Hypoxic regulation of cytoglobin and neuroglobin expression in human normal and tumor tissues

Skeletal muscle transcriptomics of sheep acclimated to cold desert and tropical regions identifies genes and pathways accentuating their diversity

The current study attempts to investigate the differences in gene expression in longissimus thoracis muscles between sheep breeds acclimated to diverse environments. Changthangi sheep inhabits the cold arid plateau of Ladakh, at an altitude above 3000 m with prevalence of rarefied atmosphere. Muzzafarnagri sheep, on the other hand is found in the sub-tropical hot and humid plains at an altitude of about 250 m. Comparative transcriptomics was used to provide a molecular perspective of the differential adaptation of the two breeds. RNA sequencing data was generated from four biological replicates of the longissimus thoracis muscles from both breeds. The common genes expressed in both breeds were involved in muscle contraction and muscle fibre organization. The most significant pathways enriched in Changthangi muscles were glycogen metabolism, reduction of cytosolic Ca++ levels and NFE2L2 regulating anti-oxidant, while those in Muzzafarnagri were extracellular matrix organization and collagen formation. The hub genes identified in Changthangi were involved in hematopoiesis and HIF signaling pathway, suggesting the molecular acclimatization of Changthangi to the high altitude cold desert of Ladakh. The nodal genes discovered in Muzzafarnagri sheep were associated with the extracellular matrix which accentuates its significance in the development, growth and repair of muscles. The observed transcriptomic differences underscore the morphological and adaptive disparity between the two breeds. The candidate genes and pathways identified in this study will form the basis for future research on adaptation to high altitude and body size in small ruminants.

Molecular analysis of the human cytoglobin mRNA isoforms

Multiple functions have been proposed for the ubiquitously expressed vertebrate globin cytoglobin (Cygb), including nitric oxide (NO) metabolism, lipid peroxidation/signalling, superoxide dismutase activity, reactive oxygen/nitrogen species (RONS) scavenging, regulation of blood pressure, antifibrosis, and both tumour suppressor and oncogenic effects. Since alternative splicing can expand the biological roles of a gene, we investigated whether this mechanism contributes to the functional diversity of Cygb. By mining of cDNA data and molecular analysis, we identified five alternative mRNA isoforms for the human CYGB gene (V-1 to V-5). Comprehensive RNA-seq analyses of public datasets from human tissues and cells confirmed that the canonical CYGB V-1 isoform is the primary CYGB transcript in the majority of analysed datasets. Interestingly, we revealed that isoform V-3 represented the predominant CYGB variant in hepatoblastoma (HB) cell lines and in the majority of analysed normal and HB liver tissues. CYGB V-3 mRNA is transcribed from an alternate upstream promoter and hypothetically encodes a N-terminally truncated CYGB protein, which is not recognized by some antibodies used in published studies. Little to no transcriptional evidence was found for the other CYGB isoforms. Comparative transcriptomics and flow cytometry on CYGB+/+ and gene-edited CYGB-/- HepG2 HB cells did not unveil a knockout phenotype and, thus, a potential function for CYGB V-3. Our study reveals that the CYGB gene is transcriptionally more complex than previously described as it expresses alternative mRNA isoforms of unknown function. Additional experimental data are needed to clarify the biological meaning of those alternative CYGB transcripts.

Comparison of Evolutionary Relationships between Branchiostoma floridae, Ciona intestinalis, and Homo sapiens Globins Provide Evidence of Gene Co-Option and Convergent Evolution

Globins have been studied as model proteins to elucidate the principles of protein evolution. This was achieved by understanding the relationship between amino acid sequence, three-dimensional structure, physicochemical properties, and physiological function. Previous molecular phylogenies of chordate globin genes revealed the monophyletic evolution of urochordate globins and suggested convergent evolution. However, to provide evidence of convergent evolution, it is necessary to determine the physicochemical and functional similarities between vertebrates and urochordate globins. In this study, we determined the expression patterns of Ciona globin genes using real-time RT-PCR. Two genes (Gb-1 and Gb-2) were predominantly expressed in the branchial sac, heart, and hemocytes and were induced under hypoxia. Combined with the sequence analysis, our findings suggest that Gb-1/-2 correspond to vertebrate hemoglobin-α/-β. However, we did not find a robust similarity between Gb-3, Gb-4, and vertebrate globins. These results suggested that, even though Ciona globins obtained their unique functions differently from vertebrate globins, the two of them shared some physicochemical features and physiological functions. Our findings offer a good example for understanding the molecular mechanisms underlying gene co-option and convergence, which could lead to evolutionary innovations.

Insights into the function of cytoglobin

Since its discovery in 2001, the function of cytoglobin has remained elusive. Through extensive in vitro and in vivo research, a range of potential physiological and pathological mechanisms has emerged for this multifunctional member of the hemoglobin family. Currently, over 200 research publications have examined different aspects of cytoglobin structure, redox chemistry and potential roles in cell signalling pathways. This research is wide ranging, but common themes have emerged throughout the research. This review examines the current structural, biochemical and in vivo knowledge of cytoglobin published over the past two decades. Radical scavenging, nitric oxide homeostasis, lipid binding and oxidation and the role of an intramolecular disulfide bond on the redox chemistry are examined, together with aspects and roles for Cygb in cancer progression and liver fibrosis.

Neuroglobin inhibits pancreatic cancer proliferation and metastasis by targeting the GNAI1/EGFR/AKT/ERK signaling axis

Pancreatic cancer is an extremely aggressive malignancy with a very disappointing prognosis. Neuroglobin (NGB), a member of the globin family, has been demonstrated to have a significant role in a variety of tumor forms. The possible role of NGB as a tumor suppressor gene in pancreatic cancer was investigated in this work. Information from the public dataset TCGA combined with GTEx was used to analyze the finding that NGB was commonly downregulated in pancreatic cancer cell lines and tissues, correlating with patient age and prognosis. The expression of NGB in pancreatic cancer was investigated via RT-PCR, qRT-PCR, and Western blot experiments. In-vitro and in-vivo assays, NGB elicited cell cycle arrest in the S phase and apoptosis, hindered migration and invasion, reversed the EMT process, and suppressed cell proliferation and development. The mechanism of action of NGB was predicted via bioinformatics analysis and validated using Western blot and co-IP experiments revealed that NGB inhibited the EGFR/AKT/ERK pathway by binding to and reducing expression of GNAI1 and p-EGFR. In addition, pancreatic cancer cells overexpressing NGB showed increased drug sensitivity to gefitinib (EGFR-TKI). In conclusion, NGB inhibits pancreatic cancer progression by specifically targeting the GNAI1/EGFR/AKT/ERK signaling axis.

Mechanism and application of ferroptosis in colorectal cancer

Colorectal cancer (CRC) is the third most common malignant tumor in the world. CRC has high morbidity and mortality rates and it is a serious threat to human health. Ferroptosis is a unique form of iron-dependent oxidative cell death that is usually accompanied by iron accumulation and lipid peroxidation. Ferroptosis has attracted worldwide attention since it was first proposed. It plays an important role in the development of a variety of diseases, such as tumors, ischemia/reperfusion injury, nervous system diseases, and kidney damage, and it may serve as a new therapeutic target. This article reviews the mechanism of ferroptosis and the possibility to target ferroptosis pathways in CRC, providing new ideas for the diagnosis and treatment of CRC.

