Tumor hypoxia induces nuclear paraspeckle formation through HIF-2α dependent transcriptional activation of NEAT1 leading to cancer cell survival.

Correction to: Oncogene (2015) 34, 4482­4490; doi:10.1038/onc.2014.378; published online 24 November 2014. Following the online publication of this article, the authors have noticed a misspelt surname: S Hider should read S Haider. There is also an addition to the acknowledgements to read 'This study makes use of data generated by the Molecular Taxonomy of Breast Cancer International Consortium, which was funded by Cancer Research UK and the British Columbia Cancer Agency Branch'. The corrected article appears in this issue. The authors would like to apologise for any inconvenience this may cause.

Tumor hypoxia induces nuclear paraspeckle formation through HIF-2α dependent transcriptional activation of NEAT1 leading to cancer cell survival.

Activation of cellular transcriptional responses, mediated by hypoxia-inducible factor (HIF), is common in many types of cancer, and generally confers a poor prognosis. Known to induce many hundreds of protein-coding genes, HIF has also recently been shown to be a key regulator of the non-coding transcriptional response. Here, we show that NEAT1 long non-coding RNA (lncRNA) is a direct transcriptional target of HIF in many breast cancer cell lines and in solid tumors. Unlike previously described lncRNAs, NEAT1 is regulated principally by HIF-2 rather than by HIF-1. NEAT1 is a nuclear lncRNA that is an essential structural component of paraspeckles and the hypoxic induction of NEAT1 induces paraspeckle formation in a manner that is dependent upon both NEAT1 and on HIF-2. Paraspeckles are multifunction nuclear structures that sequester transcriptionally active proteins as well as RNA transcripts that have been subjected to adenosine-to-inosine (A-to-I) editing. We show that the nuclear retention of one such transcript, F11R (also known as junctional adhesion molecule 1, JAM1), in hypoxia is dependent upon the hypoxic increase in NEAT1, thereby conferring a novel mechanism of HIF-dependent gene regulation. Induction of NEAT1 in hypoxia also leads to accelerated cellular proliferation, improved clonogenic survival and reduced apoptosis, all of which are hallmarks of increased tumorigenesis. Furthermore, in patients with breast cancer, high tumor NEAT1 expression correlates with poor survival. Taken together, these results indicate a new role for HIF transcriptional pathways in the regulation of nuclear structure and that this contributes to the pro-tumorigenic hypoxia-phenotype in breast cancer.

Superoxide radical scavenging and attenuation of hypoxia-reoxygenation injury by neurotransmitter ferric complexes in isolated rat hepatocytes.

Reactive oxygen species have been implicated in the pathogenesis of hypoxia-reoxygenation injury. Previously, we demonstrated that 2:1 catecholic iron complexes were more effective than uncomplexed catechols at (a) scavenging superoxide radicals generated enzymatically, and (b) protecting hepatocytes against hypoxia-reoxygenation injury [25]. Based on these findings, we sought to demonstrate similar effects using catecholamine neurotransmitters. Various catecholamine-iron complexes were shown to be more effective than uncomplexed catecholamines at scavenging superoxide radicals and could be used to protect cells from hypoxia-reoxygenation injury. alpha-Methyl-3, 4-dihydroxyphenylalanine (alpha-methylDOPA) complexed with ferric ion (2:1) showed the greatest superoxide scavenging potency amongst the catecholamine-iron complexes. The uncomplexed catecholamines were much less effective at scavenging superoxide radicals than the iron-catecholamine complexes. Dopamine was the most effective superoxide scavenger among the uncomplexed catecholamines. The superoxide scavenging effectiveness of the latter seemed to correlate with their reduction potentials, but not directly to their pK(a) values. Furthermore, dopamine:iron(III) complex protected isolated hepatocytes against hypoxia-reoxygenation injury at concentrations four-fold lower than that required for protection by dopamine alone.

What is the function of receptor and membrane endocytosis at the postsynaptic neuron?

