Inhibition of Kaposi's sarcoma-associated herpesvirus lytic replication by HIV-1 Nef and cellular microRNA hsa-miR-1258

Identification of a glycolysis-related miRNA Signature for Predicting Breast cancer Survival

Breast cancer (BC) is a common type of cancer and has a poor prognosis. In this study, we collected the mRNA and miRNA expression profiles of BC patients were obtained from The Cancer Genome Atlas (TCGA) to explore a novel prognostic strategy for BC patients using bioinformatics tools. We found that six glycolysis-related miRNAs (GRmiRs, including hsa-mir-1247, hsa-mir148b, hsa-mir-133a-2, has-mir-1307, hsa-mir-195 and hsa-mir-1258) were correlated with prognosis of BC samples. The risk score model was established based on 6 prognosis-associated GRmiRs. The outcome of high risk group was significantly poorer. Cox regression analysis showed that risk score was an independent prognostic factor. Differentially expressed genes identified between high and low risk groups were mainly enriched in inflammation and immune-related signaling pathways. The proportion of infiltration of 12 kinds of immune cells in high and low risk groups were significantly different. Risk score was closely associated with many immune indexes. Multiple DEGRGs and miRNAs were associated with drugs. In conclusion, glycolysis-related miRNA signature effectively predicts BC prognosis.

Immune evasion strategy involving propionylation by the KSHV interferon regulatory factor 1 (vIRF1)

Post-translational modifications (PTMs) are essential for host antiviral immune response and viral immune evasion. Among a set of novel acylations, lysine propionylation (Kpr) has been detected in both histone and non-histone proteins. However, whether protein propionylation occurs in any viral proteins and whether such modifications regulate viral immune evasion remain elusive. Here, we show that Kaposi's sarcoma-associated herpesvirus (KSHV)-encoded viral interferon regulatory factor 1 (vIRF1) can be propionylated in lysine residues, which is required for effective inhibition of IFN-β production and antiviral signaling. Mechanistically, vIRF1 promotes its own propionylation by blocking SIRT6's interaction with ubiquitin-specific peptidase 10 (USP10) leading to its degradation via a ubiquitin-proteasome pathway. Furthermore, vIRF1 propionylation is required for its function to block IRF3-CBP/p300 recruitment and repress the STING DNA sensing pathway. A SIRT6-specific activator, UBCS039, rescues propionylated vIRF1-mediated repression of IFN-β signaling. These results reveal a novel mechanism of viral evasion of innate immunity through propionylation of a viral protein. The findings suggest that enzymes involved in viral propionylation could be potential targets for preventing viral infections.

Mapping CircRNA-miRNA-mRNA regulatory axis identifies hsa_circ_0080942 and hsa_circ_0080135 as a potential theranostic agents for SARS-CoV-2 infection

Non-coding RNAs (ncRNAs) can control the flux of genetic information; affect RNA stability and play crucial roles in mediating epigenetic modifications. A number of studies have highlighted the potential roles of both virus-encoded and host-encoded ncRNAs in viral infections, transmission and therapeutics. However, the role of an emerging type of non-coding transcript, circular RNA (circRNA) in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has not been fully elucidated so far. Moreover, the potential pathogenic role of circRNA-miRNA-mRNA regulatory axis has not been fully explored as yet. The current study aimed to holistically map the regulatory networks driven by SARS-CoV-2 related circRNAs, miRNAs and mRNAs to uncover plausible interactions and interplay amongst them in order to explore possible therapeutic options in SARS-CoV-2 infection. Patient datasets were analyzed systematically in a unified approach to explore circRNA, miRNA, and mRNA expression profiles. CircRNA-miRNA-mRNA network was constructed based on cytokine storm related circRNAs forming a total of 165 circRNA-miRNA-mRNA pairs. This study implies the potential regulatory role of the obtained circRNA-miRNA-mRNA network and proposes that two differentially expressed circRNAs hsa_circ_0080942 and hsa_circ_0080135 might serve as a potential theranostic agents for SARS-CoV-2 infection. Collectively, the results shed light on the functional role of circRNAs as ceRNAs to sponge miRNA and regulate mRNA expression during SARS-CoV-2 infection.

Pulmonary Arterial Hypertension in Patients Infected with the Human Immunodeficiency Virus

It is important to recognize and treat human immunodeficiency virus-associated pulmonary arterial hypertension (HIV-PAH) because of the associated morbidity and mortality. With the introduction of antiretroviral therapies (ART), improved survival has changed the focus of treatment management from immunodeficiency-related opportunistic infections to chronic cardiovascular complications, including HIV-PAH. The 2018 6th World Symposium of Pulmonary Hypertension recommended a revised definition of PAH that might result in a greater number of patients with HIV-PAH; however, the implication of this change is not yet clear. Here, we review the current literature on the diagnosis, management, and outcomes of patients with HIV-PAH.

Inhibition of polo-like kinase 1 (PLK1) facilitates reactivation of gamma-herpesviruses and their elimination

Both Kaposi's sarcoma-associated herpesvirus (KSHV) and Epstein-Barr virus (EBV) establish the persistent, life-long infection primarily at the latent status, and associate with certain types of tumors, such as B cell lymphomas, especially in immuno-compromised individuals including people living with HIV (PLWH). Lytic reactivation of these viruses can be employed to kill tumor cells harboring latently infected viral episomes through the viral cytopathic effects and the subsequent antiviral immune responses. In this study, we identified that polo-like kinase 1 (PLK1) is induced by KSHV de novo infection as well as lytic switch from KSHV latency. We further demonstrated that PLK1 depletion or inhibition facilitates KSHV reactivation and promotes cell death of KSHV-infected lymphoma cells. Mechanistically, PLK1 regulates Myc that is critical to both maintenance of KSHV latency and support of cell survival, and preferentially affects the level of H3K27me3 inactive mark both globally and at certain loci of KSHV viral episomes. Furthremore, we recognized that PLK1 inhibition synergizes with STAT3 inhibition to efficiently induce KSHV reactivation. We also confirmed that PLK1 depletion or inhibition yields the similar effect on EBV lytic reactivation and cell death of EBV-infected lymphoma cells. Lastly, we noticed that PLK1 in B cells is elevated in the context of HIV infection and caused by HIV Nef protein to favor KSHV/EBV latency.

