Regulation of HIF-1alpha stability through S-nitrosylation

Tumor Hypoxia as a Barrier in Cancer Therapy: Why Levels Matter

Simple Summary

Hypoxia is a common feature of solid tumors and associated with poor outcome in most cancer types and treatment modalities, including radiotherapy, chemotherapy, surgery and, most likely, immunotherapy. Emerging strategies, such as proton therapy and combination therapies with radiation and hypoxia targeted drugs, provide new opportunities to overcome the hypoxia barrier and improve therapeutic outcome. Hypoxia is heterogeneously distributed both between and within tumors and shows large variations across patients not only in prevalence, but importantly, also in level. To best exploit the emerging strategies, a better understanding of how individual hypoxia levels from mild to severe affect tumor biology is vital. Here, we discuss our current knowledge on this topic and how we should proceed to gain more insight into the field.

Abstract

Hypoxia arises in tumor regions with insufficient oxygen supply and is a major barrier in cancer treatment. The distribution of hypoxia levels is highly heterogeneous, ranging from mild, almost non-hypoxic, to severe and anoxic levels. The individual hypoxia levels induce a variety of biological responses that impair the treatment effect. A stronger focus on hypoxia levels rather than the absence or presence of hypoxia in our investigations will help development of improved strategies to treat patients with hypoxic tumors. Current knowledge on how hypoxia levels are sensed by cancer cells and mediate cellular responses that promote treatment resistance is comprehensive. Recently, it has become evident that hypoxia also has an important, more unexplored role in the interaction between cancer cells, stroma and immune cells, influencing the composition and structure of the tumor microenvironment. Establishment of how such processes depend on the hypoxia level requires more advanced tumor models and methodology. In this review, we describe promising model systems and tools for investigations of hypoxia levels in tumors. We further present current knowledge and emerging research on cellular responses to individual levels, and discuss their impact in novel therapeutic approaches to overcome the hypoxia barrier.

The Role of Hypoxia-Inducible Factor Post-Translational Modifications in Regulating Its Localisation, Stability, and Activity

The hypoxia signalling pathway enables adaptation of cells to decreased oxygen availability. When oxygen becomes limiting, the central transcription factors of the pathway, hypoxia-inducible factors (HIFs), are stabilised and activated to induce the expression of hypoxia-regulated genes, thereby maintaining cellular homeostasis. Whilst hydroxylation has been thoroughly described as the major and canonical modification of the HIF-α subunits, regulating both HIF stability and activity, a range of other post-translational modifications decorating the entire protein play also a crucial role in altering HIF localisation, stability, and activity. These modifications, their conservation throughout evolution, and their effects on HIF-dependent signalling are discussed in this review.

Role of NO and S-nitrosylation in the Expression of Endothelial Adhesion Proteins That Regulate Leukocyte and Tumor Cell Adhesion

Leukocyte recruitment is one of the most important cellular responses to tissue damage. Leukocyte extravasation is exquisitely regulated by mechanisms of selective leukocyte-endothelium recognition through adhesion proteins in the endothelial cell surface that recognize specific integrins in the activated leukocytes. A similar mechanism is used by tumor cells during metastasis to extravasate and form a secondary tumor. Nitric oxide (NO) has been classically described as an anti-inflammatory molecule that inhibits leukocyte adhesion. However, the evidence available shows also a positive role of NO in leukocyte adhesion. These apparent discrepancies might be explained by the different NO concentrations reached during the inflammatory response, which are highly modulated by the expression of different nitric oxide synthases, along the inflammatory response and by changes in their subcellular locations.

Autophagy and Redox Homeostasis in Parkinson's: A Crucial Balancing Act

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated primarily from endogenous biochemical reactions in mitochondria, endoplasmic reticulum (ER), and peroxisomes. Typically, ROS/RNS correlate with oxidative damage and cell death; however, free radicals are also crucial for normal cellular functions, including supporting neuronal homeostasis. ROS/RNS levels influence and are influenced by antioxidant systems, including the catabolic autophagy pathways. Autophagy is an intracellular lysosomal degradation process by which invasive, damaged, or redundant cytoplasmic components, including microorganisms and defunct organelles, are removed to maintain cellular homeostasis. This process is particularly important in neurons that are required to cope with prolonged and sustained operational stress. Consequently, autophagy is a primary line of protection against neurodegenerative diseases. Parkinson's is caused by the loss of midbrain dopaminergic neurons (mDANs), resulting in progressive disruption of the nigrostriatal pathway, leading to motor, behavioural, and cognitive impairments. Mitochondrial dysfunction, with associated increases in oxidative stress, and declining proteostasis control, are key contributors during mDAN demise in Parkinson's. In this review, we analyse the crosstalk between autophagy and redoxtasis, including the molecular mechanisms involved and the detrimental effect of an imbalance in the pathogenesis of Parkinson's.

Coenzyme Q biosynthesis inhibition induces HIF-1α stabilization and metabolic switch toward glycolysis

Coenzyme Q₁₀ (CoQ, ubiquinone) is a redox-active lipid endogenously synthesized by the cells. The final stage of CoQ biosynthesis is performed at the mitochondrial level by the 'complex Q', where coq2 is responsible for the prenylation of the benzoquinone ring of the molecule. We report that the competitive coq2 inhibitor 4-nitrobenzoate (4-NB) decreased the cellular CoQ content and caused severe impairment of mitochondrial function in the T67 human glioma cell line. In parallel with the reduction in CoQ biosynthesis, the cholesterol level increased, leading to significant perturbation of the plasma membrane physicochemical properties. We show that 4-NB treatment did not significantly affect the cell viability, because of an adaptive metabolic rewiring toward glycolysis. Hypoxia-inducible factor 1α (HIF-1α) stabilization was detected in 4-NB-treated cells, possibly due to the contribution of both reduction in intracellular oxygen tension and ROS overproduction. Exogenous CoQ supplementation partially recovered cholesterol content, HIF-1α degradation, and ROS production, whereas only weakly improved the bioenergetic impairment induced by the CoQ depletion. Our data provide new insights on the effect of CoQ depletion and contribute to shed light on the pathogenic mechanisms of ubiquinone deficiency syndrome.

