Tumor‐promoting Phorbol Ester Induces Alterations of Sialidase and Sialyltransferase Activities of JB6 Cells

Abstract

Sialidase and sialyltransferase activities were studied in JB6 mouse epidermal cells before and after exposure to phorbol ester, 12‐O‐tetradecanoyl phorbol‐13‐acetate (TPA), which irreversibly induces anchorage‐independent growth and tumorigenicity. JB6 cells exhibited sialidase activities toward 4‐methylumbelliferyl‐α‐d‐N‐acetylneuraminic acid (4MU‐NeuAc) and gangliosides at pH 4.5 in the particulate fraction but apparently not in the cytosol at pH 4.5 or 6.0. In JB6 cells exposed to TPA and in the anchorage‐independent transformants, the sialidase activity toward 4MU‐NeuAc was decreased and the activity toward gangliosides was increased compared with those in untreated JB6 cells. Immunological analysis with antisera against membrane‐associated sialidases I and II revealed that plasma membrane‐associated sialidase I was increased and lysosomal membrane‐associated sialidase II was decreased under these conditions. TPA treatment also affected the sialyltransferase activities of JB6 cells: an elevation of the transfer activities toward asialo‐orosomucoid and asialo‐porcine submaxillary mucin but a reduction of GM3 and GD3 synthase activities were observed on exposure to TPA and in cells transformed by TPA to retain anchorage‐independency. These results suggest that an increase in sialic acid bound to glycoproteins and a decrease in that bound to glycolipids may occur in JB6 cells exposed to TPA and in the anchorage‐independent transformants.

Up-regulation of plasma membrane-associated ganglioside sialidase (Neu3) in human colon cancer and its involvement in apoptosis suppression

“…Unlike lysosomes, the membranes do not contain a set of glycosidases to degrade glycoproteins and glycolipids, thereby Neu3 probably plays crucial roles in the regulation of cell surface functions other than catabolism of glycoconjugates. Previous studies on a ganglioside sialidase in murine malignant cells (15,16) have suggested that altered expression of the sialidases is likely to be related to malignant transformation, although it was not identified to be Neu3 at that time. In this article, we provide evidence that human Neu3 is indeed significantly up-regulated in colon cancer.…”

Metastatic potential of transformed rat 3Y1 cell lines is inversely correlated with lysosomal‐type sialidase activity

“…In particular, the alterations in sialylation have been proposed to be intimately associated with invasiveness and metastatic ability [4,6,8,9]. To elucidate how such aberrant sialylation occurs in cancer cells, we have been studying sialidase and sialyltransferase in rat hepatoma [lo-121 and other tumor models [13]. We are now focusing on the enzyme studies in relation to invasiveness and metastasis.…”

“…Located in the lysosomal matrix [14], cytosol [15] lysosomal membrane and plasma membrane [16], they are altered quantitatively in hepatocarcinogenesis [lo] and in phorbol ester-induced malignant transformation of mouse epidermal JB6 cells [13]. We also found that Gal/R4GlcNAca 2-6 sialyltransferase activity was selectively increased in hepatomas [11,12].…”

Molecular Cloning and Characterization of a Plasma Membrane-associated Sialidase Specific for Gangliosides

“…In addition, alterations of the levels of ganglioside sialidase expression associated with malignant transformation have been described: loss of cell density-dependent suppression in 3T3-transformed cells (26) and appearance of ganglioside sialidase activity in transformed cell lines of baby hamster kidney fibroblasts (27). We previously reported an increase of plasma membrane sialidase activity associated with induction of anchorageindependent growth in mouse epidermal JB6 cells exposed to phorbol esters (28). However, little is known about the molecular mechanisms underlying such sialidase alterations.…”