# The NSP5, ORF6 and NSP13 of SARS‐CoV‐2 Cooperate to Modulate Inflammatory Cell Death Activation

## TL;DR

SARS-CoV-2 proteins NSP5, ORF6, and NSP13 work together to block cell death pathways, which may worsen outcomes in co-infections with influenza A virus.

## Contribution

The study reveals how SARS-CoV-2 inhibits ZBP1-mediated cell death through specific viral proteins, linking this to increased mortality in co-infections.

## Key findings

- SARS-CoV-2 uses NSP5 and ORF6 to block caspase-8 activity, preventing apoptosis and pyroptosis.
- NSP13 suppresses necroptosis by interfering with RIPK3-ZBP1 interactions.
- Co-infection with influenza A virus and SARS-CoV-2 increases disease severity and mortality in mice.

## Abstract

Programmed cell death is a pivotal mechanism of cell‐autonomous immune defense against viral infections. Recent studies indicate that both blocking and promoting cell death negatively affect coronavirus replication, implying that coronaviruses may fine‐tune cell death pathways to optimize their propagation. However, the mechanisms underlying this remain poorly understood. Here, it is verified that coronaviruses induce the formation of a Z‐DNA‐binding protein 1 (ZBP1)‐initiated cell death complex involving ZBP1, Z‐RNA, receptor‐interacting serine/threonine‐protein kinase 3 (RIPK3), and caspase‐8, thereby triggering apoptosis, pyroptosis, and necroptosis in human bronchial epithelial cells. To impede the activation of apoptosis and pyroptosis, NSP5 and ORF6 of SARS‐CoV‐2 concurrently inhibit caspase‐8 activity by targeting its large and small subunits, respectively. Additionally, NSP13, the viral helicase, interacts with RIPK3 to impair its binding to ZBP1, thus suppressing ZBP1‐initiated necroptosis. This inhibitory effect on cell death is likely conserved across β‐coronaviruses. Furthermore, co‐infection of influenza A virus and SARS‐CoV‐2 is demonstrated to exacerbate disease severity, although the mechanisms remain unclear. These findings suggest that β‐coronavirus‐induced inhibition of cell death enhances influenza A virus replication and worsens inflammation during their co‐infection, ultimately increasing mortality in mice. This research provides valuable insights into the regulation of coronavirus‐induced cell death, offering potential therapeutic strategies for combating highly pathogenic coronavirus infections.

ZBP1 is capable of initiating a large cell death complex to induce programmed cell death during SARS‐CoV‐2 infection. However, SARS‐CoV‐2 can inhibit the activation of ZBP1‐mediated cell death by targeting key components of this complex. This suppression of ZBP1‐mediated cell death may account for the increased mortality observed in patients co‐infected with influenza A virus and SARS‐CoV‐2.