Caveolin-1-Mediated Tumor Suppression Is Linked to Reduced HIF1α S-Nitrosylation and Transcriptional Activity in Hypoxia

Caveolin-1 (CAV1) is a well-established nitric oxide synthase inhibitor, whose function as a tumor suppressor is favored by, but not entirely dependent on, the presence of E-cadherin. Tumors are frequently hypoxic and the activation of the hypoxia-inducible factor-1α (HIF1α) promotes tumor growth. HIF1α is regulated by several post-translational modifications, including S-nitrosylation. Here, we evaluate the mechanisms underlying tumor suppression by CAV1 in cancer cells lacking E-cadherin in hypoxia. Our main findings are that CAV1 reduced HIF activity and Vascular Endothelial Growth Factor expression in vitro and in vivo. This effect was neither due to reduced HIF1α protein stability or reduced nuclear translocation. Instead, HIF1α S-nitrosylation observed in hypoxia was diminished by the presence of CAV1, and nitric oxide synthase (NOS) inhibition by Nω-Nitro-L-arginine methyl ester hydrochloride (L-NAME) reduced HIF1α transcriptional activity in cells to the same extent as observed upon CAV1 expression. Additionally, arginase inhibition by (S)-(2-Boronoethyl)-L-cysteine (BEC) partially rescued cells from the CAV1-mediated suppression of HIF1α transcriptional activity. In vivo, CAV1-mediated tumor suppression was dependent on NOS activity. In summary, CAV1-dependent tumor suppression in the absence of E-cadherin is linked to reduced HIF1α transcriptional activity via diminished NOS-mediated HIF1α S-nitrosylation.

Redox basis of exercise physiology

Redox reactions control fundamental processes of human biology. Therefore, it is safe to assume that the responses and adaptations to exercise are, at least in part, mediated by redox reactions. In this review, we are trying to show that redox reactions are the basis of exercise physiology by outlining the redox signaling pathways that regulate four characteristic acute exercise-induced responses (muscle contractile function, glucose uptake, blood flow and bioenergetics) and four chronic exercise-induced adaptations (mitochondrial biogenesis, muscle hypertrophy, angiogenesis and redox homeostasis). Based on our analysis, we argue that redox regulation should be acknowledged as central to exercise physiology.

Nitric oxide regulates ganoderic acid biosynthesis by the S-nitrosylation of aconitase under heat stress in Ganoderma lucidum

Nitric oxide (NO) is an important signalling molecule in stress response of organisms. We previously reported that NO decreases heat stress (HS)-induced ganoderic acid (GA) accumulation in Ganoderma lucidum. To explore the mechanisms by which NO modulates GA biosynthesis under HS, the effect of NO on the reactive oxygen species (ROS) content was examined. The results showed that NO decreased the production of mitochondrial ROS (mitROS) by 60% under HS. Further research revealed that NO reduced the mitROS content by inhibiting aconitase (Acon) activity. The GA content in Acon-silenced (Aconi) strains treated with NO donor did not differ significantly from that in untreated Aconi strains. To study the mechanism by which Acon activity is inhibited, the S-nitrosylation level of Acon was determined. Biotin-switch technology and mass spectrometry analysis were used to show that Acon is S-nitrosylated at the Cys-594 amino acid residue. Substitution of Cys-594 with a Ser, which cannot be S-nitrosylated, abolished the responsiveness of Acon to the NO-induced reduction in its enzymatic activity. These findings demonstrate that NO inhibits Acon activity through S-nitrosylation at Cys-594. In summary, these findings describe mechanism by which NO regulates GA biosynthesis via S-nitrosylation of Acon under HS condition in G. lucidum.

The Double-Faced Role of Nitric Oxide and Reactive Oxygen Species in Solid Tumors

Disturbed redox homeostasis represents a hallmark of cancer phenotypes, affecting cellular metabolism and redox signaling. Since reactive oxygen and nitrogen species (ROS/RNS) are involved in regulation of proliferation and apoptosis, they may play a double-faced role in cancer, entailing protumorigenic and tumor-suppressing effects in early and later stages, respectively. In addition, ROS and RNS impact the activity and communication of all tumor constituents, mediating their reprogramming from anti- to protumorigenic phenotypes, and vice versa. An important role in this dichotomic action is played by the variable amounts of O₂ in the tumor microenvironment, which dictates the ultimate outcome of the influence of ROS/RNS on carcinogenesis. Moreover, ROS/RNS levels remarkably influence the cancer response to therapy. The relevance of ROS/RNS signaling in solid tumors is witnessed by the emergence of novel targeted treatments of solid tumors with compounds that target ROS/RNS action and production, such as tyrosine kinase inhibitors and monoclonal antibodies, which might contribute to the complexity of redox regulation in cancer. Prospectively, the dual role of ROS/RNS in the different stages of tumorigenesis through different impact on oxidation and nitrosylation may also allow development of tailored diagnostic and therapeutic approaches.

When S-Nitrosylation Gets to Mitochondria: From Signaling to Age-Related Diseases

Significance: Cysteines have an essential role in redox signaling, transforming an oxidant signal into a biological response. Among reversible cysteine post-translational modifications, S-nitrosylation acts as a redox-switch in several pathophysiological states, such as ischemia/reperfusion, synaptic transmission, cancer, and muscular dysfunctions. Recent Advances: Growing pieces of in vitro and in vivo evidence argue for S-nitrosylation being deeply involved in development and aging, and playing a role in the onset of different pathological states. New findings suggest it being an enzymatically regulated cellular process, with deep impact on mitochondrial structure and function, and in cellular metabolism. In light of this, the recent discovery of the denitrosylase S-nitrosoCoA (coenzyme A) reductase takes on even greater importance and opens new perspectives on S-nitrosylation as a general mechanism of cellular homeostasis. Critical Issues: Based on these recent findings, we aim at summarizing and elaborating on the established and emerging crucial roles of S-nitrosylation in mitochondrial metabolism and mitophagy, and provide an overview of the pathophysiological effects induced by its deregulation. Future Directions: The identification of new S-nitrosylation targets, and the comprehension of the mechanisms through which S-nitrosylation modulates specific classes of proteins, that is, those impinging on diverse mitochondrial functions, may help to better understand the pathophysiology of aging, and propose lines of intervention to slow down or extend the onset of aging-related diseases.

Redox Regulation via Glutaredoxin-1 and Protein S-Glutathionylation

Significance: Over the past several years, oxidative post-translational modifications of protein cysteines have been recognized for their critical roles in physiology and pathophysiology. Cells have harnessed thiol modifications involving both oxidative and reductive steps for signaling and protein processing. One of these stages requires oxidation of cysteine to sulfenic acid, followed by two reduction reactions. First, glutathione (reduced glutathione [GSH]) forms a S-glutathionylated protein, and second, enzymatic or chemical reduction removes the modification. Under physiological conditions, these steps confer redox signaling and protect cysteines from irreversible oxidation. However, oxidative stress can overwhelm protein S-glutathionylation and irreversibly modify cysteine residues, disrupting redox signaling. Critical Issues: Glutaredoxins mainly catalyze the removal of protein-bound GSH and help maintain protein thiols in a highly reduced state without exerting direct antioxidant properties. Conversely, glutathione S-transferase (GST), peroxiredoxins, and occasionally glutaredoxins can also catalyze protein S-glutathionylation, thus promoting a dynamic redox environment. Recent Advances: The latest studies of glutaredoxin-1 (Glrx) transgenic or knockout mice demonstrate important distinct roles of Glrx in a variety of pathologies. Endogenous Glrx is essential to maintain normal hepatic lipid homeostasis and prevent fatty liver disease. Further, in vivo deletion of Glrx protects lungs from inflammation and bacterial pneumonia-induced damage, attenuates angiotensin II-induced cardiovascular hypertrophy, and improves ischemic limb vascularization. Meanwhile, exogenous Glrx administration can reverse pathological lung fibrosis. Future Directions: Although S-glutathionylation modifies many proteins, these studies suggest that S-glutathionylation and Glrx regulate specific pathways in vivo, and they implicate Glrx as a potential novel therapeutic target to treat diverse disease conditions. Antioxid. Redox Signal. 32, 677-700.

