Human DNA contains evidence of retroviral infections

Jul 22, 2008 14:47 GMT  ·  By

Viruses have always been part of our evolutionary process, constantly mutating in order to defeat the immune system, at the same time triggering changes in the structure of the DNA, which eventually gave us defense mechanisms that still work today. Some types of viruses, known as retroviruses, even have the capability of inserting themselves into the DNA, leaving traces of their existence in our genes.

Such an ancient retrovirus has been revived just last year by researchers from the Rockefeller University and Aaron Diamond AIDS Research Center, and was proven to have the ability to infect human cells and then reproduce inside them. But now, researchers looking into our DNA in search for possible evidence of past infections showed how humans developed a defense mechanism against this virus, and could still fight it off even today.

"This is the first time that we've been able to take an ancient retrovirus and analyze how it interacts with host defense mechanisms in the laboratory in the present day," says Paul Bieniasz, an associate professor at the Laboratory of Retrovirology at Rockefeller and a scientist at the Aaron Diamond AIDS Research Center.

After bringing the virus back to life, Bieniasz and graduate student Youngnam Lee decided to test its strength against the antiviral defense system of modern humans. The results of the study show that HERV-K, as the ancient retrovirus was named, is defeated by the immune system with the help of a series of antiviral proteins, including one called APOBEC3G, which can mutate the DNA of the virus into a pattern that is easily recognized.

"But this is the first time it's been shown for this ancient retrovirus," Bieniasz says. Then they went to look for possible evidence in the DNA strand of humans, from which the virus was reconstructed. Indeed, mutated copied of the HERV-K virus were present, but rendered inactive by APOBEC3G.

"We're looking at things that happened millions and millions of years ago. But these sorts of ancient interactions may have influenced how humans are able to combat these retroviruses today. These proteins help protect us against current retroviruses. Retroviruses are able to infect us and leave remnants in our DNA, and our DNA also holds evidence of what we've done to them in return. It's an illustration of the fight between host and virus," says Lee.