PDGF-induced signaling in proliferating and differentiated vascular smooth muscle: effects of altered intracellular Ca2+ regulation.
OBJECTIVE
Platelet-derived growth factor-BB (PDGF)-induced intracellular signaling is involved in phenotypic modulation of vascular smooth muscle (VSM). This study has examined the PDGF-induced Ca2+ increase and the resultant effect on signaling pathways in proliferative compared with fully differentiated VSM.


METHODS
PDGF-induced changes in Ca2+ were measured in portal vein (PV) myocytes from 2-4-day-old (proliferating), compared to 6-week-old (differentiated), Sprague Dawley rats. Phospholipase C (PLC)gamma expression and activation of extracellular signal-regulated kinase (ERK) 1/2 was determined by immunoblotting or confocal immunolabelling. Activation of the Ca(2+)-dependent transcription factor, nuclear factor of activated T-cells (NFATc), was assessed by electromobility shift assay.


RESULTS
PDGF increased the intracellular Ca2+ concentration in differentiated, but not in proliferating, PV myocytes. This is probably due to very low expression of PLC(gamma) in proliferating PV. In 6-week-old PV, PDGF stimulation induced nuclear translocation and activation of NFATc. PDGF did not induce NFATc activation in neonatal PV. PDGF-induced ERK1/2 activation was observed in both 2-4-day-old and 6-week-old PV. In 6-week-old PV, ERK1/2 activation was Ca(2+)-dependent and protein kinase C-dependent. However in 2-4-day-old PV, PDGF-induced ERK1/2 activation was via a Ca(2+)-independent, atypical protein kinase C. PLC(gamma) expression was also decreased in the neointima, compared to media, of balloon-injured rabbit subclavian arteries.


CONCLUSIONS
The regulation of PDGF-induced Ca2+ increases by PLC(gamma) expression in VSM may provide a mechanism for coordinating different signaling pathways leading to activation of specific transcription factors. This may play an important role in the phenotypic modulation of VSM.
Egan
Colin G
CG
School of Medical Sciences, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK.
Wainwright
Cherry L
CL
Wadsworth
Roger M
RM
Nixon
Graeme F
GF
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D002404:Catheterization; D002454:Cell Differentiation; D049109:Cell Proliferation; D024202:Electrophoretic Mobility Shift Assay; D007424:Intracellular Fluid / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008297:Male; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D051966:Phospholipase C gamma / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D011169:Portal Vein; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects*; D013268:Stimulation, Chemical; D013348:Subclavian Artery; D017539:Tunica Intima / Q000293:injuries / Q000378:metabolism
D010982:Platelet-Derived Growth Factor; D051966:Phospholipase C gamma; D002118:Calcium