The chemokine receptor CCR2 mediates the binding and internalization of monocyte chemoattractant protein-1 along brain microvessels.
Previous results from this laboratory revealed the presence of high-affinity saturable binding sites for monocyte chemoattractant protein-1 (MCP-1) along human brain microvessels (Andjelkovic et al., 1999; Andjelkovic and Pachter, 2000), which suggested that CC chemokine receptor 2 (CCR2), the recognized receptor for this chemokine, was expressed by the brain microvascular endothelium. To test the role of CCR2 directly in mediating MCP-1 interactions with the brain microvasculature, we assessed MCP-1 binding activity in murine brain microvessels isolated from wild-type mice and from CCR2 (-/-) mice engineered to lack this receptor. Results demonstrate that MCP-1 binding is greatly attenuated in microvessels prepared from CCR2 (-/-) mice compared with wild-type controls. Moreover, microvessels from wild-type mice exhibited MCP-1-induced downmodulation in MCP-1 binding and a recovery of binding activity that was not dependent on de novo protein synthesis. Furthermore, MCP-1 was shown to be internalized within wild-type microvessels, but not within microvessels obtained from CCR2 (-/-) mice, additionally demonstrating that CCR2 is obligatory for MCP-1 endocytosis. Last, internalization of MCP-1, but not transferrin, was observed to be inhibited by disruption of caveolae. Internalized MCP-1 also colocalized at some sites with caveolin-1, a major protein of caveolae, implying that this chemokine is endocytosed, in part, via nonclathrin-coated vesicles. These results prompt consideration that MCP-1 signals may be relayed across the blood-brain barrier by highly specialized interactions of this chemokine with its cognate receptor, CCR2, along brain microvascular endothelial cells.
Dzenko
K A
KA
Blood-Brain Barrier Laboratory, Department of Pharmacology, University of Connecticut Health Center, Farmington, Connecticut 06030, USA.
Andjelkovic
A V
AV
Kuziel
W A
WA
Pachter
J S
JS
D000818:Animals; D001667:Binding, Competitive / Q000502:physiology; D001921:Brain / Q000098:blood supply*; D021941:Caveolae / Q000187:drug effects / Q000378:metabolism; D051242:Caveolin 1; D022461:Caveolins / Q000378:metabolism; D018932:Chemokine CCL2 / Q000378:metabolism*; D018925:Chemokines / Q000378:metabolism; D003433:Crosses, Genetic; D015536:Down-Regulation; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005372:Filipin / Q000494:pharmacology; D066298:In Vitro Techniques; D008024:Ligands; D051379:Mice; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D008833:Microcirculation / Q000187:drug effects / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D054390:Receptors, CCR2; D019707:Receptors, Chemokine / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D013696:Temperature; D014168:Transferrin / Q000378:metabolism
C515334:CCR2 protein, human; C495541:Cav1 protein, mouse; D051242:Caveolin 1; D022461:Caveolins; C515335:Ccr2 protein, mouse; D018932:Chemokine CCL2; D018925:Chemokines; D008024:Ligands; D054390:Receptors, CCR2; D019707:Receptors, Chemokine; D014168:Transferrin; D005372:Filipin