CircRNA ARFGEF1 functions as a ceRNA to promote oncogenic KSHV-encoded viral interferon regulatory factor induction of cell invasion and angiogenesis by upregulating glutaredoxin 3

Circular RNAs (circRNAs) are novel single-stranded noncoding RNAs that can decoy other RNAs to inhibit their functions. Kaposi’s sarcoma (KS), caused by oncogenic Kaposi’s sarcoma-associated herpesvirus (KSHV), is a highly angiogenic and invasive vascular tumor of endothelial origin commonly found in AIDS patients. We have recently shown that KSHV-encoded viral interferon regulatory factor 1 (vIRF1) induces cell invasion, angiogenesis and cellular transformation; however, the role of circRNAs is largely unknown in the context of KSHV vIRF1. Herein, transcriptome analysis identified 22 differentially expressed cellular circRNAs regulated by vIRF1 in an endothelial cell line. Among them, circARFGEF1 was the highest upregulated circRNA. Mechanistically, vIRF1 induced circARFGEF1 transcription by binding to transcription factor lymphoid enhancer binding factor 1 (Lef1). Importantly, upregulation of circARFGEF1 was required for vIRF1-induced cell motility, proliferation and in vivo angiogenesis. circARFGEF1 functioned as a competing endogenous RNAs (ceRNAs) by binding to and inducing degradation of miR-125a-3p. Mass spectrometry analysis demonstrated that glutaredoxin 3 (GLRX3) was a direct target of miR-125a-3p. Knockdown of GLRX3 impaired cell motility, proliferation and angiogenesis induced by vIRF1. Taken together, vIRF1 transcriptionally activates circARFGEF1, potentially by binding to Lef1, to promote cell oncogenic phenotypes via inhibiting miR-125a-3p and inducing GLRX3. These findings define a novel mechanism responsible for vIRF1-induced oncogenesis and establish the scientific basis for targeting these molecules for treating KSHV-associated cancers.

Kaposi’s sarcoma-associated herpesvirus (KSHV) is the etiological agent of Kaposi’s sarcoma (KS), which frequently occurs in people with AIDS. We and others had proved that KSHV-encoded viral interferon regulatory factor 1 (vIRF1) was crucial in the pathogenesis of KSHV-induced cancers. KSHV genome transcribes viral circular RNAs (circRNAs), however, the role of cellular circRNAs in vIRF1-induced tumorigenesis remains unknown. CircRNAs serves as competitive endogenous RNAs (ceRNAs) of miRNAs, thus regulating miRNA-mRNA network to influence mRNA stability and protein expression. Here we found that vIRF1 binds to the promoter of the parental gene ARFGEF1 and activate circARFGEF1 transcription through interaction with transcription factor lymphoid enhancer binding factor 1 (Lef1). CircARFGEF1 functioned as a ceRNA by binding to and inducing degradation of miR-125a-3p, thereby abrogating the inhibition effect of this miRNA on its direct targeting of GLRX3. Significantly, circARFGEF1/miR-125a-3p/GLRX3 axis was required for vIRF1 induction of cell motility, proliferation and in vivo angiogenesis. In summary, our study describes a novel mechanism of KSHV-induced oncogenesis by hijacking host circRNAs through a viral oncogene.

Heparanase, cell signaling, and viral infections

Heparanase (HPSE) is a multifunctional protein endowed with many non-enzymatic functions and a unique enzymatic activity as an endo-β-D-glucuronidase. The latter allows it to serve as a key modulator of extracellular matrix (ECM) via a well-regulated cleavage of heparan sulfate side chains of proteoglycans at cell surfaces. The cleavage and associated changes at the ECM cause release of multiple signaling molecules with important cellular and pathological functions. New and emerging data suggest that both enzymatic as well as non-enzymatic functions of HPSE are important for health and illnesses including viral infections and virally induced cancers. This review summarizes recent findings on the roles of HPSE in activation, inhibition, or bioavailability of key signaling molecules such as AKT, VEGF, MAPK-ERK, and EGFR, which are known regulators of common viral infections in immune and non-immune cell types. Altogether, our review provides a unique overview of HPSE in cell-survival signaling pathways and how they relate to viral infections.

HIV-1 Tat Interacts with a Kaposi's Sarcoma-Associated Herpesvirus Reactivation-Upregulated Antiangiogenic Long Noncoding RNA, LINC00313, and Antagonizes Its Function

KS is a prevalent tumor associated with infections with two distinct viruses, KSHV and HIV. Since KSHV and HIV infect distinct cell types, the virus-virus interaction associated with KS formation has focused on secretory factors. HIV Tat is a well-known RNA binding protein secreted by HIV. Here, we revealed LINC00313, an lncRNA upregulated during KSHV lytic reactivation, as a novel HIV Tat-interacting lncRNA that potentially mediates HIV-KSHV interactions. We found that LINC00313 can repress endothelial cell angiogenesis-related properties potentially by interacting with chromatin remodeling complex PRC2 and downregulation of cell migration-regulating genes. An interaction between HIV Tat and LINC00313 contributed to the dissociation of PRC2 from LINC00313 and the disinhibition of LINC00313-induced repression of cell motility. Given that lncRNAs are emerging as key players in tissue physiology and disease progression, including cancer, the mechanism identified in this study may help decipher the mechanisms underlying KS pathogenesis induced by HIV and KSHV coinfection.

