Differential signaling pathways in platelet-activating factor-induced proliferation and interleukin-6 production by rat vascular smooth muscle cells.
Vascular smooth muscle cells (SMCs) can be induced to proliferate in response to several cytokines and growth factors, including interleukin (IL)-6. Platelet-activating factor (PAF) also has been shown to induce SMC proliferation. Because PAF can stimulate IL-6 production in monocytes, macrophages, and endothelial cells, our study was undertaken to determine whether PAF could induce IL-6 production by SMCs and to define the underlying signaling pathways. Exposure of rat aortic SMCs to picomolar concentrations of PAF resulted in enhanced production of IL-6. The effect was concentration dependent, selective for the active form of PAF, and mediated by specific PAF receptors. Pretreatment of the cells with Bordatella pertussis toxin (PTX) prevented the effect of PAF, suggesting the involvement of alpha i-type subunits of G proteins in the signal-transduction pathway. PAF-dependent IL-6 production was also prevented by inhibition of tyrosine kinases with genistein or erbstatin. Inhibition of eicosanoid production by blocking either phospholipase A2 or cyclooxygenase also abrogated the effect of PAF on IL-6 production. Moreover, inhibition of Ca2+-calmodulin activity with W7 or blocking of calcium channels with verapamil or nifedipine prevented PAF-mediated enhancement of IL-6 production. Whereas PAF-induced signal-transduction pathways leading to IL-6 production and SMC proliferation were partially common, they appeared to diverge downstream of PLA2 activation: inhibition of cyclooxygenase had no effect on proliferation, whereas augmentation of cyclic adenosine monophosphate (cAMP) levels or activation of protein kinase A inhibited proliferation, in contrast to IL-6 production. Our findings suggest a role for PAF in modulating vascular function by stimulating local production of IL-6 by SMCs and promoting their proliferation. The two effects are, however, associated with partially divergent signaling pathways and may not be causally related.
Gaumond
F
F
Department of Pediatrics, Faculty of Medicine, Université de Sherbrooke, Sherbrooke QC, Canada.
Fortin
D
D
Stankova
J
J
Rola-Pleszczynski
M
M
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000096:biosynthesis / Q000502:physiology; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D015232:Dinoprostone / Q000096:biosynthesis; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D015850:Interleukin-6 / Q000096:biosynthesis*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D037342:Pertussis Toxin; D010741:Phospholipases A / Q000037:antagonists & inhibitors; D054467:Phospholipases A2; D010972:Platelet Activating Factor / Q000494:pharmacology*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D051381:Rats; D015290:Second Messenger Systems / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D002121:Calcium Channel Blockers; D016861:Cyclooxygenase Inhibitors; D007202:Indicators and Reagents; D015850:Interleukin-6; D010972:Platelet Activating Factor; D010566:Virulence Factors, Bordetella; D000242:Cyclic AMP; D037342:Pertussis Toxin; D011505:Protein-Tyrosine Kinases; D010741:Phospholipases A; D054467:Phospholipases A2; D015232:Dinoprostone