Cell cycle effects of nitric oxide on vascular smooth muscle
cells.
Sarkar, Rajabrata, David Gordon, James C. Stanley and R. Clinton Webb.
Departments of Physiology, Pathology and Surgery, 1301 Catherine
Road, University of Michigan Medical Center, Ann Arbor, MI 48109
APStracts 3:0516H, 1996.
We characterized the cell cycle block induced by nitric oxide (NO) on
smooth muscle cells (SMC). We hypothesized that the inhibition of SMC
proliferation by NO was due to a specific block in cell cycle
progression. Treatment of cultured rat aortic SMC with the NO donors
S-nitroso-N-acetylpenicillamine or S-nitrosoglutathione (0.1 mM for
48 hours) resulted in a 50% decrease (p<.05) in the fraction
of cells in the S and G2+M phases and a corresponding increase in the
G1 fraction, suggesting that NO inhibits entry into S phase, causing
accumulation of cells in G1 phase. Application of both NO donors to
cycling SMC resulted in a short term, concentration-dependent (0.06
-0.3 mM) inhibition of ongoing DNA synthesis as measured by
radiothymidine incorporation, demonstrating that NO causes an S phase
arrest. The S phase arrest by NO was not mimicked by exogenous cGMP
(10 mM) and associated with, but not due to, a 20% inhibition of RNA
synthesis. The S phase block was completely reversed within 2 hours
of removal of the NO donors, similar to inhibition by the
ribonucleotide reductase inhibitor hydroxyurea. Prolonged treatment
of SMC with either NO donor (0.1 mM) did not synchronize cells at the
G1/S boundary as expected after a prolonged S phase arrest, but
instead induced a quiescent G0-like state characterized by a 12-18
hour lag before DNA synthesis returned to normal levels following NO
removal. These findings demonstrate that NO inhibition of SMC
proliferation is associated with two distinct and reversible cell
cycle arrests, an immediate cGMP-independent S phase block followed
by a shift back in the cell cycle from the G1/S boundary to a
quiescent G0-like state.
Received 12 July 1996; accepted in final form 11 November 1996.
APS Manuscript Number H622-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996