Characterisation of the in-vivo miRNA landscape in Drosophila ribonuclease mutants reveals Pacman-mediated regulation of the highly conserved let-7 cluster during apoptotic processes.

The control of gene expression is a fundamental process essential for correct development and to maintain homeostasis. Many post-transcriptional mechanisms exist to maintain the correct levels of each RNA transcript within the cell. Controlled and targeted cytoplasmic RNA degradation is one such mechanism with the 5'-3' exoribonuclease Pacman (XRN1) and the 3'-5' exoribonuclease Dis3L2 playing crucial roles. Loss of function mutations in either Pacman or Dis3L2 have been demonstrated to result in distinct phenotypes, and both have been implicated in human disease. One mechanism by which gene expression is controlled is through the function of miRNAs which have been shown to be crucial for the control of almost all cellular processes. Although the biogenesis and mechanisms of action of miRNAs have been comprehensively studied, the mechanisms regulating their own turnover are not well understood. Here we characterise the miRNA landscape in a natural developing tissue, the Drosophila melanogaster wing imaginal disc, and assess the importance of Pacman and Dis3L2 on the abundance of miRNAs. We reveal a complex landscape of miRNA expression and show that whilst a null mutation in dis3L2 has a minimal effect on the miRNA expression profile, loss of Pacman has a profound effect with a third of all detected miRNAs demonstrating Pacman sensitivity. We also reveal a role for Pacman in regulating the highly conserved let-7 cluster (containing miR-100, let-7 and miR-125) and present a genetic model outlining a positive feedback loop regulated by Pacman which enhances our understanding of the apoptotic phenotype observed in Pacman mutants.

Purriato is a conserved small open reading frame gene that interacts with the CASA pathway to regulate muscle homeostasis and epithelial tissue growth in Drosophila.

Recent advances in proteogenomic techniques and bioinformatic pipelines have permitted the detection of thousands of translated small Open Reading Frames (smORFs), which contain less than 100 codons, in eukaryotic genomes. Hundreds of these actively translated smORFs display conserved sequence, structure and evolutionary signatures indicating that the translated peptides could fulfil important biological roles. Despite their abundance, only tens of smORF genes have been fully characterised; these act mainly as regulators of canonical proteins involved in essential cellular processes. Importantly, some of these smORFs display conserved functions with their mutations being associated with pathogenesis. Thus, investigating smORF roles in Drosophila will not only expand our understanding of their functions but it may have an impact in human health. Here we describe the function of a novel and essential Drosophila smORF gene named purriato (prto). prto belongs to an ancient gene family whose members have expanded throughout the Protostomia clade. prto encodes a transmembrane peptide which is localized in endo-lysosomes and perinuclear and plasma membranes. prto is dynamically expressed in mesodermal tissues and imaginal discs. Targeted prto knockdown (KD) in these organs results in changes in nuclear morphology and endo-lysosomal distributions correlating with the loss of sarcomeric homeostasis in muscles and reduction of mitosis in wing discs. Consequently, prto KD mutants display severe reduction of motility, and shorter wings. Finally, our genetic interaction experiments show that prto function is closely associated to the CASA pathway, a conserved mechanism involved in turnover of mis-folded proteins and linked to muscle dystrophies and neurodegenerative diseases. Thus, this study shows the relevance of smORFs in regulating important cellular functions and supports the systematic characterisation of this class of genes to understand their functions and evolution.

Potential of Non-Coding RNA as Biomarkers for Progressive Supranuclear Palsy.

Objective markers for the neurodegenerative disorder progressive supranuclear palsy (PSP) are needed to provide a timely diagnosis with greater certainty. Non-coding RNA (ncRNA), including microRNA, piwi-interacting RNA, and transfer RNA, are good candidate markers in other neurodegenerative diseases, but have not been investigated in PSP. Therefore, as proof of principle, we sought to identify whether they were dysregulated in matched serum and cerebrospinal fluid (CSF) samples of patients with PSP. Small RNA-seq was undertaken on serum and CSF samples from healthy controls (n = 20) and patients with PSP (n = 31) in two cohorts, with reverse transcription-quantitative PCR (RT-qPCR) to confirm their dysregulation. Using RT-qPCR, we found in serum significant down-regulation in hsa-miR-92a-3p, hsa-miR-626, hsa-piR-31068, and tRNA-ValCAC. In CSF, both hsa-let-7a-5p and hsa-piR-31068 showed significant up-regulation, consistent with their changes observed in the RNA-seq results. Interestingly, we saw no correlation in the expression of hsa-piR-31068 within our matched serum and CSF samples, suggesting there is no common dysregulatory mechanism between the two biofluids. While these changes were in a small cohort of samples, we have provided novel evidence that ncRNA in biofluids could be possible diagnostic biomarkers for PSP and further work will help to expand this potential.

