Putative roles as oncogene or tumour suppressor of the Mid-clustered microRNAs in Gallid alphaherpesvirus 2 (GaHV2) induced Marek's disease lymphomagenesis

OncomiR mdv1-miR-M7-5p promotes avian lymphomatosis by modulating the BCL2/Bax mitochondrial apoptosis signaling pathway

Marek's disease virus (MDV) is an oncogenic alphaherpesvirus that infects poultry and causes fatal lymphomas in infected chickens. Notably, the mdv1-miR-M7-5p, a pivotal oncomiR encoded by MDV, is closely associated with viral replication and latency. Here, mdv1-miR-M7-5p was transfected into the chicken lymphoma cell line MSB1, which resulted in the inhibition of lymphoma cell apoptosis and an increase in lymphoma cell proliferation and migration. Additionally, the expression of the tumor suppressor genes p53 and ARRDC3 were significantly downregulated, while the MDV latency-associated genes such as ICP4 and ICP27 were significantly upregulated. The BCL2/Bax ratio was increased while the expression of genes involved in the apoptotic signaling pathway were decreased. Furthermore, our mitochondrial function experiments in MSB1 cells demonstrated that mdv1-miR-M7-5p enhanced mitochondrial ATP release and altered the mitochondrial membrane potential, thereby affecting mitochondrial function and inhibiting lymphoma cell apoptosis. Dual-luciferase assays revealed that mdv1-miR-M7-5p binds to caspase-6. For the in vivo study, a cholesterol-modified inhibitor of mdv1-miR-M7-5p was administered to chickens. Inhibition of mdv1-miR-M7-5p resulted in a lower mortality rate than that in the control groups. Furthermore, the expression levels of the cytokines interferon-gamma (IFN-γ), interleukin (IL)-4, and IL-17 in the plasma of MDV-infected chickens were significantly increased. A marked increase was observed in apoptosis in the spleen tissues, and the expression of apoptosis-related genes including caspase-3 and tumor suppressor gene PTEN in immune organs, including the spleen, bursa of Fabricius, and thymus, were markedly upregulated. In summary, the oncogenic miRNA mdv1-miR-M7-5p promotes MDV latency and may facilitate lymphoma formation by mediating the BCL2/CytC signaling pathway. This mediation enhances mitochondrial function and inhibits lymphoma cell apoptosis, thereby contributing to lymphoma development.

Marek's disease virus-encoded microRNA-M6-5p facilitates viral latent infection by targeting histone demethylase KDM2B

Marek's disease virus (MDV), a highly contagious and oncogenic avian alphaherpesvirus, establishes a latent infection primarily in CD4+ T cells. Latent infections are necessary for both persistent lifelong MDV infection and viral tumorigenesis. MicroRNAs (miRNAs) play critical roles as post-transcriptional regulators of viral infections. However, the role of miRNAs in regulating MDV latency remains unclear. In this study, we found that an MDV-encoded miRNA, miR-M6-5p, inhibited viral lytic replication in vitro by functional screening and that infection with an MDV mutant lacking miR-M6-5p resulted in impaired MDV latency, proliferation, and tumor formation in vivo. Importantly, we identified lysine-specific demethylase 2b (KDM2B), an important epigenetic factor, as a target of miR-M6-5p. Furthermore, KDM2B knockdown increased the level of the transcriptionally repressive histone mark H3K27me3 on the key lytic gene pp38 promoter, accompanied by suppression of pp38 expression and reduced latent-to-lytic switch in MDV-latently infected cells, while treatment of cells with H3K27me3 inhibitors (GSK126 and Tazemetostat) markedly promoted the expression of pp38 and MDV reactivation from latency. Thus, miR-M6-5p facilitates MDV latency by epigenetically suppressing pp38 expression by targeting KDM2B. These findings unravel the mechanism by which a virus-encoded miRNA plays a critical role in the regulation of latent MDV infection.IMPORTANCESimilar to other herpesviruses, MDV can establish a lifelong latent infection in the host. During the latency, MDV integrates its genome into the host genome to maintain the viral genome, which is considered a prerequisite for tumor formation. Reactivation of the latent viral genome in response to intracellular and extracellular stimuli re-enters lytic replication, resulting in pathological recurrence and/or viral shedding. However, the regulatory mechanisms underlying MDV latency remain poorly understood. In the present study, we investigated the role of virus-encoded miRNAs in MDV latency. We found that miR-M6-5p facilitated MDV latency, proliferation, and tumor formation in vivo. Mechanistically, miR-M6-5p epigenetically suppressed the expression of the viral lytic gene pp38 by directly targeting the histone demethylase KDM2B. These findings will advance our understanding of the role of virus-encoded miRNA in the regulation of viral latency and will help guide the development of novel strategies for the effective control of MDV.

