Dysregulation of cellular microRNAs by human oncogenic viruses – Implications for tumorigenesis

Infection with certain animal and human viruses, often referred to as tumor viruses, induces oncogenic processes in their host. These viruses can induce tumorigenesis through direct and/or indirect mechanisms, and the regulation of microRNAs expression has been shown to play a key role in this process. Some human oncogenic viruses can express their own microRNAs; however, they all can dysregulate the expression of cellular microRNAs, facilitating their respective life cycles. The modulation of cellular microRNAs expression brings consequences to the host cells that may lead to malignant transformation, since microRNAs regulate the expression of genes involved in oncogenic pathways. This review focus on the mechanisms used by each human oncogenic virus to dysregulate the expression of cellular microRNAs, and their impact on tumorigenesis.     

Identification and Validation of Human Papillomavirus Encoded microRNAs

We report here identification and validation of the first papillomavirus encoded microRNAs expressed in human cervical lesions and cell lines. We established small RNA libraries from ten human papillomavirus associated cervical lesions including cancer and two human papillomavirus harboring cell lines. These libraries were sequenced using SOLiD 4 technology. We used the sequencing data to predict putative viral microRNAs and discovered nine putative papillomavirus encoded microRNAs. Validation was performed for five candidates, four of which were successfully validated by qPCR from cervical tissue samples and cell lines: two were encoded by HPV 16, one by HPV 38 and one by HPV 68. The expression of HPV 16 microRNAs was further confirmed by in situ hybridization, and colocalization with p16INK4A was established. Prediction of cellular target genes of HPV 16 encoded microRNAs suggests that they may play a role in cell cycle, immune functions, cell adhesion and migration, development, and cancer. Two putative viral target sites for the two validated HPV 16 miRNAs were mapped to the E5 gene, one in the E1 gene, two in the L1 gene and one in the LCR region. This is the first report to show that papillomaviruses encode their own microRNA species. Importantly, microRNAs were found in libraries established from human cervical disease and carcinoma cell lines, and their expression was confirmed in additional tissue samples. To our knowledge, this is also the first paper to use in situ hybridization to show the expression of a viral microRNA in human tissue.     

MicroRNA let-7b targets important cell cycle molecules in malignant melanoma cells and interferes with anchorage-independent growth

A microRNA expression screen was performed analyzing 157 different microRNAs in laser-microdissected tissues from benign melanocytic nevi (n = 10) and primary malignant melanomas (n = 10), using quantitative real-time PCR. Differential expression was found for 72 microRNAs. Members of the let-7 family of microRNAs were significantly downregulated in primary melanomas as compared with benign nevi, suggestive for a possible role of these molecules as tumor suppressors in malignant melanoma. Interestingly, similar findings had been described for lung and colon cancer. Overexpression of let-7b in melanoma cells in vitro downregulated the expression of cyclins D1, D3, and A, and cyclin-dependent kinase (Cdk) 4, all of which had been described to play a role in melanoma development. The effect of let-7b on protein expression was due to targeting of 3'-untranslated regions (3'UTRs) of individual mRNAs, as exemplified by reporter gene analyses for cyclin D1. In line with its downmodulating effects on cell cycle regulators, let-7b inhibited cell cycle progression and anchorage-independent growth of melanoma cells. Taken together, these findings not only point to new regulatory mechanisms of early melanoma development, but also may open avenues for future targeted therapies of this tumor.     

Changes in micro RNA expression in a wild tuber-bearing Solanum species induced by 5-Azacytidine treatment

