The Regulated Expression, Intracellular Trafficking, and Membrane Recycling of the P2Y-like Receptor GPR17 in Oli-neu Oligodendroglial Cells

GPR17 is a G-protein-coupled receptor that is activated by two classes of molecules: uracil-nucleotides and cysteinyl-leu- kotrienes. GPR17 is required for initiating the differentiation of oligodendrocyte precursors but has to be down-regulated to allow cells to undergo terminal maturation. Although a great deal has been learned about GPR17 expression and signaling, no information is currently available about the trafficking of native receptors after the exposure of differentiating oligodendrocytes to endogenous agonists. Here, we demonstrate that neuron- conditioned medium induces the transcriptionally mediated, time-regulated expression of GPR17 in Oli-neu, an oligoden- drocyte precursor cell line, making these cells suitable for study- ing the endocytic traffic of the native receptor. Agonist-induced internalization, intracellular trafficking, and membrane recy- cling of GPR17 were analyzed by biochemical and immunofluo- rescence assays using an ad hoc-developed antibody against the extracellular N-terminal of GPR17. Both UDP-glucose and LTD4 increased GPR17 internalization, although with different efficiency. At early time points, internalized GPR17 co-localized with transferrin receptor, whereas at later times it partially co- localized with the lysosomal marker Lamp1, suggesting that a portion of GPR17 is targeted to lysosomes upon ligand binding. An analysis of receptor recycling and degradation demonstrated