Screening and Studying of Blood miRNAs as Potential Diagnostic Markers for Papillary Thyroid Carcinoma

Objective

MiRNAs play a pivotal role in tumorigenesis and development by exerting negative regulation on the expression of target genes. In this study, bioinformatics techniques and online database were employed to investigate the specific miRNA-target gene regulatory network in PTC, which was subsequently validated using human blood samples and compared to existing tumor markers.

Methods

The miRNA (GSE50901) and Gene Expression (GSE113629) chip screening data of human PTC tissues were retrieved from GEO database. A comparative analysis was conducted using the GEO2R to identify differentially expressed miRNAs and target genes of the patients with PTC. Prediction of the miRNA-target gene regulatory network, related signal transduction pathways, biological effects and their relationship to prognosis was performed based on GO, KEGG, qRT-PCR detection of human blood samples, analysis of correlation on the existing pathological tumor markers, and ROC.

Results

Compared to the corresponding normal thyroid tissues, a total of 2116 miRNAs were found to be differentially expressed in PTC patients, including 1968 up-regulated and 148 down-regulated genes. The abnormally expressed genes primarily participated in signal pathways associated with tumorigenesis and abnormal gene transcription. By utilizing data from the GEO database, five miRNAs closely linked to PTC prognosis were identified, which were miR-221-3p, miR-222-3p, miR-182-5p, miR-135a-5p, and miR-34a-5p, with elucidating the target genes. Experimental validation, correlation analysis with tumor markers along with bioinformatics analysis revealed a significant increase in expression levels of miR-182-5p in PTC patients which positively correlated with poor prognosis. These molecules could play crucial roles in both initiation and progression of PTC.

Conclusion

This study identified potential novel blood-based miRNA biomarkers for PTC through bioinformatics analysis combined with the detection of human blood samples, thereby offering new possibilities for significant biomarkers associated with diagnosis and prognosis of PTC.

Viral miRNA delivered by exosomes from Marek's disease virus-transformed lymphoma cell line exerts regulatory function in internalized primary chicken embryo fibroblast cells

In the past decade, research has demonstrated that viral miRNAs encoded by a number of viral genomes, particularly by most of the herpesvirus including Marek's disease virus (MDV), play important regulatory roles in viral infection, replication, and regulation of tumorigenesis. As macrovesicles in cells, exosomes can deliver viral miRNAs and exert gene regulatory functions. Whether the exosomes play a role in the replication, pathogenesis/tumorigenesis of avian herpesviruses such as oncogenic Marek's disease virus (MDV) remains unclear. Herein we extracted and identified the exosomes from MDV-transformed T cell line MSB-1 and demonstrated high abundance of MDV-1 miRNA expression. Using dual luciferase-based reporter assay, we also demonstrated that the exosomes derived from MSB-1 can deliver functional miRNA successfully into primary chicken embryo fibroblasts. These findings provide new insights into the role of exosomes and the mechanisms of how virus-encoded miRNA function in MDV latency/activation switching, viral replication, pathogenesis and/or tumorigenesis.

