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 characteristi cs of their epithelial origin. The most distinctive features were obse rved in MCF7 cells, which consistently showed microvilli and submembra nous granules. These ultrastructural findings served as a basis for lo calizing the binding sites of the lectin Helix pomatia agglutinin (HPA ). After use of the pre-embedding method consistent HPA labeling of th e 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 polyacrylami de gel electrophoresis and Western blotting with HPA to analyze these binding sites further. In the Western blots, however, lysates of HBL10 0 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 princip al band was of approximately 90 kDa, and it was suggested that this co uld be related to the transferrin receptor.