Nitric oxide regulates endocytosis by S-nitrosylation of dynamin

Microbiome-Stealth Regulator of Breast Homeostasis and Cancer Metastasis

Cumulative evidence attests to the essential roles of commensal microbes in the physiology of hosts. Although the microbiome has been a major research subject since the time of Luis Pasteur and William Russell over 140 years ago, recent findings that certain intracellular bacteria contribute to the pathophysiology of healthy vs. diseased tissues have brought the field of the microbiome to a new era of investigation. Particularly, in the field of breast cancer research, breast-tumor-resident bacteria are now deemed to be essential players in tumor initiation and progression. This is a resurrection of Russel's bacterial cause of cancer theory, which was in fact abandoned over 100 years ago. This review will introduce some of the recent findings that exemplify the roles of breast-tumor-resident microbes in breast carcinogenesis and metastasis and provide mechanistic explanations for these phenomena. Such information would be able to justify the utility of breast-tumor-resident microbes as biomarkers for disease progression and therapeutic targets.

Protein S-Nitrosylation: A Chemical Modification with Ubiquitous Biological Activities

Nitric oxide (NO) induces protein posttranslational modification (PTM), known as S-nitrosylation, which has started to gain attention as a critical regulator of thousands of substrate proteins. However, our understanding of the biological consequences of this emerging PTM is incomplete because of the limited number of identified S-nitrosylated proteins (S-NO proteins). Recent advances in detection methods have effectively contributed to broadening the spectrum of discovered S-NO proteins. This article briefly reviews the progress in S-NO protein detection methods and discusses how these methods are involved in characterizing the biological consequences of this PTM. Additionally, we provide insight into S-NO protein-related diseases, focusing on the role of these proteins in mitigating the severity of infectious diseases.

ROS-mediated regulation of β2AR function: Does oxidation play a meaningful role towards β2-agonist tachyphylaxis in airway obstructive diseases?

β2-adrenergic receptor (β2AR) agonists are the clinical gold standard for treatment and prophylaxis of airway constriction in pulmonary obstructive diseases such as asthma and COPD. Inhaled β2-agonists elicit rapid bronchorelaxation of the airway smooth muscle, yet, clinical tachyphylaxis to this response can occur over repeated and chronic use, which reduces the bronchodilatory effectiveness. Several mechanisms have been proposed to impart β2-agonist tachyphylaxis, most notably β2AR desensitization. However, airway tissue is known to be highly oxidative, particularly in obstructive disease states where reactive oxygen species (ROS) generation is upregulated and ROS degradation is suboptimal yielding a large oxidative burden. Recent evidence demonstrates that β2AR can regulate ROS generation and that ROS can post-translationally alter β2AR cysteine residues via oxidation, leading to distinct functional receptor outcomes. Herein, we discuss the growing evidence for β2AR mediated ROS generation in airway cells and the role of ROS in regulating β2AR via cysteine-oxidation of the receptor. Given the functional consequence of the β2AR-ROS signaling axis in the airways, we also discuss the potential role of ROS in mediating β2-agonist tachyphylaxis.

Nitrosylation of β2-Tubulin Promotes Microtubule Disassembly and Differentiated Cardiomyocyte Beating in Ischemic Mice

BACKGROUND

Beating cardiomyocyte regeneration therapies have revealed as alternative therapeutics for heart transplantation. Nonetheless, the importance of nitric oxide (NO) in cardiomyocyte regeneration has been widely suggested, little has been reported concerning endogenous NO during cardiomyocyte differentiation.

METHODS

Here, we used P19CL6 cells and a Myocardiac infarction (MI) model to confirm NO-induced protein modification and its role in cardiac beating. Two tyrosine (Tyr) residues of β2-tubulin (Y106 and Y340) underwent nitrosylation (Tyr-NO) by endogenously generated NO during cardiomyocyte differentiation from pre-cardiomyocyte-like P19CL6 cells.

RESULTS

Tyr-NO-β2-tubulin mediated the interaction with Stathmin, which promotes microtubule disassembly, and was prominently observed in spontaneously beating cell clusters and mouse embryonic heart (E11.5d). In myocardial infarction mice, Tyr-NO-β2-tubulin in transplanted cells was closely related with cardiac troponin-T expression with their functional recovery, reduced infarct size and thickened left ventricular wall.

CONCLUSION

This is the first discovery of a new target molecule of NO, β2-tubulin, that can promote normal cardiac beating and cardiomyocyte regeneration. Taken together, we suggest therapeutic potential of Tyr-NO-β2-tubulin, for ischemic cardiomyocyte, which can reduce unexpected side effect of stem cell transplantation, arrhythmogenesis.

Nitrosative stress in Parkinson's disease

Parkinson’s Disease (PD) is a neurodegenerative disorder characterized, in part, by the loss of dopaminergic neurons within the nigral-striatal pathway. Multiple lines of evidence support a role for reactive nitrogen species (RNS) in degeneration of this pathway, specifically nitric oxide (NO). This review will focus on how RNS leads to loss of dopaminergic neurons in PD and whether RNS accumulation represents a central signal in the degenerative cascade. Herein, we provide an overview of how RNS accumulates in PD by considering the various cellular sources of RNS including nNOS, iNOS, nitrate, and nitrite reduction and describe evidence that these sources are upregulating RNS in PD. We document that over 1/3 of the proteins that deposit in Lewy Bodies, are post-translationally modified (S-nitrosylated) by RNS and provide a broad description of how this elicits deleterious effects in neurons. In doing so, we identify specific proteins that are modified by RNS in neurons which are implicated in PD pathogenesis, with an emphasis on exacerbation of synucleinopathy. How nitration of alpha-synuclein (aSyn) leads to aSyn misfolding and toxicity in PD models is outlined. Furthermore, we delineate how RNS modulates known PD-related phenotypes including axo-dendritic-, mitochondrial-, and dopamine-dysfunctions. Finally, we discuss successful outcomes of therapeutics that target S-nitrosylation of proteins in Parkinson’s Disease related clinical trials. In conclusion, we argue that targeting RNS may be of therapeutic benefit for people in early clinical stages of PD.

Laminin Receptor-Mediated Nanoparticle Uptake by Tumor Cells: Interplay of Epigallocatechin Gallate and Magnetic Force at Nano–Bio Interface

Epigallocatechin gallate (EGCG), a major tea catechin, enhances cellular uptake of magnetic nanoparticles (MNPs), but the mechanism remains unclear. Since EGCG may interact with the 67-kDa laminin receptor (67LR) and epidermal growth factor receptor (EGFR), we investigate whether a receptor and its downstream signaling may mediate EGCG’s enhancement effects on nanoparticle uptake. As measured using a colorimetric iron assay, EGCG induced a concentration-dependent enhancement effect of MNP internalization by LN-229 glioma cells, which was synergistically enhanced by the application of a magnetic field. Transmission electron microscopy demonstrated that EGCG increased the number, but not the size, of internalized vesicles, whereas EGCG and the magnet synergistically increased the size of vesicles. EGCG appears to enhance particle–particle interaction and thus aggregation following a 5-min magnet application. An antibody against 67LR, knockdown of 67LR, and a 67LR peptide (amino acid 161–170 of 67LR) attenuated EGCG-induced MNP uptake by 35%, 100%, and 45%, respectively, suggesting a crucial role of 67LR in the effects of EGCG. Heparin, the 67LR-binding glycosaminoglycan, attenuated EGCG-induced MNP uptake in the absence, but not presence, of the magnet. Such enhancement effects of EGCG were attenuated by LY294002 (a phosphoinositide 3-kinase inhibitor) and Akt inhibitor, but not by agents affecting cGMP levels, suggesting potential involvement of signaling downstream of 67LR. In contrast, the antibody against EGFR exerted no effect on EGCG-enhanced internalization. These results suggest that 67LR may be potentially amenable to tumor-targeted therapeutics.

