Scientists Discover How a Protein and Enzymes Enabling Hepatitis A Virus Replication

While focusing on the viral replication cycle in the hepatitis A virus (HAV), UNC School of Medicine scientists recently discovered that replication requires specific interactions between the human protein ZCCHC14 and a group of enzymes called TENT4 poly(A) polymerases. 

They also found that the oral compound RG7834 stopped replication at a critical step, making it impossible for the virus to infect liver cells.

These findings were published in the Proceedings of the National Academy of Sciences on July 7, 2022, and are the first to demonstrate an effective drug treatment against HAV in an animal model of the disease.

“Our research demonstrates that targeting this protein complex with an orally delivered, small-molecule therapeutic halts viral replication and reverses liver inflammation in a mouse model of hepatitis A, providing proof of principle for antiviral therapy and the means to stop the spread of hepatitis A in outbreak settings,” commented senior author Stanley M. Lemon, M.D., professor in the UNC Department of Medicine and UNC Department of Microbiology & Immunology, and member of the UNC Institute for Global Health and Infectious Diseases.

Dr. Lemon, who in the 1970s and 80s was part of a Walter Reed Army Medical Center research team that developed the first inactivated HAV vaccine administered to humans, said research on HAV tapered off after the vaccine became widely available in the mid-1990s. 

The good news is HAV cases plummeted in the 2000s as vaccination rates skyrocketed.

Not everyone gets vaccinated, Lemon pointed out, and HAV can exist for long periods in the environment – such as on our hands and in food and water.

Several outbreaks have occurred over the past several years, including in San Diego in 2017, primarily driven by homelessness and illicit drug use, causing severe illness in about 600 people and killing 20. 

In 2022, a small outbreak was linked to organic strawberries in multiple states, leading to about a dozen hospitalizations.

As of July 1, 2022, since the HAV outbreaks were first identified in 2016, 37 states reported 44,696 cases, hospitalizations (61%), and 423 related fatalities.

Symptoms include fever, abdominal pain, jaundice, nausea, loss of appetite, and a sense of taste.  

Once sick, there is no treatment.

In 2013, Lemon and colleagues discovered that the hepatitis A virus changes dramatically inside the human liver. 

The virus hijacks bits of the cell membrane as it leaves liver cells, cloaking itself from antibodies that would have otherwise quarantined the virus before it spread widely through the bloodstream. 

This work was published in Nature and provided insight into how much researchers had yet to learn about this virus discovered 50 years ago and likely caused diseases dating back to ancient times.

Lemon’s lab led experiments to search for human proteins that HAV needs to replicate, and they found ZCCHC14 – a particular protein that interacts with zinc and binds to RNA.

“This was the tipping point for this current study,” Lemon said. 

“We found ZCCHC14 binds very specifically to a certain part of HAV’s RNA, the molecule that contains the virus’s genetic information. And as a result of that binding, the virus can recruit TENT4 from the human cell.”

In normal human biology, TENT4 is part of an RNA-modification process during cell growth. Essentially, HAV hijacks TENT4 and uses it to replicate its own genome.

This work suggested that stopping TENT4 recruitment could stop viral replication and limit disease. 

Lemon’s lab then tested the compound RG7834, which had previously been shown to actively block the Hepatitis B virus by targeting TENT4. 

In the new PNAS paper, the researchers detailed the precise effects of oral RG7834 on HAV in liver and feces and how the virus’s ability to cause liver injury is dramatically diminished in mice that had been genetically modified to develop HAV infection and disease. 

The research suggests the compound was safe at the dose used in this research and the acute timeframe of the study.

“This compound is a long way from human use,” Lemon said, “But it points the path to an effective way to treat a disease for which we have no treatment at all.”

The pharmaceutical company Hoffmann-La Roche developed RG7834 for use against chronic hepatitis B infections and tested it in humans in a phase 1 trial, but animal studies suggested it may be too toxic for use over long periods.

“The treatment for Hepatitis A would be short-term,” Lemon said, “and, more importantly, our group and others are working on compounds that would hit the same target without toxic effects.”

The hepatitis A vaccination is the best way to prevent HAV infection, says the CDC.

One dose of single-antigen hepatitis A vaccine has been shown to control outbreaks of hepatitis A.

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This research was a collaboration between the Lemon lab and the lab of Jason Whitmire, professor of genetics at the UNC School of Medicine. Lemon and Whitmire are members of the UNC Lineberger Comprehensive Cancer Center.

This work was supported by grants from the National Institute of Allergy and Infectious Diseases. In addition, the UNC Pathology Services Core and UNC High-Throughput Sequencing Facility were partially supported by a National Cancer Institute Center Core Support Grant to the UNC Lineberger Comprehensive Cancer Center. No industry conflicts of interest were disclosed.

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