After 40 years of hard work, it is finally time for David Pintel to pass the torch.
By Davis Suppes| Bond LSC
David Pintel is hanging up his lab coat after 40 years.
“It’s been an honor to be able to do my work at the University of Missouri. I’ve had a great group of colleagues both here and at the medical school,” Pintel said.
The Bond LSC virologist retired July 1 after a storied career. He spent 20 years at the School of Medicine before joining Bond LSC upon its completion more than 15 years ago.
Since then he has aimed to better understand the interaction between viruses and host cells. Pintel specialized in the study of parvoviruses, the smallest of all DNA viruses that infect vertebrates. In addition, the parvovirus adeno-associated virus (AAV) has been developed as a promising gene therapy vehicle.
On his last official day in his office Pintel was busy still packing up old memories while taking everything in.
“I’ve had tremendous students and tremendous colleagues, you know they were the important parts of my career,” Pintel said, “Going through all the old memories, you know, it’s gonna take a little while”
Pintel is a Curators’ Distinguished Professor as well as a Dr. R. Phillip and Diane Acuff Endowed Professor in Medical Research Molecular Microbiology and Immunology. He reflected on fond memories of his work here, but when asked what his favorite memory was his answer was the same, working with all of these people.
“It’s an emotional end, when you do something every day of your life for 40 years,” Pintel said. “I’m so thankful and grateful for the people that have worked with me, people that have been my friends here and allowed me to have a successful career.”
The future for Pintel will come in due time, but for now he is in no hurry and plans to enjoy some time off.
“To be determined,” Pintel said, “I think I will decompress for a while before I make any decisions on the next step.”
Kinjal Majumder and David Pintel | photo by Roger Meissen, Bond LSC
By Becca Wolf | Bond LSC
Four years of hard work certainly paid off for Kinjal Majumder.
Majumder, a former postdoctoral fellow in the Pintel lab at Bond Life Sciences Center, spent the past four years looking at how the parvovirus, Minute Virus of Mice (MVM), is getting to the sites in the nucleus that it needs to replicate.
Parvovirus is used as a model to study virus behavior because it is a simple, single stranded DNA virus. MVM infects mouse cells and transformed human cells.
The work builds off a paper the lab published back in 2018 where Majumder and the Pintel lab looked at where a virus goes inside the nucleus of a cell. The results of this study were published in PLOS Pathogens in October and make progress towards understanding how viruses can localize to distinct sites to set up replication centers.
“This was the next logical step in the laundry list of questions to try and figure out how it’s getting there,” Majumder said. “This is important because we’re interested in the basic mechanisms of how a virus does what it does. So, using the parvoviruses as a model system, we can slowly chip away at these questions.”
Based on their previous work, Majumder had a good idea of where the virus went once in a cell, but he had to figure out how it was happening. He found that the non-structural protein (NS1) of the virus carries the viral DNA to sites on the cell’s genome which are prone to incurring DNA breaks, after which it can start to replicate. The genome is the set of genetic material of an organism, so it is quite important for the cell.
The NS1 protein is critical for creating new copies of the virus and binds to damaged cellular DNA breaks in a cell, though it is not yet clear why.
“When the virus goes in the cell, it seeks regions where there is broken DNA like a heat seeking missile. The reason we think the virus is doing that is because broken DNA means that the cell has repair and replication proteins at those regions. The virus can then hijack and use the proteins to replicate itself,” Majumder said.
NS1 plays a key role in this process by binding and transporting the viral DNA to these cellular break sites to initiate replication.
Majumder used many resources that MU has to offer to complete this project. To create the break in DNA in the cell nucleus, he used a laser on the confocal microscopes at the Advanced Light Microscopy Core in Bond LSC. He also collaborated with the MU Genomics Technology Core Facility, Informatics Research Core Facility and the Lewis Cluster in the Engineering department.