Post-Translational Modifications in GPCR Internalization

G protein-coupled receptors (GPCRs) are the largest family of membrane receptors that serve as the most important drug targets. Classically, GPCR internalization has been considered to lead to receptor desensitization. However, many studies over the past decade have reported that internalized membrane receptors can trigger distinct signal activation. The "internalized activation" provides a completely new understanding for the receptor internalization, the mechanism of physiology/pathology and novel drug targets for precision medicine. GPCR internalization undergoes a series of strict regulations, especially by post-translational modifications (PTMs). Here, this review summarizes different PTMs in GPCR internalization and analyzes their significance in GPCR internalization dynamics, internalization routes, post-internalization fates and related diseases, which will offer new insights into the regulatory mechanism of GPCR signaling and novel drug targets for precision medicine.

Intertwined associations between oxidative and nitrosative stress and endocannabinoid system pathways: Relevance for neuropsychiatric disorders

The endocannabinoid system (ECS) appears to regulate metabolic, cardiovascular, immune, gastrointestinal, lung, and reproductive system functions, as well as the central nervous system. There is also evidence that neuropsychiatric disorders are associated with ECS abnormalities as well as oxidative and nitrosative stress pathways. The goal of this mechanistic review is to investigate the mechanisms underlying the ECS's regulation of redox signalling, as well as the mechanisms by which activated oxidative and nitrosative stress pathways may impair ECS-mediated signalling. Cannabinoid receptor (CB)1 activation and upregulation of brain CB2 receptors reduce oxidative stress in the brain, resulting in less tissue damage and less neuroinflammation. Chronically high levels of oxidative stress may impair CB1 and CB2 receptor activity. CB1 activation in peripheral cells increases nitrosative stress and inducible nitric oxide (iNOS) activity, reducing mitochondrial activity. Upregulation of CB2 in the peripheral and central nervous systems may reduce iNOS, nitrosative stress, and neuroinflammation. Nitrosative stress may have an impact on CB1 and CB2-mediated signalling. Peripheral immune activation, which frequently occurs in response to nitro-oxidative stress, may result in increased expression of CB2 receptors on T and B lymphocytes, dendritic cells, and macrophages, reducing the production of inflammatory products and limiting the duration and intensity of the immune and oxidative stress response. In conclusion, high levels of oxidative and nitrosative stress may compromise or even abolish ECS-mediated redox pathway regulation. Future research in neuropsychiatric disorders like mood disorders and deficit schizophrenia should explore abnormalities in these intertwined signalling pathways.

Oxidative Post-Translational Modifications: A Focus on Cysteine S-Sulfhydration and the Regulation of Endothelial Fitness

Significance: Changes in the oxidative balance can affect cellular physiology and adaptation through redox signaling. The endothelial cells that line blood vessels are particularly sensitive to reactive oxygen species, which can alter cell function by a number of mechanisms, including the oxidative post-translational modification (oxPTM) of proteins on critical cysteine thiols. Such modifications can act as redox-switches to alter the function of targeted proteins. Recent Advances: Mapping the cysteine oxPTM proteome and characterizing the effects of individual oxPTMs to gain insight into consequences for cellular responses has proven challenging. A recent addition to the list of reversible oxPTMs that contributes to cellular redox homeostasis is persulfidation or S-sulfhydration. Critical Issues: It has been estimated that up to 25% of proteins are S-sulfhydrated, making this modification almost as abundant as phosphorylation. In the endothelium, persulfides are generated by the trans-sulfuration pathway that catabolizes cysteine and cystathionine to generate hydrogen sulfide (H₂S) and H₂S-related sulfane sulfur compounds (H₂S_n). This pathway is of particular importance for the vascular system, as the enzyme cystathionine γ lyase (CSE) in endothelial cells accounts for a significant portion of total vascular H₂S/H₂S_n production. Future Directions: Impaired CSE activity in endothelial dysfunction has been linked with marked changes in the endothelial cell S-sulfhydrome and can contribute to the development of atherosclerosis and hypertension. It will be interesting to determine how changes in the S-sulfhydration of specific networks of proteins contribute to endothelial cell physiology and pathophysiology. Antioxid. Redox Signal. 35, 1494-1514.

The role of dynamin in absorbing lipids into endodermal epithelial cells of yolk sac membranes during embryonic development in Japanese quail

Endodermal epithelial cells (EECs) within the yolk sac membrane (YSM) of avian embryos are responsible for the absorption and utilization of lipids. The lipids in the yolk are mostly composed of very low density lipoprotein (VLDL), uptake mainly depends on clathrin-mediated endocytosis (CME). The CME relies on vesicle formation through the regulation of dynamin (DNM). However, it is still unclear whether DNMs participate in avian embryonic development. We examined mRNA expression levels of several genes involved in lipid transportation and utilization in YSM during Japanese quail embryonic development using qPCR. The mRNA levels of DNM1 and DNM3 were elevated at incubation d 8 and 10 before the increase of SOAT1, CIDEA, CIDEC, and APOB mRNA's. The elevated gene expression suggested the increased demand for DNM activity might be prior to cholesteryl ester production, lipid storage, and VLDL transport. Hinted by the result, we further investigated the role of DNMs in the embryonic development of Japanese quail. A DNM inhibitor, dynasore, was injected into fertilized eggs at incubation d 3. At incubation d 10, the dynasore-injected embryo showed increased embryonic lethality compared to control groups. Thus, the activity of DNMs was essential for the embryonic development of Japanese quail. The activities of DNMs were also verified by the absorptions of fluorescent VLDL (DiI-yVLDL) in EECs. Fluorescent signals in EECs were decreased significantly after treatment with dynasore. Finally, EECs were pretreated with S-Nitroso-L-glutathione (GSNO), a DNM activator, for 30 min; this increased the uptake of DiI-yVLDL. In conclusion, DNMs serve a critical role in mediating lipid absorption in YSM. The activity of DNMs was an integral part of development in Japanese quail. Our results suggest enhancing lipid transportation through an increase of DNM activity may improve avian embryonic development.

Aging-Induced Impairment of Vascular Function: Mitochondrial Redox Contributions and Physiological/Clinical Implications

Significance: The vasculature responds to the respiratory needs of tissue by modulating luminal diameter through smooth muscle constriction or relaxation. Coronary perfusion, diastolic function, and coronary flow reserve are drastically reduced with aging. This loss of blood flow contributes to and exacerbates pathological processes such as angina pectoris, atherosclerosis, and coronary artery and microvascular disease. Recent Advances: Increased attention has recently been given to defining mechanisms behind aging-mediated loss of vascular function and development of therapeutic strategies to restore youthful vascular responsiveness. The ultimate goal aims at providing new avenues for symptom management, reversal of tissue damage, and preventing or delaying of aging-induced vascular damage and dysfunction in the first place. Critical Issues: Our major objective is to describe how aging-associated mitochondrial dysfunction contributes to endothelial and smooth muscle dysfunction via dysregulated reactive oxygen species production, the clinical impact of this phenomenon, and to discuss emerging therapeutic strategies. Pathological changes in regulation of mitochondrial oxidative and nitrosative balance (Section 1) and mitochondrial dynamics of fission/fusion (Section 2) have widespread effects on the mechanisms underlying the ability of the vasculature to relax, leading to hyperconstriction with aging. We will focus on flow-mediated dilation, endothelial hyperpolarizing factors (Sections 3 and 4), and adrenergic receptors (Section 5), as outlined in Figure 1. The clinical implications of these changes on major adverse cardiac events and mortality are described (Section 6). Future Directions: We discuss antioxidative therapeutic strategies currently in development to restore mitochondrial redox homeostasis and subsequently vascular function and evaluate their potential clinical impact (Section 7). Antioxid. Redox Signal. 35, 974-1015.

