CXCR7/RDC-1 is a G protein-coupled receptor (GPCR) member of the CXC subfamily of chemokine receptors. Human CXCR7/RDC-1 is 362 amino acids (aa) in length with a predicted molecular weight of 41 kDa. Mouse and rat CXCR7/RDC-1 share 93% aa sequence identity with the human protein. CXCR7/RDC-1 binds to and acts as a scavenger for CXCL11/I-TAC and CXCL12/SDF-1. CXCR7/RDC-1 can also function as a co-receptor for HIV and SIV. Unlike other chemokine receptors, CXCR7/RDC-1 does not activate G protein signaling, but instead initiates beta-Arrestin-mediated receptor-ligand internalization. Although CXCR7/RDC-1 itself does not activate G protein signaling, the receptor can heterodimerize with CXCR4 to activate G proteins in response to CXCL12/SDF-1 binding. Studies on CXCR7/RDC-1 knockout mice suggest that it is critical for cardiovascular development. While CXCR7/RDC-1 does not appear to signal in normal hematopoietic cells, it is highly expressed in leukemic cells where it activates Akt signaling that promotes cell trafficking and adhesion. CXCR7/RDC-1 also mediates neuronal migration, displays aberrant signaling in astrocytes, and is highly expressed in glioma cells.