Prochlorococcus extracellular vesicles: molecular composition and adsorption to diverse microbes

Extracellular vesicles are small (~50–200 nm diameter) membrane-bound structures released by cells from all domains of life. While vesicles are abundant in the oceans, their functions, both for cells themselves and the emergent ecosystem, remain a mystery. To better characterize these particles – a prerequisite for determining function – we analysed the lipid, protein, and metabolite content of vesicles produced by the marine cyanobacterium Prochlorococcus. We show that Prochlorococcus exports a diverse array of cellular compounds into the surrounding seawater enclosed within discrete vesicles. Vesicles produced by two different strains contain some materials in common, but also display numerous strain-specific differences, reflecting functional complexity within vesicle populations. The vesicles contain active enzymes, indicating that they can mediate extracellular biogeochemical reactions in the ocean. We further demonstrate that vesicles from Prochlorococcus and other bacteria associate with diverse microbes including the most abundant marine bacterium, Pelagibacter. Together, our data point toward hypotheses concerning the functional roles of vesicles in marine ecosystems including, but not limited to, possibly mediating energy and nutrient transfers, catalysing extracellular biochemical reactions, and mitigating toxicity of reactive oxygen species.     

Inflammation and pericarditis: Are neutrophils actors behind the scenes?

The morbidity of acute pericarditis is increasing over time impacting on patient quality of life. Recent clinical trials focused especially on clinical aspects, with a modest interest in pathophysiological mechanisms. This narrative review, based on papers in English language obtained via PubMed up to April 2018, aims at focusing on the role of the innate immunity in pericarditis and discussing future potential therapeutic strategies impacting on disease pathophysiology. In developed countries, most cases of pericarditis are referred to as idiopathic, although etiological causes have been described, with autoreactive/lymphocytic, malignant, and infectious ones as the most frequent causes. Apart the known impairment of the adaptive immunity, recently a large body evidence indicated the central role of the innate immune system in the pathogenesis of recurrent pericarditis, starting from similarities with autoinflammatory diseases. Accordingly, the “inflammasome” has been shown to behave as an important player in pericarditis development. Similarly, the beneficial effect of colchicine in recurrent pericarditis confirms that neutrophils are important effectors as colchicine, which can block neutrophil chemotaxis, interferes with neutrophil adhesion and recruitment to injured tissues and abrogate superoxide production. Anyway, the role of the adaptive immune system in pericarditis cannot be reduced to a black or white issue as mechanisms often overlap. Therefore, we believe that more efficient therapeutic strategies have to be investigated by targeting neutrophil-derived mediators (such as metalloproteinases) and disentangling the strict interplay between neutrophils and platelets. In this view, some progress has been done by using the recombinant human interleukin-1 receptor antagonist anakinra.     

c-Myc inactivation by mutant max alters growth and morphology of NCI-H-630 colon cancer cells

The myc gene family has been implicated in multiple cell processes including proliferation, differentiation, tumorigenesis, and apoptosis. For its cellular growth promoting function, Myc must heterodimerize with Max. To study the effect of Myc inactivation on the growth and differentiation properties of epithelial tumor cells, we transfected the H-630 human colon cancer cell line with bm-max, a mutant Max protein in which DNA-binding activity has been abolished. Cells expressing high levels of bm-Max grow poorly, and the morphology of both colonies and single cells is altered. Moreover, increased bm-Max expression results in a prolonged G₀/G₁ phase accompanied by induced expression of p21 (WAF1/CIP1), elevated levels of alkaline phosphatase (ALP) activity, and accumulation of large fat granuli within the cells. These distinctive cell characteristics are associated with differentiation processes in numerous malignant cell lines. The results of this study support a model in which sequestering of endogenous Myc and Max proteins into “basic mutant” dimers lacking DNA-binding activity is sufficient both to inhibit proliferation and to induce changes in cell behavior consistent with differentiation. © 1996 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

The double-stranded RNA-binding protein,Staufen1, is an IRES-transacting factor regulating HIV-1 cap-independent translation initiation