Hydrogen peroxide induces heme degradation and protein aggregation in human neuroglobin: roles of the disulfide bridge and hydrogen-bonding in the distal heme cavity

In the present study, human neuroglobin (hNgb) was found to undergo H₂ O₂ -induced breakdown of the heme center at a much slower rate than other globins, namely in the timescale of hours against minutes. We investigated how the rate of the process is affected by the Cys46/Cys55 disulfide bond and the network of non-covalent interactions in the distal heme side involving Tyr44, Lys67, the His64 heme iron axial ligand and the heme propionate-7. The rate is increased by the Tyr44 to Ala and Phe mutations; however the rate is lowered by Lys67 to Ala swapping. The absence of the disulfide bridge slows down the reaction further. Therefore, the disulfide bond-controlled accessibility of the heme site and the residues at position 44 and 67 affect the activation barrier of the reaction. Wild-type and mutated species form β-amyloid aggregates in the presence of H₂ O₂ producing globular structures. Furthermore, the C46A/C55A, Y44A, Y44F and Y44F/C46A/C55A variants yield potentially harmful fibrils. Finally, the nucleation and growth kinetics for the aggregation of the amyloid structures can be successfully described by the Finke-Watzky model.

Modulating Nitric Oxide Dioxygenase and Nitrite Reductase of Cytoglobin through Point Mutations

Cytoglobin is a hexacoordinate hemoglobin with physiological roles that are not clearly understood. Previously proposed physiological functions include nitric oxide regulation, oxygen sensing, or/and protection against oxidative stress under hypoxic/ischemic conditions. Like many globins, cytoglobin rapidly consumes nitric oxide under normoxic conditions. Under hypoxia, cytoglobin generates nitric oxide, which is strongly modulated by the oxidation state of the cysteines. This gives a plausible role for this biochemistry in controlling nitric oxide homeostasis. Mutations to control specific properties of hemoglobin and myoglobin, including nitric oxide binding/scavenging and the nitrite reductase activity of various globins, have been reported. We have mapped these key mutations onto cytoglobin, which represents the E7 distal ligand, B2/E9 disulfide, and B10 heme pocket residues, and examined the nitric oxide binding, nitric oxide dioxygenase activity, and nitrite reductase activity. The Leu46Trp mutation decreases the nitric oxide dioxygenase activity > 10,000-fold over wild type, an effect 1000 times greater than similar mutations with other globins. By understanding how particular mutations can affect specific reactivities, these mutations may be used to target specific cytoglobin activities in cell or animal models to help understand the precise role(s) of cytoglobin under physiological and pathophysiological conditions.

Protective role of Cytoglobin and Neuroglobin against the Lipopolysaccharide (LPS)-induced inflammation in Leydig cells ex vivo

Leydig cells are responsible for testosterone production in male testis upon stimulation by luteinizing hormone. Inflammation and oxidative stress related Leydig cell dysfunction is one of the major causes of male infertility. Cytoglobin (CYGB) and Neuroglobin (NGB) are two globin family member proteins which protect cells against oxidative stress. In the current study, we established a Lipopolysaccharide (LPS)-induced inflammation model in TM3 Leydig cell culture to study the function of CYGB and NGB proteins under inflammatory conditions. CYGB and NGB were downregulated using siRNA and shRNA based experimental strategies. Overexpression was conducted using lentiviral pLenti-III-CYGB-2A-GFP, and pLenti-III-NGB-2A-GFP vector systems. As testicular macrophages regulate immune function upon inflammation and steroidogenesis of Leydig cells, we generated direct/indirect co-culture systems of TM3 and mouse macrophage (RAW264.7) cells ex vivo. Downregulation of CYGB and NGB induced nitride oxide (NO) release, blocked cell cycle progression, reduced testosterone production and increased inflammatory and apoptotic pathway gene expression in the presence and absence of LPS. On the other hand, CYGB and NGB overexpression reduced TNFα and COX-2 protein expressions and increased the expression of testosterone biogenesis pathway genes upon LPS stimulation. In addition, CYGB and NGB overexpression upregulated testosterone production. The present study successfully established an inflammatory interaction model of TM3 and RAW264.7 cells. Suppression of CYGB and NGB in TM3 cells changed macrophage morphology, enhanced macrophage cell number and NO release in co-culture experiments upon LPS exposure. In summary, these results demonstrate that globin family members might control LPS induced inflammation by regulating apoptotic mechanisms and macrophage response.

Neuroglobin, clues to function and mechanism

Neuroglobin is expressed in vertebrate brain and belongs to a branch of the globin family that diverged early in evolution. Sequence conservation and presence in nervous cells of several taxa suggests a relevant role in the nervous system, with tight structural restraints. Twenty years after its discovery, a rich scientific literature provides convincing evidence of the involvement of neuroglobin in sustaining neuron viability in physiological and pathological conditions however, a full and conclusive picture of its specific function, or set of functions is still lacking. The difficulty of unambiguously assigning a precise mechanism and biochemical role to neuroglobin might arise from the participation to one or more cell mechanism that redundantly guarantee the functioning of the highly specialized and metabolically demanding central nervous system of vertebrates. Here we collect findings and hypotheses arising from recent biochemical, biophysical, structural, in cell and in vivo experimental work on neuroglobin, aiming at providing an overview of the most recent literature. Proteins are said to have jobs and hobbies, it is possible that, in the case of neuroglobin, evolution has selected for it more than one job, and support to cover for its occasional failings. Disentangling the mechanisms and roles of neuroglobin is thus a challenging task that might be achieved by considering data from different disciplines and experimental approaches.

Neuroglobin: A New Possible Marker of Estrogen-Responsive Breast Cancer

The expression of the α-subtype of Estrogen Receptor (ERα) characterizes most breast cancers (more than 75%), for which endocrine therapy is the mainstay for their treatment. However, a high percentage of ERα+ breast cancers are de novo or acquired resistance to endocrine therapy, and the definition of new targets for improving therapeutic interventions and the prediction of treatment response is demanding. Our previous data identified the ERα/AKT/neuroglobin (NGB) pathway as a common pro-survival process activated in different ERα breast cancer cell lines. However, no in vivo association between the globin and the malignity of breast cancer has yet been done. Here, we evaluated the levels and localization of NGB in ERα+ breast ductal carcinoma tissue of different grades derived from pre-and post-menopausal patients. The results indicate a strong association between NGB accumulation, ERα, AKT activation, and the G3 grade, while no association with the menopausal state has been evidenced. Analyses of the data set (e.g., GOBO) strengthen the idea that NGB accumulation could be linked to tumor cell aggressiveness (high grade) and resistance to treatment. These data support the view that NGB accumulation, mainly related to ER expression and tumor grade, represents a compensatory process, which allows cancer cells to survive in an unfavorable environment.

A reliable set of reference genes to normalize oxygen-dependent cytoglobin gene expression levels in melanoma

Cytoglobin (CYGB) is a ubiquitously expressed protein with a protective role against oxidative stress, fibrosis and tumor growth, shown to be transcriptionally regulated under hypoxic conditions. Hypoxia-inducible CYGB expression is observed in several cancer cell lines and particularly in various melanoma-derived cell lines. However, reliable detection of hypoxia-inducible mRNA levels by qPCR depends on the critical choice of suitable reference genes for accurate normalization. Limited evidence exists to support selection of the commonly used reference genes in hypoxic models of melanoma. This study aimed to select the optimal reference genes to study CYGB expression levels in melanoma cell lines exposed to hypoxic conditions (0.2% O₂) and to the HIF prolyl hydroxylase inhibitor roxadustat (FG-4592). The expression levels of candidate genes were assessed by qPCR and the stability of genes was evaluated using the geNorm and NormFinder algorithms. Our results display that B2M and YWHAZ represent the most optimal reference genes to reliably quantify hypoxia-inducible CYGB expression in melanoma cell lines. We further validate hypoxia-inducible CYGB expression on protein level and by using CYGB promoter-driven luciferase reporter assays in melanoma cell lines.

