The proteasome and ERAD pathways can regulate hepatitis E virus pORF1 proteostasis and genome replication

Abstract

Hepatitis E virus (HEV) is a major cause of acute viral hepatitis, with an estimated 20 million human infections annually. Its diverse host range presents a significant zoonotic threat, yet the molecular mechanisms underpinning HEV-host interactions remain poorly characterised. Here, we used transposon-based insertion screening of the HEV pORF1 polyprotein to identify a novel region within the viral PCP domain that permits HA-epitope insertion, enabling the first epitope tagging of this domain. Combined with V5 tagging of the hypervariable region (HVR), this approach enabled the generation of a replication-competent stable cell line expressing dual-tagged ORF1. Co-immunoprecipitation and TMT-based LC-MS proteomics revealed that pORF1 interacts with host proteins involved in endoplasmic reticulum-associated degradation (ERAD) and the 26S proteasome. Pharmacological inhibition demonstrated that both pathways are required for efficient HEV replication. Treatment with the FDA-approved proteasome inhibitor bortezomib altered pORF1 precursor abundance and led to loss of full-length pORF1 through enhanced proteolysis. Importantly, the kinetics of ORF1 degradation following proteasome inhibition correlated with immediate loss of HEV replication, demonstrating a functional link between pORF1 proteostasis and viral replication. Collectively, our findings identify the ERAD network as a previously unrecognised requirement for HEV replication and establish a role for the 26S proteasome in maintaining pORF1 proteostasis.