PSGL-1 regulates transendothelial migration of MM cells. (A) HUVECs were transfected with siRNAs for E-, L-, or P-selectin. Scramble siRNA was used as a control (panel i) or cells were treated with anti–E-, anti–L-, or anti–P-neutralizing Abs. Isotype control Ab was used as a control (panel ii). Transendothelial migration of MM1s cells in response to SDF-1α (30nM) was tested. Significant inhibition of MM cell transendothelial migration was observed in HUVECS with P-selectin knockdown (panel i) and in HUVECs treated with neutralizing Ab for P-selectin (panel ii) (P < .01). (B) MM1s cells were transfected with either PSGL-1 or scramble siRNA, and transendothelial migration of MM cells in response to SDF-1α (30nM) was tested. Significant inhibition of MM cell transendothelial migration was observed in MM cells with PSGL-1 knockdown. (C) HUVECs were treated with increasing concentrations of GMI-1070 (0, 100, 250, and 500μM) for 1 hour, and transendothelial migration of nontreated MM1s cells in response to SDF-1α (30nM) was evaluated: dose-dependent inhibition of MM cell transendothelial migration was observed (P < .02). (D) MM1s cells were transfected with either PSGL-1 or scramble siRNA, and migration of MM cells (with no presence of HUVECs) in response to SDF-1α (30nM) was tested. No difference in cell migration was observed in MM cells transfected with PSGL-1 or scramble siRNA. (E) MM1s cells were treated with increasing concentrations of GMI-1070 (0, 100, 250, and 500μM) for 1 hour, and migration of MM cells (with no presence of HUVECs) in response to SDF-1α (30nM) was tested: no difference in cell migration was observed in MM cells treated with or without GMI-1070. (F) MM1s cells were treated with either isotype control or PSGL-1–blocking Ab. Transendothelial migration of MM cells was evaluated: significant inhibition of MM cells to HUVECs was observed in cells treated with PSGL-1–blocking Ab.