Down-regulation of human cytomegalovirus UL138, a novel latency-associated determinant, by hcmv-miR-UL36

Cytomegalovirus microRNAs level determination in kidney recipients post transplantation

BACKGROUND

Human cytomegalovirus (CMV) can establish a latent infection with periodic or sporadic reactivation after the first infection happens. Primary and recurrent infection, results in different problems in patients with impaired or immature immune systems, such as kidney transplant recipients (KTRs). MicroRNAs (miRNAs, miRs) are important regulatory molecules in the outcome of CMV-infected KTRs. Therefore, in this study the expression level of CMV miRNAs were evaluated in active vs. latent CMV infected KTRs.

METHODS

Expression of viral miRNAs were studied in 61 KTRs which were divided into 30 active CMV and 31 latent CMV infected individuals. In order to study the expression level of selected miRNAs, SYBR Green Real-time PCR technique was exploited. Also, mature miRNAs expression level that were produced from one precursor, studied both in active and latent situations.

RESULTS

Among studied miRNAs' expression level, CMV miR-UL112-3p/5p, -UL22A-3p/5p, -US25-1-5p, -US25-2-3p/5p, -UL36-3p/5p and -UL70-3p showed significant increase in active CMV infected KTRs in comparison to latent ones. The ROC curve analysis results for miR-UL112-3p, -UL22A-3p, -US25-2-3p, -UL36-3p and -UL70-3p showed significant difference between two studied patient groups.

CONCLUSION

This study revealed an extremely high expression level in CMV miR-UL112-3p/5p, -UL22A-3p/5p, -US25-1-5p, -US25-2-3p/5p, -UL36-3p/5p and -UL70-3p in active CMV infected KTRs in comparison to latent ones. Further studies might help in finding the capability of miRNAs to differentiate active from latent stage of CMV infection in KTRs.

Human Cytomegalovirus Induced Aberrant Expression of Non-coding RNAs

Human cytomegalovirus (HCMV) is a β-herpesvirus whose genome consists of double stranded linear DNA. HCMV genome can generate non-coding RNAs (ncRNAs) through transcription in its host cells. Besides that, HCMV infection also changes the ncRNAs expression profile of the host cells. ncRNAs play a key role in maintaining the normal physiological activity of cells, and the disorder of ncRNAs expression has numerous adverse effects on cells. However, until now, the relationship between ncRNAs and HCMV-induced adverse effects are not summarized in detail. This review aims to give a systematic summary of the role of HCMV infection in ncRNAs expression while providing insights into the molecular mechanism of unnormal cellular events caused by ncRNAs disorder. ncRNAs disorder induced by HCMV infection is highly associated with cell proliferation, apoptosis, tumorigenesis, and immune regulation, as well as the development of cardiovascular diseases, and the potential role of biomarker. We summarize the studies on HCMV associated ncRNAs disorder and suggest innovative strategies for eliminating the adverse effects caused by HCMV infection.

microRNA, a Subtle Indicator of Human Cytomegalovirus against Host Immune Cells

Human cytomegalovirus (HCMV) is a double-stranded DNA virus that belongs to the β-herpesvirus family and infects 40–90% of the adult population worldwide. HCMV infection is usually asymptomatic in healthy individuals but causes serious problems in immunocompromised people. We restricted this narrative review (PubMed, January 2022) to demonstrate the interaction and molecular mechanisms between the virus and host immune cells with a focus on HCMV-encoded miRNAs. We found a series of HCMV-encoded miRNAs (e.g., miR-UL112 and miR-UL148D) are explicitly involved in the regulation of viral DNA replication, immune evasion, as well as host cell fate. MiRNA-targeted therapies have been explored for the treatment of atherosclerosis, cardiovascular disease, cancer, diabetes, and hepatitis C virus infection. It is feasible to develop an alternative vaccine to restart peripheral immunity or to inhibit HCMV activity, which may contribute to the antiviral intervention for serious HCMV-related diseases.

