The Mechanism Of The GABA_B Receptor Mediated IGF-1Receptor Transactivation Through Lipid Rafts

G-protein-coupled receptors (GPCRs) are integral membrane, hence their structuraland functional features are modulated by both proteins and lipids. Lipid rafts are enrichedin cholesterol and sphingolipids and are resistant to non-ionic detergent-extraction at4℃in the plasma membrane, can serve as a platform for tissue-specific signaling complex ofGPCRs and regulate the efficiency and specificity of signal transduction. Several GPCRsare locate in lipid rafts through the palmitoylation on cystein residues exist in thecytoplasmic C-termini,and by the palmitoyl transferase and thioesterase reversible dualcontrol. The effect of intracellular transport and membrane lateral sorting bypalmitoylation modification kinetics of GPCRs is the current research focus.G protein coupled γ-aminobutyric acid receptor B (GABA_BR),one important memberof GPCRs,consists of GB1subunit and GB2subunit and distributes in many physiologicalprocedures. The activation of GABA_BR can protect neurons from apoptosis via IGF-1receptor transactivation. The GABA_BR activation mediated IGF-1R transactivation andthe phosphorylation of signaling proteins should form a large signaling complex. Thespatial and temporal changes of the member of the signaling complex, such as the releaseof G protein and the combination of IGF-1R, is very important to the physiological effectsinduced by GABA_BR. On the other hand, the study confirmed that GABA_BR associatedwith lipid rafts in the resting state, and removed from lipid rafts after activation. What isthe role of lipid rafts in the activation of IGF-1R GABA_BR, the spatial and temporalchanges of GABA_BR signaling complex associated with lipid rafts, the mechanism and thefactors of GABA_BR associated with lipid rafts,here is no research in this area.In HEK293cells and CGNs, through the MCD destroy the integrity of lipid rafts,thentreat with baclofen and GABA,we found the integrity of lipid rafts is necessary for theGABA_BR activation mediated IGF-1R transactivation signaling complex.We find theC874may occur the palmitoytion by biological softmare, and it may have influence on thereceptor binding with lipid rafts. When the lipid rafts intact,damageing the association ofGABA_BR with lipid rafts by mutation of palmitoylation modification，it will effect the time curve of GABA-induced phosphorylation of IGF-1R.The lack of palmitoylation willaffect the phosphorylation of IGF-1R and the dynamic movement of the members of thesignaling complex between the raft domain and non-lipid raft domain. Lipid rafts alsoaffect the affinity of members of the signaling complex. After the activation ofGABA_BR,the release of G protein and the binding of IGF-1R is different during the rafts isimpaired by ABPP pulldown.In summary,we demonstrate lipid rafts may be the intracellar platform of theGABA_BR activation mediated IGF-1R transactivation signaling complex. The integrity oflipid rafts is necessary for the signaling complex. In the transactivation, the member of thesignaling complex will occur a lateral sorting which is enriched-out in lipid rafts.And raftsalso affect the spatial and temporal changes of the member of the complex,such as therelease of G protein and the binding of IGF-1R. This study is the foundation of researcheson the modulatory mechanism of the efficiency of signal transduction of GABA_BR.Wewill fouces on the analysis of the correlation between of lateral sorting on cell membraneand the intracellular circulation in next work.