SARS-CoV-2 ORF8 Forms Intracellular Aggregates and Inhibits IFN-Induced Antiviral Gene Expression in Human Lung Epithelial Cells

Abstract

Infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes COVID-19, a disease that involves significant lung tissue damage. How SARS-CoV-2 infection leads to lung injury remains elusive. The open reading frame 8 (ORF8) protein of SARS-CoV-2 (ORF8(SARS-CoV-2)) is a unique accessory protein, yet little is known about its cellular function. We examined the cellular distribution of ORF8(SARS-CoV-2) and its role in the regulation of human lung epithelial cell proliferation and antiviral immunity. Using live imaging and immunofluorescent staining analyses, we found that ectopically expressed ORF8(SARS-CoV-2) forms aggregates in the cytosol and nuclear compartments of lung epithelial cells. Using in silico bioinformatic analysis, we found that ORF8(SARS-CoV-2) possesses an intrinsic aggregation characteristic at its N-terminal residues 1-18. Cell culture did not reveal any effects of ORF8(SARS-CoV-2) expression on lung epithelial cell proliferation and cell cycle progression, suggesting that ORF8(SARS-CoV-2) aggregates do not affect these cellular processes. Interestingly, ectopic expression of ORF8(SARS-CoV-2) in lung epithelial cells suppressed basal expression of several antiviral molecules, including DHX58, ZBP1, MX1, and MX2. In addition, expression of ORF8(SARS-CoV-2) attenuated the induction of antiviral molecules by IFN gamma but not by IFN beta in lung epithelial cells. Taken together, ORF8(SARS-CoV-2) is a unique viral accessory protein that forms aggregates when expressing in lung epithelial cells. It potently inhibits the expression of lung cellular anti-viral proteins at baseline and in response to IFN gamma in lung epithelial cells, which may facilitate SARS-CoV-2 escape from the host antiviral innate immune response during early viral infection. In addition, it seems that formation of ORF8(SARS-CoV-2) aggregate is independent from the viral infection. Thus, it would be interesting to examine whether any COVID-19 patients exhibit persistent ORF8 SARS-CoV-2 expression after recovering from SARS-CoV-2 infection. If so, the pathogenic effect of prolonged ORF8(SARS-CoV-2) expression and its association with post-COVID symptoms warrant investigation in the future.

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original_citation: Geng H, Subramanian S, Wu LT, Bu HF, Wang X, Du C, De Plaen IG, Tan XD. SARS-CoV-2 ORF8 Forms Intracellular Aggregates and Inhibits IFN gamma-Induced Antiviral Gene Expression in Human Lung Epithelial Cells. Frontiers in Immunology. 2021;12:11.

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