METCAM/MUC18 Expression and Cancer Metastasis

The aberrant expression of cell adhesion molecules (CAMs) is correlated with the malignant progression of many tumors. MUC18/CD146/A32/MelCAM/S-endo, an integral membrane glycoprotein, is a CAM in the immunoglobulin gene superfamily. MUC18 has often been mistaken as a mucin because of the misleading nomenclature. Based on its biological functions and other known biochemical properties, we propose to re-name it as METCAM (metastasis CAM). METCAM/MUC18 expression has a very interesting effect on tumor formation and metastasis. The overexpression of METCAM/MUC18 has been correlated with the malignant progression of human melanoma and human prostate cancer. In melanoma, the ectopic over-expression of METCAM/MUC18 has no effect on tumorigenesis, but augments the metastasis of cancer cells. In prostate cancer, the ectopic over-expression of human METCAM/MUC18 has an even greater effect, increasing tumorigenesis and initiating the metastasis of cancer cells. However, an opposite effect of METCAM/MUC18 on tumorigenesis and metastasis of breast cancer, some mouse melanoma cell lines, and perhaps haemangioma and nasopharygeal carcinoma has also been suggested. Taken together, we suggest that the different effect of METCAM/MUC18 on tumor formation and metastasis is dependent on the intrinsic properties of each tumor cell line. This paper will review previous experiments and results and present some possible mechanisms of METCAM/MUC18- mediated tumorigenesis and metastasis for future studies.