1.A.149.  The ORF3 Protein of Hepititis E Virus (ORF3-HEV) Family 

ORF3 of Hepititis E. Virus is a small multifunctional phosphoprotein involved in virion morphogenesis, egress and counteracting host innate immunity (Yamada et al. 2009, Nagashima et al. 2011, Ding et al. 2017, Gouttenoire et al. 2018).  It plays critical roles in the final steps of viral release by interacting with host TSG101, a member of the vacuolar protein-sorting pathway and using other cellular host proteins involved in the vesicle formation pathway (Yamada et al. 2009, Nagashima et al. 2011). It acts as a viroporin and forms ion conductive pores, allowing viral particle release (Ding et al. 2017).  It impairs the generation of type I interferon by down-regulating host TLR3 and TLR7 as well as their downstream signaling pathways (He et al. 2016, Lei et al. 2018).  It down-regulates the phosphorylation of host IRF3 via the interaction with host SIRP-alpha, thereby inhibiting IFN-I expression (Huang et al. 2016), and interacts with host microtubules (Kannan et al. 2009).

Hepatitis E virus (HEV) egresses from infected hepatocytes as quasienveloped particles containing open reading frame 3 (ORF3) protein (Srivastava et al. 2023). HEV ORF3 (small phosphoprotein) interacts with host proteins to establish a favourable environment for virus replication. It is a functional viroporin that plays an important role during virus release. Evidence suggests that pORF3 plays a pivotal role in inducing Beclin1-mediated autophagy that helps HEV-1 replication as well as its exit from cells. ORF3 interacts with host proteins involved in regulation of transcriptional activity, immune response, cellular and molecular processes, and modulation of autophagy, by interacting with proteins, DAPK1, ATG2B, ATG16L2 and also several histone deacetylases (HDACs). For autophagy induction, ORF3 utilizes the non-canonical NF-κB2 pathway and sequesters p52NF-κB and HDAC2 to upregulate DAPK1 expression, leading to enhanced Beclin1 phosphorylation. By sequestering several HDACs, HEV may prevent histone deacetylation to maintain overall cellular transcription intact to promote cell survival. These findings highlight a novel crosstalk between cell survival pathways participating in ORF3-mediated autophagy (Srivastava et al. 2023).