NGF promotes copper accumulation required for optimum neurite outgrowth and protein methylation

The physiological and pathophysiological roles of copper in the nervous system

Copper is a critical trace element in biological systems due the vast number of essential enzymes that require the metal as a cofactor, including cytochrome c oxidase, superoxide dismutase and dopamine-β-hydroxylase. Due its key role in oxidative metabolism, antioxidant defence and neurotransmitter synthesis, copper is particularly important for neuronal development and proper neuronal function. Moreover, increasing evidence suggests that copper also serves important functions in synaptic and network activity, the regulation of circadian rhythms, and arousal. However, it is important to note that because of copper's ability to redox cycle and generate reactive species, cellular levels of the metal must be tightly regulated to meet cellular needs while avoiding copper-induced oxidative stress. Therefore, it is essential that the intricate system of copper transporters, exporters, copper chaperones and copper trafficking proteins function properly and in coordinate fashion. Indeed, disorders of copper metabolism such as Menkes disease and Wilson disease, as well as diseases linked to dysfunction of copper-requiring enzymes, such as SOD1-linked amyotrophic lateral sclerosis, demonstrate the dramatic neurological consequences of altered copper homeostasis. In this review, we explore the physiological importance of copper in the nervous system as well as pathologies related to improper copper handling.

PTPN2 copper-sensing rapidly relays copper level fluctuations into EGFR/CREB activation and associated CTR1 transcriptional repression

Fluxes in human intra- and extracellular copper levels recently garnered attention for roles in cellular signaling, including affecting levels of the signaling molecule cyclic adenosine monophosphate (cAMP). We herein applied an unbiased temporal evaluation of the whole-genome transcriptional activities modulated by fluctuations in copper levels to identify the copper sensor proteins responsible for driving these activities. We found that fluctuations in physiologically-relevant copper levels rapidly modulate EGFR/MAPK/ERK signal transduction and activation of the transcription factor cAMP response element-binding protein (CREB). Both intracellular and extracellular assays support Cu 1+ inhibition of the EGFR-phosphatase PTPN2 (and potentially the homologous PTPN1)-via direct ligation to the PTPN2 active site cysteine side chain-as the underlying mechanism of copper-stimulated EGFR signal transduction activation. Depletion of copper represses this signaling pathway. We additionally show i ) copper supplementation drives transcriptional repression of the copper importer CTR1 and ii ) CREB activity is inversely correlated with CTR1 expression. In summary, our study reveals PTPN2 as a physiological copper sensor and defines a regulatory mechanism linking feedback control of copper-stimulated MAPK/ERK/CREB-signaling and CTR1 expression, thereby uncovering a previously unrecognized link between copper levels and cellular signal transduction.

Mechanistic investigation of the differential synergistic neurotoxicity between pesticide metam sodium and copper or zinc

Epidemiological studies suggest neurological disorders have been associated with the co-exposure to certain pesticides and transition metals. The present study aims to investigate whether co-exposure to the widely-used pesticide metam sodium and copper (Cu²⁺) or zinc ion (Zn²⁺) is able to cause synergistic neurotoxicity in neural PC12 cells and its possible mechanism(s). We found that both metam/Cu²⁺ and metam/Zn²⁺ synergistically induced apoptosis, intracellular Cu²⁺/Zn²⁺ uptake, reactive oxygen species (ROS) accumulation, double-strand DNA breakage, mitochondrial membrane potential decrease, and nerve function disorder. In addition, metam/Cu²⁺ was shown to release cytochrome c and apoptosis-inducing factor (AIF) from mitochondria to cytoplasm and nucleus, respectively, and activate the caspase 9, 8, 3, 7. However, metam/Zn²⁺ induced caspase 7 activation and AIF translocation and mildly activated cytochrome c/caspase 9/caspase 3 pathway. Furthermore, metam/Cu²⁺ activated caspase 3/7 by the p38 pathway, whereas metam/Zn²⁺ did so via both the p38 and JNK pathways. These results demonstrated that metam/Cu²⁺ or metam/Zn²⁺ co-exposure cause synergistic neurotoxicity via different mechanisms, indicating a potential risk to human health when they environmentally co-exist.

The Role of Metals in the Neuroregenerative Action of BDNF, GDNF, NGF and Other Neurotrophic Factors

Mature neurotrophic factors and their propeptides play key roles ranging from the regulation of neuronal growth and differentiation to prominent participation in neuronal survival and recovery after injury. Their signaling pathways sculpture neuronal circuits during brain development and regulate adaptive neuroplasticity. In addition, neurotrophic factors provide trophic support for damaged neurons, giving them a greater capacity to survive and maintain their potential to regenerate their axons. Therefore, the modulation of these factors can be a valuable target for treating or preventing neurologic disorders and age-dependent cognitive decline. Neuroregenerative medicine can take great advantage by the deepening of our knowledge on the molecular mechanisms underlying the properties of neurotrophic factors. It is indeed an intriguing topic that a significant interplay between neurotrophic factors and various metals can modulate the outcome of neuronal recovery. This review is particularly focused on the roles of GDNF, BDNF and NGF in motoneuron survival and recovery from injuries and evaluates the therapeutic potential of various neurotrophic factors in neuronal regeneration. The key role of metal homeostasis/dyshomeostasis and metal interaction with neurotrophic factors on neuronal pathophysiology is also highlighted as a novel mechanism and potential target for neuronal recovery. The progress in mechanistic studies in the field of neurotrophic factor-mediated neuroprotection and neural regeneration, aiming at a complete understanding of integrated pathways, offers possibilities for the development of novel neuroregenerative therapeutic approaches.

