Tumor Suppressor Genes

There are a growing number of genes that have been identified as having some function as tumor suppressor genes. The table below lists genes and their associated tumor types. One of the most important tumor suppressor Table 1.

Tumor suppressor genes act as gatekeepers for passage from S (synthesis) phase to G2 and mitosis. Activation of these genes, which may occur if DNA replication cannot be successfully completed, triggers apoptosis, or programmed cell death.

genes is TP53 (more commonly known as p53). This gene was originally identified as a germ-line mutation in the rare inherited cancer called Li-Fraumeni Syndrome, but it has since been shown to be involved in a wide variety of cancer types. The p53 gene is lost (e.g., the gene is deleted from the chromosome) in about 50 percent of all cancerous cells.

The p53 protein is responsible for controlling the cell cycle checkpoint at the stage where the cell makes a decision to duplicate its genome, called the G2/S boundary. Along with p21 (another essential protein at this boundary), p53 protein monitors the state of the DNA to ensure that the genome is intact and not damaged. The S phase is where the genome is duplicated to get ready for cell division, so it is important that any damage and errors be repaired. If the cell is unable to repair the damage to its DNA, p53 can induce the programmed cell death pathway (called apoptosis) that kills off the cell, thus preventing division of a cell with damaged DNA. If p53 is not functional, the cell cycle is not arrested and any errors will be duplicated and passed on when the cell divides.