Identification and characterization of a novel splice variant of the metabotropic glutamate receptor 5 gene in human hippocampus and cerebellum.
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.
Malherbe
Pari
P
Pharma Division, PRPN Preclinical CNS Research, Bldg 69/333, F. Hoffmann-La Roche Ltd, CH-4070 Basel, Switzerland. parichehr.malherbe@roche.com
Kew
James N C
JN
Richards
J Grayson
JG
Knoflach
Frédéric
F
Kratzeisen
Claudia
C
Zenner
Marie-Thérèse
MT
Faull
Richard L M
RL
Kemp
John A
JA
Mutel
Vincent
V
D000368:Aged; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002531:Cerebellum / Q000166:cytology / Q000502:physiology*; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D018690:Excitatory Amino Acid Agonists / Q000378:metabolism; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D016318:Quisqualic Acid / Q000378:metabolism; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment
D018690:Excitatory Amino Acid Agonists; C578935:GRM5 protein, human; D024661:Potassium Channels, Inwardly Rectifying; D020033:Protein Isoforms; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; D018698:Glutamic Acid; D016318:Quisqualic Acid; D002118:Calcium