Newswise: The COVID-19 pandemic has wreaked havoc across the globe. Although most infected people experience mild symptoms, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus can cause severe pneumonia, acute respiratory distress syndrome and organ damage in some patients, especially those with comorbidities. Symptoms are usually triggered by an extreme immune response that causes high levels of cytokines, known as a “cytokine storm.” However, the detailed mechanisms of proinflammatory cytokine production are not fully understood.
Previous studies have reported that the NF-κB family of transcription factors is an integral component of the process. This makes NF-κB signaling an important therapeutic target related to COVID. Interestingly, viral nucleocapsid (N) proteins can also interact with the transforming growth factor-activated kinase 1 (TAK1) and IκB kinase (IKK) complexes to activate the NF-κB pathway. Although there has been speculation to define these interactions, scientists are still trying to determine which viral genes are primarily involved.
To unravel these mechanisms, a team of researchers, including Prof. Takayuki Murata and Dr. Hironiri Nishitisuji of the Fujita Health University School of Medicine in Japan, conducted a comprehensive study that was recently published in the journal mBio (available online 20 July 2022). ). The team, which also included Dr. Kunitada Shimotohno of the National Center for Global Health and Medicine, Japan, screened 22 SARS-CoV-2 proteins to identify those that might activate NF-κB signaling. In the context of the motivation behind the study, Professor Murata explains: “We tried to identify the modifiers of cellular signals, especially those of inflammatory signals, because inflammation is central to the symptoms of COVID-19.”
The team found that two core SARS-CoV-2 proteins, nonstructural protein 6 (NSP6) and open reading frame 7a (ORF7a), were essential for activating the NF-κB pathway. Consistent with their hypothesis, expression of NSP6 and ORF7a increased the levels of proinflammatory cytokines such as interleukin 8 (IL-8) and interferon-gamma-induced protein 10 (IP-10). This suggests that viral components may be activating NF-κB to trigger the cytokine storm in the later stages of infection, as infected people experience extreme symptoms during severe COVID-19.
Using CRISPR-Cas9 knockout studies, the team further discovered that NSP6 and ORF7a act by transforming growth factor b-activated kinase 1 (TAK1) and NF-κB essential modulator (NEMO), which are players crucial in the NF-κB pathway. Interestingly, knockdown of TAK1/NEMO significantly reduced NF-κB activation induced by SARS-CoV-2, indicating that these proteins could be considered as potential targets for the treatment of COVID-19.
The researchers then studied the ubiquitination of NSP6 and ORF7a, which could be critical for exerting their downstream effects. Professor Murata and his team found that tripartite motif containing 13 (TRIM 13) and RING finger protein 121 (RNF121) were required for the ubiquitination of NSP6 and ORF7a, respectively. This process appeared essential to recruit NEMO to the NSP6-TAK1 complex and activate NF-κB.
Since suppression of cytokine production and replication of SARS-CoV-2 is halted by blocking NF-κB signaling, it is possible that the virus hijacked the pathway for its replication. “We propose that NF-κB suppression of pro-inflammatory cytokine responses while maintaining adequate immunity for viral clearance may be a good strategy to stop the virus,” adds Professor Murata.
Optimistic about the importance of their research, the team anticipates that the study could add to the toolbox of existing treatment approaches and ideas for COVID-19. “Our results provide a better understanding of the pathogenesis of SARS-CoV-2 and the host’s immune response to infection,” says Professor Murata. “Inhibitors of the molecules that mediate the activation of NF-κB can be used to reduce the severity of the symptoms of COVID-19,” he concludes.
***
Reference DOI: https://doi.org/10.1128/mbio.00971-22
About Fujita Health University Fujita Health University is a private university located in Toyoake, Aichi, Japan. It was founded in 1964 and is home to one of Japan’s largest teaching university hospitals in terms of number of beds. With more than 900 faculty members, the university is committed to providing diverse academic opportunities to international students. Fujita Health University has been ranked eighth among all universities and second among all private universities in Japan in the Times Higher Education (THE) World University Rankings 2020. THE University Impact Rankings 2019 visualized university initiatives for goals of sustainable development (ODS). For the SDG of “good health and well-being,” Fujita Health University ranked second among all universities and number one among private universities in Japan. The university became the first Japanese university to host “The Asia Universities Summit” in June 2021. The founding philosophy of the university is “Our Creativity for the People (DOKUSOU-ICHIRI)”, which reflects the belief that, as with the university’s alumni and alumni, today’s students also unlock their future by harnessing their creativity.
Website: https://www.fujita-hu.ac.jp/en/index.html
About Professor Takayuki Murata of Fujita Health UniversityProf. Takayuki Murata is a professor in the Department of Virology and Parasitology, Fujita Health University School of Medicine, Aichi, Japan. He received his doctorate in Medical Sciences from Nagoya University. Currently, he is also a visiting professor at Nagoya University, Japan. His main research interests include virology, tumor biology, Epstein-Barr virus, hepatitis B virus and SARS-CoV-2. He is a member of the prestigious American Society of Microbiology and the Fujita Medical Society. In his scientific career of more than two decades, he has more than 100 publications to his credit and has received numerous research grants.
Funding information This work was supported in part by the Takeda Science Foundation