SARS-CoV-2 Accessory Protein ORF7b Mediates Tumor Necrosis Factor-α-Induced Apoptosis in Cells

Area of Science:

• Virology
• Immunology
• Molecular Biology

Background:

• Coronaviruses utilize accessory proteins for virus-host interactions and immune modulation.
• Known SARS-CoV-2 accessory proteins (ORF3a, ORF6, ORF8) have documented roles in apoptosis and interferon signaling.
• The specific function of SARS-CoV-2 accessory protein ORF7b remains largely uncharacterized.

Purpose of the Study:

• To investigate the apoptosis-inducing activity of SARS-CoV-2 accessory protein ORF7b.
• To examine ORF7b's impact on host innate immune responses, including cytokine expression and interferon signaling.
• To elucidate the role of ORF7b in the pathogenicity of SARS-CoV-2.

Main Methods:

• Cell-based assays were used to assess apoptosis induction by ORF7b.
• Cytokine levels (IFN-β, TNF-α, IL-6) were measured.
• Activation of the type-I interferon signaling pathway via IRF3 phosphorylation was analyzed.

Main Results:

• SARS-CoV-2 ORF7b significantly promoted the expression of IFN-β, TNF-α, and IL-6.
• ORF7b activated type-I interferon signaling through IRF3 phosphorylation.
• ORF7b was found to activate TNFα-induced apoptosis in HEK293T and Vero E6 cells.

Conclusions:

• SARS-CoV-2 accessory protein ORF7b enhances innate immune responses by promoting cytokine expression and activating interferon signaling.
• ORF7b contributes to viral pathogenicity by inducing apoptosis.
• These findings deepen the understanding of SARS-CoV-2-host interactions and the function of its accessory proteins.