Downstream signalling of the disease-associated mutations on GPR56/ADGRG1

GPR56/ADGRG1 is an adhesion G protein-coupled receptor (GPCR) and mutations on this receptor cause cortical malformation due to the overmigration of neural progenitor cells on brain surface. At pial surface, GPR56 interacts with collagen III, induces Rho-dependent activation through G alpha(12/13) and inhibits the neuronal migration. In human glioma cells, GPR56 inhibits cell migration through G alpha(q)/11-dependent Rho pathway. GPR56-tetraspanin complex is known to couple G alpha(q)/11. GPR56 is an aGPCR that couples with various G proteins and signals through different downstream pathways. In this study, bilateral frontoparietal polymicrogyria (BFPP) mutants disrupting GPR56 function but remaining to be expressed on plasma membrane were used to study receptor signalling through G alpha(12), G alpha(13) and G alpha(11) with BRET biosensors. GPR56 showed coupling with all three G proteins and activated heterotrimeric G protein signalling upon stimulation with Stachel peptide. However, BFPP mutants showed different signalling defects for each G protein indicative of distinct activation and signalling properties of GPR56 for G alpha(12), G alpha(13) or G alpha(11). beta-arrestin recruitment was also investigated following the activation of GPR56 with Stachel peptide using BRET biosensors. N-terminally truncated GPR56 showed enhanced beta-arrestin recruitment; however, neither wild-type receptor nor BFPP mutants gave any measurable recruitment upon Stachel stimulation, pointing different activation mechanisms for beta-arrestin involvement.