Profiling non-coding RNA expression in cerebrospinal fluid of amyotrophic lateral sclerosis patients.

INTRODUCTION: Objective biomarkers for the fatal neurodegenerative disease amyotrophic lateral sclerosis or motor neuron disease (ALS/MND) are critical for diagnosis, drug development, clinical trials, and insight into disease pathology. Key candidates for biomarkers present in biofluids include non-coding RNA (ncRNA) transcripts including microRNA, piwi-interacting RNA and transfer RNA. To determine if the central nervous system was the source of the dysregulated ncRNA biomarkers we previously observed in serum, we sought to identify dysregulated ncRNA candidates in cerebrospinal fluid (CSF) which may provide new insight into the disease pathology. METHODS AND MATERIALS: Small RNA sequencing (RNA-seq) was undertaken on CSF samples from healthy controls (n = 18), disease mimics (n = 8), and ALS patients (n = 40) in our Oxford Study for Biomarkers of ALS cohort, with RT-qPCR used to confirm their dysregulation. RESULTS: We found a range of ncRNA that were dysregulated in the RNA-seq screen, but these failed to be validated or detected in some cases using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Additionally, our previously identified serum ncRNA biomarker showed no change in CSF or correlation to serum. CONCLUSIONS: This study suggests the CSF may not be the source of dysregulated ncRNA in the serum and highlights the difficulty in identifying ncRNA in CSF as biomarkers for ALS.KEY MESSAGESIn this current study, we investigated the expression of non-coding RNA transcripts in the cerebrospinal fluid of ALS patients compared to healthy controls.RNA-seq identified dysregulated non-coding RNA transcripts, but these were not validated with RT-qPCR.We conclude that cerebrospinal fluid is not a suitable source of diagnostic biomarkers.

Genome-wide analyses of XRN1-sensitive targets in osteosarcoma cells identify disease-relevant transcripts containing G-rich motifs.

XRN1 is a highly conserved exoribonuclease which degrades uncapped RNAs in a 5'-3' direction. Degradation of RNAs by XRN1 is important in many cellular and developmental processes and is relevant to human disease. Studies in D. melanogaster demonstrate that XRN1 can target specific RNAs, which have important consequences for developmental pathways. Osteosarcoma is a malignancy of the bone and accounts for 2% of all pediatric cancers worldwide. Five-year survival of patients has remained static since the 1970s and therefore furthering our molecular understanding of this disease is crucial. Previous work has shown a down-regulation of XRN1 in osteosarcoma cells; however, the transcripts regulated by XRN1 which might promote osteosarcoma remain elusive. Here, we confirm reduced levels of XRN1 in osteosarcoma cell lines and patient samples and identify XRN1-sensitive transcripts in human osteosarcoma cells. Using RNA-seq in XRN1-knockdown SAOS-2 cells, we show that 1178 genes are differentially regulated. Using a novel bioinformatic approach, we demonstrate that 134 transcripts show characteristics of direct post-transcriptional regulation by XRN1. Long noncoding RNAs (lncRNAs) are enriched in this group, suggesting that XRN1 normally plays an important role in controlling lncRNA expression in these cells. Among potential lncRNAs targeted by XRN1 is HOTAIR, which is known to be up-regulated in osteosarcoma and contributes to disease progression. We have also identified G-rich and GU motifs in post-transcriptionally regulated transcripts which appear to sensitize them to XRN1 degradation. Our results therefore provide significant insights into the specificity of XRN1 in human cells which are relevant to disease.

Dis3L2 regulates cell proliferation and tissue growth through a conserved mechanism.

