. We aimed to investigate whether unconjugated bilirubin influences macrophage cholesterol efflux, as a potential mechanism for the altered circulating lipoprotein concentrations observed in hyperbilirubinemic individuals.Methods and ResultsCholesterol efflux from THP‐1 macrophages was assessed using plasma obtained from normo‐ and hyperbilirubinemic (Gilbert syndrome) humans (n=60 per group) or (heterozygote/homozygote Gunn) rats (n=20 per group) as an acceptor. Hyperbilirubinemic plasma from patients with Gilbert syndrome and Gunn rats induced significantly reduced cholesterol efflux compared with normobilirubinemic plasma. Unconjugated bilirubin (3–17.1 μmol/L) exogenously added to plasma‐ or apolipoprotein A1–supplemented media also decreased macrophage cholesterol efflux in a concentration‐ and time‐dependent manner. We also showed reduced protein expression of the ATP‐binding cassette transporter A1 (ABCA1), a transmembrane cholesterol transporter involved in apolipoprotein A1–mediated cholesterol efflux, in THP‐1 macrophages treated with unconjugated bilirubin and in peripheral blood mononuclear cells obtained from hyperbilirubinemic individuals. Furthermore, we demonstrated that bilirubin accelerates the degradation rate of the ABCA1 protein in THP‐1 macrophages.ConclusionsCholesterol efflux from THP‐1 macrophages is decreased in the presence of plasma obtained from humans and rats with mild hyperbilirubinemia. A direct effect of unconjugated bilirubin on cholesterol efflux was demonstrated and is associated with decreased ABCA1 protein expression. These data improve our knowledge concerning bilirubin's impact on cholesterol transport and represent an important advancement in our understanding of bilirubin's role in cardiovascular disease.

Evodiamine, a bioactive alkaloid from the fruits of the traditional Chinese medicine Evodia rutaecarpa (Juss.) Benth. (Fructus Evodiae, Wuzhuyu), recently gained attention as a dietary supplement for weight loss and optimization of lipid metabolism. In light of its use by patients and consumers, there is an urgent need to elucidate the molecular targets affected by this natural product. Using a novel interactomics approach, the Nematic Protein Organisation Technique (NPOT), we report the identification of ATP-binding cassette transporter A1 (ABCA1), a key membrane transporter contributing to cholesterol efflux (ChE), as a direct binding target of evodiamine. The binding of evodiamine to ABCA1 is confirmed by surface plasmon resonance (SPR) experiments. Examining the functional consequences of ABCA1 binding reveals that evodiamine treatment results in increased ABCA1 stability, elevated cellular ABCA1 protein levels, and ultimately increased ChE from THP-1-derived human macrophages. The protein levels of other relevant cholesterol transporters, ABCG1 and SR-B1, remain unaffected in the presence of evodiamine, and the ABCA1 mRNA level is also not altered.

The balm of the Norway spruce (Picea abies) is a well-known traditional herbal medicine used to cure wounds. Even though clinical trials have confirmed its empirical use, the active constituents, their mode of action, and the exact composition of this natural product are still unknown. In this study, the balm was subjected to fractionated extraction and further purified employing flash chromatography, HPLC-PDA-ELSD, preparative and analytical TLC. Hydroxycinnamic acids (1–3), the lignan pinoresinol (4), four hydroxylated derivatives of dehydroabietic acid (DHAA) (5 – 8), and dehydroabietic acid (9) were isolated. Their structures were elucidated by LC-MS, 1D- and 2D-NMR. Four extracts, two commercially available resin acids–pimaric acid (10) and isopimaric acid (11)–and the isolated compounds were tested for increased re-epithelialization of cell-free areas in a human adult low calcium high temperature keratinocytes monolayer. Lysophosphatidic acid (10 µM) served as positive control and ranged between 100% and 150% rise in cell-covered area related to the vehicle control. Two extracts containing carboxylic acids and non-acidic apolar constituents, respectively, boosted wound closure by 47% and 36% at 10 and 3 µg/mL, respectively. Pinoresinol, DHAA, three of its hydroxylated derivatives, and pimaric and isopimaric acid as well as defined combinations of the hydroxylated DHAA derivatives led to a significantly enhanced wound closure by up to 90% at concentrations between 1 and 10 µM. Overall, lignans and diterpene resin acids, main constituents of Norway spruce balm, are able to increase migration or proliferation of keratinocytes in vitro. The presented data link the phytochemistry of this natural wound healing agent with boosted re-epithelialization.

Six new and four known dihydrochalcone glucoside derivatives (1-10), the phenylpropanoid coniferin (11), and the lignans (+)-pinoresinol (12) and lariciresinol (13) were isolated from the subaerial plant parts of Thonningia sanguinea in the course of a screening campaign for new antidiabetic lead compounds. The structures of the new substances were elucidated by HRESIMS, NMR, GC-MS, and ECD data evaluation. 2'- O-(3-Galloyl-4,6- O- S-hexahydroxydiphenoyl-β-d-glucopyranosyl)-3-hydroxyphloretin (4), 2'- O-(4,6- O- S-hexahydroxydiphenoyl-β-d-glucopyranosyl)phloretin (5), 2'- O-(3- O-galloyl-4,6- O- S-hexahydroxydiphenoyl-β-d-glucopyranosyl)phloretin (6), and thonningianin B (9) showed moderate protein tyrosine phosphatase-1B inhibition in an enzyme assay (IC values ranging from 19 to 25 μM), whereas thonningianin A (10) was identified as a more potent inhibitor (IC = 4.4 μM). The observed activity differences could be explained by molecular docking experiments. The activity of 10 could further be confirmed in HEPG2 liver carcinoma cells, where the compound was able to increase the level of phosphorylated insulin receptors in a concentration-dependent manner.