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

Sialidases are enzymes that catalyze the removal of sialic acids from glycoproteins and glycolipids. Previously, we have studied the effect of sialidase inhibition as a modulator of sialylation-related mechanisms of invasion and found that it induces aggressiveness in canine mammary tumors (CMTs). In this study, we aimed to assess the expression of glycoprotein-acting sialidases, Neu1, Neu2, and Neu4, in the complex multistage process of cancer metastasis. Thus, we examined their expression in a series of spontaneous malignant CMTs, CMT cell lines, and nude mice xenografts. All malignant CMT lesions expressed mammalian sialidases, although overall decreased when compared to normal adjacent mammary tissues. This difference was statistically significant regarding Neu4. In accordance, CMA07 adenoma cell line expressed higher levels of sialidase protein expression when compared with the CMT-U27 carcinoma cell line. Finally, with few tumor subpopulation exceptions, Neu1 and Neu4 expression was also overall low in primary and metastatic CMT xenografts. Thus, overall loss of sialidases seems to be an important feature for CMT progression and invasion.