Dis3L2 is a highly conserved 3'-5' exoribonuclease which is mutated in the human overgrowth disorders Perlman syndrome and Wilms' tumour of the kidney. Using Drosophila melanogaster as a model system, we have generated a new dis3L2 null mutant together with wild-type and nuclease-dead genetic lines in Drosophila to demonstrate that the catalytic activity of Dis3L2 is required to control cell proliferation. To understand the cellular pathways regulated by Dis3L2 to control proliferation, we used RNA-seq on dis3L2 mutant wing discs to show that the imaginal disc growth factor Idgf2 is responsible for driving the wing overgrowth. IDGFs are conserved proteins homologous to human chitinase-like proteins such as CHI3L1/YKL-40 which are implicated in tissue regeneration as well as cancers including colon cancer and non-small cell lung cancer. We also demonstrate that loss of DIS3L2 in human kidney HEK-293T cells results in cell proliferation, illustrating the conservation of this important cell proliferation pathway. Using these human cells, we show that loss of DIS3L2 results in an increase in the PI3-Kinase/AKT signalling pathway, which we subsequently show to contribute towards the proliferation phenotype in Drosophila. Our work therefore provides the first mechanistic explanation for DIS3L2-induced overgrowth in humans and flies and identifies an ancient proliferation pathway controlled by Dis3L2 to regulate cell proliferation and tissue growth.

Identification of a potential non-coding RNA biomarker signature for amyotrophic lateral sclerosis.

Objective biomarkers for the clinically heterogeneous adult-onset neurodegenerative disorder amyotrophic lateral sclerosis are crucial to facilitate assessing emerging therapeutics and improve the diagnostic pathway in what is a clinically heterogeneous syndrome. With non-coding RNA transcripts including microRNA, piwi-RNA and transfer RNA present in human biofluids, we sought to identify whether non-coding RNA in serum could be biomarkers for amyotrophic lateral sclerosis. Serum samples from our Oxford Study for Biomarkers in motor neurone disease/amyotrophic lateral sclerosis discovery cohort of amyotrophic lateral sclerosis patients (n = 48), disease mimics (n = 16) and age- and sex-matched healthy controls (n = 24) were profiled for non-coding RNA expression using RNA-sequencing, which showed a wide range of non-coding RNA to be dysregulated. We confirmed significant alterations with reverse transcription-quantitative PCR in the expression of hsa-miR-16-5p, hsa-miR-21-5p, hsa-miR-92a-3p, hsa-piR-33151, TRV-AAC4-1.1 and TRA-AGC6-1.1. Furthermore, hsa-miR-206, a previously identified amyotrophic lateral sclerosis biomarker, showed a binary-like pattern of expression in our samples. Using the expression of these non-coding RNA, we were able to discriminate amyotrophic lateral sclerosis samples from healthy controls in our discovery cohort using a random forest analysis with 93.7% accuracy with promise in predicting progression rate of patients. Importantly, cross-validation of this novel signature using a new geographically distinct cohort of samples from the United Kingdom and Germany with both amyotrophic lateral sclerosis and control samples (n = 156) yielded an accuracy of 73.9%. The high prediction accuracy of this non-coding RNA-based biomarker signature, even across heterogeneous cohorts, demonstrates the strength of our approach as a novel platform to identify and stratify amyotrophic lateral sclerosis patients.

Corrigendum: An Overview of MicroRNAs as Biomarkers of ALS.

[This corrects the article DOI: 10.3389/fneur.2019.00186.].

An Overview of MicroRNAs as Biomarkers of ALS.

Amyotrophic lateral sclerosis (ALS; MND, motor neuron disease) is a debilitating neurodegenerative disease affecting 4.5 per 100,000 people per year around the world. There is currently no cure for this disease, and its causes are relatively unknown. Diagnosis is based on a battery of clinical tests up to a year after symptom onset, with no robust markers of diagnosis or disease progression currently identified. A major thrust of current research is to identify potential non-invasive markers ("biomarkers") in body fluids such as blood and/or cerebrospinal fluid (CSF) to use for diagnostic or prognostic purposes. Non-coding RNAs (ncRNAs), including microRNAs (miRNAs), are found at detectable and stable levels in blood and other bodily fluids. Specific ncRNAs can vary in levels between ALS patients and non-ALS controls without the disease. In this review, we will provide an overview of early findings, demonstrate the potential of this new class as biomarkers, and discuss future challenges and opportunities taking this forward to help patients with ALS.

Regulation of cytoplasmic RNA stability: Lessons from Drosophila.

