Human Neuraminidase Enzymes alter the Lateral Mobility and Function of Integrin Receptors

Abstract

Glycolipids and glycoproteins are important components of membrane structure. Mechanisms which alter the structure of glycans at the membrane could influence cellular responses. For example, by removing an important binding epitope or else by unmasking a new one, protein-glycan interactions may be disrupted or reinforced. Our group has been working to understand the role of human neuraminidase enzymes (hNEU) in regulating cellular adhesion and migration through integrin receptors. Of the four hNEU isoenzymes, three have activity at the plasma membrane and lysosome; thus, these enzymes could regulate the composition of the plasma membrane by stripping neuraminic acid (Neu5Ac; also known as sialic acid) from membrane glycans. Using recombinant enzymes and selective hNEU inhibitors developed within our group, we can selectively probe increased or decreased activity of individual isoenzymes in vitro; allowing us to test the effect of specific enzymes. Previous studies have suggested that integrin-mediated adhesion may be altered through hNEU activity. We measured the lateral mobility of integrins in cells treated with NEU3 and NEU4 using single-dye tracking (SDT) by total-internal-reflection fluorescence microscopy (TIRF). We find that hNEU can dramatically change the diffusion of integrin receptors, and that the effect is dependent on the cell type and the isoenzyme used. Adhesion and cell migration assays of cells treated with chemical inhibitors of the enzymes reveal that hNEU activity is intimately involved in the regulation of integrin adhesion to their native ligands. We will present lateral mobility and cell migration assays with enzyme and inhibitor conditions. Our results suggest an important role for hNEU as regulators of membrane composition and the activity of adhesion receptors.