Nuclear receptor 4A2 (NR4A2) is a druggable target for glioblastomas

INTRODUCTION

The orphan nuclear receptor 4A2 (NR4A2) has been extensively characterized in subcellular regions of the brain and is necessary for the function of dopaminergic neurons. The NR4A2 ligand, 1,1-bis (3¹-indoly1)-1-(p-chlorophenyl)methane (DIM-C-pPhCl) inhibits markers of neuroinflammation and degeneration in mouse models and in this study we investigated expression and function of NR4A2 in glioblastoma (GBM).

METHODS

Established and patient-derived cell lines were used as models and the expression and functions of NR4A2 were determined by western blots and NR4A2 gene silencing by antisense oligonucleotides respectively. Effects of NR4A2 knockdown and DIM-C-pPhCl on cell growth, induction of apoptosis (Annexin V Staining) and migration/invasion (Boyden chamber and spheroid invasion assay) and transactivation of NR4A2-regulated reporter genes were determined. Tumor growth was investigated in athymic nude mice bearing U87-MG cells as xenografts.

RESULTS

NR4A2 knockdown and DIM-C-pPhCl inhibited GBM cell and tumor growth, induced apoptosis and inhibited migration and invasion of GBM cells. DIM-C-pPhCl and related analogs also inhibited NR4A2-regulated transactivation (luciferase activity) confirming that DIM-C-pPhCl acts as an NR4A2 antagonist and blocks NR4A2-dependent pro-oncogenic responses in GBM.

CONCLUSION

We demonstrate for the first time that NR4A2 is pro-oncogenic in GBM and thus a potential druggable target for patients with tumors expressing this receptor. Moreover, our bis-indole-derived NR4A2 antagonists represent a novel class of anti-cancer agents with potential future clinical applications for treating GBM.

Experimental Zika virus infection of Jamaican fruit bats (Artibeus jamaicensis) and possible entry of virus into brain via activated microglial cells

The emergence of Zika virus (ZIKV) in the New World has led to more than 200,000 human infections. Perinatal infection can cause severe neurological complications, including fetal and neonatal microcephaly, and in adults there is an association with Guillain-Barré syndrome (GBS). ZIKV is transmitted to humans by Aedes sp. mosquitoes, yet little is known about its enzootic cycle in which transmission is thought to occur between arboreal Aedes sp. mosquitos and non-human primates. In the 1950s and '60s, several bat species were shown to be naturally and experimentally susceptible to ZIKV with acute viremia and seroconversion, and some developed neurological disease with viral antigen detected in the brain. Because of ZIKV emergence in the Americas, we sought to determine susceptibility of Jamaican fruit bats (Artibeus jamaicensis), one of the most common bats in the New World. Bats were inoculated with ZIKV PRVABC59 but did not show signs of disease. Bats held to 28 days post-inoculation (PI) had detectable antibody by ELISA and viral RNA was detected by qRT-PCR in the brain, saliva and urine in some of the bats. Immunoreactivity using polyclonal anti-ZIKV antibody was detected in testes, brain, lung and salivary glands plus scrotal skin. Tropism for mononuclear cells, including macrophages/microglia and fibroblasts, was seen in the aforementioned organs in addition to testicular Leydig cells. The virus likely localized to the brain via infection of Iba1+ macrophage/microglial cells. Jamaican fruit bats, therefore, may be a useful animal model for the study of ZIKV infection. This work also raises the possibility that bats may have a role in Zika virus ecology in endemic regions, and that ZIKV may pose a wildlife disease threat to bat populations.

Dopaminergic neurotoxicants cause biphasic inhibition of purinergic calcium signaling in astrocytes

Dopaminergic nuclei in the basal ganglia are highly sensitive to damage from oxidative stress, inflammation, and environmental neurotoxins. Disruption of adenosine triphosphate (ATP)-dependent calcium (Ca2+) transients in astrocytes may represent an important target of such stressors that contributes to neuronal injury by disrupting critical Ca2+-dependent trophic functions. We therefore postulated that plasma membrane cation channels might be a common site of inhibition by structurally distinct cationic neurotoxicants that could modulate ATP-induced Ca2+ signals in astrocytes. To test this, we examined the capacity of two dopaminergic neurotoxicants to alter ATP-dependent Ca2+ waves and transients in primary murine striatal astrocytes: MPP+, the active metabolite of 1-methyl 4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and 6-hydroxydopamine (6-OHDA). Both compounds acutely decreased ATP-induced Ca2+ transients and waves in astrocytes and blocked OAG-induced Ca2+ influx at micromolar concentrations, suggesting the transient receptor potential channel, TRPC3, as an acute target. MPP+ inhibited 1-oleoyl-2-acetyl-sn-glycerol (OAG)-induced Ca2+ transients similarly to the TRPC3 antagonist, pyrazole-3, whereas 6-OHDA only partly suppressed OAG-induced transients. RNAi directed against TRPC3 inhibited the ATP-induced transient as well as entry of extracellular Ca2+, which was augmented by MPP+. Whole-cell patch clamp experiments in primary astrocytes and TRPC3-overexpressing cells demonstrated that acute application of MPP+ completely blocked OAG-induced TRPC3 currents, whereas 6-OHDA only partially inhibited OAG currents. These findings indicate that MPP+ and 6-OHDA inhibit ATP-induced Ca2+ signals in astrocytes in part by interfering with purinergic receptor mediated activation of TRPC3, suggesting a novel pathway in glia that could contribute to neurotoxic injury.