Kaposi’s sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi’s sarcoma (KS), an AIDS-defining cancer with abnormal angiogenesis. The high incidence of KS in human immunodeficiency virus (HIV)-infected AIDS patients has been ascribed to an interaction between HIV type 1 (HIV-1) and KSHV, focusing on secretory proteins. The HIV-1 secreted protein HIV Tat has been found to synergize with KSHV lytic proteins to induce angiogenesis. However, the impact and underlying mechanisms of HIV Tat in KSHV-infected endothelial cells undergoing viral lytic reactivation remain unclear. Here, we identified LINC00313 as a novel KSHV reactivation-activated long noncoding RNA (lncRNA) that interacts with HIV Tat. We found that LINC00313 overexpression inhibits cell migration, invasion, and tube formation, and this suppressive effect was relieved by HIV Tat. In addition, LINC00313 bound to polycomb repressive complex 2 (PRC2) complex components, and this interaction was disrupted by HIV Tat, suggesting that LINC00313 may mediate transcription repression through recruitment of PRC2 and that HIV Tat alleviates repression through disruption of this association. This notion was further supported by bioinformatics analysis of transcriptome profiles in LINC00313 overexpression combined with HIV Tat treatment. Ingenuity Pathway Analysis (IPA) showed that LINC00313 overexpression negatively regulates cell movement and migration pathways, and enrichment of these pathways was absent in the presence of HIV Tat. Collectively, our results illustrate that an angiogenic repressive lncRNA, LINC00313, which is upregulated during KSHV reactivation, interacts with HIV Tat to promote endothelial cell motility. These results demonstrate that an lncRNA serves as a novel connector in HIV-KSHV interactions.

IMPORTANCE KS is a prevalent tumor associated with infections with two distinct viruses, KSHV and HIV. Since KSHV and HIV infect distinct cell types, the virus-virus interaction associated with KS formation has focused on secretory factors. HIV Tat is a well-known RNA binding protein secreted by HIV. Here, we revealed LINC00313, an lncRNA upregulated during KSHV lytic reactivation, as a novel HIV Tat-interacting lncRNA that potentially mediates HIV-KSHV interactions. We found that LINC00313 can repress endothelial cell angiogenesis-related properties potentially by interacting with chromatin remodeling complex PRC2 and downregulation of cell migration-regulating genes. An interaction between HIV Tat and LINC00313 contributed to the dissociation of PRC2 from LINC00313 and the disinhibition of LINC00313-induced repression of cell motility. Given that lncRNAs are emerging as key players in tissue physiology and disease progression, including cancer, the mechanism identified in this study may help decipher the mechanisms underlying KS pathogenesis induced by HIV and KSHV coinfection.

miRNAs and their roles in KSHV pathogenesis

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman Disease (MCD). Recent mechanistic advances have discerned the importance of microRNAs in the virus-host relationship. KSHV has two modes of replication: lytic and latent phase. KSHV entry into permissive cells, establishment of infection, and maintenance of latency are contingent upon successful modulation of the host miRNA transcriptome. Apart from host cell miRNAs, KSHV also encodes viral miRNAs. Among various cellular and molecular targets, miRNAs are appearing to be key players in regulating viral pathogenesis. Therefore, the use of miRNAs as novel therapeutics has gained considerable attention as of late. This innovative approach relies on either mimicking miRNA species by identical oligonucleotides, or selective silencing of miRNA with specific oligonucleotide inhibitors. Here, we provide an overview of KSHV pathogenesis at the molecular level with special emphasis on the various roles miRNAs play during virus infection.

Suppression of the SAP18/HDAC1 complex by targeting TRIM56 and Nanog is essential for oncogenic viral FLICE-inhibitory protein-induced acetylation of p65/RelA, NF-κB activation, and promotion of cell invasion and angiogenesis

Kaposi's sarcoma (KS), a highly invasive and angiogenic tumor of endothelial spindle-shaped cells, is the most common AIDS-associated cancer caused by KS-associated herpesvirus (KSHV) infection. KSHV-encoded viral FLICE-inhibitory protein (vFLIP) is a viral oncogenic protein, but its role in the dissemination and angiogenesis of KSHV-induced cancers remains unknown. Here, we report that vFLIP facilitates cell migration, invasion, and angiogenesis by downregulating the SAP18-HDAC1 complex. vFLIP degrades SAP18 through a ubiquitin-proteasome pathway by recruiting E3 ubiquitin ligase TRIM56. Further, vFLIP represses HDAC1, a protein partner of SAP18, by inhibiting Nanog occupancy on the HDAC1 promoter. Notably, vFLIP impairs the interaction between the SAP18/HDAC1 complex and p65 subunit, leading to enhancement of p65 acetylation and NF-κB activation. Our data suggest a novel mechanism of vFLIP activation of the NF-κB by decreasing the SAP18/HDAC1 complex to promote the acetylation of p65 subunit, which contributes to vFLIP-induced activation of the NF-κB pathway, cell invasion, and angiogenesis. These findings advance our understanding of the mechanism of KSHV-induced pathogenesis, and providing a rationale for therapeutic targeting of the vFLIP/SAP18/HDAC1 complex as a novel strategy of AIDS-KS.

HIV-1 Nef-induced lncRNA AK006025 regulates CXCL9/10/11 cluster gene expression in astrocytes through interaction with CBP/P300

Background

HIV-associated neurocognitive disorder (HAND) is a neurodegenerative disease associated with persistent neuroinflammation and subsequent neuron damage. Pro-inflammatory factors and neurotoxins from activated astrocytes by HIV-1 itself and its encoded proteins, including the negative factor (Nef), are involved in the pathogenesis of HAND. This study was designed to find potential lncRNAs that regulate astrocyte functions and inflammation process.

Methods

We performed microarray analysis of lncRNAs from primary mouse astrocytes treated with Nef protein. Top ten lncRNAs were validated through real-time PCR analysis. Gene ontology (GO) and KEGG pathway analysis were applied to explore the potential functions of lncRNAs. RIP and ChIP assays were performed to demonstrate the mechanism of lncRNA regulating gene expression.

Results

There were 638 co-upregulated lncRNAs and 372 co-downregulated lncRNAs in primary astrocytes treated with Nef protein for both 6 h and 12 h. GO and KEGG pathway analysis showed that the biological functions of top differential-expressed mRNAs were associated with inflammatory cytokines and chemokine. Knockdown of lncRNA AK006025, not AK138360, inhibited significantly CXCL9, CXCL10 (IP-10), and CXCL11 expression in astrocytes treated with Nef protein. Mechanism study showed that AK006025 associated with CBP/P300 was enriched in the promoter of CXCL9, CXCL10, and CXCL11 genes.

