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Tumor Suppressor

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腫瘤抑制 Background

Tumor suppressor are proteins that slow down cell division, inhibit apoptosis or programmed cell death. When tumor suppressors don't work properly, cells can grow out of control, which can lead to cancer. Many different tumor suppressor proteins have been found, including p53, BRCA1, BRCA2, APC, and Rb protein. A tumor suppressor is like the brake pedal on a car. It normally keeps the cell from dividing too quickly, just as a brake keeps a car from going too fast. When something goes wrong with the gene, such as a mutation, cell division can get out of control. An important difference between oncogenes and tumor suppressor genes is that oncogenes result from the activation of proto-oncogenes, but tumor suppressor genes cause cancer when they are inactivated. Unlike the oncogene, tumor suppressor genes follow the "Two-hit hypothesis", which implies that both alleles that code for a particular protein must be affected before an effect is manifested. That means the mutation in tumor suppressor genes are recessive whereas mutant oncogenes are dominant.

TP53 gene encoding tumor suppressor protein p53 is normally found at low levels, but when DNA damage is sensed, p53 levels rise and initiate protective measures. p53 binds to many regulatory sites in the genome and begins production of proteins that halt cell division until the damage is repaired. Or, if the damage is too severe, p53 initiates the process of programmed cell death, or apoptosis, which directs the cell to commit suicide, permanently removing the damage.

pRB, the product of the retinoblastoma tumor suppressor gene, operates in the midst of the cell cycle clock apparatus. Its main role is to act as a signal transducer connecting the cell cycle clock with the transcriptional machinery. In this role, pRB allows the clock to control the expression of banks of genes that mediate advance of the cell through a critical phase of its growth cycle. Loss of pRB function deprives the clock and thus the cell of an important mechanism for braking cell proliferation through modulation of gene expression.

腫瘤抑制 References

  1. Weinberg RA. (1995) The Retinoblastoma Protein and Cell Cycle Control. Cell. 81,323-30.
  2. Sherr CJ. (2004) Principles of tumor suppression. Cell. 116(2): 235-46.
  3. Campisi J. (2005) Senescent cells, tumor suppression, and organismal aging: good citizens, bad neighbors. Cell. 120(4): 513-22.