Base-modified UDP-sugars reduce cell surface levels of P-selectin glycoprotein 1 (PSGL-1) on IL-1β-stimulated human monocytes

P-selectin glycoprotein ligand-1 (PSGL-1, CD162) is a cell-surface glycoprotein that is expressed, either constitutively or inducibly, on all myeloid and lymphoid cell lineages. PSGL-1 is implicated in cell-cell interactions between platelets, leukocytes and endothelial cells, and a key mediator of inflammatory cell recruitment and transmigration into tissues. Here, we have investigated the effects of the beta-1,4-galactosyltransferase inhibitor 5-(5-formylthien-2-yl) UDP-Gal (5-FT UDP-Gal, compound 1) and two close derivatives on the cell surface levels of PSGL-1 on human peripheral blood mononuclear cells (hPBMCs). PSGL-1 levels were studied both under basal conditions, and upon stimulation of hPBMCs with interleukin-1 beta (IL-1 beta). Between 1 and 24 hours after IL-1 beta stimulation, we observed initial PSGL-1 shedding, followed by an increase in PSGL-1 levels on the cell surface, with a maximal window between IL-1 beta-induced and basal levels after 72 h. All three inhibitors reduce PSGL-1 levels on IL-1 beta-stimulated cells in a concentration-dependent manner, but show no such effect in resting cells. Compound 1 also affects the cell surface levels of adhesion molecule CD11b in IL-1 beta-stimulated hPBMCs, but not of glycoproteins CD14 and CCR2. This activity profile may be linked to the inhibition of global Sialyl Lewis presentation on hPBMCs by compound 1, which we have also observed. Although this mechanistic explanation remains hypothetical at present, our results show, for the first time, that small molecules can discriminate between IL-1 beta-induced and basal levels of cell surface PSGL-1. These findings open new avenues for intervention with PSGL-1 presentation on the cell surface of primed hPBMCs and may have implications for anti-inflammatory drug development.