Human serum triggers antibiotic tolerance in Staphylococcus aureus

Staphylococcus aureus is a frequent cause of bloodstream infections. Treatment can be challenging, even when isolates appear to be drug susceptible, with high rates of persistent and relapsing infection. This is particularly the case with infections caused by methicillin resistant S. aureus (MRSA) strains, which are resistant to frontline antibiotics. To understand how the host environment influences treatment outcomes in MRSA infections, we studied the impact of human serum on staphylococcal susceptibility to daptomycin, an antibiotic of last resort. This revealed that serum triggered a very high degree of tolerance to daptomycin, as well as several other classes of antibiotics and antimicrobial peptides, including gentamicin, nitrofurantoin, vancomycin, nisin and gramicidin. Serum-induced daptomycin tolerance was due to two independent mechanisms. Firstly, the host defence peptide LL-37 present in serum induced tolerance by triggering the staphylococcal GraRS two component system. This led to increased cell wall accumulation that reduced access of daptomycin to its membrane target. Secondly, GraRS-independent changes to the membrane resulted in increased cardiolipin abundance that also contributed to daptomycin tolerance. When both mechanisms were blocked, serum exposed S. aureus cells were as susceptible to daptomycin as bacteria growing in laboratory media. These data demonstrate that host factors can significantly modulate antibiotic susceptibility via diverse mechanisms, which may in turn contribute to treatment failure. The inhibition of serum-induced cell wall accumulation by fosfomycin reduced tolerance, suggesting that this antibiotic may form a useful combination therapy with daptomycin.

The Intrinsic Virtues of EGCG, an Extremely Good Cell Guardian, on Prevention and Treatment of Diabesity Complications

The pandemic proportion of diabesity—a combination of obesity and diabetes—sets a worldwide health issue. Experimental and clinical studies have progressively reinforced the pioneering epidemiological observation of an inverse relationship between consumption of polyphenol-rich nutraceutical agents and mortality from cardiovascular and metabolic diseases. With chemical identification of epigallocatechin-3-gallate (EGCG) as the most abundant catechin of green tea, a number of cellular and molecular mechanisms underlying the activities of this unique catechin have been proposed. Favorable effects of EGCG have been initially attributed to its scavenging effects on free radicals, inhibition of ROS-generating mechanisms and upregulation of antioxidant enzymes. Biologic actions of EGCG are concentration-dependent and under certain conditions EGCG may exert pro-oxidant activities, including generation of free radicals. The discovery of 67-kDa laminin as potential EGCG membrane target has broaden the likelihood that EGCG may function not only because of its highly reactive nature, but also via receptor-mediated activation of multiple signaling pathways involved in cell proliferation, angiogenesis and apoptosis. Finally, by acting as epigenetic modulator of DNA methylation and chromatin remodeling, EGCG may alter gene expression and modify miRNA activities. Despite unceasing research providing detailed insights, ECGC composite activities are still not completely understood. This review summarizes the most recent evidence on molecular mechanisms by which EGCG may activate signal transduction pathways, regulate transcription factors or promote epigenetic changes that may contribute to prevent pathologic processes involved in diabesity and its cardiovascular complications.

LY6K promotes glioblastoma tumorigenicity via CAV-1–mediated ERK1/2 signaling enhancement

