Inside "Gene Function":

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Topics you may also like:

What is Transcription?

The Steps of Transcription

An Introduction to Tumor Suppressor p53

Tumor Suppressors: The Retinoblastoma (Rb) Gene

Selective Estrogen Receptor Modulators (SERMs)

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CancerQuest > Introduction to Cancer Biology > Introduction to Gene Function > What is Transcription? > Transcription Factors

Transcription Factors

Some examples of transcription factors that malfunction in human cancers are:

• p53 (TP53)- The gene that codes for the p53 transcription factor (protein) is mutated in over half of all cancers of any type. The protein that the p53 gene codes for is important because it controls the transcription of genes that are involved in causing cells to divide. More information on the p53 gene can be found in the section on tumor suppressors.
• Rb - The protein product of this gene is a transcription factor with an interesting function. It actually works by blocking other transcription factors. In this way, Rb prevents transcription of key genes required for cell division to progress. Initially described as a gene mutated in retinoblastoma, a cancer of the eye from which the gene derives its name, the Rb protein is now known to play a role in many different cancer types. More information on the Rb gene can be found in the section on tumor suppressors.
• The estrogen receptor (ER) - This protein binds to estrogen that enters the cell. Estrogen is a steroid (lipid) hormone produced by the ovaries. The combination of protein and hormone then acts as a transcription factor to turn on genes that enable the target cells to divide. The receptor is active in the cells of the female reproductive organs, such as breasts and ovaries. Because of this, estrogen is recognized as a factor that enhances the growth of certain cancers arising in these tissues.

The mechanism of estrogen action is shown below.

The small green ball represents estrogen. It is a small hydrophobic molecule and it enters cells by crossing through the lipid membrane. Once in the cell, the estrogen binds to its receptor (colored orange) and the complex binds to DNA in the nucleus causing genes to be transcribed.

Several drugs have been developed to try to block the gene-activating function of estrogen. A commonly prescribed example is tamoxifen, a drug that partially inhibits the activity of estrogen. Tamoxifen is colored pink in the animation below.

These drugs should slow the growth of cancers that are growing in response to the presence of estrogen and its receptor. More information on estrogen receptors and cancer can be found in the section on cancer treatments.

The importance of transcription factors to the division of cells has been stressed several times. Cancer results from uncontrolled cell division so the next process discussed is cell division. It is important to understand how this process normally functions so that we can appreciate what happens when things go wrong.