“It was really nice to have all of my resources within one building,” Majumder said. “I would go in the morning and stripe the cells, and then two minutes later I would be processing them upstairs for the next stage of the experiments, so it really expedited our research. And of course, Drs. Jurkevich and Baker, who run the Advanced Light Microscopy Core were always a great help in the laser micro-irradiation assays. It really made the project go smoother than anticipated. These experiments were first started by Dr. Matthew Fuller in the Pintel lab in 2016, who is also a coauthor on the paper.”
Since this project, Majumder has moved to the University of Wisconsin-Madison where he is starting his own lab in the Institute for Molecular Virology. The distance has not stopped him from continuing this work.
“Dave [Pintel] has been an incredibly supportive mentor. We Zoom twice a week and we talk about experiments, things that are going on in the Pintel lab, things that are starting to happen in my lab, and stuff that we can work on together going forward,” Majumder said.
Pintel has enjoyed continuing this professional relationship.
“He’s a terrific young scientist, he got a number of grants and awards while he was here, some, I think, that are really hard to get. He got a terrific job is in a terrific place,” Pintel said. “I’m very happy that I could support him and that he has something strong for him to take forward as he starts his career.”
Despite Majumder now working over 400 miles away, this project is not yet done.
“We haven’t fully completed the second step yet,” Majumder said. “We figured out that NS1 is dragging the viral DNA to the cellular site of DNA damage, but that’s only half of the picture. We’re looking at the virus’ side of the puzzle, we don’t know what’s on the host side. We want to find out what’s on the cellular side or what cellular protein is creating this bridge. That would be the next step.”
Majumder and Pintel, together with graduate student Maria Boftsi, are already beginning to study this process on a human parvovirus called Adeno-Associated Virus (AAV).
“We’re trying to do a similar thing in a different parvovirus. This is a parvovirus that people use a lot for gene therapy applications so there is a little more medical interest in it,” Pintel said. “This is a human virus and we already know that some things are a little bit different. But we’re getting close to getting an idea of what’s happening.”
Going forward, Majumder hopes to look at more viral systems in addition to these two in order to get a basic idea on how different viruses can navigate the nuclear environment.
“We can expand into more pathogenic systems like cancer causing viruses such as Hepatitis B virus or human papillomavirus,” Majumder said. “Those viruses are more complicated, so they have a more sophisticated machinery to modify the nucleus for their purposes. They employ many different mechanisms to take over the nucleus, so trying to dissect things out in them is more challenging. Those would be the future, long-term directions of these studies.”
It was another day in the lab. Kinjal Majumder, a postdoctoral fellow in the David Pintel lab at Bond Life Sciences Center, was working on his research and stopped to check his email. At that moment, he found out he just won a $700,000 grant from the National Institutes of Health.
He felt relieved.
“I wish I could say something more high minded about it, but honestly, at that point, you’re like, ‘Oh, thank God. I got the award,’” Majumder said. “Then I thought, ‘Alright. I’m gonna go back to my experiments.’”
Majumder won the NIH Pathway to Independence award from the National Institute of Allergy and Infectious Diseases that helps postdoctoral research fellows transition from working under a research mentor to starting their own lab. The application process takes time, so Majumder had to wait almost a year and a half from the time he submitted his application.
“It’s very humbling and honestly I am still processing it,” Majumder said. “The way these awards work is that you apply, you hope for the best, you walk away and try not to think about the possible outcomes.”
According to 2019 data from NIAID, applicants have a 19.1% success rate in receiving the award.
“No, I’m not surprised at all,” said Maria Boftsi, graduate student in the Pintel lab. “I think he’s worth it. He works very hard. He loves research. He loves being in the lab and doing experiments.”
Even when Majumder first started at Bond LSC, he showed promise.
“He’s a very imaginative guy, and he’s got a lot of energy,” said David Pintel, endowed professor in medical research Molecular Microbiology and Immunology. “He’s very forward thinking and he’s very creative. Those are the kind of scientists that can get to another level because they do experiments that most people wouldn’t think of.”
When he first joined Pintel’s lab, they were trying to figure out where a virus goes once it enters a cell.
