THE PROGRESSION ASSOCIATED ANTIGEN MUC18 - A UNIQUE MEMBER OF THE IMMUNOGLOBULIN SUPERGENE FAMILY

The cell surface glycoprotein MUC18 was originally identified as a pro gression associated antigen in melanoma. MUC18 is expressed most stron gly on metastatic losions and advanced primary tumours and is only rar ely detected in benign lesions. cDNA, cloning revealed MUC18 to be a n ovel member of the immunoglobulin superfamily with sequence similarity to a number of cell adhesion molecules. Cloning of both the human and mouse MUC18 genes indicate that their predicted protein structures ar e very similar with an overall amino acid identity of 75%. Like its hu man counterpart, murine MUC18 is also expressed by transformed melanoc ytes. Analysis of the promoter region of the human gene has provided e vidence for regulatory elements found in smooth muscle specific genes and in both human and mouse: this is the normal site of MUC18 expressi on. The presence of putative binding sites for the transcriptional fac tors AP-1, AP-2 and CREB, suggest that MUC18 gene expression can also be modulated by external factors.