Actin filaments are involved in the regulation of trafficking of two closely related chemokine receptors, CXCR1 and CXCR2

The ligand-induced internalization and recycling of chemokine receptors pla y a significant rule in their regulation. In this study, we analyzed the in volvement of actin filaments and of microtubules in the control of ligand-i nduced internalization and recycling of CXC chemokine receptor (CXCR)1 and CXCR2, two closely related G protein-coupled receptors that mediate ELR-exp ressing CXC chemokine-induced cellular responses. Nocodazole, a microtubule -disrupting agent, did not affect the IL-8-induced reduction in cell surfac e expression of CXCR1 and CXCR2, nor did it affect the recycling of these r eceptors following ligand removal and cell recovery at 37 degreesC. In cont rast, cytochalasin D, an actin filament depolymerizing agent, promoted the IL-8-induced reduction in cell surface expression of both CXCR1 and CXCR2, Cytochalasin D significantly inhibited the recycling of both CXCR1 and CXCR 2 following IL-8-induced internalization, the inhibition being more pronoun ced for CXCR2 than for CXCR1. Potent inhibition of recycling was observed a lso when internalization of CXCR2 was induced by another ELR-expressing CXC chemokine, granulocyte chemotactic protein-2. By the use of carboxyl termi nus-truncated CXCR1 and CXCR2 it was observed that the carboxyl terminus do mains of CXCR1 and CXCR2 were partially involved in the regulation of the a ctin-mediated process of receptor recycling. The cytochalasin D-mediated in hibition of CXCR2 recycling had a functional relevance because it impaired the ability of CXCR2-expressing cells to mediate cellular responses. These results suggest that actin filaments, but not microtubules, are involved in the regulation of the intracellular trafficking of CXCR1 and CXCR2, and th at actin filaments may be required to enable cellular resensitization follo wing a desensitized refractory period.