SPHINGOSINE-1-PHOSPHATE INHIBITS PDGF-INDUCED CHEMOTAXIS OF HUMAN ARTERIAL SMOOTH-MUSCLE CELLS - SPATIAL AND TEMPORAL-MODULATION OF PDGF CHEMOTACTIC SIGNAL-TRANSDUCTION

Activation of the PDGF receptor on human arterial smooth muscle cells (SMC) induces migration and proliferation via separable signal transdu ction pathways. Sphingosine-1-phosphate (Sph-1-P) can be formed follow ing PDGF receptor activation and therefore may be implicated in PDGF-r eceptor signal transduction. Here we show that Sph-1-P does not signif icantly affect PDGF-induced DNA synthesis, proliferation, or activatio n of mitogenic signal transduction pathways, such as the mitogen-activ ated protein (MAP) kinase cascade and PI 3-kinase, in human arterial S MC. On the other hand, Sph-1-P strongly mimics PDGF receptor-induced c hemotactic signal transduction favoring actin filament disassembly. Al though Sph-1-P mimics PDGF, exogenously added Sph-1-P induces more pro longed 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. Th is excessive and prolonged signaling favors actin filament disassembly by Sph-1-P, and results in inhibition of actin nucleation, actin fila ment assembly and formation of focal adhesion sites. Sph-1-P-induced i nterference with the dynamics of PDGF-stimulated actin filament disass embly and assembly results in a marked inhibition of cell spreading, o f extension of the leading lamellae toward PDGF, and of chemotaxis tow ard PDGF. The results suggest that spatial and temporal changes in pho sphatidylinositol turnover, calcium mobilization and actin filament di sassembly may be critical to PDGF-induced chemotaxis and suggest a pos sible role for endogenous Sph-1-P in the regulation of PDGF receptor c hemotactic signal transduction.