Sphingosine-1-phosphate stimulates smooth muscle cell migration through galpha(i)- and pi3-kinase-dependent p38(MAPK) activation.
BACKGROUND
Sphingosine-1-phosphate (S-1-P) is an extracellular mediator released in response to vessel injury. S-1-P binds to G-protein-coupled receptors, which can be Galpha(i)-, Galpha(q)-, or G(12/13)-linked. This study examines the role of p38 mitogen-activated protein kinase (p38(MAPK)) in vascular smooth muscle cell migration after stimulation with S-1-P, and pathways leading to p38(MAPK) activation. S-1-P has previously been shown to stimulate migration of vascular smooth muscle cells (VSMCs) in vitro through ERK1/2 and G(i). We hypothesized that S-1-P-induced VSMC migration is also dependent on p38(MAPK) activation through a G(i)-coupled extracellular receptor and phosphoinositide 3-kinase (PI3-K).


METHODS
VSMCs were cultured in vitro. A linear wound assay was performed in the presence of S-1-P and inhibitors of p38(MAPK) (SB203580) or epidermal growth factor (EGF) receptor kinase (AG1478). Chemotaxis stimulated by S-1-P was also assayed in a modified Boyden chamber with and without SB203580 pretreatment. Western blotting was performed to examine p38(MAPK) activation in response to S-1-P with and without SB203580, AG1478, or inhibitors of G(i) (pertussis toxin), PI3-K (Wortmannin and LY294002), or MEK1 (PD98059). Western blotting and immunoprecipitation for targets of p38(MAPK) (MAPKAP kinase-2) and PI3-K (Akt) were also performed.S-1-P stimulated migration of VSMCs in both wound and Boyden transwell assays. This migration was inhibited by SB203580 to the level of control, whereas AG478 had no effect.


RESULTS
S-1-P stimulated activation of p38(MAPK) that peaked at 10 min, as well as activation of MAPKAP kinase-2. Activation of p38(MAPK) was significantly inhibited by SB203580, pertussis toxin, Wortmannin, and LY294002, but not by PD98059 or AG1478; MAPKAP kinase-2 activation was inhibited by SB203580. Akt was activated by S-1-P at 3 to 5 min; this response was inhibited by Wortmannin and LY294002, but not by SB203580 or pertussis toxin.


CONCLUSIONS
S-1-P induced VSMC migration through a G(i)-linked and a PI3-K coupled, p38(MAPK)- dependent process. PI3-K appears to function upstream of p38(MAPK), but was not G(i)-dependent. S-1-P-stimulated activation of p38(MAPK) does not signal via transactivation of the EGF receptor. Understanding signal transduction will allow targeted molecular interventions to treat the response of a vessel to injury.
Fegley
Allison J
AJ
Vascular Biology and Therapeutics Program, Division of Vascular Surgery, Department of Surgery, and Center for Cardiovascular Research, University of Rochester, Rochester, New York, USA
Tanski
William J
WJ
Roztocil
Elisa
E
Davies
Mark G
MG
D000818:Animals; D002465:Cell Movement / Q000187:drug effects* / Q000502:physiology; D002478:Cells, Cultured; D020555:GTP-Binding Protein Regulators / Q000187:drug effects* / Q000502:physiology; D008246:Lysophospholipids; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects* / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D015398:Signal Transduction; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D048051:p38 Mitogen-Activated Protein Kinases
D020555:GTP-Binding Protein Regulators; D008246:Lysophospholipids; C060506:sphingosine 1-phosphate; D019869:Phosphatidylinositol 3-Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D013110:Sphingosine