Conclusions

Our findings uncovered the expression profiles of lncRNAs and mRNAs in vitro, which might help to understand the pathways that regulate astrocyte activation during the process of HAND.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1343-x) contains supplementary material, which is available to authorized users.

Upregulation of MicroRNA 711 Mediates HIV-1 Vpr Promotion of Kaposi's Sarcoma-Associated Herpesvirus Latency and Induction of Pro-proliferation and Pro-survival Cytokines by Targeting the Notch/NF-κB-Signaling Axis

Coinfection with HIV-1 and Kaposi's sarcoma-associated herpesvirus (KSHV) often leads to AIDS-related malignancies, including Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL). The interaction between HIV and KSHV plays a pivotal role in the progression of these malignancies. We have previously demonstrated that, by upregulating miR-942-5p, HIV-1 viral protein R (Vpr) inhibits KSHV lytic replication by targeting IκBα to activate the NF-κB signaling (Q. Yan, C. Shen, J. Qin, W. Li, M. Hu, H. Lu, D. Qin, J. Zhu, S. J. Gao, C. Lu, J Virol 90:8739-8753, 2016). Here, we show that Vpr inactivates Notch signaling, resulting in inhibition of KSHV lytic replication and induction of pro-proliferative and -survival cytokines, including interleukin-2 (IL-2), TIMP-1, IGF-1, and NT-4. Mechanistically, Vpr upregulates miR-711, which directly targets the Notch1 3' untranslated region. Suppression of miR-711 relieved Notch1 and reduced Vpr inhibition of KSHV lytic replication and Vpr induction of pro-proliferation and -survival cytokines, while overexpression of miR-711 exhibited the opposite effect. Finally, overexpression of Notch1 reduced Vpr induction of NF-κB activity by promoting IκBα promoter activity. Our novel findings reveal that by upregulating miR-711 to target Notch1, Vpr silences Notch signaling to activate the NF-κB pathway by reducing IκBα expression, leading to inhibition of KSHV lytic replication and induction of pro-proliferation and -survival cytokines. Therefore, the miR-711/Notch/NF-κB axis is important in the pathogenesis of AIDS-related malignancies and could be an attractive therapeutic target.IMPORTANCE HIV-1 infection significantly increases the risk of KS and PEL in KSHV-infected individuals. Our previous study has shown that HIV-1 Vpr regulates the KSHV life cycle by targeting IκBα to activate NF-κB signaling through upregulating cellular miR-942-5p. In this study, we have further found that Vpr inactivates Notch signaling to promote KSHV latency and production of pro-proliferation and -survival cytokines. Another Vpr-upregulated cellular microRNA, miR-711, participates in this process by directly targeting Notch1. As a result, Notch1 upregulation of the IκBα promoter activity is attenuated, resulting in reduced levels of IκBα transcript and protein. Overall, these results illustrate an alternative mechanism of HIV-1 Vpr regulation of KSHV latency and aberrant cytokines through the miR-711/Notch/NF-κB axis. Our novel findings further demonstrate the role of an HIV-1-secreted regulatory protein in the KSHV life cycle and KSHV-related malignancies.

The Diverse Roles of microRNAs at the Host⁻Virus Interface

MicroRNAs (miRNAs) are small, non-coding RNAs that regulate gene expression at the post-transcriptional level. Through this activity, they are implicated in almost every cellular process investigated to date. Hence, it is not surprising that miRNAs play diverse roles in regulation of viral infections and antiviral responses. Diverse families of DNA and RNA viruses have been shown to take advantage of cellular miRNAs or produce virally encoded miRNAs that alter host or viral gene expression. MiRNA-mediated changes in gene expression have been demonstrated to modulate viral replication, antiviral immune responses, viral latency, and pathogenesis. Interestingly, viruses mediate both canonical and non-canonical interactions with miRNAs to downregulate specific targets or to promote viral genome stability, translation, and/or RNA accumulation. In this review, we focus on recent findings elucidating several key mechanisms employed by diverse virus families, with a focus on miRNAs at the host–virus interface during herpesvirus, polyomavirus, retroviruses, pestivirus, and hepacivirus infections.

A KSHV microRNA enhances viral latency and induces angiogenesis by targeting GRK2 to activate the CXCR2/AKT pathway

Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi's sarcoma (KS), primary effusion lymphoma (PEL) and multicentric Castleman's disease (MCD). Most tumor cells in these malignancies are latently infected by KSHV. Thus, viral latency is critical for the development of tumor and induction of tumor-associated angiogenesis. KSHV encodes more than two dozens of miRNAs but their roles in KSHV-induced angiogenesis remains unknown. We have recently shown that miR-K12-3 (miR-K3) promoted cell migration and invasion by targeting GRK2/CXCR2/AKT signaling (PLoS Pathog, 2015;11(9):e1005171). Here, we further demonstrated a role of miR-K3 and its induced signal pathway in KSHV latency and KSHV-induced angiogenesis. We found that overexpression of miR-K3 not only promoted viral latency by inhibiting viral lytic replication, but also induced angiogenesis. Further, knockdown of GRK2 inhibited KSHV replication and enhanced KSHV-induced angiogenesis by enhancing the CXCR2/AKT signals. As a result, blockage of CXCR2 or AKT increased KSHV replication and decreased angiogenesis induced by PEL cells in vivo. Finally, deletion of miR-K3 from viral genome reduced KSHV-induced angiogenesis and increased KSHV replication. These findings indicate that the miR-K3/GRK2/CXCR2/AKT axis plays an essential role in KSHV-induced angiogenesis and promotes KSHV latency, and thus may be a potential therapeutic target of KSHV-associated malignancies.