Background Lymphocyte antigen 6 complex, locus K (LY6K) is a putative oncogene in various cancers. Elevated expression of LY6K is correlated with poor patient prognosis in glioblastoma (GBM). The aim of this study is to advance our understanding of the mechanism by which LY6K contributes to GBM tumor biology. Methods Bioinformatic data mining was used to investigate LY6K expression in relation to GBM clinical outcome. To understand the role of LY6K in GBM, we utilized patient-derived glioma stemlike cells (GSCs) and U87 cells and employed immunoblotting, immunofluorescent staining, radiation treatment, and orthotopic GBM xenograft models. Results Our results show that increased expression of LY6K inversely correlates with GBM patient survival. LY6K promotes tumorigenicity in GBM cells both in vitro and in vivo. The mechanism underlying this tumorigenic behavior is enhancement of extracellular signal-regulated kinase 1 and 2 (ERK1/2) signaling. Interestingly, we observed that tumor-promoting LY6K-ERK1/2 signaling is mediated by the interaction of LY6K with caveolin-1, rather than through oncogenic receptor tyrosine kinase–mediated signaling. Moreover, association of LY6K with the cell membrane is crucial for its tumorigenic functions. Finally, DNA methylation maintains LY6K silencing, and hypomethylation of the LY6K promoter increases its expression. In GSCs, ionizing radiation leads to demethylation of the LY6K promoter, thereby increasing LY6K expression and GSC resistance to radiation. Conclusions Our study highlights the importance of the contribution of LY6K to GBM tumor biology and suggests LY6K as a potential membrane target for treating GBM.

Mechanism of Action of Antimicrobial Agents

Antibacterial and antifungal agents aim to kill pathogens, or at the very least incapacitate them. To achieve this aim these agents must have a reasonable degree of toxicity at the cellular level. If this toxicity was equally manifest against all cell types then the drugs would be unusable in patients as the side effect profile would be unacceptably severe. Selective toxicity, whereby the agents are orders of magnitude more toxic to bacteria or fungi than human cells, allows for the safe and effective administration of these agents to patients. There are a number of different mechanisms by which an antimicrobial agent can yield selective toxicity: ● Target a cellular structure that exists only in bacteria/fungi—e.g. the cell wall; ● Target a cellular structure that has a significantly different structure in bacteria/ fungi— e.g. the ribosome; the fungal cell membrane; ● Target cellular enzymes that are significantly different in bacteria/fungi e.g. topoisomerase; ● Target a synthetic pathway that exists only in bacteria e.g. folate synthesis. Broadly, antibacterial drugs can be divided into the following categories: ● Agents that target the cell wall; ● Agents that target the cell membrane; ● Agents that inhibit protein synthesis; ● Agents that inhibit DNA replication/ transcription of RNA; ● Agents that target folate synthesis; ● Agents that directly damage intracellular structures. The cell wall is unique to bacteria, and therefore an ideal target. Disrupting the complex cross-linking process required to produce the cell wall leads to loss of bacterial cell integrity and therefore to cell death. The following classes of antibiotics target the cell wall: The first class to be discovered, and still in many cases the most effective, incorporates the four-membered beta-lactam ring—its homology to d-alanyl-d-alanine allows beta-lactam-containing compounds to bind to cell wall peptidoglycans and act as chain terminators. The beta-lactam ring is fused to a five-membered sulphur-containing ring. Variations in side chains account for the differing pharmacokinetics and spectra of action of the different compounds—for example, the addition of an amino group to benzylpenicillin produces ampicillin.

VHH-Photosensitizer Conjugates for Targeted Photodynamic Therapy of Met-Overexpressing Tumor Cells

Photodynamic therapy (PDT) is an approach that kills (cancer) cells by the local production of toxic reactive oxygen species upon the local illumination of a photosensitizer (PS). The specificity of PDT has been further enhanced by the development of a new water-soluble PS and by the specific delivery of PS via conjugation to tumor-targeting antibodies. To improve tissue penetration and shorten photosensitivity, we have recently introduced nanobodies, also known as VHH (variable domains from the heavy chain of llama heavy chain antibodies), for targeted PDT of cancer cells overexpressing the epidermal growth factor receptor (EGFR). Overexpression and activation of another cancer-related receptor, the hepatocyte growth factor receptor (HGFR, c-Met or Met) is also involved in the progression and metastasis of a large variety of malignancies. In this study we evaluate whether anti-Met VHHs conjugated to PS can also serve as a biopharmaceutical for targeted PDT. VHHs targeting the SEMA (semaphorin-like) subdomain of Met were provided with a C-terminal tag that allowed both straightforward purification from yeast supernatant and directional conjugation to the PS IRDye700DX using maleimide chemistry. The generated anti-Met VHH-PS showed nanomolar binding affinity and, upon illumination, specifically killed MKN45 cells with nanomolar potency. This study shows that Met can also serve as a membrane target for targeted PDT.