The lab studies a small, single stranded DNA virus called, Minute Virus of Mice, which is a parvovirus. According to Majumder, it’s a good prototype to study how small DNA viruses in general navigate the host cell’s environment to establish infection.
“So, when we started asking where a virus localizes in the nucleus of a host cell, I realized that I possessed the expertise in the techniques we need to answer those basic questions in virology [techniques I had learned during my Ph.D. at Washington University],” Majumder said. “We jumped into it headfirst and experiments started working.”
Researchers originally thought viruses set up replication centers in the nucleus of cells by randomly interacting with the factors they need to replicate. However, Majumder and a previous graduate student in the lab, Matt Fuller, started to test whether viruses went to specific places in the nucleus, particularly on the cellular genome where factors already exist to facilitate virus replication.
“For a lot of reasons, it seemed a reasonable idea although people hadn’t thought about that before, certainly in our lab,” Pintel said. “So, they started doing the experiments, and they found that’s actually what happens.”
Majumder has been working at Bond LSC for the past five years doing many collaborations.
“He has a lot of knowledge and lab experience so whenever I have troubles and I need to troubleshoot experiments, I will talk to him,” Boftsi said. “He will share thoughts, and he’ll give me advice. His advice is always helpful.”
Majumder has been studying virology ever since he first started as a post doctorate in the Pintel lab. His interest began in graduate school thanks to his colleagues in the immunology graduate program at Washington University in St. Louis.
“I had several friends in graduate school who were virologists and studied how the immune system responds to different types of viral infection. Every time they presented at departmental seminar, they insisted that viruses were super cool,” Majumder said. “Eventually I decided that, ‘Hey, maybe I’ll check this out and see what the fuss is about.’”
Turns out it was worth the hype.
Now, Majumder is going to use the grant money to further his research on studying how viruses establish infection in host cells, usurp host proteins to replicate and spread to neighboring cells.
“In this proposal, I want to study the nuts and bolts of this process and find out what are the proteins that the virus is hijacking from the cell,” Majumder said. “How is it using those proteins to replicate in the cell, and then how is it further damaging the cell’s DNA so that it creates new viral replication centers?”
Other than it being “really cool science,” as Majumder puts it, this research can eventually be applicable to human diseases. Some parvoviruses can even be modified to target cancer cells.
Majumder is planning on continuing this research in his own lab at the University of Wisconsin-Madison at the Institute for Molecular Virology and McArdle Laboratory for Cancer Research starting in October 2020.
“I think his future students will be very lucky working with him because he likes sharing his knowledge, and he really loves what he’s doing,” Boftsi said. “I think this is something that he will pass to his future students.”
Majumder received help from Bond LSC investigators David Pintel, Christian Lorson, Ron Mittler, Trupti Joshi, the MMI department faculty, the MU Postdoc Association and the MMI postdoctoral fellows in the assembly of his K99/R00 application. Majumder also relied on the Genomics Technology Core and the Advanced Light Microscopy Core at the Bond LSC for experimental support. Majumder was funded for his postdoctoral research by a Ruth L. Kirschstein Postdoctoral Individual National Service Award by the NIH.
The structure and placement of labs encourages researchers to collaborate and talk to each other and often, connections and friendships are formed.
For Kinjal Majumder, a virologist and postdoctoral fellow in the David Pintel lab at Bond Life Sciences Center, that has meant bouncing many ideas off friends and colleagues from neighboring labs. Little did he know that one connection would lead him to interesting findings in a field outside of virology.
Those results may help make progress toward understanding the machinery behind drug resistance and toxicity in the body.
“The big picture is that it will help future studies on how drugs are metabolized by our body,” Majumder said.
The connection started with Andrew Huber, the first author of the paper, who completed his Ph.D. while in the lab of Dr. Stefan Sarafianos at Bond LSC. He graduated two years ago, moved to the lab of Dr. Taosheng Chen at St. Jude Children’s Research Hospital (SJCRH) in Memphis, Tenn. and began his postdoctoral work.
