It was shown that glycoproteins represent the biological relevant ligands for selectins. While the ligands for E- and L-selectins with primary binding activity have not been identified so far, the functionally most important ligand for P-selectin has been identified. The mucin-like glycoprotein PSGL-1 (P-selectin Glycoprotein Ligand-1) has been cloned and sequenced. PSGL-1 has been shown to be a transmembrane protein which forms homodimers via disulfide bridges of two 120 kDa chains. PSGL-1 is expressed on cells of myeloid, lymphoid and dendritic lineage. The binding of P-selectin is regulated by different degrees and forms of glycosylation. An interaction of L-selectin with PSGL-1 in the process of neutrophil aggregation has been shown. However, PSGL-1 does not seem to be the primary ligand for L-selectin. Presently it is not known which cells, apart from leukocytes, express PSGL-1 and what role PSGL-1 plays on these cells. The metastic potential of the majority of cells which bind to P-selectin is however in close correlation with the functional expression of PSGL-1 on these cells. The regulation of PSGL-1 is not yet well described. Glycosyltransferases sure play an important role in activation. The deactivation of PSGL-1 is so far unclear. The cleavage of the protein from the cell surface is one mechanism involved in the deactivation process. Following this shedding, a soluble form of PSGL-1 is detectable in the circulation. This soluble isoform of PSGL-1 is still capable of binding to P-selectin, thus representing a competitor for cellular PSGL-1 through which regulation in many physiological and pathological processes can take place.

Synonyms: soluble Selectin P ligand, SELPLG, CD162