Sphingosine 1-Phosphate Transactivates the Platelet-Derived Growth Factor β Receptor and Epidermal Growth Factor Receptor in Vascular Smooth Muscle Cells

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Abstract
Sphingosine 1-phosphate (S1P) is a bioactive lipid generated during vascular injury that regulates cell growth, differentiation, survival, and motility via endothelial differentiation gene (EDG) family G protein–coupled receptors. Although several G protein–coupled receptor ligands transactivate receptor tyrosine kinases, such as the epidermal growth factor receptor (EGFR), S1P-stimulated receptor tyrosine kinase transactivation has not been well studied. We show that platelet-derived growth factor β receptor (PDGFβR) and EGFR are tyrosine phosphorylated in response to S1P in rat aortic vascular smooth muscle cells (VSMCs). S1P-stimulated transactivation of PDGFβR and EGFR was mediated via Gi-coupled EDG receptors. S1P-stimulated transactivation of EGFR and PDGFβR was dependent on Src, reactive oxygen species, and cholesterol-rich membranes. A phosphoinositide 3-kinase–Akt pathway was activated by S1P and blocked by AG1296 and AG1478. Activation of extracellular signal–regulated kinase (ERK) 1 and ERK2 pathway by S1P was blocked only by AG1478. In Chinese hamster ovary cells that expressed exogenous EDG-1, activation of Akt and ERK1/2 in response to S1P was observed and was enhanced by coexpression of PDGFβR or EGFR. S1P-mediated VSMC proliferation was shown to be secondary to transactivation, because it was suppressed by AG1296 and AG1478. These data establish S1P as an important stimulus for EGFR and PDGFβR activation in VSMCs that may have important implications for the vessel response to injury.