Hypoxia Inducible Factor-1α in Osteochondral Tissue Engineering

Damage to osteochondral (OC) tissues can lead to pain, loss of motility, and progress to osteoarthritis. Tissue engineering approaches offer the possibility of replacing damaged tissues and restoring joint function; however, replicating the spatial and functional heterogeneity of native OC tissue remains a pressing challenge. Chondrocytes in healthy cartilage exist in relatively low-oxygen conditions, while osteoblasts in the underlying bone experience higher oxygen pressures. Such oxygen gradients also exist in the limb bud, where they influence OC tissue development. The cellular response to these spatial variations in oxygen pressure, which is mediated by the hypoxia inducible factor (HIF) pathway, plays a central role in regulating osteo- and chondrogenesis by directing progenitor cell differentiation and promoting and maintaining appropriate extracellular matrix production. Understanding the role of the HIF pathway in OC tissue development may enable new approaches to engineer OC tissue. In this review, we discuss strategies to spatially and temporarily regulate the HIF pathway in progenitor cells to create functional OC tissue for regenerative therapies. Impact statement Strategies to engineer osteochondral (OC) tissue are limited by the complex and varying microenvironmental conditions in native bone and cartilage. Indeed, native cartilage experiences low-oxygen conditions, while the underlying bone is relatively normoxic. The cellular response to these low-oxygen conditions, which is mediated through the hypoxia inducible factor (HIF) pathway, is known to promote and maintain the chondrocyte phenotype. By using tissue engineering scaffolds to spatially and temporally harness the HIF pathway, it may be possible to improve OC tissue engineering strategies for the regeneration of damaged cartilage and its underlying subchondral bone.

Basic Biology of Hypoxic Responses Mediated by the Transcription Factor HIFs and its Implication for Medicine

Oxygen (O₂) is essential for human life. Molecular oxygen is vital for the production of adenosine triphosphate (ATP) in human cells. O₂ deficiency leads to a reduction in the energy levels that are required to maintain biological functions. O₂ acts as the final acceptor of electrons during oxidative phosphorylation, a series of ATP synthesis reactions that occur in conjunction with the electron transport system in mitochondria. Persistent O₂ deficiency may cause death due to malfunctioning biological processes. The above account summarizes the classic view of oxygen. However, this classic view has been reviewed over the last two decades. Although O₂ is essential for life, higher organisms such as mammals are unable to biosynthesize molecular O₂ in the body. Because the multiple organs of higher organisms are constantly exposed to the risk of “O₂ deficiency,” living organisms have evolved elaborate strategies to respond to hypoxia. In this review, I will describe the system that governs oxygen homeostasis in the living body from the point-of-view of the transcription factor hypoxia-inducible factor (HIF).

NER-factor DDB2 regulates HIF1α and hypoxia-response genes in HNSCC

Cancers in the oral/head & neck region (HNSCC) are aggressive due to high incidence of recurrence and distant metastasis. One prominent feature of aggressive HNSCC is the presence of severely hypoxic regions in tumors and activation of hypoxia-inducible factors (HIFs). In this study, we report that the XPE gene product DDB2 (damaged DNA binding protein 2), a nucleotide excision repair protein, is upregulated by hypoxia. Moreover, DDB2 inhibits HIF1α in HNSCC cells. It inhibits HIF1α in both normoxia and hypoxia by reducing mRNA expression. Knockdown of DDB2 enhances the expression of angiogenic markers and promotes tumor growth in a xenograft model. We show that DDB2 binds to an upstream promoter element in the HIF1Α gene and promotes histone H3K9 trimethylation around the binding site by recruiting Suv39h1. Also, we provide evidence that DDB2 has a significant suppressive effect on expression of the endogenous markers of hypoxia that are also prognostic indicators in HNSCC. Together, these results describe a new mechanism of hypoxia regulation that opposes expression of HIF1Α mRNA and the hypoxia-response genes.

Redox homeostasis, oxidative stress and mitophagy

Autophagy is a ubiquitous homeostatic mechanism for the degradation or turnover of cellular components. Degradation of mitochondria via autophagy (mitophagy) is involved in a number of physiological processes including cellular homeostasis, differentiation and aging. Upon stress or injury, mitophagy prevents the accumulation of damaged mitochondria and the increased steady state levels of reactive oxygen species leading to oxidative stress and cell death. A number of human diseases, particularly neurodegenerative disorders, have been linked to the dysregulation of mitophagy. In this mini-review, we aimed to review the molecular mechanisms involved in the regulation of mitophagy and their relationship with redox signaling and oxidative stress.

Exercise induces tissue hypoxia and HIF-1α redistribution in the small intestine

BACKGROUND

Exercise induces blood flow redistribution among tissues, leading to splanchnic hypoperfusion. Intestinal epithelial cells are positioned between the anaerobic lumen and the highly metabolic lamina propria with an oxygen gradient. Hypoxia-inducible factor (HIF)-1α is pivotal in the transcriptional response to the oxygen flux.

METHODS

In this study, the pimonidazole hydrochloride staining was applied to observe the tissue hypoxia in different organs, which might be affected by the blood flow redistribution. The HIF-1α luciferase reporter ROSA26 oxygen-dependent degradation domain (ODD)-Luc/⁺ mouse model (ODD domain-Luc; female, n = 3-6/group) was used to detect the HIF-1α expression in the intestine. We used 3 swimming models: moderate exercise for 30 min, heavy-intensity exercise bearing 5% bodyweight for 1.5 h, and long-time exercise for 3 h.

RESULTS

We found that 1 session of swimming at different intensities could induce tissue hypoxia redistribution in the small intestine, colon, liver and kidney, but not in the spleen, heart, and skeletal muscle. Our data showed that exercise exacerbated the extent of physiological hypoxia in the small intestine. Next, using ODD-Luc mice, we found that moderate exercise increased the in vivo HIF-1α level in the small intestine. The post-exercise HIF-1α level was gradually decreased in a time-dependent manner. Interestingly, the redistribution of tissue hypoxia and the increase of HIF-1α expression were not related to the exercise intensity and duration.

CONCLUSION

This study provided evidence that the small intestine is the primary target organ for exercise-induced tissue hypoxia and HIF-1α redistribution, suggesting that HIF-1α may be a potential target for the regulation of gastrointestinal functions after exercise.