Human Cytomegalovirus miR-UL70-3p Downregulates the H2O2-Induced Apoptosis by Targeting the Modulator of Apoptosis-1 (MOAP1)

Human Cytomegalovirus (HCMV) is a prototypic beta herpesvirus, causing persistent infections in humans. There are medications that are used to treat the symptoms; however, there is no cure yet. Thus, understanding the molecular mechanisms of HCMV replication and its persistence may reveal new prevention strategies. HCMV evasive strategies on the antiviral responses of the human host largely rely on its significant portion of genome. Numerous studies have highlighted the importance of miRNA-mediated regulation of apoptosis, which is an innate immune mechanism that eradicates virus-infected cells. In this study, we explore the antiapoptotic role of hcmv-miR-UL70-3p in HEK293T cells. We establish that hcmv-miR-UL70-3p targets the proapoptotic gene Modulator of Apoptosis-1 (MOAP1) through interaction with its 3'UTR region of mRNA. The ectopic expression of hcmv-miR-UL70-3p mimic significantly downregulates the H₂O₂-induced apoptosis through the translational repression of MOAP1. Silencing of MOAP1 through siRNA also inhibits the H₂O₂-induced apoptosis, which further supports the hcmv-miR-UL70-3p mediated antiapoptotic effect by regulating MOAP1 expression. These results uncover a role for hcmv-miR-UL70-3p and its target MOAP1 in regulating apoptosis.

Regulation of Latency and Reactivation by Human Cytomegalovirus miRNAs

Human cytomegalovirus (HCMV) encodes 22 mature microRNAs (miRNAs), which regulate a myriad of cellular processes, including vesicular trafficking, cell cycle progression, apoptosis, and immune evasion, as well as viral gene expression. Recent evidence points to a critical role for HCMV miRNAs in mediating latency in CD34⁺ hematopoietic progenitor cells through modulation of cellular signaling pathways, including attenuation of TGFβ and EGFR signaling. Moreover, HCMV miRNAs can act in concert with, or in opposition to, viral proteins in regulating host cell functions. Here, we comprehensively review the studies of HCMV miRNAs in the context of latency and highlight the novel processes that are manipulated by the virus using these small non-coding RNAs.

Human Cytomegalovirus-Encoded microRNAs Can Be Found in Saliva Samples from Renal Transplant Recipients

Human cytomegalovirus (HCMV) infections are common following renal transplantation and may have long-lasting effects. HCMV can be measured directly by viral DNA or indirectly via host immune responses. HCMV-encoded microRNA (miRNA) may alter the pathobiology of HCMV infections and contribute to the progression of HCMV disease. HCMV-encoded miRNAs can be detected in blood but have not been sought in saliva. We investigated saliva samples from 32 renal transplant recipients (RTR) and 12 seropositive healthy controls for whom immunological data was available. Five HCMV-encoded miRNAs (miR-UL112-5p, miR-US5-2-3p, miR-UL36, miR-US25-2-3p and miR-UL22A) were sought using primer probe assays. HCMV miRNA species were detected in saliva from 15 RTR and 3 healthy controls, with miR-US5-2-3p most commonly detected. The presence of HCMV miRNAs associated with increased T-cell responses to HCMV IE-1 in RTR, suggesting a link with frequent reactivations of HCMV.

Understanding HCMV Latency Using Unbiased Proteomic Analyses

Human cytomegalovirus (HCMV) establishes either a latent (non-productive) or lytic (productive) infection depending upon cell type, cytokine milieu and the differentiation status of the infected cell. Undifferentiated cells, such as precursor cells of the myeloid lineage, support a latent infection whereas terminally differentiated cells, such as monocytes or dendritic cells are an environment conducive to reactivation and support a lytic infection. The mechanisms which regulate HCMV in either a latent or lytic infection have been the focus of intense investigation with a view to developing novel treatments for HCMV-associated disease which can have a heavy clinical burden after reactivation or primary infection in, especially, the immune compromised. To this end, a number of studies have been carried out in an unbiased manner to address global changes occurring within the latently infected cell to address the molecular changes associated with HCMV latency. In this review, we will concentrate on the proteomic analyses which have been carried out in undifferentiated myeloid cells which either stably express specific viral latency associated genes in isolation or on cells which have been latently infected with virus.

