Sphingosine 1-phosphate stimulation of the p42/p44 mitogen-activated protein kinase pathway in airway smooth muscle. Role of endothelial differentiation gene 1, c-Src tyrosine kinase and phosphoinositide 3-kinase

S Rakhit, A M Conway, R Tate, T Bower, N J Pyne, S Pyne

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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.
Original languageEnglish
Pages (from-to)643-649
Number of pages7
JournalBiochemical journal
Volume338
Issue number3
DOIs
Publication statusPublished - 15 Mar 1999

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Keywords

  • animals
  • calcium-calmodulin-dependent protein kinases
  • cell line
  • enzyme activation
  • guinea pigs
  • immediate-early proteins
  • lysophospholipids
  • muscle, smooth
  • phosphatidylinositol 3-kinases
  • receptors, cell surface
  • receptors, G-protein-coupled
  • receptors, growth factor
  • receptors, lysophospholipid
  • signal transduction
  • sphingosine
  • trachea
  • transcriptional activation
  • src-family kinases

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