Canine hepacivirus, a relative of hepatitis C virus

yellow labradorContemporary human viruses most likely originated by cross-species transmission from non-human animals. Examples include HIV-1, which crossed from chimpanzees to humans, and SARS coronavirus, which originated in bats. Since the 1989 discovery of hepatitis C virus (classified as a hepacivirus in the family Flaviviridae) the origin of the virus been obscure. During the characterization of respiratory infections of domestic dogs, a virus was discovered that is the most genetically similar animal virus homolog of HCV.

HCV is a substantial human pathogen: 200 million people worldwide are chronically infected and are at risk for the development of hepatocellular carcinoma. The source of HCV is unknown because there are no closely related animal virus homologs, but the hunt for related viruses has focused mainly on nonhuman primates. The identification of a related virus was fortuitous, and came about during a study of respiratory viruses that infect dogs. Nasal swabs were obtained from dogs with respiratory illness in shelters in Texas, Utah, and Pennsylvania. Sequence analysis of viral nucleic acids revealed the presence of a virus related to HCV, which was named canine hepacivirus (CHV). The virus was found in respiratory samples from 6 of 9 and 3 of 5 dogs in two separate outbreaks of respiratory disease, but not in 60 healthy pet dogs.

CHV was present in liver, but not lung, of 5 dogs that had died from unexplained gastrointestinal illness. The amount of CHV RNA in respiratory samples was substantially higher than in liver. Viral RNA was detected in the cytoplasm of hepatocytes in canine liver, but whether CHV is hepatotropic (replicates in liver cells) in dogs is not known. In humans, the amount of HCV in respiratory samples is typically very low. CHV may therefore infect different cells and tissues in dogs than does HCV in humans.

Bioinformatic analysis of CHV revealed that it is the genetically more related to HCV than any other known virus. HCV and CHV probably shared a common ancestor that circulated between 500 and 1,000 years ago – many years after dogs were domesticated. It is possible that hepaciviruses are mainly dog viruses, and that HCV arose by transmission of the virus from a dog to a human. An alternative scenario that cannot be excluded is that hepaciviruses infect many animal species. Screening of other animals for the presence of hepaciviruses must be done to determine which hypothesis is correct.

It was not possible to infect canine cultured cells with CHV, using clinical specimens from dogs.  The reason for this failure is not known, but could mean that the cells used are not susceptible and/or permissive for viral replication. Furthermore, a full-length DNA copy of the viral genome, which could be used to produce infectious viral RNA, was not reported. Propagation of the virus in cell cultures will be essential for enabling research on CHV replication and pathogenesis.

The discovery of CHV is exciting because the virus provides clues about the origins of HCV and will likely stimulate a search for related viruses in other animals. It is possible that CHV infection of dogs might be a model for understanding the pathogenesis of HCV, which currently is only possible in chimpanzees. A convenient animal model would be valuable for devising new ways to prevent and treat HCV infections.

A. Kapoor, P. Simmonds, G. Gerold, N. Qaisar, K. Jain, J.A. Henriquez, C. Firth, D.L. Hirschberg, C. Rice, S. Shields, & W.I. Lipkin. (2011). Characterization of a canine homolog of hepatitis C virus Proc. Natl. Acad. Sci. USA

TWiV 130: Rhino tracking, wrestling pox, and HCV in the crosshairs

organ culture hrv cHosts: Vincent Racaniello, Alan Dove, and Rich Condit

Vincent, Alan, and Rich discuss growth in culture of newly identified rhinovirus C, vaccinia transmission among wrestlers and martial artists, and results of phase III clinical trial of boceprevir, a new inhibitor of hepatitis C virus replication.

Click the arrow above to play, or right-click to download TWiV #130 (45 MB .mp3, 93 minutes).

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Weekly Science Picks

Rich – Rock-paper-scissors vs computer (thanks, Megan!)
Alan –
WebCite
Vincent – Edward Jenner Museum (EID)

Listener Pick of the Week

Derek Tolly  – A Paralyzing Fear: The Story of Polio in America (IMDb)

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TWiV 121: Huskies go viral

viral huskiesHosts: Vincent Racaniello, Michael Katze, Michael Gale, Deborah Fuller, and Shawn Iadonato

Episode #121 of the podcast This Week in Virology is a conversation about careers in virology, systems biology, innate immunity, and antiviral research recorded at the University of Washington in Seattle.

