Regulation of Sialyl Lewis Antigen Expression in Colon Cancer Cells by Sialidase NEU4

Abstract

Sialyl Lewis antigens, sialyl Lewis a and sialyl Lewis x, are utilized as tumor markers, and their increase in cancer is associated with tumor progression by enhancement of cancer cell adhesion to endothelial E-selectin. However, regulation mechanisms are not fully understood. We previously demonstrated that NEU4 is the only sialidase efficiently acting on mucins and it is downregulated in colon cancer. To elucidate the significance of NEU4 down-regulation, we investigated sialyl Lewis antigens as endogenous substrates for the sialidase. NEU4 was found to hydrolyze the antigens in vitro and decrease cell surface levels much more effectively than other sialidases. Western blot, thin layer chromatography, and metabolic inhibition studies of desialylation products revealed NEU4 to preferentially catalyze sialyl Lewis antigens expressed on O-glycans. Cell adhesion to and motility and growth on E-selectin were significantly reduced by NEU4. E-selectin stimulation of colon cancer cells enhanced cell motility through activation of the p38/Hsp27/actin reorganization pathway, whereas NEU4 attenuated the signaling. On immunocytochemical analysis, some NEU4 molecules were localized at cell surfaces. Under hypoxia conditions whereby the antigens were increased concomitantly with several sialyl-and fucosyltransferases, NEU4 expression was markedly decreased. These results suggest that NEU4 plays an important role in control of sialyl Lewis antigen expression and its impairment in colon cancer.

Sialic Acids Sweeten a Tumor's Life

“…Generally it is believed that downregulation of sialidases in cancer increases their metastatic ability. For example, downregulation of the lysosomal sialidases NEU1 and NEU4 favors tumor metastasis through hypersialylation and enhanced signaling of the laminin receptor b4-integrin or reduced hydrolysis of sLe x antigens, respectively (31,32). Additional work is necessary to understand the individual and combined contribution of sialyltransferases and sialidases in cancer cell motility, tissue invasion, and metastasis formation.…”

Sialidase NEU4 Hydrolyzes Polysialic Acids of Neural Cell Adhesion Molecules and Negatively Regulates Neurite Formation by Hippocampal Neurons

“…We previously demonstrated that the human NEU4 short form, NEU4S, apparently present in almost all intracellular membranes including endoplasmic reticulum, but also partially in plasma membranes desialylating cell surface glycans such as sialyl-Le a and sialyl-Le x (37). To clarify in which cellular site murine NEU4b acts on the polySia, the subcellular localization studies were performed by immunofluorescence experiments of Neuro2a cells transfected with FLAG-NEU4b and ST8SiaIV.…”

Characterization of Sialidases Neu1, Neu2, and Neu4 in a Canine Model of Breast Cancer

“…In line with this hypothesis, recent experiments have suggested an important role for the microenvironment in the regulation of Neu4 expression. 23 Also pointing to a microenvironment role in Neu4 regulation, despite its low levels of protein expression in vitro, Neu4 was, although tenuously, expressed in primary tumor xenografts but not in all metastatic lesions. Experimental findings in the literature regarding the role of Neu4 in malignancy are somewhat contradictory.…”

“…SLe(x) and SLe(a) were recently shown to be substrates for Neu4. 23 Thus, Neu4 might downregulate the expression of SLe(x) observed in primary CMTs, 24 important for tumor cell detachment. Neu4 has important substrate specificity since it is the only sialidase that acts on mucins with high efficiency.…”