This paper explores the implications of certain new developments in cell biology upon neuroscience. Until recently it was thought that neurotransmitters and neuromodulators had only one function, which was to stimulate their specific receptors at the cell surface. From here on, all activity was supposed to be effected by postsynaptic cascades. The discovery that membrane components, particularly G-protein-linked receptors, are not static but are subject to a massive and complex process of continual endocytosis, processing in the endosome system and recycling back to the external membrane, raises the question of its functional significance. In addition, it has been found that many neuromodulators such as polypeptides have their main locus of action inside the postsynaptic neuron. This review covers the role of the endocytic mechanism on receptor desensitization and resensitization, synaptic reorganization and plasticity synaptic scaling and the possible repair of oxidative damage. The possible involvement of this system in Alzheimer's disease is discussed.

Redox aspects of signaling by catecholamines and their metabolites.

This review covers certain novel aspects of catecholamine signaling in neurons that involve redox systems and synaptic plasticity. The redox hypothesis suggests that one important factor in neurocomputation is the formation of new synapses and the removal of old ones (synaptic plasticity), which is modulated in part by the redox balance at the synapse between reactive oxygen species (ROS) (such as hydrogen peroxide and the nitric oxide radical) and neuroprotective antioxidants (such as ascorbate, glutathione, and catecholamines). Catecholamines, in particular dopamine, which signals positive reinforcement, may play a key role in this activity. Dopamine has powerful antioxidant properties by several separate mechanisms-direct ROS scavenging, activation of the synthesis of antioxidant proteins, and possibly via dismuting complexes with iron inside endosomes or in catecholaminergic synaptic vesicles. This may contribute to synaptic growth and reinforcement-directed learning. On the other hand, catecholamines are easily oxidized to toxic quinones on the neuromelanin pathway. This might contribute under certain circumstances to synaptic deletion. Evidence is presented that abnormalities in this system may contribute to the pathogenesis of Parkinson's disease and schizophrenia.

The neurochemical basis of learning and neurocomputation: the redox theory.

This paper presents a new theory of the biochemical basis of learning and neurocomputation. It has now been determined that excitatory synapses on dendritic spines in the brain are continually being formed and removed. This requires a neurochemical mechanism. There is evidence to suggest that the redox state of the glutamate synapse plays an important role in determining the growth or deletion of that synapse. This redox state is controlled by the balance between the pro-oxidants hydrogen peroxide and the nitric acid radical, and the antioxidants ascorbate, carnosine, the nitrosium ion and catecholamines. Key enzymes involved are prostaglandin H synthase and nitric acid synthase. Mediation of signals of reinforcing stimuli by the catecholamines may be mediated in part by their antioxidant effect on glutamate synapses. Some experiments to test the theory are suggested.

Consciousness: some basic issues--A neurophilosophical perspective.

This paper concentrates on the basic properties of "consciousness" that temporal coding is postulated to relate to. A description of phenomenal consciousness based on what introspection tells us about its contents is offered. This includes a consideration of the effect of various brain lesions that result in cortical blindness, apperceptive and associative agnosia, and blindsight, together with an account of the manner in which sight is regained after cortical injuries. I then discuss two therories of perception-Direct Realism and the Representative Theory. This includes a discussion of the concept of the body-image, phantom limbs, the alleged projection of sensations, the ontological status of phenomenal space, the homunculus argument, the validity of topographic coding, the difference between the stimulus field and the visual field, and two theories of brain-mind relationship-the Identity Theory and the Bohr-Heisenberg theory of brain-mind complementarity. Finally I suggest that the binocular rivalry obtained in the case of the stroboscopic patterns that result from intermittent photic stimulation of one eye, when used in animal expeiments with unit recording, offers a good experimental method of investigating the binding problem.

Redox mechanisms at the glutamate synapse and their significance: a review.