The process of RNA degradation is a critical level of regulation contributing to the control of gene expression. In the last two decades a number of studies have shown the specific and targeted nature of RNA decay and its importance in maintaining homeostasis. The key players within the pathways of RNA decay are well conserved with their mutation or disruption resulting in distinct phenotypes as well as human disease. Model organisms including Drosophila melanogaster have played a substantial role in elucidating the mechanisms conferring control over RNA stability. A particular advantage of this model organism is that the functions of ribonucleases can be assessed in the context of natural cells within tissues in addition to individual immortalized cells in culture. Drosophila RNA stability research has demonstrated how the cytoplasmic decay machines, such as the exosome, Dis3L2 and Xrn1, are responsible for regulating specific processes including apoptosis, proliferation, wound healing and fertility. The work discussed here has begun to identify specific mRNA transcripts that appear sensitive to specific decay pathways representing mechanisms through which the ribonucleases control mRNA stability. Drosophila research has also contributed to our knowledge of how specific RNAs are targeted to the ribonucleases including AU rich elements, miRNA targeting and 3' tailing. Increased understanding of these mechanisms is critical to elucidating the control elicited by the cytoplasmic ribonucleases which is relevant to human disease. This article is categorized under: RNA in Disease and Development > RNA in Development RNA Turnover and Surveillance > Regulation of RNA Stability RNA Turnover and Surveillance > Turnover/Surveillance Mechanisms.

DIS3 isoforms vary in their endoribonuclease activity and are differentially expressed within haematological cancers.

DIS3 (defective in sister chromatid joining) is the catalytic subunit of the exosome, a protein complex involved in the 3'-5' degradation of RNAs. DIS3 is a highly conserved exoribonuclease, also known as Rrp44. Global sequencing studies have identified DIS3 as being mutated in a range of cancers, with a considerable incidence in multiple myeloma. In this work, we have identified two protein-coding isoforms of DIS3. Both isoforms are functionally relevant and result from alternative splicing. They differ from each other in the size of their N-terminal PIN (PilT N-terminal) domain, which has been shown to have endoribonuclease activity and tether DIS3 to the exosome. Isoform 1 encodes a full-length PIN domain, whereas the PIN domain of isoform 2 is shorter and is missing a segment with conserved amino acids. We have carried out biochemical activity assays on both isoforms of full-length DIS3 and the isolated PIN domains. We find that isoform 2, despite missing part of the PIN domain, has greater endonuclease activity compared with isoform 1. Examination of the available structural information allows us to provide a hypothesis to explain this altered behaviour. Our results also show that multiple myeloma patient cells and all cancer cell lines tested have higher levels of isoform 1 compared with isoform 2, whereas acute myeloid leukaemia and chronic myelomonocytic leukaemia patient cells and samples from healthy donors have similar levels of isoforms 1 and 2. Taken together, our data indicate that significant changes in the ratios of the two isoforms could be symptomatic of haematological cancers.

Circulating MicroRNA Biomarkers in Melanoma: Tools and Challenges in Personalised Medicine.

Effective management of melanoma depends heavily on early diagnosis. When detected in early non-metastatic stages, melanoma is almost 100% curable by surgical resection, however when detected in late metastatic stages III and IV, 5-year survival rates drop to ~50% and 10⁻25%, respectively, due to limited efficacy of current treatment options. This presents a pressing need to identify biomarkers that can detect patients at high risk of recurrence and progression to metastatic disease, which will allow for early intervention and survival benefit. Accumulating evidence over the past few decades has highlighted the potential use of circulating molecular biomarkers for melanoma diagnosis and prognosis, including lactate dehydrogenase (LDH), S100 calcium-binding protein B (S100B) and circulating tumor DNA (ctDNA) fragments. Since 2010, circulating microRNAs (miRNAs) have been increasingly recognised as more robust non-invasive biomarkers for melanoma due to their structural stability under the harsh conditions of the blood and different conditions of sample processing and isolation. Several pre-analytical and analytical variables challenge the accurate quantification of relative miRNA levels between serum samples or plasma samples, leading to conflicting findings between studies on circulating miRNA biomarkers for melanoma. In this review, we provide a critical summary of the circulating miRNA biomarkers for melanoma published to date.

Functions of long non-coding RNAs in human disease and their conservation in Drosophila development.

Genomic analysis has found that the transcriptome in both humans and Drosophila melanogaster features large numbers of long non-coding RNA transcripts (lncRNAs). This recently discovered class of RNAs regulates gene expression in diverse ways and has been involved in a large variety of important biological functions. Importantly, an increasing number of lncRNAs have also been associated with a range of human diseases, including cancer. Comparative analyses of their functions among these organisms suggest that some of their modes of action appear to be conserved. This highlights the importance of model organisms such as Drosophila, which shares many gene regulatory networks with humans, in understanding lncRNA function and its possible impact in human health. This review discusses some known functions and mechanisms of action of lncRNAs and their implication in human diseases, together with their functional conservation and relevance in Drosophila development.

