1/13
How RNA viruses can use their dsRNA intermediate state as a de facto latent state, facilitating viral persistence.
Positive single-stranded #RNA viruses have a replication cycle that includes a double-stranded RNA (dsRNA) intermediate state.
#virology @virology #virus #virome #ViralPersistence #InfectiousDisease
2/13
Now #dsRNA, unlike dsDNA, is inherently unstable and the two strands spontaneously separate to allow viral replication to continue.
In fact, they MUST separate for viral replication to continue.
3/13
The inherently unstable nature of dsRNA is partly explained by the fact that each strand is negatively charged, and there is an electrostatic repulsion between the two strands.
It is well known that positive charges stabilize dsRNA by electroshielding.
4/13
Now, many RNA viruses have a viral protein called a #viroporin, which creates pores in membranes such as the endoplasmic reticulum.
In some viruses, such as an #enterovirus, the viroporin is well-known. (2B protein)
In other viruses, the viroporin is better known for something else, as the viroporin function is not well appreciated.
For example, in a #flavivirus, the NS2A protein is known as a capsid-assembly protein. Its function as a viroporin is less well-known.https://doi.org/10.1080/21505594.2017.1356540
Picornaviruses are associated with acute and chronic diseases. The clinical manifestations of infections are often mild, but infections may also lead to respiratory symptoms, gastroenteritis, myocarditis, meningitis, hepatitis, and poliomyelitis, with serious impacts on human health and economic losses in animal husbandry. Thus far, research on picornaviruses has mainly focused on structural proteins such as VP1, whereas the non-structural protein 2B, which plays vital roles in the life cycle of the viruses and exhibits a viroporin or viroporin-like activity, has been overlooked. Viroporins are viral proteins containing at least one amphipathic Ξ±-helical structure, which oligomerizes to form transmembrane hydrophilic pores. In this review, we mainly summarize recent research data on the viroporin or viroporin-like activity of 2B proteins, which affects the biological function of the membrane, regulates cell death, and affects the host immune response. Considering these mechanisms, the potential application of the 2B protein as a candidate target for antiviral drug development is discussed, along with research challenges and prospects toward realizing a novel treatment strategy for picornavirus infections.
6/13
As the infection in the cell proceeds, the slowly increasing Ca2+ concentration in the cytoplasm begins to stabilize the previously unstable dsRNA intermediate state.
As a result, the dsRNA intermediate state becomes less and less likely to spontaneously separate into single strands.
Late in infection, the dsRNA state is fully stabilized and viral replication halts as dsRNA.
Quantitation of the viral RNA in this case yields equal numbers of + and - strands.
https://doi.org/10.1099/0022-1317-83-5-1087
The aetiology of post-polio syndrome may involve persistence of poliovirus (PV) in the CNS. PV persists in the CNS of infected paralysed mice for over a year after the acute phase of paralytic poliomyelitis. However, infectious PV particles cannot be recovered from homogenates of CNS from paralysed mice after the acute phase of disease, indicating that PV replication is restricted. To identify the molecular mechanism by which PV replication is limited, PV RNA synthesis was analysed by estimating the relative level of genomic (plus-strand) and complementary (minus-strand) PV RNA in the CNS of persistently infected mice. PV RNA replication decreased during the 6 months following onset of paralysis, due mainly to inhibition of plus-strand RNA synthesis. Thus, restriction of PV RNA synthesis may contribute to persistence by limiting virus replication in the mouse CNS. Interestingly, viral RNA replication was similarly inhibited in neuroblastoma IMR-32 cell cultures persistently infected with PV. This in vitro model thus shows that cellular factors play a role in the inhibition of viral RNA synthesis.
7/13
In this case, the virus might persist indefinitely in the cell, in a quasi-latent dsRNA intermediate state.
Although there are cellular proteins that can detect this dsRNA, human cells have no enzyme that can degrade this quasi-latent long dsRNA intermediate state.
So, although many RNA viruses do not have a "true" latent state, they may have the next best thing:
A very long-lived quasi-latent dsRNA intermediate state.
@Angie_rasmussen explains the significance below:
#ViralPersistence
8/13
A raised Ca2+ concentration in the cytoplasm can have many other consequences, as Ca2+ is a player in many different cellular processes.
These consequences take on a special complexity in neurons and muscle cells, as both these cell types can activate upon electrochemical stimulation.
