Density-dependent shift of transforming growth factor-beta-1 from inhibition to stimulation of vascular smooth muscle cell growth is based on unconventional regulation of proliferation, apoptosis and contact inhibition.
BACKGROUND
TGF-beta shifts from inhibition to stimulation of vascular smooth muscle cell (vSMC) growth when cell density increases. How proliferation and apoptosis contribute to this shift is still unknown.


METHODS
In sparse and confluent V8 vSMC treated or not with TGF-beta(1) (1 ng/ml) for 3 days, cell number, mitotic activity, cell-cycle-regulatory protein levels, caspase-3 and phosphoinositide 3-kinase (PI3-K) activities were studied.


RESULTS
In TGF-beta(1)-treated cells, (i) the growth curve rose constantly compared to controls, reaching post-confluent densities; (ii) mitotic activity, which was constant at all cell densities, was lower than in sparse but higher than in contact-inhibited control cells, and (iii) apoptosis occurred at sparse densities only. The mechanism of proliferation control by TGF-beta(1) was very unconventional in V8 vSMCs: (i) p15(INK4b) and cyclin D levels were similar in cells treated or not with TGF-beta(1), and (ii) p27(Kip1) levels remained very low even at high densities while cyclin E levels were not markedly decreased. TGF-beta(1)-induced apoptosis in sparse cultures and its reversal in dense cultures were inversely correlated to PI3-K activation.


CONCLUSIONS
TGF-beta(1) slowed sparse V8 vSMC growth by inhibiting proliferation and inducing apoptosis. TGF-beta(1)-treated confluent vSMCs escaped contact inhibition and kept growing through unconventional regulation of p27(Kip1), cyclin E and suppression of apoptosis.
Hneino
Mohammad
M
Institut National de la Santé et de la Recherche Médicale (INSERM ERI 22), Université Claude Bernard Lyon 1 (EA 4173) et Institut Fédératif de Recherche Lyon-Est, Lyon, France. mohammad.hneino@sante.univ-lyon1.fr
Bouazza
Lamia
L
Bricca
Giampiero
G
Li
Jacques Yuan
JY
Langlois
Dominique
D
D000818:Animals; D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism; D002461:Cell Line, Transformed; D049109:Cell Proliferation; D003260:Contact Inhibition; D056741:Cyclin D; D019927:Cyclin E / Q000378:metabolism; D050762:Cyclin-Dependent Kinase Inhibitor p15 / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D004261:DNA Replication; D008297:Male; D008938:Mitosis; D009131:Muscle, Smooth, Vascular / Q000201:enzymology / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000201:enzymology / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar; D016160:Retinoblastoma Protein / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*
C493962:Cdkn1b protein, rat; D056741:Cyclin D; D019927:Cyclin E; D050762:Cyclin-Dependent Kinase Inhibitor p15; D016213:Cyclins; D016160:Retinoblastoma Protein; D053773:Transforming Growth Factor beta1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D019869:Phosphatidylinositol 3-Kinases; C505410:Casp3 protein, rat; D053148:Caspase 3