CSIG-27. MODULATION OF GPR133 (ADGRD1) SIGNALING BY ITS INTRACELLULAR INTERACTION PARTNER EXTENDED SYNAPTOTAGMIN 1 (ESYT1)

Abstract GPR133 (ADGRD1), a member of the adhesion GPCR (aGPCR) family, has been recently implicated in pathogenesis glioblastoma. Like other aGPCRs, is characterized by large N-terminus, which possesses conserved autoproteolysis-inducing (GAIN) domain catalyzing cleavage at proteolysis site (GPS), resulting C-terminal fragment (CTF) and an N-terminal (NTF). We showed that dissociation cleaved NTF CTF plasma membrane correlates with increased signaling, mediated coupling to Gs increase cytosolic cAMP. Since absent normal brain cells de novo expressed GBM, it represents potential target for GBM treatment. However, little known about receptor’s protein interactome its effects on receptor function signaling. To identify intracellular interactors GPR133, we used proximity biotinylation/mass spectrometry approach HEK293T expressing wild-type or signaling-incompetent mutant GPR133. identified Extended Synaptotagmin 1 (ESYT1), responsible Ca2+-dependent formation endoplasmic reticulum-plasma bridges, as strongest interaction partner both versions receptor. Co-immunoprecipitation confirmed robust binding ESYT1 Knockdown/knockout while overexpression had opposite effect. This effect was not changes expression trafficking. are currently performing additional studies elucidate mechanism whereby modulates Collectively, these data suggest signaling modulated through novel cytosolic, signaling-independent ESYT1.