Exon-skipping splice variants of excitatory amino acid transporter-2 (EAAT2) form heteromeric complexes with full-length EAAT2. 2010

Florian M Gebhardt, and Ann D Mitrovic, and Daniel F Gilbert, and Robert J Vandenberg, and Joseph W Lynch, and Peter R Dodd
School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane 4072, Australia.

The glial transporter excitatory amino acid transporter-2 (EAAT2) is the main mediator of glutamate clearance in brain. The wild-type transporter (EAAT2wt) forms trimeric membrane complexes in which each protomer functions autonomously. Several EAAT2 variants are found in control and Alzheimer-diseased human brains; their expression increases with pathological severity. These variants might alter EAAT2wt-mediated transport by abrogating membrane trafficking, or by changing the configuration or functionality of the assembled transporter complex. HEK293 cells were transfected with EAAT2wt; EAAT2b, a C-terminal variant; or either of two exon-skipping variants: alone or in combination. Surface biotinylation studies showed that only the exon-7 deletion variant was not trafficked to the membrane when transfected alone, and that all variants could reach the membrane when co-transfected with EAAT2wt. Fluorescence resonance energy transfer (FRET) studies showed that co-transfected EAAT2wt and EAAT2 splice variants were expressed in close proximity. Glutamate transporter function was measured using a whole cell patch clamp technique, or by changes in membrane potential indexed by a voltage-sensitive fluorescent dye (FMP assay): the two methods gave comparable results. Cells transfected with EAAT2wt or EAAT2b showed glutamate-dependent membrane potential changes consistent with functional expression. Cells transfected with EAAT2 exon-skipping variants alone gave no response to glutamate. Co-transfection of EAAT2wt (or EAAT2b) and splice variants in various ratios significantly raised glutamate EC(50) and decreased Hill coefficients. We conclude that exon-skipping variants form heteromeric complexes with EAAT2wt or EAAT2b that traffic to the membrane but show reduced glutamate-dependent activity. This could allow glutamate to accumulate extracellularly and promote excitotoxicity.

UI MeSH Term Description Entries
D008564 Membrane Potentials The voltage differences across a membrane. For cellular membranes they are computed by subtracting the voltage measured outside the membrane from the voltage measured inside the membrane. They result from differences of inside versus outside concentration of potassium, sodium, chloride, and other ions across cells' or ORGANELLES membranes. For excitable cells, the resting membrane potentials range between -30 and -100 millivolts. Physical, chemical, or electrical stimuli can make a membrane potential more negative (hyperpolarization), or less negative (depolarization). Resting Potentials,Transmembrane Potentials,Delta Psi,Resting Membrane Potential,Transmembrane Electrical Potential Difference,Transmembrane Potential Difference,Difference, Transmembrane Potential,Differences, Transmembrane Potential,Membrane Potential,Membrane Potential, Resting,Membrane Potentials, Resting,Potential Difference, Transmembrane,Potential Differences, Transmembrane,Potential, Membrane,Potential, Resting,Potential, Transmembrane,Potentials, Membrane,Potentials, Resting,Potentials, Transmembrane,Resting Membrane Potentials,Resting Potential,Transmembrane Potential,Transmembrane Potential Differences
D002460 Cell Line Established cell cultures that have the potential to propagate indefinitely. Cell Lines,Line, Cell,Lines, Cell
D005091 Exons The parts of a transcript of a split GENE remaining after the INTRONS are removed. They are spliced together to become a MESSENGER RNA or other functional RNA. Mini-Exon,Exon,Mini Exon,Mini-Exons
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D001483 Base Sequence The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence. DNA Sequence,Nucleotide Sequence,RNA Sequence,DNA Sequences,Base Sequences,Nucleotide Sequences,RNA Sequences,Sequence, Base,Sequence, DNA,Sequence, Nucleotide,Sequence, RNA,Sequences, Base,Sequences, DNA,Sequences, Nucleotide,Sequences, RNA
D017384 Sequence Deletion Deletion of sequences of nucleic acids from the genetic material of an individual. Deletion Mutation,Deletion Mutations,Deletion, Sequence,Deletions, Sequence,Mutation, Deletion,Mutations, Deletion,Sequence Deletions
D017398 Alternative Splicing A process whereby multiple RNA transcripts are generated from a single gene. Alternative splicing involves the splicing together of other possible sets of EXONS during the processing of some, but not all, transcripts of the gene. Thus a particular exon may be connected to any one of several alternative exons to form a mature RNA. The alternative forms of mature MESSENGER RNA produce PROTEIN ISOFORMS in which one part of the isoforms is common while the other parts are different. RNA Splicing, Alternative,Splicing, Alternative,Alternate Splicing,Nested Transcripts,Alternate Splicings,Alternative RNA Splicing,Alternative RNA Splicings,Alternative Splicings,Nested Transcript,RNA Splicings, Alternative,Splicing, Alternate,Splicing, Alternative RNA,Splicings, Alternate,Splicings, Alternative,Splicings, Alternative RNA,Transcript, Nested,Transcripts, Nested
D046912 Multiprotein Complexes Macromolecular complexes formed from the association of defined protein subunits. Macromolecular Protein Complexes,Complexes, Macromolecular Protein,Complexes, Multiprotein,Protein Complexes, Macromolecular
D050491 Glutamate Plasma Membrane Transport Proteins A family of plasma membrane neurotransmitter transporter proteins that couple the uptake of GLUTAMATE with the import of SODIUM ions and PROTONS and the export of POTASSIUM ions. In the CENTRAL NERVOUS SYSTEM they regulate neurotransmission through synaptic reuptake of the excitatory neurotransmitter glutamate. Outside the central nervous system they function as signal mediators and regulators of glutamate metabolism. Neurotransmitter Transport Proteins, Glutamate-Specific,Neurotransmitter Transporters, Glutamate-Specific,EAAT Proteins,Excitatory Amino Acid Transport Proteins,Excitatory Amino Acid Transporter Proteins,Glutamate Plasma Membrane Transporter Proteins,Sodium-Glutamate Cotransporter,Sodium-Glutamate Transporter,Cotransporter, Sodium-Glutamate,Glutamate-Specific Neurotransmitter Transporters,Neurotransmitter Transport Proteins, Glutamate Specific,Neurotransmitter Transporters, Glutamate Specific,Sodium Glutamate Cotransporter,Sodium Glutamate Transporter,Transporters, Glutamate-Specific Neurotransmitter
D018698 Glutamic Acid A non-essential amino acid naturally occurring in the L-form. Glutamic acid is the most common excitatory neurotransmitter in the CENTRAL NERVOUS SYSTEM. Aluminum L-Glutamate,Glutamate,Potassium Glutamate,D-Glutamate,Glutamic Acid, (D)-Isomer,L-Glutamate,L-Glutamic Acid,Aluminum L Glutamate,D Glutamate,Glutamate, Potassium,L Glutamate,L Glutamic Acid,L-Glutamate, Aluminum

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