Expression of Myoglobin in Normal and Cancer Brain Tissues: Correlation With Hypoxia Markers

Background

Myoglobin (MB) is increasingly recognized as a key player in cancer growth and metastasis. Low oxygen tensions, commonly associated with highly aggressive and recurrent cancers, have been shown to regulate its expression in several cancers such as lung, neck, prostate and breast cancer. However, it is not yet known whether it contributes to the growth and spread of brain cancers especially Glioblastoma multiforme (GBM).

Methods

Here we investigate the expression of MB, and its correlation with the hypoxia markers carbonic anhydrase IX (CAIX) and lactate dehydrogenase A (LDHA), in human tissue microarrays of multiple organ tumors, brain tumors, and GBM tumors, and their respective cancer-adjacent normal tissues. Correlation between MB protein expression and tumor grade was also assessed.

Results

We show that MB protein is expressed in a wide variety of cancers, benign tumors, cancer-adjacent normal tissues, hyperplastic tissue samples and normal brain tissue, and low oxygen tensions modulate MB protein expression in different brain cancers, including GBM. Enhanced nuclear LDHA immune-reactivity in GBM was also observed. Finally, we report for the first time a positive correlation between MB expression and brain tumor grade.

Conclusion

Our data suggest that hypoxia regulate MB expression in different brain cancers (including GBM) and that its expression is associated with a more aggressive phenotype as indicated by the positive correlation with the brain tumor grade. Additionally, a role for nuclear LDHA in promoting aggressive tumor phenotype is also suggested based on enhanced nuclear expression which was observed only in GBM.

Neuroglobin and neuroprotection: the role of natural and synthetic compounds in neuroglobin pharmacological induction

Neuroglobin (Ngb) is a 17 kDa monomeric hexa-coordinated heme protein belonging to the globin family. Ngb is mainly expressed in neurons of the central and peripheral nervous system, although moderate levels of Ngb have been detected in non-nervous tissues. In the past decade, Ngb has been studied for its neuroprotective role in a large number of neurological disorders such as Alzheimer's disease, Huntington's disease, brain ischemia and hypoxia. This review discusses and summarizes the natural compounds and the small synthetic molecules capable of modulating Ngb expression that exhibits a protective role against various neurodegenerative diseases.

Lessons from the post-genomic era: Globin diversity beyond oxygen binding and transport

Vertebrate hemoglobin (Hb) and myoglobin (Mb) were among the first proteins whose structures and sequences were determined over 50 years ago. In the subsequent pregenomic period, numerous related proteins came to light in plants, invertebrates and bacteria, that shared the myoglobin fold, a signature sequence motif characteristic of a 3-on-3 α-helical sandwich. Concomitantly, eukaryote and bacterial globins with a truncated 2-on-2 α-helical fold were discovered. Genomic information over the last 20 years has dramatically expanded the list of known globins, demonstrating their existence in a limited number of archaeal genomes, a majority of bacterial genomes and an overwhelming majority of eukaryote genomes. In vertebrates, 6 additional globin types were identified, namely neuroglobin (Ngb), cytoglobin (Cygb), globin E (GbE), globin X (GbX), globin Y (GbY) and androglobin (Adgb). Furthermore, functions beyond the familiar oxygen transport and storage have been discovered within the vertebrate globin family, including NO metabolism, peroxidase activity, scavenging of free radicals, and signaling functions. The extension of the knowledge on globin functions suggests that the original roles of bacterial globins must have been enzymatic, involved in defense against NO toxicity, and perhaps also as sensors of O₂, regulating taxis away or towards high O₂ concentrations. In this review, we aimed to discuss the evolution and remarkable functional diversity of vertebrate globins with particular focus on the variety of non-canonical expression sites of mammalian globins and their according impressive variability of atypical functions.

Redox State Control of Human Cytoglobin by Direct Electrochemical Method to Investigate Its Function in Molecular Basis

The direct electron transfer between human cytoglobin (Cygb) and the electrode surface, which would allow manipulating the oxidation states of the heme iron in Cygb, was first observed by immobilizing Cygb on a nanoporous gold (NPG) electrode via a carboxy-terminated alkanethiol. The voltammetric performances of the wild type and mutated Cygb-immobilized NPG electrodes were evaluated in the absence or presence of potential substrates. The obtained results demonstrated that the usefulness of the proposed method in understanding the function of Cygb in molecular basis.

Role of cytoglobin, a novel radical scavenger, in stellate cell activation and hepatic fibrosis

Cytoglobin (Cygb), a stellate cell-specific globin, has recently drawn attention due to its association with liver fibrosis. In the livers of both humans and rodents, Cygb is expressed only in stellate cells and can be utilized as a marker to distinguish stellate cells from hepatic fibroblast-derived myofibroblasts. Loss of Cygb accelerates liver fibrosis and cancer development in mouse models of chronic liver injury including diethylnitrosamine-induced hepatocellular carcinoma, bile duct ligation-induced cholestasis, thioacetamide-induced hepatic fibrosis, and choline-deficient L-amino acid-defined diet-induced non-alcoholic steatohepatitis. This review focuses on the history of research into the role of reactive oxygen species and nitrogen species in liver fibrosis and discusses the current perception of Cygb as a novel radical scavenger with an emphasis on its role in hepatic stellate cell activation and fibrosis.

Emerging perspectives on cytoglobin, beyond NO dioxygenase and peroxidase

Cytoglobin is an evolutionary ancient hemoglobin with poor functional annotation. Rather than constrained to penta coordination, cytoglobin's heme iron may exist either as a penta or hexacoordinated arrangement when exposed to different intracellular environments. Two cysteine residues at the surface of the protein form an intramolecular disulfide bond that regulates iron coordination, ligand binding, and peroxidase activity. Overall, biochemical results do not support a role for cytoglobin as a direct antioxidant enzyme that scavenges hydrogen peroxide because the rate of the reaction of cytoglobin with hydrogen peroxide is several orders of magnitude slower than metal and thiol-based peroxidases. Thus, alternative substrates such as fatty acids have been suggested and regulation of nitric oxide bioavailability through nitric oxide dioxygenase and nitrite reductase activities has received experimental support. Cytoglobin is broadly expressed in connective, muscle, and nervous tissues. Rational for differential cellular distribution is poorly understood but inducibility in response to hypoxia is one of the most established features of cytoglobin expression with regulation through the transcription factor hypoxia-inducible factor (HIF). Phenotypic characterization of cytoglobin deletion in the mouse have indicated broad changes that include a heightened inflammatory response and fibrosis, increase tumor burden, cardiovascular dysfunction, and hallmarks of senescence. Some of these changes might be reversed upon inhibition of nitric oxide synthase. However, subcellular and molecular interactions have been seldom characterized. In addition, specific molecular mechanisms of action are still lacking. We speculate that cytoglobin functionality will extend beyond nitric oxide handling and will have to encompass indirect regulatory antioxidant and redox sensing functions.