Phenotypic plasticity is often postulated as a principal characteristic of tuber-bearing wild Solanum species. The hypotheses to explore this observation have been developed based on the presence of genetic variation. In this context, evolutionary changes and adaptation are impossible without genetic variation. However, epigenetic effects, which include DNA methylation and microRNAs expression control, could be another source of phenotypic variation in ecologically relevant traits. To achieve a detailed mechanistic understanding of these processes, it is necessary to separate epigenetic from DNA sequence-based effects and to evaluate their relative importance on phenotypic variability. We explored the potential relevance of epigenetic effects in individuals with the same genotype. For this purpose, a clone of the wild potato Solanum ruiz-lealii, a non-model species in which natural methylation variability has been demonstrated, was selected and its DNA methylation was manipulated applying 5-Azacytidine (AzaC), a demethylating agent. The AzaC treatment induced early flowering and changes in leaf morphology. Using quantitative real-time PCR, we identified four miRNAs up-regulated in the AzaC-treated plants. One of them, miRNA172, could play a role on the early flowering phenotype. In this work, we showed that the treatment with AzaC could provide meaningful results allowing to study both the phenotypic plasticity in tuber-bearing Solanum species and the inter-relation between DNA methylation and miRNA accumulations in a wide range of species.     

piRNA：一类新的非编码小RNA

piRNA（Piwi-interacting RNA）是从哺乳动物生殖细胞中分离得到的一类长度约为30nt的小RNA,并且这种小RNA与PIWI蛋白家族成员相结合才能发挥它的调控作用。目前,越来越多的文献表明piRNA在生殖细胞的生长发育中的调控是由于Piwi-piRNA复合物引起的基因沉默导致的,但由于对piRNA的研究尚处于初级阶段,它的一些具体的功能和生源论尚在研究当中。本文主要综述了piRNA的最新研究进展。     

The relationship between body mass and relative investment in testes mass in cetaceans: Implications for inferring interspecific variations in the extent of sperm competition

Based on sperm competition theory, percentage testes mass (% of total body mass) has been used to infer variations in the extent of sperm competition within mating systems of cetaceans. However, in most amniote taxa, including mammals, there is an underlying negative relationship between body mass and relative investment in testes mass, which must first be taken into account. Here, I identify a very strong nonlinear, negative relationship between body mass in cetaceans and relative investment in testes mass based on data from 31 species. As a result, if percentage testes mass alone is used to infer the relative extent of sperm competition in cetaceans, its importance in mating systems of smaller species is likely to be overestimated, whereas its role in larger species is likely to be underestimated. Similarly, there will also be systematic biases if this relationship is assumed to be linear when it is not. Therefore, it is essential that the underlying, nonlinear body mass–testes mass relationship is correctly taken into account when using relative investment in testes mass to estimate the relative levels of sperm competition in cetaceans. This is particularly important if such inferences are used to inform conservation strategies for endangered cetacean species.     

病毒编码的miRNA:基因表达新的调控因子

微小RNA(microRNA,miRNA)是一类长约22个核苷酸的RNA,在数量、序列、结构、表达和功能上具有多样性。目前,通过生物信息学手段和分子克隆方法,已发现了3518种miRNA,在控制细胞的生长发育、分化、凋亡等过程中发挥着十分重要的作用。最近研究发现疱疹病毒、多瘤病毒、逆转录病毒的某些病毒基因组也能够编码miRNA,这些miRNA在调控病毒基因自身表达以及病毒与宿主相互作用方面可能起重要的作用。某些病毒甚至能够利用宿主体内的miRNA调控其自身表达。找出病毒可能编码的miRNA,探索其对病毒感染、复制、表达的作用,有助于病毒分子生物学的研究,也会为研发防治病毒的新方法和新途径提供新的思路。     

Profiling microRNAs in lung tissue from pigs infected with Actinobacillus pleuropneumoniae

ABSTRACT: BACKGROUND: MicroRNAs (miRNAs) are a class of non-protein-coding genes that play a crucial regulatory role in mammalian development and disease. Whereas a large number of miRNAs have been annotated at the structural level during the latest years, functional annotation is sparse. Actinobacillus pleuropneumoniae (APP) causes serious lung infections in pigs. Severe damage to the lungs, in many cases deadly, is caused by toxins released by the bacterium and to some degree by host mediated tissue damage. However, understanding of the role of microRNAs in the course of this infectious disease in porcine is still very limited. RESULTS: In this study, the RNA extracted from visually unaffected and necrotic tissue from pigs infected with Actinobacillus pleuropneumoniae was subjected to small RNA deep sequencing. We identified 169 conserved and 11 candidate novel microRNAs in the pig. Of these, 17 were significantly up-regulated in the necrotic sample and 12 were down-regulated. The expression analysis of a number of candidates revealed microRNAs of potential importance in the innate immune response. MiR-155, a known key player in inflammation, was found expressed in both samples. Moreover, miR-664-5p, miR-451 and miR-15a appear as very promising candidates for microRNAs involved in response to pathogen infection. CONCLUSIONS: This is the first study revealing significant differences in composition and expression profiles of miRNAs in lungs infected with a bacterial pathogen. Our results extend annotation of microRNA in pig and provide insight into the role of a number of microRNAs in regulation of bacteria induced immune and inflammatory response in porcine lung.     

