Glial cells play an important role in sequestering neuronally released glutamate via Naϩ -dependent transporters. Surprisingly, these transporters are not operational in glial-derived tumors (gliomas). Instead, gliomas release glutamate, causing excitotoxic death of neurons in the vicinity of the tumor. We now show that glutamate release from glioma cells is an obligatory by-product of cellular cystine uptake via system x c Ϫ , an electroneutral cystine-glutamate exchanger. Cystine is an essential precursor for the biosynthesis of glutathione, a major redox regulatory molecule that protects cells from endogenously produced reactive oxygen species (ROS). Glioma cells, but not neurons or astrocytes, rely primarily on cystine uptake via system x c Ϫ for their glutathione synthesis. Inhibition of system x c Ϫ causes a rapid depletion of glutathione, and the resulting loss of ROS defense causes caspase-mediated apoptosis. Glioma cells can be rescued if glutathione status is experimentally restored or if glutathione is substituted by alternate cellular antioxidants, confirming that ROS are indeed mediators of cell death. We describe two potent drugs that permit pharmacological inhibition of system x c Ϫ . One of these drugs, sulfasalazine, is clinically used to treat inflammatory bowel disease and rheumatoid arthritis. Sulfasalazine was able to reduce glutathione levels in tumor tissue and slow tumor growth in vivo in a commonly used intracranial xenograft animal model for human gliomas when administered by intraperitoneal injection. These data suggest that inhibition of cystine uptake into glioma cells through the pharmacological inhibition of system x c Ϫ may be a viable therapeutic strategy with a Food and Drug Administration-approved drug already in hand.

Synapse-associated proteins (SAPs) are constituents of the pre- and postsynaptic submembraneous cytomatrix. Here, we present SAP102, a novel 102kDa SAP detected in dendritic shafts and spines of asymmetric type 1 synapses. SAP102 is enriched in preparations of synaptic junctions, where it biochemically behaves as a component of the cortical cytoskeleton. Antibodies directed against NMDA receptors coimmunoprecipitate SAP102 from rat brain synaptosomes. Recombinant proteins containing the carboxy-terminal tail of NMDA receptor subunit NR2B interact with SAP102 from rat brain homogenates. All three PDZ domains in SAP102 bind the cytoplasmic tail of NR2B in vitro. These data represent direct evidence that in vivo SAP102 is involved in linking NMDA receptors to the submembraneous cytomatrix associated with postsynaptic densities at excitatory synapses.

Malignant gliomas have been shown to release glutamate, which kills surrounding brain cells, creating room for tumor expansion. This glutamate release occurs primarily via system x C À , a Na + -independent cystine-glutamate exchanger. We show here, in addition, that the released glutamate acts as an essential autocrine/paracrine signal that promotes cell invasion. Specifically, chemotactic invasion and scrape motility assays each show dose-dependent inhibition of cell migration when glutamate release was inhibited using either S-(4)-CPG or sulfasalazine, both potent blockers of system x C À . This inhibition could be overcome by the addition of exogenous glutamate (100 Mmol/L) in the continued presence of the inhibitors. Migration/invasion was also inhibited when Ca 2+ -permeable A-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors (AMPA-R) were blocked using GYKI or Joro spider toxin, whereas CNQX was ineffective. Ca 2+ imaging experiments show that the released glutamate activates Ca 2+ -permeable AMPA-R and induces intracellular Ca 2+ oscillations that are essential for cell migration. Importantly, glioma cells release glutamate in sufficient quantities to activate AMPA-Rs on themselves or neighboring cells, thus acting in an autocrine and/or paracrine fashion. System x C À and the appropriate AMPA-R subunits are expressed in all glioma cell lines, patient-derived glioma cells, and acute patient biopsies investigated. Furthermore, animal studies in which human gliomas were xenographed into scid mice show that chronic inhibition of system x C À -mediated glutamate release leads to smaller and less invasive tumors compared with saline-treated controls. These data suggest that glioma invasion is effectively disrupted by inhibiting an autocrine glutamate signaling loop with a clinically approved candidate drug, sulfasalazine, already in hand.

Piccolo is a novel component of the presynaptic cytoskeletal matrix (PCM) assembled at the active zone of neurotransmitter release. Analysis of its primary structure reveals that Piccolo is a multidomain zinc finger protein structurally related to Bassoon, another PCM protein. Both proteins were found to be shared components of glutamatergic and GABAergic CNS synapses but not of the cholinergic neuromuscular junction. The Piccolo zinc fingers were found to interact with the dual prenylated rab3A and VAMP2/Synaptobrevin II receptor PRA1. We show that PRA1 is a synaptic vesicle-associated protein that is colocalized with Piccolo in nerve terminals of hippocampal primary neurons. These data suggest that Piccolo plays a role in the trafficking of synaptic vesicles (SVs) at the active zone.

