UDP-GlcNAc2-epimerase regulates cell surface sialylation and cell adhesion to extracellular matrix in Burkitt's lymphoma

Alteration of cell surface glycoconjugates plays a crucial role in many biological phenomenon, including invasion and metastasis. In the present study, we investigated the relationship between cell surface sialylation and the adhesive properties of two clones (3G3 and 3D2) of a human Burkitt's lymphoma cell line, HBL-8 to extracellular matrix. By flow cytometric analysis we found that the cell surface of 3G3 clone was highly sialylated and that of the 3D2 clone were hyposialylated. Moreover, cell surface sialic acid content was significantly greater in the 3G3 clone than in the 3D2 clone. In vitro adhesion assays showed that cell surface sialylation in the 3G3 clone cells might reduce their attachment to collagen type IV and fibronectin, compared to 3D2 clone. Sialic acid metabolic complementation assays using several precursors of sialic acid suggested that hyposialylation in the 3D2 clone resulted from low activities of uridine diphosphate-N-acetylglucosamine-2-epimerase (UDP-GlcNAc2-epimerase) which is a key enzyme in sialic acid biosynthesis. From RT-PCR analysis the expression of UDP-GlcNAc2-epimerase mRNA was found to be correlated with sialic acid content in the two clones of HBL-8. Therefore, expression of UDP-GlcNAc2-epimerase mRNA may regulate the expression of sialoglycoconjugates which affect the adhesion of lymphoma cells to collagen type IV and fibronectin.