Comparative Approach to the Temporo-Spatial Organization of the Tumor Microenvironment

The complex ecosystem in which tumor cells reside and interact, termed the tumor microenvironment (TME), encompasses all cells and components associated with a neoplasm that are not transformed cells. Interactions between tumor cells and the TME are complex and fluid, with each facet coercing the other, largely, into promoting tumor progression. While the TME in humans is relatively well-described, a compilation and comparison of the TME in our canine counterparts has not yet been described. As is the case in humans, dog tumors exhibit greater heterogeneity than what is appreciated in laboratory animal models, although the current level of knowledge on similarities and differences in the TME between dogs and humans, and the practical implications of that information, require further investigation. This review summarizes some of the complexities of the human and mouse TME and interjects with what is known in the dog, relaying the information in the context of the temporo-spatial organization of the TME. To the authors' knowledge, the development of the TME over space and time has not been widely discussed, and a comprehensive review of the canine TME has not been done. The specific topics covered in this review include cellular invasion and interactions within the TME, metabolic derangements in the TME and vascular invasion, and the involvement of the TME in tumor spread and metastasis.

Prioritizing natural-selection signals from the deep-sequencing genomic data suggests multi-variant adaptation in Tibetan highlanders

Human genetic adaptation to high altitudes (>2500 m) has been extensively studied over the last few years, but few functional adaptive genetic variants have been identified, largely owing to the lack of deep-genome sequencing data available to previous studies. Here, we build a list of putative adaptive variants, including 63 missense, 7 loss-of-function, 1,298 evolutionarily conserved variants and 509 expression quantitative traits loci. Notably, the top signal of selection is located in TMEM247, a transmembrane protein-coding gene. The Tibetan version of TMEM247 harbors one high-frequency (76.3%) missense variant, rs116983452 (c.248C > T; p.Ala83Val), with the T allele derived from archaic ancestry and carried by >94% of Tibetans but absent or in low frequencies (<3%) in non-Tibetan populations. The rs116983452-T is strongly and positively correlated with altitude and significantly associated with reduced hemoglobin concentration (p = 5.78 × 10-5), red blood cell count (p = 5.72 × 10-7) and hematocrit (p = 2.57 × 10-6). In particular, TMEM247-rs116983452 shows greater effect size and better predicts the phenotypic outcome than any EPAS1 variants in association with adaptive traits in Tibetans. Modeling the interaction between TMEM247-rs116983452 and EPAS1 variants indicates weak but statistically significant epistatic effects. Our results support that multiple variants may jointly deliver the fitness of the Tibetans on the plateau, where a complex model is needed to elucidate the adaptive evolution mechanism.

The Yin-Yang Regulation of Reactive Oxygen Species and MicroRNAs in Cancer

Reactive oxygen species (ROS) are highly reactive oxygen-containing chemical species formed as a by-product of normal aerobic respiration and also from a number of other cellular enzymatic reactions. ROS function as key mediators of cellular signaling pathways involved in proliferation, survival, apoptosis, and immune response. However, elevated and sustained ROS production promotes tumor initiation by inducing DNA damage or mutation and activates oncogenic signaling pathways to promote cancer progression. Recent studies have shown that ROS can facilitate carcinogenesis by controlling microRNA (miRNA) expression through regulating miRNA biogenesis, transcription, and epigenetic modifications. Likewise, miRNAs have been shown to control cellular ROS homeostasis by regulating the expression of proteins involved in ROS production and elimination. In this review, we summarized the significance of ROS in cancer initiation, progression, and the regulatory crosstalk between ROS and miRNAs in cancer.

The Antioxidant and Antiproliferative Activities of 1,2,3-Triazolyl-L-Ascorbic Acid Derivatives

The novel 4-substituted 1,2,3-triazole L-ascorbic acid (L-ASA) conjugates with hydroxyethylene spacer as well as their conformationally restricted 4,5-unsaturated analogues were synthesized as potential antioxidant and antiproliferative agents. An evaluation of the antioxidant activity of novel compounds showed that the majority of the 4,5-unsaturated L-ASA derivatives showed a better antioxidant activity compared to their saturated counterparts. m-Hydroxyphenyl (7j), p-pentylphenyl (7k) and 2-hydroxyethyl (7q) substituted 4,5-unsaturated 1,2,3-triazole L-ASA derivatives exhibited very efficient and rapid (within 5 min) 2,2-diphenyl-1-picrylhydrazyl (DPPH^•) radical scavenging activity (7j, 7k: IC₅₀ = 0.06 mM; 7q: IC₅₀ = 0.07 mM). In vitro scavenging activity data were supported by in silico quantum-chemical modelling. Thermodynamic parameters for hydrogen-atom transfer and electron-transfer radical scavenging pathways of anions deprotonated at C2-OH or C3-OH groups of L-ASA fragments were calculated. The structure activity analysis (SAR) through principal component analysis indicated radical scavenging activity by the participation of OH group with favorable reaction parameters: the C3-OH group of saturated C4-C5(OH) derivatives and the C2-OH group of their unsaturated C4=C5 analogues. The antiproliferative evaluation showed that p-bromophenyl (4e: IC₅₀ = 6.72 μM) and p-pentylphenyl-substituted 1,2,3-triazole L-ASA conjugate (4k: IC₅₀ = 26.91 μM) had a selective cytotoxic effect on breast adenocarcinoma MCF-7 cells. Moreover, compound 4e did not inhibit the growth of foreskin fibroblasts (IC₅₀ > 100 μM). In MCF-7 cells treated with 4e, a significant increase of hydroxylated hypoxia-inducible transcription factor 1 alpha (HIF-1α) expression and decreased expression of nitric oxide synthase 2 (NOS2) were observed, suggesting the involvement of 4e in the HIF-1α signaling pathway for its strong growth-inhibition effect on MCF-7 cells.

Nitric oxide and its derivatives in the cancer battlefield

Elevated levels of reactive nitrogen species, alteration in redox balance and deregulated redox signaling are common hallmarks of cancer progression and chemoresistance. However, depending on the cellular context, distinct reactive nitrogen species are also hypothesized to mediate cytotoxic activity and are thus used in anticancer therapies. We present here the dual face of nitric oxide and its derivatives in cancer biology. Main derivatives of nitric oxide, such as nitrogen dioxide and peroxynitrite cause cell death by inducing protein and lipid peroxidation and/or DNA damage. Moreover, they control the activity of important protein players within the pro- and anti-apoptotic signaling pathways. Thus, the control of intracellular reactive nitrogen species may become a sophisticated tool in anticancer strategies.

HIF-1α as a central mediator of cellular resistance to intracellular pathogens

Hypoxia-inducible transcription factor-1α (HIF-1α) was originally identified as a master regulator of cellular responses to hypoxia. More recently, HIF-1α has emerged as a critical regulator of immune cell function that couples shifts in cellular metabolism to cell type-specific transcriptional outputs. Activation of macrophages with inflammatory stimuli leads to induction of the metabolic program aerobic glycolysis and to HIF-1α stabilization, which reinforce one another in a positive feedback loop that helps drive macrophage activation. This activation of aerobic glycolysis and HIF-1α is important both for production of inflammatory cytokines, such as IL-1β, and for cell intrinsic control of infection. Here, we review the importance of HIF-1α for control of bacterial, fungal, and protozoan intracellular pathogens, highlighting recent findings that reveal mechanisms by which HIF-1α is activated during infection and how HIF-1α coordinates antimicrobial responses of macrophages.