Neuroglobin As Key Mediator in the 17β-Estradiol-Induced Antioxidant Cell Response to Oxidative Stress

Aims: Nuclear factor (erythroid-derived 2)-like-2 factor (NRF-2) is a transcription factor well known to provide an advantage for cancer growth and survival regulating the cellular redox pathway. In breast cancer cells, we recently identified the monomeric heme-globin neuroglobin (NGB) as part of a new mechanism induced by the steroid hormone 17β-estradiol (E2) against oxidative stress. While there is mounting evidence suggesting a critical role of NGB as a sensor of oxidative stress, scarce information is available about its involvement in NRF-2 pathway activation in breast cancer cells. Results: Although NGB is not involved in the rapid E2-induced NRF-2 stability, E2 loses the capacity to regulate the expression of NRF-2-dependent genes in NGB-depleted MCF-7 cells. These data strongly sustain a role of NGB as a compensatory protein in the E2-activated intracellular pathway devoted to the increase of cancer cells tolerance to reactive oxygen species (ROS) generation in stressing conditions acting as key regulator of NRF-2 pathway activity in a time-dependent manner. Innovation: In this study, we identified a new role of NGB in the cell response to oxidative stress. Conclusion: Altogether, reported results open new insights on the NGB effect in regulating intracellular pathways related to cell adaptive response to stress and, as consequence, to cell survival, beyond its direct effect as ROS scavenger, opening new prospective in cancer therapeutic intervention.

Adaptations to environmental change: Globin superfamily evolution in Antarctic fishes

The ancient origins and functional versatility of globins make them ideal subjects for studying physiological adaptation to environmental change. Our goals in this review are to describe the evolution of the vertebrate globin gene superfamily and to explore the structure/function relationships of hemoglobin, myoglobin, neuroglobin and cytoglobin in teleost fishes. We focus on the globins of Antarctic notothenioids, emphasizing their adaptive features as inferred from comparisons with human proteins. We dedicate this review to Guido di Prisco, our co-author, colleague, friend, and husband of C.V. Ever thoughtful, creative, and enthusiastic, Guido spearheaded study of the structure, function, and evolution of the hemoglobins of polar fishes - this review is testimony to his wide-ranging contributions. Throughout his career, Guido inspired younger scientists to embrace polar biological research, and he challenged researchers of all ages to explore evolutionary adaptation in the context of global climate change. Beyond his scientific contributions, we will miss his warmth, his culture, and his great intellect. Guido has left an outstanding legacy, one that will continue to inspire us and our research.

Neuroglobin: A Novel Player in the Oxidative Stress Response of Cancer Cells

Reactive oxygen species (ROS) result from intracellular aerobic metabolism and/or extracellular stimuli. Although endogenous antioxidant systems exquisitely balance ROS production, an excess of ROS production, commonly found in diverse human degenerative pathologies including cancer, gives rise to the oxidative stress. Increased oxidative stress in cancer is related to the sustained proliferation and metabolism of cancer cells. However, cancer cells show an intrinsic higher antioxidant capacity with respect to the normal counterpart as well as an ability to cope with oxidative stress-induced cell death by establishing mechanisms of adaptation, which define a selective advantage against the adverse oxidative stress environment. The identification of survival factors and adaptive pathways, set up by cancer cells against oxidative stress, provides multiple targets for the therapeutic intervention against cancer. Neuroglobin (NGB), a globin primarily described in neurons as an oxidative stress sensor and cytoprotective factor against redox imbalance, has been recently recognized as a novel tumor-associated protein. In this review, the involvement of NGB in the cancer cell adaptation and resistance to oxidative stress will be discussed highlighting the globin role in the regulation of both the stress-induced apoptotic pathway and antioxidant systems activated by cancer cells.

Neuroglobin Expression Models as a Tool to Study Its Function

Neuroglobin (Ngb) is an evolutionary conserved member of the globin family with a primary expression in neurons of which the exact functions remain elusive. A plethora of in vivo and in vitro model systems has been generated to this day to determine the functional biological roles of Ngb. Here, we provide a comprehensive overview and discussion of the different Ngb models, covering animal and cellular models of both overexpression and knockout strategies. Intriguingly, an in-depth literature search of available Ngb expression models revealed crucial discrepancies in the outcomes observed in different models. Not only does the level of Ngb expression—either physiologically, overexpressed, or downregulated—alter its functional properties, the experimental setup, being in vitro or in vivo, does impact the functional outcome as well and, hence, whether or not a physiological and/or therapeutic role is ascribed to Ngb. These differences could highlight either technical or biological adaptations and should be considered until elucidation of the Ngb biology.

Effect of cytoglobin overexpression on extracellular matrix component synthesis in human tenon fibroblasts

BACKGROUND

Conjunctival filtering bleb scar formation is the main reason for the failure of glaucoma filtration surgery. Cytoglobin (Cygb) has been reported to play an important role in extracellular matrix (ECM) remodeling, fibrosis and tissue damage repairing. This study aimed to investigate the role of Cygb in anti-scarring during excessive conjunctival wound healing after glaucoma filtration surgery.

METHODS

Cygb was overexpressed in human tenon fibroblasts (hTFs) by transfecting hTFs with lentiviral particles encoding pLenti6.2-FLAG-Cygb. Changes in the mRNA and protein levels of fibronectin, collagen I, collagen III, TGF-β1, and HIF1α were determined by RT-PCR and western blotting respectively.

RESULTS

After Cygb overexpression, hTFs displayed no significant changes in visual appearance and cell counts compared to controls. Whereas, Cygb overexpression significantly decreased the mRNA and protein expression levels of collagen I, collagen III and fibronectin compared with control (p < 0.01). There was also a statistically significant decrease in the mRNA and protein levels of TGF-β1 and HIF-1α in hTFs with overexpressed Cygb compared with control group (p < 0.05).

CONCLUSION

Our study provided evidence that overexpression of Cygb decreased the expression levels of fibronectin, collagen I, collagen III, TGF-β1 and HIF-1α in hTFs. Therefore, therapies targeting Cygb expression in hTFs may pave a new way for clinicians to solve the problem of post-glaucoma surgery scarring.

The epigenetically downregulated factor CYGB suppresses breast cancer through inhibition of glucose metabolism

Background

Recent studies suggested the globin family member cytoglobin (CYGB) as a potential tumor suppressor; however, the mechanism by which CYGB suppresses cancer is elusive. We investigated the role and mechanism of CYGB in suppressing breast cancer.

Methods

CYGB expression was examined by reverse transcription PCR, quantitative reverse transcription PCR and open database analysis. Promoter methylation was examined by methylation-specific PCR. Metabolomics and proteomics were analyzed by gas chromatography-mass spectrometry and isobaric tags for relative and absolute quantitation, respectively. The effects and mechanisms of ectopic CYGB expression in breast cancer cells were assessed with molecular biological and cellular approaches in vitro and with a xenograft tumor model in nude mice.

Results

CYGB expression was downregulated in breast cancer tissues and cell lines, which was associated with promoter methylation. Ectopic CYGB expression suppressed proliferation, migration, invasion and induced apoptosis in breast cancer cell lines MCF7 (p53WT) and MB231 (p53mt) in vitro, and inhibited xenograft tumor growth in vivo. By proteomics and metabolomics analysis, glucose metabolism was found to be one of the main pathways suppressed by CYGB. The CYGB-expressing cells had lower ATP and compromised glycolysis. Additionally, CYGB suppressed key glucose metabolism factors including GLUT1 and HXK2 in p53-dependent and -independent manners. Restoration of GLUT1 or HXK2 expression attenuated CYGB-mediated proliferation suppression and apoptosis induction.

Conclusions

CYGB is a potential tumor suppressor in breast cancer that is epigenetically suppressed. The results for the first time suggest that CYGB suppresses breast cancer through inhibiting glucose metabolism, which could be exploited for breast cancer prevention and therapy.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0979-9) contains supplementary material, which is available to authorized users.

