Activation of NF-κB and induction of proinflammatory cytokine expressions mediated by ORF7a protein of SARS-CoV-2

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent for coronavirus disease 2019 (COVID-19) that emerged in human populations recently. Severely ill COVID-19 patients exhibit the elevation of proinflammatory cytokines, and such an unbalanced production of proinflammatory cytokines is linked to acute respiratory distress syndrome with high mortality in COVID-19 patients. Our study provides evidence that the ORF3a, M, ORF7a, and N proteins of SARS-CoV-2 were NF-κB activators. The viral sequence from infected zoo lions belonged to clade V, and a single mutation of G251V is found for ORF3a gene compared to all other clades. No significant functional difference was found for clade V ORF3a, indicating the NF-κB activation is conserved among COVID-19 variants. Of the four viral proteins, the ORF7a protein induced the NF-κB dictated proinflammatory cytokines including IL-1α, IL-1β, IL-6, IL-8, IL-10, TNF-α, and IFNβ. The ORF7a protein also induced IL-3, IL-4, IL-7, IL-23. Of 15 different chemokines examined in the study, CCL11, CCL17, CCL19, CCL20, CCL21, CCL22, CCL25, CCL26, CCL27, and CXCL9 were significantly upregulated by ORF7. These cytokines and chemokines were frequently elevated in severely ill COVID-19 patients. Our data provide an insight into how SARS-CoV-2 modulates NF-κB signaling and inflammatory cytokine expressions. The ORF7a protein may be a desirable target for strategic developments to minimize uncontrolled inflammation in COVID-19 patients.

Expansion of a SARS-CoV-2 Delta variant with an 872 nt deletion encompassing ORF7a, ORF7b and ORF8, Poland, July to August 2021

“…The deletions within the ORF7a and ORF7b region have also previously been reported [ 15 - 18 ]. ORF7a activates the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kappa B) pathway and induces proinflammatory cytokine expression [ 19 , 20 ]. The function of ORF7b is largely unknown, but a recent study has shown that the protein activates the type-I interferon (IFN) signalling pathway and promotes expression of IFN-beta, interleukin (IL)-6, and tumor necrosis factor (TNF)-alpha, which induce apoptosis [ 21 ].…”

The Immunology of SARS-CoV-2 Infection and Vaccines in Solid Organ Transplant Recipients

“…The innate immune response to SARS-CoV-2 is crucial for determining the fate of COVID-19 symptomatology. SARS-CoV-2 hampers the IFN pathway and stimulates the hyperproduction of proinflammatory cytokines and chemokines via NF-κB activation, which is conserved among COVID-19 variants [ 29 , 30 ]. Overall, an exuberant innate immunoinflammatory response is a hallmark of severe COVID-19.…”

COVID-19 Is a Multi-Organ Aggressor: Epigenetic and Clinical Marks

“…Although other molecules and pathways (e.g. nuclear factor erythroid 2-related factor 2/Nrf2 and NLRP3) could also be interesting to be mentioned and included in this section (184,185,272), we decided to focus on the AHR due to its prominent roles in diverse diseases, including COVID-19. The AHR is a ligand-activating transcription factor that may be activated in response to infection.…”