Hi globalpilot, the wikipedia is wrong I think. RNase L does NOT destroy all RNA. It has specific RNA sequences it targets, sequences that are common in viruses. However, some human proteins will match those sequences - I am not sure which proteins those are, I have never read a study on this.
There has been a lot of research into RNase L even a collection of research papers published as a book. Not everyone with ME or CFS test positive for RNase L or its 37 kDa variant. The 37 kDa (kilodalton) variant was once thought to be a biomarker. However, this was complicated by finding it in both multiple sclerosis and rheumatoid arthritis. What does appear to be a biomarker, but nobody seems to be researching it much, is the combination of elastase and the 37 kDa RNase L. Elastase cleaves RNase L into fragments resulting in the short form. Elevated elastase is not found in MS or RA apparently. This needs a lot more research to become a good biomarker I think. A patent was lodged in 2004 I think using a combination of short RNase L and elastase as a marker. So far nothing has come of it to my knowledge.
One of the problems with RNase L is that it is variable - it goes up and down. If you have any kind of viral infection it will go up. The short form is even more variable, there was some suggestion that it is high in relapse, but I don't know if this research was ever confirmed or further investigated. It may be hard to use as a treatment marker.
Most doctors will not know what to make of RNase L as a marker. For most patients, depending on their doctor, this would not be a good option without more research. Dr Chia being a leading researcher may well have the expertise to understand this. You should ask him.
I too have suspected calpain (m-calpain?) as a cleaving agent based on my own research. It is another enzyme that can cleave RNase L. We know elastase is elevated commonly in us however - calpain may either represent a subset, is another pathway, or is not relevant. I would need to see good data to suspect calpain when elastase is more probable. It does warrant further study though - if calpain is involved it offers another target for therapy, and not just by treating methylation issues.
Recent research implicates increased LPS translocation (Maes) as a primary cause of elevated elastase. This also needs more research to be sure.
Bye
Alex
Hi, Alex.
I had an email exchange in 2008 with Prof. Kenny de Meirleir and Marc Fremont, in his group, about which enzyme cleaves RNase-L. Here's what I wrote to them:
"It is my understanding that inside living cells, the RNase-L is found in the
cytoplasm and in the nucleus. Elastase, on the other hand, is found within
macrophages and neutrophils, in granules and vesicles that are isolated from the
cytoplasm and the nucleus by membranes that do not permit the passage of
elastase. It seems to me that if elastase were not isolated in this way, it
would cleave enzymes within these cells, and the cells would not survive. If
elastase is indeed physically isolated from RNase-L by this compartmentalization,
I do not understand how it could cleave RNase-L within these phaogocytic cells."
This was the response I received from Marc Fremont:
"Thank you for your comments. I think they relate to two questions that are actually still opened. The first one is the possible presence of elastase in monocytes; the second relates to the exact identification of the proteases involved in the cleavage of RNase L.
"As you say elastase is produced mainly by neutrophils and macrophages. It is relatively unlikely (although not impossible, it happens in certain cell types) that elastase released in the plasma can cross the membrane and re-enter PBMCs, so if elastase is present in monocytes it was probably expressed there.
In a normal situation elastase expression in monocytes is repressed by the transcriptional repressor Gfi1. However CFS is not a normal situation, and we can consider a number of pathological mechanisms that could lead to the abnormal expression of elastase. For instance, since Gfi1 is a known target of proteasome, one possibility would be that immune cell dysregulation (apoptosis) activates proteasome that will degrade Gfi1, leading to the synthesis of elastase. The involvement of Gfi1 is still speculative (we will investigate this point) but we have evidence for the activation of proteasome so this is already one plausible mechanism.
"Another thing is that elastase is not the only enzyme that can cleave RNase L. We can very efficiently prevent the cleavage of recombinant RNase L by PBMC extracts, by adding several elastase inhibitors or purified alpha-1-antitrypsin (AAT), the natural inhibitor of elastase in plasma. However these inhibitors (even AAT) have a relatively broad specificity so this does not rule out the possibility that other enzymes contribute to the cleavage. The initial study reporting the involvement of elastase was the 2002 publication (Demettre et al, JBC 277(38), p35746-51). In this publication, the possible implication of other proteases such as calpain or cathepsin G was already mentioned. Other enzymes (metalloproteinases, proteasome-related proteases...) could also be involved. Since most of them are biochemically related to elastase they're not easy to distinguish; in fact the RNase L fragments we do observe are most likely produced by several proteases, not only one. There is currently a research project ongoing that should, I hope, clarify this point.
"Finally, regarding the assay itself elastase inhibitor, as well as other protease inhibitors, are added during the extraction to make sure that the cleavage we measure is not generated during the assay process, but was already present in the living cells.
"All these are complex but very interesting questions. You are right in saying that elastase should not cleave RNase L, since it is contained in vesicles. The question is, why does this happen in CFS? Activation of proteasome is one possibility but there are others. Implication of other proteases is also possible. Actually it may be that different dysregulations occur in different patients, depending on the initial trigger of the disease (viral infection, chronic inflammation...) and that the proteases that cause the cleavage will not be the same in different patient sub-groups. Identification of these mechanisms is the main focus of our research at this time.
"As you see I cannot give a definitive answer to your comment, because these are still open questions that we currently investigate. I'm confident we will one day get a clear picture of what happens in the disease."
I haven't seen any new results concerning this issue since then. I continue to doubt that elastase is responsible for the cleavage of RNase-L, for the reason I gave. Compartmentalization will prevent it, in my opinion.
Best regards,
Rich
