(86b) Role of c-Abl Activity On L-Selectin Mechanical Shedding From the Neutrophil Surface Under Flow

Neutrophils roll on the blood vessel wall, adhere near sites of injury or infection, extend pseudopodia with focal adhesion points, and leave the blood stream by passing through the endothelium that lines the blood vessel. The rolling and adhesion of neutrophils along the vascular endothelium via neutrophil-expressed L-selectin and other adhesion receptors are key steps in the inflammatory cascade. We previously showed that L-selectin is shed from the neutrophil surface as they roll on sialyl Lewis-x coated surfaces in a force-, ADAM-17 sheddase-, and p38 MAP kinase- dependent manner under flow [J Biol Chem 282(7): 4812-21]. This phenomenon has been called L-selectin ?mechanical shedding.? C-Abl (ABL1) is a tyrosine kinase that has been shown to activate following L-selectin cross-linking, and also mediates actin polymerization. We studied the effect of Gleevec®, a specific c-Abl inhibitor used to treat chronic myelogenous leukemia, on L-selectin mechanical shedding from primary human neutrophils. Results indicated that pretreatment with Gleevec® significantly affects neutrophil adhesion via L-selectin, by decreasing the average rolling velocity and increasing the flux of rolling cells. The change in surface receptor expression was verified by flow cytometry. C-Abl phosphorylation in neutrophils was quantified before and after rolling. Neutrophils treated with Gleevec® showed a decrease in c-Abl phosphorylation while retaining L-selectin after exposure to shear flow. These findings implicate the c-Abl signaling molecule in regulating L-selectin mechanical shedding, and suggest changes in the cellular immune response caused by Gleevec that have not been previously reported in the literature.