A viral microRNA downregulates metastasis suppressor CD82 and induces cell invasion and angiogenesis by activating the c-Met signaling

Kaposi’s sarcoma (KS) is the most common AIDS-associated malignancy etiologically caused by Kaposi’s sarcoma-associated herpesvirus (KSHV). KS is a highly disseminated and vascularized tumor comprised of poorly differentiated spindle-shaped endothelial cells. KSHV encodes 12 pre-microRNAs (pre-miRNAs) that yield 25 mature miRNAs, but their roles in KSHV-induced tumor dissemination and angiogenesis remain largely unknown. KSHV-encoded miR-K12-6 (miR-K6) can produce two mature miRNAs, miR-K6-3p and miR-K6-5p. Recently, we have shown that miR-K6-3p promoted cell migration and angiogenesis by directly targeting SH3 domain binding glutamate-rich protein (SH3BGR) (PLoS Pathog. 2016;12(4):e1005605). Here, by using mass spectrometry, bioinformatics analysis and luciferase reporter assay, we showed that miR-K6-5p directly targeted the coding sequence (CDS) of CD82 molecule (CD82), a metastasis suppressor. Ectopic expression of miR-K6-5p specifically inhibited the expression of endogenous CD82 and strongly promoted endothelial cells invasion in vitro and angiogenesis in vivo. Overexpression of CD82 significantly inhibited cell invasion and angiogenesis induced by miR-K6-5p. Mechanistically, CD82 directly interacted with c-Met to inhibit its activation. MiR-K6-5p directly repressed CD82, relieving its inhibition on c-Met activation and inducing cell invasion and angiogenesis. Deletion of miR-K6 from KSHV genome abrogated KSHV suppression of CD82 resulting in compromised KSHV activation of c-Met pathway, and KSHV-induced invasion and angiogenesis. In conclusion, these results show that by inhibiting CD82, KSHV miR-K6-5p promotes cell invasion and angiogenesis by activating the c-Met pathway. Our findings illustrate that KSHV miRNAs may play an essential role in the dissemination and angiogenesis of KSHV-induced malignancies.

Multiple viral infections in primary effusion lymphoma: a model of viral cooperation in lymphomagenesis

INTRODUCTION

Primary effusion lymphoma (PEL) is a rare B-cell lymphoid neoplasm mainly associated with HIV infection, presenting as pleural, peritoneal, and pericardial effusions. A defining property of PEL is its consistent association with Kaposi sarcoma associated herpesvirus (KSHV) infection, and, in most cases, Epstein Barr virus (EBV) co-infection. On these grounds, a review of the literature related to viral cooperation and lymphomagenesis can help to understand the complex interplay between KSHV and EBV in PEL pathogenesis. Areas covered: In this review, the authors highlight clinical, pathologic, genetic and proteomic features of PEL, in the context of viral cooperation in PEL lymphomagenesis. Expert commentary: Tumour cells are characterized by the overexpression of genes that are involved in inflammation and invasion. Coherently, PEL secretomes are enriched in proteins probably responsible for the particular tropism (cell adhesion and migration) of PEL cells. The development of PEL in HIV+ patients is multifactorial and involves a complex interplay among co-infection with oncogenic viruses (EBV and KSHV), inflammatory factors, and environmental conditions.

Kaposi's sarcoma-associated herpesvirus (KSHV)-encoded microRNAs promote matrix metalloproteinases (MMPs) expression and pro-angiogenic cytokine secretion in endothelial cells

The human oncogenic virus Kaposi's sarcoma-associated herpesvirus (KSHV) is linked to Kaposi's sarcoma (KS), a tumor of endothelial cells characterized by angiogenesis and invasiveness. KSHV genome encodes 25 mature microRNAs (miRNAs), but their roles in KSHV-induced tumor dissemination and angiogenesis are not fully understood. In this study, we constructed the sensor reporters of KSHV miRNAs and used a luciferase reporter assay to demonstrate the function of the mimics of KSHV miRNAs. Then, we examined the expression of matrix metalloproteinases (MMPs) and pro-angiogenic cytokines that are related to cell migration and angiogenesis in the KSHV 25 miRNAs transfected endothelial cells. We found that all KSHV miRNAs increased the expression of the transcripts of MMP1, MMP13, VEGFA, and VEGFR2 in different degrees, as well as the secretion of VEGFA protein in the supernatant of endothelial cells. Our results reveal that KSHV miRNAs contribute to regulating MMPs and expression of pro-angiogenic factors, thus, suggesting that these miRNAs might play a crucial role in KSHV-induced cell motility and angiogenesis.

Infection of KSHV and Interaction with HIV: The Bad Romance

Kaposi's sarcoma-associated herpesvirus (KSHV), namely, human herpesvirus 8 (HHV-8), is considered as the pathogen of Kaposi's sarcoma (KS), the most frequent cancer in untreated HIV-infected individuals. Patients infected with HIV have a much higher possibility developing KS than average individual. Researchers have found that HIV, which functions as a cofactor of KS, contributes a lot to the development of KS. In this article, we will give a brief introduction of KS and KSHV and how the interaction between KSHV and HIV contributes to the development of KS. Also we will take a glance at the development of treatment in KS, especially AIDS-KS.

Does persistent HIV replication explain continued lymphoma incidence in the era of effective antiretroviral therapy?

Non-Hodgkin lymphomas are highly increased in incidence in individuals infected with HIV, and this continues to be the case in spite of highly effective combined antiretroviral therapy (cART). New evidence has demonstrated that while successful virtual recovery of CD4 counts and elimination of HIV from peripheral blood can be achieved with cART, viral replication can still occur in lymphoid tissues. In addition, recent studies have suggested that adipose tissue provides an additional reservoir for HIV-infected macrophages and T lymphocytes even in the context of successful cART therapy. In this review article, we discuss possible mechanisms leading to the development of lymphoma in the cART era.