Splenic proteome profiling in response to Marek's disease virus strain GX0101 infection

Marek's disease virus (MDV) strain GX0101 was the first reported field strain of recombinant gallid herpesvirus type 2 (GaHV-2). However, the splenic proteome of MDV-infected chickens remains unclear. In this study, a total of 28 1-day-old SPF chickens were intraperitoneally injected with chicken embryo fibroblast (CEF) containing 2000 PFU GX0101. Additionally, a control group, consisting of four one-day-old SPF chickens, received intraperitoneal equal doses of CEF. Blood and various tissue samples were collected at different intervals (7, 14, 21, 30, 45, 60, and 90 days post-infection; dpi) for histopathological, real-time PCR, and label-free quantitative analyses. The results showed that the serum expressions of MDV-related genes, meq and gB, peaked at 45 dpi. The heart, liver, and spleen were dissected at 30 and 45 dpi, and their hematoxylin-eosin staining indicated that virus infection compromised the normal organizational structure at 45 dpi. Particularly, the spleen structure was severely damaged, and the lymphocytes in the white medulla were significantly reduced. Furthermore, liquid chromatography-mass spectrometry (LC-MS) and label-free techniques were used to analyze the difference in splenic proteome profiles of the experimental and control groups at 30 and 45 dpi. Proteomic analysis identified 1660 and 1244 differentially expressed proteins (DEPs) at 30 and 40 dpi, respectively, compared with the uninfected spleen tissues. According to GO analysis, these DEPs were involved in processes such as organelle organization, cellular component biogenesis, cellular component assembly, anion binding, small molecule binding, metal ion binding, cation binding, cytosol, nuclear part, etc. Additionally, KEGG analysis indicated that the following pathways were linked to MDV-induced inflammation, apoptosis, and tumor: Wnt, Hippo, AMPK, cAMP, Notch, TGF-β, PI3K-Akt, Rap1, Ras, Calcium, NF-κB, PPAR, cGMP-PKG, Apoptosis, VEGF, mTOR, FoxO, TNF, JAK-STAT, MAPK, Prion disease, T cell receptor, and B cell receptor. We finally screened 674 DEPs that were linked to MDV infection in spleen tissue. This study improves our understanding of the MDV response mechanism in the spleen.

Breast cancer: miRNAs monitoring chemoresistance and systemic therapy

With a high mortality rate that accounts for millions of cancer-related deaths each year, breast cancer is the second most common malignancy in women. Chemotherapy has significant potential in the prevention and spreading of breast cancer; however, drug resistance often hinders therapy in breast cancer patients. The identification and the use of novel molecular biomarkers, which can predict response to chemotherapy, might lead to tailoring breast cancer treatment. In this context, accumulating research has reported microRNAs (miRNAs) as potential biomarkers for early cancer detection, and are conducive to designing a more specific treatment plan by helping analyze drug resistance and sensitivity in breast cancer treatment. In this review, miRNAs are discussed in two alternative ways-as tumor suppressors to be used in miRNA replacement therapy to reduce oncogenesis and as oncomirs to lessen the translation of the target miRNA. Different miRNAs like miR-638, miR-17, miR-20b, miR-342, miR-484, miR-21, miR-24, miR-27, miR-23 and miR-200 are involved in the regulation of chemoresistance through diverse genetic targets. For instance, tumor-suppressing miRNAs like miR-342, miR-16, miR-214, and miR-128 and tumor-promoting miRNAs like miR101 and miR-106-25 cluster regulate the cell cycle, apoptosis, epithelial to mesenchymal transition and other pathways to impart breast cancer drug resistance. Hence, in this review, we have discussed the significance of miRNA biomarkers that could assist in providing novel therapeutic targets to overcome potential chemotherapy resistance to systemic therapy and further facilitate the design of tailored therapy for enhanced efficacy against breast cancer.