Abnormal Development of Neural Stem Cell Niche in the Dentate Gyrus of Menkes Disease

Background and Objectives

Menkes disease (MNK) is a rare X-linked recessive disease, caused by mutations in the copper transporting ATP7A gene that is required for copper homeostasis. MNK patients experience various clinical symptoms including neurological defects that are closely related to the prognosis of MNK patients. Neural stem cells (NSCs) in the hippocampal dentate gyrus (DG) produce new neurons throughout life, and defects in DG neurogenesis are often correlated with cognitive and behavioral problems. However, neurodevelopmental defects in the DG during postnatal period in MNK have not been understood yet.

Methods and Results

Mottled-brindled (Mo^Br/y) mice (MNK mice) and littermate controls were used in this study. In vivo microCT imaging and immunohistochemistry results demonstrate that blood vasculatures in hippocampus are abnormally decreased in MNK mice. Furthermore, postnatal establishment of NSC population and their neurogenesis are severely compromised in the DG of MNK mice. In addition, in vitro analyses using hippocampal neurosphere culture followed by immunocytochemistry and immunoblotting suggest that neurogenesis from MNK NSCs is also significantly compromised, corresponding to defective neurogenic gene expression in MNK derived neurons.

Conclusions

Our study is the first reports demonstrating that improper expansion of the postnatal NSC population followed by significant reduction of neurogenesis may contribute to neurodevelopmental symptoms in MNK. In conclusion, our results provide new insight into early neurodevelopmental defects in MNK and emphasize the needs for early diagnosis and new therapeutic strategies in the postnatal central nerve system damage of MNK patients.

Copper Dyshomeostasis in Neurodegenerative Diseases-Therapeutic Implications

Copper is one of the most abundant basic transition metals in the human body. It takes part in oxygen metabolism, collagen synthesis, and skin pigmentation, maintaining the integrity of blood vessels, as well as in iron homeostasis, antioxidant defense, and neurotransmitter synthesis. It may also be involved in cell signaling and may participate in modulation of membrane receptor-ligand interactions, control of kinase and related phosphatase functions, as well as many cellular pathways. Its role is also important in controlling gene expression in the nucleus. In the nervous system in particular, copper is involved in myelination, and by modulating synaptic activity as well as excitotoxic cell death and signaling cascades induced by neurotrophic factors, copper is important for various neuronal functions. Current data suggest that both excess copper levels and copper deficiency can be harmful, and careful homeostatic control is important. This knowledge opens up an important new area for potential therapeutic interventions based on copper supplementation or removal in neurodegenerative diseases including Wilson's disease (WD), Menkes disease (MD), Alzheimer's disease (AD), Parkinson's disease (PD), and others. However, much remains to be discovered, in particular, how to regulate copper homeostasis to prevent neurodegeneration, when to chelate copper, and when to supplement it.

Inorganic Biomaterials for Regenerative Medicine

Regenerative medicine leverages the innate potential of the human body to efficiently repair and regenerate damaged tissues using engineered biomaterials. By designing responsive biomaterials with the appropriate biophysical and biochemical characteristics, cellular response can be modulated to direct tissue healing. Recently, inorganic biomaterials have been shown to regulate cellular responses including cell-cell and cell-matrix interactions. Moreover, ions released from these mineral-based biomaterials play a vital role in defining cell identity, as well as driving tissue-specific functions. The intrinsic properties of inorganic biomaterials, such as the release of bioactive ions (e.g., Ca, Mg, Sr, Si, B, Fe, Cu, Zn, Cr, Co, Mo, Mn, Au, Ag, V, Eu, and La), can be leveraged to induce phenotypic changes in cells or modulate the immune microenvironment to direct tissue healing and regeneration. Biophysical characteristics of biomaterials, such as topography, charge, size, electrostatic interactions, and stiffness can be modulated by addition of inorganic micro- and nanoparticles to polymeric networks have also been shown to play an important role in their biological response. In this Review, we discuss the recent emergence of inorganic biomaterials to harness the innate regenerative potential of the body. Specifically, we will discuss various biophysical or biochemical effects of inorganic-based materials in directing cellular response for regenerative medicine applications.

