Ribonuclease L orRNase L (forlatent), known sometimes asribonuclease 4 or2'-5' oligoadenylate synthetase-dependent ribonuclease, is aninterferon (IFN)-inducedribonuclease which, upon activation, destroys allRNA within thecell (both cellular and viral) as well as inhibiting mRNA export.[5][6] RNase L is anenzyme that in humans is encoded by theRNASELgene.[7]
This gene encodes a component of the interferon-regulated 2'-5'oligoadenylate (2'-5'A) system that functions in the antiviral and antiproliferative roles of interferons. RNase L is activated by dimerization, which occurs upon 2'-5'A binding, and results in cleavage of all RNA in the cell. This can lead to activation ofMDA5, anRNA helicase involved in the production of interferons.
RNase L activation pathway-IFN factors bind the receptor and lead transcription and modifications of OAS. Viral dsRNA binds OAS, so that 2'-5'A is produced leading to the dimerization of RNase L. Activated RNase L cleaves all RNA in the cell, which can activate MDA5 leading to interferon production.
RNase L is present in very minute quantities during the normal cell cycle. When interferon binds to cell receptors, it activates transcription of around 300 genes to bring about the antiviral state. Among the enzymes produced is RNase L, which is initially in an inactive form. A set of transcribed genes codes for2'-5' Oligoadenylate Synthetase (OAS).[8] The transcribed RNA is then spliced and modified in the nucleus before reaching the cytoplasm and being translated into an inactive form of OAS. The location of OAS in the cell and the length of the 2'-5' oligoadenylate depends on the post-transcriptional and post-translational modifications of OAS.[8]
OAS is only activated under a viral infection, when a tight binding of the inactive form of the protein with a viraldsRNA, consisting of theretrovirus' ssRNA and itscomplementary strand, takes place. Once active, OAS convertsATP topyrophosphate and 2'-5'-linked oligoadenylates (2-5A), which are 5' end phosphorylated.[9] 2-5 A molecules then bind to RNase L, promoting its activation by dimerization. In its activated form RNase L cleaves all RNA molecules in the cell leading toautophagy andapoptosis. Some of the resulting RNA fragments can also further induce the production of IFN-β as noted in the Significance section.[10]
Thisdimerization and activation of RNase L can be recognized usingFluorescence Resonance Energy Transfer (FRET), as oligoribonucleotides containing a quencher and a fluorophore on opposite sites are added to a solution with inactive RNase L. The FRET signal is then recorded as the quencher and the fluorophore are very close to each other. Upon the addition of 2-5A molecules, RNase L becomes active, cleaving the oligoribonucleotides and interfering in the FRET signal.[11]
In vitro, RNase L can be inhibited bycurcumin.[12]
RNase L is part of the body's innate immune defense, namely the antiviral state of the cell. When a cell is in the antiviral state, it is highly resistant to viral attacks and is also ready to undergoapoptosis upon successful viral infection. Degradation of all RNA within the cell (which usually occurs with cessation of translation activity caused byprotein kinase R) is the cell's last stand against a virus before it attempts apoptosis.
Interferon beta (IFN-β), a type I interferon responsible for antiviral activity, is induced by RNase L andmelanoma differentiation-associated protein 5 (MDA5) in the infected cell. The relationship between RNase L and MDA5 in the production of IFNs has been confirmed withsiRNA tests silencing the expression of either molecule and noting a marked decline in IFN production.[13] MDA5, anRNA helicase, is known to be activated by complex high molecular weight dsRNA transcribed from the viral genome.[13][14] In a cell with RNase L, MDA5 activity may be further enhanced.[13] When active, RNase L cleaves and identifies viral RNA and feeds it into MDA5 activation sites, enhancing the production of IFN-β. The RNA fragments produced by RNase L have double stranded regions, as well as specific markers, that allow them to be identified by the RNase L and MDA5.[10] Some studies have suggested that high levels of RNase L may actually inhibit IFN-β production, but a clear linkage still exists between RNase L activity and IFN-β production.[10]
Furthermore, it has been shown that RNase L is involved in many diseases. In 2002, the "hereditary prostate cancer 1" locus (HPC1) was mapped to theRNASEL gene, indicating that mutations in this gene cause a predisposition to prostate cancer.[15][16][17] Impairments of the OAS/RNase L pathway inchronic fatigue syndrome (CFS) have been investigated.[18][19]
^Squire J, Zhou A, Hassel BA, Nie H, Silverman RH (January 1994). "Localization of the interferon-induced, 2-5A-dependent RNase gene (RNS4) to human chromosome 1q25".Genomics.19 (1):174–5.doi:10.1006/geno.1994.1033.PMID7514564.
^abSarkar SN, Pandey M, Sen GC (2005). "Assays for the Interferon-Induced Enzyme 2′,5′ Oligoadenylate Synthetases".Interferon Methods and Protocols. Methods in Molecular Medicine. Vol. 116. Human Press Inc. pp. 81–101.doi:10.1385/1-59259-939-7:081.ISBN978-1-58829-418-0.PMID16000856.
^Thakur CS, Xu Z, Wang Z, Novince Z, Silverman RH (2005). "A Convenient and Sensitive Fluorescence Resonance Energy Transfer Assay for RNase L and 2′,5′ Oligoadenylates".Interferon Methods and Protocols. Methods in Molecular Medicine. Vol. 116. Human Press Inc. pp. 103–13.doi:10.1385/1-59259-939-7:103.ISBN978-1-58829-418-0.PMID16000857.
^Nijs J, De Meirleir K (Nov–Dec 2005). "Impairments of the 2-5A synthetase/RNase L pathway in chronic fatigue syndrome".In Vivo.19 (6):1013–21.PMID16277015.
^Suhadolnik RJ, Peterson DL, O'Brien K, Cheney PR, Herst CV, Reichenbach NL, et al. (July 1997). "Biochemical evidence for a novel low molecular weight 2-5A-dependent RNase L in chronic fatigue syndrome".Journal of Interferon & Cytokine Research.17 (7):377–85.doi:10.1089/jir.1997.17.377.PMID9243369.
Silverman RH (February 2003). "Implications for RNase L in prostate cancer biology".Biochemistry.42 (7):1805–12.doi:10.1021/bi027147i.PMID12590567.
Kieffer N, Schmitz M, Scheiden R, Nathan M, Faber JC (2006). "Involvement of the RNAse L gene in prostate cancer".Bulletin de la Société des Sciences Médicales du Grand-Duché de Luxembourg (1):21–8.PMID16869093.
Zhou A, Nie H, Silverman RH (November 2000). "Analysis and origins of the human and mouse RNase L genes: mediators of interferon action".Mammalian Genome.11 (11):989–92.doi:10.1007/s003350010194.PMID11063255.S2CID35650613.
