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Inhibition of ras-induced proliferation and cellular transformation by p16INK4
M Serrano1, E Gómez-Lahoz, R A DePinho
1Howard Hughes Medical Institute, Cold Spring Harbor Laboratory, NY 11724.
Abstract:
The cyclin-dependent kinase 4 (CDK4) regulates progression through the G1 phase of the cell cycle. The activity of CDK4 is controlled by the opposing effects of the D-type cyclin, an activating subunit, and p16INK4, an inhibitory subunit. Ectopic expression of p16INK4 blocked entry into S phase of the cell cycle induced by oncogenic Ha-Ras, and this block was relieved by coexpression of a catalytically inactive CDK4 mutant. Expression of p16INK4 suppressed cellular transformation of primary rat embryo fibroblasts by oncogenic Ha-Ras and Myc, but not by Ha-Ras and E1a. Together, these observations provide direct evidence that p16INK4 can inhibit cell growth.
Insights
The protein p16INK4 inhibits cell growth by blocking the cell cycle. It acts as a tumor suppressor by preventing cell proliferation, as demonstrated in experiments with oncogenic proteins.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- Cyclin-dependent kinase 4 (CDK4) is a key regulator of the G1 phase in the cell cycle.
- CDK4 activity is modulated by D-type cyclins (activating) and p16INK4 (inhibitory).
Purpose of the Study:
- To investigate the inhibitory role of p16INK4 in cell cycle progression and cellular transformation.
- To provide direct evidence for p16INK4's function as a cell growth inhibitor.
Main Methods:
- Utilized ectopic expression of p16INK4 in primary rat embryo fibroblasts.
- Assessed the effects of p16INK4 on cell cycle entry (S phase) induced by oncogenic Ha-Ras.
- Examined the impact of p16INK4 on cellular transformation mediated by oncogenic Ha-Ras/Myc and Ha-Ras/E1a.
Main Results:
- Ectopic p16INK4 expression blocked G1 to S phase transition induced by oncogenic Ha-Ras.
- This cell cycle block was reversible with a catalytically inactive CDK4 mutant.
- p16INK4 suppressed cellular transformation by Ha-Ras/Myc but not by Ha-Ras/E1a.
Conclusions:
- p16INK4 directly inhibits cell growth by regulating cell cycle progression.
- p16INK4 functions as a tumor suppressor, with its efficacy potentially dependent on other viral oncoproteins.