Michael Gale, Ph.D.
2007 - When the engine in Michael Gale’s 1968 Ford Mustang is not purring smoothly, he takes it apart to find the problem and then rebuilds it.
As a scientist, he reacts similarly when faced with a stubborn question, such as how the hepatitis C virus (HCV) escapes the body’s natural defenses to cause persistent infections. By deconstructing infected cells, Dr. Gale’s laboratory at the University of Texas Southwestern Medical Center in Dallas discovered which basic parts of the cell’s signaling system are made sluggish and unresponsive by the virus.
Dr. Gale, who holds a Ph.D. from the University of Washington, conducted much of this research with support from a Burroughs Wellcome Fund Investigator in Pathogenesis of Infectious Disease award that he received in 2003. In August 2006, Dr. Gale received the Seymour and Vivian Milstein Award for showing that an HCV protein can block the innate immune response that cells use to stop the spread of viral infections. The award, which recognizes exceptional contributions to the field of interferon and cytokine research, was presented to Dr. Gale and his colleague Takashi Fujita of Kyoto University by the International Society for Interferon and Cytokine Research.
HCV is a bloodborne infection that affects nearly 200 million people globally and can lead to cirrhosis and liver cancer. Because it causes a chronic infection in most patients, it continues to be transmitted between individuals.
“Hepatitis C is a very successful virus that typically causes a chronic, lifelong infection,” Dr. Gale said. “A major reason that the virus can persist is because it can successfully evade the innate immune response.”
The immune response normally gets turned on when a cell senses that it has been infected by a virus. The virus activates certain signals that instruct the cell to turn on immune genes and, most important, to start producing interferon, a molecule that interferes with virus replication.
“The innate immune response is geared to shut down infection at the local site where the virus is replicating,” Dr. Gale said. “When it doesn’t work, the virus can spread and take over other cells.”
The Gale lab wanted to figure out what HCV was doing to cells that blocked the innate immune response. Since the response is kicked off by the activation of a protein called IRF3, the team began by looking for individual virus proteins that might block activation of IRF3.
Graduate student Eileen Foy’s job was to screen all of the HCV proteins for blocking IRF3 activation. Luckily, the virus makes only 10 proteins. She identified a protein called NS3/4A as the culprit. NS3/4A is a protease (an enzyme that chops up other proteins) that already was known to be critical for processing the other virus proteins into their final form for making new virus particles.
Dr. Foy, who is now an intern at the University of California-San Francisco Medical Center, and Dr. Gale next asked if the enzyme activity of NS3/4A was important for its ability to block the innate immune response. They found that by treating HCV-infected cells with a protease inhibitor, they could restore immunity, which meant that the NS3/4A protease was indeed using its chopping action to stop immunity—but on what cellular protein?
At this point Dr. Foy’s project intersected with the work of another graduate student in the lab, Rhea Sumpter Jr., now a resident at the University of Texas Southwestern, who was trying to determine how the presence of a virus inside a cell triggers IRF3 activation.
Dr. Sumpter was working with a particular line of human liver cells that cannot activate IRF3 because they either lack a key protein “factor” or the protein is mutated. Dr. Sumpter conducted a so-called complementation analysis to identify the key factor—that is, he added back normal proteins that a liver cell makes individually until the cell line initiated a normal immune response. It would be sort of like a mechanic diagnosing a stalled engine by replacing individual parts with a new part until the ignition started properly.
This experiment identified a mutation in a gene that makes a protein called RIG-I. The mutation caused a short circuit in signaling of the innate immune response, enabling the team to identify RIG-I as the key factor for activating the immune response against HCV. RIG-I acts as a surveillance camera in the cell, spotting any genetic material from a virus and binding to it.
“So we put two and two together and decided that if RIG-I was important for initiating innate immunity, then we would test to see if the NS3/4A protease blocked RIG-I’s function,” Dr. Gale explained.
But mixing RIG-I with the protease in a test tube had no effect—the protease did not chop it up or affect its stability in any way. “We reasoned that there must be yet another mystery factor,” Dr. Gale said.
The team knew that the RIG-I protein contains a segment, called the caspase activation and recruitment domain, or CARD, that likes to stick to other proteins with a similar CARD segment. So the team guessed that another CARD protein would be the target of the NS3/4A protease.
“It took us a year to figure it out, but it was exactly what we predicted,” Dr. Gale said. They identified the other protein, called IPS-1, and showed that during HCV infection, IPS-1 is cleaved by NS3/4A, which means that it cannot activate IRF3 to turn the ignition of the cell’s immune defenses.
“It is a great example of a virus doing one thing—cleaving IPS-1—to avoid triggering immunity to infection. It’s absolutely incredible,” Dr. Gale said. “I like this kind of work, because I like the mechanics of figuring out how things function. Basically, the cell and the virus are like machines.”
Beyond the satisfaction of identifying the cellular and viral moving parts involved in innate immunity, the Gale laboratory discoveries have implications for treating hepatitis C in humans and for fighting other types of viral infections.
Although hepatitis C patients today can be given direct injections of interferon, the treatment has severe side effects that not all patients can tolerate and cures only about half of all patients. Interferon must be taken for six to 12 months, and it causes patients to feel as if they have the flu continuously.
“So there is still a lot to be desired for HCV therapy,” Dr. Gale said. Companies have already designed protease inhibitor drugs that could block the action of NS3/4A. Dr. Gale explains that these compounds have the potential to restore innate immunity in what would be a “one-two punch” of both stopping virus replication and restoring immunity. Such potent drugs also may help slow the process by which the virus becomes resistant to treatment.
“The goal is to develop a therapy cocktail consisting of protease inhibitors, interferon, and other inhibitors of virus replication” Dr. Gale said. “I believe HCV is a curable disease with the right drug combination.”
Dr. Gale said receiving the Milstein Award was a great honor because it recognizes discoveries that advance this field by great leaps. It turns out that the process he and his team identified in HCV infection turns out to be the way almost all RNA viruses, including West Nile, influenza, and the common cold, trigger innate immunity.
“Since then, the field has shown that RIG-I is essential for immunity to many other RNA viruses,” Dr. Gale said. “That validated our work and then it took on a life of its own.”
In May 2007, Dr. Gale moved his lab to the University of Washington in Seattle, where he is an associate professor of immunology. But much to his regret, he did not get to drive his prized dark-green Mustang through the mountains, as the car was shipped ahead. Still, he said, he tinkers on weekends.
By Kendall Powell a freelance science journalist based out of Broomfield, Colorado.