Ultrastructural localization of Helix pomatia agglutinin (HPA)-binding sites in human breast cancer cell lines and characterization of HPA-binding glycoproteins by western blotting.

Ultrastructurally, cells of five human breast cancer cell lines (MCF7, BT549, BT20, T47D, and HBL100) generally displayed many characteristics of their epithelial origin. The most distinctive features were observed in MCF7 cells, which consistently showed microvilli and submembranous granules. These ultrastructural findings served as a basis for localizing the binding sites of the lectin Helix pomatia agglutinin (HPA). After use of the pre-embedding method consistent HPA labeling of the cell membrane was obtained in all the cell lines, and in association with microvilli and submembranous granules in the MCF7 cells. The HBL 100 cells were not labeled by HPA irrespective of the method used. In addition, lysates from these cell lines were subjected to polyacrylamide gel electrophoresis and Western blotting with HPA to analyze these binding sites further. In the Western blots, however, lysates of JBL100 cells, in common with all those from the other cell lines, revealed a number of HPA-reactive bands, indicating the greater sensitivity of Western blots compared with the histochemical preparation. The principal band was of approximately 90 kDa, and it was suggested that this could be related to the transferrin receptor.