Tumour susceptibility gene 101 and the vacuolar protein sorting pathway are required for the release of hepatitis E virions

We have previously demonstrated that an intact PSAP motif in the ORF3 protein is required for the formation and release of membrane-associated hepatitis E virus (HEV) particles with ORF3 proteins on their surface. In this study, we investigated the direct interaction between the ORF3 protein and tumour susceptibility gene 101 (Tsg101), a cellular factor involved in the budding of viruses containing the P(T/S)AP late-domain, in PLC/PRF/5 cells expressing the wild-type or PSAP-mutated ORF3 protein and Tsg101 by co-immunoprecipitation. Tsg101 bound to wild-type ORF3 protein, but not to the PSAP-inactive ORF3 protein. To examine whether HEV utilizes the multivesicular body (MVB) pathway to release the virus particles, we analysed the efficiency of virion release from cells upon introduction of small interfering RNA (siRNA) against Tsg101 or dominant-negative (DN) mutants of Vps4 (Vps4A and Vps4B). The relative levels of virus particles released from cells depleted of Tsg101 decreased to 6.4% of those transfected with negative control siRNA. Similarly, virion egress was significantly reduced by the overexpression of DN forms (Vps4AEO or Vps4BEQ). The relative levels of virus particles released from cells expressing Vps4AEQ and Vps4BEQ were 19.2 and 15.6%, respectively, while the overexpression of wild-type Vps4A and Vps4B did not alter the levels of virus release. These results indicate that the ORF3 protein interacts with Tsg101 through the PSAP motifs in infected cells, and that Tsg101 and the enzymic activities of Vps4A and Vps4B are involved in HEV release, thus suggesting that HEV requires the MVB pathway for egress of virus particles.