Members of the C-X-C or α chemokine family are characterized by a pair of cysteine residues separated by a single amino acid and primarily function as chemoattractants for neutrophils. The C-X-C family includes IL-8, NAP-2, MSGA and stromal cell derived factor-1 (SDF-1). Receptors for the C-X-C family are G protein-coupled, seven pass transmembrane domain proteins and include proteins such as IL-8RA, IL-8RB, CXCR-3 and fusin (also designated LESTR or CXCR-4). C-X-C chemokine receptor type 7 (CXCR-7), also known as RDC-1, is a 362 amino acid receptor for SDF-1. Initially identified as a receptor for vasoactive intestinal peptide (VIP), it is now considered to be an orphan receptor. CXCR-7, with CSCR-4, also acts as a coreceptor for human immunodeficiency viruses (HIV). Highly expressed in monocytes, B-cells and basophils, and highly active in various biological processes, including cell growth, cell adhesion and tumor growth, CXCR-7 may play a role in tumorigenesis.
