Oncogene formation from proto-oncogenes
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Proto-Oncogenes and Their Normal Cellular Functions
Proto-oncogenes are normal genes found in cells that play important roles in regulating cell growth, differentiation, and proliferation. Many proto-oncogenes encode proteins such as growth factors, growth factor receptors, and other signaling molecules that help control how cells develop and divide in a healthy organism 169. These genes are also expressed in a stage-specific manner during processes like gametogenesis and embryogenesis, indicating their involvement in normal developmental pathways 18.
Mechanisms of Oncogene Formation from Proto-Oncogenes
Oncogenes are formed when proto-oncogenes undergo genetic changes that disrupt their normal regulation. The main mechanisms that convert proto-oncogenes into oncogenes include:
- Point Mutations: Small changes in the DNA sequence can activate proto-oncogenes, as seen with the ras gene in many human tumors 510.
- Gene Amplification: An increase in the number of copies of a proto-oncogene can lead to overproduction of its protein product, contributing to uncontrolled cell growth 4510.
- Chromosomal Translocation or Rearrangement: Parts of chromosomes can break and reattach in new ways, placing proto-oncogenes under the control of different regulatory elements or creating fusion genes with new functions. This is common in certain blood cancers and thyroid carcinomas 4510.
These alterations remove the normal regulatory constraints on proto-oncogenes, allowing them to drive continuous cell division and survival, which can lead to cancer 134510.
Oncogene Activation and Cancer Development
Once a proto-oncogene becomes an oncogene, it can cause cells to grow and divide uncontrollably, a hallmark of cancer. The activation of oncogenes is often one of the earliest steps in the transformation of a normal cell into a cancerous one 2510. This process is frequently accompanied by the inactivation of tumor suppressor genes, further tipping the balance toward unchecked cell proliferation 2510.
Oncogenes can also help cancer cells avoid programmed cell death (apoptosis), making them more likely to survive and form tumors 210. The clonal theory of oncogenesis suggests that tumors often originate from a single cell in which a proto-oncogene has been activated 210.
Summary
Proto-oncogenes are essential for normal cell function, but when they are altered by mutations, amplifications, or chromosomal rearrangements, they become oncogenes that can drive cancer development. Understanding how proto-oncogenes are converted into oncogenes is crucial for developing targeted cancer therapies and improving outcomes for patients 1234510.
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