Related Experiment Videos
Analysis of wild-type and mutant p21WAF-1 gene activities
J Lin1, C Reichner, X Wu
1Department of Molecular Biology, Princeton University, New Jersey 08544, USA.
Abstract:
The p21WAF-1 gene is positively regulated by the wild-type p53 protein. p21WAF-1 has been shown to interact with several cyclin-dependent kinase complexes and block the activity of G1 cyclin-dependent kinases (cdks). Mutational analysis with the p21WAF-1 gene localized a site, at amino acid residues 21 and 24 in the amino terminus of the protein, for p21WAF-1 binding to cyclins D and E. This region of the protein is conserved (residues 21 to 26) in other p21WAF-1 family members, p27kip-1 and p57kip-2. The same p21WAF-121,24 mutant also fails to bind to cyclin D1-cdk 4 or cyclin E-cdk 2 complexes in vitro, suggesting that amino acid residues 21 and 24 are important for p21WAF-1-cdk-cyclin trimeric complex interactions. The p21WAF-1 wild-type protein will suppress tumor cell growth in culture while p21WAF-1 mutant proteins with defects in residues 21 and 24 fail to suppress tumor cell growth. The overexpression of cyclin D or E in these cells will partially overcome the growth suppression of wild-type p21WAF-1 protein in cells. These results provide evidence that p21WAF-1 acts through cyclin D1-cdk4 and cyclin E-cdk2 complexes in vivo to induce the growth suppression. The p21WAF-1 binding sites for cyclins (residues 21 to 26), cdk2 (residues 49 to 71), and proliferating-cell nuclear antigen (residues 124 to 164) have all been mapped to discrete sites on the protein.
Insights
The p21WAF-1 protein binds to cyclin-dependent kinases (cdks) and cyclins D/E, inhibiting cell growth. Specific mutations in p21WAF-1 at residues 21 and 24 disrupt these interactions and abolish tumor suppression, highlighting key binding sites for its function.
Area of Science:
- Molecular Biology
- Cell Cycle Regulation
- Cancer Biology
Background:
- The p21WAF-1 gene is a key regulator of cell cycle progression, positively controlled by wild-type p53.
- p21WAF-1 interacts with cyclin-dependent kinase (cdk) complexes, inhibiting their activity, particularly in the G1 phase.
Purpose of the Study:
- To identify specific amino acid residues in p21WAF-1 crucial for binding to cyclins and cdks.
- To elucidate the role of these interactions in p21WAF-1-mediated tumor growth suppression.
Main Methods:
- Mutational analysis of the p21WAF-1 gene to pinpoint critical binding sites.
- In vitro binding assays using p21WAF-1 mutants with cyclin D1-cdk4 and cyclin E-cdk2 complexes.
- Assessment of tumor cell growth suppression by wild-type and mutant p21WAF-1 proteins.
Main Results:
- Amino acid residues 21 and 24 in the p21WAF-1 amino terminus are essential for binding to cyclins D and E.
- Mutations at residues 21 and 24 prevent the formation of functional p21WAF-1-cyclin-cdk trimeric complexes.
- Wild-type p21WAF-1 suppresses tumor cell growth, while mutants at residues 21 and 24 lose this ability.
- Overexpression of cyclins D or E can partially rescue the growth suppression mediated by wild-type p21WAF-1.
Conclusions:
- p21WAF-1 exerts its tumor suppressor function by interacting with cyclin D1-cdk4 and cyclin E-cdk2 complexes in vivo.
- Specific residues (21-26 for cyclins, 49-71 for cdk2, 124-164 for PCNA) are critical for p21WAF-1's diverse protein interactions.