Potentiation of paclitaxel effect by resveratrol in human breast cancer cells by counteracting the 17β-estradiol/estrogen receptor α/neuroglobin pathway

Neuroglobin (NGB), an antiapoptotic protein upregulated by 17β-estradiol (E2), is part of E2/estrogen receptor α (ERα) pathway pointed to preserve cancer cell survival in presence of microenvironmental stressors including chemotherapeutic drugs. Here, the possibility that resveratrol (Res), an anticancer plant polyphenol, could increase the susceptibility of breast cancer cells to paclitaxel (Pacl) by affecting E2/ERα/NGB pathway has been evaluated. In MCF-7 and T47D (ERα-positive), but not in MDA-MB 231 (ERα-negative) nor in SK-N-BE (ERα and ERβ positive), Res decreases NGB levels interfering with E2/ERα-induced NGB upregulation and with E2-induced ERα and protein kinase B phosphorylation. Although Res treatment does not reduce cell viability by itself, this compound potentiates Pacl proapoptotic effects. Notably, the increase of NGB levels by NGB expression vector transfection prevents Pacl or Res/Pacl effects. Taken together, these findings indicate a new Res-based mechanism that acts on tumor cells impairing the E2/ERα/NGB signaling pathways and increasing cancer cell susceptibility to chemotherapeutic agent.

Neuroglobin as a Novel Biomarker for Predicting Poor Outcomes in Aneurysmal Subarachnoid Hemorrhage

OBJECTIVE

Neuroglobin (Ngb) has a high affinity for oxygen and helps prevent hypoxic-ischemic brain damage. In this study we analyzed the relationship between Ngb levels and clinical outcomes of aneurysmal subarachnoid hemorrhage (aSAH).

METHODS

Serum Ngb levels were measured in 58 patients with aSAH and 27 control individuals using the enzyme-linked immunosorbent assay. To continuously assess aSAH, we measured serum Ngb levels on days 1, 2, 3, 5, and 7 after aSAH. Clinical data were collected using the Hunt and Hess Scale, the Glasgow Coma Scale (GCS), the World Federation of Neurological Surgeons (WFNS) Scale, and the modified Fisher Scale. Clinical outcomes included 6-month mortality and 6-month unfavorable outcomes (modified Rankin Scale (mRS) score of 3-6).

RESULTS

Serum Ngb levels increased after aSAH, peaked on day 2, and then gradually decreased. Serum Ngb levels on admission were higher in the patient group than in the control group (7.67 ± 2.56 ng/mL vs. 6.45 ± 0.88 ng/mL, P < 0.05). Multivariate logistic regression analysis indicated that serum Ngb levels on day 2 after aSAH were independently related to 6-month mortality (odds ratio [OR] = 0.265, 95% confidence interval [CI] = 0.094-0.747, P < 0.05) and 6-month unfavorable outcomes (OR = 1.919, 95% CI = 1.158-3.180, P < 0.05), and receiver operating characteristic curve analysis showed that serum Ngb levels on day 2 predicted 6-month mortality and 6-month unfavorable outcomes, with areas under the curve of 0.893 (P < 0.05; 95% CI, 0.812-0.974) and 0.818 (P < 0.05; 95% CI, 0.691-0.954), respectively, based on the best thresholds.

CONCLUSIONS

Serum Ngb levels on day 2 after aSAH were strongly associated with poor outcomes in aSAH, suggesting that Ngb may be a novel biomarker for predicting poor outcomes in aSAH.

Cytoglobin affects tumorigenesis and the expression of ulcerative colitis-associated genes under chemically induced colitis in mice

Cytoglobin (Cygb) is a member of the hemoglobin family and is thought to protect against cellular hypoxia and oxidative stress. These functions may be particularly important in inflammation-induced cancer, e.g., in patients with ulcerative colitis (UC). In this study, we investigated the development of inflammation and tumors in a murine model of inflammation-induced colorectal cancer using a combined treatment of azoxymethane and dextran sulfate sodium. A bioinformatics analysis of genome-wide expression data revealed increased colonic inflammation at the molecular level accompanied by enhanced macroscopic tumor development in Cygb-deficient mice. Moreover, the expression of the UC-associated gene neurexophilin and PC-esterase domain family member 4 (Nxpe4) depended on the presence of Cygb in the inflamed colonic mucosa. Compared to wild type mice, RT-qPCR confirmed a 14-fold (p = 0.0003) decrease in Nxpe4 expression in the inflamed colonic mucosa from Cygb-deficient mice. An analysis of Cygb protein expression suggested that Cygb is expressed in fibroblast-like cells surrounding the colonic crypts. Histological examinations of early induced lesions suggested that the effect of Cygb is primarily at the level of tumor promotion. In conclusion, in this model, Cygb primarily seemed to inhibit the development of established microadenomas.

Compensatory role of Neuroglobin in nervous and non-nervous cancer cells in response to the nutrient deprivation

Environmental factors or adverse growth conditions that may reduce cell function or viability are considered stress. The cell ability to sense and respond to environmental stresses determine its function and survival destiny. We recently defined Neuroglobin (NGB), a heme-protein, as a compensatory protein in the 17β-Estradiol (E2) anti-apoptotic activity and as a sensor of oxidative stress in both neurons and breast cancer cells. Here, the possibility that NGB levels could represent a pivotal regulator of integrated response of cancer cells to stress has been evaluated. Data obtained in neuroblastoma and in breast cancer cell lines evidence that nutrient deprivation significantly up-regulated NGB levels at different time points. However, the analysis of autophagy activation led to exclude any possible role of stress- or E2-induced NGB in the upstream regulation of general autophagy. However, the over-expression of Flag-NGB in ERα stable transfected HEK-293 cells completely affects nutrient deprivation-induced decrease in cell number. In addition, reported results indicate that modulation of the anti-apoptotic Bcl-2 level may play a key role in the protective NGB function against energetic stress. Overall, these data define a role of NGB as compensatory protein in the cell machinery activated in response to stress and as general stress adaptation marker of cancer cells susceptible to oxidative stress, oxygen and, as demonstrated here for the first time, even to nutrient willingness. Despite the lacking of any direct NGB role on autophagic flux activated by energetic stress, NGB upregulation appears functional in delaying stress-related cell death allowing an appropriate cell response and adaptation to the changing extracellular conditions.

Identification of neuroglobin as a novel player in anti-bacterial responses in amphioxus

Theoretical considerations support various functions of neuroglobin (Ngb), but further studies are required for full characterization of these functions. In this study, we identified the presence of a single Ngb gene, BjNgb, in the amphioxus Branchiostoma japonicum. BjNgb was expressed in various tissues including the notochord, gonads (ovary and testis) and gill, and up-regulated significantly in response to the challenge with LPS and LTA, suggesting involvement in immune response of amphioxus against bacterial infection. In accord, we demonstrated for the first time that recombinant BjNgb (rBjNgb) not only interacted with the Gram-positive and negative bacteria as well as their conserved surface components LPS and LTA, but also enhanced the phagocytosis of bacteria by macrophages. Collectively, these data suggest that BjNgb is a novel player in amphioxus, via functioning as a pattern recognition molecule and an opsonin.

