The Oncogene and its Potential Role in Carcinogenesis
Cellular onc genes are a group of evolutionarily conserved sequences which are homologous to the transforming genes (v-onc) of oncogenic retroviruses. Although their functions in normal cells are largely not known, the sequence homology between viral and cellular onc genes is consistent with the idea that neoplastic transformation may, in some cases, be due to abnormal levels of cellular onc gene expression. Several models can be proposed for such a mechanism, including the insertion nearby of a viral promoter, alteration of the physiological promoter by a mutagenic agent, gene amplification, relocation in a transcriptionally active region of the genome as a consequence of chromosomal rearrangements and point mutations induced by external factors. Examples of these different mechanisms of onc gene activation can be found in animal and human tumors. Finally, the detail description of one cellular one gene (c-sis), its relation to the viral gene and to a known cellular growth factor and its possible mode of activation in neoplastic transformation is presented.
Key wordsCellular Oncogene Transforming genes Retrovirus Carcinogenesis
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