Role of Rho kinase in sphingosine 1‐phosphate‐mediated smooth muscle and endothelial cell function

The role of sphingosine 1‐phosphate (S1P)‐induced Rho kinase (ROCK) activation in the angiogenic responses of pulmonary artery‐derived endothelial (PAEC) and smooth muscle cells (PASMC) was examined. S1P promoted PAEC chemotaxis and capillary morphogenesis; furthermore, this activity was unaltered by pretreatment with the pharmacological inhibitor of ROCK, H1152. In contrast, S1P significantly inhibited spontaneous PASMC chemotaxis and differentiation; however, this inhibition was eradicated upon H1152 pretreatment. Similarly, PASMCs transfected with ROCK II siRNA diminished the S1P‐induced inhibition of the development of capillary‐like structures. Analysis by RT‐PCR of the S1P receptor expression identified the presence of S1P1 and S1P3 receptors in PAECs and PASMCs, while S1P2 receptor expression was confined to PASMCs. We confirmed the role of the S1P2 receptors in mediating the S1P‐induced inhibition of PASMC differentiation by pretreatment with JTE013. The S1P1 and S1P3 receptor antagonist, VPC23019 , did not impede the S1P‐induced inhibition of differentiation in PASMCs; however, S1P‐induced PAEC differentiation was virtually abolished. This study suggests a regulatory role for Rho kinase in S1P2 receptor‐mediated curtailment of PASMC function; moreover, S1P‐induced PAEC angiogenic responses are regulated by S1P1 and/or S1P3 receptors, independent of ROCK activation.