Advances in the mechanism of high copper diets in restraining pigs growth

High copper feed has been widely used as an inexpensive and highly effective feed additive to promote growth performance of pigs. However, long-term feeding of high copper feed may reduce the growth-promoting effects of copper, time-dependent accumulation of copper in animal tissues and organs, and copper toxicity thereby reducing the growth performance of pigs. Due to the widespread effects of high copper supplementation in animals' diets, the benefits and drawbacks of high copper feeding in pigs have been reported in several studies. Meanwhile, few of these studies have systematically described the mechanism by which high copper diets restrain pig growth. Therefore, to address the concerns and give a better understanding of the mechanism of high copper diet in restraining pig growth in different systems, this paper reviews the research progress of long-term supplementation of high copper on the growth of pigs and provides some suggestions and further research directions.

Copper complexes of synthetic peptides mimicking neurotrophin-3 enhance neurite outgrowth and CREB phosphorylation

In this work we report on the synthesis and physiochemical/biological characterization of a peptide encompassing the first thirteen residues of neurotrophin-3 (NT-3). The protein capability to promote neurite outgrowth and axonal branching by a downstream mechanism that involves the increase of the cAMP response element-binding level (CREB) was found for the NT3(1-13) peptide, thus validating its protein mimetic behaviour. Since copper ions are also involved in neurotransmission and their internalization may be an essential step in neuron differentiation and CREB phosphorylation, the peptide and its copper complexes were characterized by potentiometric and spectroscopic techniques, including UV-visible, CD and EPR. To have a detailed picture of the coordination features of the copper complexes with NT3(1-13), we also scrutinized the two peptide fragments encompassing the shorter sequences 1-5 and 5-13, respectively, showing that the amino group is the main anchoring site for Cu(ii) at physiological pH. The peptide activity increased in the presence of copper ions. The effect of copper(ii) addition is more marked for NT3(1-13) than the other two peptide fragments, in agreement with its higher affinity for metal ions. Confocal microscopy measurements carried out on fluorescently labelled NT3(1-13) indicated that copper ions increase peptide internalization.

The Copper(II)-Assisted Connection between NGF and BDNF by Means of Nerve Growth Factor-Mimicking Short Peptides

Nerve growth factor (NGF) is a protein necessary for development and maintenance of the sympathetic and sensory nervous systems. We have previously shown that the NGF N-terminus peptide NGF(1-14) is sufficient to activate TrkA signaling pathways essential for neuronal survival and to induce an increase in brain-derived neurotrophic factor (BDNF) expression. Cu2+ ions played a critical role in the modulation of the biological activity of NGF(1-14). Using computational, spectroscopic, and biochemical techniques, here we report on the ability of a newly synthesized peptide named d-NGF(1-15), which is the dimeric form of NGF(1-14), to interact with TrkA. We found that d-NGF(1-15) interacts with the TrkA-D5 domain and induces the activation of its signaling pathways. Copper binding to d-NGF(1-15) stabilizes the secondary structure of the peptides, suggesting a strengthening of the noncovalent interactions that allow for the molecular recognition of D5 domain of TrkA and the activation of the signaling pathways. Intriguingly, the signaling cascade induced by the NGF peptides ultimately involves cAMP response element-binding protein (CREB) activation and an increase in BDNF protein level, in keeping with our previous result showing an increase of BDNF mRNA. All these promising connections can pave the way for developing interesting novel drugs for neurodegenerative diseases.

Copper Binding Features of Tropomyosin-Receptor-Kinase-A Fragment: Clue for Neurotrophic Factors and Metals Link

The nerve growth factor (NGF) is a neurotrophin essential for the development and maintenance of neurons, whose activity is influenced by copper ions. The NGF protein exerts its action by binding to its specific receptor, TrkA. In this study, a specific domain of the TrkA receptor, region 58⁻64, was synthesized and its copper(II) complexes characterized by means of potentiometric and spectroscopic studies. The two vicinal histidine residues provide excellent metal anchoring sites and, at physiological pH, a complex with the involvement of the peptide backbone amide nitrogen is the predominant species. The TrkA peptide is competitive for metal binding with analogous peptides due to the N-terminal domain of NGF. These data provide cues for future exploration of the effect of metal ions on the activity of the NGF and its specific cellular receptor.

