ULTRACYTOCHEMICAL LOCALIZATION OF ALKALINE PHOSPHATASE ISOZYMES IN HUMAN CANCER CELL LINES IN VITRO

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Biochemically identified cancer-associated alkaline phosphatase (orthophosphoric monoester phosphohydrolase, EC 3.1.3.1) isozymes were studied by electron microscopic cytochemistry in four human cancer cell lines, as follows: chorion isozyme in KMK-2, Regan isozyme in CaR-1 and HeLa S3-10, and Kasahara isozyme in HeLa S3-5. Using ultracytochemical techniques, the chorion isozyme in KMK-2 cells was demonstrated almost exclusively on the microvilli facing the culture medium and not on the lateral surface adjacent to the neighbouring cells with interdigitating folds. In contrast, in both the HeLa sublines, which are thought to represent more immature cells, the Regan and Kasahara isozymes were demonstrated on the whole plasma membrane. The Regan isozyme in CaR-1 cells was strongly demonstrated in the intracytoplasmic microcysts in addition to the whole plasma membrane. These localizations might be related to the differentiation and deviated formation of the plasma membrane in cancer cells.