Sulfur metabolism and its contribution to malignancy

Metabolic dysregulation is an appreciated hallmark of cancer and a target for therapeutic intervention. Cellular metabolism involves a series of oxidation/reduction (redox) reactions that yield the energy and biomass required for tumor growth. Cells require diverse molecular species with constituent sulfur atoms to facilitate these processes. For humans, this sulfur is derived from the dietary consumption of the proteinogenic amino acids cysteine and methionine, as only lower organisms (e.g., bacteria, fungi, and plants) can synthesize them de novo. In addition to providing the sulfur required to sustain redox chemistry, the metabolism of these sulfur-containing amino acids yield intermediate metabolites that constitute the cellular antioxidant system, mediate inter- and intracellular signaling, and facilitate the epigenetic regulation of gene expression, all of which contribute to tumorigenesis.

Myalgic encephalomyelitis or chronic fatigue syndrome: how could the illness develop?

A model of the development and progression of chronic fatigue syndrome (myalgic encephalomyelitis), the aetiology of which is currently unknown, is put forward, starting with a consideration of the post-infection role of damage-associated molecular patterns and the development of chronic inflammatory, oxidative and nitrosative stress in genetically predisposed individuals. The consequences are detailed, including the role of increased intestinal permeability and the translocation of commensal antigens into the circulation, and the development of dysautonomia, neuroinflammation, and neurocognitive and neuroimaging abnormalities. Increasing levels of such stress and the switch to immune and metabolic downregulation are detailed next in relation to the advent of hypernitrosylation, impaired mitochondrial performance, immune suppression, cellular hibernation, endotoxin tolerance and sirtuin 1 activation. The role of chronic stress and the development of endotoxin tolerance via indoleamine 2,3-dioxygenase upregulation and the characteristics of neutrophils, monocytes, macrophages and T cells, including regulatory T cells, in endotoxin tolerance are detailed next. Finally, it is shown how the immune and metabolic abnormalities of chronic fatigue syndrome can be explained by endotoxin tolerance, thus completing the model.

mRNA-to-protein translation in hypoxia

Cells respond to hypoxia by shifting cellular processes from general housekeeping functions to activating specialized hypoxia-response pathways. Oxygen plays an important role in generating ATP to maintain a productive rate of protein synthesis in normoxia. In hypoxia, the rate of the canonical protein synthesis pathway is significantly slowed and impaired due to limited ATP availability, necessitating an alternative mechanism to mediate protein synthesis and facilitate adaptation. Hypoxia adaptation is largely mediated by hypoxia-inducible factors (HIFs). While HIFs are well known for their transcriptional functions, they also play imperative roles in translation to mediate hypoxic protein synthesis. Such adaptations to hypoxia are often hyperactive in solid tumors, contributing to the expression of cancer hallmarks, including treatment resistance. The current literature on protein synthesis in hypoxia is reviewed here, inclusive of hypoxia-specific mRNA selection to translation termination. Current HIF targeting therapies are also discussed as are the opportunities involved with targeting hypoxia specific protein synthesis pathways.

S-nitrosylation and its role in breast cancer angiogenesis and metastasis

S-nitrosylation, the modification by nitric oxide of free sulfhydryl groups in cysteines, has become an important regulatory mechanism in carcinogenesis and metastasis. S-nitrosylation of targets in tumor cells contributes to metastasis regulating epithelial to mesenchymal transition, migration and invasion. In the tumor environment, the role of S-nitrosylation in endothelium has not been addressed; however, the evidence points out that S-nitrosylation of endothelial proteins may regulate angiogenesis, adhesion of tumor cells to the endothelium, intra and extravasation of tumor cells and contribute to metastasis.

Hypoxia-Inducible Factors and the Regulation of Lipid Metabolism

Oxygen deprivation or hypoxia characterizes a number of serious pathological conditions and elicits a number of adaptive changes that are mainly mediated at the transcriptional level by the family of hypoxia-inducible factors (HIFs). The HIF target gene repertoire includes genes responsible for the regulation of metabolism, oxygen delivery and cell survival. Although the involvement of HIFs in the regulation of carbohydrate metabolism and the switch to anaerobic glycolysis under hypoxia is well established, their role in the control of lipid anabolism and catabolism remains still relatively obscure. Recent evidence indicates that many aspects of lipid metabolism are modified during hypoxia or in tumor cells in a HIF-dependent manner, contributing significantly to the pathogenesis and/or progression of cancer and metabolic disorders. However, direct transcriptional regulation by HIFs has been only demonstrated in relatively few cases, leaving open the exact and isoform-specific mechanisms that underlie HIF-dependency. This review summarizes the evidence for both direct and indirect roles of HIFs in the regulation of genes involved in lipid metabolism as well as the involvement of HIFs in various diseases as demonstrated by studies with transgenic animal models.

Identification of S-nitrosylation sites based on multiple features combination

Protein S-nitrosylation (SNO) is a typical reversible, redox-dependent and post-translational modification that involves covalent modification of cysteine residues with nitric oxide (NO) for the thiol group. Numerous experiments have shown that SNO plays a major role in cell function and pathophysiology. In order to rapidly analysis the big sets of data, the computing methods for identifying the SNO sites are being considered as necessary auxiliary tools. In this study, multiple features including Parallel correlation pseudo amino acid composition (PC-PseAAC), Basic kmer1 (kmer1), Basic kmer2 (kmer2), General parallel correlation pseudo amino acid composition (PC-PseAAC_G), Adapted Normal distribution Bi-Profile Bayes (ANBPB), Double Bi-Profile Bayes (DBPB), Bi-Profile Bayes (BPB), Incorporating Amino Acid Pairwise (IAAPair) and Position-specific Tri-Amino Acid Propensity(PSTAAP) were employed to extract the sequence information. To remove information redundancy, information gain (IG) was applied to evaluate the importance of amino acids, which is the information entropy of class after subtracting the conditional entropy for the given amino acid. The prediction performance of the SNO sites was found to be best by using the cross-validation and independent tests. In addition, we also calculated four commonly used performance measurements, i.e. Sensitivity (Sn), Specificity (Sp), Accuracy (Acc), and the Matthew's Correlation Coefficient (MCC). For the training dataset, the overall Acc was 83.11%, the MCC was 0.6617. For an independent test dataset, Acc was 73.17%, and MCC was 0.3788. The results indicate that our method is likely to complement the existing prediction methods and is a useful tool for effective identification of the SNO sites.

