While Epstein-Barr Virus (EBV), a type of herpes virus that also causes infectious mononucleosis, infects most people without causing disease, it can wreak havoc for those with a compromised immune system.
The virus is no longer latent, and after 24 hours produces viral DNA (red) in factories within the cell.
After 36 hours, the infected cell is filled with a significant amount of viral DNA (red).
The research team has found a way to use the tools of a far different scientific field – astronomy – to do just that.
Just as vaccines for human papilloma virus (HPV) can prevent infections which cause cervical cancer, an Epstein-Barr Virus therapy or vaccine could treat or even prevent the both the “kissing disease” and an estimated 200,000 new cases of cancer each year.
By studying how Epstein-Barr Virus DNA is replicated in an infected cell, researchers hope to learn how to block the process and stop tumor growth. Published in the journal Cell Host & Microbe, the new study outlines a novel technique that allows researchers to visually follow a single infected cell with its viral DNA through its life cycle.
Unlike some viruses, EBV uses the host cell’s own reproductive process to its advantage, passing on viral DNA to daughter cells instead of destroying the host.
“The kinds of experiments we’ve done before are all biochemical, but that meant we were looking at average events over many cells,” said Bill Sugden, professor of oncology at the UW School of Medicine and Public Health and a researcher at the McArdle Laboratory for Cancer Research. “We can measure EBV DNA in large cell cultures by a variety of techniques, but we don’t know what’s happening in any one cell.”
To visually follow a single cell through a microscope, a completely new technique was required because prolonged UV light will damage, disrupt and eventually kill exposed cells.
Dinner conversation at home eventually led to the creation of this new technique. Arthur Sugden, Bill’s son who now is a neuroscience graduate student at Brown University, did undergraduate work in astronomy, a field quite comfortable with making discoveries using the very dim light of stars trillions of miles away.
The study’s first author Ya-Fang Chiu – a postdoctoral researcher at McArdle – Arthur, and Bill created their own computer software to make sense of thousands of low-light images. Each cell was photographed 86 times per hour for 70 hours to visually track the infected cell. Cells were exposed to a dim light source for between five and 50 milliseconds per image.
“What we’ve done is make it possible to trace viral DNA as it’s being synthesized in concert with cellular DNA and watch as the virus takes over the cell and make 1,000 times more of itself. What’s new is our ability to visualize the DNA molecules and follow them in live cells over days,” said Sugden.
Instead of using histones, a protein that helps wrap cellular DNA into compact strands, EBV DNA is wrapped up with polyamines, organic compounds derived from the amino acid arginine. It was previously unclear how EBV DNA was spared from being wrapped up with histones as it is replicated. Through this new technique, researchers have found that the virus actually inhibits the cellular machinery that does this wrapping.
Sugden’s lab group at McArdle continues to explore the processes necessary for proper DNA synthesis and replication of Epstein-Barr Virus to better understand how it can be inhibited. All EBV-associated tumors depend on the viral DNA for cells to remain as tumors; blocking its synthesis and distribution to daughter tumor cells kills those cells.
The lab is developing assays to allow screening for small-molecule inhibitors of a protein McArdle scientists have proven to be essential in keeping the viral DNA from being synthesized and partitioned in cells.
“We’ve learned how to inhibit the synthesis and maintenance of that viral DNA in the lab and we can cure tumors in a test tube, but that isn’t the same as doing it in people,” said Sugden. “We have identified the correct molecular target that could be used to treat EBV-associated cancers. What we have to do is make it practical, and we are working very hard to do so.”
University of Wisconsin School of Medicine and Public Health