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The alternative product from the human CDKN2A locus, p14(ARF), participates in a regulatory feedback loop with p53
F J Stott1, S Bates, M C James
1Imperial Cancer Research Fund Laboratories, P.O. Box 123, 44 Lincoln's Inn Fields, London WC2A 3PX, UK.
Abstract:
The two distinct proteins encoded by the CDKN2A locus are specified by translating the common second exon in alternative reading frames. The product of the alpha transcript, p16(INK4a), is a recognized tumour suppressor that induces a G1 cell cycle arrest by inhibiting the phosphorylation of the retinoblastoma protein by the cyclin-dependent kinases, CDK4 and CDK6. In contrast, the product of the human CDKN2A beta transcript, p14(ARF), activates a p53 response manifest in elevated levels of MDM2 and p21(CIP1) and cell cycle arrest in both G1 and G2/M. As a consequence, p14(ARF)-induced cell cycle arrest is p53 dependent and can be abrogated by the co-expression of human papilloma virus E6 protein. p14(ARF) acts by binding directly to MDM2, resulting in the stabilization of both p53 and MDM2. Conversely, p53 negatively regulates p14(ARF) expression and there is an inverse correlation between p14(ARF) expression and p53 function in human tumour cell lines. However, p14(ARF) expression is not involved in the response to DNA damage. These results place p14(ARF) in an independent pathway upstream of p53 and imply that CDKN2A encodes two proteins that are involved in tumour suppression.
Insights
The CDKN2A gene produces two tumor suppressors: p16INK4a, which halts cell division by inhibiting CDK4/6, and p14ARF, which triggers a p53-dependent cell cycle arrest. Both proteins are crucial for tumor suppression.
Area of Science:
- Molecular Biology
- Cancer Biology
- Genetics
Background:
- The CDKN2A locus encodes two distinct tumor suppressor proteins, p16INK4a and p14ARF, through alternative reading frames of a common exon.
- p16INK4a inhibits cyclin-dependent kinases CDK4 and CDK6, inducing G1 cell cycle arrest.
- p14ARF activates a p53-dependent pathway, leading to cell cycle arrest and stabilization of p53 and MDM2.
Purpose of the Study:
- To elucidate the distinct roles and regulatory mechanisms of the two CDKN2A proteins, p16INK4a and p14ARF, in tumor suppression.
- To investigate the relationship between p14ARF, p53, and MDM2 in cellular pathways.
- To determine if p14ARF is involved in the DNA damage response.
Main Methods:
- Analysis of protein products from the CDKN2A locus, p16INK4a and p14ARF.
- Investigation of cell cycle arrest mechanisms (G1, G2/M).
- Assessment of p53 pathway activation, including MDM2 and p21(CIP1) levels.
- Examination of protein-protein interactions (p14ARF and MDM2).
- Correlation analysis of p14ARF expression and p53 function in tumor cell lines.
Main Results:
- p16INK4a induces G1 arrest by inhibiting CDK4/6-mediated retinoblastoma protein phosphorylation.
- p14ARF activates p53, increasing MDM2 and p21(CIP1), causing G1 and G2/M arrest.
- p14ARF-induced arrest is p53-dependent and can be overcome by HPV E6.
- p14ARF binds MDM2, stabilizing both proteins.
- p53 negatively regulates p14ARF expression, showing an inverse correlation in tumor cells.
- p14ARF is not involved in the DNA damage response.
Conclusions:
- The CDKN2A locus encodes two independent tumor suppressor pathways.
- p14ARF acts upstream of p53, independent of the DNA damage response.
- Both p16INK4a and p14ARF contribute to tumor suppression through distinct mechanisms.