Translation initiation of the viral genomic mRNA (vRNA) of human immunodeficiency virus-type 1 (HIV-1) can be mediated by a cap- or an internal ribosome entry site (IRES)-dependent mechanism. A previous report shows that Staufen1, a cellular double-stranded (ds) RNA-binding protein (RBP), binds to the 5’untranslated region (5′UTR) of the HIV-1 vRNA and promotes its cap-dependent translation. In this study, we now evaluate the role of Staufen1 as an HIV-1 IRES-transacting factor (ITAF). We first confirm that Staufen1 associates with both the HIV-1 vRNA and the Gag protein during HIV-1 replication. We found that in HIV-1-expressing cells, siRNA-mediated depletion of Staufen1 reduces HIV-1 vRNA translation. Using dual-luciferase bicistronic mRNAs, we show that the siRNA-mediated depletion and cDNA-mediated overexpression of Staufen1 acutely regulates HIV-1 IRES activity. Furthermore, we show that Staufen1-vRNA interaction is required for the enhancement of HIV-1 IRES activity. Interestingly, we find that only Staufen1 harboring an intact dsRNA-binding domain 3 (dsRBD3) rescues HIV-1 IRES activity in Staufen1 CRISPR-Cas9 gene edited cells. Finally, we show that the expression of Staufen1-dsRBD3 alone enhances HIV-1 IRES activity. This study provides evidence of a novel role for Staufen1 as an ITAF promoting HIV-1 vRNA IRES activity.     

SIRT6 stabilization and cytoplasmic localization in macrophages regulates acute and chronic inflammation in mice

Acute and chronic inflammations are key homeostatic events in health and disease. Sirtuins (SIRTs), a family of NAD-dependent protein deacylases, play a pivotal role in the regulation of these inflammatory responses. Indeed, SIRTs have anti-inflammatory effects through a myriad of signaling cascades, including histone deacetylation and gene silencing, p65/RelA deacetylation and inactivation, and nucleotide‑binding oligomerization domain, leucine rich repeat, and pyrin domain‑containing protein 3 inflammasome inhibition. Nevertheless, recent findings show that SIRTs, specifically SIRT6, are also necessary for mounting an active inflammatory response in macrophages. SIRT6 has been shown to positively regulate tumor necrosis factor alpha (TNFα) secretion by demyristoylating pro-TNFα in the cytoplasm. However, how SIRT6, a nuclear chromatin-binding protein, fulfills this function in the cytoplasm is currently unknown. Herein, we show by Western blot and immunofluorescence that in macrophages and fibroblasts there is a subpopulation of SIRT6 that is highly unstable and quickly degraded via the proteasome. Upon lipopolysaccharide stimulation in Raw 264.7, bone marrow, and peritoneal macrophages, this population of SIRT6 is rapidly stabilized and localizes in the cytoplasm, specifically in the vicinity of the endoplasmic reticulum, promoting TNFα secretion. Furthermore, we also found that acute SIRT6 inhibition dampens TNFα secretion both in vitro and in vivo, decreasing lipopolysaccharide-induced septic shock. Finally, we tested SIRT6 relevance in systemic inflammation using an obesity-induced chronic inflammatory in vivo model, where TNFα plays a key role, and we show that short-term genetic deletion of SIRT6 in macrophages of obese mice ameliorated systemic inflammation and hyperglycemia, suggesting that SIRT6 plays an active role in inflammation-mediated glucose intolerance during obesity.     

N-acetyl-L-cysteine protects SHSY5Y neuroblastoma cells from oxidative stress and cell cytotoxicity: effects on beta-amyloid secretion and tau phosphorylation

Redox changes within neurones are increasingly being implicated as an important causative agent in brain ageing and neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD) and Alzheimer's disease (AD). Cells have developed a number of defensive mechanisms to maintain intracellular redox homeostasis, including the glutathione (GSH) system and antioxidant enzymes. Here we examine the effects of N-acetyl-L-cysteine (NAC) on beta-amyloid (A beta) secretion and tau phosphorylation in SHSY5Y neuroblastoma cells after exposure to oxidative stress inducing/cytotoxic compounds (H(2)O(2), UV light and toxic A beta peptides). A beta and tau protein are hallmark molecules in the pathology of AD while the stress factors are implicated in the aetiology of AD. The results show that H(2)O(2), UV light, A beta 1-42 and toxic A beta 25-35, but not the inactive A beta 35-25, produce a significant induction of oxidative stress and cell cytotoxicity. The effects are reversed when cells are pre-treated with 30 mM NAC. Cells exposed to H(2)O(2), UV light and A beta 25-35, but not A beta 35-25, secrete significantly higher amounts of A beta 1-40 and A beta 1-42 into the culture medium. NAC pre-treatment increased the release of A beta 1-40 compared with controls and potentiated the release of both A beta 1-40 and A beta 1-42 in A beta 25-35-treated cells. Tau phosphorylation was markedly reduced by H(2)O(2) and UV light but increased by A beta 25-35. NAC strongly lowered phospho-tau levels in the presence or absence of stress treatment.     