The Inorganic Side of NGF: Copper(II) and Zinc(II) Affect the NGF Mimicking Signaling of the N-Terminus Peptides Encompassing the Recognition Domain of TrkA Receptor

The nerve growth factor (NGF) N-terminus peptide, NGF(1–14), and its acetylated form, Ac-NGF(1–14), were investigated to scrutinize the ability of this neurotrophin domain to mimic the whole protein. Theoretical calculations demonstrated that non-covalent forces assist the molecular recognition of TrkA receptor by both peptides. Combined parallel tempering/docking simulations discriminated the effect of the N-terminal acetylation on the recognition of NGF(1–14) by the domain 5 of TrkA (TrkA-D5). Experimental findings demonstrated that both NGF(1–14) and Ac-NGF(1–14) activate TrkA signaling pathways essential for neuronal survival. The NGF-induced TrkA internalization was slightly inhibited in the presence of Cu²⁺ and Zn²⁺ ions, whereas the metal ions elicited the NGF(1–14)-induced internalization of TrkA and no significant differences were found in the weak Ac-NGF(1–14)-induced receptor internalization. The crucial role of the metals was confirmed by experiments with the metal-chelator bathocuproine disulfonic acid, which showed different inhibitory effects in the signaling cascade, due to different metal affinity of NGF, NGF(1–14) and Ac-NGF(1–14). The NGF signaling cascade, activated by the two peptides, induced CREB phosphorylation, but the copper addition further stimulated the Akt, ERK and CREB phosphorylation in the presence of NGF and NGF(1–14) only. A dynamic and quick influx of both peptides into PC12 cells was tracked by live cell imaging with confocal microscopy. A significant role of copper ions was found in the modulation of peptide sub-cellular localization, especially at the nuclear level. Furthermore, a strong copper ionophoric ability of NGF(1–14) was measured. The Ac-NGF(1–14) peptide, which binds copper ions with a lower stability constant than NGF(1–14), exhibited a lower nuclear localization with respect to the total cellular uptake. These findings were correlated to the metal-induced increase of CREB and BDNF expression caused by NGF(1–14) stimulation. In summary, we here validated NGF(1–14) and Ac-NGF(1–14) as first examples of monomer and linear peptides able to activate the NGF-TrkA signaling cascade. Metal ions modulated the activity of both NGF protein and the NGF-mimicking peptides. Such findings demonstrated that NGF(1–14) sequence can reproduce the signal transduction of whole protein, therefore representing a very promising drug candidate for further pre-clinical studies.

Changes in intracellular copper concentration and copper-regulating gene expression after PC12 differentiation into neurons

It is suspected that some neurodegenerative diseases are a result of the disturbance of copper (Cu) homeostasis, although it remains unclear whether the disturbance of Cu homeostasis has aberrant effects on neurons. Herein, we investigated Cu metabolism specifically in neurons in terms of changes in the intracellular Cu concentration and the expression of Cu-regulating genes, such as Cu transporters and metallothioneins (MTs), before and after the differentiation of rat pheochromocytoma cells (PC12 cells) into neurons. After the differentiation, Cu and Zn imaging with fluorescent probes revealed an increase in intracellular Cu concentration. The concentrations of other essential metals, which were determined by an inductively coupled plasma mass spectrometer, were not altered. The mRNA expression of the Cu influx transporter, Ctr1, was decreased after the differentiation, and the differentiated cells acquired tolerance to Cu and cisplatin, another substrate of Ctr1. In addition, the expression of MT-3, a brain-specific isoform, was increased, contrary to the decreased expression of MT-1 and MT-2. Taken together, the differentiation of PC12 cells into neurons induced MT-3 expression, thereby resulting in intracellular Cu accumulation. The decrease in Ctr1 expression was assumed to be a response aimed at abolishing the physiological accumulation of Cu after the differentiation.

Influence of the N-terminus acetylation of Semax, a synthetic analog of ACTH(4-10), on copper(II) and zinc(II) coordination and biological properties

Semax is a heptapeptide (Met-Glu-His-Phe-Pro-Gly-Pro) that encompasses the sequence 4-7 of N-terminal domain of the adrenocorticotropic hormone and a C-terminal Pro-Gly-Pro tripeptide. N-terminal amino group acetylation (Ac-Semax) modulates the chemical and biological properties of parental peptide, modifying the ability of Semax to form complex species with Cu(II) ion. At physiological pH, the main complex species formed by Ac-Semax, [CuLH_-2]^2-, consists in a distorted CuN₃O chromophore with a weak apical interaction of the methionine sulphur. Such a complex differs from the Cu(II)-Semax complex system, which exhibits a CuN₄ chromophore. The reduced ligand field affects the [CuLH_-2]^2- formal redox potential, which is more positive than that of Cu(II)-Semax corresponding species. In the amino-free form, the resulting complex species is redox-stable and unreactive against ascorbic acid, unlike the acetylated form. Semax acetylation did not protect from Cu(II) induced toxicity on a SH-SY5Y neuroblastoma cell line, thus demonstrating the crucial role played by the free NH₂ terminus in the cell protection. Since several brain diseases are associated either to Cu(II) or Zn(II) dyshomeostasis, here we characterized also the complex species formed by Zn(II) with Semax and Ac-Semax. Both peptides were able to form Zn(II) complex species with comparable strength. Confocal microscopy imaging confirmed that peptide group acetylation does not affect the Zn(II) influx in neuroblastoma cells. Moreover, a punctuate distribution of Zn(II) within the cells suggests a preferred subcellular localization that might explain the zinc toxic effect. A future perspective can be the use of Ac-Semax as ionophore in antibody drug conjugates to produce a dysmetallostasis in tumor cells.

