AGONIST-INDUCED SEQUESTRATION, RECYCLING, AND RESENSITIZATION OF PLATELET-ACTIVATING-FACTOR RECEPTOR - ROLE OF CYTOPLASMIC TAIL PHOSPHORYLATION IN EACH PROCESS

Agonist-induced sequestration, recycling, and resensitization of plate let-activating factor (PAF) receptor were characterized in transfected Chinese hamster ovary cells. Exposure of the cells to PAF led to rapi d sequestration of the receptors into the intracellular compartment an d desensitization of the response to PAF, The sequestration was inhibi ted by pretreatments that perturbed the clathrin-mediated pathway. Sub sequent removal of PAF by washing with receptor antagonists led to rap id recycling of the sequestered receptors to the cell surface accompan ied by resensitization to PAF, To evaluate the potential role of phosp horylation in the receptor cytoplasmic tail during these processes, mu tant receptors in which the tails were truncated or substituted, so as to lack serine/threonine residues, were created. PAF phosphorylated t he wildtype receptor rapidly and strongly, but the mutants did not. Th e maximal extent of sequestration of each mutant was lower than that o f the wild-type, and one of the substituted mutants showed no sequestr ation. Furthermore, the sequestration-defective mutant showed evidence of desensitization after agonist stimulation but not resensitization after agonist removal, Thus, agonist-induced phosphorylation of the cy toplasmic tail facilitates but is not essential for receptor sequestra tion, and sequestration/recycling appears important in receptor resens itization.