Metabotropic glutamate receptor 1 (mGluR1) forms hetero-oligomer with other G-protein coupled receptors and they regulate their signal transduction each other at neurons

[Speaker] Hakushun Sakairi:1
[Co-author] Yuji Kamikubo:2, Masayoshi Abe:3, Kenta Matsuoka:3, Toshihide Tabata:3, Takashi Sakurai:1,2
1:Department of Pharmacology, Juntendo University Graduate School of Medicine, Japan, 2:Department of Pharmacology, Juntendo University School of Medicine, Japan, 3:Laboratory for Neural Information, Graduate School of Science and Engineering, University of Toyama, Japan

G-protein coupled receptors (GPCRs) constitute a large protein family of receptors expressed in cells of eukaryotes. GPCRs play crucial roles in intracellular signaling and are involved in various physiological and pathological phenomena. Hence, approximately one-third of medicinal agents are targeted to any of GPCRs. G proteins are classified by types of α-subunit of coupled G-protein: Gs, Gi/o, and Gq/11. Each G-protein transduces signal by stimulating or inhibiting cAMP signal pathway (Gs, Gi/o) or by activating phosphatidylinositol signal pathway (Gq/11). Recently, the evidence is increasing that multiple GPCRs constitute homo- or hetero-oligomer and induce atypical signal which cannot be caused by either individual GPCRs only. Although heteromeric GPCR complexes are suggested to occur in many neurons, their contribution to neuronal function remains unclear. In previous study, we address this question using two GPCRs expressed in cerebellar Purkinje cells: type-1 metabotropic glutamate receptor (mGluR1), which mediates cerebellar long-term depression, a form of synaptic plasticity crucial for cerebellar motor learning, and adenosine A1 receptor (A1R), which regulates neurotransmitter release and neuronal excitability in central neurons. We showed that functional interaction and complex formation between mGluR1 and A1R. We inferred that mGluR1 might constitute hetero-oligomer with other cAMP pathway-dependent GPCR (GsPCR or Gi/oPCR) and be able to mediate signals of each.
Thus, we examined possibility of forming complex between mGluR1 and other GPCR by Förster resonance energy transfer(FRET), Bimolecular fluorescence complementation(BiFC), and co-immunoprecipitation. Moreover, we evaluated GPCR complex formation mediate signaling modulation using Ca2+ imaging and cAMP homogenous FRET assay. These analyses revealed that mGluR1 and some GPCRs closely colocalized and formed heteromeric complexes on the cell surfaces. Furthermore, our signaling analysis showed that these complex formations regulate their function each other. Our results provide a new insight into neuronal GPCR signaling and demonstrate a novel regulatory mechanism of synaptic plasticity.
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