MODULATION OF THE SHEDDING OF A RAT TUMOR-ASSOCIATED ANTIGEN BY GROWTH-REGULATION AND ANTICANCER DRUGS

CE7 antigen is shed from A3 cell surfaces by cells grown in medium con taining a sufficient (10%) amount of fetal calf serum (FCS), but shedd ing of the antigen decreases with a decrease in FCS content in the cul ture medium. However, the cells contain similar amounts of antigen as evidenced by Western blotting, indicating that low FCS levels interfer e with antigen shedding but not antigen synthesis. Antigen expression by A3 cells treated with mitomycin C gradually shifted from negative t o a strong positive with time, and on day 2, two peaks corresponding t o negative and positive cells within the population can be observed. I n contrast, A3 cells treated with bleomycin and cyclophosphamide shift ed as a whole from negative to weakly positive. When A3 cells in media containing 10% FCS were incubated at 4-degrees-C, although the cells did not proliferate, antigen expression could not be detected by flow cytometry.