Neuroglobin promotes the proliferation and suppresses the apoptosis of glioma cells by activating the PI3K/AKT pathway

Our previous study demonstrated that neuroglobin (Ngb) functions as an independent predictive indicator of the prognosis of patients with glioma and promotes cancer cell growth by suppressing apoptosis. However, the understanding of the mechanisms underlying the survival‑enhancing function of Ngb in glioma is limited. In the present study, KEGG PathwayFinder by gene correlation analysis was performed on the R2: Genomics Analysis and Visualization Platform, which revealed a high association between Ngb and the phosphatidylinositol 3‑kinase (PI3K)/AKT pathway using glioma data (GSE4290) from the Gene Expression Omnibus database. Furthermore, western blotting experiments were performed in U251 and U87 glioma cells, and Ngb knockdown using short hairpin RNA reduced the protein levels of phosphorylated (p)‑AKT, p‑mammalian target of rapamycin (mTOR) and antiapoptotic factor Bcl‑2, and increased the expression of the proapoptotic protein Bcl‑2‑associated X, in U251 cells. In addition, Ngb overexpression promoted the activation of the PI3K/AKT pathway in U87 cells. MK2206, a PI3K/AKT signaling inhibitor, reduced the expression of p‑AKT and increased the levels of apoptosis‑associated proteins, including cleaved poly(ADP‑ribose) polymerase 1 and cleaved caspase‑3/7/8, in Ngb‑overexpressing U87 cells. Furthermore, MK2206 treatment reduced the proliferation and induced the apoptosis of Ngb‑overexpressing U87 cells, as indicated by the results of MTT, colony formation and flow cytometry assays. In addition, insulin‑like growth factor‑1, a PI3K/AKT signaling activator, reversed Ngb knockdown‑induced growth arrest and apoptosis in U251 cells. In conclusion, the results of the present study indicate that Ngb may facilitate a malignant phenotype of glioma cells by activating the PI3K/AKT pathway.

Roles of N- and C-terminal domains in the ligand-binding properties of cytoglobin

Cytoglobin (Cygb) is a member of the hexacoordinated globin protein family and is expressed ubiquitously in rat and human tissues. Although Cygb is reportedly upregulated under hypoxic conditions both in vivo and in vitro, suggesting a physiological function to protect cells under hypoxic/ischemic conditions by scavenging reactive oxygen species or by signal transduction, the mechanisms associated with this function have not been fully elucidated. Recent studies comparing Cygbs among several species suggest that mammalian Cygbs show a distinctly longer C-terminal domain potentially involved in unique physiological functions. In this study, we prepared human Cygb mutants (ΔC, ΔN, and ΔNC) with either one or both terminal domains truncated and investigated the enzymatic functions and structural features by spectroscopic methods. Evaluation of the superoxide-scavenging activity between Cygb variants showed that the ΔC and ΔNC mutants exhibited slightly higher activity involving superoxide scavenging as compared with wild-type Cygb. Subsequent experiments involving ligand titration, flash photolysis, and resonance Raman spectroscopic studies suggested that the truncation of the C- and N-terminal domains resulted in less effective to dissociation constants and binding rates for carbon monoxide, respectively. Furthermore, structural stability was assessed by guanidine hydrochloride and revealed that the C-terminal domain might play a vital role in improving structure, whereas the N-terminal domain did not exert a similar effect. These findings indicated that long terminal domains could be important not only in regulating enzymatic activity but also for structural stability, and that the domains might be relevant to other hypothesized physiological functions for Cygb.

Tumor grade related expression of neuroglobin is negatively regulated by PPARγ and confers antioxidant activity in glioma progression

Neuroglobin (NGB), distributed mainly in central and peripheral nervous systems, is a nerve globin with neuroprotective effects against oxidative stress resulting from hypoxia and ischemia. Recent studies have indicated that the expression of NGB is related to neurodegenerative disorders and cancers, but the molecular mechanisms for its transcriptional regulation and protection are not well defined. Here, we report that the expression of NGB in glioma is grade related and is negatively regulated by PPARγ. Specific PPARγ agonist reduces the expression of NGB, while its inhibitor enhances the expression. Moreover, NGB participates in regulating the phosphorylation of AKT in glioma cells, which may contribute to the glioma progression where accumulating oxidative pressure presents. Overexpression of NGB could protect glioma cells against 4-HNE induced cell death, and partially reverse PPARγ's pro-apoptotic and anti-proliferative abilities. These results display an important role of NGB in glioma progression and a mechanism for its transcriptional regulation, and suggest that the treatment on glioma through PPARγ agonist appears to be triggered by the modulation of NGB.

Advances in Hypoxia-Mediated Mechanisms in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common and the third most deadly malignant tumor worldwide. Hypoxia and related oxidative stress are heavily involved in the process of HCC development and its therapies. However, direct and accurate measurement of oxygen concentration and evaluation of hypoxic effects in HCC prove difficult. Moreover, the hypoxia-mediated mechanisms in HCC remain elusive. Here, we summarize recent major evidence of hypoxia in HCC lesions shown by measuring partial pressure of oxygen (pO₂), the clinical importance of hypoxic markers in HCC, and recent advances in hypoxia-related mechanisms and therapies in HCC. For the mechanisms, we focus mainly on the roles of oxygen-sensing proteins (i.e., hypoxia-inducible factor and neuroglobin) and hypoxia-induced signaling proteins (e.g., matrix metalloproteinases, high mobility group box 1, Beclin 1, glucose metabolism enzymes, and vascular endothelial growth factor). With respect to therapies, we discuss mainly YQ23, sorafenib, 2-methoxyestradiol, and celastrol. This review focuses primarily on the results of clinical and animal studies.

Possible Involvement of Nitric Oxide in Enhanced Liver Injury and Fibrogenesis during Cholestasis in Cytoglobin-deficient Mice

This study clarified the role of Cygb, the fourth globin in mammals originally discovered in rat hepatic stellate cells (HSCs), in cholestatic liver disease. Bile duct ligation (BDL) augmented inflammatory reactions as revealed by increased infiltrating neutrophils, CD68⁺-macrophages, and chemokine expression in Cygb^-/- mice. In these mice, impairment of bile canalicular indicated by the loss of CD10 expression, down-regulation of bile salt transporters, increased total bile acid, and massive apoptotic and necrotic hepatocytes occurred with the release of cytochrome c, activation of caspase 3, resulting in reduced animal survival compared to wild-type mice. In Cygb^-/- mouse liver, all of NO metabolites and oxidative stress were increased. Treatment with NO inhibitor restrained all above phenotypes and restored CD10 expression in BDL Cygb^-/- mice, while administration of NO donor aggravated liver damage in BDL-wild type mice to the same extent of BDL-Cygb^-/- mice. N-acetylcysteine administration had a negligible effect in all groups. In mice of BDL for 1-3 weeks, expression of all fibrosis-related markers was significantly increased in Cygb^-/- mice compared with wild-type mice. Thus, Cygb deficiency in HSCs enhances hepatocyte damage and inflammation in early phase and fibrosis development in late phase in mice subjected to BDL, presumably via altered NO metabolism.

Neuroglobin functions as a prognostic marker and promotes the tumor growth of glioma via suppressing apoptosis

Neuroglobin (Ngb) has been reported to be upregulated by hypoxia and plays an anti-apoptotic function. Previous studies have reported that Ngb is expressed in human glioblastoma cells and up-regulated in hypoxic microregions of glioblastoma tumor xenografts. While, the clinical significance of Ngb and its function in human glioma keep unknown. Ngb expression was analyzed in 86 glioma tissues and 20 normal brain tissues. Results showed that Ngb was significantly overexpressed in glioma tissues compared to normal brain tissues. In addition, increased levels of Ngb also observed in glioma cell lines. Clinicopathological analysis verified that the positive expression of Ngb was associated with histological type and world health organization (WHO) grade of glioma. Moreover, Kaplan-Meier analysis found that Ngb overexpression led to a shorter survival. Multivariate Cox regression analysis demonstrated that Ngb expression was an independent prognostic marker. Further experiments illustrated that Ngb knockdown significantly inhibited proliferation and facilitated apoptosis in U251 cells. In vivo experiments further confirmed that Ngb silencing notably prohibited the tumor growth of glioma in nude mice. While, Ngb overexpression prominently promoted proliferation and suppressed apoptosis in U87 cells. Taken together, this work support the first evidence that Ngb can be potentially used as a promising biomarker and target for novel treatment of human glioma.

