FTY720 Phosphate Activates Sphingosine-1-Phosphate Receptor 2 and Selectively Couples to Gα12/13/Rho/ROCK to Induce Myofibroblast Contraction

FTY720 phosphate (FTY720-P; 2-amino-2-[2-(4-octylphenyl)ethyl]-1,3-propanediol, monodihydrogen phosphate ester) is a nonselective sphingosine-1-phosphate (S1P) receptor agonist thought to be devoid of activity at the S1P(2) receptor subtype. However, we have recently shown that FTY720-P displays significant S1P(2) receptor agonist activity in recombinant cells and fibroblasts expressing endogenous S1P(2) receptors. To elucidate the S1P(2)-dependent signaling pathways that were activated by FTY720-P, we employed second messenger assays and impedance-based assays in combination with pharmacological and small interfering RNA-based pathway inhibition in recombinant Chinese hamster ovary (CHO)-S1P(2) cells as well as human lung myofibroblasts generated in vitro. In CHO-S1P(2) cells, FTY720-P did not modulate cAMP or calcium levels. However, reporter-gene assays, impedance-based assays with a selective Rho-associated kinase (ROCK) inhibitor, G alpha(12/13) knockdown and activated Rho-pull-down assays demonstrated that FTY720-P potently activated G alpha(12/13)/Rho/ROCK signaling. S1P similarly activated G alpha(12/13)/Rho/ROCK signaling via S1P(2) receptors, whereas the two selective S1P(1) receptor agonists (Z, Z)-5-(3-chloro-4-[(2R)-2,3-dihydroxypropoxy]-benzylidene)-2-propylimino-3-o-tolyl-thiazolidin-4-one (ponesimond) and 5-[4-phenyl-5-(trifluoromethyl)thiophen-2-yl]-3-[3-(trifluoromethyl) phenyl] 1,2,4-oxadiazole (SEW2871) were inactive. In lung myofibroblasts, which mainly expressed the S1P(2) receptor subtype, we showed that FTY720-P selectively activated the G alpha(12/13)/Rho/ROCK pathway via the S1P(2) receptor. Moreover, the activation of the G alpha(12/13)/Rho/ROCK pathway in myofibroblasts by FTY720-P caused potent myofibroblast contraction similar to that induced by the natural ligand S1P. Thus, complementing second messenger assays with unbiased label-free assays or phenotypic assays in native expression systems can uncover activation of additional pathways, such as G alpha(12/13)/Rho/ROCK signaling.