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

Abstract

Background: TGF-β 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-β₁ (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-β₁-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-β₁ was very unconventional in V8 vSMCs: (i) p15^INK4b and cyclin D levels were similar in cells treated or not with TGF-β₁, and (ii) p27^Kip1 levels remained very low even at high densities while cyclin E levels were not markedly decreased. TGF-β₁-induced apoptosis in sparse cultures and its reversal in dense cultures were inversely correlated to PI3-K activation. Conclusions: TGF-β₁ slowed sparse V8 vSMC growth by inhibiting proliferation and inducing apoptosis. TGF-β₁-treated confluent vSMCs escaped contact inhibition and kept growing through unconventional regulation of p27^Kip1, cyclin E and suppression of apoptosis.

Mechanical trapping of the nucleus on micropillared surfaces inhibits the proliferation of vascular smooth muscle cells but not cervical cancer HeLa cells

“…2I and J). It has generally been suggested that contact inhibition of cell proliferation occurs when a cell culture reaches confluence (Hneino et al, 2009). However, the proliferation of SMCs was significantly inhibited in the micropillar substrates even though the cells did not reach the confluent state (compare Fig.…”

AMP-activated protein kinase inhibits transforming growth factor-β-mediated vascular smooth muscle cell growth: implications for a Smad-3-dependent mechanism

“…In VSMCs, TGF-␤ has historically been considered antiproliferative (2, 14 -16); however, other findings suggest that TGF-␤ and its downstream Smads stimulate growth in primary VSMCs (9,18,19,(25)(26)(27). Adding to this uncertainty, in cultured cells TGF-␤1 is suggested to switch between growth stimulation and growth suppression depending on concentration (3,18) and cell density (9). This pleiotropic and often discordant nature of TGF-␤/Smad signaling and its control of tissue growth demand clarity.…”

Conditional inactivation of TGF-β type II receptor in smooth muscle cells and epicardium causes lethal aortic and cardiac defects

“…TGF-b controls VSMC proliferation (Hneino et al 2008). Altered VSMC proliferation by abrogation of TGF-b signaling could take part in the anomalies of Sections from the descending aorta stained with a-SMA from E14.5 (a, b), E15.5 (c, d), E17.5 (e, f), E18.5 (g, h) embryos.…”