From Pinocytosis to Methuosis-Fluid Consumption as a Risk Factor for Cell Death

The volumes of a cell [cell volume (CV)] and its organelles are adjusted by osmoregulatory processes. During pinocytosis, extracellular fluid volume equivalent to its CV is incorporated within an hour and membrane area equivalent to the cell's surface within 30 min. Since neither fluid uptake nor membrane consumption leads to swelling or shrinkage, cells must be equipped with potent volume regulatory mechanisms. Normally, cells respond to outwardly or inwardly directed osmotic gradients by a volume decrease and increase, respectively, i.e., they shrink or swell but then try to recover their CV. However, when a cell death (CD) pathway is triggered, CV persistently decreases in isotonic conditions in apoptosis and it increases in necrosis. One type of CD associated with cell swelling is due to a dysfunctional pinocytosis. Methuosis, a non-apoptotic CD phenotype, occurs when cells accumulate too much fluid by macropinocytosis. In contrast to functional pinocytosis, in methuosis, macropinosomes neither recycle nor fuse with lysosomes but with each other to form giant vacuoles, which finally cause rupture of the plasma membrane (PM). Understanding methuosis longs for the understanding of the ionic mechanisms of cell volume regulation (CVR) and vesicular volume regulation (VVR). In nascent macropinosomes, ion channels and transporters are derived from the PM. Along trafficking from the PM to the perinuclear area, the equipment of channels and transporters of the vesicle membrane changes by retrieval, addition, and recycling from and back to the PM, causing profound changes in vesicular ion concentrations, acidification, and-most importantly-shrinkage of the macropinosome, which is indispensable for its proper targeting and cargo processing. In this review, we discuss ion and water transport mechanisms with respect to CVR and VVR and with special emphasis on pinocytosis and methuosis. We describe various aspects of the complex mutual interplay between extracellular and intracellular ions and ion gradients, the PM and vesicular membrane, phosphoinositides, monomeric G proteins and their targets, as well as the submembranous cytoskeleton. Our aim is to highlight important cellular mechanisms, components, and processes that may lead to methuotic CD upon their derangement.

Cellular crosstalk in cardioprotection: Where and when do reactive oxygen species play a role?

A well-balanced intercellular communication between the different cells within the heart is vital for the maintenance of cardiac homeostasis and function. Despite remarkable advances on disease management and treatment, acute myocardial infarction remains the major cause of morbidity and mortality worldwide. Gold standard reperfusion strategies, namely primary percutaneous coronary intervention, are crucial to preserve heart function. However, reestablishment of blood flow and oxygen levels to the infarcted area are also associated with an accumulation of reactive oxygen species (ROS), leading to oxidative damage and cardiomyocyte death, a phenomenon termed myocardial reperfusion injury. In addition, ROS signaling has been demonstrated to regulate multiple biological pathways, including cell differentiation and intercellular communication. Given the importance of cell-cell crosstalk in the coordinated response after cell injury, in this review, we will discuss the impact of ROS in the different forms of inter- and intracellular communication, as well as the role of gap junctions, tunneling nanotubes and extracellular vesicles in the propagation of oxidative damage in cardiac diseases, particularly in the context of ischemia/reperfusion injury.

Identification of SARS-CoV-2-induced pathways reveals drug repurposing strategies

The global outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) necessitates the rapid development of new therapies against coronavirus disease 2019 (COVID-19) infection. Here, we present the identification of 200 approved drugs, appropriate for repurposing against COVID-19. We constructed a SARS-CoV-2-induced protein network, based on disease signatures defined by COVID-19 multiomics datasets, and cross-examined these pathways against approved drugs. This analysis identified 200 drugs predicted to target SARS-CoV-2-induced pathways, 40 of which are already in COVID-19 clinical trials, testifying to the validity of the approach. Using artificial neural network analysis, we classified these 200 drugs into nine distinct pathways, within two overarching mechanisms of action (MoAs): viral replication (126) and immune response (74). Two drugs (proguanil and sulfasalazine) implicated in viral replication were shown to inhibit replication in cell assays. This unbiased and validated analysis opens new avenues for the rapid repurposing of approved drugs into clinical trials.

S-Nitrosylation in Tumor Microenvironment

S-nitrosylation is a selective and reversible post-translational modification of protein thiols by nitric oxide (NO), which is a bioactive signaling molecule, to exert a variety of effects. These effects include the modulation of protein conformation, activity, stability, and protein-protein interactions. S-nitrosylation plays a central role in propagating NO signals within a cell, tissue, and tissue microenvironment, as the nitrosyl moiety can rapidly be transferred from one protein to another upon contact. This modification has also been reported to confer either tumor-suppressing or tumor-promoting effects and is portrayed as a process involved in every stage of cancer progression. In particular, S-nitrosylation has recently been found as an essential regulator of the tumor microenvironment (TME), the environment around a tumor governing the disease pathogenesis. This review aims to outline the effects of S-nitrosylation on different resident cells in the TME and the diverse outcomes in a context-dependent manner. Furthermore, we will discuss the therapeutic potentials of modulating S-nitrosylation levels in tumors.

A miRNA stabilizing polydopamine nano-platform for intraocular delivery of miR-21-5p in glaucoma therapy

The elevation of intraocular pressure (IOP) is an important risk factor in the development of primary open angle glaucoma (POAG), which is the main cause of irreversible vision loss. miRNAs are promising new anti-glaucoma therapeutic agents. However, the low stability and cellular transfection of miRNA in vivo hinder its further application. This study aims to investigate the use of polydopamine-polyethylenimine nanoparticles (PDA/PEI NPs) as miRNA carriers in the treatment of ocular hypertension and glaucoma. The in vitro study proves that the carrier preserves the activity of nucleic acid for a long period. Besides, it has comparable transfection efficiency with commercially available vehicles, while having lower cytotoxicity. It has been demonstrated in the animal model that PDA/PEI NPs successfully reach the target tissues without an obvious inflammatory response. PDA/PEI NPs/miR-21-5p increases the permeability of porcine angular aqueous plexus cells, thereby reducing IOP by facilitating the conventional outflow pathway at least partially through the pathway involving endothelial nitric oxide synthase. Our results indicate that PDA/PEI NPs/miR-21-5p is a promising anti-glaucoma drug for treating POAG. And the delivery strategy may be extended to other gene therapy in treating intraocular diseases.

Nitric oxide affects seed oil accumulation and fatty acid composition through protein S-nitrosation

Nitric oxide (NO) is a key signaling molecule regulating several plant developmental and stress responses. Here, we report that NO plays an important role in seed oil content and fatty acid composition. RNAi silencing of Arabidopsis S-nitrosoglutathione reductase 1 (GSNOR1) led to reduced seed oil content. In contrast, nitrate reductase double mutant nia1nia2 had increased seed oil content, compared with wild-type plants. Moreover, the concentrations of palmitic acid (C16:0), linoleic acid (C18:2), and linolenic acid (C18:3) were higher, whereas those of stearic acid (C18:0), oleic acid (C18:1), and arachidonic acid (C20:1) were lower, in seeds of GSNOR1 RNAi lines. Similar results were obtained with rapeseed embryos cultured in vitro with the NO donor sodium nitroprusside (SNP), and the NO inhibitor NG-Nitro-L-arginine Methyl Ester (L-NAME). Compared with non-treated embryos, the oil content decreased in SNP-treated embryos, and increased in L-NAME-treated embryos. Relative concentrations of C16:0, C18:2 and C18:3 were higher, whereas C18:1 concentration decreased in rapeseed embryos treated with SNP. Proteomics and transcriptome analysis revealed that three S-nitrosated proteins and some key genes involved in oil synthesis, were differentially regulated in SNP-treated embryos. Therefore, regulating NO content could be a novel approach to increasing seed oil content in cultivated oil crops.

