Endocytosis and Compartmentalized Intracellular Signaling of the Prostaglandin Receptor EP4 Mediate Pain
Prostaglandin E2 (PGE2) is recognized as a major mediator of inflammatory pain. However, the intracellular signaling mechanisms by which PGE2 mediates pain remain unclear. Here, we show that pain-like responses evoked by PGE2 in dorsal root ganglion (DRG) nociceptors are mediated by internalization and compartmentalized signaling of the EP4 receptor. The EP4-selective agonist L-902,688 induced immediate nocifensive behavior and prolonged mechanical allodynia in mice and sensitized isolated DRG nociceptors. Pharmacological inhibition of clathrin- and dynamin-mediated endocytosis (using pitstop2 and dyngo4a) and siRNA knockdown of Dnm1 prevented EP4-induced nociception and sensitization, implicating receptor trafficking in pain signaling. Using genetically-encoded biosensors, we monitored EP4 trafficking and downstream signaling within subcellular compartments of HEK293 cells. PGE2 stimulated dynamin- and {beta}-arrestin-dependent EP4 trafficking from the plasma membrane to early, late and recycling endosomes and Golgi apparatus, and mobilized intracellular EP4 pools from the endoplasmic reticulum. PGE2 induced the assembly of EP4, G proteins and {beta}-arrestin signaling complexes in endosomes and the Golgi apparatus. Inhibition of EP4 endocytosis suppressed intracellular cAMP production and ERK activation. Our findings reveal that EP4-mediated nociceptive signaling originates from intracellular compartments and suggest that modulating EP4 internalization and subcellular signaling dynamics could offer a novel strategy for inflammatory pain management.