Dr. Chen’s lab focuses on mechanisms of cellular drug metabolism, one of which functions through the pregnane X receptor (PXR) protein.
PXR is found in the liver and is activated by drugs and other substances in the blood. Once activated, it binds to DNA and activates genes responsible for detoxifying the system. However, this system often leads to metabolism and reduced efficacy of administered drugs such as chemotherapies and antibiotics.
“When Andrew was in the Sarafianos lab, we’d talk science often and we collaborated on how different viral proteins bind to host and virus DNA, and how this can aid viral life cycles,” Majumder said, “When he moved on to his postdoctoral work, he saw that he can start applying similar techniques to study how the liver metabolizes toxins. So that’s when we set up this collaboration to pursue these things together.”
Majumder studies how viral DNA and proteins interact in virus-infected cells. One technique he uses is called chromatin immunoprecipitation assay (ChIP) which determines where proteins of interest can bind to DNA molecules. Majumder freezes protein and DNA that are interacting together in the process and he pulls that complex down with an antibody. “It’s like going fishing,” he said.
In order to apply ChIP and other techniques to study PXR signaling, Majumder drove down to SJCRH in Memphis to work with Huber on these assays.
Once in Memphis, Majumder and his collaborators worked and conducted experiments around the clock, but they also found time to explore the city and have fun.
“We go into lab and try to get done as many experiments as we can,” Majumder said, “And whenever we have a long break we go out on the town. It’s usually a really fun way to go and experience the life and scientific culture of a new place.”
It is a lot to pack into one week, but Majumder and his collaborators make the most of it, finding a way to effectively balance their studies on PXR with soaking up life in Memphis.
Majumder compares PXR to a light dimmer switch. When activated, it “brightens” by increasing drug metabolism, leading to decreased drug efficacy. PXR inhibitors work to “dim” this effect. At St. Jude, Dr. Chen’s group found that of the 434 amino acids that make up PXR, only one mutation is needed to “turn a dimmer into a brightener.”
“We sort of got lucky, we thought that you’d have to make a lot of changes in order to make PXR do something different,” Majumder said, “Without making too many changes — Dr. Chen’s group just switched one thing — and that was sufficient enough to turn it into a brightener. So that was a happy and unexpected outcome.”
Once these results were reviewed, the Cellular and Molecular Life Sciences journal accepted their results and published them this March in an article titled “Mutation of a single amino acid of pregnane X receptor switches an antagonist to agonist by altering AF-2 helix positioning.”
Looking ahead, Majumder and his collaborators hope to make more progress in understanding how drugs are metabolized in the body.
All of this would not have been possible if it wasn’t for the connections Majumder made at Bond LSC a few years ago.
“It was so cool to have this opportunity to collaborate with someone from the LSC that I have collaborated with before and apply our experimental techniques to study a new system,” Majumder said, “It feels very encouraging that now the work can be expanded upon and applied to other systems and settings.”
Figuring out how a virus takes over cells could help with gene therapy
By Mariah Cox | Bond LSC
When we catch a cold or contract the flu, we usually attribute it to picking up a virus from a friend or someone we know. Our bodies’ built-up immune systems have a way of attacking viruses to help us stay healthy, but sometimes viruses can hide.
A study published in eLife by lead researcher Kinjal Majumder, a postdoctoral fellow in the Bond LSC lab of David Pintel, sought to understand where a virus goes when it hijacks a host cell. This basic science may one day help researchers use viruses to better treat human diseases.
In general, when cancer-causing viruses infect a host cell, they translocate their genetic material into the DNA of healthy cells, taking over and causing disease in the host organism.
Majumder and his collaborators developed an experimental system to identify the ‘zip codes’ within the nucleus where the virus localizes.
“When looking at the mouse DNA in infected cells we noticed that the virus seems to associate with particular sites,” Majumder said. “When we mapped where those sites were, we found that the virus localizes to regions of the genome that are prone to DNA breaks. If you unravel all the DNA, which comes out to be about six meters in length, there are very distinct sites where the virus seems to associate.”