Tracing the path of inhaled nitric oxide: Biological consequences of protein nitrosylation

Nitric oxide (NO) is a comprehensive regulator of vascular and airway tone. Endogenous NO produced by nitric oxide synthases regulates multiple signaling cascades, including activation of soluble guanylate cyclase to generate cGMP, relaxing smooth muscle cells. Inhaled NO is an established therapy for pulmonary hypertension in neonates, and has been recently proposed for the treatment of hypoxic respiratory failure and acute respiratory distress syndrome due to COVID-19. In this review, we summarize the effects of endogenous and exogenous NO on protein S-nitrosylation, which is the selective and reversible covalent attachment of a nitrogen monoxide group to the thiol side chain of cysteine. This posttranslational modification targets specific cysteines based on the acid/base sequence of surrounding residues, with significant impacts on protein interactions and function. S-nitrosothiol (SNO) formation is tightly compartmentalized and enzymatically controlled, but also propagated by nonenzymatic transnitrosylation of downstream protein targets. Redox-based nitrosylation and denitrosylation pathways dynamically regulate the equilibrium of SNO-proteins. We review the physiological roles of SNO proteins, including nitrosohemoglobin and autoregulation of blood flow through hypoxic vasodilation, and pathological effects of nitrosylation including inhibition of critical vasodilator enzymes; and discuss the intersection of NO source and dose with redox environment, in determining the effects of protein nitrosylation.

Nitric Oxide and S-Nitrosylation in Cardiac Regulation: G Protein-Coupled Receptor Kinase-2 and β-Arrestins as Targets

Cardiac diseases including heart failure (HF), are the leading cause of morbidity and mortality globally. Among the prominent characteristics of HF is the loss of β-adrenoceptor (AR)-mediated inotropic reserve. This is primarily due to the derangements in myocardial regulatory signaling proteins, G protein-coupled receptor (GPCR) kinases (GRKs) and β-arrestins (β-Arr) that modulate β-AR signal termination via receptor desensitization and downregulation. GRK2 and β-Arr2 activities are elevated in the heart after injury/stress and participate in HF through receptor inactivation. These GPCR regulators are modulated profoundly by nitric oxide (NO) produced by NO synthase (NOS) enzymes through S-nitrosylation due to receptor-coupled NO generation. S-nitrosylation, which is NO-mediated modification of protein cysteine residues to generate an S-nitrosothiol (SNO), mediates many effects of NO independently from its canonical guanylyl cyclase/cGMP/protein kinase G signaling. Herein, we review the knowledge on the NO system in the heart and S-nitrosylation-dependent modifications of myocardial GPCR signaling components GRKs and β-Arrs.

Systems biology reveals reprogramming of the S-nitroso-proteome in the cortical and striatal regions of mice during aging process

Cell aging depends on the rate of cumulative oxidative and nitrosative damage to DNA and proteins. Accumulated data indicate the involvement of protein S-nitrosylation (SNO), the nitric oxide (NO)-mediated posttranslational modification (PTM) of cysteine thiols, in different brain disorders. However, the changes and involvement of SNO in aging including the development of the organism from juvenile to adult state is still unknown. In this study, using the state-of-the-art mass spectrometry technology to identify S-nitrosylated proteins combined with large-scale computational biology, we tested the S-nitroso-proteome in juvenile and adult mice in both cortical and striatal regions. We found reprogramming of the S-nitroso-proteome in adult mice of both cortex and striatum regions. Significant biological processes and protein–protein clusters associated with synaptic and neuronal terms were enriched in adult mice. Extensive quantitative analysis revealed a large set of potentially pathological proteins that were significantly upregulated in adult mice. Our approach, combined with large scale computational biology allowed us to perform a system-level characterization and identification of the key proteins and biological processes that can serve as drug targets for aging and brain disorders in future studies.

Cysteine redox state regulates human β2-adrenergic receptor binding and function

Bronchoconstrictive airway disorders such as asthma are characterized by inflammation and increases in reactive oxygen species (ROS), which produce a highly oxidative environment. β2-adrenergic receptor (β2AR) agonists are a mainstay of clinical therapy for asthma and provide bronchorelaxation upon inhalation. We have previously shown that β2AR agonism generates intracellular ROS, an effect that is required for receptor function, and which post-translationally oxidizes β2AR cysteine thiols to Cys-S-sulfenic acids (Cys-S-OH). Furthermore, highly oxidative environments can irreversibly oxidize Cys-S-OH to Cys-S-sulfinic (Cys-SO₂H) or S-sulfonic (Cys-SO₃H) acids, which are incapable of further participating in homeostatic redox reactions (i.e., redox-deficient). The aim of this study was to examine the vitality of β2AR-ROS interplay and the resultant functional consequences of β2AR Cys-redox in the receptors native, oxidized, and redox-deficient states. Here, we show for the first time that β2AR can be oxidized to Cys-S-OH in situ, moreover, using both clonal cells and a human airway epithelial cell line endogenously expressing β2AR, we show that receptor redox state profoundly influences β2AR orthosteric ligand binding and downstream function. Specifically, homeostatic β2AR redox states are vital toward agonist-induced cAMP formation and subsequent CREB and G-protein-dependent ERK1/2 phosphorylation, in addition to β-arrestin-2 recruitment and downstream arrestin-dependent ERK1/2 phosphorylation and internalization. On the contrary, redox-deficient β2AR states exhibit decreased ability to signal via either Gαs or β-arrestin. Together, our results demonstrate a β2AR-ROS redox axis, which if disturbed, interferes with proper receptor function.

Protein S-Nitrosylation: Determinants of Specificity and Enzymatic Regulation of S-Nitrosothiol-Based Signaling

SIGNIFICANCE

Protein S-nitrosylation, the oxidative modification of cysteine by nitric oxide (NO) to form protein S-nitrosothiols (SNOs), mediates redox-based signaling that conveys, in large part, the ubiquitous influence of NO on cellular function. S-nitrosylation regulates protein activity, stability, localization, and protein-protein interactions across myriad physiological processes, and aberrant S-nitrosylation is associated with diverse pathophysiologies. Recent Advances: It is recently recognized that S-nitrosylation endows S-nitroso-protein (SNO-proteins) with S-nitrosylase activity, that is, the potential to trans-S-nitrosylate additional proteins, thereby propagating SNO-based signals, analogous to kinase-mediated signaling cascades. In addition, it is increasingly appreciated that cellular S-nitrosylation is governed by dynamically coupled equilibria between SNO-proteins and low-molecular-weight SNOs, which are controlled by a growing set of enzymatic denitrosylases comprising two main classes (high and low molecular weight). S-nitrosylases and denitrosylases, which together control steady-state SNO levels, may be identified with distinct physiology and pathophysiology ranging from cardiovascular and respiratory disorders to neurodegeneration and cancer.

CRITICAL ISSUES

The target specificity of protein S-nitrosylation and the stability and reactivity of protein SNOs are determined substantially by enzymatic machinery comprising highly conserved transnitrosylases and denitrosylases. Understanding the differential functionality of SNO-regulatory enzymes is essential, and is amenable to genetic and pharmacological analyses, read out as perturbation of specific equilibria within the SNO circuitry.

