The human cytomegalovirus (HCMV) is extremely prevalent in the human population.

The human cytomegalovirus (HCMV) is extremely prevalent in the human population. for this induction and we show that ADAR1-p110 can edit miR-376a. Accordingly, we demonstrate that the levels of the edited-miR-376a (miR-376a(e)) increase during HCMV infection. Importantly, we show that miR-376a(e) downregulates the immune modulating molecule HLA-E and that this consequently renders HCMV infected cells susceptible to elimination by NK cells. Author Summary The human cytomegalovirus (HCMV) infects a high percentage of the human population. HCMV infection is life threatening to immune-compromised individuals and when transmitted to the fetus can cause severe birth defects. Thus, it is crucial to understand the anti-viral strategies that are induced in response to HCMV infection. By using molecular tools, next generation deep sequencing of small RNAs and a novel human decidual organ culture we demonstrate that in response to HCMV infection the cell launches an anti-viral response that via miRNA editing enables the elimination of HCMV infected cells. We find that following HCMV infection a specific ADAR1 isoform, ADAR1-p110, is strongly induced and that in addition editing of miR-376a is also increases. We continue to show that the Rabbit Polyclonal to VGF edited-miR-376a then downregulates the inhibitory molecule HLA-E, and by doing so promotes the elimination of HCMV infected cells by NK cells. Finally we demonstrate that in decidual tissues ADAR1-p110 is induced and that HLA-E levels are reduced in response to HCMV infection. Introduction HCMV is a dsDNA herpesvirus, which is highly prevalent in the human population. It establishes its life 518303-20-3 IC50 long latency by using a diverse panel of sophisticated immune evasion strategies, and specifically by manipulating the expression of Human Leukocyte Antigen (HLA) class I molecules [1]C[4]. One of the fascinating examples with this regard is the viral protein UL40 that encodes a signal peptide similar in its sequence to the signal peptide of HLA class I molecules. The UL40 signal peptide is processed and loaded specifically in the groove of HLA-E and thus induces its surface expression, where it can inhibit NK cells function [5], [6]. Natural Killer (NK) cells are innate immune lymphocytes, which recognize and eliminate hazardous cells such as virally infected, transformed and damaged cells. The activity of NK cells is regulated 518303-20-3 IC50 by a balance of signals generated by activating and inhibitory receptors [7]C[10]. While the activating ligands of NK cells are 518303-20-3 IC50 diverse, most of the NK inhibitory ligands belong to the HLA class I family. Thus, reduction in the normal expression levels of HLA class I proteins will result in the activation of NK cells [11], [12]. Among the HLA class I proteins, the non-classical HLA-E is distinct in that it presents in its groove only a limited variety of peptides, which are primarily derived from the signal peptides of other HLA class I molecules [13], [14]. HLA-E is mainly recognized by the inhibitory CD94/NKG2A heterodimer and by the activating CD94/NKG2C receptors, both are expressed by T cells and NK cells [15]. Interestingly, expansion of NK clones expressing NKG2C is often seen HCMV-seropositive individuals [16], yet the function of these NK clones is unclear. Several activating NK cell receptors exist, that bind to divers ligands. The NKG2D receptor is one of the potent NK cell activating receptors, recognizing 8 different ligands: UPBP 1C6, MICA and MICB [17], [18]. While the ULBP family has orthologous in mice and in primates, mice do not encode MIC genes and most primates encode only a single MIC gene. We have shown in the past that the expression of MICA and MICB is controlled by cellular and by viral miRNAs [19]C[21]. Interestingly, one of the miRNA that was shown by us to target MICB, miR-376a [19], is known to be edited by ADAR enzymes [22]. RNA editing is a post-transcriptional modification that generates diversity in RNA molecules and in proteins. A-to-I RNA editing is catalyzed by the adenosine deaminase acting on RNA (ADAR) enzymes [23], [24], which bind dsRNA structures (that are not completely defined), and can thus edit protein-coding mRNAs and non-coding RNA molecules such as microRNAs (miRNAs). The editing of miRNAs can result in a change in the specificity of the miRNA, especially if the editing event occurs in the seed sequence [24]. Two active 518303-20-3 IC50 ubiquitously expressed ADAR genes are known, ADAR1 and ADAR2 [24]. The ADAR1 enzyme has two considerably different isoforms; ADAR1-p150, which is induced by type I interferon (IFN) [25] and is located mainly in the cytoplasm and ADAR1-p110, that is thought to be constitutively expressed and is located mainly in the nucleus [26]C[28]. ADAR proteins are physiologically crucial as knock-out of Adar1 is embryonic lethal [29]C[31] and knock-out of Adar2 results in behavioral abnormalities including epileptic seizures [32]. ADAR proteins also function during viral infections and were shown to be either proviral or antiviral [33]. Here we show that specifically during HCMV infection ADAR1-p110, and not ADAR1-p150, is induced. We further show that increased editing of miR-376a is observed.