Manganese and its role in Parkinson's disease: from transport to neuropathology

The purpose of this review is to highlight recent advances in the neuropathology associated with Mn exposures. We commence with a discussion on occupational manganism and clinical aspects of the disorder. This is followed by novel considerations on Mn transport (see also chapter by Yokel, this volume), advancing new hypotheses on the involvement of several transporters in Mn entry into the brain. This is followed by a brief description of the effects of Mn on neurotransmitter systems that are putative modulators of dopamine (DA) biology (the primary target of Mn neurotoxicity), as well as its effects on mitochondrial dysfunction and disruption of cellular energy metabolism. Next, we discuss inflammatory activation of glia in neuronal injury and how disruption of synaptic transmission and glial-neuronal communication may serve as underlying mechanisms of Mn-induced neurodegeneration commensurate with the cross-talk between glia and neurons. We conclude with a discussion on therapeutic aspects of Mn exposure. Emphasis is directed at treatment modalities and the utility of chelators in attenuating the neurodegenerative sequelae of exposure to Mn. For additional reading on several topics inherent to this review as well as others, the reader may wish to consult Aschner and Dorman (Toxicological Review 25:147-154, 2007) and Bowman et al. (Metals and neurodegeneration, 2009).

Fluorescent nanosensors for intracellular chemical analysis: decyl methacrylate liquid polymer matrix and ion-exchange-based potassium PEBBLE sensors with real-time application to viable rat C6 glioma cells

Fluorescent spherical nanosensors, or PEBBLEs (probes encapsulated by biologically localized embedding), in the 500 nm-1 microm size range have been developed using decyl methacrylate as a matrix. A general scheme for the polymerization and introduction of sensing components creates a matrix that allows for the utilization of the highly selective ionophores used in poly(vinyl chloride) and decyl methacrylate ion-selective electrodes. We have applied these optically silent ionophores to fluorescence-based sensing by using ion-exchange and highly selective pH chromoionophores. This allows the tailoring of selective submicrometer sensors for use in intracellular measurements of important analytes for which selective enough fluorescent probes do not exist. The protocol for sensor development has been worked out for potassium sensing. It is based on the BME-44 ionophore (2-dodecyl-2-methyl-1,3-propanediylbis[N-[5'nitro(benzo-15-crown-5)-4'-yl]carbamate]). The general scheme should work for any available ionophore used in PVC or decyl methacrylate ion-selective electrodes, with minor adjustments to account for differences in ionophore charge and analyte binding constant. The reversible and highly selective sensors developed have a subsecond response time and an adjustable dynamic range. Applications to live C6 glioma cells demonstrate their utility; the intracellular potassium activity is followed in real time upon extracellular administration of kainic acid.

Irradiation of mitochondria initiates apoptosis in a cell free system

The ability to modulate the sensitivity of mammalian cells to ionizing radiation (IR) (e.g. using chemotherapeutics) is dependent on our understanding of the primary target and biochemical pathway that leads to IR-induced apoptosis. We demonstrate using a cell free assay that irradiation of mitochondria is a primary event that initiates IR-induced apoptosis. IR results in loss of mitochondrial membrane potential, opening of the permeability transition pore (PTP) and the release of cytochrome c (cyto c). Apaf-1 and ATP were required to initiate apoptosis upon release of cyto c from mitochondria. The importance of mitochondrial events in the initiation of IR-induced apoptosis was also supported by the observation that inhibition of caspase-9 by the over-expression of dominant negative mutants resulted in the inhibition of IR-induced apoptosis. In contrast, inhibition of caspase-8 had only a minor impact on IR-induced apoptosis. Over-expression of Bcl-X(L) inhibited the initiation of IR-induced apoptosis due to its ability to prevent the loss of mitochondrial membrane potential, PTP opening and cytochrome c release. In a cell free assay for apoptosis, mitochondria as well as cytosol derived from Bcl-X(L) over-expressing cells were less efficient at supporting apoptosis in response to IR suggesting multiple roles for Bcl-X(L) in the regulation of apoptosis.

Optical nanosensors for chemical analysis inside single living cells. 2. Sensors for pH and calcium and the intracellular application of PEBBLE sensors

Optical nanosensors, or PEBBLEs (probes encapsulated by biologically localized embedding), have been produced for intracellular measurements of pH and calcium. Five varieties of pH-sensitive sensors and three different calcium-selective sensors are presented and discussed. Each sensor combines an ion-selective fluorescent indicator and an ion-insensitive internal standard entrapped within an acrylamide polymeric matrix. Calibrations and linear ranges are presented for each sensor. The photobleaching of dyes incorporated into PEBBLEs is comparable to that of the respective free dye that is incorporated within the matrix. These PEBBLE sensors are fully reversible over many measurements. The leaching of fluorescent indicator from the polymer is less than 50% over a 48-h period (note that a typical application time is only a few hours). The PEBBLE sensors have also been applied to intracellular analysis of the calcium flux in the cytoplasm of neural cells during the mitochondrial permeability transition. Specifically, a distinct difference is noted between cells of different types (astrocyte vs neuron-derived cells) with respect to their response to the toxicant m-dinitrobenzene (DNB). Use of PEBBLE sensors permits the quantitative discrimination of subtle differences between the ability of human SY5Y neuroblastoma and C6 glioma to respond to challenge with DNB. Specifically, measurement of intracellular calcium, the precursor to cell death, has been achieved.