SRC is the first oncogene ever discovered. It was identified as the transforming (cancer causing) agent of the Rous sarcoma virus (RSV), which infects chickens and other animals. RSV is a retrovirus. It infects cells and then inserts its own genes into the cellular DNA. This quickly results in the development of cancer. The virus is therefore called an acutely transforming virus. When infected, chickens develop large tumors within two weeks. Researchers discovered that the protein from a particular gene in RSV causes cells to grow in an abnormal manner. A corresponding proto-oncogene was found in the human genome. The human gene, when activated into an oncogene, functions in a similar manner.
The SRC protein is a tyrosine kinase. Kinases are enzymes that transfer phosphate groups onto target molecules. The important aspect of this process is that the removal/addition of phosphates changes biomolecules and is a key way by which the activities of cells are regulated. The phosphate addition/removal process acts like an on/off switch to control the activity of the target molecules. The src proteins alter several target molecules, resulting in the transmission of signals to the nucleus that help regulate the cell.1
There are at least nine different known SRC genes. Due to different processing of the mRNA produced by these genes, at least 14 different proteins may be produced. C-SRC is normally found in most cells at a low level, but have been found to be overexpressed in certain cancer types, including human neuroblastoma, small-cell lung, colon, and breast carcinomas, and rhabdomyosarcoma.2