FUTURE DIRECTIONS

The emerging picture of NO biology entails equilibria among potentially thousands of different SNOs, governed by denitrosylases and nitrosylases. Thus, to elucidate the operation and consequences of S-nitrosylation in cellular contexts, studies should consider the roles of SNO-proteins as both targets and transducers of S-nitrosylation, functioning according to enzymatically governed equilibria.

Nitric oxide-releasing nanoparticles improve doxorubicin anticancer activity

Purpose

Anticancer drug delivery systems are often limited by hurdles, such as off-target distribution, slow cellular internalization, limited lysosomal escape, and drug resistance. To overcome these limitations, we have developed a stable nitric oxide (NO)-releasing nanoparticle (polystyrene-maleic acid [SMA]-tert-dodecane S-nitrosothiol [tDodSNO]) with the aim of enhancing the anticancer properties of doxorubicin (Dox) and a Dox-loaded nanoparticle (SMA-Dox) carrier.

Materials and methods

Effects of SMA-tDodSNO and/or in combination with Dox or SMA-Dox on cell viability, apoptosis, mitochondrial membrane potential, lysosomal membrane permeability, tumor tissue, and tumor growth were studied using in vitro and in vivo model of triple-negative breast cancer (TNBC). In addition, the concentrations of SMA-Dox and Dox in combination with SMA-tDodSNO were measured in cells and tumor tissues.

Results

Combination of SMA-tDodSNO and Dox synergistically decreased cell viability and induced apoptosis in 4T1 (TNBC cells). Incubation of 4T1 cells with SMA-tDodSNO (40 µM) significantly enhanced the cellular uptake of SMA-Dox and increased Dox concentration in the cells resulting in a twofold increase (P<0.001). Lysosomal membrane integrity, evaluated by acridine orange (AO) staining, was impaired by 40 µM SMA-tDodSNO (P<0.05 vs control) and when combined with SMA-Dox, this effect was significantly potentiated (P<0.001 vs SMA-Dox). Subcutaneous administration of SMA-tDodSNO (1 mg/kg) to xenografted mice bearing 4T1 cells showed that SMA-tDodSNO alone caused a twofold decrease in the tumor size compared to the control group. SMA-tDodSNO in combination with SMA-Dox resulted in a statistically significant 4.7-fold reduction in the tumor volume (P<0.001 vs control), without causing significant toxicity as monitored through body weight loss.

Conclusion

Taken together, these results suggest that SMA-tDodSNO can be used as a successful strategy to increase the efficacy of Dox and SMA-Dox in a model of TNBC.

Uropathogenic Escherichia coli invades bladder epithelial cells by activating kinase networks in host cells

Uropathogenic Escherichia coli (UPEC) is the causative bacterium in most urinary tract infections (UTIs). UPEC cells adhere to and invade bladder epithelial cells (BECs) and cause uropathogenicity. Invading UPEC cells may encounter one of several fates, including degradation in the lysosome, expulsion to the extracellular milieu for clearance, or survival as an intracellular bacterial community and quiescent intracellular reservoir that can cause later infections. Here we considered the possibility that UPEC cells secrete factors that activate specific host cell signaling networks to facilitate the UPEC invasion of BECs. Using GFP-based reporters and Western blot analysis, we found that the representative human cystitis isolate E. coli UTI89 and its derivative UTI89ΔFimH, which does not bind to BECs, equally activate phosphatidylinositol 4,5-bisphosphate 3-OH kinase (PI3K), Akt kinase, and mTOR complex (mTORC) 1 and 2 in BECs. We also found that conditioned medium taken from UTI89 and UTI89ΔFimH cultures similarly activates epidermal growth factor receptor (EGFR), PI3K, Akt, and mTORC and that inhibition of EGFR and mTORC2, but not mTORC1, abrogates UTI89 invasion in vitro and in animal models of UTI. Our results reveal a key molecular mechanism of UPEC invasion and the host cells it targets, insights that may have therapeutic utility for managing the ever-increasing number of persistent and chronic UTIs.

Alterations in neuronal metabolism contribute to the pathogenesis of prion disease

Neurodegenerative conditions are characterised by a progressive loss of neurons, which is believed to be initiated by misfolded protein aggregations. During this time period, many physiological and metabolomic alterations and changes in gene expression contribute to the decline in neuronal function. However, these pathological effects have not been fully characterised. In this study, we utilised a metabolomic approach to investigate the metabolic changes occurring in the hippocampus and cortex of mice infected with misfolded prion protein. In order to identify these changes, the samples were analysed by ultrahigh-performance liquid chromatography-tandem mass spectroscopy. The present dataset comprises a total of 498 compounds of known identity, named biochemicals, which have undergone principal component analysis and supervised machine learning. The results generated are consistent with the prion-inoculated mice having significantly altered metabolic profiles. In particular, we highlight the alterations associated with the metabolism of glucose, neuropeptides, fatty acids, L-arginine/nitric oxide and prostaglandins, all of which undergo significant changes during the disease. These data provide possibilities for future studies targeting and investigating specific pathways to better understand the processes involved in neuronal dysfunction in neurodegenerative diseases.

Nitrosative stress uncovers potent β2-adrenergic receptor-linked vasodilation further enhanced by blockade of clathrin endosome formation

This study investigated the effect of sodium nitroprusside (SNP) preexposure on vasodilation via the β-adrenergic receptor (BAR) system. SNP was used as a nitrosative/oxidative proinflammatory insult. Small arterioles were visualized by intravital microscopy in the hamster cheek pouch tissue (isoflurane, n = 45). Control dilation to isoproterenol (EC50: 10-7 mol/l) became biphasic as a function of concentration after 2 min of exposure to SNP (10-4 M), with increased potency at picomolar dilation uncovered and decreased efficacy at the micromolar dilation. Control dilation to curcumin was likewise altered after SNP, but only the increased potency at a low dose was uncovered, whereas micromolar dilation was eliminated. The picomolar dilations were blocked by the potent BAR-2 inverse agonist carazolol (10-9 mol/l). Dynamin inhibition with dynasore mimicked this effect, suggesting that SNP preexposure prevented BAR agonist internalization. Using HeLa cells transfected with BAR-2 tagged with monomeric red fluorescent protein, exposure to 10-8-10-6 mol/l curcumin resulted in internalization and colocalization of BAR-2 and curcumin (FRET) that was prevented by oxidative stress (10-3 mol/l CoCl2), supporting that stress prevented internalization of the BAR agonist with the micromolar agonist. This study presents novel data supporting that distinct pools of BARs are differentially available after inflammatory insult. NEW & NOTEWORTHY Preexposure to an oxidative/nitrosative proinflammatory insult provides a "protective preconditioning" against future oxidative damage. We examined immediate vasoactive and molecular consequences of a brief preexposure via β-adrenergic receptor signaling in small arterioles. Blocked receptor internalization with elevated reactive oxygen levels coincides with a significant and unexpected vasodilation to β-adrenergic agonists at picomolar doses.

S-Nitrosylation of β-Arrestins Biases Receptor Signaling and Confers Ligand Independence

Most G protein-coupled receptors (GPCRs) signal through both heterotrimeric G proteins and β-arrestins (βarr1 and βarr2). Although synthetic ligands can elicit biased signaling by G protein- vis-à-vis βarr-mediated transduction, endogenous mechanisms for biasing signaling remain elusive. Here we report that S-nitrosylation of a novel site within βarr1/2 provides a general mechanism to bias ligand-induced signaling through GPCRs by selectively inhibiting βarr-mediated transduction. Concomitantly, S-nitrosylation endows cytosolic βarrs with receptor-independent function. Enhanced βarr S-nitrosylation characterizes inflammation and aging as well as human and murine heart failure. In genetically engineered mice lacking βarr2-Cys253 S-nitrosylation, heart failure is exacerbated in association with greatly compromised β-adrenergic chronotropy and inotropy, reflecting βarr-biased transduction and β-adrenergic receptor downregulation. Thus, S-nitrosylation regulates βarr function and, thereby, biases transduction through GPCRs, demonstrating a novel role for nitric oxide in cellular signaling with potentially broad implications for patho/physiological GPCR function, including a previously unrecognized role in heart failure.

