Effects of differentiating agents on cell surface expression of the breast carcinoma-associated DF3-P epitope

The DF3 antigen is a member of a family of high-molecular-weight glycoproteins aberrantly expressed in human breast carcinomas. Recent work has described the generation of a monoclonal antibody (MAb), designated DF3-P, that reacts with immature, underglycosylated precursors of DF3 antigen. Immunoperoxidase staining studies have demonstrated that MAb DF3-P exhibits selective reactivity with malignant mammary epithelium. Using flow cytometry and live cell radioimmunoassays, the present studies demonstrate that the epitope recognized by MAb DF3-P is expressed on the surface of MCF-7 and other human breast carcinoma cell lines. We also demonstrate that treatment of MCF-7 cells with 12-O-tetradecanoylphorbol-13-acetate, an agent known to induce a more differentiated mammary cell phenotype, is associated with increased expression of the DF3-P epitope. Similar findings were obtained with sodium butyrate. The results indicate that these agents increase both cell surface DF3-P antigen density and the percentage of DF3-P-positive cells. Immunofluorescence studies performed on chamber slides further demonstrate that MAb DF3-P-reactive cells are detectable in small clones or clusters. Similar studies with 12-O-tetradecanoylphorbol-13-acetate- and butyrate-treated cells demonstrate increases in the size and number of these clusters. Taken together, these results indicate that the DF3-P epitope is expressed on the surface of human breast carcinoma cell lines and that the heterogeneity of this expression is related to the presence of differentiating signals.