HCV is a significant human pathogen, infecting more than three percent of the world’s population. The incidence of infection in the United States has been estimated to be as high as 4 million cases.
In the March issue of the journal PLoS Pathogens, Timothy Tellinghuisen, an assistant professor in the Department of Infectology at Scripps Florida, and his colleagues describe how they used mutations of the viral NS5A phosphoprotein to disrupt virus particle production at an early stage of assembly. NS5A has long been proposed as a regulator of events in the HCV life cycle, but exactly how it orchestrates these events has been unclear.
“The interesting thing about this mutant is that while it triggers totally normal RNA replication, it causes severe defects in the output of infectious virus—in fact, it releases no infectious virus that we can detect,” says Tellinghuisen. “And though this discovery isn’t a cure for HCV, it is an important research tool that stops the assembly pathway.” Total disruption of the replication process would be a cure for the disease, he adds, and that’s the team’s long-term goal.
HCV infection is roughly five to seven times more prevalent than HIV, underscoring the pandemic nature of HCV infection. HCV occurs when blood from an infected person enters the body of someone who is not infected. Most new HCV infections are due to illegal drug injections and sharing needles. However, those who had blood transfusions prior to blood donor screening in 1991, healthcare workers who had needle stick accidents, and hemodialysis patients are also at risk for developing HCV infection. The virus predominantly infects the liver, and following many decades of virus reproduction serious disease such as hepatitis (liver inflammation), cirrhosis (liver scarring), and carcinoma (liver cancer) develop. Ultimately, HCV infection destroys the liver, resulting in death. Attempts at curing HCV infections with drug therapy have been only marginally successful.
Before more effective therapies can be developed, scientists need to understand, at the molecular level, the detailed mechanisms HCV uses to infect cells, replicate itself, assemble progeny virus, and exit the cell. Each of these processes could potentially be a target for a new drug to eliminate HCV infection. HCV, like all viruses, requires the normal cellular machinery for its replication and has developed strategies to utilize normal cell physiology for its own benefit (often to the detriment of the host).
The Tellinghuisen team, which includes Research Assistants Katie L. Foss and Jason Treadaway, has focused recent efforts on NS5A to understand the regulation of events used by the virus to assemble infectious copies of itself and exit the cell. NS5A is a three-domain protein, which means it is comprised of three compactly folded regions roughly 50 to 300 amino acids in length. The requirement of domains I and II for RNA replication is well documented. NS5A domain III, however, is not required for RNA replication, and the function of this region in the HCV life cycle is unknown.
Using standard molecular biology, the researchers removed from domain III of NS5A a coding sequence corresponding to roughly 15 amino acids. Then they generated a clone of the virus, transcribed the RNA from that clone, and purified the RNA. This RNA, which is directly infectious, was then transfected into a liver cell line where it produced all the HCV proteins that are encoded by that RNA genome.
“Those proteins assemble in the cell to make a structure called a replicase that then copies the viral RNA,” Tellinghuisen explains. “We measured that RNA accumulation and observed no defect in RNA replication, but found, surprisingly, that no infectious viral particles were released from the cells.” The team also found that no viral RNA nor nucleocapsid protein are released from cells, indicating that an early event in virus assembly had been affected.
Using genetic mapping and biochemical analyses, the authors were able to show that their deletion altered a phosphorylation signal controlling the switch from RNA replication to virus particle assembly. This signal was attributed to the activity of a cellular kinase that when inhibited by genetic or chemical means led to a reduction in infectious virus production without altering HCV RNA replication.
“These data provide the first evidence for a function of domain III of NS5A and implicate NS5A as an important regulator of the RNA replication and virion assembly of HCV,” Tellinghuisen says. “The ability to uncouple virus production from RNA replication may be useful in understanding HCV assembly and may become therapeutically important.”
Charles M. Rice, head of the Center for the Study of Hepatitis C at Rockefeller University, comments, “This is a spectacular advance linking a specific phosphorylation event by a cellular kinase to hepatitis C virus assembly. Remarkably, the target is a viral nonstructural protein, NS5A, and the data point to a pivotal role for this protein in regulating RNA amplification and infectious virus production. These new data make this multifunctional protein an even more attractive target for developing new anti-virals for treating hepatitis C.”
This project was funded by a Career Development Award from the National Institutes of Allergy and Infectious Diseases of the National Institutes of Health, and by the State of Florida.
About The Scripps Research Institute
The Scripps Research Institute is one of the world's largest independent, non-profit biomedical research organizations, at the forefront of basic biomedical science that seeks to comprehend the most fundamental processes of life. Scripps Research is internationally recognized for its discoveries in immunology, molecular and cellular biology, chemistry, neurosciences, autoimmune, cardiovascular, and infectious diseases, and synthetic vaccine development. Established in its current configuration in 1961, it employs approximately 3,000 scientists, postdoctoral fellows, scientific and other technicians, doctoral degree graduate students, and administrative and technical support personnel. Scripps Research is headquartered in La Jolla, California. It also includes Scripps Florida, whose researchers focus on basic biomedical science, drug discovery, and technology development. Currently operating from temporary facilities in Jupiter, Scripps Florida will move to its permanent campus in 2009.
For information:Keith McKeown
Keith McKeown | EurekAlert!
Algae-killing viruses spur nutrient recycling in oceans
18.07.2019 | Rutgers University
How are pollen distributed in the air?
18.07.2019 | Leibniz-Institut für Troposphärenforschung e. V.
Scientists have visualised the electronic structure in a microelectronic device for the first time, opening up opportunities for finely-tuned high performance electronic devices.
Physicists from the University of Warwick and the University of Washington have developed a technique to measure the energy and momentum of electrons in...
Scientists at the University Würzburg and University Hospital of Würzburg found that megakaryocytes act as “bouncers” and thus modulate bone marrow niche properties and cell migration dynamics. The study was published in July in the Journal “Haematologica”.
Hematopoiesis is the process of forming blood cells, which occurs predominantly in the bone marrow. The bone marrow produces all types of blood cells: red...
For some phenomena in quantum many-body physics several competing theories exist. But which of them describes a quantum phenomenon best? A team of researchers from the Technical University of Munich (TUM) and Harvard University in the United States has now successfully deployed artificial neural networks for image analysis of quantum systems.
Is that a dog or a cat? Such a classification is a prime example of machine learning: artificial neural networks can be trained to analyze images by looking...
An international research group led by scientists from the University of Bayreuth has produced a previously unknown material: Rhenium nitride pernitride. Thanks to combining properties that were previously considered incompatible, it looks set to become highly attractive for technological applications. Indeed, it is a super-hard metallic conductor that can withstand extremely high pressures like a diamond. A process now developed in Bayreuth opens up the possibility of producing rhenium nitride pernitride and other technologically interesting materials in sufficiently large quantity for their properties characterisation. The new findings are presented in "Nature Communications".
The possibility of finding a compound that was metallically conductive, super-hard, and ultra-incompressible was long considered unlikely in science. It was...
An interdisciplinary research team at the Technical University of Munich (TUM) has built platinum nanoparticles for catalysis in fuel cells: The new size-optimized catalysts are twice as good as the best process commercially available today.
Fuel cells may well replace batteries as the power source for electric cars. They consume hydrogen, a gas which could be produced for example using surplus...
24.06.2019 | Event News
29.04.2019 | Event News
17.04.2019 | Event News
18.07.2019 | Health and Medicine
18.07.2019 | Life Sciences
18.07.2019 | Health and Medicine