Oxidized phospholipid-induced endothelial cell/monocyte interaction is mediated by a cAMP-dependent R-Ras/PI3-kinase pathway.
OBJECTIVE
Previous studies have demonstrated the importance of endothelial apical expression of connecting segment-1 (CS-1) fibronectin in mediating the entry of monocytes into atherosclerotic lesions and other sites of chronic inflammation. We previously demonstrated that oxidized PAPC (OxPAPC) increases monocyte-specific binding to arterial endothelium by causing deposition of CS-1 fibronectin on apical alpha5beta1 integrin. The present studies identify important signal transduction components regulating this pathway.


RESULTS
Using endothelial cells in culture, we demonstrate that activation of R-Ras is responsible for CS-1-mediated monocyte binding. Although few natural activators of R-Ras have been demonstrated, OxPAPC activated endothelial R-Ras by 2.5-fold but decreased levels of activated H-Ras. The importance of R-Ras/H-Ras balance in regulating monocyte binding was shown by overexpression studies. Constitutively active R-Ras enhanced monocyte adhesion, whereas coexpression with constitutively active H-Ras was inhibitory. Elevated cAMP, mediated by OxPAPC and specific components POVPC and PEIPC, was responsible for R-Ras activation, and dibutyryl cAMP and pertussis toxin were also effective activators of R-Ras. Using inhibitor and dominant-negative constructs, we demonstrated that phosphatidylinositol 3-kinase (PI3K) was a key downstream effector of R-Ras in this pathway.


CONCLUSIONS
OxPAPC, POVPC, and PEIPC induce a cAMP/R-Ras/PI3K signaling pathway that contributes to monocyte/endothelial cell adhesion and potentially atherosclerosis.
Cole
Amy L
AL
David Geffen School of Medicine at University of California Los Angeles, Los Angeles, Calif, USA.
Subbanagounder
Ganesamoorthy
G
Mukhopadhyay
Srirupa
S
Berliner
Judith A
JA
Vora
Devendra K
DK
D000818:Animals; D002417:Cattle; D002448:Cell Adhesion / Q000502:physiology; D000242:Cyclic AMP / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D006801:Humans; D019012:Integrin beta1 / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins; D009000:Monocytes / Q000378:metabolism*; D010084:Oxidation-Reduction; D010455:Peptides / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism / Q000494:pharmacology; D010742:Phospholipid Ethers / Q000494:pharmacology; D010743:Phospholipids / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D018631:ras Proteins / Q000378:metabolism*
C400184:1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphorylcholine; D019012:Integrin beta1; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D010713:Phosphatidylcholines; D010742:Phospholipid Ethers; D010743:Phospholipids; C472349:oxidized-L-alpha-1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine; C076687:CS1 peptide; D000242:Cyclic AMP; D020558:GTP Phosphohydrolases; C085929:RRAS protein, human; D018631:ras Proteins