Identification and characterization of a novel splice variant of the metabotropic glutamate receptor 5 gene in human hippocampus and cerebellum

Brain Res Mol Brain Res. 2002 Dec 30;109(1-2):168-78. doi: 10.1016/s0169-328x(02)00557-0.

Abstract

The G-protein coupled metabotropic glutamate receptor mGlu5 plays a pivotal role as a modulator of synaptic plasticity, ion channel activity and excitotoxicity. Two splice variants, hmGlu5a and -5b have been reported previously. During screening of a human brain cDNA library for hmGlu5a, we identified a novel variant (hmGlu5d) generated by alternative splicing at the C-terminal domain. The predicted hmGlu5d protein has a C-terminal 267 amino acid shorter than that of hmGlu5a. The pattern of mRNA expression of mGluR5 variants in human brain were analyzed by RT-PCR and in situ hybridization histochemistry. RT-PCR analysis demonstrated the presence of the hmGlu5d transcript, although at low level, in human whole brain, cerebellum, cerebral cortex and hippocampus. [3H]Quisqualate displayed similar affinity at the hmGlu5 splice variants (K(D) values of 80+/-8 and 54+/-17 nM for hmGlu5a and -5d receptors, respectively). For the five mGlu agonists studied, a similar rank order of potency was observed on both hmGlu5a and -5d receptors: quisqualate>glutamate>DHPG>L-CCGI approximately ACPD. MPEP inhibited the glutamate (2 microM)-induced [Ca(2+)](i) response in hmGlu5a and -5d-HEK293 cells also with similar potency (IC(50) values 25+/-1.5 and 20+/-1.4 nM, respectively). Therefore, the large truncation of the C-terminal tail of mGlu5 does not have any apparent major effect on the potency and efficacy of agonists as measured by the [Ca(2+)](i) responses or by activation of recombinant G-protein coupled inwardly rectifying K(+) (GIRK) channel currents. The only major functional difference is the increased sensitivity of hmGlu5d to protein kinase C (PKC)-mediated desensitization, relative to hmGlu5a.

MeSH terms

  • Aged
  • Alternative Splicing*
  • Amino Acid Sequence
  • Animals
  • Calcium / metabolism
  • Cell Line
  • Cerebellum / cytology
  • Cerebellum / physiology*
  • Cricetinae
  • Dose-Response Relationship, Drug
  • Excitatory Amino Acid Agonists / metabolism
  • Female
  • Glutamic Acid / metabolism
  • Hippocampus / cytology
  • Hippocampus / physiology*
  • Humans
  • Male
  • Middle Aged
  • Molecular Sequence Data
  • Potassium Channels, Inwardly Rectifying / genetics
  • Potassium Channels, Inwardly Rectifying / metabolism
  • Protein Isoforms / genetics
  • Protein Isoforms / metabolism
  • Quisqualic Acid / metabolism
  • Receptor, Metabotropic Glutamate 5
  • Receptors, Metabotropic Glutamate / chemistry
  • Receptors, Metabotropic Glutamate / genetics*
  • Receptors, Metabotropic Glutamate / metabolism
  • Sequence Alignment

Substances

  • Excitatory Amino Acid Agonists
  • GRM5 protein, human
  • Potassium Channels, Inwardly Rectifying
  • Protein Isoforms
  • Receptor, Metabotropic Glutamate 5
  • Receptors, Metabotropic Glutamate
  • Glutamic Acid
  • Quisqualic Acid
  • Calcium