Regulation of dynamin family proteins by post-translational modifications

Dynamin superfamily proteins comprising classical dynamins and related proteins are membrane remodelling agents involved in several biological processes such as endocytosis, maintenance of organelle morphology and viral resistance. These large GTPases couple GTP hydrolysis with membrane alterations such as fission, fusion or tubulation by undergoing repeated cycles of self-assembly/disassembly. The functions of these proteins are regulated by various post-translational modifications that affect their GTPase activity, multimerization or membrane association. Recently, several reports have demonstrated variety of such modifications providing a better understanding of the mechanisms by which dynamin proteins influence cellular responses to physiological and environmental cues. In this review, we discuss major post-translational modifications along with their roles in the mechanism of dynamin functions and implications in various cellular processes.

Nitrite potentiates the vasodilatory signaling of S-nitrosothiols

Nitrite and S-nitrosothiols (SNOs) are both byproducts of nitric oxide (NO) metabolism and are proposed to cause vasodilation via activation of soluble guanylate cyclase (sGC). We have previously reported that while SNOs are potent vasodilators at physiological concentrations, nitrite itself only produces vasodilation at supraphysiological concentrations. Here, we tested the hypothesis that sub-vasoactive concentrations of nitrite potentiate the vasodilatory effects of SNOs. Multiple exposures of isolated sheep arteries to S-nitroso-glutathione (GSNO) resulted in a tachyphylactic decreased vasodilatory response to GSNO but not to NO, suggesting attenuation of signaling steps upstream from sGC. Exposure of arteries to 1 μM nitrite potentiated the vasodilatory effects of GSNO in naive arteries and abrogated the tachyphylactic response to GSNO in pre-exposed arteries, suggesting that nitrite facilitates GSNO-mediated activation of sGC. In intact anesthetized sheep and rats, inhibition of NO synthases to decrease plasma nitrite levels attenuated vasodilatory responses to exogenous infusions of GSNO, an effect that was reversed by exogenous infusion of nitrite at sub-vasodilating levels. This study suggests nitrite potentiates SNO-mediated vasodilation via a mechanism that lies upstream from activation of sGC.

Chronicles of a reductase: Biochemistry, genetics and physio-pathological role of GSNOR

S-nitrosylation is a major redox posttranslational modification involved in cell signaling. The steady state concentration of S-nitrosylated proteins depends on the balance between the relative ability to generate nitric oxide (NO) via NO synthase and to reduce nitrosothiols by denitrosylases. Numerous works have been published in last decades regarding the role of NO and S-nitrosylation in the regulation of protein structure and function, and in driving cellular activities in vertebrates. Notwithstanding an increasing number of observations indicates that impairment of denitrosylation equally affects cellular homeostasis, there is still no report providing comprehensive knowledge on the impact that denitrosylation has on maintaining correct physiological processes and organ activities. Among denitrosylases, S-nitrosoglutathione reductase (GSNOR) represents the prototype enzyme to disclose how denitrosylation plays a crucial role in tuning NO-bioactivity and how much it deeply impacts on cell homeostasis and human patho-physiology. In this review we attempt to illustrate the history of GSNOR discovery and provide the evidence so far reported in support of GSNOR implications in development and human disease.

Invasion of Host Cells and Tissues by Uropathogenic Bacteria

Within the mammalian urinary tract uropathogenic bacteria face many challenges, including the shearing flow of urine, numerous antibacterial molecules, the bactericidal effects of phagocytes, and a scarcity of nutrients. These problems may be circumvented in part by the ability of uropathogenic Escherichia coli and several other uropathogens to invade the epithelial cells that line the urinary tract. By entering host cells, uropathogens can gain access to additional nutrients and protection from both host defenses and antibiotic treatments. Translocation through host cells can facilitate bacterial dissemination within the urinary tract, while the establishment of stable intracellular bacterial populations may create reservoirs for relapsing and chronic urinary tract infections. Here we review the mechanisms and consequences of host cell invasion by uropathogenic bacteria, with consideration of the defenses that are brought to bear against facultative intracellular pathogens within the urinary tract. The relevance of host cell invasion to the pathogenesis of urinary tract infections in human patients is also assessed, along with some of the emerging treatment options that build upon our growing understanding of the infectious life cycle of uropathogenic E. coli and other uropathogens.

iNOS-Derived Nitric Oxide Induces Integrin-Linked Kinase Endocytic Lysosome-Mediated Degradation in the Vascular Endothelium

Objective—

ILK (integrin-linked kinase) plays a key role in controlling vasomotor tone and is decreased in atherosclerosis. The objective of this study is to test whether nitric oxide (NO) regulates ILK in vascular remodeling.

Approach and Results—

We found a striking correlation between increased levels of inducible nitric oxide and decreased ILK levels in human atherosclerosis and in a mouse model of vascular remodeling (carotid artery ligation) comparing with iNOS (inducible NO synthase) knockout mice. iNOS induction produced the same result in mouse aortic endothelial cells, and these effects were mimicked by an NO donor in a time-dependent manner. We found that NO decreased ILK protein stability by promoting the dissociation of the complex ILK/Hsp90 (heat shock protein 90)/eNOS (endothelial NO synthase), leading to eNOS uncoupling. NO also destabilized ILK signaling platform and lead to decreased levels of paxillin and α-parvin. ILK phosphorylation of its downstream target GSK3-β (glycogen synthase kinase 3 beta) was decreased by NO. Mechanistically, NO increased ILK ubiquitination mediated by the E3 ubiquitin ligase CHIP (C terminus of HSC70-interacting protein), but ILK ubiquitination was not followed by proteasome degradation. Alternatively, NO drove ILK to degradation through the endocytic-lysosomal pathway. ILK colocalized with the lysosome marker LAMP-1 (lysosomal-associated membrane protein 1) in endothelial cells, and inhibition of lysosome activity with chloroquine reversed the effect of NO. Likewise, ILK colocalized with the early endosome marker EEA1 (early endosome antigen 1). ILK endocytosis proceeded via dynamin because a specific inhibitor of dynamin (Dyngo 4a) was able to reverse ILK endocytosis and its lysosome degradation.

Conclusions—

Endocytosis regulates ILK signaling in vascular remodeling where there is an overload of inducible NO, and thus its inhibition may represent a novel target to fight atherosclerotic disease.

Gasotransmitter Heterocellular Signaling

SIGNIFICANCE

The family of gasotransmitter molecules, nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), has emerged as an important mediator of numerous cellular signal transduction and pathophysiological responses. As such, these molecules have been reported to influence a diverse array of biochemical, molecular, and cell biology events often impacting one another. Recent Advances: Discrete regulation of gasotransmitter molecule formation, movement, and reaction is critical to their biological function. Due to the chemical nature of these molecules, they can move rapidly throughout cells and tissues acting on targets through reactions with metal groups, reactive chemical species, and protein amino acids.

CRITICAL ISSUES

Given the breadth and complexity of gasotransmitter reactions, this field of research is expanding into exciting, yet sometimes confusing, areas of study with significant promise for understanding health and disease. The precise amounts of tissue and cellular gasotransmitter levels and where they are formed, as well as how they react with molecular targets or themselves, all remain poorly understood.

