CHEMOATTRACTANT RECEPTOR-INDUCED PHOSPHORYLATION OF L-SELECTIN

The selectin adhesion molecules and chemoattractant receptors synergis tically regulate leukocyte migration into lymphoid tissues and sites o f inflammation, but little is known about how these families of recept ors modulate each other's function. In this study, L-selectin was foun d to be phosphorylated in lymphoblastoid cell lines, and phosphorylati on was enhanced by phorbol ester (phorbol la-myristate 13-acetate (PMA )) treatment. Interactions between L selectin and chemoattractant rece ptors were therefore examined using transfected rat basophilic leukemi a cell lines (RBL-2H3) that expressed human L-selectin along with huma n leukocyte chemoattractant receptors, L-selectin was rapidly phosphor ylated in cells treated with chemoattractants, thrombin, IgE receptor agonists, or PMA, Pertussis toxin or the protein kinase C inhibitor, s taurosporine, completely blocked chemoattractant receptor-induced phos phorylation of L-selectin, PMA-induced phosphorylation was on serine r esidues within the cytoplasmic tail of L selectin that have been well conserved during recent evolution, Although L-selectin phosphorylation was not essential for basal levels of adhesion through L-selectin in transformed cell lines, the rapid increase in ligand binding activity of L-selectin that occurs following leukocyte activation was blocked b y staurosporine, These results demonstrate that L-selectin can be phos phorylated following engagement of chemoattractant receptors and sugge st that this may be a physiologically relevant mechanism for the syner gistic regulation of these receptors during leukocyte migration.