Antiviral function of BET protein against SARS-CoV-2 infection

To contain the ongoing pandemic of coronavirus disease 2019 (COVID-19), caused by the rapid spread of the serious acute respiratory disease coronavirus-2 (SARS-CoV-2), scientists are working on a new vaccine. And developed a cure. However, the available COVID-19 vaccine was designed against the original SARS-CoV-2 strain first reported in Wuhan, China in late December 2019, and viral evolution threatened them. increase. Effectiveness.. Therefore, it is imperative to develop more effective treatments to reduce the infection and mortality rates caused by the new SARS-CoV-2 mutants.

Characteristics and functions of BET protein

Proteins in the bromodomain and extraterminal domain (BET) families include BRD2, BRD3, BRD4, and BRDT. Characteristics of BET protein family members include the presence of two highly conserved N-terminal bromodomains (BD) and extra-terminal (ET) domains. Previous studies have pointed out that BET interacts with histones and cellular transcriptional mechanisms.

One of the important roles of BD is its function as a genuine leader domain of acetylated lysine for histone and non-histone proteins. These proteins are molecular targets for small molecule BET inhibitors (eg, JQ1). Early studies have shown that the ET domain has lower protein binding properties than BD.

BET proteins are involved in many cellular functions such as chromatin remodeling, cell proliferation, and gene expression. Among the BET proteins, BRD4 is a widely studied protein that exists in a variety of splice isoforms: long (BRD4L) and short (BRD4S) isoforms. Intermediate or third isoforms were found only in osteosarcoma cells. Scientists have shown that BRD2, BRD3, and BRD4 interact with the viral proteins of herpesviruses, flaviviruses, and papillomaviruses.

The role of BET in viral infections

Patients infected with SARS-CoV-2 often experience impaired type I interferon (IFN-I) response and overproduction of inflammatory cytokines. BRD4 is recognized as an antiviral gene and as a potent coactivator of inflammatory cytokines. In this regard, scientists have reported that BRD4 co-activates the interferon-stimulating gene (ISG) in the lung during viral infection by using P-TEFb. It also causes pro-inflammatory reactions in chronic obstructive pulmonary disease, pulmonary fibrosis, and asthma.

Interestingly, previous studies have shown that BET inhibitors can successfully attenuate the transcriptional activation of antiviral responses in influenza A infections. In addition, recent studies have confirmed that BRD4 and BRD2 are reliable interacting factors for the SARS-CoV-2E protein.

Most importantly, BRD2 functions as a transcriptional regulator of angiotensin converting enzyme 2 (ACE2), the entry point for the SARS-CoV-2 virus. These studies also show that knockout of the BRD2 gene or prophylactic application of BET inhibitors reduces ACE2 expression and thus reduces viral infection.

Given a fragment of historical evidence for BRD2 and BRD4 associated with viral infections, researchers recently evaluated the function of all relevant BET proteins during COVID-19 infection. In this regard, they reported that inhibition of the BET protein after viral entry, or knockout of the BRD3 or BRD4 gene in the cell, led to overexpression of ACE2, which significantly enhances viral replication.This study is available at bioRxiv* Preprint server.

Host SARS-CoV-2E and BET proteins

In this study, researchers suggest that the BET protein (BRD4> BRD3> BRD2) has significant antiviral function, especially after SARS-CoV-2 invades the host cell. In addition, the BET protein is essential for type I interferon response and complete induction of IL-6 inflammatory cytokines and may inhibit COVID-19 infection at the post-entry stage. In addition, researchers said viral replication intensified after inactivation of the BET protein by chemical or genetic methods.

This study revealed that the SARS-CoV-2 E protein antagonizes a new function, namely the expression of interferon and ISG. In particular, researchers have reported that the acetylated form of the viral E protein can effectively prevent antiviral function by binding to the second bromodomain of BRD4. This study reported that among the BET proteins, BRD2 is the most proviral due to its ability to actively regulate ACE2 expression.

In addition, BRD4 has a powerful antiviral function due to the role of the coactivator in inducing the interferon gene. BRD2 and BRD4 share 70% sequence similarity at the N-terminus, but the difference lies in the domain structure.

BET protein is a positive regulator of ACE2 expression A. RT-qPCR of ACE2 RNA isolated from Calu3 cells with BETKO shown. The data is represented in relation to RNP-only cells. The average of three independent experiments analyzed by triple ± SEM is shown and compared with the RNP-only sample by ANOVA: **** p <0.0001. B. Survival of A549-ACE2 cells treated with DMSO (vehicle), JQ1 (500nM), dBET6 (500nM), and ABBV-744 (500nM) for 48 hours compared to DMSO. C. Survival rate compared to DMSO of Calu3 cells treated with DMSO (vehicle), JQ1 (500nM), and dBET6 (500nM) for 48 hours.

Scientists also found increased viral replication, hypothermia and hyperthermia, severe weight loss, and intestinal inflammation in a K18-hACE2 mouse model treated with SARS-CoV-2 infection and BET inhibitors. Did.

The findings are consistent with previous studies reporting that therapeutic application of BET inhibitors to K18-hACE2 mice resulted in severe lung lesions and significant viral RNA in the lungs. This study emphasizes the importance of the BET protein as a positive regulator of antiviral gene expression.

Conclusion

Current studies reveal the therapeutic impact of BET inhibitors during COVID-19 infection. Researchers have shed new light on the antiviral function of BET proteins during infection. The authors found that the use of BET inhibitors during SARS-CoV-2 infection was Viral load..

*Important Notices

bioRxiv Publish preliminary scientific reports that should not be considered definitive as they have not been peer-reviewed, guide clinical practice / health-related behaviors, and should not be treated as established information.