Arginine Methyltransferase 1 in the Nucleus Accumbens Regulates Behavioral Effects of Cocaine

Recent evidence suggests that histone modifications play a role in the behavioral effects of cocaine in rodent models. Histone arginine is known to be methylated by protein arginine N-methyltransferases (PRMTs). Evidence shows that PRMT1 contributes to >90% of cellular PRMT activity, which regulates histone H4 arginine 3 asymmetric dimethylation (H4R3me2a). Though histone arginine methylation represents a chemical modification that is relatively stable compared with other histone alterations, it is less well studied in the setting of addiction. Here, we demonstrate that repeated noncontingent cocaine injections increase PRMT1 activity in the nucleus accumbens (NAc) of C57BL/6 mice. We, subsequently, identify a selective inhibitor of PRMT1, SKLB-639, and show that systemic injections of the drug decrease cocaine-induced conditioned place preference to levels observed with genetic knockdown of PRMT1. NAc-specific downregulation of PRMT1 leads to hypomethylation of H4R3me2a, and hypoacetylation of histone H3 lysine 9 and 14. We also found that H4R3me2a is upregulated in NAc after repeated cocaine administration, and that H4R3me2a upregulation in turn controls the expression of Cdk5 and CaMKII. Additionally, the suppression of PRMT1 in NAc with lentiviral-short hairpin PMRT1 decreases levels of CaMKII and Cdk5 in the cocaine-treated group, demonstrating that PRMT1 affects the ability of cocaine to induce CaMKII and Cdk5 in NAc. Notably, increased H4R3me2a by repeated cocaine injections is relatively long-lived, as increased expression was observed for up to 7 d after the last cocaine injection. These results show the role of PRMT1 in the behavioral effects of cocaine.

SIGNIFICANCE STATEMENT

This work demonstrated that repeated cocaine injections led to an increase of protein arginine N-methyltransferase (PRMT1) in nucleus accumbens (NAc). We then identified a selective inhibitor of PRMT1 (SKLB-639), which inhibited cocaine-induced conditioned place preference (CPP). Additionally, genetic downregulation of PRMT1 in NAc also attenuated cocaine-caused CPP and locomotion activity, which was associated with decreased expression of histone H4 arginine 3 asymmetric demethylation (H4R3me2a) and hypoacetylation of histone H3 lysine 9 and 14 (acH3K9/K14). This study also showed that H4R3me2a controlled transcriptions of Cdk5 and CaMKII, and that PRMT1 negatively affected the ability of cocaine to induce CaMKII and Cdk5 in NAc. Notably, increased H4R3me2a by repeated cocaine injection was relatively long-lived as increased expression was observed up to 7 d after withdrawal from cocaine. Together, this study suggests that PRMT1 inhibition may serve as a potential therapeutic strategy for cocaine addiction.

Copper as a key regulator of cell signalling pathways

Copper is an essential element in many biological processes. The critical functions associated with copper have resulted from evolutionary harnessing of its potent redox activity. This same property also places copper in a unique role as a key modulator of cell signal transduction pathways. These pathways are the complex sequence of molecular interactions that drive all cellular mechanisms and are often associated with the interplay of key enzymes including kinases and phosphatases but also including intracellular changes in pools of smaller molecules. A growing body of evidence is beginning to delineate the how, when and where of copper-mediated control over cell signal transduction. This has been driven by research demonstrating critical changes to copper homeostasis in many disorders including cancer and neurodegeneration and therapeutic potential through control of disease-associated cell signalling changes by modulation of copper-protein interactions. This timely review brings together for the first time the diverse actions of copper as a key regulator of cell signalling pathways and discusses the potential strategies for controlling disease-associated signalling processes using copper modulators. It is hoped that this review will provide a valuable insight into copper as a key signal regulator and stimulate further research to promote our understanding of copper in disease and therapy.

Neuroprotective copper bis(thiosemicarbazonato) complexes promote neurite elongation

Abnormal biometal homeostasis is a central feature of many neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD), and motor neuron disease. Recent studies have shown that metal complexing compounds behaving as ionophores such as clioquinol and PBT2 have robust therapeutic activity in animal models of neurodegenerative disease; however, the mechanism of neuroprotective action remains unclear. These neuroprotective or neurogenerative processes may be related to the delivery or redistribution of biometals, such as copper and zinc, by metal ionophores. To investigate this further, we examined the effect of the bis(thiosemicarbazonato)-copper complex, Cu(II)(gtsm) on neuritogenesis and neurite elongation (neurogenerative outcomes) in PC12 neuronal-related cultures. We found that Cu(II)(gtsm) induced robust neurite elongation in PC12 cells when delivered at concentrations of 25 or 50 nM overnight. Analogous effects were observed with an alternative copper bis(thiosemicarbazonato) complex, Cu(II)(atsm), but at a higher concentration. Induction of neurite elongation by Cu(II)(gtsm) was restricted to neurites within the length range of 75-99 µm with a 2.3-fold increase in numbers of neurites in this length range with 50 nM Cu(II)(gtsm) treatment. The mechanism of neurogenerative action was investigated and revealed that Cu(II)(gtsm) inhibited cellular phosphatase activity. Treatment of cultures with 5 nM FK506 (calcineurin phosphatase inhibitor) resulted in analogous elongation of neurites compared to 50 nM Cu(II)(gtsm), suggesting a potential link between Cu(II)(gtsm)-mediated phosphatase inhibition and neurogenerative outcomes.

