HEV-ORF3 Encoding Phosphoprotein Interacts With Hepsin

Structural aspects of hepatitis E virus

Hepatitis E virus (HEV) is a leading cause of acute hepatitis worldwide. Hepatitis E is an enterically transmitted zoonotic disease that causes large waterborne epidemic outbreaks in developing countries and has become an increasing public-health concern in industrialized countries. In this setting, the infection is usually acute and self-limiting in immunocompetent individuals, although chronic cases in immunocompromised patients have been reported, frequently associated with several extrahepatic manifestations. Moreover, extrahepatic manifestations have also been reported in immunocompetent individuals with acute HEV infection. HEV belongs to the alphavirus-like supergroup III of single-stranded positive-sense RNA viruses, and its genome contains three partially overlapping open reading frames (ORFs). ORF1 encodes a nonstructural protein with eight domains, most of which have not been extensively characterized: methyltransferase, Y domain, papain-like cysteine protease, hypervariable region, proline-rich region, X domain, Hel domain, and RNA-dependent RNA polymerase. ORF2 and ORF3 encode the capsid protein and a multifunctional protein believed to be involved in virion release, respectively. The novel ORF4 is only expressed in HEV genotype 1 under endoplasmic reticulum stress conditions, and its exact function has not yet been elucidated. Despite important advances in recent years, the biological and molecular processes underlying HEV replication remain poorly understood, primarily due to a lack of detailed information about the functions of the viral proteins and the mechanisms involved in host-pathogen interactions. This review summarizes the current knowledge concerning HEV proteins and their biological properties, providing updated detailed data describing their function and focusing in detail on their structural characteristics. Furthermore, we review some unclear aspects of the four proteins encoded by the ORFs, highlighting the current key information gaps and discussing potential novel experimental strategies for shedding light on those issues.

Hepatitis E virus: advances and challenges

At least 20 million hepatitis E virus (HEV) infections occur annually, with >3 million symptomatic cases and ∼60,000 fatalities. Hepatitis E is generally self-limiting, with a case fatality rate of 0.5-3% in young adults. However, it can cause up to 30% mortality in pregnant women in the third trimester and can become chronic in immunocompromised individuals, such as those receiving organ transplants or chemotherapy and individuals with HIV infection. HEV is transmitted primarily via the faecal-oral route and was previously thought to be a public health concern only in developing countries. It is now also being frequently reported in industrialized countries, where it is transmitted zoonotically or through organ transplantation or blood transfusions. Although a vaccine for HEV has been developed, it is only licensed in China. Additionally, no effective, non-teratogenic and specific treatments against HEV infections are currently available. Although progress has been made in characterizing HEV biology, the scarcity of adequate experimental platforms has hampered further research. In this Review, we focus on providing an update on the HEV life cycle. We will further discuss existing cell culture and animal models and highlight platforms that have proven to be useful and/or are emerging for studying other hepatotropic (viral) pathogens.

Replacement of the hepatitis E virus ORF3 protein PxxP motif with heterologous late domain motifs affects virus release via interaction with TSG101

The ORF3 protein of hepatitis E virus (HEV) contains a "PSAP" amino acid late domain motif, which allows for interaction with the endosomal sorting complexes required for transport (ESCRT) pathway aiding virion release. Late domain motifs are interchangeable with other viral late domain motifs in several enveloped viruses, however, it remains unknown whether HEV shares this functional interchangeability and what implications this might have on viral replication. In this study, by substituting heterologous late domain motifs (PPPY, YPDL, and PSAA) for the HEV ORF3 late domain (PSAP), we demonstrated that deviation from the PSAP motif reduces virus release as measured by viral RNA in culture media. Virus release could not be restored by insertion of a heterologous late domain motif or by supplying wild-type ORF3 in trans, suggesting that the HEV PSAP motif is required for viral exit which cannot be bypassed by the use of alternative heterologous late domains.

Therapeutic targets for the treatment of hepatitis E virus infection

INTRODUCTION

Hepatitis E virus (HEV) is one of the most common causes of acute viral hepatitis in the world with an estimated 20 million infections per year. Although the mortality rate is < 1% among the general population, pregnant women can have a fatality rate of up to 30%. Additionally, chronic hepatitis E has increasingly become a significant clinical problem in immunocompromised individuals. Effective antivirals against HEV are needed.

AREAS COVERED

This review article addresses the current state of knowledge of HEV infections with regard to animal and cell culture model systems that are important for antiviral discovery and testing, our current understanding of the molecular mechanisms of virus replication, our understanding of how each viral protein functions, and areas that can potentially be exploited as therapeutic targets.

EXPERT OPINION

Lack of an efficient cell culture system for HEV propagation, the limited knowledge of HEV lifecycle, and the inherent self-limiting infection within the normal populace make the development of new therapeutic agents against HEV challenging. There are many promising therapeutic targets, and the tools for identifying and testing potential antivirals are rapidly evolving. The development of effective therapeutics against HEV in immunocompromised and pregnant patient populations is warranted.

Molecular detection of hepatitis E virus in sheep from southern Xinjiang, China

Hepatitis E virus (HEV) is a causative agent of infectious hepatitis in animals and humans both in developing and developed countries. Here, we collected 500 sheep sera and 75 raw sheep liver samples from a slaughterhouse in the southern part of the Xinjiang region, China, along with 26 sera of butchers from the same slaughterhouse. All serum samples were tested for anti-HEV antibody by enzyme-linked immunosorbent assay. Both serum and liver samples were evaluated for the presence of HEV RNA by nested polymerase chain reaction targeting partial nucleotide sequences of open reading frame 2 (ORF2). The results indicate that sheep seroprevalence was 35.20 % (176/500) and that four of the 75 (5.3 %) sheep livers showed detectable amounts of HEV RNA. The seroprevalence of the butchers was 57.7 % (15/26). The four amplicons shared 97.8-100 % nucleotide sequence identity and had pairwise sequence identities of 81.6-85.3 %, 84.2-85.3 %, 82.1-85.3 % and 84.7-97.9 % with the corresponding regions of genotypes 1, 2, 3 and 4 of HEV, respectively. A phylogenetic tree was constructed based on alignments of an amplified 186-bp ORF2 sequence and corresponding reference strains. The analysis showed that the four sheep strains detected in our study formed a lineage within a genotype 4 cluster that contains hb-3, bjsw1, T1, swCH189 and swCH25, all of which belong to genotype 4, subtype 4d. The results indicated a high level of seroconversion in sheep and suggested that sheep liver may be a source of foodborne HEV infection in humans.