This paper reviews what is currently known about the redox state of the glutamate synapse and its possible role in modulating synaptic plasticity and thus learning and neurocomputation. The hypothesis is presented that the growth or pruning of the synaptic spine is controlled in part by the balance in the synapse between neurodestructive pro-oxidants (e.g., nitric acid radical and hydrogen peroxide) and neuroprotective antioxidants (e.g., ascorbate and carnosine). In addition, there may be a role for catecholamines, in particular dopamine, related to its role in reinforcement signalling. Activation of the dopamine D2 receptor induces the synthesis of an antioxidant enzyme, possibly catalase. Dopamine may also affect the redox balance in the glutamate synapse directly by diffusion from the adjacent dopaminergic bouton-en-passage. Catecholamines are powerful antioxidants, scavengers of free radicals and iron chelators. Catecholamine-iron complexes are potent dismuters of superoxide ions. Additional agents participating in spine pruning may be neurotoxic catecholamine o-quinones present in the brain. This system may be at fault in schizophrenia and Parkinson's disease. Experiments to test the hypothesis are suggested.

The neurotoxicity of glutamate, dopamine, iron and reactive oxygen species: functional interrelationships in health and disease: a review-discussion.

The fact that glutamate, dopamine, iron and reactive oxygen species are potentially individually highly neurotoxic molecules is well known. The purpose of this review is to examine the less well known complex ways in which their normal biological, as well as their neurotoxic activity, are interconnected in relation to fundamental neuronal functions. These functions include synaptic plasticity (formation and removal of synapses), endocytosis-based recycling of receptors for neurotransmitters and neuromodulators, the role of the redox balance between reactive oxygen species and antioxidants in synaptic function, and the possible role of iron-catecholamine complexes in antioxidant protection and intraneuronal iron transport. These systems are closely involved in several diseases of the nervous system including Parkinson's disease, schizophrenia and Alzheimer's disease. In all these oxidative stress and a failure of antioxidant defenses are involved. In the former two the neurotoxicity of catecholaminergic o-quinones is important. In the later excessive oxidation of neuronal membranes and excessive endocytosis and receptor recycling may be an important factor.

The oxidative metabolism of catecholamines in the brain: a review.

This paper summarizes the strong evidence that we now have that the oxidative pathway of metabolism of the catecholamines, dopamine and norepinephrine via their respective quinones occurs in vivo in the brain. This fact is not yet widely appreciated. The evidence is based on the chemical structure of neuromelanin, advanced mass spectrometry techniques and the identification of intermediates of this system, such as 5-cysteinyl dopamine, in the brain. Supportive evidence is presented from a number of sources including enzymology. A suggestion as to the possible normal function of this system is made.

Oxidative reactions and schizophrenia: a review-discussion.

Now that definitive direct evidence has been obtained that oxidized metabolites of catecholamines-aminochrome (derived from dopamine) and related compounds-occur in the human brain the question this paper explores is what is their function there, if any. They are precursors of neuromelanin and are formed inter alia by co-oxidation by prostaglandin H synthase during the synthesis of prostaglandin H from arachidonic acid. Their further metabolism by NAHPD-cytochrome P450 reductase forms the highly neurotoxic o-semiquinone together with free oxygen radicals. The defenses against these orthoquinones (o-quinones) and o-semiquinones (which include reduction, O-methylation, 5-cysteinylization, glutathione conjugation, conversion to the o-hydroquinone, and neuromelanin formation), and their possible status in schizophrenia, are reviewed. This system is closely linked with glutamate neurotoxicity because glutamate receptors activate PGH synthase and because dopamine toxicity is mediated by these o-quinones acting on NMDA receptors. Interactions between glutamate and dopamine neurotoxicity are explored, including a possible role for the redox properties of catecholamines. The hypothesis is presented that some of the demonstrated cellular damage in the schizophrenic brain may be mediated by catecholamine o-quinones. The significance of the evidence from previous studies carried out 40 years ago, that a closely related catecholamine o-quinone-adrenochrome-has psychotomimetic properties in humans and behavior disrupting properties in animals, is reviewed in the light of these recent findings.

The biochemical basis of synaptic plasticity and neurocomputation: a new theory.

