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Molecular and Cellular Biology, July 1999, p. 4623-4632, Vol. 19, No. 7
Department of Molecular Biology, The Lerner
Research Institute, The Cleveland Clinic Foundation, Cleveland,
Ohio 44195
Received 9 February 1999/Returned for modification 19 March
1999/Accepted 5 April 1999
Novel techniques were used to determine when in the cell cycle of
proliferating NIH 3T3 cells cellular Ras and cyclin D1 are required.
For comparison, in quiescent cells, all four of the inhibitors of cell
cycle progression tested (anti-Ras, anti-cyclin D1, serum removal, and
cycloheximide) became ineffective at essentially the same point in
G1 phase, approximately 4 h prior to the beginning of
DNA synthesis. To extend these studies to cycling cells, a time-lapse
approach was used to determine the approximate cell cycle position of
individual cells in an asynchronous culture at the time of inhibitor
treatment and then to determine the effects of the inhibitor upon
recipient cells. With this approach, anti-Ras antibody efficiently
inhibited entry into S phase only when introduced into cells prior to
the preceding mitosis, several hours before the beginning of S phase.
Anti-cyclin D1, on the other hand, was an efficient inhibitor when
introduced up until just before the initiation of DNA synthesis.
Cycloheximide treatment, like anti-cyclin D1 microinjection, was
inhibitory throughout G1 phase (which lasts a total of 4 to
5 h in these cells). Finally, serum removal blocked entry into S
phase only during the first hour following mitosis. Kinetic analysis
and a novel dual-labeling technique were used to confirm the
differences in cell cycle requirements for Ras, cyclin D1, and
cycloheximide. These studies demonstrate a fundamental difference in
mitogenic signal transduction between quiescent and cycling NIH 3T3
cells and reveal a sequence of signaling events required for cell cycle
progression in proliferating NIH 3T3 cells.
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Cellular Ras and Cyclin D1 Are Required during
Different Cell Cycle Periods in Cycling NIH 3T3 Cells
*
Corresponding author. Mailing address: Department of
Molecular Biology, NC2-151, The Lerner Research Institute, The
Cleveland Clinic Foundation, 9500 Euclid Ave., Cleveland, OH 44195. Phone: (216) 444-0633. Fax: (216) 444-0512. E-mail:
staceyd{at}ccf.org.
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