FUTURE DIRECTIONS

Elucidation of specific molecular targets, characteristics of gasotransmitter molecule heterotypic interactions, and spatiotemporal formation and metabolism are all important to better understand their true pathophysiological importance in various organ systems. Antioxid. Redox Signal. 26, 936-960.

Detection of Nitric Oxide Induced by Angiotensin II Receptor Type 1 Using Soluble Guanylate Cyclase beta1 Subunit Fused to a Yellow Fluorescent Protein, Venus

Nitric oxide (NO) is an important gaseous molecule involved in many physiological and pathophysiological processes, including the regulation of G protein-coupled receptors (GPCRs). Here, we report the development of a high-affinity method to detect NO using soluble guanylate cyclase beta1 subunit fused to Venus, a variant of yellow fluorescent protein (sGC-Venus). We measured the fluorescence intensity of sGC-Venus with and without an NO donor using purified probes. At 560 nm emission, the fluorescence intensity of sGC-Venus at 405 nm excitation was increased by approximately 2.5-fold by the NO donor, but the fluorescence intensities of sGC-Venus excited by other wavelengths showed much less of an increase or no significant increase. To measure NO in living cells, the fluorescence intensity of sGC-Venus at 405 nm excitation was normalized to that at 488 nm excitation because it showed no significant difference with or without the NO donor. In HEK293 cells overexpressing the angiotensin II receptor type 1 (AT1 receptor), the production of NO induced by activation of the AT1 receptor was detected using sGC-Venus. These data indicate that sGC-Venus will be a useful tool for visualizing intracellular NO in living cells and that NO might be a common tool to regulate GPCRs.

Nitrosative Stress, Hypernitrosylation, and Autoimmune Responses to Nitrosylated Proteins: New Pathways in Neuroprogressive Disorders Including Depression and Chronic Fatigue Syndrome

Nitric oxide plays an indispensable role in modulating cellular signaling and redox pathways. This role is mainly effected by the readily reversible nitrosylation of selective protein cysteine thiols. The reversibility and sophistication of this signaling system is enabled and regulated by a number of enzymes which form part of the thioredoxin, glutathione, and pyridoxine antioxidant systems. Increases in nitric oxide levels initially lead to a defensive increase in the number of nitrosylated proteins in an effort to preserve their function. However, in an environment of chronic oxidative and nitrosative stress (O&NS), nitrosylation of crucial cysteine groups within key enzymes of the thioredoxin, glutathione, and pyridoxine systems leads to their inactivation thereby disabling denitrosylation and transnitrosylation and subsequently a state described as "hypernitrosylation." This state leads to the development of pathology in multiple domains such as the inhibition of enzymes of the electron transport chain, decreased mitochondrial function, and altered conformation of proteins and amino acids leading to loss of immune tolerance and development of autoimmunity. Hypernitrosylation also leads to altered function or inactivation of proteins involved in the regulation of apoptosis, autophagy, proteomic degradation, transcription factor activity, immune-inflammatory pathways, energy production, and neural function and survival. Hypernitrosylation, as a consequence of chronically elevated O&NS and activated immune-inflammatory pathways, can explain many characteristic abnormalities observed in neuroprogressive disease including major depression and chronic fatigue syndrome/myalgic encephalomyelitis. In those disorders, increased bacterial translocation may drive hypernitrosylation and autoimmune responses against nitrosylated proteins.

Nitric Oxide-Mediated Posttranslational Modifications: Impacts at the Synapse

Nitric oxide (NO) is an important gasotransmitter molecule that is involved in numerous physiological processes throughout the nervous system. In addition to its involvement in physiological plasticity processes (long-term potentiation, LTP; long-term depression, LTD) which can include NMDAR-mediated calcium-dependent activation of neuronal nitric oxide synthase (nNOS), new insights into physiological and pathological consequences of nitrergic signalling have recently emerged. In addition to the canonical cGMP-mediated signalling, NO is also implicated in numerous pathways involving posttranslational modifications. In this review we discuss the multiple effects of S-nitrosylation and 3-nitrotyrosination on proteins with potential modulation of function but limit the analyses to signalling involved in synaptic transmission and vesicular release. Here, crucial proteins which mediate synaptic transmission can undergo posttranslational modifications with either pre- or postsynaptic origin. During normal brain function, both pathways serve as important cellular signalling cascades that modulate a diverse array of physiological processes, including synaptic plasticity, transcriptional activity, and neuronal survival. In contrast, evidence suggests that aging and disease can induce nitrosative stress via excessive NO production. Consequently, uncontrolled S-nitrosylation/3-nitrotyrosination can occur and represent pathological features that contribute to the onset and progression of various neurodegenerative diseases, including Parkinson's, Alzheimer's, and Huntington's.

Commensal bacterial internalization by epithelial cells: An alternative portal for gut leakiness

Co-existing paracellular and transcellular barrier defect in intestinal epithelium was documented in inflammatory bowel disease, celiac disease, and intestinal obstruction. Mechanisms regarding tight junction disruption have been extensively studied; however, limited progress has been made in research on bacterial transcytosis. Densely packed brush border (BB), with cholesterol-based lipid rafts in the intermicrovillous membrane invagination, serves as an ultrastructural barrier to prevent direct contact of luminal microbes with the cellular soma. Evidence in in vitro epithelial cell cultures and in vivo animal models of bowel obstruction and antibiotic-resistant bacterial infection had indicated that nonpathogenic, noninvasive enteric bacteria may hijack the lipid raft-mediated endocytic pathways. Our studies have shown that low dose interferon-gamma (IFNγ) causes long myosin light chain kinase (MLCK)-dependent terminal web (TW) contraction and BB fanning, allowing bacteria to pass through the consequently widened intermicrovillous cleft to be endocytosed via caveolin-associated lipid rafts. Activation of intracellular innate immune receptors by bacteria-containing endosomes may further induce inflammatory and oxidative stress, leading to secondary tight junction damage. The finding of bacterial internalization preceding tight junction damage suggests that abnormal bacterial uptake by epithelial cells may contribute to the initiation or relapse of chronic intestinal inflammation.

GRK2 in the heart: a GPCR kinase and beyond

SIGNIFICANCE

Heart failure (HF) is a common end point for many underlying cardiovascular diseases. Down-regulation and desensitization of β-adrenergic receptors (β-AR) caused by G-protein-coupled receptor (GPCR) kinase 2 (GRK2) are prominent features of HF. Recent Advances and Critical Issues: Significant progress has been made to understand the pathological role of GRK2 in the heart both as a GPCR kinase and as a molecule that can exert GPCR-independent effects. Inhibition of cardiac GRK2 has proved to be therapeutic in the failing heart and may offer synergistic and additional benefits to β-blocker therapy. However, the mechanisms of how GRK2 directly contributes to the pathogenesis of HF need further investigation, and additional verification of the mechanistic details are needed before GRK2 inhibition can be used for the treatment of HF.

FUTURE DIRECTIONS

The newly identified characteristics of GRK2, including the S-nitrosylation of GRK2 and the localization of GRK2 on mitochondria, merit further investigation. They may contribute to it being a pro-death kinase and result in HF under stressed conditions through regulation of intracellular signaling, including cardiac reduction-oxidation (redox) balance. A thorough understanding of the functions of GRK2 in the heart is necessary in order to finalize it as a candidate for drug development.

