How Ancient Viruses Fuel Modern-Day Disease
Peek inside the human genome and, among the 20,000 or so genes that serve as building blocks of life, you’ll find flecks of DNA left behind by viruses that infected our primate ancestors tens of millions of years ago.
Scientists have long considered these ancient hitchhikers, known as endogenous retroviruses, as inert or "junk" DNA that were rendered harmless millennia ago. But new CU research shows that, when reawakened, they can play a critical role in helping cancer survive and thrive. The study also suggests that silencing certain endogenous retroviruses can make cancer treatments work better.
“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,” said Edward Chuong, an assistant professor of molecular, cellular and developmental biology at CU Boulder’s BioFrontiers Institute.
After slipping into the cells of our primate ancestors, these invaders coaxed their unknowing hosts into copying and carrying their genetic material — passing their DNA on to future generations.
While endogenous retroviruses can no longer sicken their hosts or spread like live viruses, they can act as switches that turn on nearby genes, with both good and bad results.
On the plus side, they contributed to the development of the placenta, a critical milestone in human evolution. Chuong’s research also shows they can switch on genes that help us fight infection.
However, endogenous retroviruses also have a dark side.
Chuong’s latest study found that a lineage known as LTR10 is remarkably active in about a third of colon cancer tumors, where it appears to fire up genes that inflame cancer.
The good news: When those viral relics are silenced, the cancer-promoting genes go dark too, and tumor-shrinking treatments become more effective.
As a leading researcher in the burgeoning field, Chuong hopes that by better understanding these oft-neglected bits of the genome, scientists can come up with new ways to treat modern-day illnesses.
Photo by Glenn Asakawa