Through this research, Majumder was able to figure out where the virus goes when it infects a host cell and why it is attracted to those certain locations. These DNA sequence sites are prone to having breaks which is indicated by the presence of DNA repair machinery, making them more vulnerable to viruses. His current research focuses on how viruses hijack these break sites and take over the repair machinery to replicate.
“Viruses are very intelligent,” Majumder said. “What we’re now trying to do is to understand how they move about in the nucleus. We found out the where, we think we know the why, now we want to know how they know to attach to these sites.”
In order to conduct his research, Majumder is using a simple ‘test-tube’ model virus called minute virus of mice (MVM), which is a rodent parvovirus, to look at host-virus interactions. This model is particularly easy to work with in a lab setting and results are easily transferable to other viruses in animals and humans.
Other cancer-causing viruses that function similarly to parvovirus, such as human papillomavirus (HPV) and hepatitis B, have also been found to integrate into breaks in DNA chains and drive cancer progression.
“There is a close relationship between a replicating virus and the cell’s DNA repair machinery which normally protects us from cancer. Now we are starting to see that MVM localizes to the sites in the nucleus which contain a lot of these repair proteins,” Majumder said. “It’s an interesting phenomenon and we are starting to study the mechanism of how this might be happening.”
Majumder adapted an experimental system called chromosome conformation capture assay by chemically cross-linking virus DNA and the cellular DNA that are close together and generating hybrid DNA fragments in a test tube. After sequencing these fragments, Majumder and his team could determine the exact sites that the viruses associated with.
In order to confirm the location of these sites, they used powerful confocal microscopes in MU’s Advanced Light Microscopy Core. By using a laser to make a DNA break in a cell, Majumder could also show that virus localized near the induced breaks.
“If we can figure out how the virus is going to those regions, it opens up the possibility of finding whether other viruses, such as HPV or hepatitis B, utilize similar mechanisms to go to those sites,” Majumder said. “Knowing that may help study how oncogenic viruses cause cancer.”
Understanding how viruses hijack host cells and utilize cellular DNA breaks may allow future researchers to design improved cancer therapies.
Parvoviruses, in a broader sense, are used in oncolytic therapies to treat cancers using viruses. Cancer cells can arise due to dysregulation of DNA repair machinery in cells. They can also occur due to mutations in DNA breaks that can cause translocations. Parvoviruses have the ability to replicate in cancer cells, which is why they are being used as gene therapy vectors in clinical trials to target cancer.
“Knowing where gene therapy vectors stay long-term and how they interact with DNA repair proteins is important because they can express throughout their lifetime,” Majumder said. “For example, if you have cystic fibrosis, you have a mutation in one particular gene, so you don’t make specific proteins and as a result, you get a lot of health problems. Gene therapy adds a wild-type piece of DNA to express the correct version of the protein.”
For his Ph.D., Majumder looked at how the genome folds upon itself, gets packaged into the nucleus, and how this packaging regulates immune system development. His previous research on the genome is currently helping him advance his work with viruses.
“When I started working with viruses, I realized I could easily utilize those techniques to map how viral DNA interacts with the host’s DNA,” Majumder said.
Majumder hopes a better understanding of how viruses interact with DNA damage responses will move forward gene therapy.
“If you know how these viruses interact with the host’s proteins in the nucleus, you can design more effective gene therapy vectors.”
This research was published in the Journal “eLife” in July 2018 and was funded by the National Institute of Allergy and Infectious Disease of the National Institutes of Health.
Change is hard. Especially when you’re comparing weather, like Maria Boftsi, a second year Ph.D. student in the Pintel Lab at Bond LSC, did.
From the sunny skies of a small town in Northern Greece, where she’s originally from, to the contrastingly harsh winter of mid-Missouri, Boftsi was in for a lot of change when she came to Mizzou.