Hypoxia and Hypoxia-Inducible Factors in Kidney Injury and Repair

Acute kidney injury (AKI) is a major kidney disease characterized by an abrupt loss of renal function. Accumulating evidence indicates that incomplete or maladaptive repair after AKI can result in kidney fibrosis and the development and progression of chronic kidney disease (CKD). Hypoxia, a condition of insufficient supply of oxygen to cells and tissues, occurs in both acute and chronic kidney diseases under a variety of clinical and experimental conditions. Hypoxia-inducible factors (HIFs) are the "master" transcription factors responsible for gene expression in hypoxia. Recent researches demonstrate that HIFs play an important role in kidney injury and repair by regulating HIF target genes, including microRNAs. However, there are controversies regarding the pathological roles of HIFs in kidney injury and repair. In this review, we describe the regulation, expression, and functions of HIFs, and their target genes and related functions. We also discuss the involvement of HIFs in AKI and kidney repair, presenting HIFs as effective therapeutic targets.

Redox control of chondrocyte differentiation and chondrogenesis

Chondrogenesis involves the recruitment and migration of mesenchymal cells, mesenchymal condensation, and chondrocyte differentiation and hypertrophy. Multiple factors precisely regulate chondrogenesis. Recent studies have demonstrated that the redox status of chondrocytes plays an essential role in the regulation of chondrocyte differentiation and chondrogenesis. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are important factors that change the intracellular redox status. Physiological levels of ROS/RNS act as intracellular signals in chondrocytes, and oxidative stress impairs the metabolism of chondrocytes. Under physiological conditions, the balance between ROS/RNS production and elimination ensures that redox-sensitive signalling proteins function correctly. The redox homeostasis of chondrocytes ensures that they respond appropriately to endogenous and exogenous stimuli. This review focuses on the redox regulation of key signalling pathways and transcription factors that control chondrogenesis and chondrocyte differentiation. Additionally, the mechanism by which ROS/RNS regulate signalling proteins and transcription factors in chondrocytes is also reviewed.

A bioinformatics study on characteristics, metabolic pathways, and cellular functions of the identified S-nitrosylated proteins in postmortem pork muscle

This study aimed to determine the characteristics, metabolic pathways and cellular functions of S-nitrosylated proteins from pork postmortem muscle using bioinformatics analysis. The results showed that S-nitrosylated proteins had a broad range of molecular weight and pI value and were mainly located in the functional region of secondary structure. The motif revealed the lysine (K) positioned at -5, -7, +1 and +5 through the S-nitrosocysteine while "C-X-X-C" was identified as the motif for non-S-nitrosylation-modified cysteine. The proteins were widely localized in cell compartments and mostly belonged to enzymes participating in the metabolic process. Glycolysis was the most significant pathways of S-nitrosylated proteins in postmortem muscle. The cell death of muscle cells was predicted to be inhibited by S-nitrosylation with the potential influence on the apoptosis. Those identified pathways and cellular functions of S-nitrosylation are proposed to have a profound influence on meat quality and should be highly regarded.

S-nitrosation impairs KLF4 activity and instigates endothelial dysfunction in pulmonary arterial hypertension

Krüppel-like factor 4 (KLF4) is a transcription factor with conserved zinc finger domains. As an essential regulator of vascular homeostasis, KLF4 exerts a protective effect in endothelial cells (ECs), including regulating vasodilation, inflammation, coagulation and oxidative stress. However, the underlying mechanisms modifying KLF4 activity in mediating vascular function remain poorly understood. Recently, essential roles for S-nitrosation have been implicated in many pathophysiologic processes of cardiovascular disease. Here, we demonstrated that KLF4 could undergo S-nitrosation in response to nitrosative stress in ECs, leading to the decreased nuclear localization with compromised transactivity. Mass-spectrometry and site-directed mutagenesis revealed that S-nitrosation modified KLF4 predominantly at Cys437. Functionally, KLF4 dependent vasodilatory response was impaired after S-nitrosoglutathione (GSNO) treatment. In ECs, endothelin-1 (ET-1) induced KLF4 S-nitrosation, which was inhibited by an endothelin receptor antagonist Bosentan. In hypoxia-induced rat model of pulmonary arterial hypertension (PAH), S-nitrosated KLF4 (SNO-KLF4) was significantly increased in lung tissues, along with decreased nuclear localization of KLF4. In summary, we demonstrated that S-nitrosation is a novel mechanism for the post-translational modification of KLF4 in ECs. Moreover, these findings suggested that KLF4 S-nitrosation may be implicated in the pathogenesis of vascular dysfunction and diseases such as PAH.

Bioinformatic Prediction of S-Nitrosylation Sites in Large Protein Datasets

S-nitrosylation is an essential and reversible posttranslational modification of proteins involved in numerous biological processes. The experimental determination of S-nitrosylation sites is laborious and time-consuming. Therefore, the use of computational prediction tools of this modification represents a convenient first approach to generate useful information for subsequent experimental verification. Here we describe an in silico analysis pipeline to integrate the use of several bionformatic tools while dealing with big query protein sets.

The role of reactive oxygen species in angiogenesis and preventing tissue injury after brain ischemia

Oxidative stress, which is defined as an imbalance between proxidant and antioxidant systems, is the essential mechanism involving in the ischemic process. During the early stage of brain ischemia, reactive oxygen species (ROS) are increased. Increased ROS are thought of a consequence of brain ischemia and exacerbating disease due to inducing cell death, apoptosis and senescence by oxidative stress. During brain tissue repair, ROS are act as signaling molecules and may be benefical for regulating angiogenesis and preventing tissue injury. New blood vessel formation is essentially required for rescuing tissue from brain ischemia. In ischemic conditions, ROS promotes angiogenesis, either directly or via the generation of active oxidation products. ROS-induced angiogenesis involves several signaling pathways. This paper reviewed current understanding of the role of ROS as a mediator and modulator of angiogenesis in brain ischemia.

Potential Role of CXCR4 Targeting in the Context of Radiotherapy and Immunotherapy of Cancer

Cancer immunotherapy has been established as standard of care in different tumor entities. After the first reports on synergistic effects with radiotherapy and the induction of abscopal effects-tumor shrinkage outside the irradiated volume attributed to immunological effects of radiotherapy-several treatment combinations have been evaluated. Different immunotherapy strategies (e.g., immune checkpoint inhibition, vaccination, cytokine based therapies) have been combined with local tumor irradiation in preclinical models. Clinical trials are ongoing in different cancer entities with a broad range of immunotherapeutics and radiation schedules. SDF-1 (CXCL12)/CXCR4 signaling has been described to play a major role in tumor biology, especially in hypoxia adaptation, metastasis and migration. Local tumor irradiation is a known inducer of SDF-1 expression and release. CXCR4 also plays a major role in immunological processes. CXCR4 antagonists have been approved for the use of hematopoietic stem cell mobilization from the bone marrow. In addition, several groups reported an influence of the SDF-1/CXCR4 axis on intratumoral immune cell subsets and anti-tumor immune response. The aim of this review is to merge the knowledge on the role of SDF-1/CXCR4 in tumor biology, radiotherapy and immunotherapy of cancer and in combinatorial approaches.

