Sphingosine-1-phosphate receptor 1 transmits estrogens' effects in endothelial cells

We have previously reported that the steroid hormone estrogens stimulate activation of sphingosine kinase 1 (SphK1) and sphingosine-1-phosphate (SIP) receptors in breast cancer cells. Both estrogens and SIP are potent biological modulators of endothelial function in vasculature able to activate multiple effectors, including endothelial nitric oxide synthase (eNOS). In this study we report that treatment of endothelial cells (ECs) with 17 beta-estradiol (E-2) resulted in a rapid, transient, and dose-dependent increase in SphK activity and increased SIP production. The effect was not reproduced by the inactive E-2 analogue 17 alpha-E-2. Expression of the dominant-negative mutant SphK1(G82D) or transfection of SphK1-targeted siRNA in ECs caused not only a defect in SphK activation by E-2, but also a significant inhibition of E-2-induced activation of Akt/eNOS. Furthermore, E-2 treatment induced internalization of plasma membrane S1P1 receptor, accompanied with an increase in the amount of cytosolic SIPI. By down-regulating S1P1 receptor expression, the S1P1-specific antisense oligonucleotides significantly inhibited E-2-induced activation of Akt/eNOS in ECs. E-2-induced EC migration and tube formation were also inhibited by S1P1 down-regulation. Thus, the findings indicate an important role of the SphK1/S1P1 pathway in mediating estrogen signaling and its actions in vasculature. (C) 2015 Elsevier Inc. All rights reserved.