Regulating the ribosome: a spotlight on RNA dark matter

Xiaotan Sanjie Decoction Inhibits Gastric Cancer Cell Proliferation, Migration, and Invasion through lncRNA-ATB and miR-200A

This study is aimed at exploring whether Xiaotan Sanjie decoction (XTSJ) inhibits gastric cancer (GC) proliferation and metastasis by regulating lncRNA-ATB expression. qRT-PCR and Western blot were used to analyze lncRNA-ATB and downstream-regulated genes/proteins in human GC cells. CCK8, Edu, and flow cytometry assays were used to detect the inhibitory effect of XTSJ on cell proliferation and apoptosis. Moreover, transwell and wound healing assays were used to detect the inhibitory effect of XTSJ on migration and invasion. qRT-PCR and Western blot were used to detect regulated genes and proteins levels. The HGC-27 cell line was used for follow-up analysis due to the high level of lncRNA-ATB and cell characteristics. XTSJ inhibited the proliferation and metastasis of HGC-27 in a dose-dependent manner. Further research found that XTSJ downregulated lncRNA-ATB, Vimentin, and N-cadherin, while it upregulated miR-200a and E-cadherin in a dose-dependent manner. XTSJ also upregulated Caspase 3, Caspase 9, Bax, and downregulated Bcl-2. Furthermore, XTSJ inhibited tumor growth in vivo and downregulated EMT signaling pathways. These results indicate that XTSJ may affect EMT and Bcl-2 signaling pathways by regulating lncRNA-ATB and miR-200a, thus inhibiting proliferation, migration, and invasion of HGC-27 cells. Therefore, XTSJ may be an effective treatment for the high levels of lncRNA-ATB in GC.

Ribosome-Associated ncRNAs (rancRNAs) Adjust Translation and Shape Proteomes

The regulation of protein synthesis is of extreme importance for cell survival in challenging environmental conditions. Modulating gene expression at the level of translation allows a swift and low-energy-cost response to external stimuli. In the last decade, an emerging class of regulatory ncRNAs, namely ribosome-associated non-coding RNAs (rancRNAs), has been discovered. These rancRNAs have proven to be efficient players in the regulation of translation as a first wave of stress adaptation by directly targeting the ribosome, the central enzyme of protein production. This underlying principle appears to be highly conserved, since rancRNAs are present in all three domains of life. Here, we review the major findings and mechanistic peculiarities of rancRNAs, a class of transcripts that is providing new and broader perspectives on the complexity of the ribosome and translation regulation.

A small ribosome-associated ncRNA globally inhibits translation by restricting ribosome dynamics

Ribosome-associated non-coding RNAs (rancRNAs) have been recognized as an emerging class of regulatory molecules capable of fine-tuning translation in all domains of life. RancRNAs are ideally suited for allowing a swift response to changing environments and are therefore considered pivotal during the first wave of stress adaptation. Previously, we identified an mRNA-derived 18 nucleotides long rancRNA (rancRNA_18) in Saccharomyces cerevisiae that rapidly downregulates protein synthesis during hyperosmotic stress. However, the molecular mechanism of action remained enigmatic. Here, we combine biochemical, genetic, transcriptome-wide and structural evidence, thus revealing rancRNA_18 as global translation inhibitor by targeting the E-site region of the large ribosomal subunit. Ribosomes carrying rancRNA_18 possess decreased affinity for A-site tRNA and impaired structural dynamics. Cumulatively, these discoveries reveal the mode of action of a rancRNA involved in modulating protein biosynthesis at a thus far unequalled precision.

Exploiting transfer learning for the reconstruction of the human gene regulatory network

MOTIVATION

The reconstruction of gene regulatory networks (GRNs) from gene expression data has received increasing attention in recent years, due to its usefulness in the understanding of regulatory mechanisms involved in human diseases. Most of the existing methods reconstruct the network through machine learning approaches, by analyzing known examples of interactions. However, (i) they often produce poor results when the amount of labeled examples is limited, or when no negative example is available and (ii) they are not able to exploit information extracted from GRNs of other (better studied) related organisms, when this information is available.

