A model system to study the interactions of PSGL-1 and P-selectin

P-selectin (CD62P) is a member of the selectin family of adhesion molecules involved in the regulation of leukocyte traffic. P-selectin is rapidly expressed on platelets and endothelium stimulated by thrombin, histamine and phorbol esters, and binds to monocytes, neutrophils and some T cells. PSGL-1 (PSelectin Glycoprotein Ligand-1), a mucin-like protein, is expressed on leukocytes and thought to be a primary ligand for P-selectin. The interaction of P-selectin with PSGL-1 results in rolling and recruitment of leukocytes to sites of inflammation and tissue injury. However, the expression of PSGL-1 alone is insufficient for binding to P-selectin. In addition to PSGL1, leukocytes must express al,3-fucosyltransferase (FucT) activity. Using stably transfected K562 cells, we have developed a model system for studying the interactions of these molecules. K562 cells express FucTTV but not FucTVII or PSGL-1 and do not bind to P-selectin. K562 cells transfected with PSGL-1 cDNA alone did not bind to COS cells transfected with either E- or P-selectin. K562 cells transfected with FucTVII cDNA only did bind to E-selectin, but not P-selectin. Cotransfection with both FucTVII and PSGL-1 resulted in adhesion to P-selectin. Thus, neither PSGL-1 nor FucTVII alone are sufficient to confer binding to P-selectin; expression of both FucTVII and PSGL-1 are necessary and sufficient for binding to P-selectin. Furthermore, the expression of FucTVII alone is sufficient for E-selectin binding, indicating that the expression of PSGL-1 is not required for binding to E-selectin. This system represents the first reconstitution of P-selectin binding in a stably transfected hematopoetic cell line and will be a useful tool to further explore these interactions.