- 1. Any of a family of genes that normally encode proteins involved in cell growth or regulation (e.g., protein kinases, GTPases, nuclear proteins, growth factors) but that may foster malignant processes if mutated or activated by contact with retroviruses. Identified oncongenes include ras, originally noted in bladder tumors, and p53, a mutated version of a gene on chromosome 17 that has been shown to be involved in more than half of all human cancers. Oncogenes can work in concert to produce cancer, and their action may be exacerbated by retroviruses, jumping genes, or inherited genetic mutations. SEE ALSO: tumor suppressor gene. 2. A gene found in certain DNA tumor viruses. It is required for viral replication. SYN: transforming gene. [onco- + gene] Genes whose mutations can permit or induce uncontrolled cellular proliferation and malignant change are of 2 types: protooncogenes and tumor suppressor genes (antioncogenes). Protooncogenes encode proteins that stimulate DNA synthesis and cell division, including peptide growth factors and their cellular membrane receptors; second-messenger cascade proteins, which transmit information from cell membrane to nucleus; and nuclear transcription factors, which control gene expression by binding to DNA. Conversion of a protooncogene to an o. by amplification, translocation, or point mutation can lead to unrestrained cellular proliferation and malignant change. Only 1 copy (allele) of a protooncogene need undergo mutation to induce tumor formation. Protooncogenes are not involved in inherited cancer syndromes, with the exception of the RET protooncogene in multiple endocrine neoplasia. Tumor suppressor genes (antioncogenes), which encode proteins that normally serve to restrain cell proliferation, can be inactivated by point mutation, deletion, or loss of expression. An inherited mutation in 1 copy of a tumor suppressor gene is the basis of most familial predispositions to cancer. Malignant cellular proliferation does not occur until the remaining, functional copy of the gene is inactivated by mutation or by deletion of part or all of its chromosome. In a person born with 2 normal copies of a tumor suppressor gene, both must be inactivated by mutation before tumor formation occurs. BRCA1 and BRCA2, which are associated with familial early-onset breast cancer and ovarian cancer, are tumor suppressor genes.- ras o. point mutations first described in rat sarcoma cells that can be shown to have transforming activity in culture as well as in tumorigenesis models in mice; the ras gene family is composed of three closely related genes on three different chromosomes; abnormalities have been identified in a variety of human tumors.
* * *on·co·gene 'äŋ-kō-.jēn n a gene having the potential to cause a normal cell to become cancerous
* * *n.a gene in viruses (v-onc) and mammalian cells (c-onc) that can cause cancer. It results from the mutation of a normal gene. An oncogene is capable of both initiation and continuation of malignant transformation of normal cells. It probably produces proteins (growth factor) regulating cell division that, under certain conditions, become uncontrolled and may transform a normal cell to a malignant state.
* * *on·co·gene (ongґko-jēn) a gene capable under certain conditions of causing the initial and continuing conversion of normal cells into cancer cells. The term may be used to denote such a gene occurring in a viral genome (v-onc) or a cellular gene derived from alteration of a proto-oncogene (c-onc).
Medical dictionary. 2011.