Ras is active throughout the cell cycle, but is able to induce cyclin D1 only during G2 phase.
The control of cell cycle progression has been studied in asynchronous cultures using image analysis and time lapse techniques. This approach allows determination of the cycle phase and signaling properties of individual cells, and avoids the need for synchronization. In past studies this approach demonstrated that continuous cell cycle progression requires the induction of cyclin D1 levels by Ras, and that this induction takes place during G2 phase. These studies were designed to understand how Ras could induce cyclin D1 levels only during G2 phase. First, in studies with a Ras-specific promoter and cellular migration we find that endogenous Ras is active in all cell cycle phases of actively cycling NIH3T3 cells. This suggests that cyclin D1 induction during G2 phase is not the result of Ras activation specifically during this cell cycle period. To confirm this suggestion oncogenic Ras, which is expected to be active in all cell cycle phases, was microinjected into asynchronous cells. The injected protein induced cyclin D1 levels rapidly, but only in G2 phase cells. We conclude that in the continuously cycling cell the targets of Ras activity are controlled by cell cycle phase, and that this phenomenon is vital to cell cycle progression.
Sa
Gaurisankar
G
The Department of Molecular Biology, The Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Ave, Ohio 44195, USA.
Hitomi
Masahiro
M
Harwalkar
Jyoti
J
Stacey
Andrew W
AW
GC
Guan Chen
GC
Stacey
Dennis W
DW
D016475:3T3 Cells; D000818:Animals; D000951:Antigens, Neoplasm; D002453:Cell Cycle / Q000502:physiology; D019938:Cyclin D1 / Q000378:metabolism*; D004250:DNA Topoisomerases, Type II / Q000235:genetics; D004268:DNA-Binding Proteins; D016195:G2 Phase / Q000502:physiology*; D051379:Mice; D018631:ras Proteins / Q000378:metabolism*
D000951:Antigens, Neoplasm; D004268:DNA-Binding Proteins; D019938:Cyclin D1; D018631:ras Proteins; D004250:DNA Topoisomerases, Type II