Sex-Biased Expression of MicroRNAs in Schistosoma mansoni

Schistosomiasis is an important neglected tropical disease caused by digenean helminth parasites of the genus Schistosoma. Schistosomes are unusual in that they are dioecious and the adult worms live in the blood system. MicroRNAs play crucial roles during gene regulation and are likely to be important in sex differentiation in dioecious species. Here we characterize 112 microRNAs from adult Schistosoma mansoni individuals, including 84 novel microRNA families, and investigate the expression pattern in different sexes. By deep sequencing, we measured the relative expression levels of conserved and newly identified microRNAs between male and female samples. We observed that 13 microRNAs exhibited sex-biased expression, 10 of which are more abundant in females than in males. Sex chromosomes showed a paucity of female-biased genes, as predicted by theoretical evolutionary models. We propose that the recent emergence of separate sexes in Schistosoma had an effect on the chromosomal distribution and evolution of microRNAs, and that microRNAs are likely to participate in the sex differentiation/maintenance process.     

Misexpression of Testicular MicroRNA in Sterile Xenopus Hybrids Points to Tetrapod-Specific MicroRNAs Associated with Male Fertility

Spermatogenesis is one of the most complex biological processes undergone by any organism, making it susceptible to perturbations that result in male sterility. Research has demonstrated that mutant phenotypes can be obtained from the disruption of epigenetic modifications, which are commonly microRNA guided. Employing the Xenopus system, whereby homogametic interspecies males are always sterile, thus violating Haldane's Rule, we deep-sequenced testes-specific small-RNAs to identify microRNAs most frequently misexpressed between sterile hybrids and their fertile parental taxa. Using these data, we cross-referenced our expression information with previously published mouse (Mus musculus) data and identified a subset of seven microRNAs common to both (miR-338, miR-222, miR-18, miR-30, miR-10, miR-196, and miR-365). We propose that these microRNAs are likely critical for spermatogenesis in all tetrapods, having retained testicular expression across ~350 million years of evolution (Amphibian-Mammal split). Gene targets of six of these microRNAs are known, and all the six associate with zinc and zinc finger proteins (both previously found critical in male fertility), and three with Hox genes (some of which have also previously been deemed critical for testicular development and male fertility). Expression information for these targets revealed that all those associated with zinc have previously been found to express in mammalian testes. One Hox target has known mammalian testicular expression, two have close relatives with known mammalian testicular expression, and two more are associated with proteins known to have mammalian testicular expression. In addition, miR-222 has prior association with spermatogenesis, and miR-30 has been found to be abundantly expressed in both mouse and human testes.     

疱疹病毒编码的miRNAs的研究进展

MicroRNAs (miRNAs)是一类长约22个核苷酸的RNA,在数量、序列、结构、表达和功能上具有多样性。目前,通过生物信息学手段和分子克隆方法,已发现了3518种miRNAs,在控制细胞的生长发育、分化、凋亡等过程中发挥着十分重要的作用。最近研究发现某些病毒基因组也能够编码miRNAs,其中大部分为疱疹病毒,这些miRNAs在调控病毒自身表达以及病毒与宿主相互作用方面可能起到重要的作用。找出病毒可能编码的miRNAs,探索其对病毒感染、复制、表达的作用,有助于病毒分子生物学的研究,也会为研发防治病毒的新方法和新途径提供新的思路。