Viral Remnants Millions of Years Old – A New Key to Cancer Treatment

An ancient virus that infected our ancestors millions of years ago may be helping trigger cancer today. A study published on July 17, 2024 in Science Advances shows that these viral remnants are still present in our DNA and could lead to more effective cancer treatments with fewer side effects.

Why Does This Study Matter?

Pan-cancer epigenomic analysis and other next-generation genetic analyses are helping us better understand the effects of ancient retroviral sequences.

Once thought to have no biological function, "endogenous retroviruses" (endogenous retroviruses) actually regulate genes, allowing some to be switched on and off.

Recent research has suggested that these viral remnants may play a role in diseases such as cancer.

Study Details

Research Methods and Findings

Senior author Edward Chuong, a genome biologist at the University of Colorado Boulder, notes that most research has examined whether endogenous retroviruses encode proteins. These ancient viral sequences generally do not, however. Chuong and his team used epigenomic analysis data to explore their role in gene regulation and whether they help cancer. The Cancer Genome Atlas provided maps of 21 cancer types that they studied, identifying 19 virus-derived DNA sequences with the potential to cause cancer.

Epigenetics is the science of how gene expression, or switching genes on and off, is regulated without altering the DNA sequence. This regulation occurs through chemical changes such as DNA methylation and histone modifications, affecting how genetic information is used.

Epigenomic analysis systematically examines epigenetic changes across an organism's entire genome. It maps epigenetic marks affecting gene expression and helps explain their functions.

LTR10 and Cancer

The DNA Sequence in Focus: LTR10

The researchers examined LTR10 because it showed high activity in several cancers, including lung and colorectal cancer. This DNA segment entered our ancestors' genome 30 million years ago and is active in one-third of colorectal cancers. Using CRISPR gene-editing technology, Chuong's team silenced LTR10, reducing the activity of nearby genes promoted by cancer.

Treatment and Next Steps

MAP Kinase Inhibitors and Targeted Treatment

The study also identified mitogen-activated protein (MAP) kinase, which is overactive in approximately 40% of human cancers, as the factor driving LTR10's cancer-promoting activity. Some existing cancer medicines already target MAP kinase. These findings could help develop more targeted therapies or optimize existing treatments.

However, applying the findings to actual cancer patients will require more laboratory research, human trials and several years. Because CRISPR epigenome editing is still being developed for clinical use, directly targeting these elements as treatment is at least 5 years away.

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Further Reading: The Components of Human DNA

The chart below shows the elements composing our genome as percentages.

• Genes (1-2%): Protein-coding DNA sequences. The human genome contains approximately 20 thousand to 25 thousand genes, located among approximately 6 billion nucleotide pairs and encoding the body's various proteins. Much of the genome consists of regions outside genes that play roles in gene regulation and other biological functions. 
• Transposons (45%): DNA sequences that move and multiply within the genome. This group includes retrotransposons (8.3%), LINEs (20.4%) and SINEs (13.1%).
• Endogenous Retroviruses (ERVs) (8%): DNA fragments left by ancient viral infections that can affect gene expression.
• Pseudogenes (1.2%): Genes that have lost their function or are incomplete.
• Repetitive Sequences (3%): Telomeres and other short repetitive DNA sequences.
• Other (40%): Introns, regulatory elements and other noncoding DNA.