HIV-1 Vpr Inhibits Kaposi's Sarcoma-Associated Herpesvirus Lytic Replication by Inducing MicroRNA miR-942-5p and Activating NF-κB Signaling

Kaposi's sarcoma-associated herpesvirus (KSHV) infection is required for the development of several AIDS-related malignancies, including Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL). The high incidence of AIDS-KS has been ascribed to the interaction of KSHV and HIV-1. We have previously shown that HIV-1-secreted proteins Tat and Nef regulate the KSHV life cycle and synergize with KSHV oncogenes to promote angiogenesis and tumorigenesis. Here, we examined the regulation of KSHV latency by HIV-1 viral protein R (Vpr). We found that soluble Vpr inhibits the expression of KSHV lytic transcripts and proteins, as well as viral particle production by activating NF-κB signaling following internalization into PEL cells. By analyzing the expression profiles of microRNAs combined with target search by bioinformatics and luciferase reporter analyses, we identified a Vpr-upregulated cellular microRNA (miRNA), miR-942-5p, that directly targeted IκBα. Suppression of miR-942-5p relieved the expression of IκBα and reduced Vpr inhibition of KSHV lytic replication, while overexpression of miR-942-5p enhanced Vpr inhibition of KSHV lytic replication. Our findings collectively illustrate that, by activating NF-κB signaling through upregulating a cellular miRNA to target IκBα, internalized HIV-1 Vpr inhibits KSHV lytic replication. These results have demonstrated an essential role of Vpr in the life cycle of KSHV.

IMPORTANCE

Coinfection by HIV-1 promotes the aggressive growth of Kaposi's sarcoma-associated herpesvirus (KSHV)-related malignancies, including Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL). In this study, we have shown that soluble HIV-1 Vpr inhibits KSHV lytic replication by activating NF-κB signaling following internalization into PEL cells. Mechanistic studies revealed that a cellular microRNA upregulated by Vpr, miR-942-5p, directly targeted IκBα. Suppression of miR-942-5p relieved IκBα expression and reduced Vpr inhibition of KSHV replication, while overexpression of miR-942-5p enhanced Vpr inhibition of KSHV replication. These results indicate that by activating NF-κB signaling through upregulating a cellular miRNA to target IκBα, internalized Vpr inhibits KSHV lytic replication. This work illustrates a molecular mechanism by which HIV-1-secreted regulatory protein Vpr regulates KSHV latency and the pathogenesis of AIDS-related malignancies.

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.

The SH3BGR/STAT3 Pathway Regulates Cell Migration and Angiogenesis Induced by a Gammaherpesvirus MicroRNA

Kaposi’s sarcoma (KS)-associated herpesvirus (KSHV) is a gammaherpesvirus etiologically associated with KS, a highly disseminated angiogenic tumor of hyperproliferative spindle endothelial cells. KSHV encodes 25 mature microRNAs but their roles in KSHV-induced tumor dissemination and angiogenesis remain unknown. Here, we investigated KSHV-encoded miR-K12-6-3p (miR-K6-3p) promotion of endothelial cell migration and angiogenesis, which are the underlying mechanisms of tumor dissemination and angiogenesis. We found that ectopic expression of miR-K6-3p promoted endothelial cell migration and angiogenesis. Mass spectrometry, bioinformatics and luciferase reporter analyses revealed that miR-K6-3p directly targeted sequence in the 3’ untranslated region (UTR) of SH3 domain binding glutamate-rich protein (SH3BGR). Overexpression of SH3BGR reversed miR-K6-3p induction of cell migration and angiogenesis. Mechanistically, miR-K6-3p downregulated SH3BGR, hence relieved STAT3 from SH3BGR direct binding and inhibition, which was required for miR-K6-3p maximum activation of STAT3 and induction of cell migration and angiogenesis. Finally, deletion of miR-K6 from the KSHV genome abrogated its effect on the SH3BGR/STAT3 pathway, and KSHV-induced migration and angiogenesis. Our results illustrated that, by inhibiting SH3BGR, miR-K6-3p enhances cell migration and angiogenesis by activating the STAT3 pathway, and thus contributes to the dissemination and angiogenesis of KSHV-induced malignancies.

Kaposi’s Sarcoma (KS), caused by infection of Kaposi’s sarcoma (KS)-associated herpesvirus (KSHV), is a tumor of endothelial cells characterized by angiogenesis and invasiveness. In vitro, KSHV-infected endothelial cells display an increased invasiveness and angiogenicity. KSHV encodes twelve precursor miRNAs (pre-miRNAs), which are processed into at least 25 mature miRNAs. However, the roles of these miRNAs in KSHV-induced tumor dissemination and angiogenesis remain unknown. Here, we investigated KSHV-encoded miR-K12-6-3p (miR-K6-3p) promotion of endothelial cell migration and angiogenesis, which are the underlying mechanisms of tumor dissemination and angiogenesis. We demonstrated that miR-K6-3p promoted cell migration and angiogenesis by directly targeting SH3 domain binding glutamate-rich protein (SH3BGR). Furthermore, we found that STAT3, which was negatively regulated by SH3BGR mediated miR-K6-3p-induced cell migration and angiogenesis. MiR-K6-3p downregulation of SH3BGR, hence relieved SH3BGR direct inhibition of STAT3 resulting in the activation of STAT3 and induction of cell migration and angiogenesis. These results identify miR-K6-3p and its the downstream pathway as potential therapeutic targets for the treatment of KSHV-associated malignancies.

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.

MiRNA-891a-5p mediates HIV-1 Tat and KSHV Orf-K1 synergistic induction of angiogenesis by activating NF-κB signaling

Co-infection with HIV-1 and Kaposi's sarcoma-associated herpesvirus (KSHV) is the cause of aggressive AIDS-related Kaposi's sarcoma (AIDS-KS) characterized by abnormal angiogenesis. The impact of HIV-1 and KSHV interaction on the pathogenesis and extensive angiogenesis of AIDS-KS remains unclear. Here, we explored the synergistic effect of HIV-1 Tat and KSHV oncogene Orf-K1 on angiogenesis. Our results showed that soluble Tat or ectopic expression of Tat enhanced K1-induced cell proliferation, microtubule formation and angiogenesis in chorioallantoic membrane and nude mice models. Mechanistic studies revealed that Tat promoted K1-induced angiogenesis by enhancing NF-κB signaling. Mechanistically, we showed that Tat synergized with K1 to induce the expression of miR-891a-5p, which directly targeted IκBα 3′ untranslated region, leading to NF-κB activation. Consequently, inhibition of miR-891a-5p increased IκBα level, prevented nuclear translocation of NF-κB p65 and ultimately suppressed the synergistic effect of Tat- and K1-induced angiogenesis. Our results illustrate that, by targeting IκBα to activate the NF-κB pathway, miR-891a-5p mediates Tat and K1 synergistic induction of angiogenesis. Therefore, the miR-891a-5p/NF-κB pathway is important in the pathogenesis of AIDS-KS, which could be an attractive therapeutic target for AIDS-KS.