Critical roles of non-coding RNAs in lifecycle and biology of Marek's disease herpesvirus

Over the past two decades, numerous non-coding RNAs (ncRNAs) have been identified in different biological systems including virology, especially in large DNA viruses such as herpesviruses. As a representative oncogenic alphaherpesvirus, Marek's disease virus (MDV) causes an important immunosuppressive and rapid-onset neoplastic disease of poultry, namely Marek's disease (MD). Vaccinations can efficiently prevent the onset of MD lymphomas and other clinical disease, often heralded as the first successful example of vaccination-based control of cancer. MDV infection is also an excellent model for research into virally-induced tumorigenesis. Recently, great progress has been made in understanding the functions of ncRNAs in MD biology. Herein, we give a review of the discovery and identification of MDV-encoded viral miRNAs, focusing on the genomics, expression profiles, and emerging critical roles of MDV-1 miRNAs as oncogenic miRNAs (oncomiRs) or tumor suppressor genes involved in the induction of MD lymphomas. We also described the involvements of host cellular miRNAs, lincRNAs, and circRNAs participating in MDV life cycle, pathogenesis, and/or tumorigenesis. The prospects, strategies, and new techniques such as the CRISPR/Cas9-based gene editing applicable for further investigation into the ncRNA-mediated regulatory mechanisms in MDV pathogenesis/oncogenesis were also discussed, together with the possibilities of future studies on antiviral therapy and the development of new efficient MD vaccines.

Marek's disease virus encoded miR-M6 and miR-M10 are dispensable for virus replication and pathogenesis in chickens

MicroRNAs (miRNAs) are a class of approximately 22 nucleotides long non-coding RNAs, and virus-encoded miRNAs play an important role in pathogenesis. Marek's disease virus (MDV) is an oncogenic avian alphaherpesvirus that causes immunosuppression and tumors in its natural host, chicken. In the MDV genome, 14 miRNA precursors and 26 mature miRNAs were identified, thus MDV has been used as a model to study the function of viral miRNAs in vivo. Recently, a cluster of miRNAs encoded by MDV, Cluster 3 miRNAs (miR-M8-M10), has been shown to restrict early cytolytic replication and pathogenesis of MDV. In this study, we further analyzed the role of miR-M6 and miR-M10, members of cluster miR-M8-M10, in MDV replication and pathogenicity. We found that, compared to parental MDV, deletion of miR-M6-5p significantly enhanced the replication of MDV in cell culture, but not in chickens. The replication of miR-M6-5p deletion MDV was restored once the deleted sequences were re-inserted. Our results also showed that deletion of miR-M10-5p did not affect the replication of MDV in vitro and in vivo. In addition, our animal study results showed that deletion of miR-M6-5p or miR-M10-5p did not alter the pathogenesis of MDV. In conclusion, our study shows that both miR-M6 and miR-M10 are dispensable for MDV replication and pathogenesis in chickens, while also suggests a repressive role of miR-M6 in MDV replication in cell culture.

Virus-encoded microRNA-M7 restricts early cytolytic replication and pathogenesis of Marek's disease virus

MicroRNAs (miRNAs) are a class of ∼22 nucleotides non-coding RNAs that are encoded by a wide range of hosts. Viruses, especially herpesviruses, encode a variety of miRNAs that involved in disease progression. Recently, a cluster of virus-encoded miRNAs, miR-M8-M10, have been shown to restrict early cytolytic replication and pathogenesis of Marek's disease virus (MDV), an oncogenic avian alphaherpesvirus that causes lymphoproliferative disease in chickens. In this study, we specifically dissected the role of miR-M7, a member of cluster miR-M8-M10, in regulating MDV replication and pathogenesis. We found that deletion of miR-M7-5p did not affect the virus plaque size and growth in cell culture. However, compared to parental virus, infection of miR-M7-5p deletion virus significantly increased MDV genome copy number at 5 days post infection, suggesting that miR-M7 plays a role to restrict MDV replication during early cytolytic phase. In addition, our results showed that infection of miR-M7-5p deletion virus significantly enhanced the mortality of chickens, even it induced lymphoid organ atrophy similar to parental and revertant viruses. Taken together, our study revealed that the miR-M7 acts as a repressive factor of MDV replication and pathogenesis.

