Identification and molecular characterization of rat CXCR3: Receptor expression and interferon-inducible protein-10 binding are increased in focal stroke

We describe here the cloning and characterization of a rat homolog of the c hemokine receptor CXCR3. The predicted amino acid sequence of rat CXCR3 con tains 367 amino acid residues, sharing 96 and 87% amino acid sequence ident ity to the murine and human CXCR3, respectively. Among a large panel of che mokines tested, only interferon-inducible protein-10 (IP-10), interferon-ga mma-induced monokine, and interferon-inducible T cell alpha-chemoattractant demonstrated specific abilities to induce an intracellular calcium mobiliz ation response in human embryonic kidney 293 cells transfected with rat CXC R3 expression vector. I-125-IP-10 competition binding studies to the CXCR3- transfected human embryonic kidney 293 cells demonstrated that human IP-10 and interferon-inducible T cell alpha-chemoattractant are more potent ligan ds than human interferon-gamma-induced monokine. Following our previous obs ervation for the induced expression of IP-10 in focal stroke, we demonstrat e here the time-dependent up-regulation of CXCR3 mRNA in the rat ischemic c ortex after permanent occlusion of the middle cerebral artery. A significan t increase in I-125-IP-10-specific binding to ischemic cerebral cortical sa mples was obtained and paralleled the increase in CXCR3 mRNA expression. Th e changes in receptor expression and ligand binding correlate highly with k nown changes in leukocyte accumulation, and gliosis occurred after focal st roke. These data suggest that CXCR3/IP-10 may be a potential novel therapeu tic target in focal stroke. In addition, the cloning of rat CXCR3 provides an important tool for the investigation of the pathophysiological role of C XCR3 in other rodent disease models.