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

Neuroglobin Facilitates Neuronal Oxygenation through Tropic Migration under Hypoxia or Anemia in Rat: How Does the Brain Breathe?

The discovery of neuroglobin (Ngb), a brain- or neuron-specific member of the hemoglobin family, has revolutionized our understanding of brain oxygen metabolism. Currently, how Ngb plays such a role remains far from clear. Here, we report a novel mechanism by which Ngb might facilitate neuronal oxygenation upon hypoxia or anemia. We found that Ngb was present in, co-localized to, and co-migrated with mitochondria in the cell body and neurites of neurons. Hypoxia induced a sudden and prominent migration of Ngb towards the cytoplasmic membrane (CM) or cell surface in living neurons, and this was accompanied by the mitochondria. In vivo, hypotonic and anemic hypoxia induced a reversible Ngb migration toward the CM in cerebral cortical neurons in rat brains but did not alter the expression level of Ngb or its cytoplasm/mitochondria ratio. Knock-down of Ngb by RNA interference significantly diminished respiratory succinate dehydrogenase (SDH) and ATPase activity in neuronal N2a cells. Over-expression of Ngb enhanced SDH activity in N2a cells upon hypoxia. Mutation of Ngb at its oxygen-binding site (His64) significantly increased SDH activity and reduced ATPase activity in N2a cells. Taken together, Ngb was physically and functionally linked to mitochondria. In response to an insufficient oxygen supply, Ngb migrated towards the source of oxygen to facilitate neuronal oxygenation. This novel mechanism of neuronal respiration provides new insights into the understanding and treatment of neurological diseases such as stroke and Alzheimer's disease and diseases that cause hypoxia in the brain such as anemia.

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.

Neuroglobin plays as tumor suppressor by disrupting the stability of GPR35 in colorectal cancer

BACKGROUND

The incidence of colorectal cancer (CRC) has increased in recent years. Identification of accurate tumor markers has become the focus of CRC research. Early and frequent DNA methylation tends to occur in cancer. Thus, identifying accurate methylation biomarkers would improve the efficacy of CRC treatment. Neuroglobin (NGB) is involved in neurological and oncological diseases. However, there are currently no reports on epigenetic regulation involvement of NGB in CRC.

RESULTS

NGB was downregulated or silenced in majority CRC tissues and cell lines. The hypermethylation of NGB was detected in tumor tissue, but no or a very low methylation frequency in normal tissues. Overexpression of NGB induced G2/M phase arrest and apoptosis, suppressed proliferation, migration, invasion in vitro, and inhibited CRC tumor growth and angiogenesis in vivo. Isobaric tag for relative and absolute quantitation (Itraq)-based proteomics identified approximately 40% proteins related to cell-cell adhesion, invasion, and tumor vessel formation in the tumor microenvironment, among which GPR35 was proved critical for NGB-regulated tumor angiogenesis suppression in CRC.

CONCLUSIONS

NGB, an epigenetically silenced factor, inhibits metastasis through the GPR35 in CRC. It is expected to grow into a potential cancer risk assessment factor and a valuable biomarker for early diagnosis and prognosis assessment of CRC.

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.

Proteomic and Bioinformatic Investigation of Altered Pathways in Neuroglobin-Deficient Breast Cancer Cells

Neuroglobin (NGB) is a myoglobin-like monomeric globin that is involved in several processes, displaying a pivotal redox-dependent protective role in neuronal and extra-neuronal cells. NGB remarkably exerts its function upon upregulation by NGB inducers, such as 17β-estradiol (E2) and H₂O₂. However, the molecular bases of NGB’s functions remain undefined, mainly in non-neuronal cancer cells. Human MCF-7 breast cancer cells with a knocked-out (KO) NGB gene obtained using CRISPR/Cas9 technology were analyzed using shotgun label-free quantitative proteomics in comparison with control cells. The differential proteomics experiments were also performed after treatment with E2, H₂O₂, and E2 + H₂O₂. All the runs acquired using liquid chromatography–tandem mass spectrometry were elaborated within the same MaxQuant analysis, leading to the quantification of 1872 proteins in the global proteomic dataset. Then, a differentially regulated protein dataset was obtained for each specific treatment. After the proteomic study, multiple bioinformatics analyses were performed to highlight unbalanced pathways and processes. Here, we report the proteomic and bioinformatic investigations concerning the effects on cellular processes of NGB deficiency and cell treatments. Globally, the main processes that were affected were related to the response to stress, cytoskeleton dynamics, apoptosis, and mitochondria-driven pathways.

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.

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.

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.

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 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.