Nitric oxide mediated redox regulation of protein homeostasis

Nitric oxide is a versatile diffusible signaling molecule, whose biosynthesis by three NO synthases (NOS) is tightly regulated at transcriptional and posttranslational levels, availability of co-factors, and calcium binding. Above normal levels of NO have beneficial protective effects for example in the cardiovascular system, but also contribute to the pathophysiology in the context of inflammatory diseases, and to aging and neurodegeneration in the nervous system. The effect specificity relies on the functional and spatial specificity of the NOS isoenzymes, and on the duality of two major signaling mechanisms (i) activation of soluble guanylycylase (sGC)-dependent cGMP production and (ii) direct S-nitrosylation of redox sensitive cysteines of susceptible proteins. The present review summarizes the functional implications of S-nitrosylation in the context of proteostasis, and focuses on two NO target proteins, heat shock cognate of 70 kDa (Hsc70/HSPA8) and the ubiquitin 2 ligase (UBE2D), because both are modified on functionally critical cysteines and are key regulators of chaperone mediated and assisted autophagy and proteasomal protein degradation. SNO modifications of these candidates are associated with protein accumulations and adoption of a senescent phenotype of neuronal cells suggesting that S-nitrosylations of protein homeostatic machineries contribute to aging phenomena.

Nitric oxide contributes to protein homeostasis by S-nitrosylations of the chaperone HSPA8 and the ubiquitin ligase UBE2D

Upregulations of neuronal nitric oxide synthase (nNOS) in the rodent brain have been associated with neuronal aging. To address underlying mechanisms we generated SH-SY5Y neuronal cells constitutively expressing nNOS at a level similar to mouse brain (nNOS+ versus MOCK). Initial experiments revealed S-nitrosylations (SNO) of key players of protein homeostasis: heat shock cognate HSC70/HSPA8 within its nucleotide-binding site, and UBE2D ubiquitin conjugating enzymes at the catalytic site cysteine. HSPA8 is involved in protein folding, organelle import/export and chaperone-mediated LAMP2a-dependent autophagy (CMA). A set of deep redox and full proteome analyses, plus analysis of autophagy, CMA and ubiquitination with rapamycin and starvation as stimuli confirmed the initial observations and revealed a substantial increase of SNO modifications in nNOS+ cells, in particular targeting protein networks involved in protein catabolism, ubiquitination, carbohydrate metabolism and cell cycle control. Importantly, NO-independent reversible oxidations similarly occurred in both cell lines. Functionally, nNOS caused an accumulation of proteins, including CMA substrates and loss of LAMP2a. UBE2D activity and proteasome activity were impaired, resulting in dysregulations of cell cycle checkpoint proteins. The observed changes of protein degradation pathways caused an expansion of the cytoplasm, large lysosomes, slowing of the cell cycle and suppression of proliferation suggesting a switch of the phenotype towards aging, supported by downregulations of neuronal progenitor markers but increase of senescence-associated proteins. Hence, upregulation of nNOS in neuronal cells imposes aging by SNOing of key players of ubiquitination, chaperones and of substrate proteins leading to interference with crucial steps of protein homeostasis.

The significance of SUMOylation of angiogenic factors in cancer progression

Angiogenesis is the process of endothelial cell migration and proliferation induced by angiogenic factors, which is essential for the development of tumors. In recent years, studies have reported that SUMOylation acts on tumor angiogenesis by targeting angiogenic factors as one of post-translational modifications of proteins. Anti-angiogenic therapy is a new treatment method for tumor treatment following radiotherapy and chemotherapy, and it inhibits tumor growth by blocking tumor blood vessels. Therefore, SUMOylation may become a potential target for anti-angiogenesis therapy. This article focuses on the effect of SUMOylation on vascular growth factors, important signaling pathways proteins, and the migration and function of endothelial cells, in order to provide a new research idea for the anti-angiogenic therapy of tumors.

Computational Structural Biology of S-nitrosylation of Cancer Targets

Nitric oxide (NO) plays an essential role in redox signaling in normal and pathological cellular conditions. In particular, it is well known to react in vivo with cysteines by the so-called S-nitrosylation reaction. S-nitrosylation is a selective and reversible post-translational modification that exerts a myriad of different effects, such as the modulation of protein conformation, activity, stability, and biological interaction networks. We have appreciated, over the last years, the role of S-nitrosylation in normal and disease conditions. In this context, structural and computational studies can help to dissect the complex and multifaceted role of this redox post-translational modification. In this review article, we summarized the current state-of-the-art on the mechanism of S-nitrosylation, along with the structural and computational studies that have helped to unveil its effects and biological roles. We also discussed the need to move new steps forward especially in the direction of employing computational structural biology to address the molecular and atomistic details of S-nitrosylation. Indeed, this redox modification has been so far an underappreciated redox post-translational modification by the computational biochemistry community. In our review, we primarily focus on S-nitrosylated proteins that are attractive cancer targets due to the emerging relevance of this redox modification in a cancer setting.

Metabolic regulation of macrophages in tumor microenvironment

PURPOSE OF REVIEW

Insight into the metabolic changes in cancer has become so important that cancer is regarded as a disease entity full of metabolic implications. We summarize the recent findings pertaining to cancer cell-derived metabolic changes that regulate the function of macrophages to favor cancer cell survival, and the reported approaches to reverse these changes.

RECENT FINDINGS

Since the observation and dramatic revitalization of the Warburg effect, metabolic changes were thought to be confined in cancer cells. However, the Warburg effect has recently been proven to exist in various types of immune cells in tumor tissue. A growing number of publications now indicate that cancer cells interact with other cells in the tumor microenvironment, not only through traditional inflammatory mediators, but also through oncometabolites, and that metabolic changes in immune cells by oncometabolites are the key factors favoring the survival of cancer cells and pro-tumoral function of immune cells. Notably, these metabolic changes do not occur uniformly in tumor progression.

SUMMARY

Understanding of the complex metabolic interactions in the tumor microenvironment can not only set a new paradigm for tumor progression, but also provide new breakthroughs to control cancer by modulation of function in tumor-associated macrophages.

Immunological Mechanisms Responsible for Radiation-Induced Abscopal Effect

Radiotherapy has been used for more than a hundred years as a local tumor treatment. The occurrence of systemic antitumor effects manifesting as regression of tumors outside of the irradiated field (abscopal effect) was occasionally observed but deemed too rare and unpredictable to be a therapeutic goal. This has changed with the advent of immunotherapy. Remarkable systemic effects have been observed in patients receiving radiotherapy to control tumors that were progressing during immune checkpoint blockade, stimulating interest in using radiation to overcome primary and acquired cancer resistance to immunotherapy. Here, we review the immunological mechanisms that are responsible for the ability of focal radiation to promote antitumor T cell responses that mediate tumor rejection and, in some cases, result in systemic effects.

