In this article, the TRIM5α protein and its effect on the herpes simplex virus (HSV) discussed. HSV is a smart virus, and uses several mechanisms to get around replication blocks within a cell. It can do so by silencing some of the host cell's genes, blocking interferon, and/or degrading proteins. Several different species of monkeys were used in this experiment including the rhesus macaques, the squirrel monkey, and the African green monkey. The rhesus macaque is the simian of most importance in this experiment because of it being a suitable nonhuman primate model for certain viral diseases such as SIV. For some unknown reason, a rhesus macaque infected with HSV is not guaranteed to become diseased. It was speculated in the article that TRIM5α may play a role in this. This protein is also responsible for the inability of HIV-1 to infect Old World Monkeys (OWM) such as the rhesus macaque.
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Because TRIM proteins can affect viral replication at certain stages, the purpose of the experiment discussed in this article is to discover if TRIM5α can manipulate HSV replication. The scientists would also like to know if TRIM5α restrict viral replication in non-retroviruses.
In the first test performed, HSV-1 and 2 were introduced into the fibroblasts of a rhesus monkey to see how well the virus grew in rhesus monkey cells. The results from this were compared to how well the HSV virus replicated in HeLa (human) cells. The final results revealed that HSV grew more successfully in the human cells than in the
monkey cells, and were translated onto a line graph. The graph illustrated that viral replication in the rhesus macaque cells were 100 times lower than that in the HeLa cells. It was this information that prompted the scientists to go a step further, and explore if maybe the TRIM5α protein is the reason for the limited growth in the monkey cells.
Only those HeLa cells that possessed the TRIM5α protein and were infected with HSV were studied. H-R cells were infected with HSV-1 and 2 while H-L cells were used as the control. The multiplicity of infection (MOI) ranged from 1-30 PFU/cell. The results showed that at a low MOI, TRIM5α can reduce HSV replication, but can't overcome a high (i.e. 30) MOI. These results were recorded in a bar graph.
Since the effects of the TRIM5α protein are species-specific, the scientists' next experiment included the effects of the TRIM5α protein from other primates on HSV. The outcome of TRIM5α from 3 different species of monkeys (rhesus, African green, and squirrel), and human were compared with one another. The results were transferred to a bar graph which showed that TRIM5α proteins do contain species-specific properties. The TRIM5α proteins in the H-R and H-AGM cells (both OWM) were the most effective at reducing HSV replication.
The next step was to see if TRIM5α effect the viral replication of HSV at its early stages as it does with retroviruses. For this, viral protein synthesis was measured. H-L and H-R cells were infected with HSV. Because proteins were being measured, the Western blot test was used to analyze the data. The results showed that IE genes affect HSV-1 and 2 replication by way of protein synthesis. HSV-2 replication showed a 5-7 fold reduction in comparison to HSV-1.
Next, the scientists investigated to find out if the replication cycle of other strains of HSV, (other than HSV-1 KOS strain and HSV-2 strain 186 syn+) would be
rhesus TRIM5α sensitive. This also included clinical isolates. H-R and H-L cells were infected with a HSV-2 clinical isolate, and the HSV strain 186 syn+. The results were demonstrated in a bar graph and showed that replication had been reduced in both strains of HSV. It was deduced that TRIM5α is more strain-specific than species-specific.
It was next thought that maybe TRIM5α increased ICPO in the cytoplasm of an infected cell. The ICPO (infected cell protein) dispersal in HSV-1 KOS virus infected H-L, H-R, and H-H cells was studied to test this idea. The proteins were stained (fluorescent staining), and the results showed that rhesus TRIM5α increased ICPO in the cytoplasm, and keeps it from entering the nucleus. ICPO needs to be in the nucleus to replicate.
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It was also questioned if ICPO had an affect on how well TRIM5α performed. To test this hypothesis, infected H-L and H-R cells with the ICPO null were used. Viruses were taken from the cells and their yields measured. The results were placed in a table and showed that ICPO negative yields lower H-R in cells and ICPO positive yields higher H-R in cells.
It was discovered that TRIM5α levels decreased as the HSV infection prolonged. To explain this phenomenon, a Western blot analysis was used on HSV-infected H-R and H-L cells. TRIM5α was decreased in both HSV-1 and 2 infected cells. This could prove that HSV may have evolved to reduce the amount of TRIM5α in order to limit its (TRIM5α) restrictive ability. TRIM5α is reduced only when there's a threat. This could be why it's reduced in OWM.
In conclusion, I thought that this was a very interesting article. Some of these experiments could be used to answer the same questions for other viruses. I thought that the experiments were all well done from what was described, and that the results were well represented (i.e. bar graph, line graph, etc.). This kind of work is very important because it may make scientists think about other medical issues that can be solved by using the methods described in this article.