One beautiful aspect of Science is that it can inspire people and influence their lives. The story of our publication on the circadian regulation of flavivirus replication  began with the dedication of our post-doc Alan. It inspired PhD student Helene to join the lab, and is now sparking the interest of Tatiana, who is just starting her PhD. We will present these three perspectives to describe what happened after the paper.
A real adventure for Alan: dissecting the molecular link between the circadian clock and viral infection
After working in translational medicine, I was looking for a change, a research area with a more exploratory nature. It was at that time that I first met Jane and she discussed some recent data showing a day-time variation in hepatitis C viral RNA levels in patients following a liver transplant . She asked whether I would be interested in exploring this largely unknown area and to understand whether the circadian clock can talk to viruses - I accepted the challenge with a big YES. After several years of hard work and with many great collaborators, we published our story last year in one of our favourite journals, Nature Communications, where we provided the first molecular basis for how the circadian pathway regulates hepatitis C virus (HCV) replication. In summary we discovered:
- HCV entry is time of day dependent due to the circadian expression of host receptors that are essential for virus uptake into cells.
- After entering the cell, the replication of the viral RNA genome is influenced by circadian regulated lipid genesis pathways.
- We extended these observations to two other flaviviruses, Dengue and Zika viruses.
Clock-virus interaction beyond flaviviruses
Our paper encouraged me to pursue this direction further, and asking the right scientific question is vital to a successful project. The flavivirus family is comprised of RNA viruses- how about DNA viruses? Could the circadian transcriptional feedback loop directly regulate the transcription of viral DNA? Do DNA viruses have circadian regulatory motifs? Which DNA virus shall I start with? These are important questions for the next steps!
Since the liver is a well-recognised circadian regulated organ, I was interested to study another clinically important virus that infects the liver – Hepatitis B virus (HBV). Despite having a very small DNA genome, the virus encodes multiple genetic elements that can bind circadian transcription factors. Interestingly, these motifs are conserved among all HBV genotypes and higher primates highlighting a conserved evolutionary role for the circadian pathway to regulate these viruses!
Perfect timing for a new project for Helene
Circadian rhythms have always fascinated me; they are everywhere: I knew that they could influence day and night cycles, our daily routines, our nutrition, sleep, psyche and already Plato wrote
“Rhythm and harmony find their way into the inward places of the soul”
- Plato, The Republic, c. 375 BC
But reading this paper I discovered evidence for their regulation of viral infections – wow! It convinced me immediately to start researching this in more detail.
Is HIV running out of time?
While the paper focused on flaviviruses, my interest focuses on Human Immunodeficiency Virus 1 (HIV‐1), which is a life‐threatening pathogen that still lacks a curative therapy or vaccine. How impressive would it be if modifying the circadian clock could influence HIV replication? That is exactly what we tried using pharmacological activation of the circadian component REV-ERB, and guess what: it worked! We were able to show how a synthetic REV-ERB agonist inhibits HIV-1 replication in cellular models . This may provide an additional drug class as adjuvants or to aid in current combination therapy and could potentially be used in “shock and kill” HIV eradication strategies.
Circadian rhythms and global pandemics
We reviewed the literature in the field and found more and more evidence of the interplay between the circadian clock and viral infections . When the SARS-CoV-2 pandemic started, we and others asked the obvious question: is SARS-CoV-2 circadian regulated? We are currently working on it and I can already give a hint that exciting results will be published soon.
Circadian biologist Tatiana explores the virus world
As a biochemist, I have always had an interest in life at the molecular level, and it fascinates me how this results in organisms that can adapt to a complex and ever-changing environment. This is why I found circadian rhythms so exciting- their synchronisation of life to the day-night cycle occurs at the level of the most fundamental processes inside the cell, from poly-adenylation of mRNA  to post-translational modification . I believe we can only fully understand processes that are subject to circadian regulation if we study them at all times of day (something which is frequently overlooked!).
I started researching the circadian system during my Master’s, and like many, the pandemic unexpectedly affected my work, but it also brought new insights into my field. During the summer of 2020, the European Biological Rhythms Society organised a virtual conference, the Chronobiology of COVID-19, and it was there that I was introduced to Jane’s work and interactions between the circadian system and viral replication, a connection that pivots on circadian control of transcription for both the host and the virus .
Now in the first year of my DPhil, I have taken the exciting opportunity to work with Jane and her lab to investigate the circadian regulation of hepatitis B virus replication.
Why should we care about circadian rhythms and viruses?
As we live in an era of shift work–related sleep disorders, social jet lag, and global viral pandemics, together with emergent viral drug resistance, exploiting biological rhythms could provide novel treatment modalities and new drugs for treating viral infections. It is time to combine our expertise in multidisciplinary approaches involving virology, circadian biology, immunology, and pharmacology to learn more about this exciting field of research.
- Zhuang, X., et al., The circadian clock components BMAL1 and REV-ERBalpha regulate flavivirus replication. Nat Commun, 2019. 10(1).
- Zhuang, X., et al., Daytime variation in hepatitis C virus replication kinetics following liver transplant.Wellcome Open Res, 2018. 3.
- Borrmann, H., et al., Pharmacological activation of the circadian component REV-ERB inhibits HIV-1 replication. Sci Rep, 2020. 10(1).
- Borrmann, H., McKeating, J.A., and Zhuang, X., The Circadian Clock and Viral Infections. Journal of Biological Rhythms. Online ahead of print.
- Mateos, J.L., et al., Beyond Transcription: Fine-Tuning of Circadian Timekeeping by Post-Transcriptional Regulation. Genes (Basel), 2018. 9(12).
- Durgan, D.J., et al., O-GlcNAcylation, novel post-translational modification linking myocardial metabolism and cardiomyocyte circadian clock. J Biol Chem, 2011. 286(52).
- Sengupta, S., et al., Clocks, viruses and immunity: lessons for the COVID-19 pandemic. Journal of Biological Rhythms, 2020, In press (pending revision).
Picture 1: The Native Antigen Company, Dengue Virus Serotype 3 NS1 Protein (HEK293), accessed 30 November 2020, <https://thenativeantigencompany.com/products/dengue-virus-serotype-3-ns1-protein-hek293/>
Picture 2: Microbiology Society, Viral Hepatitis and Hepatocellular Carcinoma, accessed 30 November 2020, <https://microbiologysociety.org/resource_library/knowledge-search/viral-hepatitis-and-hepatocellular-carcinoma.html>
Picture 3: Kuhn and Rossmann research groups Purdue University, A representation of the surface of the Zika virus, with protruding envelope glycoproteins shown in red, accessed 30 November 2020, <https://www.nih.gov/news-events/nih-research-matters/zika-virus-structure-revealed>
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