The activation of RhoC in vascular endothelial cells is required for the S1P receptor type 2-induced inhibition of angiogenesis

Sphingosine-1-phosphate (SIP) is a multifunctional phospholipid inducing a variety of cellular responses in endothelial cells (EC). SW responses are mediated by five G protein coupled receptors of which three types (S1P(1)R-S1P(3)R) have been described to be of importance in vascular endothelial cells (EC). Whereas the S1P(1)R regulates endothelial barrier function by coupling to G alpha(i) and the monomeric GTPase Rac1, the signaling pathways involved in the S1P-induced regulation of angiogenesis are ill defined. We therefore studied the sprouting of human umbilical vein EC (HUVEC) in vitro and analyzed the activation of the RhoGTPases RhoA and RhoC. Physiological relevant concentrations of S1P (100-300 nM) induce a moderate activation of RhoA and RhoC. Inhibition or siRNA-mediated depletion of the S1P(2)R preferentially decreased the activation of RhoC Both manipulations caused an increase of sprouting in a spheroid based in vitro sprouting assay. Interestingly, a similar increase in sprouting was detected after effective siRNA-mediated knockdown of RhoC. In contrast, the depletion of RhoA had no influence on sprouting. Furthermore, suppression of the activity of G proteins of the G alpha(12/13) subfamily by adenoviral overexpression of the regulator of G protein signaling domain of LSC as well as siRNA-mediated knockdown of the Rho specific guanine nucleotide exchange factor leukemia associated RhoGEF (LARG) inhibited the S1P-induced activation of RhoC and concomitantly increased sprouting of HUVEC with similar efficacy. We conclude that the angiogenic sprouting of EC is suppressed via the S1P(2)R subtype. Thus, the increase in basal sprouting can be attributed to blocking of the inhibitory action of autocrine SIP stimulating the SiP2R. This inhibitory pathway involves the activation of RhoC via G alpha(12/13) and LARG, while the simultaneously occurring activation of RhoA is apparently dispensable here. (C) 2013 Elsevier Inc. All rights reserved.