Changes in division may lead to cancer in men and women
The human papilloma virus turns healthy cells into “zombies” and controls how frequently they reproduce, according to West Virginia University researcher Ivan Martinez. Those changes in cell division can lead to cancer in women and — unbeknownst to many — men.
“People have a misconception that because 99 percent of cervical cancers are related to the HPV infection, only women can have HPV-positive cancer,” said Martinez, an associate professor in the WVU Cancer Institute and School of Medicine, who receives support from the West Virginia Clinical and Translational Science Institute.
In fact, men can develop various HPV-related cancers, too.
“Twenty-five years ago, if you’d asked me how many head-and-neck cancers were HPV-positive — specifically in the oropharyngeal area behind the tongue — I would have told you only 20 to 25 percent,” he said. “Right now, we are talking about between 60 to 70 percent. And actually a good percentage of those cases are in males.”
In a study funded by the National Institutes of Health, Martinez is exploring how HPV produces and modifies tiny molecules of RNA — called “non-coding RNAs” — in infected human cells. Using cell lines from cervical and head-and-neck cancers that test positive for HPV, he’s investigating how the virus uses these RNAs to trick the human cells into multiplying too fast and forming tumors.
Challenging the ‘dogma’ of biology
For decades, the research community thought all types of RNA served a single purpose: Instructing cells to build proteins.
“The dogma of molecular biology that we’ve been following for the last 60 years is very simple: DNA is the library that contains the information to make a whole organism,” Martinez said. “But that information has to be translated to make proteins, so it is transcribed to RNA, a messenger molecule that gets the information to another part of the cell. It’s as simple as that. DNA becomes RNA; RNA becomes protein.”
Turns out, it wasn’t that simple at all. When researchers mapped the genomes of various life forms in the early 2000s, they found that almost all of bacteria’s RNA eventually became protein. But only 70 percent of insects’ RNA did. The other 30 percent seemed to be “hanging out,” Martinez said.
“Then they asked the same question about humans,” he said. “How much of our RNA becomes protein to make a human being? Only two percent.”
What does the other 98 percent of our RNA do? Scientists are still figuring that out. In the meantime, they’re calling this universe of RNAs “non-coding” because the RNAs don’t code for — or aren’t translated into — any protein.
“How many non-coding RNAs are there in humans? Thousands, if not hundreds of thousands,” Martinez said.
How many of them have functions that scientists understand?
“Probably not even 5 percent,” he said.
How RNA helps turn cells into ‘zombies’
What scientists do know is that RNAs perform multiple jobs. Taken together, they’re more like a Swiss Army knife than a block of steak knives. For instance, they can regulate genes. They can “turn off” other RNAs by binding to them and destroying them. And — like the RNA at the heart of Martinez’s study — they can manipulate how cells divide.
Martinez is focusing on circular non-coding RNAs. No one knew they existed until 2013, when researchers identified them in a range of organisms: humans, mice, flies, worms.
When Martinez learned of their discovery, he wondered whether viruses could make their own circular RNAs, too.
“Because viruses can copy almost everything a regular cell does,” he said. “So I told my postdoc, ‘Hey, let’s go and see if we can discover some circular RNAs coming from HPV.’ And we discovered two.”
Their subsequent work revealed that one of these two RNAs help HPV hijack healthy cells.
“The virus wants to sequester the ability of the cell to stop dividing or continue dividing,” Martinez said. “The cell becomes a zombie. The virus takes over and tells it, ‘Divide now; don’t divide now. Divide now; don’t divide now.’ ”
One trait that separates cancer cells from healthy ones is that they divide—or produce new cells—too fast and without control. So if HPV can use circular non-coding RNA to crank out more infected cells, cancer may become more likely.
Martinez and his colleagues also found that these RNAs can change the number of non-coding circular RNAs that human cells produce.
“Why?” he asked. “We don’t know yet.”
That’s a topic his new study is delving into. He and his research team are parsing the interplay between the viral and human RNAs in HPV-positive cancer cells.
Preventing HPV-related cancers, today and tomorrow
Just as scientists’ knowledge of non-coding RNA has undergone a rapid and recent shift, men’s sexual practices across the United States have changed. So have their smoking and drinking habits. Those changes might be why more men are developing HPV-related cancers now.
“Before, most of the head-and-neck cancers were related to alcohol and tobacco intake. Now, in general, people are smoking less and drinking less,” Martinez said.
Declines in smoking and drinking may correlate to a drop in cigarette- and alcohol-related cancers, which would increase the proportion of cancers linked to HPV.
“But the other hypothesis is the difference in sexual activities between different generations,” he said.
One idea is that the increase in HPV-positive head-and-neck cancers is related to younger men’s performing more oral sex. Another idea is that the greater “openness and freedom in the gay community now could also increase the probabilities to have more sexual partners and a higher risk of HPV infection,” he said.
The National Cancer Institute has reported that men who have sex with other men tend to face a higher risk of cancers linked to HPV infection. According to NCI, 70 percent of head-and-neck cancers are HPV-related. So are 60 percent of penile cancers and more than 90 percent of anal cancers.
“People just don’t think about HPV in general, regardless of if you’re the parent of a boy or a girl,” said Kathryn Moffett, who leads WVU’s Pediatric Infectious Diseases Division. “It’s just not something that’s top of mind because people don’t like to talk about HPV. But this is a preventable cancer, and why wouldn’t we want to vaccinate to protect our boys and girls who will grow up to become men and women?
“The vaccine is safe. Three hundred million doses have been administered worldwide.”
What Martinez and his team discover may lead to new ways to prevent, screen for and treat HPV-related cancers.
“For example, we know now that a lot of these cells — normal cells and tumor cells — are producing exosomes,” Martinez said. “Exosomes are like these little bags that come out from the cell, and inside the bags are RNAs and proteins.”
Because the exosomes are released into the bloodstream, it may be possible to detect them with a blood test in the future. If the exosomes fit a certain profile, they may hint that cancer is present, even before conventional screening methods would sense it.
One day, drugs may target the non-coding RNAs that HPV relies on to “zombify” healthy cells. By inhibiting or destroying those RNAs, doctors may be able to stop HPV from proliferating and causing cancer.
“People call non-coding RNAs the ‘dark matter of biology,’ ” Martinez said. “That’s why I love studying them. Because if you really want to understand a disease — and here specifically cancer — you have to look not only at 2 percent of the picture. You have to look at the entire picture.”