Three-dimensional structure of α-conotoxin EI determined by 1H NMR spectroscopy H resonance assignments of α-conotoxin EI

-Conotoxin EI is an 18-residue peptide (RDOCCYHPTCNMSNPQIC; 4–10, 5–18) isolated from the venom of Conus ermineus, the only fish-hunting cone snail of the Atlantic Ocean. This peptide targets specifically the nicotinic acetylcholine receptor (nAChR) found in mammalian skeletal muscle and the electric organ Torpedo, showing a novel selectivity profile when compared to other -conotoxins. The 3D structure of EI has been determined by 2D-NMR methods in combination with dynamical simulated annealing protocols. A total of 133 NOE-derived distances were used to produce 13 structures with minimum energy that complied with the NOE restraints. The structure of EI is characterized by a helical loop between Thr⁹ and Met¹² that is stabilized by the Cys⁴-Cys¹⁰ disulfide bond and turns involving Cys⁴-Cys⁵ and Asn¹⁴-Pro¹⁵. Other regions of the peptide appear to be flexible. The overall fold of EI is similar to that of other 4/7-conotoxins (PnIA/B, MII, EpI). However, unlike these other 4/7-conotoxins, EI targets the muscular type nAChR. The differences in selectivity can be attributed to differences in the surface charge distribution among these 4/7-conotoxins. The implications for binding of EI to the muscular nAChR are discussed with respect to the current NMR structure of EI.     

In vivo and in vitro development of mouse pancreatic β-cells in organotypic slices

Taking tissue slices of the embryonic and newborn pancreas is a novel approach for the study of the perinatal development of this gland. The aim of this study was to describe the morphology and physiology of in vivo and in vitro developing -cells. In addition, we wanted to lay a foundation for the functional analysis of other pancreatic cells, either alone or as part of an integrative pancreatic physiology approach. We used cytochemistry and light microscopy to detect specific markers and the whole-cell patch-clamp to assess the function of single -cells. The insulin signal in the embryonic -cells was condensed to a subcellular compartment and redistributed throughout the cytosol during the first 2 days after birth. The hormone distribution correlated well with the development of membrane excitability and hormone release competence in -cells. Endocrine cells survived in the organotypic tissue culture and maintained their physiological properties for weeks. We conclude that our preparation fulfills the criteria for a method of choice to characterize the function of developing pancreas in wild-type and genetically modified mice that die at birth. We suggest organotypic culture for in vitro studies of the development and regeneration of -cells.This work was supported by the European Commission (grant QLG1-CT-2001-02233 to TMR, AR and MR), the DFG Research Center for Molecular Physiology of the Brain (CMPB) and the Max-Planck Society (MR)     

Stereospecific activity of two glutamate analogs

Two glutamic acid analogs, (+)-(S)- and (-)-(R)-4-(2,2-diphenyl-1,3,2-oxazaborolidin-5-oxo)propionic acid ((+)-(S)- and (-)-(R)-Trujillon, respectively), were prepared. The stereospecific activity of their pharmacological properties was studied. The median convulsant dose (CD(50)) and median lethal dose (LD(50)) were analyzed in female Swiss Webster mice and their effects in vivo on unitary electrical activity in globus pallidus neurons were elucidated in male Wistar rats. Compounds were characterized by (1)H, (13)C, and (11)B nuclear magnetic resonance. The LD(50) of (+)-(S)-Trujillon was 449.08 mg/kg and it increased spontaneous motor activity, while with (-)-(R)-Trujillon there was no mortality up to 1,000 mg/kg and it decreased spontaneous motor activity. The CD(50) in experiments with (+)-(S)-Trujillon was 199.34 mg/kg. Unitary recording in globus pallidus neurons showed i.v. administration (+)-(S)-Trujillon (50 mg/kg) increased frequency 79.0 +/- 23.0% in relation to basal response. (-)-(R)-Trujillon and (+)-(S)-glutamate (50 mg/kg each) did not provoke changes in spontaneous basal firing. Local infusion of (+)-(S)-Trujillon (1 nMol) increased spontaneous firing in most neurons tested by 269.0 +/- 83.0% in relation to basal values. Intrapallidal infusion of (-)-(R)-Trujillon (1 nMol) and saline solution did not cause statistically significant changes in globus pallidus spiking. Results showed that (+)-(S)-Trujillon crosses the blood-brain barrier and has stereospecific activity.