Sialidase treatment exposes the beta 1-integrin active ligand binding siteon HL60 cells and increases binding to fibronectin

The migration of neutrophils from the circulation to areas of inflammation is the result of the sequential activation of multiple cellular adhesion mo lecules. beta 1-Integrins are cell surface glycoproteins and the class of a dhesion molecules responsible for binding to the extracellular matrix. The goal of this study was to determine the contribution of glycosylation, spec ifically the presence of sialic acid, to beta 1-integrin adhesion in a neut rophil model. beta 1-Integrins on differentiated HL60 cells were remodeled by treatment with the exoglycosidases, sialidase and beta-galactosidase. be ta 1-Integrin activity was determined by measuring adherence to the extrace llular matrix protein fibronectin. The expression of beta 1-integrins, beta 2-integrins and activated beta 1-integrins was determined by flow cytometr y, Remodeling of beta 1 -integrins by treatment with sialidase increased ad hesion by greater than 100%. Flow cytometric analysis of remodeled beta 1-i ntegrins demonstrated an increased expression of the activated beta 1-integ rin, but only minor increases in the expression of total beta 1- and beta 2 -integrins. We postulate that glycosidase treatment increases adhesion and expression of activated beta 1-integrins by exposure of the normally hidden ligand-binding site, The glycosylation of beta 1-integrins on neutrophils may act to hide the ligand-binding site in unstimulated cells thereby contr ibuting to the affinity modulation observed in neutrophil beta 1-integrin f unction.