Regulation of the ER Stress Response by the Ion Channel Activity of the Infectious Bronchitis Coronavirus Envelope Protein Modulates Virion Release, Apoptosis, Viral Fitness, and Pathogenesis

Abstract

Coronavirus (CoV) envelope (E) protein is a small structural protein critical for virion morphogenesis and release. The recently characterized E protein ion channel activity (EIC) has also been implicated in modulating viral pathogenesis. In this study, we used infectious bronchitis coronavirus (IBV) as a model to study EIC. Two recombinant IBVs (rIBVs) harboring EIC-inactivating mutations -rT16A and rA26F -were serially passaged, and several compensatory mutations were identified in the transmembrane domain (TMD). Two rIBVs harboring these putative EICreverting mutations -rT16A/A26V and rA26F/F14N -were recovered. Compared with the parental rIBV-p65 control, all four EIC mutants exhibited comparable levels of intracellular RNA synthesis, structural protein production, and virion assembly. Our results showed that the IBV EIC contributed to the induction of ER stress response, as up-regulation of ER stress-related genes was markedly reduced in cells infected with the EIC-defective mutants. EIC-defective mutants also formed smaller plaques, released significantly less infectious virions into the culture supernatant, and had lower levels of viral fitness in cell culture. Significantly, all these defective phenotypes were restored in cells infected with the putative EIC revertants. EIC mutations were also implicated in regulating IBV-induced apoptosis, induction of pro-inflammatory cytokines, and viral pathogenicity in vivo. Taken together, this study highlights the importance of CoV EIC in modulating virion release and various aspects of CoV -host interaction.

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“…Among the structural proteins of the SARS-CoV-2, E protein is considered as a potential drug target. The E protein is relatively small (75 aa), and plays a significant role in the viral morphogenesis and assembly [66]. The E protein is known to act as viroporins that assemble into host membrane forming protein-lipid pores involved in ion transport.…”

Bulk and single-cell gene expression profiling of SARS-CoV-2 infected human cell lines identifies molecular targets for therapeutic intervention

“…This is then in turn integrated with double stranded RNA sensing at the level of eukaryotic initiation factor 2 alpha (eIF2alpha) phosphorylation [14]. The ER stress response is likely attenuated by the viral E protein [15,16]. Accordingly, heat shock proteins (HSPs), which ameliorate ER stress, have been described to be generally relevant in virus infections [17].…”

Similarities between the effect of SARS-CoV-2 and HCV on the cellular level, and the possible role of ion channels in COVID19 progression: a review of potential targets for diagnosis and treatment

“…Importantly, apart from enhancing the rate of viral replication, viroporins also enhance the pathogenicity of viruses [ 29 ]. In the recent past, the pathogenicity of viruses has been connected to ion conductivity or other roles, such as encoding of ion channels or using viral proteins as ion channels, as exemplified by the SARS-CoV accessory proteins 3a and 8a [ 35 ].…”