The Study Of Metabotropic Glutamate Receptor 2 And ?-aminobutyric Acid Type B Receptor Cell Signaling Pathway

G protein-coupled receptors?GPCRs?,the largest family of membrane receptors,mediate various extracellular stimuli,including neurotransmitters and hormones.GPCRs has been divided into five main classes.Among them,metabotropic glutamate receptor 2?mGluR2?and?-aminobutyric acid type B receptor?GABA_BR?belong to Class C GPCRs,and are widely distributed in the central nervous system.They are metabotropic receptors for the excitable neurotransmitter glutamate and the inhibitory neurotransmitter?-aminobutyric acid,respectively.They are involved in physiological processes such as learning,memory and synaptic transmission,and are closely related to neurological and psychiatric disorders.However,the mechanisms of the activation and the downstream signaling pathways of these two receptors have not been well illustrated.mGluR2 is involved in pathophysiology of neurological and psychiatric diseases,and is a promising antipsychotic target.However,the specific role of mGluR2 signaling remains unclear,which limits the study of the pathophysiological function of mGluR2.A CHO-mGluR2 cell line that stably expresses mGluR2 was generated and showed that activation of mGluR2 by LY379286 was able to transactivate insulin like growth factor 1receptor?IGF-1R?.We further determined that the G??subunits,phospholipase C,and focal adhesion kinase?FAK?were involved in the IGF-1R transactivation signaling axis,which further induced the phosphorylation of extracellular signal regulated kinase1/2?ERK1/2?and cAMP response element binding protein?CREB?.In primary mouse cortical neurons,similar signaling pathways were observed when mGluR2 was stimulated by LY487379,a mGluR2 positive allosteric modulator.In addition,we also found that activation of mGluR2 in neurons enhanced amyloid-?induced apoptosis and nutritional deprivation induced apoptosis.Recent studies suggest that GABA_BR mediates slow inhibitory nerve conduction and synaptic plasticity in the central nervous system,and its disorder leads to cell dysfunction,damage and even cell apoptosis.Regulation of receptor cell surface availability is one fundamental process contributing to receptor signaling activity modulation.The specific signaling pathway regulating GABA_BR cell surface availability is to be elucidated,as GABA_BR don't couple to classical?-arrestin pathway.Therefore,we have studied the mechanism of receptor membrane expression in HEK293 cells expressing GABA_BR.It was found that Ca²⁺-independent protein kinase C?PKC?subtypes were involved in regulation of GABA_BR constitutive internalization.In active state,GABA_BR activated and recruited PKC?through FAK,PKC?promoted the degradation of internalized receptors,resulting in the decrease of cell surface receptors expression.In conclusion,we studied downstream signaling pathways of mGluR2 and GABA_BR.We found transactivation signaling from mGluR2 to IGF-1R and the key role of PKC in GABA_BR membrane expression regulation.The above works illustrated the signaling mechanisms of these two neurotransmitters GPCRs,which will provide a theoretical basis for the study of drugs targeting mGluR2 and GABA_BR.