Immunohistochemical detection of arginine methylated proteins (MeRP) in archival tissues

AIMS

To (i) determine whether methylarginine-specific antibodies can be employed for standard immunohistochemical analysis of paraffin-embedded tissues, (ii) analyse methylarginine expression in normal and neoplastic tissues and (iii) correlate methylarginine expression with that of protein arginine methyltransferase (PRMT1), the predominant cellular arginine methyltransferase.

METHODS AND RESULTS

Immunohistochemistry of normal and cancer tissues was performed utilizing three commercial polyclonal antibodies: anti-methylarginine-specific antibody (anti-mRG) raised against a methylarginine peptide, Control antibody (anti-RG), a control antiserum raised against a corresponding arginine peptide without any methylated residues and anti-PRMT1. Nuclear and/or cytoplasmic methylarginine expression was detected in all keratinized and non-keratinized epithelia. A preliminary survey of a series of thyroid, pancreatic, colonic and gastric cancers identified a different pattern of methylarginine expression in comparison with normal tissue. A correlation between methylarginine staining and PRMT1 expression was found in all normal and cancer tissues analysed.

CONCLUSION

Methylarginine-specific antibodies are capable of recognizing methylarginine proteins (MeRP) in paraffin-embedded tissues. Methylarginine proteins are expressed widely and show differences in subcellular localization in various organs and neoplastic conditions. The efficient detection of methylproteins by standard immunohistochemistry provides a new tool to investigate the role of methylarginine proteins (MeRP) in biological processes including carcinogenesis.

Copper promotes the trafficking of the amyloid precursor protein

Accumulation of the amyloid β peptide in the cortical and hippocampal regions of the brain is a major pathological feature of Alzheimer disease. Amyloid β peptide is generated from the sequential protease cleavage of the amyloid precursor protein (APP). We reported previously that copper increases the level of APP at the cell surface. Here we report that copper, but not iron or zinc, promotes APP trafficking in cultured polarized epithelial cells and neuronal cells. In SH-SY5Y neuronal cells and primary cortical neurons, copper promoted a redistribution of APP from a perinuclear localization to a wider distribution, including neurites. Importantly, a change in APP localization was not attributed to an up-regulation of APP protein synthesis. Using live cell imaging and endocytosis assays, we found that copper promotes an increase in cell surface APP by increasing its exocytosis and reducing its endocytosis, respectively. This study identifies a novel mechanism by which copper regulates the localization and presumably the function of APP, which is of major significance for understanding the role of APP in copper homeostasis and the role of copper in Alzheimer disease.

Influence of copper on early development: prenatal and postnatal considerations

Copper (Cu) is an essential nutrient whose requirement is increased during pregnancy and lactation. These represent times of critical growth and development, and the fetus and neonate are particularly vulnerable to deficiencies of this nutrient. Genetic mutations that predispose the offspring to inadequate stores of Cu can be life threatening as is observed in children with Menkes disease. During the last decade, severe Cu deficiency, once thought to be a rare condition, has been reported in the literature at an increasing frequency. Secondary Cu deficiencies can be induced by a variety of ways such as excessive zinc or iron intake, certain drugs, and bariatric surgery. Premature and low birth weight infants can be born with low Cu stores. A number of mechanisms can contribute to the teratogenicity of Cu including decreased activity of select cuproenzymes, increased oxidative stress, decreased nitric oxide availability, altered iron metabolism, abnormal extracellular matrix protein crosslinking, decreased angiogenesis and altered cell signaling among others. The brain, heart, and vessels as well as tissues such as lung, skin and hair, and systems including the skeletal, immune, and blood systems, are negatively affected by suboptimal Cu during development. Additionally, persistent structural, biochemical, and functional adverse effects in the offspring are noted even when Cu supplementation is initiated after birth, supporting the concept that adequate Cu nutriture during pregnancy and lactation is critical for normal development. Although Cu-containing IUDs are an effective method for increasing intrauterine Cu concentrations and for reducing the risk of pregnancy, high amounts of dietary Cu are not thought to represent a direct developmental risk.