Role of microRNA and long non-coding RNA in Marek's disease tumorigenesis in chicken

Marek's disease virus (MDV), the causative agent of Marek's disease (MD), results in highly infectious phymatosis, lymphatic tissue hyperplasia, and neoplasia. MD is associated with high morbidity and mortality rate. Non-coding RNAs (ncRNAs) entails long non-coding RNA (lncRNA) and microRNA (miRNA). Numerous studies have reported that specific miRNAs and lncRNAs participate in multiple cellular processes, such as proliferation, migration, and tumor cell invasion. Specialized miRNAs and lncRNAs militate a similar role in MD tumor oncogenesis. Despite its growing popularity, only a few reviews are available on ncRNA in MDV tumor oncogenes. Herein, we summarized the role of the miRNAs and lncRNAs in MD tumorigenesis. Altogether, we brought forth the research issues, such as MD prevention, screening, regulatory network formation, novel miRNAs, and lncRNAs analysis in MD that needs to be explored further. This review provides a theoretical platform for the further analysis of miRNAs and lncRNAs functions and the prevention and control of MD and malignancies in domestic animals.

Virus-encoded miR-155 ortholog in Marek's disease virus promotes cell proliferation via suppressing apoptosis by targeting tumor suppressor WWOX

Marek's disease virus serotype 1 (MDV-1) is an important oncogenic α-herpesvirus that induces immunosuppressive and rapid-onset T-cell lymphomatous disease in poultry commonly referred to as Marek's disease (MD). As an excellent biomodel for the study of virally-induced cancers in natural hosts, MDV-1 encoded microRNAs (miRNAs) have been previously demonstrated with the potential roles to act as critical regulators in virus replication, latency, pathogenesis and especially in oncogenesis. Similar to the oncogenic γ-herpesvirus Kaposi's sarcoma-associated herpesvirus (KSHV), miR-M4-5p, the cellular microRNA-155 (miR-155) ortholog encoded by MDV-1, is also involved in MD oncogenesis. In lymphoblastoid cell lines derived from MDV-induced T-cell lymphomas, miR-M4-5p has been shown to be highly expressed and participate in inducing MD lymphomagenesis by regulating multiple signal pathways. Herein we report the new identification of the host WW domain-containing oxidoreductase (WWOX) as a biological target for miR-M4-5p. Further experiments revealed that as a critical oncomiRNA, miR-M4-5p promotes the proliferations of both chicken embryo fibroblast (CEF) and MSB-1 cells via suppressing cell apoptosis by targeting WWOX, a well-known tumor suppressor. Our data presents a novel insight in elucidating the regulatory mechanisms mediated by the viral analog of miR-155 that potentially contribute to MD tumorigenesis.

Marek's Disease Virus (Gallid alphaherpesvirus 2)-Encoded miR-M2-5p Simultaneously Promotes Cell Proliferation and Suppresses Apoptosis Through RBM24 and MYOD1-Mediated Signaling Pathways

MicroRNAs (miRNAs) have been demonstrated for their involvement in virus biology and pathogenesis, including functioning as key determinants of virally-induced cancers. As an important oncogenic α-herpesvirus affecting poultry health, Marek’s disease virus serotype 1 [Gallid alphaherpesvirus 2 (GaHV-2)] induces rapid-onset T-cell lymphomatous disease commonly referred to as Marek’s disease (MD), an excellent biological model for the study of virally-induced cancer in the natural hosts. Previously, we have demonstrated that GaHV-2-encoded miRNAs (especially those within the Meq-cluster) have the potential to act as critical regulators of multiple processes such as virus replication, latency, pathogenesis, and/or oncogenesis. In addition to miR-M4-5p (miR-155 homolog) and miR-M3-5p, we have recently found that miR-M2-5p possibly participate in inducing MD lymphomagenesis. Here, we report the identification of two tumor suppressors, the RNA-binding protein 24 (RBM24) and myogenic differentiation 1 (MYOD1), being two biological targets for miR-M2-5p. Our experiments revealed that as a critical miRNA, miR-M2-5p promotes cell proliferation via regulating the RBM24-mediated p63 overexpression and MYOD1-mediated IGF2 signaling and suppresses apoptosis by targeting the MYOD1-mediated Caspase-3 signaling pathway. Our data present a new strategy of a single viral miRNA exerting dual role to potentially participate in the virally-induced T-cell lymphomagenesis by simultaneously promoting the cell proliferation and suppressing apoptosis.