A KSHV microRNA Directly Targets G Protein-Coupled Receptor Kinase 2 to Promote the Migration and Invasion of Endothelial Cells by Inducing CXCR2 and Activating AKT Signaling

Kaposi's sarcoma (KS) is a highly disseminated angiogenic tumor of endothelial cells linked to infection by Kaposi's sarcoma-associated herpesvirus (KSHV). KSHV encodes more than two dozens of miRNAs but their roles in KSHV-induced tumor dissemination and metastasis remain unknown. Here, we found that ectopic expression of miR-K12-3 (miR-K3) promoted endothelial cell migration and invasion. Bioinformatics and luciferase reporter analyses showed that miR-K3 directly targeted G protein-coupled receptor (GPCR) kinase 2 (GRK2, official gene symbol ADRBK1). Importantly, overexpression of GRK2 reversed miR-K3 induction of cell migration and invasion. Furthermore, the chemokine receptor CXCR2, which was negatively regulated by GRK2, was upregulated in miR-K3-transduced endothelial cells. Knock down of CXCR2 abolished miR-K3-induced cell migration and invasion. Moreover, miR-K3 downregulation of GRK2 relieved its direct inhibitory effect on AKT. Both CXCR2 induction and the release of AKT from GRK2 were required for miR-K3 maximum activation of AKT and induction of cell migration and invasion. Finally, deletion of miR-K3 from the KSHV genome abrogated its effect on the GRK2/CXCR2/AKT pathway and KSHV-induced migration and invasion. Our data provide the first-line evidence that, by repressing GRK2, miR-K3 facilitates cell migration and invasion via activation of CXCR2/AKT signaling, which likely contribute to the dissemination of KSHV-induced tumors.

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of Kaposi's sarcoma (KS). KS is a highly disseminated tumor often involved with visceral organs. Experimentally, KSHV infection induces the invasiveness of endothelial cells. KSHV encodes twelve precursor miRNAs (pre-miRNAs), which are processed into at least 25 mature miRNAs. However, the roles of these miRNAs in KSHV-induced tumor dissemination remain unknown. Here, we investigated KSHV-encoded miR-K12-3 (miR-K3) promotion of endothelial cell migration and invasion, which are the underlying mechanisms of tumor dissemination. We demonstrated that miR-K3 promoted cell migration and invasion by directly targeting G protein-coupled receptor (GPCR) kinase 2 (GRK2). Furthermore, we found that the chemokine receptor CXCR2, which was negatively regulated by GRK2, and its downstream AKT signaling positively mediated miR-K3-induced cell migration and invasion. miR-K3 downregulation of GRK2 relieved its direct inhibitory effect on AKT, and both CXCR2 induction and the release of AKT from GRK2 were required for miR-K3 maximum activation of AKT and induction of cell migration and invasion. These results show that miR-K3 and its the downstream pathway may be potential therapeutic targets for the treatment of KSHV-associated malignancies.

How do viruses trick B cells into becoming lymphomas?

PURPOSE OF REVIEW

Since the discovery of Epstein-Barr virus in Burkitt's lymphoma 50  years ago, only one other virus, namely Kaposi's sarcoma-associated herpesvirus/human herpesvirus-8, has been confirmed to be a direct cause of B-cell lymphoma. Here we will review the evidence for Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus as causal lymphoma agents.

RECENT FINDINGS

A deeper understanding of specific mechanisms by which Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus cause B-cell lymphomas has been acquired over the past years, in particular with respect to viral protein interactions with host cell pathways, and microRNA functions. Specific therapies based on knowledge of viral functions are beginning to be evaluated, mostly in preclinical models.

SUMMARY

Understanding the causal associations of specific infectious agents with certain B-cell lymphomas has allowed more accurate diagnosis and classification. A deeper knowledge of the specific mechanisms of transformation is essential to begin assessing whether virus-targeted treatment modalities may be used in the future.

MicroRNA regulation of viral immunity, latency, and carcinogenesis of selected tumor viruses and HIV

MicroRNAs (miRNAs) function as key regulators in immune responses and cancer development. In the contexts of infection with oncogenic viruses, miRNAs are engaged in viral persistence, latency establishment and maintenance, and oncogenesis. In this review, we summarize the potential roles and mechanisms of viral and cellular miRNAs in the host-pathogen interactions during infection with selected tumor viruses and HIV, which include (i) repressing viral replication and facilitating latency establishment by targeting viral transcripts, (ii) evading innate and adaptive immune responses via toll-like receptors, RIG-I-like receptors, T-cell receptor, and B-cell receptor pathways by targeting signaling molecules such as TRAF6, IRAK1, IKKε, and MyD88, as well as downstream targets including regulatory cytokines such as tumor necrosis factor α, interferon γ, interleukin 10, and transforming growth factor β, (iii) antagonizing intrinsic and extrinsic apoptosis pathways by targeting pro-apoptotic or anti-apoptotic gene transcripts such as the Bcl-2 family and caspase-3, (iv) modulating cell proliferation and survival through regulation of the Wnt, PI3K/Akt, Erk/MAPK, and Jak/STAT signaling pathways, as well as the signaling pathways triggered by viral oncoproteins such as Epstein-Barr Virus LMP1, by targeting Wnt-inhibiting factor 1, SHIP, pTEN, and SOCSs, and (v) regulating cell cycle progression by targeting cell cycle inhibitors such as p21/WAF1 and p27/KIP1. Further elucidation of the interaction between miRNAs and these key biological events will facilitate our understanding of the pathogenesis of viral latency and oncogenesis and may lead to the identification of miRNAs as novel targets for developing new therapeutic or preventive interventions.