“The summer after my third year of undergraduate I came to work in the Sarafianos Lab. Then I went back to Greece to finish my bachelor’s degree,” Boftsi said. “When he moved to a different university, I joined the Pintel Lab about six months ago.”
In the Pintel lab, Boftsi studies parvovirus interactions with the host genome. This virus is among the smallest in terms of DNA.
“We study the parvovirus Minute Virus of mice, or MVM,” Boftsi said. “MVM infection leads to a sustained DNA damage response in cells, which the virus exploits to enhance its replication.”
The replication process is anything but simple. Boftsi uses previous work to better understand this aspect of the virus life cycle.
“Recent studies in our lab have shown that the virus establishes replication centers at specific sites of the cellular genome,” Boftsi said. “I’m trying to investigate the role of viral proteins on virus-host interactions.”
Once the lab does that, they’ll be able to apply what they’ve learned to future projects.
“Parvoviruses are important pathogens and cause infections in many animal species,” Boftsi said. “Our work can provide important insights into virus-host cell interactions in general.”
That kind of impact is what allowed Boftsi’s original interest in science to grow.
“I first got into research because of a biology class I had in high school,” Boftsi said. “Then I realized how amazing it is to study something closely and learn the details.”
And the curiosity she’s developed is a driving factor in her decision to keep her education going.
“I want to do a postdoc,” Boftsi said. “I really want to continue research.”
Even though being thousands of miles away from home is hard, Boftsi has grown from the experience, and she’s grateful for the opportunities she’s had thus far.
“It’s been great. I really like it here,” Boftsi said. “The environment is amazing, and the people are so friendly and helpful.”
Lab explores how parvo wins in tug of war with cells
By Samantha Kummerer | Bond LSC
At the start of any tug of war game, the battle is even. But it doesn’t stay that way for long. After a back and forth, the inevitable happens — the stronger team gives the rope one last tug and send the losers toppling over, claiming their dominance.
This is a game cells and viruses know well. In their version of tug of war, the virus eventually overtakes the cell and not only topples it but causes a consequence far worse than a few scraped knees.
This is how post-doctoral fellow Kinjal Majumder thinks of the interaction between parvoviruses and the dividing cells it conquers.
Majumder and others in the lab of David Pintel at Bond Life Sciences Center recently gained insight into how the virus achieves victory over the cell. These findings could improve human therapies and even play a role in treating cancer.
Meet the Champion
Parvoviruses are some of the smallest, simplest viruses. With only two genes, it has fewer DNA base pairs than most other viruses, up to ten times smaller in some cases. The virus’ size and simplicity, however, do not make it any easier to understand.
Pintel’s lab works at the “nitty gritty” level of the virus to study its basic molecular mechanism.
The group understands a little about how the virus operates but is working on the why.
Like a sly culprit, the virus uses its tiny nature to sneak inside the cell. The cell recognizes the presence of the virus as a foreign piece of DNA and responds to try to remove it. Once the cell responds, the virus begins replicating inside until it overtakes the cell. But, the tug of war game ends up more one-sided, so perhaps viewing the virus as a ruthless conqueror would be more accurate.
Majumder’s experiments specifically focus on DNA damage response, an intrinsic function of cells. The DNA damage response constantly works to protect us from cancer by continuously repairing broken DNA to prevent harmful mutations in cells . This response uses a network of cellular pathways to monitor and provide checkpoints in the cell cycle to prevent damage from being passed on to the next generation of cells. But parvoviruses also tricks cells to begin a DNA damage response, which they use to eventually take over the host cell.
In July, the lab published the latest finding from a series of papers exploring a type of these parvoviruses called minute virus of mice (MVM). The discovery began when the team found that the virus stops cells from dividing within infected cells.
To do this, MVM uses the DNA damage response to stop cells from dividing, but still allows virus replication to continue. The group developed a system to examine how the virus took over the cell. Further experiments revealed the virus transcriptionally regulates cell cycle genes.