Brain globins in physiology and pathology

Globins are globular proteins for either transport or storage of oxygen which are critical for cellular metabolism. Four globins have been identified in rodent and human brains. Among them, neuroglobin, cytoglobin and hemoglobin chains are constitutively expressed in normal brain, while myoglobin is only expressed in some neurological disorders. Studies on the molecular structure, expression and functional features of these brain globins indicated that they may play crucial roles in maintenance of neural cell survival and activity, including neurons and astrocytes. Their regulation in neurological disorders may help thoroughly understand initiation and progression of ischemia, Alzheimer's disease and glioma, etc. Elucidation of the brain globin functions might remarkably improve medical strategies that sustain neurological homeostasis and treat neurological diseases. Here the expression pattern and functions of brain globins and their involvement in neurological disorders are reviewed.

Electrochemical Evidence for Neuroglobin Activity on NO at Physiological Concentrations

The true function of neuroglobin (Ngb) and, particularly, human Ngb (NGB) has been under debate since its discovery 15 years ago. It has been expected to play a role in oxygen binding/supply, but a variety of other functions have been put forward, including NO dioxygenase activity. However, in vitro studies that could unravel these potential roles have been hampered by the lack of an Ngb-specific reductase. In this work, we used electrochemical measurements to investigate the role of an intermittent internal disulfide bridge in determining NO oxidation kinetics at physiological NO concentrations. The use of a polarized electrode to efficiently interconvert the ferric (Fe(3+)) and ferrous (Fe(2+)) forms of an immobilized NGB showed that the disulfide bridge both defines the kinetics of NO dioxygenase activity and regulates appearance of the free ferrous deoxy-NGB, which is the redox active form of the protein in contrast to oxy-NGB. Our studies further identified a role for the distal histidine, interacting with the hexacoordinated iron atom of the heme, in oxidation kinetics. These findings may be relevant in vivo, for example, in blocking apoptosis by reduction of ferric cytochrome c, and gentle tuning of NO concentration in the tissues.

Absence of cytoglobin promotes multiple organ abnormalities in aged mice

Cytoglobin (Cygb) was identified in hepatic stellate cells (HSCs) and pericytes of all organs; however, the effects of Cygb on cellular functions remain unclear. Here, we report spontaneous and age-dependent malformations in multiple organs of Cygb(-/-) mice. Twenty-six percent of young Cygb(-/-) mice (<1 year old) showed heart hypertrophy, cystic disease in the kidney or ovary, loss of balance, liver fibrosis and lymphoma. Furthermore, 71.3% (82/115) of aged Cygb(-/-) mice (1-2 years old) exhibited abnormalities, such as heart hypertrophy and cancer development in multiple organs; by contrast, 5.8% (4/68) of aged wild-type (WT) mice had abnormalities (p < 0.0001). Interestingly, serum and urine analysis demonstrated that the concentration of nitric oxide metabolites increased significantly in Cygb(-/-) mice, resulting in an imbalance in the oxidative stress and antioxidant defence system that was reversed by N(G)-monomethyl-L-arginine treatment. A senescent phenotype and evidence of DNA damage were found in primary HSCs and the liver of aged Cygb(-/-) mice. Moreover, compared with HSC(+/+), HSC(-/-) showed high expression of Il-6 and chemokine mRNA when cocultured with mouse Hepa 1-6 cells. Thus, the absence of Cygb in pericytes provokes organ abnormalities, possibly via derangement of the nitric oxide and antioxidant defence system and through accelerated cellular senescence.

Neuroglobin in Breast Cancer Cells: Effect of Hypoxia and Oxidative Stress on Protein Level, Localization, and Anti-Apoptotic Function

The over-expression of human neuroglobin (NGB), a heme-protein preferentially expressed in the brain, displays anti-apoptotic effects against hypoxic/ischemic and oxidative stresses enhancing neuron survival. As hypoxic and oxidative stress injury frequently occurs in fast proliferating neoplastic tissues, here, the effect of these stressors on the level, localization, and anti-apoptotic function of NGB in wild type and NGB-stable-silenced MCF-7 breast cancer cells has been assessed. The well-known endogenous NGB inducer 17β-estradiol (E2) has been used as positive control. The median pO2 present in tumor microenvironment of breast cancer patients (i.e., 2% O₂) does not affect the NGB level in breast cancer cells, whereas hydrogen peroxide and lead(IV) acetate, which increase intracellular reactive oxygen species (ROS) level, enhance the NGB levels outside the mitochondria and still activate apoptosis. However, E2-induced NGB up-regulation in mitochondria completely reverse lead(IV) acetate-induced PARP cleavage. These results indicate that the NGB level could represent a marker of oxidative-stress in MCF-7 breast cancer cells; however, the NGB ability to respond to injuring stimuli by preventing apoptosis requires its re-allocation into the mitochondria. As a whole, present data might lead to a new direction in understanding NGB function in cancer opening new avenues for the therapeutic intervention.

Cytoglobin as a Biomarker in Cancer: Potential Perspective for Diagnosis and Management

The search for biomarkers to detect the earliest glimpse of cancer has been one of the primary objectives of cancer research initiatives. These endeavours, in spite of constant clinical challenges, are now more focused as early cancer detection provides increased opportunities for different interventions and therapies, with higher potential for improving patient survival and quality of life. With the progress of the omics technologies, proteomics and metabolomics are currently being used for identification of biomarkers. In this line, cytoglobin (Cygb), a ubiquitously found protein, has been actively reviewed for its functional role. Cytoglobin is dynamically responsive to a number of insults, namely, fibrosis, oxidative stress, and hypoxia. Recently, it has been reported that Cygb is downregulated in a number of malignancies and that an induced overexpression reduces the proliferative characteristics of cancer cells. Thus, the upregulation of cytoglobin can be indicative of a tumour suppressor ability. Nevertheless, without a comprehensive outlook of the molecular and functional role of the globin, it will be most unlikely to consider cytoglobin as a biomarker for early detection of cancer or as a therapeutic option. This review provides an overview of the proposed role of cytoglobin and explores its potential functional role as a biomarker for cancer and other diseases.

Biodistribution and radiation dosimetry of the carbonic anhydrase IX imaging agent [(18) F]VM4-037 determined from PET/CT scans in healthy volunteers

PURPOSE

[(18) F]VM4-037 has been developed as a positron emission tomography (PET) imaging marker to detect carbonic anhydrase IX (CA-IX) overexpression and is being investigated for use as a surrogate marker for tissue hypoxia. The purpose of this study was to determine the biodistribution and estimate the radiation dose from [(18) F]VM4-037 using whole-body PET/CT scans in healthy human volunteers.

PROCEDURES

Successive whole-body PET/CT scans were performed after intravenous injection of [(18) F]VM4-037 in four healthy humans. The radiotracer uptakes in different organs were determined from the analysis of the PET scans. Human radiation doses were estimated using OLINDA/EXM software.

