Researchers from the Institute of Virology and AIDS Research at The First Hospital of Jilin University, Changchun, Jilin-China, and the Chinese Academy of Medical Sciences, Changchun, Jilin-China, have made a significant breakthrough in the fight against the COVID-19 virus. Their study focuses on a host protein called PRPF19 and its role in inhibiting SARS-CoV-2 infection by degrading a viral accessory protein called ORF6.
SARS-CoV-2, the virus responsible for COVID-19, has evolved mechanisms to suppress the production of interferons, which are crucial for the antiviral response. ORF6 plays a pivotal role in evading the host immune system by inhibiting interferon responses. The researchers discovered that the CUL4B-DDB1-PRPF19 E3 Ubiquitin Ligase Complex acts as a mediator of proteasomal degradation of ORF6, thus suppressing SARS-CoV-2 replication.
Through a systematic investigation, the researchers uncovered the molecular details of how PRPF19 inhibits SARS-CoV-2 infection. They found that PRPF19 forms a complex with other proteins and catalyzes the degradation of ORF6. This degradation leads to the alleviation of interferon inhibition and the inhibition of SARS-CoV-2 replication.
The study also investigated the specificity of PRPF19 in targeting ORF6 for degradation. The researchers found that PRPF19 specifically affected ORF6 stability without impacting the stability of other viral proteins. This highlights the specific role of PRPF19 in the degradation of ORF6.
The researchers confirmed the interaction between PRPF19 and ORF6 through various experiments. They also discovered that PRPF19 catalyzes a specific type of ubiquitin chain responsible for ORF6 degradation.
ORF6 is a key antagonist of the interferon signaling pathway. The degradation of ORF6 by PRPF19 leads to the release of interferon-stimulated response element and the loss of interferon-antagonizing effects. PRPF19 also enhances the levels of interferon and interferon-stimulated genes, further demonstrating its role in antagonizing ORF6-mediated interferon signaling inhibition.
To assess the broader implications of PRPF19 in SARS-CoV-2 replication, the researchers examined its impact on viral protein expression and replication in cellular and animal models. They found that knockdown of PRPF19 increased the levels of viral proteins, indicating enhanced SARS-CoV-2 replication. Conversely, overexpression of PRPF19 restricted viral replication, establishing PRPF19 as a crucial factor in inhibiting SARS-CoV-2 replication.
The researchers also investigated the regulatory role of a post-translational modification called neddylation on CUL4B activity. They identified a potential activator of CUL4B neddylation called etoposide, which reduced the levels of ORF6 and inhibited SARS-CoV-2 replication in cellular and animal models. In a mouse infection model, etoposide treatment significantly reduced viral replication, lung lesions, and cytokine production.
This research provides valuable insights into the molecular mechanisms underlying SARS-CoV-2 pathogenesis. The CUL4B-DDB1-PRPF19 E3 Ubiquitin Ligase Complex plays a crucial role in inhibiting viral replication by degrading ORF6. The study also suggests etoposide as a potential therapeutic candidate for further investigation. These findings contribute to the ongoing efforts to develop targeted interventions against the COVID-19 pandemic. The research was published in the peer-reviewed journal mBio.