Intracellular trafficking of human CXCR1 and CXCR2: regulation by receptor domains and actin-related kinases

Abstract

In this study we investigated the regulation of CXCR1 and CXCR2 intracellular trafficking. First, we produced a chimeric CXCR2 receptor that contained the internalization motifs of both CXCR2 and CXCR1 (CXCR2: LLKIL sequence; CXCR1: C‐terminal phosphorylation sites). Elevated levels of internalization were induced by different ELR‐expressing CXC chemokines on the chimeric receptor, as compared to wild‐type CXCR2. Analysis of inter‐relationships between CXCR1 and CXCR2 during internalization indicated that the exposure of cells that expressed both CXCR1 and CXCR2 to CXCL8 or CXCL6 resulted in decreased levels of CXCR1 internalization as compared to those in cells that expressed only CXCR1. To characterize the role of actin‐related components in CXCR1 and CXCR2 trafficking, wortmannin, a potent inhibitor of phosphatidylinositol kinases, was used. The presence of wortmannin during receptor recycling inhibited CXCR1 and CXCR2 re‐expression following CXCL8‐induced internalization, and resulted in a marked disruption of the proper organization of actin filaments. The kinase‐dependent recycling process required CXCR2 C‐terminal phosphorylation sites. Our results suggest that actin‐related kinases are required for the proper functionality of actin filaments, which are the instrumental factors needed for receptor recycling. In all, CXCR1 and CXCR2 internalization and recycling are tightly regulated by receptor domains and by actin‐related kinases.

Chemokine receptor internalization and intracellular trafficking

“…The kinase-dependent recycling of CXCR2 requires the phosphorylation sites in the carboxyl-terminus of CXCR2. This phosphorylation is most likely associated with alterations in actin rearrangements, which are required for the movement of endocytic compartments [95]. These results implicate the importance of the carboxyl-terminus in the regulation of chemokine receptor recycling.…”

Interleukin-8 Differentially Regulates Migration of Tumor-Associated and Normal Human Brain Endothelial Cells

“…In the case of IL-8, high levels of this chemokine are associated with receptor desensitization due to receptor internalization; once the ligand is removed, the receptor is recycled to the cell surface (28,29). Because TuBECs do not seem to be responsive to IL-8, the possibility exists that there may be aberrant recycling of the IL-8 receptor.…”

Critical role of endothelial CXCR2 in LPS-induced neutrophil migration into the lung

“…Both chemokines are functional homologs of human CXCL8 (IL-8), which has been associated with the development and outcome of ARDS (9,10). Upon activation, CXCR2 is phosphorylated, leading to receptor desensitization and internalization, intracellular removal of the ligand, and finally, degradation or re-expression of the receptor on the cell membrane (11). CXCR2 is expressed on PMNs, where its activation induces a variety of cell responses including degranulation, respiratory burst, phagocytosis, directed cell movement, integrin activation, and transmigration (12)(13)(14).…”