RESULTS

In this paper, we propose a novel machine learning method that overcomes these limitations, by exploiting the knowledge about the GRN of a source organism for the reconstruction of the GRN of the target organism, by means of a novel transfer learning technique. Moreover, the proposed method is natively able to work in the positive-unlabeled setting, where no negative example is available, by fruitfully exploiting a (possibly large) set of unlabeled examples. In our experiments, we reconstructed the human GRN, by exploiting the knowledge of the GRN of Mus musculus. Results showed that the proposed method outperforms state-of-the-art approaches and identifies previously unknown functional relationships among the analyzed genes.

AVAILABILITY AND IMPLEMENTATION

http://www.di.uniba.it/∼mignone/systems/biosfer/index.html.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Research progress on the interactions between long non-coding RNAs and microRNAs in human cancer

Numerous types of molecular mechanisms mediate the development of cancer. Non-coding RNAs (ncRNAs) are being increasingly recognized to play important role in mediating the development of diseases, including cancer. Long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) are the two most widely studied ncRNAs. Thus far, lncRNAs are known to have biological roles through a variety of mechanisms, including genetic imprinting, chromatin remodeling, cell cycle control, splicing regulation, mRNA decay and translational regulation, and miRNAs regulate gene expression through the degradation of mRNAs and lncRNAs. Although ncRNAs account for a major proportion of the total RNA, the mechanisms underlying the physiological or pathological processes mediated by various types of ncRNAs, and the specific interaction mechanisms between miRNAs and lncRNAs in various physiological and pathological processes, remain largely unknown. Thus, further research in this field is required. In general, the interaction mechanisms between miRNAs and lncRNAs in human cancer have become important research topics, and the study thereof has led to the recent development of related technologies. By providing examples and descriptions, and performing chart analysis, the present study aimed to review the interaction mechanisms and research approaches for these two types of ncRNAs, as well as their roles in the occurrence and development of cancer. These details have far-reaching significance for the utilization of these molecules in the diagnosis and treatment of cancer.

Role of lncRNA-ATB in ovarian cancer and its mechanisms of action

This study aimed to elucidate the role of long non-coding RNA activated by transforming growth factor-β (lncRNA-ATB) in ovarian cancer and its underlying mechanisms of action. Expression levels of lncRNA-ATB in ovarian cancer cell line SKOV3 and in a healthy human ovarian cell line were compared using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The results indicated that lncRNA-ATB was expressed at significantly higher levels in SKOV3 cells compared with the healthy cell line. After downregulation of lncRNA-ATB expression in SKOV3 cells using lncRNA-ATB-short hairpin RNA, cell proliferation, apoptosis, invasion and migration were assessed using Cell counting kit-8, Live Dead staining, Transwell assay and wound healing assay, respectively. RT-qPCR and western blotting were used to quantify the expression of signal transducer and activator of transcription 3 (STAT3), phosphorylated (p)-STAT3, and the additional epithelial to mesenchymal transition (EMT)-related proteins E-cadherin and vimentin in SKOV3 cells. LncRNA-ATB downregulation significantly reduced SKOV3 cell proliferation, invasion and migration, promoted apoptosis, decreased the expression of p-STAT3 and vimentin, and increased E-cadherin expression. Taken together, these results suggest that lncRNA-ATB downregulation can inhibit ovarian cancer cell proliferation, invasion and migration, and promote cell apoptosis. Lnc-RNA-ATB may therefore be a new target for ovarian cancer treatment.

eIF4A2 drives repression of translation at initiation by Ccr4-Not through purine-rich motifs in the 5'UTR

BACKGROUND

Regulation of the mRNA life cycle is central to gene expression control and determination of cell fate. miRNAs represent a critical mRNA regulatory mechanism, but despite decades of research, their mode of action is still not fully understood.