The Effects of Single Nucleotide Polymorphisms in Cancer RNAi Therapies

Tremendous progress in RNAi delivery methods and design has allowed for the effective development of siRNA-based therapeutics that are currently under clinical investigation for various cancer treatments. This approach has the potential to revolutionize cancer therapy by providing the ability to specifically downregulate or upregulate the mRNA of any protein of interest. This exquisite specificity, unfortunately, also has a downside. Genetic variations in the human population are common because of the presence of single nucleotide polymorphisms (SNPs). SNPs lead to synonymous and non-synonymous changes and they occur once in every 300 base pairs in both coding and non-coding regions in the human genome. Much less common are the somatic mosaicism variations associated with genetically distinct populations of cells within an individual that is derived from postzygotic mutations. These heterogeneities in the population can affect the RNAi's efficacy or more problematically, which can lead to unpredictable and sometimes adverse side effects. From a more positive viewpoint, both SNPs and somatic mosaicisms have also been implicated in human diseases, including cancer, and these specific changes could offer the ability to effectively and, more importantly, selectively target the cancer cells. In this review, we discuss how SNPs in the human population can influence the development and success of novel anticancer RNAi therapies and the importance of why SNPs should be carefully considered.

Efficient Mutagenesis of Marek's Disease Virus-Encoded microRNAs Using a CRISPR/Cas9-Based Gene Editing System

The virus-encoded microRNAs (miRNAs) have been demonstrated to have important regulatory roles in herpesvirus biology, including virus replication, latency, pathogenesis and/or tumorigenesis. As an emerging efficient tool for gene editing, the clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9 system has been successfully applied in manipulating the genomes of large DNA viruses. Herein, utilizing the CRISPR/Cas9 system with a double-guide RNAs transfection/virus infection strategy, we have established a new platform for mutagenesis of viral miRNAs encoded by the Marek's disease virus serotype 1 (MDV-1), an oncogenic alphaherpesvirus that can induce rapid-onset T-cell lymphomas in chickens. A series of miRNA-knocked out (miR-KO) mutants with deletions of the Meq- or the mid-clustered miRNAs, namely RB-1B∆Meq-miRs, RB-1B∆M9-M2, RB-1B∆M4, RB-1B∆M9 and RB-1B∆M11, were generated from vvMDV strain RB-1B virus. Interestingly, mutagenesis of the targeted miRNAs showed changes in the in vitro virus growth kinetics, which is consistent with that of the in vivo proliferation curves of our previously reported GX0101 mutants produced by the bacterial artificial chromosome (BAC) clone and Rec E/T homologous recombination techniques. Our data demonstrate that the CRISPR/Cas9-based gene editing is a simple, efficient and relatively nondisruptive approach for manipulating the small non-coding genes from the genome of herpesvirus and will undoubtedly contribute significantly to the future progress in herpesvirus biology.

Effect of gga-miR-155 on cell proliferation, apoptosis and invasion of Marek's disease virus (MDV) transformed cell line MSB1 by targeting RORA

BACKGROUND

Marek's disease (MD) is caused by the oncogenic Marek's disease virus (MDV), and is a highly contagious avian infection with a complex underlying pathology that involves lymphoproliferative neoplasm formation. MicroRNAs (miRNAs) act as oncogenes or tumor suppressors in most cancers. The gga-miR-155 is downregulated in the MDV-infected chicken tissues or lymphocyte lines, although its exact role in tumorigenesis remains unclear. The aim of this study was to analyze the effects of gga-miR-155 on the proliferation, apoptosis and invasiveness of an MDV-transformed lymphocyte line MSB1 and elucidate the underlying mechanisms.

