MULTIPLE FORMS OF MAMMALIAN SIALIDASE - ALTERED EXPRESSION IN CARCINOGENESIS

We have demonstrated that rat liver contains at least four types of si alidase differing in subcellular location, in catalytic property and i mmunologically. They are intralysosomal, cytosolic and membrane-associ ated sialidases I and II. Membrane sialidase I locates mainly in plasm a membrane and sialidase II in lysosomal membrane. Immunological study reveals that the same types of sialidase exist in various tissues of rat and of other mammalian species. Based on these results, we examine d the sialidases in rat hepatomas and in transformed cells of JB6 mous e epidermal cell. Hepatomas were found to possess four types of sialid ase and the three of them altered quantitatively. Intralysosomal siali dase activity was higher but cytosolic and lysosomal membrane sialidas e activities were lower in hepatomas than in control liver. When the s ialidases of transformants of JB6 cells were compared with those of co ntrol cells, the activities of two lysosomal sialidases were decreased and contrarily plasma membrane sialidase was increased. We discussed a possible significance of the sialidase alterations in carcinogenesis .