The
mucin family of
proteins is largely expressed on sedentary epithelial cells lining the gastrointestinal, pulmonary, and reproductive tracts and their associated organs and malignant
tumors. It is less well-known that
mucins are also expressed on circulatory cells of the immune and inflammatory systems, such as monocytes, macrophages, leukemic, and
lymphoma cells. The epithelial
mucins function in (a) protection and lubrication of mucosal linings, (b) cell adhesion and cell-to-cell contact, (c) cell migration and
metastasis, and (d) signal transduction. It would be logical to presume that
mucins expressed on circulating mononuclear cells could perform similar functions. Recently, it was proposed that the
alpha-fetoprotein (AFP) receptor, known to be present on solid epithelial-derived malignant
tumor cells, can be identified as a
mucin glycoprotein. Interestingly, it was also reported that AFP binds to a receptor on circulating cells and sedentary
tumor cells of lymphoreticular origin, especially monocytes associated with
lymphomas and
leukemias. The primary objective of the present commentary is to present literature-based evidence that some of the cell surface
mucins on sedentary epithelial
tumor cells and certain
mucins expressed on circulating monocytes/macrophages are identical to the AFP receptor. The secondary objective is to discuss the role of AFP and its derived
peptides in the growth suppression of
adenocarcinomas and
lymphomas using the AFP-
mucin receptor concept as a key to the mechanism of
tumor growth inhibition.