The team used CRISPR to target a cellular gene that the virus must inactivate for it to replicate. Expression of this gene is required for the cell to divide. They discovered the virus actually blocks the transcription of this gene so it cannot make its protein. Blocking this function also prevents the cell from dividing. Without cell division, the virus is free to rapidly replicate inside the cell.
Majumder said parvo’s manipulation of infected cell cycles is different from other viruses because it can only replicate in cells that are actively synthesizing DNA. It eventually halts the process of cell division in infected cells by dysregulating transcription factors that regulate cell cycle gene expression. That’s what makes this discovery unique.
This discovery only scratches the surface.
Majumder said the lab constantly thinks of new experiments to explore parvovirus biology. The simplicity of its DNA expedites the process of culturing and growing the virus, leaving more time for what Majumder calls the “fun experiments.”
“We try to be thorough and confident of our findings, so we attack experiments from many different angles,” Majumder said.
Imagine viewing an object from multiple angles under varying light conditions. The change in perspective reveals something different about it with each new look. This approach expands their understanding of parvoviruses.
Majumder explained the lab makes use of everything from high-resolution imaging and CRISPR technology to proteomics and deep sequencing to study the tug-of-war between MVM and the DNA damage response.
“The thing about being a postdoc is you kind of have to be a jack of all trades,” Majumder said about his ability to conduct the range of experiments.
While parvoviruses are not a deadly threat to humans, understanding it has major implications for humans.
Parvoviruses are used to develop gene therapy tools to treat disorders like muscular dystrophy and spinal muscular atrophy. The Pintel lab collaborates with labs such as the Lorson and Sarafianos lab in Bond LSC, to explore its therapeutic potential.
Majumder explained the lab is also interested in understanding how the virus could improve cancer treatment. Parvo’s tendency to replicate in dividing cells links it to how cells divide uncontrollably in cancer. Majumder explained those scientists are trying to use that function of the virus to target cancer cells.
This makes work in the Pintel lab that much more important. But, before the virus can fully improve humans’ conditions, researchers better grasp its capabilities. And that means more of the daily experiments within the Pintel lab.
“What we learn from studying a simple virus can be expanded to more complicated viruses because there are some viruses that can make a dozen different proteins, so that’s a more complicated system,” Majumder said. “Before you can get to the more complicated systems, you need to be able to understand the one that makes just a few proteins.”
For now, scientists will play their own tug of war as they go back and forth in their findings and experiments to uncover the mystery surrounding this small, unique virus.
But an average virus dwarfs the diminutive variety known as parvoviruses, which are among the most minuscule pathogens known to science.
Tucked inside a protective protein shell, or capsid, parvoviruses contain a single DNA strand of about 5,000 nucleotides. If parvo’s genetic material is like an hour-long stroll around your neighborhood, a bigger virus like herpes is equivalent to walking from St. Louis to Columbia, Missouri.
“I joke that we can do the whole parvovirus genome project in an afternoon, because it’s just taking it downstairs and having it sequenced,” said David Pintel, a Bond Life Sciences Center virologist and Dr. R. Phillip and Diane Acuff endowed professor in medical research at the University of Missouri. “It’s the size of one gene in the mammalian chromosome.”
But that little stretch of DNA still has plenty of tricks up its sleeve.
Pintel has spent nearly 35 years studying parvo and is one of the world’s foremost experts on the virus, but he’s still plumbing the tiny pathogen’s depths.
His lab focuses on unraveling how parvo interferes with a host cell’s lifecycle and understanding the virus’ quirky RNA processing strategies.
“Even though the virus is small, it’s not simple,” David Pintel said. “Otherwise we’d be out of business.”
Over the last two decades, parvo has become an important tool for gene therapy, an experimental technique that fights a disease by inactivating or replacing the genes that cause it. Researchers enlist a kind of parvovirus known as adeno-associated virus as a gene therapy vector, the vehicle that delivers a new gene to a cell’s nucleus. Pintel helped suss out the virus’ basic biology, an important step for developing effective gene therapy.
