RESUMEN
G protein-coupled receptors (GPCRs) for lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) transduce signals to many functions of normal cells. Most human cancer cells upregulate S1P and LPA GPCRs, in patterns distinctive for each type of tumor. The findings that 1-alpha, 25-dihydroxy-vitamin D(3) (VD3) and all-trans retinoic acid (RA) differentially alter expression of the predominant S1P(3) (Edg-3) R and S1P(2) (Edg-5) R in human breast cancer cells (BCCs) permitted analyses of their individual activities, despite a lack of selective pharmacological probes. S1P-evoked increases in [Ca(2+)](i) in S1P(3) R-predominant BCCs were suppressed by concentrations of VD3 and RA which decreased expression of S1P(3) Rs, despite RA-induced increases in S1P(2) Rs. S1P-elicited chemokinetic migration of S1P(3) R-predominant BCCs across a type IV collagen-coated micropore filter also was inhibited by concentrations of VD3 and RA which decreased expression of S1P(3) Rs. The RA-induced increase in expression of S1P(2) Rs did not prevent suppression by RA of S1P-elicited chemokinesis, which appears to be mediated by S1P(3) Rs, but instead exposed S1P(2) R-mediated inhibition of epidermal growth factor-stimulated chemotaxis of BCCs. In contrast, expression of the predominant LPA(2) Rs, LPA-evoked increase in [Ca(2+)](i) and LPA-stimulated chemokinetic migration were suppressed concomitantly by RA but not VD3. Thus two structurally-homologous S1P Rs of BCCs differ in coupling to [Ca(2+)](i) signaling and have opposite effects on protein growth factor-stimulated chemotaxis.