The Role of the Human Cytomegalovirus UL133-UL138 Gene Locus in Latency and Reactivation

Human cytomegalovirus (HCMV) latency, the means by which the virus persists indefinitely in an infected individual, is a major frontier of current research efforts in the field. Towards developing a comprehensive understanding of HCMV latency and its reactivation from latency, viral determinants of latency and reactivation and their host interactions that govern the latent state and reactivation from latency have been identified. The polycistronic UL133-UL138 locus encodes determinants of both latency and reactivation. In this review, we survey the model systems used to investigate latency and new findings from these systems. Particular focus is given to the roles of the UL133, UL135, UL136 and UL138 proteins in regulating viral latency and how their known host interactions contribute to regulating host signaling pathways towards the establishment of or exit from latency. Understanding the mechanisms underlying viral latency and reactivation is important in developing strategies to block reactivation and prevent CMV disease in immunocompromised individuals, such as transplant patients.

MicroRNAs expressed by human cytomegalovirus

Background

MicroRNAs (miRNAs) are small non-coding RNAs about 22 nucleotides in length, which play an important role in gene regulation of both eukaryotes and viruses. They can promote RNA cleavage and repress translation via base-pairing with complementary sequences within mRNA molecules.

Main body

Human cytomegalovirus (HCMV) encodes a large number of miRNAs that regulate transcriptions of both host cells and themselves to favor viral infection and inhibit the host’s immune response. To date, ~ 26 mature HCMV miRNAs have been identified. Nevertheless, their roles in viral infection are ambiguous, and the mechanisms have not been fully revealed. Therefore, we discuss the methods used in HCMV miRNA research and summarize the important roles of HCMV miRNAs and their potential mechanisms in infection.

Conclusions

To study the miRNAs encoded by viruses and their roles in viral replication, expression, and infection will not only contribute to the planning of effective antiviral therapies, but also provide new molecular targets for the development of antiviral drugs.

Functional Profile of Human Cytomegalovirus Genes and Their Associated Diseases: A Review

The human cytomegalovirus (HCMV), whose genome is 235 ± 1.9 kbp long, is a common herpesvirus. However, the functions of many of its genes are still unknown. HCMV is closely associated with various human diseases and infects 60-90% of the global population. It can infect various human cells, including fibroblasts, epithelial cells, endothelial cells, smooth muscle cells, and monocytes. Although HCMV infection is generally asymptomatic and causes subtle clinical symptoms, it can generate a robust immune response and establish a latent infection in immunocompromised individuals, including those with AIDS, transplant recipients, and developing fetuses. Currently available antivirals approved for the treatment of HCMV-associated diseases are limited by dose-limiting toxicity and the emergence of resistance; however, vaccines and immunoglobulins are unavailable. In this review, we have summarized the recent literature on 43 newly identified HCMV genes. We have described their novel functions on the viral replication cycle, latency, and host immune evasion. Further, we have discussed HCMV-associated diseases and current therapeutic targets. Our review may provide a foundational basis for studies aiming to prevent and develop targeted therapies for HCMV-associated diseases.

The Role of microRNAs in the Viral Infections

MicroRNAs (miRNAs) are non-coding RNAs with 19 to 24 nucleotides which are evolutionally conserved. MicroRNAs play a regulatory role in many cellular functions such as immune mechanisms, apoptosis, and tumorigenesis. The main function of miRNAs is the post-transcriptional regulation of gene expression via mRNA degradation or inhibition of translation. In fact, many of them act as an oncogene or tumor suppressor. These molecular structures participate in many physiological and pathological processes of the cell. The virus can also produce them for developing its pathogenic processes. It was initially thought that viruses without nuclear replication cycle such as Poxviridae and RNA viruses can not code miRNA, but recently, it has been proven that RNA viruses can also produce miRNA. The aim of this articles is to describe viral miRNAs biogenesis and their effects on cellular and viral genes.

