Extracellular matrix metalloproteinase (MMP) inducer (EMMPRIN), also known as basigin and CD147, is a 44-66 kDa, variably glycosylated, type I transmembrane protein that belongs to the immunoglobulin superfamily (1-4). Human EMMPRIN is 269 amino acids (aa) in length and contains a 24 aa signal sequence, a 183 aa extracellular domain (ECD), a 21 aa transmembrane (TM) domain and a 41 aa intracellular domain. The ECD contains one C2-type and one V-type Ig-like domain. There is one 385 aa splice variant that contains an extra N-terminal IgCAM domain and is found only in the retina (5). mRNA transcripts, but not protein, have been reported for additional 432, 388, 205, 176, and 174 aa variants.
EMMPRIN is expressed in areas of tissue remodeling, including tumors, endometrium, placenta, skin, and regions undergoing angiogenesis (1, 2, 6-9). It is also expressed in cells with high metabolic activity, such as lymphoblasts, macrophages and tumor cells (2, 10). On cells with elevated metabolic rates, EMMPRIN is often co-expressed with the amino acid transporter CD98h (11). EMMPRIN also interacts with caveolin-1 (via its C2-like domain), and this reduces the level of EMMPRIN glycosylation and subsequent EMMPRIN multimerization and activity (12). EMMPRIN’s TM sequence contains a Glu and a Pro which are important for intracellular interactions with cyclophilins (CyP) (3, 13, 14). CyPA (cyclosporin A receptor) and CyP60 interactions with the TM segment promote leukocyte inflammatory chemotaxis and surface expression of EMMPRIN, respectively (13, 14). An active 22 kDa fragment can be shed from tumor cells by MT1-MMP (1). Tumor cells can also release active, full-length EMMPRIN in microvesicles (15, 16). Functionally, EMMPRIN is known to induce urokinase-type plasminogen activator (uPA), VEGF, hyaluronan, and multiple MMPs (1, 2, 7, 8, 9). Human EMMPRIN (269 aa) shows 58%, 58%, 62%, and 52% aa identity with mouse, rat, bovine, and chicken EMMPRIN, respectively. It also shows 25% and 38% aa identity with the related proteins, embigin and neuroplastin (SDR-1), respectively (4).