Oncogene (Encyclopedia of Genetic Disorders)
In a cell with normal control regulation (non-cancerous), genes produce proteins that provide regulated cell division. Cancer is the disease caused by cells that have lost their ability to control their regulation. The abnormal proteins allowing the non-regulated cancerous state are produced by genes known as oncogenes. The normal gene from which the oncogene evolved is called a protooncogene.
The word oncogene comes from the Greek term oncos, which means tumor. Oncogenes were originally discovered in certain types of animal viruses that were capable of inducing tumors in the animals they infected. These viral oncogenes, called v-onc, were later found in human tumors, although most human cancers do not appear to be caused by viruses. Since their original discovery, hundreds of oncogenes have been found, but only a small number of them are known to affect humans. Although different oncogenes have different functions, they are all somehow involved in the process of transformation (change) of normal cells to cancerous cells.
The transformation of normal cells...
(The entire section is 2318 words.)
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Oncogene (World of Microbiology and Immunology)
An oncogene is a special type of gene that is capable of transforming host cells and triggering carcinogenesis. The name is derived from the Greek onkos, meaning bulk, or mass, because of the ability to cause tumor growth. Oncogenes were first discovered in retroviruses (viruses containing the enzyme reverse transcriptase, and RNA, rather than DNA) that were found to cause cancer in many animals (e.g., feline leukemia virus, simian sarcoma virus). Although this is a relatively common mechanism of oncogenesis in animals, very few oncogene-carrying viruses have been identified in man. The ones that are known include the papilloma virus HPV16 that is associated with cervical cancer, HTLV-1 and HTLV-2 associated with T-cell leukemia, and HIV-1 associated with Kaposi sarcoma.
Studies of humans led to the discovery of related genes called proto-oncogenes that exist naturally in the human genome. These genes have DNA sequences that are similar to oncogenes, but under normal conditions, the proto-oncogenes do not cause cancer. However, specific mutations in these genes can transform them to an oncogenic form that may lead to carcinogenesis. So, in humans, there are two unique ways in which oncogenesis occurs, by true viral infection and by mutation of proto-oncogenes that already exist in human cells.
See also Molecular biology and molecular genetics; Oncogenetic research; Viral genetics; Viral vectors in gene therapy; Virology; Virus replication; Viruses and responses to viral infection