Click the arrow above to play, or right-click to download TWiV #121 (65 MB .mp3, 90 minutes).

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Weekly Science Picks

Michael K – Pasteur Museum
Deborah – Undaunted Courage by Stephen Ambros
Michael G – The Eighth Day of Creation by Horace Freeland Judson
Vincent –
The Emperor of All Maladies by Siddhartha Mukherjee

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TWiV 97: California virology

Hosts: Vincent Racaniello, Peter Sarnow, and Bert Semler

On episode #97 of the podcast This Week in Virology, Vincent visited Peter Sarnow and Bert Semler during a trip to California, and spoke with them about their work on internal ribosome entry, and the requirement for a cellular microRNA for hepatitis C virus replication.

Click the arrow above to play, or right-click to download TWiV #97 (66 MB .mp3, 91 minutes)

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Links for this episode:

  • Eukaryotic mRNAs that might contain an IRES (PNAS)
  • Modulation of HCV RNA abundance by a liver-specific microRNA (Science)
  • Viral small RNAs (PLoS Pathogens)
  • Bridging IRES elements to the translation apparatus (Biochim Biophys Acta)
  • A nucleo-cytoplasmic SR protein functions in viral IRES mediated translation (EMBO J)
  • Nuclear vs cytoplasmic routes to IRES mediated translation (Trends in Microbiology)
  • Letter read on TWiV 97

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A new target for hepatitis C virus

When infection with hepatitis C virus goes from acute to chronic, severe liver disease may occur which requires organ transplantation. Nearly 200 million people are chronically infected with HCV, necessitating approaches to preventing and treating infections. No HCV vaccine is available, and current antiviral therapy consists of administration of interferon plus ribavirin, a combination that is effective about half the time and is associated with undesirable side effects. New antiviral compounds that target a viral protease and RNA polymerase are currently in clinical trials may eventually reach the market. But our experience with HIV-1 has shown that combinations of three drugs are the most effective for derailing the emergences of drug resistant viruses. The third target for HCV could be NS5A, a viral protein without a known function.

To identify new inhibitors of HCV, a chemical library of one million compounds was screened for the ability to inhibit viral replication in cell culture. The active compound were then subjected to a second screen to eliminate inhibitors of known viral enzymes: the viral protease, RNA polymerase, and helicase. One of the remaining inhibitors was further refined chemically until a very potent derivative was obtained. This molecule, called BMS-790052, has a 50% inhibitory concentration in the picomolar range, and inhibits all the viral genotypes tested. It is the most powerful inhibitor of HCV discovered.

The compound was tested for safety and bioavailability in various animal species. After oral administration, the compound was found in plasma and liver, despite a molecular mass of over 700 daltons. Six different levels of the compound were tested in HCV infected individuals. No adverse effects were reported, and the highest amount administered reduced viral levels in the blood 2,000 fold after one day. These results are promising, but larger trials will now be needed to further confirm the safety and efficacy of the drug.

What is the target of BMS-790052? Two lines of evidence suggest that the compound inhibits the viral protein NS5A. The drug appears to bind NS5A, and viruses resistant to the drug have amino acid changes in this protein. Although NS5A is known to be required for viral replication, its precise function is not known. Because NS5A does not have an easily assayable enzymatic function, it has not previously been a target of drug discovery. The identification of a compound that inhibits NS5A function is an important step forward in HCV drug development. The general approach used to discover BMS-790052 should be useful in identifying inhibitors of other viral proteins that do not have well defined and measurable activities.

I discussed this paper on Futures in Biotech episode #60. If you would like to listen only to the conversation about BMS-790052, download this mp3 file, or listen to the discussion below.

