Sphingosine-1-phosphate inhibits PDGF-induced chemotaxis of human arterial smooth muscle cells: spatial and temporal modulation of PDGF chemotactic signal transduction.

Abstract

Abstract. Activation of the PDGF receptor on human arterial smooth muscle cells (SMC) induces migration and proliferation via separable signal transduction pathways. Sphingosine-l-phosphate (Sph-l-P) can be formed following PDGF receptor activation and therefore may be implicated in PDGF-receptor signal transduction. Here we show that Sph-l-P does not significantly affect PDGF-induced DNA synthesis, proliferation, or activation of mitogenic signal transduction pathways, such as the mitogen-activated protein (MAP) kinase cascade and PI 3-kinase, in human arterial SMC. On the other hand, Sph-l-P strongly mimics PDGF receptor-induced chemotactic signal transduction favoring actin filament disassembly. Although Sph-l-P mimics PDGF, exogenously added Sph-l-P induces more prolonged and quantitatively greater PIP2 hydrolysis compared to PDGF-BB, a markedly stronger calcium mobilization and a subsequent increase in cyclic AMP levels and activation of cAMP-dependent protein kinase. This excessive and prolonged signaling favors actin filament disassembly by Sph-l-P, and results in inhibition of actin nucleation, actin filament assembly and formation of focal adhesion sites. Sph-l-P-induced interference with the dynamics of PDGF-stimulated actin filament disassembly and assembly results in a marked inhibition of cell spreading, of extension of the leading lamellae toward PDGF, and of chemotaxis toward PDGF. The results suggest that spatial and temporal changes in phosphatidylinositol turnover, calcium mobilization and actin filament disassembly may be critical to PDGF-induced chemotaxis and suggest a possible role for endogenous Sph-l-P in the regulation of PDGF receptor chemotactic signal transduction.T rIE accumulation of smooth muscle cells (SMC) 1 during formation and progression of atherosclerotic lesions and in restenosis after angioplasty is due to a combination of proliferation and directed migration of the cells from the media into and within the intimal layer of the artery wall (for review see Ross, 1993). Initiation of both these events is most likely mediated by a number of regulatory polypeptides that are present in the lesion, such as

Inhibitory Regulation of Rac Activation, Membrane Ruffling, and Cell Migration by the G Protein-Coupled Sphingosine-1-Phosphate Receptor EDG5 but Not EDG1 or EDG3

“…In addition, it was shown that sphingosine, a precursor of S1P, could alter cellular PAK activity (11) and PDK1 activity (33). It was also noted that higher concentrations of S1P are required for inhibition of cell motility in breast cancer cells (72,74) than in vascular smooth muscle cells (12) and B16 melanoma cells (59,77). Moreover, dihydro-S1P, an agonist for the EDG S1P receptors (70,71), is ineffective in inhibiting the motility of the breast cancer cells (74), which contrasts with the present data for CHO-EDG5 cells (Table 1).…”

“…Cellular mechanisms by which the chemorepellants suppress cell migration have remained largely unknown. S1P is unique and distinct from these chemorepellants in that it bidirectionally regulates cell migration, i.e., S1P acts as a chemoattractant for certain cell types (34,40,41,73), while it strongly inhibits cell migration in others (12,31,59,72,77); the latter include several tumorderived cell types. S1P is a normal constituent of the blood and is present at a substantially high concentration (Ͼ0.1 M), most of which is bound to albumin (79).…”

“…1A). It was previously demonstrated that human vascular smooth muscle cells (12) and certain tumor cells including B16 melanoma cells (59,72,74,77) respond to S1P with inhibition of directed cell migration. We identified EDG5 as a dominant EDG subtype expressed in vascular smooth muscle cells and B16 melanoma cells (H. Okamoto, H. Yamaguchi, Y. Ryu, and Y. Takuwa, unpublished observations).…”

“…Strikingly, S1P inhibits, rather than stimulates, the migration of vascular smooth muscle cells (12) and neutrophils (31) and also the invasiveness of some tumor cells including melanoma cells (59,77), osteosarcoma cells (59), and breast carcinoma cells (72,74). The inhibitory actions of S1P on motility of melanoma cells are suggested to be mediated by cell surface action, because immobilized S1P inhibits migration as effectively as soluble S1P (77).…”

Sphingolipids in Atherosclerosis and Vascular Biology

“…98 The finding that sphingosine-1-phosphate may be an inhibitor of plateletderived growth factor-induced migration of ASMCs is of considerable significance. 74,75 In addition, the protective role of trimethylsphingosine of the myocardium and endothelium in ischemia/reperfusion injury has been suggested. 71 Several mechanisms have been implicated in the initiation of early atherogenesis.…”