Wednesday, August 27, 2014

Cancer Leaves an Epigenetic Fingerprint on DNA

Cancer cells splitting.  (stock image)
Epigenetic modifications to the genome switch genes on and off based on environmental exposure, and essentially tell cells what to do.  It turns out that illness can also cause epigenetic changes through large-scale, genome-wide DNA methylation.  A new study out of John Hopkins University, and published in the lovely open access journal Genome Medicine, has found that cancer leaves a very distinct epigenetic signature in the genome.  These modifications are key to cancer development, allowing tumor cells to quickly adapt to changes in their environment.

This study looked at six different types of cancers: breast, colon, lung, two different pancreal cancers, and thyroid.  Using microarray analysis, the researchers analyzed the methylation patterns of the DNA isolated from the cancer cells.  They found that, compared to normal cells, the tumor cells had completely different methylation patterns.  Some large blocks of DNA in the tumor cells were demethylated while smaller sections had lots of methylation.  All of the cancer types had these large demethylated sections, with some types having smaller regions within these blocks that were highly methylated.  These epigenetic modifications occur at the earliest stages of tumor development.

DNA methylation in chromosome 5.  Normal cells are shown in the top
panel, cancer cells in the bottom panel.
The authors conclude that these distinct methylation patterns in tumor cells allows the cells to turn genes off and on quickly.  For example, normal cells have self-destruct mechanisms when they notice something is amiss (known as apoptosis), which cancer cells are able to turn off.  Cancer cells are also able to turn on genes that are involved in early cell development, allowing the cancer to spread quickly.  This epigenetic fingerprint basically gives cancer cells a toolbox that their normal neighbors are lacking.

But it's not all bad news, the researchers are confident that this new information on cancer epigenetics could provide a foundation for the development of early screening and diagnosis.  Epigenetic screens could be used to distinguish cancer cells from benign growths.

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