Copper modulates the differentiation of mouse hematopoietic progenitor cells in culture

Copper chelation has been shown to favor the expansion of human hematopoietic stem/progenitor cells in vitro. To further understand the effects of copper modulation on defined subsets of stem cells versus progenitor cells, we extended the studies in a mouse system. We isolated mouse hematopoietic stem cells (HSCs) or hematopoietic progenitor cells (HPCs) and cultured them with or without the copper chelator tetraethylenepentamine (TEPA) or CuCl(2). Cytokine-stimulated HPC cultures treated with TEPA for 7 days generated about two to three times more total and erythroid colony-forming cells (CFCs) compared to control cultures. In contrast, CuCl(2) treatment decreased the CFC numbers. Similar results were seen with HSC after 14, but not 7, days of culture. Transplant studies showed that HPCs cultured for 7 days in TEPA had about twofold higher short-term erythroid repopulation potential compared to control cultures, while CuCl(2) decreased the erythroid potential of cultured HPCs compared to control cultures. HSCs cultured with TEPA for 7 days did not exhibit significantly higher repopulation potential in either leukocyte or erythrocyte lineages compared to control cultures in short-term or long-term assays. Based on JC-1 staining, the mitochondrial membrane potential of HPCs cultured with TEPA was lower relative to control cultures. Our data suggest that decreasing the cellular copper content with TEPA results in preferential expansion or maintenance of HPC that are biased for erythroid differentiation in vivo, but does not enhance the maintenance of HSC activity in culture.

ATP7A is a novel target of retinoic acid receptor beta2 in neuroblastoma cells

Increased retinoic acid receptor β (RARβ₂) gene expression is a hallmark of cancer cell responsiveness to retinoid anticancer effects. Moreover, low basal or induced RARβ₂ expression is a common feature of many human cancers, suggesting that RARβ₂ may act as a tumour suppressor gene in the absence of supplemented retinoid. We have previously shown that low RARβ₂ expression is a feature of advanced neuroblastoma. Here, we demonstrate that the ABC domain of the RARβ₂ protein alone was sufficient for the growth inhibitory effects of RARβ₂ on neuroblastoma cells. ATP7A, the copper efflux pump, is a retinoid-responsive gene, was upregulated by ectopic overexpression of RARβ₂. The ectopic overexpression of the RARβ₂ ABC domain was sufficient to induce ATP7A expression, whereas, RARβ₂ siRNA blocked the induction of ATP7A expression in retinoid-treated neuroblastoma cells. Forced downregulation of ATP7A reduced copper efflux and increased viability of retinoid-treated neuroblastoma cells. Copper supplementation enhanced cell growth and reduced retinoid-responsiveness, whereas copper chelation reduced the viability and proliferative capacity. Taken together, our data demonstrates ATP7A expression is regulated by retinoic acid receptor β and it has effects on intracellular copper levels, revealing a link between the anticancer action of retinoids and copper metabolism.

PRMT1 and Btg2 regulates neurite outgrowth of Neuro2a cells

Neurite outgrowth is one of the crucial events in the formation of neural circuits. The majority of studies on neurite outgrowth have focused on signal transduction processes based on phosphorylation and acetylation; a few studies have suggested the involvement of other molecular mechanisms. Recent progress in understanding the nature of protein arginine N-methyltransferases (PRMTs) raises the possibility of the involvement of protein methylation accompanied by cell shape changes during neuronal differentiation. Here, we show that PRMT1 play a pivotal role in the neurite outgrowth of Neuro2a cells. Our results revealed that PRMT1 depletion specifically affected neurite outgrowth but not the physiological processes involved in cell growth and differentiation. Furthermore, we demonstrated that Btg2, one of the PRMT1 binding partner, depletion down-regulated arginine methylation in the nucleus and inhibited neurite outgrowth. These results indicate that protein arginine methylation by PRMT1 in the nucleus is an important step in neuritogenesis.

Novel role of antioxidant-1 (Atox1) as a copper-dependent transcription factor involved in cell proliferation

Copper plays a fundamental role in regulating cell growth. Many types of human cancer tissues have higher copper levels than normal tissues. Copper can also induce gene expression. However, transcription factors that mediate copper-induced cell proliferation have not been identified in mammals. Here we show that antioxidant-1 (Atox1), previously appreciated as a copper chaperone, represents a novel copper-dependent transcription factor that mediates copper-induced cell proliferation. Stimulation of mouse embryonic fibroblasts (MEFs) with copper markedly increased cell proliferation, cyclin D1 expression, and entry into S phase, which were completely abolished in Atox1(-/-) MEFs. Promoter analysis and EMSA revealed that copper stimulates the Atox1 binding to a previously undescribed cis element in the cyclin D1 promoter. The ChIP assay confirms that copper stimulates Atox1 binding to the DNA in vivo. Transfection of Atox1 fused to the DNA-binding domain of Gal4 demonstrated a copper-dependent transactivation in various cell types, including endothelial and cancer cells. Furthermore, Atox1 translocated to the nucleus in response to copper through its highly conserved C-terminal KKTGK motif and N-terminal copper-binding sites. Finally, the functional role of nuclear Atox1 is demonstrated by the observation that re-expression of nuclear-targeted Atox1 in Atox1(-/-) MEFs rescued the defective copper-induced cell proliferation. Thus, Atox1 functions as a novel transcription factor that, when activated by copper, undergoes nuclear translocation, DNA binding, and transactivation, thereby contributing to cell proliferation.

