ENGAGEMENT OF L-SELECTIN IMPAIRS THE ACTIN POLYMERIZING CAPACITY OF BETA(2)-INTEGRINS ON NEUTROPHILS

A sequential activation of L-selectin and beta(2)-integrins on neutrop hils is crucial for the rolling, adherence and subsequent migration of these cells on the endothelium, However, little is known about a poss ible interplay between these adhesion receptors in the final regulatio n of cell motility, The results presented here show that sulfatides th emselves (here used as tools to activate L-selectins), have no major e ffect on the cellular content of filamentous actin (F-actin), but caus e a time-related decrease in the beta(2)-integrin-induced formation of F-actin, This effect of sulfatides was abolished in cells lacking L-s electin as a result of pretreatment with chymotrypsin, A similar sulfa tide-induced activation of L-selectin also caused a pronounced and tim e-related decrease of a subsequent chemotactic peptide-induced F-actin response, The effect of sulfatides on both beta(2)-integrin- and chem otactic peptide-induced F-actin were abolished if L-selectin were bloc ked by preincubating the cells with specific antibodies to L-selectin, These effects of L-selectin engagement on cellular F-actin content we re neither abolished by blocking the cytosolic free Ca2+ signal with b is-(2-amino-5-methylphenoxy)ethane-N,N,N',N acid tetraacetoxymethyly e ster (MAPT/AM) nor by blocking a cAMP-induced activation of protein ki nase A by pretreating the cells with adenosine-3',5'-cyclic monophosph orothioate (Rp-cAMPS), Instead we found that L-selectin engagement imp aired an early beta(2)-integrin-induced tyrosine kinase activation, an event shown to be necessary for a normal beta(2)-integrin-mediated F- actin response, The present demonstration of a negative feed-back func tion of L-selectin on beta(2)-integrin-induced modulations of the acti n cytoskeleton, suggests that the relative distribution and/or density of the respective L-selectin and beta(2)-integrin ligands on endothel ial cells might be important factors in determining the final site of firm adhesion and extravasation of neutrophils.