Sphingosine 1-phosphate stimulation of the p42/p44 mitogen-activated protein kinase pathway in airway smooth muscle

Abstract

We report here that cultured airway smooth muscle cells contain transcripts of endothelial differentiation gene 1 (EDG-1), a prototypical orphan Gi-coupled receptor whose natural ligand is sphingosine 1-phosphate (S1P). This is consistent with data that showed that S1P activated both c-Src and p42/p44 mitogen-activated protein kinase (p42/p44 MAPK) in a pertussis toxin (PTX)-sensitive manner in these cells. An essential role for c-Src was confirmed by using the c-Src inhibitor, PP1, which markedly decreased p42/p44 MAPK activation. We have also shown that phosphoinositide 3-kinase (PI-3K) inhibitors (wortmannin and LY294002) decreased p42/p44 MAPK activation. An essential role for PI-3K was supported by experiments that showed that PI-3K activity was increased in Grb-2 immunoprecipitates from S1P-stimulated cells. Significantly, Grb-2 associated PI-3K activity was decreased by pretreatment of cells with PTX. Finally, we have shown that the co-stimulation of cells with platelet-derived growth factor (PDGF) and S1P (which failed to stimulate DNA synthesis) elicited a larger p42/p44 MAPK activation over a 30 min stimulation compared with each agonist alone. This was associated with a S1P-dependent increase in PDGF-stimulated DNA synthesis. These results demonstrate that S1P activates c-Src and Grb-2-PI-3K (intermediates in the p42/p44 MAPK cascade) via a PTX-sensitive mechanism. This action of S1P is consistent with the stimulation of EDG-1 receptors. S1P might also function as a co-mitogen with PDGF, producing a more robust activation of a common permissive signal transduction pathway linked to DNA synthesis.

TNF-α-Induced Sphingosine 1-Phosphate Inhibits Apoptosis Through a Phosphatidylinositol 3-Kinase/Akt Pathway in Human Hepatocytes

“…Activation of SphK and S1P formation peaked at 10 min, thus preceding Akt activation (detectable at 15 min) after TNF-␣ treatment. S1P activates c-Src tyrosine kinases and promotes Grb2-PI3K complex formation (41). These findings suggest that S1P formation induced activation of Akt in TNF-␣-treated human hepatocytes.…”

Sphingosine kinase-1 mediates TNF-α-induced MCP-1 gene expression in endothelial cells: upregulation by oscillatory flow

“…ERK1/2 activation by TNF-␣ and platelet-derived growth factor is at least partially dependent on SphK (28,35). Also, S1P stimulates ERK1/2 MAPK in airway smooth muscle cells (27). The p38 MAPK regulates expression of many inflammatory genes, such as MCP-1 (10), IL-6 (5), VCAM-1 (26), and TNF-␣ (39).…”

Insights into Seven and Single Transmembrane-Spanning Domain Receptors and Their Signaling Pathways in Human Natural Killer Cells

“…S1P induces endothelial cell migration Kimura et al, 2000), human umbilical vein endothelial cell proliferation (Hisano et al, 1999), platelet activation (Yatomi et al, 1997b), calcium mobilization (Meyer zu Heringdorf et al, 1998), invasion of primitive hematopoietic cells into stromal cell layers of the bone marrow (Yanai et al, 2000), angiogenesis , phosphorylation of ERK2 in airway smooth muscle cells (Rakhit et al, 1999), and accumulation of integrins at the focal sites through Rho activation (Windh et al, 1999). S1P also inhibits adenylyl cyclase, ERK1 activation (Lee et al, 1996), tumor cell invasion (Sadahira et al, 1992), and apoptosis (Radeff-Huang et al, 2004).…”