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A p18 mutant defective in CDK6 binding in human breast cancer cells
J Lapointe1, Y Lachance, Y Labrie
1Laboratory of Molecular Endocrinology, CHUL Research Center and Laval University, Quebec, Canada.
Abstract:
Progression from G1 to the S-phase of the cell cycle is controlled by a family of low molecular weight cyclin-dependent kinase (CDK) inhibitors. The importance of these proteins in cell growth control is underscored by the observation that some members of this family are deleted or mutated in human cancers. For example, the gene encoding the CDK inhibitor p18 is located on a segment of chromosome 1 that is often abnormal in human breast tumors. We have identified an alanine to proline substitution at codon 72 of the p18 gene in BT-20 human breast cancer cells. This mutation abrogates the ability of p18 to interact with CDK6 and renders p18 deficient in suppressing cell growth in a colony formation assay. Our results suggest that p18 inactivation by point mutations may contribute to deregulated growth control in certain cell lines and/or tumors.
Insights
A mutation in the p18 gene disrupts its function, impairing cell cycle control. This inactivation of cyclin-dependent kinase (CDK) inhibitors may contribute to uncontrolled cell growth in breast tumors.
Area of Science:
- Molecular Biology
- Cell Cycle Regulation
- Cancer Genetics
Background:
- Cell cycle progression is regulated by cyclin-dependent kinase (CDK) inhibitors.
- Alterations in CDK inhibitor genes are implicated in human cancers, including breast cancer.
- The p18 gene, a CDK inhibitor, is located on chromosome 1, frequently altered in breast tumors.
Purpose of the Study:
- To investigate the role of p18 gene mutations in human breast cancer.
- To identify specific mutations in the p18 gene within breast cancer cell lines.
- To determine the functional consequences of identified p18 mutations on CDK interaction and cell growth.
Main Methods:
- Sequencing of the p18 gene in BT-20 human breast cancer cells.
- Analysis of p18 protein interaction with CDK6.
- Colony formation assays to assess cell growth suppression.
Main Results:
- An alanine to proline substitution at codon 72 of the p18 gene was identified in BT-20 cells.
- This p18 mutation prevents interaction with CDK6.
- The mutated p18 protein is unable to suppress cell growth in colony formation assays.
Conclusions:
- Point mutations in the p18 gene can inactivate its function as a CDK inhibitor.
- Inactivation of p18 through mutation may contribute to deregulated cell growth in breast cancer.
- These findings highlight the significance of p18 in tumor suppressor pathways.