Oxidized LDL-induced smooth muscle cell proliferation involves the EGF receptor/PI-3 kinase/Akt and the sphingolipid signaling pathways.
OBJECTIVE
Oxidized low-density lipoprotein (oxLDL)-induced smooth muscle cell (SMC) proliferation requires the coactivation of various signaling pathways, namely sphingomyelin/ceramide/sphingosine-1-phosphate, epithelial growth factor receptor (EGFR), and phosphoinositide 3-kinase (PI-3K) pathways. This study aimed to clarify the respective role and the hypothetical cross-talk between sphingomyelin/ceramide/sphingosine-1-phosphate, EGFR, and PI-3K/Akt pathways in the balance between mitogenic and cytotoxic effects elicited by oxLDL.


RESULTS
Coimmunoprecipitation experiments and the use of inhibitors and dominant-negative mutant showed that oxLDL-induced PI-3K activation is dependent on EGFR. PI-3K activation is independent of the sphingomyelin/ceramide/sphingosine-1-phosphate pathway, because PI-3K inhibition by LY294002 or dominant-negative Deltap85 mutant does not abrogate sphingomyelin hydrolysis, and, conversely, the use of permeant C2-ceramide and of N,N-dimethyl-sphingosine, a sphingosine kinase inhibitor, does not alter PI-3K activity. Activation of Akt/PKB by oxLDL requires PI-3K, as shown by the inhibition by LY204002 and in Deltap85 SMC. The inhibition of Akt/PKB by PI-3K inhibitor LY204002 or by overexpression of kinase-dead Akt shifted the mitogenic effect of oxLDL toward apoptosis, thus suggesting that the PI-3K/Akt pathway acts as a survival pathway.


CONCLUSIONS
SMC proliferation elicited by moderate concentrations of oxLDL involves the sphingomyelin/ceramide/sphingosine-1-phosphate pathway, which leads to extracellular regulated kinase 1/2 activation and DNA synthesis, and the EGFR/PI-3K/Akt pathway, which prevents the apoptotic effect of oxLDL.
Auge
Nathalie
N
INSERM U-466, Université Paul Sabatier, Toulouse, France.
Garcia
Virginie
V
Maupas-Schwalm
Françoise
F
Levade
Thierry
T
Salvayre
Robert
R
Negre-Salvayre
Anne
A
D019870:1-Phosphatidylinositol 4-Kinase / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002518:Ceramides / Q000378:metabolism / Q000502:physiology; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D066246:ErbB Receptors / Q000378:metabolism / Q000502:physiology*; D005263:Femoral Artery / Q000166:cytology / Q000187:drug effects; D008077:Lipoproteins, LDL / Q000494:pharmacology*; D008246:Lysophospholipids; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D010084:Oxidation-Reduction; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D011817:Rabbits; D013109:Sphingomyelins / Q000378:metabolism / Q000502:physiology*; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000502:physiology
D002518:Ceramides; D008077:Lipoproteins, LDL; D008246:Lysophospholipids; D011518:Proto-Oncogene Proteins; D013109:Sphingomyelins; C099252:oxidized low density lipoprotein; C060506:sphingosine 1-phosphate; D019870:1-Phosphatidylinositol 4-Kinase; D066246:ErbB Receptors; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D013110:Sphingosine