Interaction of coronavirus E protein with BRD2 plays important regulatory roles in viral replication and induction of pro-inflammatory response.

The devastating COVID-19 pandemic has urged continuous efforts to uncover innovative intervention measures through a thorough understanding of viral and associated host protein functions. In this study, we investigate the interaction of coronavirus E protein with BRD2, a member of the bromodomain and extra-terminal (BET) protein family, and the mechanism underlying the regulatory role of BRD2 in promoting pro-inflammatory responses during coronavirus infection, based on the reported potential interaction of BRD2 with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) E protein and our transcriptomic assay. We show that coronavirus infection significantly upregulates the expression of pro-inflammatory cytokines and BET family genes and activates the NF-κB pathway, although the ion channel (IC) activity of the avian infectious bronchitis virus (IBV) E protein only minimally affects the upregulation of BRD2 transcription. Furthermore, BRD2 was verified to interact with the E protein from IBV, SARS-CoV, and SARS-CoV-2, via the BDII-containing C-terminal region of BRD2 and the C-terminal region of the E protein. This interaction resulted in the partial translocation of BRD2 from the nucleus to the cytoplasm in IBV-infected cells and its close association with viral particles. Overexpression of BRD2 and IBV E protein independently induced the expression of pro-inflammatory cytokines, and a synergistic role was demonstrated in cells co-expressing the two proteins. BRD2 was further found to activate the NF-κB signaling pathway and enhance the expression of pro-inflammatory cytokines IL-6, IL-8, and TNF-α at the mRNA level. Conversely, knockdown of BRD2 promotes viral replication and apoptosis. These findings underscore the interaction between BRD2 and E protein, elucidating their roles in regulating coronavirus replication and promoting the pro-inflammatory response.IMPORTANCESevere coronavirus infections usually result in excessive secretion of inflammatory cytokines and chemokines, leading to cell death and ultimately collapse of the immune system with fatal outcomes. So far, intensive studies on host-pathogen interactions have partially elucidated the immunopathogenesis of COVID-19 and other coronavirus infections. This study reveals that coronavirus infection induces the expression of BRD2 and activates the NF-κB pathway. BRD2 interacts with coronavirus E protein, and the two proteins work together to play a synergistic role to promote pro-inflammatory response during coronavirus infection. Furthermore, BRD2 was shown to independently activate the NF-κB pathway and enhance the expression of IL-6, IL-8, TNF-α, and several other proteins related to the pro-inflammatory and inflammatory responses. The interaction of BRD2 with coronavirus E protein and its regulatory role in inflammation would make it a potential therapeutic target for severe coronavirus infections.