SummaryRecently developed reprogramming and genome editing technologies make possible the derivation of corrected patient-specific pluripotent stem cell sources—potentially useful for the development of new therapeutic approaches. Starting with skin fibroblasts from patients diagnosed with cystic fibrosis, we derived and characterized induced pluripotent stem cell (iPSC) lines. We then utilized zinc-finger nucleases (ZFNs), designed to target the endogenous CFTR gene, to mediate correction of the inherited genetic mutation in these patient-derived lines via homology-directed repair (HDR). We observed an exquisitely sensitive, homology-dependent preference for targeting one CFTR allele versus the other. The corrected cystic fibrosis iPSCs, when induced to differentiate in vitro, expressed the corrected CFTR gene; importantly, CFTR correction resulted in restored expression of the mature CFTR glycoprotein and restoration of CFTR chloride channel function in iPSC-derived epithelial cells.

Ionotropic glutamate receptors are known to cluster at high concentration on the postsynaptic membrane of excitatory synapses, but the mechanism by which this occurs is poorly understood. Studies on the neuromuscular junction and central inhibitory synapses suggest that clustering of neurotransmitter receptors requires its interaction with a cytoplasmic protein. Recently, in vitro studies have shown that members of the N-methyl--aspartate (NMDA) class of glutamate receptors interact with a synapse-associated protein, SAP90 (PSD-95). However, evidence for the in vivo interaction of NMDA receptors with SAPs is still lacking. In the present study, we demonstrate the specific interaction between SAP102, a novel synapse-associated protein, and the NMDA receptor complex from the rat cortical synaptic plasma membranes using co-immunoprecipitation techniques. No association was observed between SAP102 and GluR1, a member of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate class of glutamate receptors. To identify the domain on the NMDA receptor responsible for this interaction, we constructed hexahistidine fusion proteins from different regions of the NR1a and NR2 subunits of the NMDA receptor. Immunoblot overlay experiments showed that while the C-terminal domain of the NR2 subunit displayed strong binding, the NR1a intracellular C-terminal tail did not interact with SAP102. The site of interaction was more precisely located to the last 20 amino acids of the NR2 subunit as indicated by the interaction of the synthetic peptide with SAP102. In summary, we demonstrate here for the first time an in vivo interaction between the native NMDA receptor complex and a synapse-associated protein. These results suggest that SAP102 may play an important role in NMDA receptor clustering and immobilization at excitatory synapses.

Piccolo is a high molecular weight multi-domain protein shown to be a structural component of the presynaptic CAZ (cytoskeletal matrix assembled at active zones). These features indicate that Piccolo may act to scaffold proteins involved in synaptic vesicle endo-and exocytosis near their site of action. To test this hypothesis, we have utilized a functional cell-based endocytosis assay and identified the N-terminal proline-rich Q domain in Piccolo as a region that interferes with clathrinmediated endocytosis. Utilizing the Piccolo Q domain as bait in a yeast two-hybrid screen, we have identified the F-actin-binding protein Abp1 (also called SH3P7 or HIP-55) as a potential binding partner for this domain. The physiological relevance of this interaction is supported by in vitro binding studies, colocalization in nerve terminals, in vivo recruitment studies, and immunoprecipitation experiments. Intriguingly, Abp1 binds to both Factin and the GTPase dynamin and has been implicated in linking the actin cytoskeleton to clathrin-mediated endocytosis. Our results suggest that Piccolo, as a structural protein of the CAZ, may serve to localize Abp1 at active zones where it can actively participate in creating a functional connection between the dynamic actin cytoskeleton and synaptic vesicle recycling.

Nuclear factor‐κB (NF‐κB) is a pleiotropic transcription factor that generally enhances cellular resistance to apoptotic cell death. It has been shown to be constitutively active in some cancers and is being pursued as potential anticancer target. Sulfasalazine which is used clinically to treat Crohn’s disease has emerged as a potential inhibitor of NF‐κB and has shown promising results in two pre‐clinical studies to target primary brain tumors, gliomas. Once digested, sulfasalazine is cleaved into sulfapyridine and 5‐aminosalicylic acid (5‐ASA; mesalamine) by colonic bacteria, and the latter, too, is reported to suppress NF‐κB activity. We now show that glioma cells obtained from patient biopsies or glioma cell lines do not show significant constitutive NF‐κB activation, unless exposed to inflammatory cytokines. This does not change when gliomas are implanted into the cerebrum of severe combined immundeficient mice. Nevertheless, sulfasalazine but not its cleaved form 5‐ASA caused a dose‐dependent inhibition of glioma growth. This effect was entirely attributable to the inhibition of cystine uptake via the system xc− cystine–glutamate transporter. It could be mimicked by S‐4‐carboxy‐phenylglycine (S‐4‐CPG) a more specific system xc− inhibitor, and lentiviral expression of a constitutively active form of IκB kinase b was unable to overcome the growth retarding effects of sulfasalazine or S‐4‐CPG. Both drugs inhibited cystine uptake causing a chronic depletion of intracellular GSH and consequently compromised cellular redox defense which stymied tumor growth. This data suggests that system xc− is a promising therapeutic target in gliomas and possibly other cancers and that it can be pharmacologically inhibited by Sulfasalazine, an FDA‐approved drug.