How oncogenes are produced form proto-oncogenes?

Proto-oncogenes are genes whose products promote cell growth and division. They do this by encoding transcription factors that stimulate the expression of other genes, signal transduction molecules that stimulate cell division, or cell cycle regulators that move the ell through the cell cycle. Proto-oncogene products may be located in the plasma membrane, cytoplasm, or nucleus, and their activities are controlled in various ways, including regulation at the transcpritional, translational, and protein-modification levels. When cells become quiescent and cease division, they repress the expression of most proto-oncogene products. In cancer cells, one or more proto-oncogenes are altered in such a way that tier activities cannot be controlled in a normal fashion. This is sometimes due to a mutation in the proto-oncogene resulting in a protein product that acts abnormally. In other cases, proto-oncogenes may encode normal protein products, but the genes are overexpressed or cannot be transcriptionally repressed at the correct time. In these cases, the proto-oncogene product is continually in an "on" state, which may constantly stimulate the cell to divide. When a proto-oncogene is mutated or aberrantly expressed, and contributes to the development of cancer, it is known as an oncogene. Oncogenes are those that have experienced a gain-of-function alteration. As a result, only one allele of a proto-oncogene needs to be mutated or mis-expressed in order to trigger uncontrolled growth. Hence, oncogenes confer a dominant cancer phenotype.