RhoB plays an essential role in CXCR2 sorting decisions

The CXCR2 chemokine receptor is a G-protein-coupled receptor that undergoes clathrin-mediated endocytosis upon ligand binding. The trafficking of CXCR2 is crucial for cells to maintain a proper chemotactic response. The mechanisms that regulate the recycling/degradation sorting decision are unknown. In this study, we used dominant-negative (T19N) and GTPase-deficient activated (Q63L) RhoB mutants, as well as RhoB small interfering RNA (siRNA) to investigate the role of RhoB in CXCR2 trafficking. Expression of either of the RhoB mutants or transfection of RhoB siRNA impaired CXCR2-mediated chemotaxis. Expression of RhoB T19N and transfection of RhoB siRNA impaired sorting of CXCR2 to the lysosome after 3 hours of CXCL8 stimulation and impaired CXCL8-induced CXCR2 degradation. In cells expressing the RhoB Q63L mutant, CXCR2 recycling through the Rab11a recycling compartment was impaired after 30 minutes of CXCL8 stimulation as was CXCL8-induced CXCR2 degradation. For cells expressing activated RhoB, CXCR2 colocalized with Rab4, a marker for the rapid recycling pathway, and with the mannose-6-phosphate receptor, which traffics between the trans-Golgi network and endosomes. These data suggest that CXCR2 recycles through alternative pathways. We conclude that oscillation of RhoB GTPase activity is essential for appropriate sorting decisions, and for directing CXCR2 degradation and recycling--events that are required for optimal chemotaxis.