Study: Ancient ‘Zombie’ Viruses May Have Accelerated Cancer Development

In human genomes, certain ancient viruses, passed down through generations via foreign DNA, remain hidden and unnoticed. These so-called “zombie viruses” were long thought to be inactive. However, recent research suggests these genetic sequences can potentially cause significant issues.

A research team led by University of Colorado bioinformatician Atma Ivancevic discovered that some cancer cells exploit parts of these zombie viruses for their growth. Genome biologist and senior author Edward Chuong stated, “Our study shows that diseases today can be significantly influenced by these ancient viral infections that until recently very few researchers were paying attention to.”

These ancient genes, once dismissed as ‘junk’ DNA, are actually remnants of viruses known as endogenous retroviruses (ERVs). They have played a crucial role in mammalian evolution, particularly in the development of the placenta. However, not all ERVs are beneficial to humans.

Chuong explained, “We know that cancer cells express a lot of genes that are not supposed to be on, but no one really knows what is turning them on. It turns out many of the switches turning them on are derived from these ancient viruses.”

So, how did the researchers determine that ancient genes are promoting cancer? Ivancevic and her team analyzed epigenomic data from 21 types of cancer and identified a specific ERV family called long terminal repeat 10 (LTR10), which was highly active. This virus originally infected our primate ancestors around 30 million years ago.

Through a functional study on colorectal cancer cell lines, the team found that LTR10 regulates gene expression linked to tumor development. When these LTR10 genes were deactivated in human colorectal tumor cells and mice, the genes known to promote cancer growth, such as XRCC4, were also deactivated.

Ivancevic and her team discovered that LTR10 acts as an epigenetic switch controlling these genes. They also found that cancer has been using this ancient virus to alter gene expression patterns in tumors. The researchers concluded that these zombie viruses could potentially reactivate when human defenses are weakened, leading to health issues.