Cancer fusion transcripts with human non-coding RNAs

Cancer chimeric, or fusion, transcripts are thought to most frequently appear due to chromosomal aberrations that combine moieties of unrelated normal genes. When being expressed, this results in chimeric RNAs having upstream and downstream parts relatively to the breakpoint position for the 5’- and 3’-fusion components, respectively. As many other types of cancer mutations, fusion genes can be of either driver or passenger type. The driver fusions may have pivotal roles in malignisation by regulating survival, growth, and proliferation of tumor cells, whereas the passenger fusions most likely have no specific function in cancer. The majority of research on fusion gene formation events is concentrated on identifying fusion proteins through chimeric transcripts. However, contemporary studies evidence that fusion events involving non-coding RNA (ncRNA) genes may also have strong oncogenic potential. In this review we highlight most frequent classes of ncRNAs fusions and summarize current understanding of their functional roles. In many cases, cancer ncRNA fusion can result in altered concentration of the non-coding RNA itself, or it can promote protein expression from the protein-coding fusion moiety. Differential splicing, in turn, can enrich the repertoire of cancer chimeric transcripts, e.g. as observed for the fusions of circular RNAs and long non-coding RNAs. These and other ncRNA fusions are being increasingly recognized as cancer biomarkers and even potential therapeutic targets. Finally, we discuss the use of ncRNA fusion genes in the context of cancer detection and therapy

Chimeric retrogenes suggest a role for the nucleolus in LINE amplification

AbstractChimeric retrogenes, found in mammalian and fungal genomes, are bipartite elements composed of DNA copies of cellular transcripts either directly fused to each other or fused to the 3′ part of a LINE retrotransposon. These cellular transcripts correspond to messenger RNAs, ribosomal RNAs, small nuclear RNAs and 7SL RNA. The chimeras are likely formed by RNA template switches during reverse transcription of LINE elements by their retrotranspositional machinery. The 5′ part of chimeras are copies of nucleolar RNAs, suggesting that the nucleolus plays a significant role in LINE retrotransposition. RNAs from the nucleolus might have protective function against retroelement invasion or, alternatively, the nucleolus may be required for retrotranspositional complex assembly and maturation. These hypotheses will be discussed in this review

How many antiviral small interfering RNAs may be encoded by the mammalian genomes?

<p>Abstract</p> <p>Background</p> <p>The discovery of RNA interference phenomenon (RNAi) and understanding of its mechanisms has revolutionized our views on many molecular processes in the living cell. Among the other, RNAi is involved in silencing of transposable elements and in inhibition of virus infection in various eukaryotic organisms. Recent experimental studies demonstrate few cases of viral replication suppression via complementary interactions between the mammalian small RNAs and viral transcripts.</p> <p>Presentation of the hypothesis</p> <p>It was found that >50% of the human genome is transcribed in different cell types and that these transcripts are mainly not associated with known protein coding genes, but represent non-coding RNAs of unknown functions. We propose a hypothesis that mammalian DNAs encode thousands RNA motifs that may serve for antiviral protection. We also presume that the evolutional success of some groups of genomic repeats and, in particular, of transposable elements (TEs) may be due to their ability to provide antiviral RNA motifs to the host organism. Intense genomic repeat propagation into the genome would inevitably cause bidirectional transcription of these sequences, and the resulting double-stranded RNAs may be recognized and processed by the RNA interference enzymatic machinery. Provided that these processed target motifs may be complementary to viral transcripts, fixation of the repeats into the host genome may be of a considerable benefit to the host. It fits with our bioinformatical data revealing thousands of 21-28 bp long motifs identical between human DNA and human-pathogenic adenoviral and herpesviral genomes. Many of these motifs are transcribed in human cells, and the transcribed part grows proportionally to their lengths. Many such motifs are included in human TEs. For example, one 23 nt-long motif that is a part of human abundant Alu retrotransposon, shares sequence identity with eight human adenoviral genomes.</p> <p>Testing the hypothesis</p> <p>This hypothesis could be tested on various mammalian species and viruses infecting mammalian cells.</p> <p>Implications of the hypothesis</p> <p>This hypothesis proposes that mammalian organisms may use their own genomes as sources of thousands of putative interfering RNA motifs that can be recruited to repress intracellular pathogens like proliferating viruses.</p> <p>Reviewers</p> <p>This article was reviewed by Eugene V. Koonin, Valerian V. Dolja and Yuri V. Shpakovski.</p

Uniformly shaped harmonization combines human transcriptomic data from different platforms while retaining their biological properties and differential gene expression patterns

Introduction: Co-normalization of RNA profiles obtained using different experimental platforms and protocols opens avenue for comprehensive comparison of relevant features like differentially expressed genes associated with disease. Currently, most of bioinformatic tools enable normalization in a flexible format that depends on the individual datasets under analysis. Thus, the output data of such normalizations will be poorly compatible with each other. Recently we proposed a new approach to gene expression data normalization termed Shambhala which returns harmonized data in a uniform shape, where every expression profile is transformed into a pre-defined universal format. We previously showed that following shambhalization of human RNA profiles, overall tissue-specific clustering features are strongly retained while platform-specific clustering is dramatically reduced.Methods: Here, we tested Shambhala performance in retention of fold-change gene expression features and other functional characteristics of gene clusters such as pathway activation levels and predicted cancer drug activity scores.Results: Using 6,793 cancer and 11,135 normal tissue gene expression profiles from the literature and experimental datasets, we applied twelve performance criteria for different versions of Shambhala and other methods of transcriptomic harmonization with flexible output data format. Such criteria dealt with the biological type classifiers, hierarchical clustering, correlation/regression properties, stability of drug efficiency scores, and data quality for using machine learning classifiers.Discussion: Shambhala-2 harmonizer demonstrated the best results with the close to 1 correlation and linear regression coefficients for the comparison of training vs validation datasets and more than two times lesser instability for calculation of drug efficiency scores compared to other methods