RESULTS

Here, we show that eIF4A2 is a major effector of the repressive miRNA pathway functioning via the Ccr4-Not complex. We demonstrate that while DDX6 interacts with Ccr4-Not, its effects in the mechanism are not as pronounced. Through its interaction with the Ccr4-Not complex, eIF4A2 represses mRNAs at translation initiation. We show evidence that native eIF4A2 has similar RNA selectivity to chemically inhibited eIF4A1. eIF4A2 exerts its repressive effect by binding purine-rich motifs which are enriched in the 5'UTR of target mRNAs directly upstream of the AUG start codon.

CONCLUSIONS

Our data support a model whereby purine motifs towards the 3' end of the 5'UTR are associated with increased ribosome occupancy and possible uORF activation upon eIF4A2 binding.

Control of structure-specific endonucleases to maintain genome stability

Structure-specific endonucleases (SSEs) have key roles in DNA replication, recombination and repair, and emerging roles in transcription. These enzymes have specificity for DNA secondary structure rather than for sequence, and therefore their activity must be precisely controlled to ensure genome stability. In this Review, we discuss how SSEs are controlled as part of genome maintenance pathways in eukaryotes, with an emphasis on the elaborate mechanisms that regulate the members of the major SSE families - including the xeroderma pigmentosum group F-complementing protein (XPF) and MMS and UV-sensitive protein 81 (MUS81)-dependent nucleases, and the flap endonuclease 1 (FEN1), XPG and XPG-like endonuclease 1 (GEN1) enzymes - during processes such as DNA adduct repair, Holliday junction processing and replication stress. We also discuss newly characterized connections between SSEs and other classes of DNA-remodelling enzymes and cell cycle control machineries, which reveal the importance of SSE scaffolds such as the synthetic lethal of unknown function 4 (SLX4) tumour suppressor for the maintenance of genome stability.

Ribosome-associated ncRNAs: an emerging class of translation regulators

Accumulating recent evidence identified the ribosome as binding target for numerous small and long non-protein-coding RNAs (ncRNAs) in various organisms of all 3 domains of life. Therefore it appears that ribosome-associated ncRNAs (rancRNAs) are a prevalent, yet poorly understood class of cellular transcripts. Since rancRNAs are associated with the arguable most central enzyme of the cell it seems plausible to propose a role in translation control. Indeed first experimental evidence on small rancRNAs has been presented, linking ribosome association with fine-tuning the rate of protein biosynthesis in a stress-dependent manner.

Pre-mRNA splicing is facilitated by an optimal RNA polymerase II elongation rate

Fong et al. examined cotranscriptional pre-mRNA splicing using RNA polymerase II mutants that change average elongation rates genome-wide. Slow and fast elongation affected constitutive and alternative splicing and often both increased or both decreased inclusion of a particular exon or retained intron. These results suggest that an optimal rate of transcriptional elongation is required for normal cotranscriptional pre-mRNA splicing.

Alternative splicing modulates expression of most human genes. The kinetic model of cotranscriptional splicing suggests that slow elongation expands and that fast elongation compresses the “window of opportunity” for recognition of upstream splice sites, thereby increasing or decreasing inclusion of alternative exons. We tested the model using RNA polymerase II mutants that change average elongation rates genome-wide. Slow and fast elongation affected constitutive and alternative splicing, frequently altering exon inclusion and intron retention in ways not predicted by the model. Cassette exons included by slow and excluded by fast elongation (type I) have weaker splice sites, shorter flanking introns, and distinct sequence motifs relative to “slow-excluded” and “fast-included” exons (type II). Many rate-sensitive exons are misspliced in tumors. Unexpectedly, slow and fast elongation often both increased or both decreased inclusion of a particular exon or retained intron. These results suggest that an optimal rate of transcriptional elongation is required for normal cotranscriptional pre-mRNA splicing.