RESULTS

The expression level of gga-miR-155 was manipulated in MSB1 cells using specific mimics and inhibitors. While overexpression of gga-miR-155 increased proliferation, decreased the proportion of G1 phase cells relative to that in S and G2 phases, reduced apoptosis rates and increased invasiveness. However, its downregulation had the opposite effects. Furthermore, gga-miR-155 directly targeted the RORA gene and downregulated its expression in the MSB1 cells.

CONCLUSION

The gga-miR-155 promotes the proliferation and invasiveness of the MDV-transformed lymphocyte line MSB1 and inhibits apoptosis by targeting the RORA gene.

The Roles of MicroRNAs (miRNAs) in Avian Response to Viral Infection and Pathogenesis of Avian Immunosuppressive Diseases

MicroRNAs (miRNAs) are a class of non-coding small RNAs that play important roles in the regulation of various biological processes including cell development and differentiation, apoptosis, tumorigenesis, immunoregulation and viral infections. Avian immunosuppressive diseases refer to those avian diseases caused by pathogens that target and damage the immune organs or cells of the host, increasing susceptibility to other microbial infections and the risk of failure in subsequent vaccination against other diseases. As such, once a disease with an immunosuppressive feature occurs in flocks, it would be difficult for the stakeholders to have an optimal economic income. Infectious bursal disease (IBD), avian leukemia (AL), Marek’s disease (MD), chicken infectious anemia (CIA), reticuloendotheliosis (RE) and avian reovirus infection are on the top list of commonly-seen avian diseases with a feature of immunosuppression, posing an unmeasurable threat to the poultry industry across the globe. Understanding the pathogenesis of avian immunosuppressive disease is the basis for disease prevention and control. miRNAs have been shown to be involved in host response to pathogenic infections in chickens, including regulation of immunity, tumorigenesis, cell proliferation and viral replication. Here we summarize current knowledge on the roles of miRNAs in avian response to viral infection and pathogenesis of avian immunosuppressive diseases, in particular, MD, AL, IBD and RE.

Imaging Mass Spectrometry and Proteome Analysis of Marek's Disease Virus-Induced Tumors

The highly oncogenic alphaherpesvirus Marek's disease virus (MDV) causes immense economic losses in the poultry industry. MDV induces a variety of symptoms in infected chickens, including neurological disorders and immunosuppression. Most notably, MDV induces transformation of lymphocytes, leading to T cell lymphomas in visceral organs with a mortality of up to 100%. While several factors involved in MDV tumorigenesis have been identified, the transformation process and tumor composition remain poorly understood. Here we developed an imaging mass spectrometry (IMS) approach that allows sensitive visualization of MDV-induced lymphoma with a specific mass profile and precise differentiation from the surrounding tissue. To identify potential tumor markers in tumors derived from a very virulent wild-type virus and a telomerase RNA-deficient mutant, we performed laser capture microdissection (LCM) and thereby obtained tumor samples with no or minimal contamination from surrounding nontumor tissue. The proteomes of the LCM samples were subsequently analyzed by quantitative mass spectrometry based on stable isotope labeling. Several proteins, like interferon gamma-inducible protein 30 and a 70-kDa heat shock protein, were identified that are differentially expressed in tumor tissue compared to surrounding tissue and naive T cells. Taken together, our results demonstrate for the first time that MDV-induced tumors can be visualized using IMS, and we identified potential MDV tumor markers by analyzing the proteomes of virus-induced tumors.IMPORTANCE Marek's disease virus (MDV) is an oncogenic alphaherpesvirus that infects chickens and causes the most frequent clinically diagnosed cancer in the animal kingdom. Not only is MDV an important pathogen that threatens the poultry industry but it is also used as a natural virus-host model for herpesvirus-induced tumor formation. In order to visualize MDV-induced lymphoma and to identify potential biomarkers in an unbiased approach, we performed imaging mass spectrometry (IMS) and noncontact laser capture microdissection. This study provides a first description of the visualization of MDV-induced tumors by IMS that could be applied also for diagnostic purposes. In addition, we identified and validated potential biomarkers for MDV-induced tumors that could provide the basis for future research on pathogenesis and tumorigenesis of this malignancy.