Nitric oxide and carbon monoxide antagonize TGF-β through ligand-independent internalization of TβR1/ALK5

Transforming growth factor (TGF)-β plays a central role in vascular homeostasis and in the pathology of vascular disease. There is a growing appreciation for the role of nitric oxide (NO) and carbon monoxide (CO) as highly diffusible, bioactive signaling molecules in the vasculature. We hypothesized that both NO and CO increase endocytosis of TGF-β receptor type 1 (TβR1) in vascular smooth muscle cells (VSMCs) through activation of dynamin-2, shielding cells from the effects of circulating TGF-β. In this study, primary cultures of VSMCs from Sprague-Dawley rats were treated with NO-releasing molecule 3 (a NO chemical donor), CO-releasing molecule 2 (a CO chemical donor), or control. NO and CO stimulated dynamin-2 activation in VSMCs. NO and CO promoted time- and dose-dependent endocytosis of TβR1. By decreasing TβR1 surface expression through this dynamin-2-dependent process, NO and CO diminished the effects of TGF-β on VSMCs. These findings help explain an important mechanism by which NO and CO signal in the vasculature by decreasing surface expression of TβR1 and the cellular response to TGF-β.

Nitric oxide: an effective weapon of the plant or the pathogen?

An explosion of research in plant nitric oxide (NO) biology during the last two decades has revealed that NO is a key signal involved in plant development, abiotic stress responses and plant immunity. During the course of evolutionary changes, microorganisms parasitizing plants have developed highly effective offensive strategies, in which NO also seems to be implicated. NO production has been demonstrated in several plant pathogens, including fungi, but the origin of NO seems to be as puzzling as in plants. So far, published studies have been spread over multiple species of pathogenic microorganisms in various developmental stages; however, the data clearly indicate that pathogen-derived NO is an important regulatory molecule involved not only in developmental processes, but also in pathogen virulence and its survival in the host. This review also focuses on the search for potential mechanisms by which pathogens convert NO messages into a physiological response or detoxify both endo- and exogenous NO. Finally, taking into account the data available from model bacteria and yeast, a basic draft for the mode of NO action in phytopathogenic microorganisms is proposed.

Diverse post-translational modifications of the pannexin family of channel-forming proteins

The pannexin family of channel-forming proteins is composed of 3 distinct but related members called Panx1, Panx2, and Panx3. Pannexins have been implicated in many physiological processes as well as pathological conditions, primarily through their function as ATP release channels. However, it is currently unclear if all pannexins are subject to similar or different post-translational modifications as most studies have focused primarily on Panx1. Using in vitro biochemical assays performed on ectopically expressed pannexins in HEK-293T cells, we confirmed that all 3 pannexins are N-glycosylated to different degrees, but they are not modified by sialylation or O-linked glycosylation in a manner that changes their apparent molecular weight. Using cell-free caspase assays, we also discovered that similar to Panx1, the C-terminus of Panx2 is a substrate for caspase cleavage. Panx3, on the other hand, is not subject to caspase digestion but an in vitro biotin switch assay revealed that it was S-nitrosylated by nitric oxide donors. Taken together, our findings uncover novel and diverse pannexin post-translational modifications suggesting that they may be differentially regulated for distinct or overlapping cellular and physiological functions.

Protective role of S-nitrosoglutathione (GSNO) against cognitive impairment in rat model of chronic cerebral hypoperfusion

Chronic cerebral hypoperfusion (CCH), featuring in most of the Alzheimer's disease spectrum, plays a detrimental role in brain amyloid-β (Aβ) homeostasis, cerebrovascular morbidity, and cognitive decline; therefore, early management of cerebrovascular pathology is considered to be important for intervention in the impending cognitive decline. S-nitrosoglutathione (GSNO) is an endogenous nitric oxide carrier modulating endothelial function, inflammation, and neurotransmission. Therefore, the effect of GSNO treatment on CCH-associated neurocognitive pathologies was determined in vivo by using rats with permanent bilateral common carotid artery occlusion (BCCAO), a rat model of chronic cerebral hypoperfusion. We observed that rats subjected to permanent BCCAO showed a significant decrease in learning/memory performance and increases in brain levels of Aβ and vascular inflammatory markers. GSNO treatment (50 μg/kg/day for 2 months) significantly improved learning and memory performance of BCCAO rats and reduced the Aβ levels and ICAM-1/VCAM-1 expression in the brain. Further, in in vitro cell culture studies, GSNO treatment also decreased the cytokine-induced proinflammatory responses, such as activations of NFκB and STAT3 and expression of ICAM-1 and VCAM-1 in endothelial cells. In addition, GSNO treatment increased the endothelial and microglial Aβ uptake. Additionally, GSNO treatment inhibited the β-secretase activity in primary rat neuron cell culture, thus reducing secretion of Aβ, suggesting GSNO mediated mechanisms in anti-inflammatory and anti-amyloidogenic activities. Taken together, these data document that systemic GSNO treatment is beneficial for improvement of cognitive decline under the conditions of chronic cerebral hypoperfusion and suggests a potential therapeutic use of GSNO for cerebral hypoperfusion associated mild cognitive impairment in Alzheimer's disease.

Maintenance of androgen receptor inactivation by S-nitrosylation

Antiandrogens target ligand-binding domain of androgen receptor (AR) and are used as first-line therapeutics to treat patients diagnosed with locally advanced and metastatic prostate cancer. Although initially beneficial as judged with actual tumor mass shrinkage, this therapy invariably fails and the cancer reappears as castration-resistant disease. Here, we report that increased intracellular nitric oxide (NO) levels lead to growth inhibition of both androgen-dependent and castration-resistant prostate tumors through a mechanism that involves AR function inactivation by S-nitrosylation of a single C601 residue present in the DNA-binding domain. AR S-nitrosylation does not impact its subcellular distribution but attenuates its ability to bind AR-responsive elements in promoter region of target genes. Mechanistically, AR is transnitrosylated by its partner HSP90 protein. Ubiquitous small-molecule NO donors promote the AR S-nitrosylation and inhibit growth of castration-resistant prostate tumors. These findings reveal a new mechanism of regulating AR function and suggest that sequential targeting of distinct domains of AR may extend therapeutic efficacy for patients with advanced prostate cancer.

S-nitrosylation of dynamin-related protein 1 mediates mutant huntingtin-induced mitochondrial fragmentation and neuronal injury in Huntington's disease

AIMS

Dynamin-related protein1 (Drp1) is a large GTPase that mediates mitochondrial fission. We recently reported in Alzheimer's disease (AD) that S-nitrosylation of Drp1 (forming S-nitroso [SNO]-Drp1) results in GTPase hyperactivity and mitochondrial fragmentation, thus impairing bioenergetics and inducing synaptic damage and neuronal loss. Here, since aberrant mitochondrial dynamics are also key features of Huntington's disease (HD), we investigated whether formation of SNO-Drp1 contributes to the pathogenesis of HD in cell-based and animal models.

RESULTS

We found that expression of mutant huntingtin (mutHTT) protein in primary cultured neurons triggers significant production of nitric oxide (NO). Consistent with this result, increased levels of SNO-Drp1 were found in the striatum of a transgenic mouse model of HD as well as in human postmortem brains from HD patients. Using specific fluorescence markers, we found that formation of SNO-Drp1 induced excessive mitochondrial fragmentation followed by loss of dendritic spines, signifying synaptic damage. These neurotoxic events were significantly abrogated after transfection with non-nitrosylatable mutant Drp1(C644A), or by the blocking of NO production using an nitric oxide synthase inhibitor. These findings suggest that SNO-Drp1 is a key mediator of mutHTT toxicity, and, thus, may represent a novel drug target for HD.

INNOVATION AND CONCLUSION

Our findings indicate that aberrant S-nitrosylation of Drp1 is a prominent pathological feature of neurodegenerative diseases such as AD and HD. Moreover, the SNO-Drp1 signaling pathway links mutHTT neurotoxicity to a malfunction in mitochondrial dynamics, resulting in neuronal synaptic damage in HD.