[audio:http://www.virology.ws/fib60.mp3 | titles=FIB 60]

Gao M, Nettles RE, Belema M, Snyder LB, Nguyen VN, Fridell RA, Serrano-Wu MH, Langley DR, Sun JH, O’Boyle DR 2nd, Lemm JA, Wang C, Knipe JO, Chien C, Colonno RJ, Grasela DM, Meanwell NA, & Hamann LG (2010). Chemical genetics strategy identifies an HCV NS5A inhibitor with a potent clinical effect. Nature, 465 (7294), 96-100 PMID: 20410884

TWiV 85: Hepatitis C virus with Professor Michael Gale

Hosts: Vincent Racaniello and Michael Gale

On episode 85 of the podcast This Week in Virology, Vincent and Michael Gale discuss the origin, pathogenesis, prevention, of hepatitis C virus, and how it evades innate immune responses.

This episode is sponsored by Data Robotics Inc. Use the promotion code TWIVPOD to receive $75-$500 off a Drobo.

Click the arrow above to play, or right-click to download TWiV #85 (40 MB .mp3, 56 minutes)

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Links for this episode:

  • The Gale Laboratory at the University of Washington
  • Incredible view from the Gale laboratory (jpg)
  • Evasion and disruption of innate immune signalling by hepatitis C and West Nile viruses (review)
  • New potent HCV inhibitor
  • HCV virion and genome structures at ViralZone

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Futures in Biotech 60: Do you come to this cave often?

I joined Marc Pelletier on futures-in-biotechepisode 60 of Futures in Biotech for a conversation with Dave Brodbeck, George Farr, and Andre Nantel. We talked about primate face recognition, discovery of a new antiviral compound to treat hepatitis C virus infection, changing the length of a codon from three to four bases, and the sequence of the neanderthal genome.

[audio:http://www.podtrac.com/pts/redirect.mp3/twit.cachefly.net/fib0060.mp3 | titles=FiB 60]

Download FiB #60 (44 MB .mp3, 91 minutes)

Video courtesy of Team ODTV

 

Download video (179 MB .mp4)

Mouse model for hepatitis C virus infection?

pvrtgNo, not yet. But the recent identification of human occludin as a cell protein required for entry of hepatitis C virus into mouse cells is a huge step in the right direction.

Small animal models for virus infection are of great value for studying viral pathogenesis, testing new vaccines, and developing antiviral drugs. However, mice are often not susceptible or permissive for infection by many important viruses. For example, mice and mouse cells are permissive for poliovirus replication, but are not susceptible to infection with the virus. Mice can be made susceptible to poliovirus infection by transgenic expression of the human poliovirus receptor. In a similar way, a transgenic mouse model for measles virus infection has been produced. But it has been far more difficult to create transgenic mice susceptible to other important viruses, including HIV-1 and hepatitis C virus (HCV).

Mouse cells are permissive for HCV replication (the viral RNA can replicate when transfected into cells), but they are not susceptible: for example, they cannot be infected by lentiviral particles bearing HCV glycoproteins.  Three cellular proteins required for HCV entry into cells were previously identified: CD81, scavenger receptor class B type I or SCARB1, and claudin-1. Most recently a fourth cellular protein, occludin, was found to be essential for HCV entry into cells. HCV can enter mouse cells that synthesize human occludin and CD81; apparently the murine versions of SCARB1 and claudin-1 can promote HCV entry. The human versions of these four proteins was sufficient to confer permissivity to HCV entry in a variety of human, murine, or hamster cell lines.

Because the major block to HCV entry in murine cells can be overcome by synthesis of human CD81 and occludin, will it now be possible to produce transgenic mice susceptible to HCV? Perhaps not yet: there are other blocks to HCV replication in murine cells. For example, viral RNA replication in mouse cells is not efficient, nor has assembly of infectious virions been demonstrated. But these problems can now be readily addressed, and I would not be surprised to find that CD81/occludin transgenic mice already exist and are being tested for susceptibility to HCV in at least one laboratory.

Ploss, A., Evans, M., Gaysinskaya, V., Panis, M., You, H., de Jong, Y., & Rice, C. (2009). Human occludin is a hepatitis C virus entry factor required for infection of mouse cells Nature, 457 (7231), 882-886 DOI: 10.1038/nature07684