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| ras oncogenes. These messengers attach to a cell's surface, initiating events through a series of receptors and intermediate compounds that control cellular function both within and outside of the cell. If a ras gene is mutated, it leads to an overexpression of a molecule called MAP (mitogen-activated kinase), which then causes uncontrolled cell growth. MAP is expressed five to twenty times more in cancers with the mutated ras gene. This mutated gene is found in 95 percent of all pancreatic cancers, one of the most difficult cancers to treat. |
| Proto-oncogenes |
| Proto-oncogenes are believed to be involved in normal growth and development. In general, they encode proteins, which are components of signaling pathways that regulate cell growth. These signaling pathways bind to specific membrane receptors and trigger a cascade of intracellular signals, and transcription of genes linked to proliferation follows. |
| There are three ways in which proto-oncogenes are transformed: |
| 1. Amplification signifies the presence of multiple copies of the gene, which results in overproduction of the genetic product. It is interesting to note here that vitamin D's inhibiting effect on cancer is believed to be its ability to reduce such overamplification. |
| 2. Point mutations occur as a result of a spontaneous or chemical carcinogenic reaction. They can then produce abnormal protein products leading to genetic damage. |
| 3. Translocation occurs when a proto-oncogene moves from its usual location on a particular chromosome (where it may be benign) to a different chromosome where it can be activated by neighboring genes (which can act as promoters or enhancers of transformation) into a cancer cell. |
| Sometimes a compound is not carcinogenic on its own; when combined with other compounds, however, it will accelerate or stimulate a cancer-producing reaction. These compounds are referred to as cocarcinogens, substances that become cancerous only when combined with other substances. It is important to understand that many of the chemicals and hormones we ingest may cause little or no harm by themselves, but when combined with other chemicals they may react and initiate or promote cancer. For example, the action between hormone metabolites and DDT produces DDE, a very toxic by-product. |
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