HCMV miRNA Targets Reveal Important Cellular Pathways for Viral Replication, Latency, and Reactivation

It is now well appreciated that microRNAs (miRNAs) play a critical role in the lifecycles of many herpes viruses. The human cytomegalovirus (HCMV) replication cycle varies significantly depending on the cell type infected, with lytic replication occurring in fully-differentiated cells such as fibroblasts, endothelial cells, or macrophages, and latent infection occurring in less-differentiated CD14+ monocytes and CD34+ hematopoietic progenitor cells where viral gene expression is severely diminished and progeny virus is not produced. Given their non-immunogenic nature and their capacity to target numerous cellular and viral transcripts, miRNAs represent a particularly advantageous means for HCMV to manipulate viral gene expression and cellular signaling pathways during lytic and latent infection. This review will focus on our current knowledge of HCMV miRNA viral and cellular targets, and discuss their importance in lytic and latent infection, highlight the challenges of studying HCMV miRNAs, and describe how viral miRNAs can help us to better understand the cellular processes involved in HCMV latency.

Transcriptional regulation and influence on replication of the human cytomegalovirus UL138 1.4 kb transcript

Human cytomegalovirus (HCMV) exists in a latent form in hematopoietic progenitors and undifferentiated cells of myeloid lineage. Protein UL138, encoded by the UL/b' region of the viral genome, serves an important role in the establishment and/or persistence of HCMV latency. However, little information about transcriptional regulation of the UL138 gene has been reported thus far. In the present study, the transcriptional regulation element (TRE) of the 1.4 kb UL138 region was identified using a series of dual‑luciferase constructs that contain 5' truncated deletion fragments located upstream of the transcription start site of the gene. The results demonstrated that the region from nucleotide 188995‑188962 of the Han strain genome exhibits promoter activity and harbors the functional binding motif for transcription factor AP‑1 (Ap‑1). Using electrophoretic mobility shift assays the physical interaction of the transcription factor to a minimal essential core sequence was demonstrated. Northern blotting revealed that deletion of the TRE in a HCMV bacterial artificial chromosome or inhibition of Ap‑1 using RNA interference eliminated or reduced the production of the UL138 1.4 kb mRNA transcript in infected human embryonic lung fibroblast cells (HELF). Deletion of the UL138 1.4 kb transcript resulted in acceleration of HCMV replication in HELF cells. To the best of the authors' knowledge, the present study is the first to analyze the transcriptional regulation of the UL138 1.4 kb transcript. Knowledge of the transcriptional regulation of the UL138 gene will enhance understanding of its mechanism in HCMV latency.

Human cytomegalovirus miR-US4-5p promotes apoptosis via downregulation of p21-activated kinase 2 in cultured cells

The human cytomegalovirus (HCMV) encodes ≥26 microRNAs (miRNAs). These miRNAs are utilized by HCMV to regulate its own genes in addition to the genes of the host cell, during infection. The present study first identified p21‑activated kinase 2 (PAK2) as a target of hcmv‑miR‑US4‑5p, via hybrid polymerase chain reaction, which was further verified using a luciferase reporter assay. The protein expression level of PAK2, detected via western blotting, was demonstrated to be directly downregulated by overexpression of hcmv‑miR‑US4‑5p in HEK293, HELF and THP‑1 cells. Furthermore, it was demonstrated that the PAK2 protein level in naturally infected HELF cells was gradually decreased at 24, 48 and 72 h post infection with increased hcmv‑miR‑US4‑5p expression. The use of PAK2‑specific small interfering RNA and an inhibitor for hcmv‑miR‑US4‑5p, demonstrated that the promotion of apoptosis by hcmv‑miR‑US4‑5p in these cells was specifically mediated via inhibition of PAK2 expression. These results indicated that hcmv‑miR‑US4‑5p may exhibit this activity during natural HCMV infection, in order to establish a balance between the host cell and virus.

