CXC Chemokine Receptor

The CXC subfamily (or α-chemokines), a pleiotropic family of cytokines, is characterized by four highly conserved cysteine amino acid residues, with two cysteine residues (C) and a non-cysteine amino acid (X) between them. The CXC family is known for its ability to promote trafficking of various leukocytes and to regulate angiogenesis and vascular remodelling. Depending on the presence or absence of the ELR motif (the sequence Glu-Leu-Arg), which immediately precedes the first cysteine residue near the amino-terminal end, CXC chemokines are potent promoters or inhibitors of angiogenesis.
The ELR-positive chemokines (i.e., CXCL1 to CXCL3 and CXCL5 to CXCL8) are angiogenic and act mainly through the CXCR2 receptor.  The ELR motif, along with the CXC residues, is required for receptor activation. By contrast, the non-ELR chemokines (CXCL4, CXCL9, CXCL10, CXCL11 and CXCL17) are angiostatic and act mainly through the CXCR3B receptor. The exception to this is CXCL12, which is a non-ELR chemokine but is angiogenic and exerts its effects on the vasculature primarily by binding to CXCR4 and CXCR7.