The recent finding that dendritic spines (on which 90% of all excitatory synapses on pyramidal cells are formed) are not permanent structures but are continually being formed and adsorbed has implications for the present theoretical basis of neurocomputation, which is largely based on the concept of fixed nerve nets. This evidence would tend to support the recent theories of Edelman, Freeman, Globus, Pribram and others that neuronal networks in the brain operate mainly as nonlinear dynamic, chaotic systems. This paper presents a hypothesis of a possible neurochemical mechanism underlying this synaptic plasticity based on reactive oxygen species and toxic 0-semiquinones derived from catecholamines (i) by the enzyme prostaglandin H synthetase induced by glutamatergic NMDA receptor activation and (ii) by reactive nitrogen species derived from nitric oxide in a low ascorbate environment. A key factor in this neuromodulation may be the fact that catecholamines are potent antioxidants and free radical scavengers and are thus able to affect the redox mediated balance at the glutamate receptors between synapse formation and synapse removal that may be a key factor in neurocomputational plasticity. But catecholamines are also easily oxidized to neurotoxic 0-semiquinones and this may be relevant to the pathology of several diseases including schizophrenia. The relationship between dopamine release and positive reinforcement is relevant to this hypothesis.

The functional neuroanatomy of awareness: with a focus on the role of various anatomical systems in the control of intermodal attention.

This review considers a number of recent theories on the neural basis of consciousness, with particular attention to the theories of Bogen, Crick, Llinás, Newman, and Changeux. These theories allot different roles to various key brain areas, in particular the reticular and intralaminar nuclei of the thalamus and the cortex. Crick's hypothesis is that awareness is a function of reverberating corticothalamic loops and that the spotlight of intramodal attention is controlled by the reticular nucleus of the thalamus. He also proposed different mechanisms for attention and intention ("will"). The current review presents a new hypothesis, based on elements from these hypotheses, including intermodal attention and olfaction and pain, which may pose problems for Crick's original theory. This work reviews the possible role in awareness and intermodal attention and intention of the cholinergic system in the basal forebrain and the tegmentum; the reticular, the intralaminar, and the dorsomedial thalamic nuclei; the raphe and locus coeruleus; the reticular formation; the ventral striatum and extended amygdala; insula cortex, and other selected cortical, areas. Both clinical and basic research data are covered. The conclusion is reached that the brain may work by largely nonlinear parallel processing and much intramodal shifts of attention may be effected by intracortical, or multiple corticothalamic mechanisms (small local "flashlights" rather than one major "searchlight"). But this is constrained by the functional anatomy of the circuits concerned and waking "awareness" is modulated by the many "nonspecific" systems (cholinergic from the basal forebrain, noradrenergic from the locus coeruleus, dopaminergic from the substantia nigra and ventral tegmentum, and serotoninergic from the raphe). But the principal agents for intermodal attention shifts, the "searchlight," may be two key nuclei of the cholinergic system in the mesencephalon. Clinical loss of consciousness results from damage to these nuclei but not from damage to the cholinergic nucleus basalis of the basal forebrain.

On the functional of neuromelanin.

The hypothesis is presented, based on the chemical structure of neuromelanin, that one of its functions in the catecholamine neurons in the brain is to protect the cell against toxic quinones (such as dopaminchrome and noradrenochrome, or their dihydroxy isomers) produced from the catecholamines dopamine and noradrenaline (and possibly adrenaline) during the course of prostaglandin synthesis by the enzyme prostaglandin H synthetase, or possibly by spontaneous oxidation. One aminochrome-adrenochrome-has been shown to be neurotoxic and to have psychotomimetic properties in humans. Depending on the site of production these compounds may be involved in the pathogenesis of Parkinson's disease or schizophrenia.

A note on the concept of the visual field in neurology, psychology, and visual neuroscience.

Some current confusions in visual neuroscience and psychology over the use of the terms 'visual field', 'field of vision', 'stimulus field', and topographic 'brain maps' are reviewed. These are often used as synonyms, whereas they refer to quite different things. A plea is made that visual scientists should use these terms correctly to avoid conceptual and engineering confusion.