Nitric oxide promotes cancer cell dedifferentiation by disrupting an Oct4:caveolin-1 complex: A new regulatory mechanism for cancer stem cell formation

Cancer stem cells (CSCs) are unique populations of cells that can self-renew and generate different cancer cell lineages. Although CSCs are believed to be a promising target for novel therapies, the specific mechanisms by which these putative therapeutics could intervene are less clear. Nitric oxide (NO) is a biological mediator frequently up-regulated in tumors and has been linked to cancer aggressiveness. Here, we search for targets of NO that could explain its activity. We find that it directly affects the stability and function of octamer-binding transcription factor 4 (Oct4), known to drive the stemness of lung cancer cells. We demonstrated that NO promotes the CSC-regulatory activity of Oct4 through a mechanism that involves complex formation between Oct4 and the scaffolding protein caveolin-1 (Cav-1). In the absence of NO, Oct4 forms a molecular complex with Cav-1, which promotes the ubiquitin-mediated proteasomal degradation of Oct4. NO promotes Akt-dependent phosphorylation of Cav-1 at tyrosine 14, disrupting the Cav-1:Oct4 complex. Site-directed mutagenesis and computational modeling studies revealed that the hydroxyl moiety at tyrosine 14 of Cav-1 is crucial for its interaction with Oct4. Both removal of the hydroxyl via mutation to phenylalanine and phosphorylation lead to an increase in binding free energy (ΔG_bind) between Oct4 and Cav-1, destabilizing the complex. Together, these results unveiled a novel mechanism of CSC regulation through NO-mediated stabilization of Oct4, a key stem cell transcription factor, and point to new opportunities to design CSC-related therapeutics.

Role of Nitric Oxide and Hydrogen Sulfide in Ischemic Stroke and the Emergent Epigenetic Underpinnings

Nitric oxide (NO) and hydrogen sulfide (H₂S) are the key gasotransmitters with an imperious role in the maintenance of cerebrovascular homeostasis. A decline in their levels contributes to endothelial dysfunction that portends ischemic stroke (IS) or cerebral ischemia/reperfusion (CI/R). Nevertheless, their exorbitant production during CI/R is associated with exacerbation of cerebrovascular injury in the post-stroke epoch. NO-producing nitric oxide synthases are implicated in IS pathology and their activity is regulated, inter alia, by various post-translational modifications and chromatin-based mechanisms. These account for heterogeneous alterations in NO production in a disease setting like IS. Interestingly, NO per se has been posited as an endogenous epigenetic modulator. Further, there is compelling evidence for an ingenious crosstalk between NO and H₂S in effecting the canonical (direct) and non-canonical (off-target collateral) functions. In this regard, NO-mediated S-nitrosylation and H₂S-mediated S-sulfhydration of specific reactive thiols in an expanding array of target proteins are the principal modalities mediating the all-pervasive influence of NO and H₂S on cell fate in an ischemic brain. An integrated stress response subsuming unfolded protein response and autophagy to cellular stressors like endoplasmic reticulum stress, in part, is entrenched in such signaling modalities that substantiate the role of NO and H₂S in priming the cells for stress response. The precis presented here provides a comprehension on the multifarious actions of NO and H₂S and their epigenetic underpinnings, their crosstalk in maintenance of cerebrovascular homeostasis, and their "Janus bifrons" effect in IS milieu together with plausible therapeutic implications.

A charge-sensing region in the stromal interaction molecule 1 luminal domain confers stabilization-mediated inhibition of SOCE in response to S-nitrosylation

Store-operated Ca2+ entry (SOCE) is a major Ca2+ signaling pathway facilitating extracellular Ca2+ influx in response to the initial release of intracellular endo/sarcoplasmic reticulum (ER/SR) Ca2+ stores. Stromal interaction molecule 1 (STIM1) is the Ca2+ sensor that activates SOCE following ER/SR Ca2+ depletion. The EF-hand and the adjacent sterile α-motif (EFSAM) domains of STIM1 are essential for detecting changes in luminal Ca2+ concentrations. Low ER Ca2+ levels trigger STIM1 destabilization and oligomerization, culminating in the opening of Orai1-composed Ca2+ channels on the plasma membrane. NO-mediated S-nitrosylation of cysteine thiols regulates myriad protein functions, but its effects on the structural mechanisms that regulate SOCE are unclear. Here, we demonstrate that S-nitrosylation of Cys49 and Cys56 in STIM1 enhances the thermodynamic stability of its luminal domain, resulting in suppressed hydrophobic exposure and diminished Ca2+ depletion-dependent oligomerization. Using solution NMR spectroscopy, we pinpointed a structural mechanism for STIM1 stabilization driven by complementary charge interactions between an electropositive patch on the core EFSAM domain and the S-nitrosylated nonconserved region of STIM1. Finally, using live cells, we found that the enhanced luminal domain stability conferred by either Cys49 and Cys56S-nitrosylation or incorporation of negatively charged residues into the EFSAM electropositive patch in the full-length STIM1 context significantly suppresses SOCE. Collectively, our results suggest that S-nitrosylation of STIM1 inhibits SOCE by interacting with an electropositive patch on the EFSAM core, which modulates the thermodynamic stability of the STIM1 luminal domain.

Sanyang Xuedai enhances the radiosensitivity of human non-small cell lung cancer cells via increasing iNOS/NO production

OBJECTIVE

In this research, we aimed at finding out how San Yang Xue Dai (SYKT) promotes the radiosensitivity of non-small cell lung cancer (NSCLC) cell line NCI-H460.

METHODS

Survival rate of NSCLC cells (A549, NCI-H460, NCI-H1650 and NCI-H1975) after the SYKT treatment or irradiation (IR) was calculated by the MTT assay. The radiosensitization of SYKT (0.5 g/mL and 1.0 g/mL) on cell line NCI-H460 and the radioresistant cell line NCI-H460R was studied by MTT assay and clone formation assay. The protein expression levels of iNOS, Cyclin B1 and CDC2 were determined by western blot, and the expression of NO was measured by Griess method. Finally, cell cycle and apoptotic rate of NSCLC cell line NCI-H460 were accessed by flow cytometry assay. BrdU staining was also applied to detect the cell proliferation after IR with or without SYKT treatment.

RESULTS

The IC10 value of SYKT for NCI-H460 cells was 1.03 g/mL. After 1.0 g/mL SYKT treatment, the radiosensitivity of NCI-H460R cells was enhanced. The level of iNOS in the cells was found decreased after IR. We also found that SYKT could enhance iNOS and NO expressions while inhibit cyclin B1 and CDC2 expressions in radiation resistant cells. Combining β-irradiation with SYKT caused cell cycle arrest in G2/M phase and increased cell apoptosis.

CONCLUSION

SYKT resensitized radioresistant NCI-H460R cells via increasing cell apoptosis and cell cycle arrest. This was due to an elevated NO level caused by accumulating iNOS and effects of SYKT on radiosensitization of NSCLC should be further investigated in clinical application.