Human cytomegalovirus microRNAs are carried by virions and dense bodies and are delivered to target cells

Human cytomegalovirus (HCMV) infection results in the production of virions, dense bodies (DBs) and non-infectious enveloped particles, all of which incorporate proteins and RNAs that can be transferred to host cells. Here, we investigated whether virions and DBs also carry microRNAs (miRNAs) and assessed their delivery and functionality in cells. Human lung fibroblasts (MRC-5) were infected with the HCMV strain AD169, and conditioned cell culture medium was collected and centrifuged. The pellets were treated with RNase-ONE, and the virions and DBs were purified with a potassium tartrate–glycerol gradient and dialysed. The virions and DBs were incubated with micrococcal nuclease, DNA and RNA were extracted and then analysed with TaqMan PCR assays, while the proteins were examined with Western blots. To assess the delivery of miRNAs to cells and their functionality, virions and DBs were irradiated with UV light. The purity of the virions and DBs was confirmed by typical morphology, the presence of the structural protein pp65 and the HCMV genome, the ability to infect MRC-5 cells and the absence of the host genome. RNA analysis revealed the presence of 14 HCMV-encoded miRNAs (UL22A-5p, US25-1-5p, UL22A-3p, US5-2-3p, UL112-3p, US25-2-3p, US25-2-5p, US33-3p, US5-1, UL36-5p, US4-5p, UL36-3p, UL70-5p and US25-1-3p), HCMV immediate-early mRNA and long non-coding RNA2.7, moreover, two host-encoded miRNAs (hsa-miR-218-5p and hsa-miR-21-5p) and beta-2-microglobulin RNA. UV-irradiated virions and DBs delivered viral miRNAs (US25-1-5p and UL112-3p) to the host cells, and miR-US25-1-5p was functional in a luciferase reporter assay. We conclude that virions and DBs carry miRNAs that are biologically functional and can be delivered to cells, which may affect cellular processes.

Manipulation of Viral MicroRNAs as a Potential Antiviral Strategy for the Treatment of Cytomegalovirus Infection

Cytomegalovirus (CMV) infection leads to notable morbidity and mortality in immunosuppressed patients. Current antiviral drugs are effective but seriously limited in their long-term use due to their relatively high toxicity. In the present study, we characterized the expression of murine CMV microRNAs (MCMV miRNAs) both in vitro and in vivo. Although 29 miRNAs were detectable during in vitro infection, only 11 miRNAs (classified as Group 1) were detectable during in vivo infection, and as many as 18 viral miRNAs (classified as Group 2) were less detectable (<50% of animals) in both the liver and lungs. In addition, viral miRNA profiles in the blood revealed unstable and reduced expression. We next explored the in vitro effects of viral miRNAs on MCMV replication. The inhibition of Group 1 viral miRNAs had little effect on virus production, but transfected cells overexpressing miR-m01-3-5p, miR-M23-1-5p, miR-M55-1, and miR-m107-1-5p in Group 2 showed statistically lower viral loads than those transfected with control miRNA (29%, 29%, 39%, and 43%, respectively, versus control). Finally, we performed hydrodynamic injection of viral miRNA agomirs and observed lower levels of MCMV recurrence in the livers of animals overexpressing the miR-m01-3-5p or mcmv-miR-M23-1-5p agomirs compared with those of animals transfected with control agomir, confirming the antiviral effects of viral miRNA manipulation in vivo. Therefore, the manipulation of viral miRNA expression shows great therapeutic potential and represents a novel antiviral strategy for the miRNA-based treatment of cytomegalovirus infection.

Long and Short Isoforms of the Human Cytomegalovirus UL138 Protein Silence IE Transcription and Promote Latency

The UL133-138 locus present in clinical strains of human cytomegalovirus (HCMV) encodes proteins required for latency and reactivation in CD34(+) hematopoietic progenitor cells and virion maturation in endothelial cells. The encoded proteins form multiple homo- and hetero-interactions and localize within secretory membranes. One of these genes, UL136 gene, is expressed as at least five different protein isoforms with overlapping and unique functions. Here we show that another gene from this locus, the UL138 gene, also generates more than one protein isoform. A long form of UL138 (pUL138-L) initiates translation from codon 1, possesses an amino-terminal signal sequence, and is a type one integral membrane protein. Here we identify a short protein isoform (pUL138-S) initiating from codon 16 that displays a subcellular localization similar to that of pUL138-L. Reporter, short-term transcription, and long-term virus production assays revealed that both pUL138-L and pUL138-S are able to suppress major immediate early (IE) gene transcription and the generation of infectious virions in cells in which HCMV latency is studied. The long form appears to be more potent at silencing IE transcription shortly after infection, while the short form seems more potent at restricting progeny virion production at later times, indicating that both isoforms of UL138 likely cooperate to promote HCMV latency.