Proof of an Outer Membrane Target of the Efflux Inhibitor Phe-Arg-β-Naphthylamide from Random Mutagenesis

Phe-Arg-β-naphthylamide (PAβN) has been characterized as an efflux pump inhibitor (EPI) acting on the major multidrug resistance efflux transporters of Gram-negative bacteria, such as AcrB in Eschericha coli. In the present study, in vitro random mutagenesis was used to evolve resistance to the sensitizing activity of PAβN with the aim of elucidating its mechanism of action. A strain was obtained that was phenotypically similar to a previously reported mutant from a serial selection approach that had no efflux-associated mutations. We could confirm that acrB mutations in the new mutant were unrelated to PAβN resistance. The next-generation sequencing of the two mutants revealed loss-of-function mutations in lpxM. An engineered lpxM knockout strain showed up to 16-fold decreased PAβN activity with large lipophilic drugs, while its efflux capacity, as well as the efficacy of other EPIs, remained unchanged. LpxM is responsible for the last acylation step in lipopolysaccharide (LPS) synthesis, and lpxM deficiency has been shown to result in penta-acylated instead of hexa-acylated lipid A. Modeling the two lipid A types revealed steric conformational changes due to underacylation. The findings provide evidence of a target site of PAβN in the LPS layer, and prove membrane activity contributing to its drug-sensitizing potency.

Wrapping of a nanowire by a supported lipid membrane

We explore the wrapping of a lipid membrane around a long cylindrical object in the presence of a substrate mimicking the cytoskeleton and obtain a wrapping phase diagram in terms of membrane–cytoskeleton and membrane–target adhesion energies.

oxLDL-mediated cellular senescence is associated with increased NADPH oxidase p47phox recruitment to caveolae

Atherosclerosis develops as a consequence of inflammation and cell senescence. In critical factors involved in the atherosclerotic changes, reactive oxygen species (ROS) generation is considered a leading cause. While NADPH oxidases, particularly NOX2, are the main sources of ROS, how they are regulated in the disease is incompletely understood. In addition, how caveolae, the membrane structure implicated in oxLDL deposition under vascular endothelia, is involved in the oxLDL-mediated ROS production remains mostly elusive. We report here that macrophages exposed to oxLDL up-regulate its caveolin-1 expression, and the latter in turn up-regulates NOX2 p47phox level. This combination effect results in increased cellular senescence. Interestingly, oxLDL treatment causes the p47phox residing in the cytosol to translocate to the caveolae. Immunoprecipitation assays confirms that cavelin-1 is in high degree association with p47phox. These results suggest caveolin-1 may serve as the membrane target for p47phox and as a switch for ROS production following oxLDL exposure. Our results reveal a previously unknown molecular event in oxLDL-mediated cellular ageing, and may provide a target for clinical intervention for atherosclerosis.

Clustering enzymes using E.coli inner cell membrane as scaffold in metabolic pathway

Clustering enzymes in the same metabolism pathway is a natural strategy to enhance the productivity. Several systems have been designed to artificially cluster desired enzymes in the cell, such as synthetic protein scaffold and nucleic acid scaffold. However, these scaffolds require complicated construction process and have limited slots for target enzymes. Following this direction, we designed a scaffold system based on natural cell membrane. Target enzymes (FabZ, FabG, FabI and TesA’ in fatty acid synthesis II pathway) are anchored on the E.coli inner membrane, showing the enhanced metabolism flux without the requirement of the further artificial interactions to force the clustering. Furthermore, anchoring the enzymes on the membrane enhances the products exportation, which further increases the productivity. Together, the proposed system has potential applications in producing valuable biomaterials.