What Is A Tumor Suppressor Gene?

November 12, 2012

What Is A Tumor Suppressor Gene?

Cells are microscopic but yet contain vast dictionaries of information. Scientists and geneticists are just beginning to learn the language of genes. One of the reasons why scientists are so concerned about genes is because many illnesses are caused by faulty or mutated genes. Problems with a tumor suppressor gene, for example, can predispose a person into developing deadly types of cancer.

Also called anti-oncogenes, tumor suppressor genes help keep a healthy cell from becoming a tumor cell. Tumor cells need to merge with a healthy cell and change the healthy cell’s DNA in order to create more tumor cells and grow a potentially cancerous tumors. According to experiments done by Henry Harris in 1969, tumor suppressor genes secrete special proteins that prevent tumor cells from merging (hybridizing) with healthy cells.

Two-Hit Hypothesis

We still don’t know exactly how cancerous tumors are formed or what chemicals need to interact in order to “turn off” tumor suppressor genes. The most generally accepted hypothesis is the “two-hit hypothesis,” also called the Knudson hypothesis after its author, geneticist Alfred G. Knudson. He also discovered the very first tumor suppressor gene called the retinoblastoma tumor suppressor gene or Rb. These gene works only to hinder the development of one type of cancer – retinoblastoma, a hereditary cancer of the retina that usually affects children.

Knudson’s hypothesis was that in order to be successful, tumor cells had to “hit” at DNA multiple times. In the case of Rb, it only needed to be hit twice in order for the tumor suppressor gene to mutate.

Genesis of Retinoblastoma

Humans contain 23 pairs of chromosomes or 46 in total. Rb is located on chromosome 13. There are two forms or alleles on the chromosome. These forms are dominant and recessive traits. Believe it or not, developing retinoblastoma is a dominant trait. If it wasn’t for tumor suppressor genes like Rb, a large part of the population would suffer from retina cancer. Fortunately for us, both alleles must be hit and mutate in order for retinoblastoma cells to begin development. If only one allele is hit, then tumors do not start to grow in the retina.

But what does Rb do? Rb secretes a protein that stops a tumor cell protein, E2f, from working. What’s so important about protein E2f? It helps the tumor cell to divide during a specific phase called the S-phase and thus reproduce. Just how tumor cells can “turn off” Rb is still a mystery that hopefully can be solved soon.


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