Role of host microRNAs in Kaposi's sarcoma-associated herpesvirus pathogenesis

MicroRNAs (miRNAs) are small non-coding RNA species that can bind to both untranslated and coding regions of target mRNAs, causing their degradation or post-transcriptional modification. Currently, over 2500 miRNAs have been identified in the human genome. Burgeoning evidence suggests that dysregulation of human miRNAs can play a role in the pathogenesis of a variety of diseases, including cancer. In contrast, only a small subset of human miRNAs has been functionally validated in the pathogenesis of oncogenic viruses, in particular, Kaposi’s sarcoma-associated herpesvirus (KSHV). KSHV is the etiologic agent of several human cancers, such as primary effusion lymphoma (PEL) and Kaposi’s sarcoma (KS), which are mostly seen in acquired immune deficiency syndrome (AIDS) patients or other immuno-suppressed subpopulation. This review summarizes recent literature outlining mechanisms for KSHV/viral proteins regulation of cellular miRNAs contributing to viral pathogenesis, as well as recent findings about the unique signature of miRNAs induced by KSHV infection or KSHV-related malignancies.

HIV-1 Nef and KSHV oncogene K1 synergistically promote angiogenesis by inducing cellular miR-718 to regulate the PTEN/AKT/mTOR signaling pathway

Kaposi's sarcoma (KS) is an AIDS-defining cancer with aberrant neovascularization caused by KS-associated herpesvirus (KSHV). Although the interaction between HIV-1 and KSHV plays a pivotal role in promoting the aggressive manifestations of KS, the pathogenesis underlying AIDS-KS remains largely unknown. Here we examined HIV-1 Nef protein promotion of KSHV oncoprotein K1-induced angiogenesis. We showed that both internalized and ectopic expression of Nef in endothelial cells synergized with K1 to facilitate vascular tube formation and cell proliferation, and enhance angiogenesis in a chicken CAM model. In vivo experiments further indicated that Nef accelerated K1-induced angiogenesis and tumorigenesis in athymic nu/nu mice. Mechanistic studies revealed that Nef and K1 synergistically activated PI3K/AKT/mTOR signaling by downregulating PTEN. Furthermore, Nef and K1 induced cellular miR-718, which inhibited PTEN expression by directly targeting a seed sequence in the 3' UTR of its mRNA. Inhibition of miR-718 expression increased PTEN synthesis and suppressed the synergistic effect of Nef- and K1-induced angiogenesis and tumorigenesis. These results indicate that, by targeting PTEN, miR-718 mediates Nef- and K1-induced angiogenesis via activation of AKT/mTOR signaling. Our results demonstrate an essential role of miR-718/AKT/mTOR axis in AIDS-KS and thus may represent an attractive therapeutic target.

MicroRNA miR-BART20-5p stabilizes Epstein-Barr virus latency by directly targeting BZLF1 and BRLF1

Epstein-Barr virus (EBV) is a human herpesvirus associated with various tumors. Rather than going through the lytic cycle, EBV maintains latency by limiting the expression of viral genes in tumors. Viral microRNAs (miRNAs) of some herpesviruses have been reported to directly target immediate early genes and suppress lytic induction. In this study, we investigated whether BamHI-A rightward transcript (BART) miRNAs targeted two EBV immediate early genes, BZLF1 and BRLF1. Bioinformatic analysis predicted that 12 different BART miRNAs would target BRLF1. Of these, the results of a luciferase reporter assay indicated that only one interacted with the 3' untranslated region (UTR) of BRLF1: miR-BART20-5p. miR-BART20-5p's effect on gene expression involved two putative seed match sites in the BRLF1 3' UTR, but a mutant version of the miRNA, miR-BART20-5pm, had no effect on expression. As expected from the fact that the entire 3' UTR of BZLF1 resides within the 3' UTR of BRLF1, miR-BART20-5p interacted with the 3' UTR of BZLF1 as well. BZLF1 and BRLF1 mRNA and protein expression was suppressed in cells of an AGS cell line infected with the recombinant Akata strain of EBV (AGS-EBV) transfected with a miR-BART20-5p mimic. The expression of various EBV early proteins was also suppressed by the miR-BART20-5p mimic. In contrast, BZLF1 and BRLF1 expression in AGS-EBV cells transfected with a miR-BART20-5p inhibitor was enhanced. Furthermore, progeny virus production was suppressed by the miR-BART20-5p mimic and enhanced by the miR-BART20-5p inhibitor in AGS-EBV cells induced for the lytic cycle. Our data suggest that miR-BART20-5p plays a key role in latency maintenance in EBV-associated tumors by directly targeting immediate early genes.

IMPORTANCE

Herpesviruses maintain latency using various mechanisms and establish lifelong infection in the host. From time to time, herpesviruses are reactivated and express immediate early genes which trigger a lytic cascade, leading to the production of progeny viruses. Recently, some herpesviruses have been shown to use their own microRNAs (miRNAs) to downregulate immediate early genes to inhibit the lytic cycle. This study presents evidence that EBV also downregulates two immediate early genes by miR-BART20-5p to suppress the lytic cycle and progeny virus production. Overall, this is the first study to report the direct regulation of EBV immediate early genes by an EBV miRNA, implying its likely importance in latency maintenance in EBV-associated tumors.

Viral miRNA targeting of bicistronic and polycistronic transcripts

Successful viral infection entails a choreographic regulation of viral gene expression program. Kaposi's sarcoma-associated herpesvirus (KSHV) encodes numerous miRNAs that regulate viral life cycle. However, few viral targets have been identified due to the lack of information on KSHV 3' untranslated regions (3'UTRs). Recent genome-wide mapping of KSHV transcripts and 3'UTRs has revealed abundant bicistronic and polycistronic transcripts. The extended 3'UTRs of the 5' proximal genes of bicistronic and polycistronic transcripts offer additional regulatory targets. Indeed, a genome-wide screening of KSHV 3'UTRs has identified several bicistronic and polycistronic transcripts as the novel targets of viral miRNAs. Together, these works have expanded our knowledge of the unique features of KSHV gene regulation program and provided valuable resources for the research community.