IMPORTANCE

Latency allows herpesviruses to persist for the lives of their hosts in the face of effective immune control measures for productively infected cells. Controlling latent reservoirs is an attractive antiviral approach complicated by knowledge deficits for how latently infected cells are established, maintained, and reactivated. This is especially true for betaherpesviruses. The functional consequences of HCMV UL138 protein expression during latency include repression of viral IE1 transcription and suppression of virus replication. Here we show that short and long isoforms of UL138 exist and can themselves support latency but may do so in temporally distinct manners. Understanding the complexity of gene expression and its impact on latency is important for considering potential antivirals targeting latent reservoirs.

The Role of microRNAs in the Pathogenesis of Herpesvirus Infection

MicroRNAs (miRNAs) are small non-coding RNAs important in gene regulation. They are able to regulate mRNA translation through base-pair complementarity. Cellular miRNAs have been involved in the regulation of nearly all cellular pathways, and their deregulation has been associated with several diseases such as cancer. Given the importance of microRNAs to cell homeostasis, it is no surprise that viruses have evolved to take advantage of this cellular pathway. Viruses have been reported to be able to encode and express functional viral microRNAs that target both viral and cellular transcripts. Moreover, viral inhibition of key proteins from the microRNA pathway and important changes in cellular microRNA pool have been reported upon viral infection. In addition, viruses have developed multiple mechanisms to avoid being targeted by cellular microRNAs. This complex interaction between host and viruses to control the microRNA pathway usually favors viral infection and persistence by either reducing immune detection, avoiding apoptosis, promoting cell growth, or promoting lytic or latent infection. One of the best examples of this virus-host-microRNA interplay emanates from members of the Herperviridae family, namely the herpes simplex virus type 1 and type 2 (HSV-1 and HSV-2), human cytomegalovirus (HCMV), human herpesvirus 8 (HHV-8), and the Epstein–Barr virus (EBV). In this review, we will focus on the general functions of microRNAs and the interactions between herpesviruses, human hosts, and microRNAs and will delve into the related mechanisms that contribute to infection and pathogenesis.

MicroRNAs Expressed during Viral Infection: Biomarker Potential and Therapeutic Considerations

MicroRNAs (miRNAs) are short sequences of noncoding single-stranded RNAs that exhibit inhibitory effects on complementary target mRNAs. Recently, it has been discovered that certain viruses express their own miRNAs, while other viruses activate the transcription of cellular miRNAs for their own benefit. This review summarizes the viral and/or cellular miRNAs that are transcribed during infection, with a focus on the biomarker and therapeutic potential of miRNAs (or their antagomirs). Several human viruses of clinical importance are discussed, namely, herpesviruses, polyomaviruses, hepatitis B virus, hepatitis C virus, human papillomavirus, and human immunodeficiency virus.

Human cytomegalovirus encoded microRNAs: hitting targets

Human cytomegalovirus (HCMV) infection is of particular concern in immunodeficient individuals notably transplant recipients, leading to increased morbidity and mortality. HCMV is predicted to encode multiple microRNAs (miRNAs) and several have been characterized in vitro. Furthermore, these miRNAs have been shown to target human and viral mRNAs. Pathways involved in human cellular targets have key roles in vesicle trafficking, immune evasion and cell cycle control. This demonstration of viral miRNA targets provides novel insights into viral pathogenesis. This review details the evidence for the existence of HCMV-encoded miRNA and their targets. HCMV miRNA in blood and other tissues is a potential diagnostic tool and blocking the effects of specific HCMV-encoded miRNA with sequence specific antagomirs is a potential new therapy.