Severity of Systemic Inflammatory Response Syndrome Affects the Blood Levels of Circulating Inflammatory-Relevant MicroRNAs.

The systemic inflammatory response syndrome (SIRS) is a potentially lethal response triggered by diverse forms of tissue injury and infection. When systemic inflammation is triggered by infection, the term sepsis is used. Understanding how inflammation is mediated and regulated is of enormous medical importance. We previously demonstrated that circulating inflammatory-relevant microRNAs (CIR-miRNAs) are candidate biomarkers for differentiating sepsis from SIRS. Here, we set out to determine how CIR-miRNA levels reflect SIRS severity and whether they derive from activated immune cells. Clinical disease severity scores and markers of red blood cell (RBC) damage or immune cell activation were correlated with CIR-miRNA levels in patients with SIRS and sepsis. The release of CIR-miRNAs modulated during SIRS was assessed in immune cell cultures. We show that severity of non-infective SIRS, but not sepsis is reflected in the levels of miR-378a-3p, miR-30a-5p, miR-30d-5p, and miR-192-5p. These CIR-miRNA levels positively correlate with levels of the redox biomarker, peroxiredoxin-1 (Prdx-1), which has previously been shown to be released by immune cells during inflammation. Furthermore, in vitro activated immune cells produce SIRS-associated miR-378a-3p, miR-30a-5p, miR-30d-5p, and miR-192-5p. Our study furthers the understanding of the origin, role, and trafficking of CIR-miRNAs as potential regulators of inflammation.

The roles of the exoribonucleases DIS3L2 and XRN1 in human disease.

RNA degradation is a vital post-transcriptional process which ensures that transcripts are maintained at the correct level within the cell. DIS3L2 and XRN1 are conserved exoribonucleases that are critical for the degradation of cytoplasmic RNAs. Although the molecular mechanisms of RNA degradation by DIS3L2 and XRN1 have been well studied, less is known about their specific roles in the development of multicellular organisms or human disease. This review focusses on the roles of DIS3L2 and XRN1 in the pathogenesis of human disease, particularly in relation to phenotypes seen in model organisms. The known diseases associated with loss of activity of DIS3L2 and XRN1 are discussed, together with possible mechanisms and cellular pathways leading to these disease conditions.

A novel role for the 3'-5' exoribonuclease Dis3L2 in controlling cell proliferation and tissue growth.

In a complex organism, cell proliferation and apoptosis need to be precisely controlled in order for tissues to develop correctly. Excessive cell proliferation can lead to diseases such as cancer. We have shown that the exoribonuclease Dis3L2 is required for the correct regulation of proliferation in a natural tissue within the model organism Drosophila melanogaster. Dis3L2 is a member of a highly conserved family of exoribonucleases that degrade RNA in a 3'-5' direction. We show that knockdown of dis3L2 in the Drosophila wing imaginal discs results in substantial wing overgrowth due to increased cellular proliferation rather than an increase in cell size. Imaginal discs are specified in the embryo before proliferating and differentiating to form the adult structures of the fly. Using RNA-seq we identified a small set of mRNAs that are sensitive to Dis3L2 activity. Of the mRNAs which increase in levels and are therefore potential targets of Dis3L2, we identified 2 that change at the post-transcriptional level but not at the transcriptional level, namely CG2678 (a transcription factor) and pyrexia (a TRP cation channel). We also demonstrate a compensatory effect between Dis3L2 and the 5'-3' exoribonuclease Pacman demonstrating that these 2 exoribonucleases function to regulate opposing pathways within the developing tissue. This work provides the first description of the molecular and developmental consequences of Dis3L2 inactivation in a non-human animal model. The work is directly relevant to the understanding of human overgrowth syndromes such as Perlman syndrome.

Circulating Plasma microRNAs can differentiate Human Sepsis and Systemic Inflammatory Response Syndrome (SIRS).

