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Researching Retrovirals

A visit with Marc Johnson Assistant Professor, Department of Molecular Microbiology and Immunology

Published: - Topics: fish virus retrovirus HIV research virus
By Tanya Sneddon

Marc Johnson began his research career studying a rabies-like virus in fish. For a Missouri kid, who had always wanted to study marine biology, life was great. “Working with fish viruses is really cool research,” he notes, but there are just not a lot of people doing it,” and that sense of isolation was eventually too much. “We cloned the virus’ entire genome and worked out a reverse genetics strategy. It was the breakthrough of my research, but what really bothered me was that no one really cared.”

Johnson missed the collaboration, the community, and the interaction of more mainstream research life. “So I went to the absolute opposite of fish viruses to HIV, where there are thousands of labs studying it, and it’s very competitive. But it’s also very interactive,” he recalls which is what I wanted.”

Since that switch, Johnson has dedicated his research efforts to the study of these related humans viruses. Ten years later, now an assistant professor in the MU’s Department of Microbiology and Immunology, Johnson and his collaborators have made great progress in understanding how the HIV virus works in order to develop new therapeutics to combat the disease.

HIV belongs to a unique family of viruses known as retroviruses. Johnson explains: “There are two general kinds of viruses—the RNA viruses and the DNA viruses. You can couple them by the kinds of diseases they cause: RNA viruses are typically short-term viruses causing acute diseases such as the flu, the common cold, and Ebola. DNA viruses often are more long term, like herpes where, if you get it, you have it for the rest of your life.” Johnson describes retroviruses, however, as a unique blend in between RNA and DNA. “They are technically an RNA virus, yet they are a DNA virus in part of their lifecycle. The magical thing is that they can jump between these two states. They’re like a DNA virus that can replicate with RNA strategies.” However, retroviruses can cause long-term diseases, unlike most RNA viruses. For now, when someone contracts HIV, they will have the disease for life. While the science community has developed many extremely successful treatments for the symptoms of the disease, they have yet to discover a cure. Johnson explains: “With HIV, we have very good therapies. We have the ultimate Patriot missiles. If a missile gets shot at you, then you send up another missile to blow it up. We’ve got that. Whenever a virus is released from an infected cell into our bloodstream, we have drugs that kill that virus immediately, such that there are no new infections. After that, the few cells that were infected would die off, or the immune system would kill them.” With any other virus, that would be enough to cure the person from the disease; but HIV is different.

“HIV just has our immune system’s ‘number.’ The trouble with retroviruses, particularly with HIV, is that those last few infected cells, as long as they’re alive, just keep kicking out viruses and our immune system cannot identify them as infected cells,” Johnson says. Since the body is unable to kill off those last few infected cells, the body is never able to entirely rid itself of the disease. Drugs known as anti-retrovirals have been greatly successful in curbing the viral replication and improving the quality of life in infected persons, but “there’s still a few infected cells, and if your take someone off their anti-retrovirals, the infection comes back.”

Using this understanding of HIV, Johnson has been working to further understand the structure of the HIV virus and the function of each component, in hopes that if they “can mess it up at the right step, it might throw the virus off its game and allow the infected cells to be exposed as infected,” thereby potentially eliminating the HIV infection. There are three key structural components of the HIV virus, all of which function like the parts of a missile. “The protein Gag is the structural protein that forms the actual physical virus particle that moves around and attacks things. It’s like the missile shell. There’s also a protein called Pol, which is like the payload of a missile, responsible for replicating the genome. And a third protein, Env, determines which cell the virus is going to attack next, like the trajectory system of a missile. “Mostly I study gag,” says Johnson, “how it assembles itself, how it tricks the cell into helping it assemble a virus and how the other components of the virus get to the right place.” The sheer probability that all these components will find each other is daunting, like “three people in the state of Missouri finding their ways to the same cornfield.” This is just one of the many questions Johnson hopes to answer through his research.

With a complete understanding of the structure of the HIV retrovirus, suggests Johnson, several things will be possible. First, new therapies will be developed, new missiles to shoot in defense as the HIV virus sends up its own. “There are four, maybe five steps of the HIV lifecycle that we can target,” Johnson says, “but we’re learning that there are more ways to block it and plenty more reasons to continue to improve the therapies.” The second is in the area of gene therapy. “There are diseases like Cystic Fibrosis” for example, “where we know people are missing just one gene in their cells, and if we could just treat them with the virus (use the virus to reintroduce the gene), it would be there forever.” Or, he adds, they could make tiny mutations in the genomes and then insert them into a human host cell.

Finally, Johnson believes that understanding these viruses will lead to a better understanding of how the human cell works: “Almost everything we know about modern molecular biology--how DNA replicates, how RNA is transcribed, how RNA is processed, how gene regulation occurs—came from studying viruses.”

“It’s pretty remarkable, and there’s clearly a lot about it that we don’t know yet,” Johnson admits, but he has noticed that progress in this line of virus research draws more attention than his earlier studies of fish.