Inhibitors of UHRF1 base flipping activity showing cytotoxicity against cancer cells

Ubiquitin-like containing PHD and RING finger domain 1 (UHRF1) is a nuclear multi-domain protein overexpressed in numerous human cancer types. We previously disclosed the anthraquinone derivative UM63 that inhibits UHRF1-SRA domain base-flipping activity, although having DNA intercalating properties. Herein, based on the UM63 structure, new UHRF1-SRA inhibitors were identified through a multidisciplinary approach, combining molecular modelling, biophysical assays, molecular and cell biology experiments. We identified AMSA2 and MPB7, that inhibit UHRF1-SRA mediated base flipping at low micromolar concentrations, but do not intercalate into DNA, which is a key advantage over UM63. These molecules prevent UHRF1/DNMT1 interaction at replication forks and decrease the overall DNA methylation in cells. Moreover, both compounds specifically induce cell death in numerous cancer cell lines, displaying marginal effect on non-cancer cells, as they preferentially affect cells with high level of UHRF1. Overall, these two compounds are promising leads for the development of anti-cancer drugs targeting UHRF1.

Thienoguanosine brightness in DNA duplexes is governed by the localization of its ππ* excitation in the lowest energy absorption band

Thienoguanosine (thG) is an isomorphic fluorescent guanosine (G) surrogate, which almost perfectly mimics the natural G in DNA duplexes and may therefore be used to sensitively investigate for example protein-induced local conformational changes. To fully exploit the information given by the probe, we carefully re-investigated the thG spectroscopic properties in 12-bp duplexes, when the Set and Ring Associated (SRA) domain of UHRF1 flips its 5' flanking methylcytosine (mC). The SRA-induced flipping of mC was found to strongly increase the fluorescence intensity of thG, but this increase was much larger when thG was flanked in 3' by a C residue as compared to an A residue. Surprisingly, the quantum yield and fluorescence lifetime values of thG were nearly constant, regardless of the presence of SRA and the nature of the 3' flanking residue, suggesting that the differences in fluorescence intensities might be related to changes in absorption properties. We evidenced that thG lowest energy absorption band in the duplexes can be deconvoluted into two bands peaking at ~350 nm and ~310 nm, respectively red-shifted and blue-shifted, compared to the spectrum of thG monomer. Using quantum mechanical calculations, we attributed the former to a nearly pure * excitation localized on thG and the latter to excited states with charge transfer character. The amplitude of thG red-shifted band strongly increased when its 3' flanking C residue was replaced by an A residue in the free duplex, or when its 5' flanking mC residue was flipped by SRA. As only the species associated with the red-shifted band were found to be emissive, the highly unusual finding of this work is that the brightness of thG in free duplexes as well as its changes on SRA-induced mC flipping almost entirely depend on the relative population and/or absorption coefficient of the red-shifted absorbing species.

Panton-Valentine Leucocidin of Staphylococcus aureus Induces Oxidative Stress and Neurotransmitter Imbalance in a Retinal Explant Model

Purpose

Endophthalmitis models have reported the virulent role of Panton-Valentine leucocidin (PVL) secreted by Staphylococcus aureus on the retina. PVL targets retinal ganglion cells (RGCs), expressing PVL membrane receptor C5aR. Interactions between PVL and retinal cells lead to glial activation, retinal inflammation, and apoptosis. In this study, we explored oxidative stress and retinal neurotransmitters in a rabbit retinal explant model incubated with PVL.

Methods

Reactive oxygen species (ROS) production in RGCs has been assessed with fluorescent probes and immunohistochemistry. Nuclear magnetic resonance (NMR) spectroscopy quantified retinal concentrations of antioxidant molecules and neurotransmitters, and concentrations of neurotransmitters released in the culture medium. Quantifying the expression of some pro-inflammatory and anti-inflammatory factors was performed using RT-qPCR.

Results

PVL induced a mitochondrial ROS production in RGCs after four hours’ incubation with the toxin. Enzymatic sources of ROS, involving nicotinamide adenine dinucleotide phosphate–oxidase and xanthine oxidase, were also activated after four hours in PVL-treated retinal explants. Retinal antioxidants defenses, that is, glutathione, ascorbate and taurine, decreased after two hours’ incubation with PVL. Glutamate retinal concentrations and glutamate release in the culture medium remained unaltered in PVL-treated retinas. GABA, glycine, and acetylcholine (Ach) retinal concentrations decreased after PVL treatment. Glycine release in the culture medium decreased, whereas Ach release increased after PVL treatment. Expression of proinflammatory and anti-inflammatory cytokines remained unchanged in PVL-treated explants.

