Downstream signaling of the disease associated mutations on GPR56/ADGRG1.

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