For example, the T-type calcium channels in neurons could be rendered unusable by the slight membrane depolarization that occurs with a raised Ca2+ concentration.
https://doi.org/10.4161/chan.4.6.14106
9/13
Hypothesis:
When an infected neuron fires, there is a rapid flow of Ca2+ ions out of the cytoplasm as the ion pumps in the plasma membrane re-polarize the neuron appropriately.
Thus, neuronal firing might remove the excess intracellular Ca2+ ions, rendering the dsRNA intermediate state unstable, once again.
In this way, anything that causes infected neurons to fire might re-awaken viruses from the quasi-latent dsRNA state. This might be either physical or cognitive activity.
#PEM #PESE
10/13
Further reading:
1) A 1992 study of persistent enterovirus-induced myocarditis found that "during acute infection, viral genomic plus-strand RNA is synthesized in great excess in comparison with the synthesis of relatively low-copy numbers of the negative-strand RNA intermediate... In contrast to acute infection, the amount of viral plus-strand RNA in myocardial cells of persistently infected mice appears similar to the amount of minus-strand RNA."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC48227/pdf/pnas01075-0330.pdf
11/13
Further reading: (cont.)
2) A 1997 paper on persistent enteroviral myocarditis found that "approximately equal amounts of plus and minus strand RNA were detected in cases of persistent cardiac infection."
https://doi.org/10.1002/(sici)1096-9071(199706)52:2%3C206::aid-jmv15%3E3.0.co;2-i
3) A 1999 paper on persistent #coxsackievirus infection of muscle cells found that "plus- and minus-strand viral RNAs were present at nearly equivalent levels in muscle and that they persisted in a double-stranded conformation."
https://doi.org/10.1128/jvi.73.12.10113-10121.1999
12/13
Further reading: (cont.)
4) The SARS-CoV-1 coronavirus envelope protein functions as a viroporin:
https://doi.org/10.1016/j.virol.2004.09.033
5) The SARS-CoV-2 3a protein might also function as a viroporin:
https://doi.org/10.1073%2Fpnas.0605402103
6) The envelope protein of other coronaviruses also functions as a viroporin:
https://doi.org/10.1016/j.virol.2006.05.028
7) The #Ebola Virus Delta Peptide Is a Viroporin:
https://doi.org/10.1128/JVI.00438-17
13/13
Related discussions:
"Replicating chikungunya #virus, which occurs inside a 'spherule', apparently spends 80% of its time in the double-stranded #RNA intermediate state."
https://mstdn.science/@pyrrhus/109554463124601744
"We... found indications of latency and compartmentalization that were particularly associated with longer infection times... These findings raise the possibility that #SARSCoV2 enters a slower replication state as infection continues, and warrants further investigation."
https://mstdn.science/@pyrrhus/110127777237239858
Replicating #chikungunya #virus, which occurs inside a 'spherule', apparently spends 80% of its time in the double-stranded #RNA intermediate state. From the preprint: "A first characterization of the filamentous material in the spherule indicated that each spherule contains a single copy of the viral genome, ~80% of which is present in #dsRNA form." https://www.biorxiv.org/content/10.1101/2022.12.19.521029v1
P.S.
And for comparison, here's a completely different model of how an RNA #virus can establish a quasi-latent state to facilitate #ViralPersistence:
"Some #RNA viruses, such as mumps, can establish persistent infections by freezing its intracellular viral replication factories as condensates."
https://mstdn.science/@pyrrhus/110275180043677194
Attached: 1 image Some #RNA viruses, such as mumps, can establish persistent infections by freezing its intracellular viral replication factories as condensates. A fascinating new paper shows in detail how cellular stress can awaken the mumps #virus from this latent state: "Molecular mechanisms of stress-induced reactivation in mumps virus condensates" https://doi.org/10.1016/j.cell.2023.03.015 Great work by Julia Mahamid and colleagues at EMBL Heidelberg! #virology @virology@a.gup.pe #InfectiousDisease #ViralPersistence
That's correct. The electrostatic repulsion between strands is balanced by the hydrogen bonding holding strands together.
The same applies to RNA, except that dsRNA just happens to be much less thermodynamically stable than dsDNA.
I hope this is clear.
I'm so glad it gave you an idea to try! π π π
I hope the idea proves to be fruitful.
Eric Pyrrhus
christoph_STCmicrobeblog
Gal Haimovich π·π¬β£π³οΈβππ³οΈββ§