Fig. 6

The crosstalk between canonical and extracellular vesicle-mediated HEV life cycle. A The schematic illustrates the genome structure of HEV, featuring three open reading frames (ORFs): one for the viral replicase (ORF1), another for the capsid (ORF2), and a third (ORF3) encoding a small protein involved in virion secretion. B The HEV life cycle initiates with the initial contact between HEV and host cells, mediated by interactions with receptors such as HSPGs and HAVCR1, which are not fully characterized. After endocytosis and uncoating, the viral genome is released into the cytoplasm, where the host translational machinery promotes translation and generates the ORF1 replicase. The ORF1 replicase facilitates viral RNA replication and generates a negative-strand RNA intermediate serving as a template for two mRNAs, one for ORF2 and another for ORF3. ORF2 is utilized for capsidation, leading to subsequent virion assembly and release, although the mechanism of non-enveloped HEV (neHEV) release is currently unknown. In exosomal HEV (or quasi-enveloped HEV, eHEV), the exosome surface reportedly contains phosphatidylserine but lacks known surface protein markers. However, ESCRT-related proteins such as TSG101, HRS, VPS4A, and VPS4B are localized within eHEV. Additionally, HEV ORF3 is also found within eHEV. The entry of eHEV is reported to involve Clathrin/Dynamin-dependent endocytosis, facilitated by Rab5. The endosome containing eHEV enters multivesicular bodies (MVBs), perhaps through membrane fusion, and then faces two possible fates: fusion with the lysosome to release the viral genome or re-secretion into the extracellular space as an exosome, facilitated by Rab27A. The crosstalk between canonical and eHEV replication and transmission involves ORF3-mediated entry of the MVBs thorugh direct interaction with ESCRT machinery such as TSG101 and VPS4B. Additionally, it is reported that neutral sphingomyelinase 2 (nSMase 2) contributes an important role in regulating eHEV biogenesis, although the detailed mechanisms remain unclear. The question mark denotes an unknown or unclear process and molecular mechanism