In cancer cells, silenced genes commonly show a specific combination of epigenetic changes in their promoter region. What is that combination?
ADNA demethylation of CpG islands together with histone acetylation
BComplete deletion of the gene's promoter sequence
CAddition of a poly-A tail directly onto the promoter DNA
DDNA methylation of CpG islands together with histone deacetylation
Answer & Solution
Correct answer: D. DNA methylation of CpG islands together with histone deacetylation
1. Silencing genes through epigenetic mechanisms is very common in cancer cells.
2. In cancer cells, the DNA in the promoter region of silenced genes is methylated on cytosine residues in CpG islands.
3. The surrounding histone proteins also lack the acetylation modification present when those genes are normally expressed.
4. This combination of DNA methylation and histone deacetylation is commonly found in cancer and leads to gene silencing.
5. Because these changes are temporary and reversible, drugs that block histone deacetylase or DNA methyltransferase can potentially reverse the silencing.
6. The option describing demethylation with acetylation describes the opposite, gene-activating pattern, not the silencing pattern found in cancer.
7. Complete deletion of the promoter or attaching a poly-A tail to DNA are not the epigenetic modifications described for cancer gene silencing.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 16 "Gene Expression", section Cancer and Epigenetic Alterations_
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