Human cytomegalovirus miR-UL36-5p inhibits apoptosis via downregulation of adenine nucleotide translocator 3 in cultured cells

Human cytomegalovirus (HCMV) encodes at least 26 microRNAs (miRNA). These miRNAs are utilized by HCMV to regulate its own genes as well as the genes of the host cell during infection. It has been reported that a cellular gene, solute carrier family 25, member 6 (SLC25A6), which is also designated adenine nucleotide translocator 3 (ANT3), was identified as a candidate target of hcmv-miR-UL36-5p by hybrid PCR. In this study, ANT3 was further demonstrated to be a direct target of hcmv-miR-UL36-5p by luciferase reporter assays. The expression level of ANT3 protein was confirmed, by western blotting, to be directly downregulated by overexpression of hcmv-miR-UL36-5p in HEK293 cells, U373 cells and HELF cells. Moreover, HCMV-infected cells showed a decrease in the ANT3 protein level. Using ANT3-specific small interfering RNA (siRNA) and an inhibitor for hcmv-miR-UL36-5p, it was shown that inhibition of apoptosis by hcmv-miR-UL36-5p in these cells specifically occurred via inhibition of ANT3 expression. These results imply that hcmv-miR-UL36-5 may play the same role during actual HCMV infection in order to establish a balance between the host cell and the virus.

Hcmv-miR-UL22A-5p: A Biomarker in Transplantation With Broad Impact on Host Gene Expression and Potential Immunological Implications

Cytomegalovirus (CMV) encodes multiple microRNAs. While these have been partially characterized in vitro, their relevance to clinical CMV infection has not been evaluated. We analyzed samples from a cohort of solid organ transplant patients with CMV disease (n = 245) for viral microRNA expression. Several CMV microRNAs were readily detectable in patients with CMV disease in variable relative abundance. Expression level generally correlated with DNA viral load and the absence of viral microRNA was associated with faster viral clearance. Detection of hcmv-miR-UL22A-5p at baseline independently predicted the recurrence of CMV viremia upon discontinuation of antiviral therapy (OR 3.024, 95% CI: 1.35-6.8; p = 0.007). A combination of direct mRNA targeting by the microRNA and indirect modulation of gene expression involving isoforms of the transcriptional regulator C-MYC may be responsible for the broad effects seen in the association of gene transcripts with the RNA-induced silencing complex and in global protein expression upon hcmv-miR-UL22A-5p transfection. This novel study of in vivo viral microRNA expression profiles provides unique insight into the complexity of clinical CMV infection following transplantation. We provide evidence that viral microRNAs may have complex effects on gene expression and be associated with specific virologic and clinical outcomes, and thus could be further evaluated as biomarkers.

Human cytomegalovirus miR-US33-5p inhibits viral DNA synthesis and viral replication by down-regulating expression of the host Syntaxin3

During infection with human cytomegalovirus (HCMV), overexpression of hcmv-miR-US33 can inhibit the lytic viral replication and down-regulate US29 mRNA. However, it remains unknown whether inhibition of viral replication by miR-US33 is mediated by down-regulation of expression of US29 or another host gene. Here, we identified the host gene Syntaxin3 (STX3) to be a direct target of hcmv-miR-US33-5p using Hybrid-PCR and luciferase-reporter assays. It was further demonstrated that the levels of STX3 protein were down-regulated in hcmv-miR-US33-5p-overexpressing cells. Experiments with STX3-specific siRNA, or with an inhibitor of hcmv-miR-US33-5p confirmed that hcmv-miR-US33-5p-mediated inhibition of HCMV DNA synthesis and of viral replication are specifically mediated by down-regulation of STX3 expression.

Balance and Stealth: The Role of Noncoding RNAs in the Regulation of Virus Gene Expression

In the past two decades, our knowledge of gene regulation has been greatly expanded by the discovery of microRNAs (miRNAs). miRNAs are small (19-24 nt) noncoding RNAs (ncRNAs) found in metazoans, plants, and some viruses. They have been shown to regulate many cellular processes, including differentiation, maintenance of homeostasis, apoptosis, and the immune response. At present, there are over 300 known viral miRNAs encoded by diverse virus families. One well-characterized function of some viral miRNAs is the regulation of viral transcripts. Host miRNAs can also regulate viral gene expression. We propose that viruses take advantage of both host and viral ncRNA regulation to balance replication and infectious state (for example, latent versus lytic infection). As miRNA regulation can be reversed upon certain cellular stresses, we hypothesize that ncRNAs can serve viruses as barometers for cellular stress.

