Isolation and characterization of different clones including myoepithelial-like variants from a clonal neoplastic epithelial duct cell line of human salivary gland origin.

A clonal neoplastic epithelial duct cell (HSGc) of human salivary gland origin has a fine structure similar to the intercalated duct cell and the capacity to express secretory component and lactoferrin. HSGc cells tend to form an occasional glandular arrangement in vitro and in vivo, and transplantation of cells into nude mice resulted in production of adenocarcinoma. By repeated single cell cloning, different types of clones could be isolated from HSGc. Cuboidal clones resemble the parent cell, but fail to form the glandular arrangement or express lactoferrin, suggesting a less differentiated type. Elongated clones have a fine structure similar to myoepithelial cells and carry myoepithelial markers such as S100 protein, actin, and myosin which are not detected in the HSGc and its cuboidal clones. These myoepithelial-like clones are able to express secretory component, lactoferrin, and lysozyme and to produce glycosaminoglycans, suggesting that they are a functionally active form of the neoplastic cell but different from the normal myoepithelial cell. Judging from their growth properties in vitro and in vivo, the myoepithelial-like clones are less malignant than HSGc or its cuboidal clones. Of four elongated clones, two did not produce tumors in athymic mice, while all of the cuboidal clones were tumorigenic. These findings suggest a possible conversion of the neoplastic duct cell to myoepithelial-like variants with low malignancy.