COVID-19 News: South Korean Study Shows That SARS-CoV-2 Exploits Cellular RAD51 To Promote Viral Propagation!

COVID-19 News: The relentless evolution of viruses presents a constant challenge to our efforts to combat infectious diseases. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), has proven to be no exception. Emerging in December 2019, SARS-CoV-2 swiftly spread globally, infecting over 780 million people and causing over 7.2 million deaths to date. As a Betacoronavirus, SARS-CoV-2 shares similarities with other respiratory pathogens like severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV).


Vero E6 cells were either mock infected or infected with wild-type (MOI = 0.01), Delta (MOI = 0.1), and Omicron stealth (MOI = 4) variant of SARS-CoV-2, respectively, for 1 h and further cultured in fresh media. At 24 h postinfection, cells were fixed with 4% paraformaldehyde, and immunofluorescence staining was performed by using either J2 antibody and FITC-conjugated goat anti-mouse IgG to detect dsRNA (green) or anti-Rad51 antibody and TRITC-conjugated donkey anti-rabbit IgG to detect RAD51 (red). Cells were counterstained with 4′,6′-diamidino-2-phenylindole to label nuclei (blue). Plot profile corresponding to the white arrow is traced in the merged panel. Scale bar = 20 µm.

While numerous prophylactic vaccines have been deployed to mitigate the impact of COVID-19, the continuous emergence of variants of concern (VOCs) challenges the effectiveness of existing strategies. Notably, the Delta variant (B.1.617.2) was succeeded by the Omicron variant (B.1.1.529), known for its heightened immune evasion capabilities. In this dynamic landscape, the search for effective antiviral therapies remains imperative.
 
A recent study covered in this COVID-19 News report by the Korea Zoonosis Research Institute at Jeonbuk National University sheds light on the potential role of RAD51, a DNA repair protein, in the propagation of SARS-CoV-2. This discovery opens the door to exploring RAD51 inhibitors as a novel class of therapeutics for COVID-19 treatment.
 
RAD51 and Viral Replication
RAD51, a pivotal player in homologous recombination (HR) and DNA repair, has previously been implicated in the replication processes of various viruses, including human immunodeficiency virus (HIV), human papillomavirus (HPV), hepatitis B virus (HBV), and hepatitis C virus (HCV). The current study builds on previous findings indicating that hepatitis C virus exploits cellular RAD51 for viral propagation.
 
The investigation sought to ascertain whether SARS-CoV-2, an RNA virus like HCV, similarly exploits RAD51 for its propagation. The results were compelling - silencing RAD51 impaired SARS-CoV-2 propagation, underscoring the protein's significance in the virus's life cycle. Furthermore, the study revealed that RAD51 colocalized with SARS-CoV-2 RNA in infected cells, suggesting the formation of a replication complex.
 
RAD51 Interaction with SARS-CoV-2 3CL Protease
Intriguingly, the study unveiled a novel facet of the interaction bet ween RAD51 and SARS-CoV-2. The investigation identified an interaction between RAD51 and the virus's 3CL protease, a key enzyme in viral replication. This interaction provides valuable insights into the mechanisms employed by SARS-CoV-2 to ensure its replication within host cells.
 
RAD51 Inhibitors as Potential Therapeutics
Building on these discoveries, the researchers explored the potential of RAD51 inhibitors as therapeutic agents for COVID-19. Among the inhibitors evaluated, B02, 4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), IBR2, and RI(dl)-2 exhibited significant promise in reducing RNA, protein, and infectious virion levels of both Wuhan and variant strains of SARS-CoV-2.
 
The study employed various RAD51 inhibitors, each with distinct modes of action. B02, for instance, inhibits RAD51 through interference with both single-stranded and double-stranded DNA binding. DIDS, a clinically used anion transporter inhibitor and chloride channel blocker, directly binds RAD51, affecting its homologous pairing and strand exchange activities. IBR2 disrupts the hydrophobic pocket of RAD51, inhibiting its oligomerization and filament formation. RI(dl)-2 specifically targets RAD51-mediated D-loop formation.
 
Molecular Docking Insights
To understand the structural basis of RAD51 inhibition and its impact on SARS-CoV-2 propagation, the researchers conducted molecular docking analyses. The results revealed that B02, DIDS, IBR2, and RI(dl)-2 exhibited high affinity at the dimerization interface of RAD51, highlighting their potential to interfere with the protein's function crucial for SARS-CoV-2 replication.
 
In Vivo Efficacy of RAD51 Inhibitor
To validate the therapeutic potential of RAD51 inhibitors in a live organism, the study focused on DIDS, which displayed exceptional anti-SARS-CoV-2 activity. Syrian hamsters were intranasally infected with SARS-CoV-2 and treated with DIDS. The results showed a significant reduction in infectious virus titer in the lungs of DIDS-treated hamsters. Moreover, DIDS demonstrated a modulatory effect on the host immune response, influencing the expression of pro-inflammatory cytokines and interferon-related genes.
 
Implications for COVID-19 Treatment
The findings from this comprehensive study contribute significant insights into the intricate interplay between SARS-CoV-2 and host cellular machinery, specifically highlighting the exploitation of RAD51 for viral propagation. The interaction between RAD51 and the virus's 3CL protease adds another layer to our understanding of viral replication strategies.
 
RAD51 inhibitors, particularly B02, DIDS, IBR2, and RI(dl)-2, exhibit promising potential as broad-spectrum antiviral agents against SARS-CoV-2. The structural details obtained through molecular docking analyses provide a rationale for their inhibitory effects on RAD51 and, consequently, on viral propagation.
 
The in vivo efficacy of DIDS in reducing infectious virus titers in Syrian hamsters further underscores the translational potential of RAD51 inhibitors. Notably, DIDS, a clinically used compound for other conditions, demonstrated a favorable safety profile and therapeutic impact on SARS-CoV-2 infection.
 
Considering the continuous evolution of SARS-CoV-2 and the emergence of new variants, the study's demonstration of the efficacy of RAD51 inhibitors against known variants, including Delta and Omicron, is particularly significant. Targeting conserved host proteins, such as RAD51, offers a potential advantage in developing therapeutics with a high genetic barrier to viral resistance.
 
Conclusion
In conclusion, this South Korean study presents a compelling case for RAD51 as a critical player in SARS-CoV-2 propagation and introduces RAD51 inhibitors as a promising avenue for COVID-19 therapeutics. The intricate details of RAD51 interaction with the virus, the structural insights gained through molecular docking analyses, and the in vivo efficacy of RAD51 inhibitors collectively support the potential repurposing of these compounds for COVID-19 treatment.
 
As the global community continues to grapple with the challenges posed by the pandemic, the pursuit of innovative therapeutic strategies remains crucial. The identification of RAD51 as a potential druggable target opens up new possibilities for developing effective antiviral agents. Further research is warranted to elucidate the molecular mechanisms underlying RAD51 inhibition and to explore additional RAD51 inhibitors, paving the way for the development of clinically viable therapeutics against COVID-19.
 
The study findings were published in the peer reviewed Journal of Virology.
https://journals.asm.org/doi/10.1128/jvi.01737-23
 
Thailand Medical News would also like to add that there are also other more worrisome implications from this study findings as the protein RAD51 is also involved directly and indirectly in the development and progression of various cancers, upregulation or downregulation of it can potentially have adverse effects. We will be covering on this in another coming article.
 
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