Tripartite chimeric pseudogene from the genome of rice blast fungus Magnaporthe grisea suggests double template jumps during long interspersed nuclear element (LINE) reverse transcription

<p>Abstract</p> <p>Background</p> <p>A systematic survey of loci carrying retrotransposons in the genome of the rice blast fungus <it>Magnaporthe grisea </it>allowed the identification of novel non-canonical retropseudogenes. These elements are chimeric retrogenes composed of DNA copies from different cellular transcripts directly fused to each other. Their components are copies of a non protein-coding highly expressed RNA of unknown function termed WEIRD and of two fungal retrotransposons: MGL and Mg-SINE. Many of these chimeras are transcribed in various <it>M. grisea </it>tissues and during plant infection. Chimeric retroelements with a similar structure were recently found in three mammalian genomes. All these chimeras are likely formed by RNA template switches during the reverse transcription of diverse LINE elements.</p> <p>Results</p> <p>We have shown that in <it>M. grisea </it>template switching occurs at specific sites within the initial template RNA which contains a characteristic consensus sequence. We also provide evidence that both single and double template switches may occur during LINE retrotransposition, resulting in the fusion of three different transcript copies. In addition to the 33 bipartite elements, one tripartite chimera corresponding to the fusion of three retrotranscripts (WEIRD, Mg-SINE, MGL-LINE) was identified in the <it>M. grisea </it>genome. Unlike the previously reported two human tripartite elements, this fungal retroelement is flanked by identical 14 bp-long direct repeats. The presence of these short terminal direct repeats demonstrates that the LINE enzymatic machinery was involved in the formation of this chimera and its integration in the <it>M. grisea </it>genome.</p> <p>Conclusion</p> <p>A survey of mammalian genomic databases also revealed two novel tripartite chimeric retroelements, suggesting that double template switches occur during reverse transcription of LINE retrotransposons in different eukaryotic organisms.</p

Friends-Enemies: Endogenous Retroviruses Are Major Transcriptional Regulators of Human DNA

Endogenous retroviruses are mobile genetic elements hardly distinguishable from infectious, or “exogenous,” retroviruses at the time of insertion in the host DNA. Human endogenous retroviruses (HERVs) are not rare. They gave rise to multiple families of closely related mobile elements that occupy ~8% of the human genome. Together, they shape genomic regulatory landscape by providing at least ~320,000 human transcription factor binding sites (TFBS) located on ~110,000 individual HERV elements. The HERVs host as many as 155,000 mapped DNaseI hypersensitivity sites, which denote loci active in the regulation of gene expression or chromatin structure. The contemporary view of the HERVs evolutionary dynamics suggests that at the early stages after insertion, the HERV is treated by the host cells as a foreign genetic element, and is likely to be suppressed by the targeted methylation and mutations. However, at the later stages, when significant number of mutations has been already accumulated and when the retroviral genes are broken, the regulatory potential of a HERV may be released and recruited to modify the genomic balance of transcription factor binding sites. This process goes together with further accumulation and selection of mutations, which reshape the regulatory landscape of the human DNA. However, developmental reprogramming, stress or pathological conditions like cancer, inflammation and infectious diseases, can remove the blocks limiting expression and HERV-mediated host gene regulation. This, in turn, can dramatically alter the gene expression equilibrium and shift it to a newer state, thus further amplifying instability and exacerbating the stressful situation

Functional human endogenous retroviral LTR transcription start sites are located between the R and U5 regions

AbstractHuman endogenous retroviruses (HERVs) occupy about 5% of human DNA and are thought to be remnants of ancient retroviral infections of human ancestors' germ cells. HERVs can modify expression of host cell genes through their cis-regulatory elements concentrated in their long terminal repeats (LTRs). Although numerous HERV-related RNAs were identified in the human transcriptome, for most of them, it remains unclear whether they are LTR-promoted or read-through products initiated from neighboring genomic promoters. Here, we describe mapping of transcriptional start sites within solitary and proviral LTRs of the HERV-K (HML-2) human-specific subfamily of endogenous retroviruses. Surprisingly, the transcription was initiated predominantly from the very 3′ termini of the LTR R regions. The data presented here may shed light on adaptive coevolution of human endogenous retroviruses with their host cells

FLOating-Window Projective Separator (FloWPS): A Data Trimming Tool for Support Vector Machines (SVM) to Improve Robustness of the Classifier

Here, we propose a heuristic technique of data trimming for SVM termed FLOating Window Projective Separator (FloWPS), tailored for personalized predictions based on molecular data. This procedure can operate with high throughput genetic datasets like gene expression or mutation profiles. Its application prevents SVM from extrapolation by excluding non-informative features. FloWPS requires training on the data for the individuals with known clinical outcomes to create a clinically relevant classifier. The genetic profiles linked with the outcomes are broken as usual into the training and validation datasets. The unique property of FloWPS is that irrelevant features in validation dataset that don’t have significant number of neighboring hits in the training dataset are removed from further analyses. Next, similarly to the k nearest neighbors (kNN) method, for each point of a validation dataset, FloWPS takes into account only the proximal points of the training dataset. Thus, for every point of a validation dataset, the training dataset is adjusted to form a floating window. FloWPS performance was tested on ten gene expression datasets for 992 cancer patients either responding or not on the different types of chemotherapy. We experimentally confirmed by leave-one-out cross-validation that FloWPS enables to significantly increase quality of a classifier built based on the classical SVM in most of the applications, particularly for polynomial kernels