Systemic inflammation in humans may be triggered by infection, termed sepsis, or non-infective processes, termed non-infective systemic inflammatory response syndrome (SIRS). MicroRNAs regulate cellular processes including inflammation and may be detected in blood. We aimed to establish definitive proof-of-principle that circulating microRNAs are differentially affected during sepsis and non-infective SIRS. Critically ill patients with severe (n = 21) or non-severe (n = 8) intra-abdominal sepsis; severe (n = 23) or non-severe (n = 21) non-infective SIRS; or no SIRS (n = 16) were studied. Next-generation sequencing and qRT-PCR were used to measure plasma microRNAs. Detectable blood miRNAs (n = 116) were generally up-regulated in SIRS compared to no-SIRS patients. Levels of these 'circulating inflammation-related microRNAs' (CIR-miRNAs) were 2.64 (IQR: 2.10-3.29) and 1.52 (IQR: 1.15-1.92) fold higher for non-infective SIRS and sepsis respectively (p < 0.0001), hence CIR-miRNAs appeared less abundant in sepsis than in SIRS. Six CIR-miRNAs (miR-30d-5p, miR-30a-5p, miR-192-5p, miR-26a-5p, miR-23a-5p, miR-191-5p) provided good-to-excellent discrimination of severe sepsis from severe SIRS (0.742-0.917 AUC of ROC curves). CIR-miRNA levels inversely correlated with pro-inflammatory cytokines (IL-1, IL-6 and others). Thus, among critically ill patients, sepsis and non-infective SIRS are associated with substantial, differential changes in CIR-miRNAs. CIR-miRNAs may be regulators of inflammation and warrant thorough evaluation as diagnostic and therapeutic targets.

RNA-seq reveals post-transcriptional regulation of Drosophila insulin-like peptide dilp8 and the neuropeptide-like precursor Nplp2 by the exoribonuclease Pacman/XRN1.

Ribonucleases are critically important in many cellular and developmental processes and defects in their expression are associated with human disease. Pacman/XRN1 is a highly conserved cytoplasmic exoribonuclease which degrades RNAs in a 5'-3' direction. In Drosophila, null mutations in pacman result in small imaginal discs, a delay in onset of pupariation and lethality during the early pupal stage. In this paper, we have used RNA-seq in a genome-wide search for mRNAs misregulated in pacman null wing imaginal discs. Only 4.2% of genes are misregulated ±>2-fold in pacman null mutants compared to controls, in line with previous work showing that Pacman has specificity for particular mRNAs. Further analysis of the most upregulated mRNAs showed that Pacman post-transcriptionally regulates the expression of the secreted insulin-like peptide Dilp8. Dilp8 is related to human IGF-1, and has been shown to coordinate tissue growth with developmental timing in Drosophila. The increased expression of Dilp8 is consistent with the developmental delay seen in pacman null mutants. Our analysis, together with our previous results, show that the normal role of this exoribonuclease in imaginal discs is to suppress the expression of transcripts that are crucial in apoptosis and growth control during normal development.

Mechanisms of regulation of mature miRNAs.

miRNAs are short RNA molecules of ∼22-nt in length that play important roles in post-transcriptional control of gene expression. miRNAs normally function as negative regulators of mRNA expression by binding complementary sequences in the 3'-UTR of target mRNAs and causing translational repression and/or target degradation. Much research has been undertaken to enhance understanding of the biogenesis, function and targeting of miRNAs. However, until recently, the mechanisms underlying the regulation of the levels of mature miRNAs themselves have been largely overlooked. Although it has generally been assumed that miRNAs are stable molecules, recent evidence indicates that the stability of specific mature miRNAs can be regulated during key cellular and developmental processes in certain cell types. Here we discuss the current knowledge of the mechanisms by which mature miRNAs are regulated in the cell and the factors that contribute to the control of their stability.

The 3' to 5' Exoribonuclease DIS3: From Structure and Mechanisms to Biological Functions and Role in Human Disease.

DIS3 is a conserved exoribonuclease and catalytic subunit of the exosome, a protein complex involved in the 3' to 5' degradation and processing of both nuclear and cytoplasmic RNA species. Recently, aberrant expression of DIS3 has been found to be implicated in a range of different cancers. Perhaps most striking is the finding that DIS3 is recurrently mutated in 11% of multiple myeloma patients. Much work has been done to elucidate the structural and biochemical characteristics of DIS3, including the mechanistic details of its role as an effector of RNA decay pathways. Nevertheless, we do not understand how DIS3 mutations can lead to cancer. There are a number of studies that pertain to the function of DIS3 at the organismal level. Mutant phenotypes in S. pombe, S. cerevisiae and Drosophila suggest DIS3 homologues have a common role in cell-cycle progression and microtubule assembly. DIS3 has also recently been implicated in antibody diversification of mouse B-cells. This article aims to review current knowledge of the structure, mechanisms and functions of DIS3 as well as highlighting the genetic patterns observed within myeloma patients, in order to yield insight into the putative role of DIS3 mutations in oncogenesis.