Since we recently reported that high density lipoprotein, which contains the bioactive lipid sphingosine-I-phosphate (SIP) induced human coronary artery endothelial cell (HCEC) tube formation mediated by a Ras/Raf/ERK (extracellular signal-activated kinase) pathway [Arterioscler. Thromb. Vase. Biol. 23 (2003) 802], we thought that it would be very important to evaluate whether the signal in SIP-induced tube formation is Ras-dependent or -independent. In an in vitro model of HCEC tube formation on a matrix gel, SIP-induced tube formation. ERK1/2 inhibitor (PD98059) and pertussis toxin (PTX) suppressed SIP-induced tube formation. SIP activated phospho(p)-ERK1/2, while dominant-negative RasN17 blocked SIP-induced p-ERK1/2. Moreover, RasN17 inhibited SIP-induced tube formation. SIP activated Ras/Raf1 by Ras pull-down assay and this effect was inhibited by PTX. These results demonstrate that Ras/Raf1-dependent ERK activation mediated by PTX-sensitive G protein-coupled receptors may be a potent signal in SIP-induced HCEC tube formation. (C) 2003 Elsevier Science (USA). All rights reserved.