Tumor suppressors

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Tumor suppressors are proteins that control the cell cycle or trigger apoptosis . This means that the probability is high that if such a protein is defective or deficient, a tumor cell will develop from a cell into a multicellular cell . It is less a description of a protein function than a physiological definition.

A mutation or deletion of a gene coding for a tumor suppressor gene ( tumor suppressor gene ) increases the likelihood of tumor formation. In this sense, tumor suppressor genes have a comparable effect on mutations as proto- oncogenes .

Functions

Tumor suppressor proteins have the following functions:

  • Suppression of gene expression of growth factors , resulting inhibition of the cell cycle and thus no further cell division.
  • Stop the cell cycle if the DNA is damaged. If the damage proves to be repairable by DNA repair , the cell cycle continues.
  • If there is irreparable DNA damage, the tumor suppressor gene initiates apoptosis of the cell in order to protect the organism from damage by the potential tumor cell.
  • Some of the proteins involved in cell adhesion prevent tumor cells from spreading in the body and inhibit the formation of metastases .

Examples

Examples of tumor suppressors are:

  • p16 : This protein family inhibits the CDKs and thus prevents a transition from the G1 to the S phase of the cell cycle.
  • p27 : This protein controls the transition from G 0 to G 1 phase of the cell cycle and prevents it if it is produced in excess. Cells infected by viruses promote p27 formation via a tissue mediator ( TGF-β ), as do neighboring cells during contact inhibition .
  • The pRB normally encloses the transcription factor E2F like a shell , which is absolutely necessary to initiate the S-phase. The envelope gradually opens through phosphorylation and the transcription factor is "released". In tumor cells, the gene for the RB protein is mutated in over 60% of cases. The regulation (i.e. the phosphorylation mechanism) of the RB protein is disturbed in some way even in every tumor cell.
  • The p53 : This protein ensures that a cell only divides if its genome is intact. This is not the case with a tumor cell. Then p53 shows two main effects:
    • the cell cycle arrest,
    • and in the case of irreparable damage, the initiation of apoptosis.
  • Mitochondrial tumor suppressor 1

literature

Individual evidence

  1. ↑ GO: 0008181 tumor suppressor. In: Gene Ontology. EBI, accessed on September 2, 2010 : "This term was made obsolete because it does not represent a true biological function, rather a pathology that occurs when a particular gene product is inactivated in some way."