ADGRD1 and glioblastoma: In glioblastoma GPR133/ADGRD1 can be activated by its extracellular binding partner, the transmembrane protein PTK7.18 In combination with external forces, the interaction of PTK7 with GPR133/ADGRD1 in trans likely releases the N-terminal fragment, thereby exposing the internal agonistic Stachel sequence.