Expression of short hairpin RNAs using the compact architecture of retroviral microRNA genes

Analysis of Nucleotide Sequence of Tax, miRNA and LTR of Bovine Leukemia Virus in Cattle with Different Levels of Persistent Lymphocytosis in Russia

Bovine Leukemia Virus (BLV) is the etiological agent of enzootic bovine leucosis (EBL), a lymphoproliferative disease of the bovine species. In BLV-infected cells, the long terminal repeat (LTR), the viral Tax protein and viral miRNAs promote viral and cell proliferation as well as tumorigenesis. Although their respective roles are decisive in BLV biology, little is known about the genetic sequence variation of these parts of the BLV genome and their impact on disease outcome. Therefore, the objective of this study was to assess the relationship between disease progression and sequence variation of the BLV Tax, miRNA and LTR regions in infected animals displaying either low or high levels of persistent lymphocytosis (PL). A statistically significant association was observed between the A(+187)C polymorphism in the downstream activator sequence (DAS) region in LTR (p-value = 0.00737) and high lymphocytosis. Our study also showed that the mutation A(−4)G in the CAP site occurred in 70% of isolates with low PL and was not found in the high PL group. Conversely, the mutations G(−133)A/C in CRE2 (46.7%), C(+160)T in DAS (30%) and A(310)del in BLV-mir-B4-5p, A(357)G in BLV-mir-B4-3p, A(462)G in BLV-mir-B5-5p, and GA(497–498)AG in BLV-mir-B5-3p (26.5%) were often seen in isolates with high PL and did not occur in the low PL group. In conclusion, we found several significant polymorphisms among BLV genomic sequences in Russia that would explain a progression towards higher or lower lymphoproliferation. The data presented in this article enabled the classification between two different genotypes; however, clear association between genotypes and the PL development was not found.

Modulating the Crosstalk between the Tumor and Its Microenvironment Using RNA Interference: A Treatment Strategy for Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most common primary liver malignancy with one of the highest mortality rates among solid cancers. It develops almost exclusively in the background of chronic liver inflammation, which can be caused by viral hepatitis, chronic alcohol consumption or an unhealthy diet. Chronic inflammation deregulates the innate and adaptive immune responses that contribute to the proliferation, survival and migration of tumor cells. The continuous communication between the tumor and its microenvironment components serves as the overriding force of the tumor against the body's defenses. The importance of this crosstalk between the tumor microenvironment and immune cells in the process of hepatocarcinogenesis has been shown, and therapeutic strategies modulating this communication have improved the outcomes of patients with liver cancer. To target this communication, an RNA interference (RNAi)-based approach can be used, an innovative and promising strategy that can disrupt the crosstalk at the transcriptomic level. Moreover, RNAi offers the advantage of specificity in comparison to the treatments currently used for HCC in clinics. In this review, we will provide the recent data pertaining to the modulation of a tumor and its microenvironment by using RNAi and its potential for therapeutic intervention in HCC.

Ablation of non-coding RNAs affects bovine leukemia virus B lymphocyte proliferation and abrogates oncogenesis

Viruses have developed different strategies to escape from immune response. Among these, viral non-coding RNAs are invisible to the immune system and may affect the fate of the host cell. Bovine leukemia virus (BLV) encodes both short (miRNAs) and long (antisense AS1 and AS2) non-coding RNAs. To elucidate the mechanisms associated with BLV non-coding RNAs, we performed phenotypic and transcriptomic analyzes in a reverse genetics system. RNA sequencing of B-lymphocytes revealed that cell proliferation is the most significant mechanism associated with ablation of the viral non-coding RNAs. To assess the biological relevance of this observation, we determined the cell kinetic parameters in vivo using intravenous injection of BrdU and CFSE. Fitting the data to a mathematical model provided the rates of cell proliferation and death. Our data show that deletion of miRNAs correlates with reduced proliferation of the infected cell and lack of pathogenesis.

BLV is a retrovirus that integrates into the genomic DNA of B-lymphocytes from a series of ruminant species (cattle, sheep, zebu, water buffalo and yack). Expression of viral proteins is almost undetectable in infected animals. In contrast, the BLV genome contains a cluster of 10 microRNAs that are abundantly transcribed in BLV-infected cells in vivo. In this report, we show that these microRNAs primarily regulate host cell proliferation. Ablation of the viral microRNAs affects BLV replication and suppresses leukemia development.

Bovine Foamy Virus: Shared and Unique Molecular Features In Vitro and In Vivo

The retroviral subfamily of Spumaretrovirinae consists of five genera of foamy (spuma) viruses (FVs) that are endemic in some mammalian hosts [1]. Closely related species may be susceptible to the same or highly related FVs. FVs are not known to induce overt disease and thus do not pose medical problems to humans and livestock or companion animals. A robust lab animal model is not available or is a lab animal a natural host of a FV. Due to this, research is limited and often focused on the simian FVs with their well-established zoonotic potential. The authors of this review and their groups have conducted several studies on bovine FV (BFV) in the past with the intention of (i) exploring the risk of zoonotic infection via beef and raw cattle products, (ii) studying a co-factorial role of BFV in different cattle diseases with unclear etiology, (iii) exploring unique features of FV molecular biology and replication strategies in non-simian FVs, and (iv) conducting animal studies and functional virology in BFV-infected calves as a model for corresponding studies in primates or small lab animals. These studies gained new insights into FV-host interactions, mechanisms of gene expression, and transcriptional regulation, including miRNA biology, host-directed restriction of FV replication, spread and distribution in the infected animal, and at the population level. The current review attempts to summarize these findings in BFV and tries to connect them to findings from other FVs.

Functional characterization of the bovine foamy virus miRNA expression cassette and its dumbbell-shaped pri-miRNA

Foamy viruses are unconventional and complex retroviruses distinct from the other members of the Retroviridae family. Currently, no disease has been firmly linked to persistent foamy virus infection of their cognate host including simians, bovines, felines, and equines or upon zoonotic transmission of different simian foamy viruses to humans. Bovine and simian foamy viruses have been recently shown to encode a RNA polymerase-III-driven micro RNA cluster which likely modulates and regulates host-virus interactions at different levels. Using sub-genomic bovine foamy virus micro RNA expression plasmids and dual luciferase reporter assays as readout, the requirements for expression and processing of the bovine foamy virus micro RNAs have been analyzed. Here, we report that the minimal BFV micro RNA cassette is significantly weaker than a U6 promoter-based construct and strongly suppressed by flanking sequences. The primary micro RNA sequence can be manipulated and chimerized as long as the dumbbell-like folding of the primary micro RNA is maintained. Since more subtle changes are associated with reduced functionality, the overall structure and shape, but possibly individual elements and residues also, are important for the expression and processing of the bovine foamy virus micro RNAs.