Generation of polyclonal antiserum for the detection of methylarginine proteins

This report describes an approach for the study of the biology of methylarginine proteins based on the generation of immunological reagents capable of recognizing the methylarginine status of cellular proteins. Two forms of an immunizing peptide were prepared based upon an amino acid sequence motif found most prevalently among verified dimethylarginine-containing proteins. One form of the peptide was constructed with 7 arginine residues alternating with 8 glycine residues. None of the arginines used in the synthesis were methylated. The alternative form of the peptide was synthesized with the identical repeating GRG sequence, but with asymmetrical dimethylarginine at each arginine residue. A methylarginine-specific antiserum was generated using the latter peptide. ELISA and western blotting of glycine arginine-rich peptides, each synthesized with or without asymmetric dimethylarginine, demonstrate the methyl specificity of the antiserum. The methylarginine-specific antibody co-localizes with the highly methylated native nucleolin protein conspicuously concentrated in the nucleolus. The methylarginine-specific antiserum recognizes a GRG peptide and bacterially expressed RBP16 only after incubation of the peptide or RBP16 with recombinant protein arginine methyltransferase 1, or cell extracts, respectively. Proteins isolated from cells in different developmental states exhibit different patterns of reactivity observed by western blots. Finally, the methylarginine-specific reagent interacts specifically with the methylarginine of cellular hnRNPA1 and human fragile X mental retardation protein expressed in cultured PC12 cells. An immunological reagent capable of detecting the methylarginine status of cellular methylproteins will facilitate the cellular and molecular analysis of protein arginine methylation in a wide variety of research and biomedical applications.

ATP7A (Menkes protein) functions in axonal targeting and synaptogenesis

Menkes disease (MD) is a neurodegenerative disorder caused by mutations in the copper transporter, ATP7A, a P-type ATPase. We previously used the olfactory system to demonstrate that ATP7A expression is developmentally, not constitutive, regulated, peaking during synaptogenesis when it is highly expressed in extending axons in a copper-independent manner. Although not known to be associated with axonal functions, we explored the possibility that the inability of mutant ATP7A to support axon outgrowth contributes to the neurodegeneration seen in MD. In vivo analysis of the olfactory system in mottled brindled (Atp7aMobr) mice, a rodent model for MD, demonstrates that ATP7A deficiency affects olfactory sensory neuron (OSN) maturation. Disrupted OSN axonal projections and mitral/tufted cell dendritic growth lead to altered synapse integrity and glomerular disorganization in the olfactory bulbs of Atp7aMobr mice. Our data indicate that the neuronal abnormalities observed in MD are a result of specific age-dependent developmental defects. This study demonstrates a role for ATP7A and/or copper in axon outgrowth and synaptogenesis, and will further help identify the cause of the neuropathology that characterizes MD.

Chelatable cellular copper modulates differentiation and self-renewal of cord blood-derived hematopoietic progenitor cells

OBJECTIVES

We have demonstrated epigenetic modulation of CD34(+) cell differentiation by the high-affinity copper (Cu) chelator tetraethylenepentamine (TEPA). TEPA slowed down the rate of CD34(+) cell differentiation and increased their engraftability in SCID mice. TEPA biological activity was attributed to its effect on cellular Cu levels as (a) treatment with TEPA resulted in reduction of cellular Cu, and (b) excess of Cu reversed TEPA's activity and accelerated differentiation. In the present study we further evaluated the role of cellular Cu in TEPA's biological activity.

METHODS

The effects of Cu-chloride, TEPA, TEPA/Cu mixtures at various ratios, and a synthesized, stable, TEPA-Cu complex on short- and long-term cord blood-derived CD34(+) cell cultures as well as on the overall and chelatable cellular Cu were investigated.

RESULTS

Addition of TEPA, TEPA/Cu mixtures at up to equimolar concentrations, and the TEPA-Cu complex to CD34(+) cell cultures resulted in inhibition of differentiation and enhancement of long-term self-renewal. Measurement of the overall cellular Cu by atomic absorption spectrophotometry showed 20 to 40% decrease by TEPA while the TEPA-Cu mixture and the TEPA-Cu complex increased cellular Cu by 10- to 20-fold, as did CuCl(2). However, measurement of the cellular pool of labile Cu showed similar reduction (50% from the control) by all the TEPA forms, while CuCl(2) increased it. Thus, inhibition of differentiation and enhancement of self-renewal of CD34(+) cells was correlated with reduction in the cellular chelatable Cu content.

CONCLUSION

The results suggest that decreasing of the chelatable Cu pool, rather than overall Cu, is the mechanism that stands behind TEPA's biological activity.