Sialidase Treatment Exposes the βT1-Integrin Active Ligand Binding Site on HL60 Cells and Increases Binding to Fibronectin

Abstract

The migration of neutrophils from the circulation to areas of inflammation is the result of the sequential activation of multiple cellular adhesion molecules. βT1-Integrins are cell surface glycoproteins and the class of adhesion molecules responsible for binding to the extracellular matrix. The goal of this study was to determine the contribution of glycosylation, specifically the presence of sialic acid, to βT1-integrin adhesion in a neutrophil model. βT1-Integrins on differentiated HL60 cells were remodeled by treatment with the exoglycosidases, sialidase and βT-galactosidase. βT1-Integrin activity was determined by measuring adherence to the extracellular matrix protein fibronectin. The expression of βT1-integrins, βT2-integrins and activated βT1-integrins was determined by flow cytometry. Remodeling of βT1-integrins by treatment with sialidase increased adhesion by greater than 100%. Flow cytometric analysis of remodeled βT1-integrins demonstrated an increased expression of the activated βT1-integrin, but only minor increases in the expression of total βT1-and βT2-integrins. We postulate that glycosidase treatment increases adhesion and expression of activated βT1-integrins by exposure of the normally hidden ligand-binding site. The glycosylation of βT1-integrins on neutrophils may act to hide the ligand-binding site in unstimulated cells thereby contributing to the affinity modulation observed in neutrophil pl-integrin function.