RESULTS

High uptake of [(18) F]VM4-037 was observed in the liver and kidneys, with little clearance of activity during the study period, with mean standardized uptake values of ~35 in liver and ~22 in kidneys at ~1 h after injection. The estimated effective dose was 28 ± 1 μSv/MBq and the absorbed doses for the kidneys and liver were 273 ± 31 and 240 ± 68 μGy/MBq, respectively, for the adult male phantom. Hence, the effective dose would be 10 ± 0.5 mSv for the anticipated injected activity of 370 MBq, and the kidney and liver doses would be 101 ± 11 and 89 ± 25 mGy, respectively.

CONCLUSIONS

[(18) F]VM4-037 displayed very high uptake in the liver and kidneys with little clearance of activity during the study period, resulting in these organs receiving the highest radiation doses among all bodily organs. Though the effective dose and the organ doses are within the limits considered as safe, the enhanced uptake of [(18) F]VM4-037 in the kidneys and liver will make the compound unsuitable for imaging overexpression of CA-IX in those two organs. However, the tracer may be suitable for imaging overexpression of CA-IX in lesions in other regions of the body such as in the lungs or head and neck region.

ΔNp63 targets cytoglobin to inhibit oxidative stress-induced apoptosis in keratinocytes and lung cancer

During physiological aerobic metabolism, the epidermis undergoes significant oxidative stress as a result of the production of reactive oxygen species (ROS). To maintain a balanced oxidative state, cells have developed protective antioxidant systems, and preliminary studies suggest that the transcriptional factor p63 is involved in cellular oxidative defence. Supporting this hypothesis, the ΔNp63α isoform of p63 is expressed at high levels in the proliferative basal layer of the epidermis. Here we identify the CYGB gene as a novel transcriptional target of ΔNp63 that is involved in maintaining epidermal oxidative defence. The CYGB gene encodes cytoglobin, a member of the globin protein family, which facilitates the diffusion of oxygen through tissues and acts as a scavenger for nitric oxide or other ROS. By performing promoter activity assays and chromatin immunoprecipitation, reverse transcriptase quantitative PCR and western blotting analyses, we confirm the direct regulation of CYGB by ΔNp63α. We also demonstrate that CYGB has a protective role in proliferating keratinocytes grown under normal conditions, as well as in cells treated with exogenous hydrogen peroxide. These results indicate that ΔNp63, through its target CYGB has an important role in the cellular antioxidant system and protects keratinocytes from oxidative stress-induced apoptosis. The ΔNp63-CYGB axis is also present in lung and breast cancer cell lines, indicating that CYGB-mediated ROS-scavenging activity may also have a role in epithelial tumours. In human lung cancer data sets, the p63-CYGB interaction significantly predicts reduction of patient survival.

ERβ-dependent neuroglobin up-regulation impairs 17β-estradiol-induced apoptosis in DLD-1 colon cancer cells upon oxidative stress injury

Besides other mechanism(s) 17β-estradiol (E2) facilitates neuronal survival by increasing, via estrogen receptor β (ERβ), the levels of neuroglobin (NGB) an anti-apoptotic protein. In contrast, E2 could exert protective effects in cancer cells by activating apoptosis when the ERβ level prevails on that of ERα as in colon cancer cell lines. These apparently contrasting results raise the possibility that E2-induced NGB up-regulation could regulate the ERβ activities shunning this receptor subtype to trigger an apoptotic cascade in neurons but not in non-neuronal cells. Here, human colorectal adenocarcinoma cell line (DLD-1) that only expresses ERβ and HeLa cells transiently transfected with ERβ encoding vector has been used to verify this hypothesis. In addition, neuroblastoma SK-N-BE cells were used as positive control. Surprisingly, E2 also induced NGB up-regulation, in a dose- and time-dependent manner, in DLD-1 cells. The ERβ-mediated activation of p38/MAPK was necessary for this E2 effect. E2 induced NGB re-allocation in mitochondria where, subsequently to an oxidative stress injury (i.e., 100μM H2O2), NGB interacted with cytochrome c preventing its release into the cytosol and the activation of an apoptotic cascade. As a whole, these results demonstrate that E2-induced NGB up-regulation could act as an oxidative stress sensor, which does not oppose to the pro-apoptotic E2 effect in ERβ-containing colon cancer cells unless a rise of oxidative stress occurs. These results support the concept that oxidative stress plays a critical role in E2-induced carcinogenesis and further open an important scenario to develop novel therapeutic strategies that target NGB against E2-related cancers.

The globin superfamily: functions in nitric oxide formation and decay

Globin proteins are ubiquitous in living organisms and carry out a variety of functions related to the ability of their prosthetic heme group to bind gaseous ligands, such as oxygen, nitric oxide (NO), and CO. Moreover, they catalyze important reactions with nitrogen oxide species, such as NO dioxygenation and nitrite reduction. The formation of NO from nitrite is a reaction catalyzed by globins that has received increasing attention due to its potential as a hypoxic NO signaling mechanism. In this review, we revisit the current knowledge about the role of globins in NO formation and its physiological implications.

Neuroglobin, a pro-survival player in estrogen receptor α-positive cancer cells

Recently, we reported that human neuroglobin (NGB) is a new player in the signal transduction pathways that lead to 17β-estradiol (E2)-induced neuron survival. Indeed, E2 induces in neuron mitochondria the enhancement of NGB level, which in turn impairs the activation of a pro-apoptotic cascade. Nowadays, the existence of a similar pathway activated by E2 in non-neuronal cells is completely unknown. Here, the role of E2-induced NGB upregulation in tumor cells is reported. E2 induced the upregulation of NGB in a dose- and time-dependent manner in MCF-7, HepG2, SK-N-BE, and HeLa cells transfected with estrogen receptor α (ERα), whereas E2 was unable to modulate the NGB expression in the ERα-devoid HeLa cells. Both transcriptional and extranuclear ERα signals were required for the E2-dependent upregulation of NGB in MCF-7 and HepG2 cell lines. E2 stimulation modified NGB intracellular localization, inducing a significant reduction of NGB in the nucleus with a parallel increase of NGB in the mitochondria in both HepG2 and MCF-7 cells. Remarkably, E2 pretreatment did not counteract the H2O2-induced caspase-3 and poly (ADP-ribose) polymerase 1 (PARP-1) cleavage, as well as Bcl-2 overexpression in MCF-7 and HepG2 cells in which NGB was stably silenced by using shRNA lentiviral particles, highlighting the pivotal role of NGB in E2-induced antiapoptotic pathways in cancer cells. Present results indicate that the E2-induced NGB upregulation in cancer cells could represent a defense mechanism of E2-related cancers rendering them insensitive to oxidative stress. As a whole, these data open new avenues to develop therapeutic strategies against E2-related cancers.

Cytoglobin in tumor hypoxia: novel insights into cancer suppression

Emerging new and intriguing roles of cytoglobin (Cygb) have attracted considerable attention of cancer researchers in recent years. Hypoxic upregulation of Cygb as well as its altered expression in various human cancers suggest another possible role of this newly discovered globin in tumor cell response under low oxygen tension. Since tumor hypoxia is strongly associated with malignant progression of disease and poor treatment response, it constitutes an area of paramount importance for rational design of cancer selective therapies. However, the mechanisms involved during this process are still elusive. This review outlines the current understanding of Cygb's involvement in tumor hypoxia and discusses its role in tumorigenesis. A better perception of Cygb in tumor hypoxia response is likely to open novel perspectives for future tumor therapy.