MicroRNA replacement therapy in cancer

Despite the recent progress in cancer management approaches, the mortality rate of cancer is still growing and there are lots of challenges in the clinics in terms of novel therapeutics. MicroRNAs (miRNA) are regulatory small noncoding RNAs and are already confirmed to have a great role in regulating gene expression level by targeting multiple molecules that affect cell physiology and disease development. Recently, miRNAs have been introduced as promising therapeutic targets for cancer treatment. Regulatory potential of tumor suppressor miRNAs, which enables regulation of entire signaling networks within the cells, makes them an interesting option for developing cancer therapeutics. In this regard, over recent decades, scientists have aimed at developing powerful and safe targeting approaches to restore these suppressive miRNAs in cancerous cells. The present review summarizes the function of miRNAs in tumor development and presents recent findings on how miRNAs have served as therapeutic agents against cancer, with a special focus on tumor suppressor miRNAs (mimics). Moreover, the latest investigations on the therapeutic strategies of miRNA delivery have been presented.

A Tiny RNA that Packs a Big Punch: The Critical Role of a Viral miR-155 Ortholog in Lymphomagenesis in Marek's Disease

MicroRNAs (miRNAs) are small non-coding RNAs that have been identified in animals, plants, and viruses. These small RNAs play important roles in post-transcriptional regulation of various cellular processes, including development, differentiation, and all aspects of cancer biology. Rapid-onset T-cell lymphoma of chickens, namely Marek’s disease (MD), induced by Gallid alphaherpesvirus 2 (GaHV2), could provide an ideal natural animal model for herpesvirus-related cancer research. GaHV2 encodes 26 mature miRNAs derived from 14 precursors assembled in three distinct gene clusters in the viral genome. One of the most highly expressed GaHV2 miRNAs, miR-M4-5p, shows high sequence similarity to the cellular miR-155 and the miR-K12-11 encoded by Kaposi’s sarcoma-associated herpesvirus, particularly in the miRNA “seed region.” As with miR-K12-11, miR-M4-5p shares a common set of host and viral target genes with miR-155, suggesting that they may target the same regulatory cellular networks; however, differences in regulatory function between miR-155 and miR-M4-5p may distinguish non-viral and viral mediated tumorigenesis. In this review, we focus on the functions of miR-M4-5p as the viral ortholog of miR-155 to explore how the virus mimics a host pathway to benefit the viral life cycle and trigger virus-induced tumorigenesis.

Marek's disease virus type 1 encoded analog of miR-155 promotes proliferation of chicken embryo fibroblast and DF-1 cells by targeting hnRNPAB

Marek's disease virus type 1 (MDV-1) is a representative oncogenic Alpha herpesvirus that causes an immunosuppressive and neoplastic lymphoproliferative avian disease, namely Marek's disease (MD). The rapid-onset T-cell lymphoma in chickens induced by MDV-1 has been historically regarded as an ideal natural model for herpesvirus-related cancer research. As a viral analog of cellular miR-155, the MDV-1-encoded miR-M4-5p has been shown to be crucial for the virally-induced MD tumorigenesis. Our previous studies demonstrated that miR-M4-5p induces an over-expression of oncogene c-Myc by targeting LTBP1 and suppressing the TGF-β signaling pathway during MDV-1 infection. We have now further identified the chicken heterogeneous nuclear ribonucleoprotein AB (hnRNPAB) as a new cellular biological target for miR-M4-5p. Suppression of hnRNPAB expression mediated by miR-M4-5p promotes the proliferation, but not the apoptosis, of both primary chicken embryo fibroblasts (CEFs) and transformed chicken fibroblast DF-1 cell line. HnRNPAB is a member of the hnRNP family of proteins that play important roles in normal biological processes as well as cancer development. Our data suggests that the recognition and down-regulation of hnRNPAB by miR-M4-5p may be one of the important strategies for MDV-1 to trigger the development of MD lymphomas.