Nuclear localization of alkaline phosphatase in cultured human cancer cells

The nucleolar localization of alkaline phosphatase (ALPase) was observed by electron microscopic cytochemistry. The culture cells used in this study were normal human cells (fibroblast, WI-38) and human cancer cells (hepatocellular carcinoma, Hep-G2; malignant melanoma, A-375; pancreatic carcinoma, BxPC-3). Cultured cells in almost all strains contained high ALPase activity in the nucleolus, and the localization of ALPase changed during the cell cycle stages. The pattern of ALPase localization during the interphase was divided into three groups: cytoplasmic type, nucleus type, and both types. Moreover, at the mitotic phase, the reaction products were observed on the chromosome. In the cultured malignant melanoma cells, the appearance ratio of ALPase reaction products on the nucleolus (33.9%) showed a higher ratio compared with normal cultured fibroblasts (6.3%). This phenomenon suggests that the high level of the ALPase reaction product may be related to the high level of proliferation of cancer cells.