Sphingosine-1-phosphate receptor 1 expression in angiosarcoma : Possible role in metastasis and a potential therapeutic target

[ABSTRACT] Sphingosine-1-phosphate (S1P) is a potent lipid mediator that has been implicated in the migration of lymphocytes and endothelial cells through S1P receptors. S1PR1 is strongly expressed in angiosarcoma, a malignant tumor of endothelial cell origin that has a high propensity for metastasis and poor prognosis; however, the pathological significance of S1PR1 expression is not clear. In this study, we investigated the effect of S1PR1 modulation on cell migration, and examined its potential role as a therapeutic target against metastatic dissemination of angiosarcoma. S1PR1 expression in the human angiosarcoma cell line MO-LAS was assessed by immunocytochemical examination and Western blotting. Effects of S1PR1-specific small interfering RNA (siRNA) and that of FTY720-P (a functional S1PR1-antagonist) on MO-LAS cell chemotactic migration towards sphingosine-1-phosphate (S1P) or 10% fetal bovine serum (FBS) were assessed by Transwell migration assay; wound healing assays for random cell migration were performed using a live cell analyzer. Immunostaining revealed high expression of S1PR1 on the MO-LAS cell membrane. Transwell and wound-healing assays showed that S1P enhanced chemotactic and random migration of MO-LAS cells, respectively. Inhibition of S1PR1 expression with siRNA significantly attenuated chemotaxis of cells towards S1P and 10% FBS. Further, FTY720-P strongly induced the internalization and degradation of S1PR1 even in the presence of serum containing S1P. It attenuated chemotactic cell migration of MO-LAS towards both S1P and serum, as well as the random motility of cells at nanomolar concentrations. These results suggest that the S1P/S1PR1 axis may be a potential therapeutic target for inhibition of angiosarcoma metastasis by controlling its cell motility.