What Are Oncogenes and How Do They Work
In a healthy organism, genes known as oncogenes serve a vital physiological purpose. They encode specific proteins that ensure normal proliferation (division) and differentiation of cell populations. Products of these genes include various growth factors, nuclear proteins, GTPases, and protein kinases.
It is important to understand that tumor development cannot be attributed to a mutation in a single oncogene alone. Malignant transformation requires the coordinated interaction of multiple oncogenes, as well as genes responsible for cell cycle regulation.
Key examples of oncogenes and their functions:
- c-erbB — encodes the epidermal growth factor receptor (EGFR).
- erbA — encodes a steroid hormone receptor.
- MYC — a multifunctional gene that acts as a potent stimulator of cell division.
- BCR-ABL — a pathological chimeric gene producing a fusion protein with unregulated tyrosine kinase activity.
- Aberrant JAK2 kinase — activates the STAT family of transcription factors, allowing the cell to autonomously maintain proliferation even in the absence of external growth factors.
- Cyclin and cyclin-dependent kinase genes — facilitate the entry of resting cells into the mitotic cycle.
Tumor Suppressor Genes
While oncogenes stimulate cell division, tumor suppressors (anti-oncogenes) perform the exact opposite function. Under normal conditions, they inhibit excessive cell proliferation, acting as a biological safeguard.
The pathogenesis of tumor growth is closely linked to the disruption of these structures. Genetic mutations lead to a loss of suppressor function. Consequently, the cell loses its inhibitory mechanisms, creating ideal conditions for repeated divisions and unchecked growth of the transformed cell pool.
Guardian of the Genome: The p53 Protein
The p53 protein is one of the most critical regulators of the cell cycle. Its activation and structural modification occur in response to cellular stressors such as viral infection, hypoxia, or direct DNA damage.
The mechanism of action of p53 involves specific binding to DNA regulatory elements to arrest cell growth in the G1 phase. This halts the cell cycle until damage is fully repaired. In damaged cells, p53 levels rise sharply, giving the cell time for DNA repair.
If the damage is critical and unrepairable, p53 normally initiates apoptosis (programmed cell death). In tumor cells, this protective mechanism is typically broken, with p53 gene mutations identified in nearly 50% of all neoplasms.
The Role of p27 in the Cell Cycle
Another significant tumor suppressor is the p27 protein. Its mechanism of action is based on direct interaction with cyclins and cyclin-dependent kinases (CDKs). By forming a complex with them, p27 reliably blocks cell entry into the S phase of the cell cycle, preventing premature replication of genetic material.
The clinical significance of this protein is particularly high in clinical oncology. Specifically, evaluating its activity is useful in breast cancer diagnostics. Evidence shows that decreased p27 expression is a poor prognostic marker indicating aggressive disease progression.