Tumor Suppressor Gene – Definition and Significance
A tumor suppressor gene is a gene that prevents uncontrolled cell growth. Mutations in these genes can lead to the development of cancer.
Things worth knowing about "Tumor Suppressor Gene"
A tumor suppressor gene is a gene that prevents uncontrolled cell growth. Mutations in these genes can lead to the development of cancer.
What Is a Tumor Suppressor Gene?
A tumor suppressor gene is a gene within the human genome whose primary function is to control cell growth, regulate cell division, and trigger programmed cell death (apoptosis) in damaged cells. These genes act like molecular brakes in the cell cycle. When functioning correctly, they prevent cells from growing and dividing in an uncontrolled manner – a process that can otherwise lead to tumor formation.
Tumor suppressor genes stand in contrast to so-called oncogenes, which promote cell growth. The balance between these two gene groups is essential for normal cell function and the prevention of cancer.
Function and Mechanism of Action
Tumor suppressor genes serve several critical functions within the body:
- Cell cycle control: They regulate when and how frequently a cell divides by monitoring specific checkpoints within the cell cycle.
- DNA repair: When genetic damage occurs, these genes signal the cell to halt division and initiate repair of the damaged DNA.
- Apoptosis (programmed cell death): If a cell is too severely damaged to be repaired, tumor suppressor genes trigger its controlled self-destruction to prevent the formation of cancerous cells.
- Inhibition of angiogenesis: They can suppress the formation of new blood vessels that would otherwise supply a growing tumor.
Well-Known Tumor Suppressor Genes
Among the most extensively studied tumor suppressor genes are:
- TP53 (p53): Often referred to as the guardian of the genome, p53 is the most frequently mutated gene in human cancers. It coordinates the cellular response to DNA damage.
- BRCA1 and BRCA2: These genes play a central role in DNA repair. Mutations in BRCA1 or BRCA2 significantly increase the risk of breast and ovarian cancer.
- RB1 (Retinoblastoma gene): The first tumor suppressor gene to be identified, originally discovered in retinoblastoma (a tumor of the retina). It regulates the transition between phases of the cell cycle.
- APC: Mutations in this gene are frequently associated with colorectal cancer.
- PTEN: This gene inhibits cell growth and is altered in many types of cancer.
How Gene Mutations Lead to Cancer
According to the two-hit model (Two-Hit Hypothesis) proposed by Alfred Knudson, both copies (alleles) of a tumor suppressor gene typically need to be mutated or inactivated before the protective function is lost. Every person carries two copies of each gene – one inherited from each parent.
In hereditary cancer syndromes, one copy of the gene is already mutated at birth (the first hit). A second defect in the remaining healthy copy – caused by environmental factors, radiation, or random copying errors during cell division – is then sufficient to eliminate tumor suppression (the second hit).
Clinical Relevance and Diagnosis
Understanding tumor suppressor genes has fundamentally transformed oncology. Genetic testing can now identify mutations in key genes such as BRCA1, BRCA2, and TP53, helping to:
- Assess individual cancer risk
- Plan targeted screening and surveillance programs
- Inform family members about potential inherited risks
- Guide the selection of targeted (molecular) therapies
The analysis of tumor suppressor genes is carried out using molecular genetic methods, such as Next-Generation Sequencing (NGS) or targeted sequencing of specific gene regions.
Therapeutic Approaches
Since inactivated tumor suppressor genes represent a central mechanism in cancer development, they are important targets in modern cancer therapy:
- Gene therapy: Approaches to restore the function of defective tumor suppressor genes are currently under investigation.
- PARP inhibitors: In tumors with BRCA mutations, PARP inhibitors are used to selectively impair DNA repair in cancer cells.
- Checkpoint inhibitors: Immunotherapies that enhance the body's immune response against tumor cells harboring defective suppressor genes.
References
- Lodish H, Berk A, Kaiser CA et al. - Molecular Cell Biology. 8th edition. W.H. Freeman and Company, 2016.
- Knudson AG - Mutation and cancer: statistical study of retinoblastoma. Proceedings of the National Academy of Sciences, 1971; 68(4): 820-823.
- National Cancer Institute (NCI) - Tumor Suppressor Genes. https://www.cancer.gov (accessed 2024).
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