General Functions of Tumor Suppressor Genes

Tumor suppressor genes are genes that, by their inactivation due to mutations or deletion, promote tumor formation. The proteins for which they code are known as tumor suppressor proteins. Many of the known tumor suppressor proteins have a suppressing and negatively regulating effect on processes that are either directly associated with regulation of cell division or influence this in an indirect way. Other, equally important functions of tumor suppressor proteins are in the areas of DNA repair and cell adhesion. Inactivation of tumor suppressor genes can have various consequences  

Loss of Negative, Suppressing Signals in Cell Division 

A cell that has suffered DNA damage can bring about a halt in the cell cycle with the help of intrinsic control mechanisms (DNA damage checkpoints, see 13.7). The aim is 

Apoptosis or programmed cell death is a program that brings about the death of the cell in a targeted maimer in the presence of DNA damage (see Chapter 15). Apoptosis is a protection against formation of tumor cells. If a cell is affected by DNA damage, apoptosis can help to initiate cell death before further mutations accumulate that would favor transition to the tumor state. The tumor suppressor protein p53 also plays an important role here. 

Based on the functions in tumor formation, the tumor suppressor proteins can be roughly divided into two classes (Kinzler and Vogelstein, 1998)  

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