Conclusions

PVL activates oxidative pathways and alters neurotransmitter retinal concentrations and release, supporting the hypothesis that PVL could induce a neurogenic inflammation in the retina.

Staphylococcus aureus Panton-Valentine Leukocidin triggers an alternative NETosis process targeting mitochondria

Panton-Valentine Leukocidin (PVL) is a bicomponent leukotoxin produced by 3%-10% of clinical Staphylococcus aureus (SA) strains involved in the severity of hospital and community-acquired infections. Although PVL was long known as a pore-forming toxin, recent studies have challenged the formation of a pore at the plasma membrane, while its endocytosis and the exact mode of action remain to be defined. In vitro immunolabeling of human neutrophils shows that Neutrophil Extracellular Traps (NETosis) is triggered by the action of purified PVL, but not by Gamma hemolysin CB (HlgCB), a structurally similar SA leukotoxin. PVL causes the ejection of chromatin fibers (NETs) decorated with antibacterial peptides independently of the NADPH oxidase oxidative burst. Leukotoxin partially colocalizes with mitochondria and enhances the production of reactive oxygen species from these organelles, while showing an increased autophagy, which results unnecessary for NETs ejection. PVL NETosis is elicited through Ca²⁺ -activated SK channels and Myeloperoxidase activity but is abolished by Allopurinol pretreatment of neutrophils. Moreover, massive citrullination of the histone H3 is performed by peptidyl arginine deiminases. Inhibition of this latter enzymes fails to abolish NET extrusion. Unexpectedly, PVL NETosis does not seem to involve Src kinases, which is the main kinase family activated downstream the binding of PVL F subunit to CD45 receptor, while the specific kinase pathway differs from the NADPH oxidase-dependent NETosis. PVL alone causes a different and specific form of NETosis that may rather represent a bacterial strategy conceived to disarm and disrupt the immune response, eventually allowing SA to spread.

Cardiac sources of cerebral embolism in people with migraine

BACKGROUND AND PURPOSE

Whether the reported association between migraine with aura (MA) and cardioembolic stroke may be explained by a higher rate of atrial fibrillation (AF) or by other potential cardiac sources of cerebral embolism remains to be determined.

METHODS

In the setting of a single centre cohort study of consecutive patients with acute brain ischaemia stratified by migraine status, the association between AF as well as patent foramen ovale (PFO) and migraine was explored.

RESULTS

In all, 1738 patients (1017 [58.5%] men, mean age 67.9 ± 14.9 years) qualified for the analysis. Aging was inversely associated with migraine, whilst women had a >3-fold increased disease risk (odds ratio [OR] 3.82, 95% confidence interval [CI] 2.58-5.66). No association between AF and history of migraine or its pathogenic subtypes was detected. Conversely, migraine was associated with PFO, both in the entire cohort (OR 1.84, 95% CI 1.07-3.16) and in patients aged ≤55 years (OR 2.21, 95% CI 1.16-4.22). This association was significant for MA (OR 2.92, 95% CI 1.32-6.45 in the entire cohort; OR 2.92, 95% CI 1.15-7.41 in patients aged ≤55 years) and in women (OR 8.23, 95% CI 2.06-32.77), but not for migraine without aura.

CONCLUSIONS

In patients with brain ischaemia migraine is not associated with AF. Conversely, there is a probable relation between migraine, especially MA, and PFO in patients who are younger and have a more favourable vascular risk factor profile, and in women.

Persistent organic pollutants in cork used for production of wine stoppers

Owing to the lipophilic character of some components of cork and the long periods in the open air (during growth and barks storage), there is a risk of the cork becoming environmentally polluted. Moreover, cork stoppers are in contact with wines for periods ranging from a few months to several years; so they must maintain high levels of hygiene. The present work aims to investigate the level of PCBs, organochlorine pesticides, and PAHs in cork from different countries, used for the manufacturing of one-piece wine stoppers. Samples of cork were analysed using a multi-residue method. PCBs were not detected in all the samples; only a few samples contained detectable amounts of DDE; phenanthrene and anthracene were found in all the samples and fluoranthene in fewer cases. It was not possible to find a significant correlation between POPs concentration and origin of cork. Globally, the detected amounts are consistent with values found in foods, so the investigated cork show a suitable hygienic quality.