A varied virus
The name ‘parvo’ comes from the Latin word for ‘small.’ But the virus’ size makes it a resourceful, versatile enemy and a valuable model for understanding viruses and how they interact with hosts.
Parvoviruses fall into five main groups. They infect a broad swath of animal species from mammals such as humans and mice to invertebrates such as insects, crabs and shrimp.
Canine parvovirus, or CPV, is perhaps the best-known type.
It targets the rapidly dividing cells in a dog’s gastrointestinal tract and causes lethargy, vomiting, extreme diarrhea and sometimes death. In humans, Fifth disease, caused by parvovirus B19, is the most common. This relatively innocuous virus usually infects children and causes cold-like symptoms followed by a “slapped cheek” rash. There is no vaccine for Fifth disease, but infections typically resolve without intervention.
Reading the transcript
Pintel surveyed the whole parvo family to understand its idiosyncrasies.
To study bocavirus – a kind of parvo recently linked to a human disease – Pintel looked closely at the dog version, minute virus of canines (MVC). MCV serves as a good model for the human disease-causing virus. While examining MVC, he noticed an unexpected signal in the center of the viral genome. The signal terminates RNA encoding proteins for the virus’ shell, a vital part of the pathogen.
Finding such a misplaced signal in the middle of a stretch of RNA is like coming across a paragraph break in the middle of a sentence.
Pintel knew the virus bypassed this stop sign somehow, because the blueprint for the viral capsid lies further down the genome.
To overcome this stop sign, this particular parvovirus makes a protein found in no other virus. The protein performs double-duty for the virus: It suppresses the internal termination signal and splices together two introns, or segments of RNA that do not directly code information but whose removal is necessary for protein production. Splicing the introns together ensures that the gene responsible for producing the viral capsid is interpreted correctly.
Viruses and hosts: a game of cat and mouse
The conflict between a virus and a host is a constantly escalating battle of assault and deception.
Viruses need a host cell’s infrastructure to replicate, but have to fool or outmaneuver its defenses.
Pintel discovered one example of this trickery in mice, where parvo triggers a cellular onslaught known as the DNA damage response, or DDR. This type of parvo co-opts that defense. Normally DDR pauses the cell cycle to keep damaged DNA from being passed on to the next generation of cells, but parvo exploits that delay, buying time for the virus to multiply.
“For many, many hours the cells are just held there by the virus while the virus continues to replicate,” Pintel said. “And then that cell never survives; the virus kills the cell. It’s that holding of the cell cycle — which is part of the DNA damage response — that the virus hijacks to hold the cell cycle. It’s really cool.”
Parvo’s small size makes it especially beholden to their hosts. But that can make them particularly revelatory for researchers.
“It’s a twofold thing,” Pintel said, “Because it’s a virus that’s dependent on the cell, when you learn how the virus is doing these things, you learn how the cell does those basic processes. If we’re looking at a viral-cell interaction, yes, we’re looking at it from a viral point of view, but on the other hand we’re trying to understand the basic cellular process.”
Uncovering such nuanced interactions is a painstaking, laborious process that often goes unheralded by mass media. But those fundamental discoveries provide the building blocks upon which other researchers depend, said Femi Fasina, a postdoc in Pintel’s lab.
“When you understand basic biology, people can walk on those advancements. Although we don’t see the impact immediately, such things lead to breakthroughs that will revolutionize a lot of things.”
A small question
Despite his deepening understanding of how parvo works, there remains one debate about the virus that Pintel deems beyond the scope of his research: Are the tiny slivers of DNA that comprise parvoviruses even alive?
“I think that’s a crazy question,” he said. “It’s semantics. The virus is a genome. It goes into a cell, it doesn’t do anything until it’s inside of a cell and then it does stuff.” So whether you write parvoviruses into the book of life depends entirely on how you define the word ‘alive.’
“I put that in the realm of philosophy,” Pintel said, “not the realm of science.”