Expression and functional characterization of the P-selectin glycoprotein ligand-1 in various cells

We have examined the expression and function of P-selectin glycoprotein ligand-1 (PSGL-1), which is a high affinity ligand for P-selectin. Northern blot and flow cytometric analysis demonstrated that a variety of hematopoietic cells and cell lines expressed PSGL-1. However, P-selectin binding ability was dependent on the additional expression of a carbohydrate structure, sialyl Lewis x (sLex). All the peripheral lymphocytes expressed PSGL-1 and subpopulation expressed sLex. Two color analysis showed that the majority of the cells that bound P-selectin were sLex-negative I lymphocytes, and most of the sLex-positive cells were B lymphocytes that did not blind P-selectin, indicating that the carbohydrate on T lymphocytes recognized by P-selectin is not sLex, and that the sLex on B lymphocytes is not readily presented for P-selectin recognition. Transfected 293 cells detectably bound P-selectin only when the cells expressed both PSGL-1 and sLex. When cysteine 310 of PSGL-1 was mutated to alanine, P-selectin binding was markedly reduced, suggesting the importance of dimerization of PSGL-1. These findings indicate that a preferable conformation of both carbohydrate and protein structure is necessary for a functional P-selectin ligand.