Comprehensive analysis of human cytomegalovirus microRNA expression during lytic and quiescent infection

BACKGROUND

Human cytomegalovirus (HCMV) encodes microRNAs (miRNAs) that function as post-transcriptional regulators of gene expression during lytic infection in permissive cells. Some miRNAs have been shown to suppress virus replication, which could help HCMV to establish or maintain latent infection. However, HCMV miRNA expression has not been comprehensively examined and compared using cell culture systems representing permissive (lytic) and semi-permissive vs. non-permissive (latent-like) infection.

METHODS

Viral miRNAs levels and expression kinetics during HCMV infection were determined by miRNA-specific stem-loop RT-PCR. HCMV infected THP-1 (non-permissive), differentiated THP-1 (d-THP-1, semi-permissive) and human embryo lung fibroblasts (HELs, fully-permissive) were examined. The impact of selected miRNAs on HCMV infection (gene expression, genome replication and virus release) was determined by Western blotting, RT-PCR, qPCR, and plaque assay.

RESULTS

Abundant expression of 15 HCMV miRNAs was observed during lytic infection in HELs; highest peak inductions (11- to 1502-fold) occurred at 48 hpi. In d-THP-1s, fourteen mRNAs were detected with moderate induction (3- to 288-fold), but kinetics of expression was generally delayed for 24 h relative to HELs. In contrast, only three miRNAs were induced to low levels (3- to 4-fold) during quiescent infection in THP-1s. Interestingly, miR-UL70-3p was poorly induced in HEL (1.5-fold), moderately in THP-1s (4-fold), and strongly (58-fold) in d-THP-1s, suggesting a potentially specific role for miR-UL70-3p in THP-1s and d-THP-1s. MiR-US33, -UL22A and -UL70 were further evaluated for their impact on HCMV replication in HELs. Ectopic expression of miR-UL22A and miR-UL70 did not affect HCMV replication in HELs, whereas miR-US33 inhibited HCMV replication and reduced levels of HCMV US29 mRNA, confirming that US29 is a target of miR-US33.

CONCLUSIONS

Viral miRNA expression kinetics differs between permissive, semi-permissive and quiescent infections, and miR-US33 down-regulates HCMV replication. These results suggest that miR-US33 may function to impair entry into lytic replication and hence promote establishment of latency.

MicroRNA-217 promotes angiogenesis of human cytomegalovirus-infected endothelial cells through downregulation of SIRT1 and FOXO3A

Human cytomegalovirus(HCMV) infection has been shown to contribute to vascular disease through the induction of angiogenesis. However, the role of microRNA in angiogenesis induced by HCMV infection remains unclear. The present study was thus designed to explore the potential effect of miR-1217 on angiogenesis and to disclose the underlying mechanism in endothelial cells. We found that HCMV infection of endothelial cells(ECs) enhanced expression of miR-217 and reduced SIRT1 and FOXO3A protein level in 24 hours post infection(hpi). Transfection of miR-217 inhibitor not only depressed cellular migration and tube formation induced by HCMV infection, but also enhanced SIRT1 and FOXO3A protein expression. Additionally, luciferase assay confirmed that miR-217 directly targeted FOXO3A mRNA 3`UTR. Furthermore, pretreatment with resveratrol depressed motility and tube formation of HCMV-infected ECs, which could be reversed by SIRT1 siRNA. Similarly, delivery of FOXO3A overexpression lentivirus suppressed proliferative rate, migration and tube formation of HCMV-infected ECs, which reversed by transfection of FOXO3A siRNA. In summary, HCMV infection of endothelial cells induces angiogenesis by both of miR-217/SIRT1 and miR-217/FOXO3A axis.