SC1, an immunoglobulin superfamily cell adhesion molecule, is expressed in embryonic tissues and plays an important role in development through its cell adhesive activity. SC1 is also found in a variety of tumors and its expression is associated with a poor prognosis. The expressional patterns of SC1 were examined in sporadic cases of canine mammary gland tumors and it was found that this molecule is enriched in adenocarcinomas and is weaker in benign mixed tumors. SC1 might therefore be involved in the malignancy and progression of canine mammary gland tumors. To confirm this paradigm, the mammary gland cell line JYG-B was used as the recipient of SC1 cDNA. The resulting SC1-transfected cells were subsequently analyzed using a convenient in vitro model system. The self-aggregation activity of SC1-transfected cells was significantly increased and was blocked by an anti-SC1 antibody generated by hyper-immunized ostrich yolk. In addition, cell locomotion assays revealed an enhanced migration activity of SC1-transfected cells on SC1-coated transwell chambers. The in vivo activities of the cells were examined by subcutaneous implantation into nude mice. Tumor growth was significantly promoted in the mice after implantation with SC1-transfected cells, in comparison to parental- and mock-transfectants. This growth was inhibited by oral administration of gold-ion water. The invasion of SC1-transfectants into the surrounding muscular and adipose tissues was rigorously enhanced. These findings suggest that SC1 might promote the progression of mammary gland tumor cells by increasing cell adhesion.

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