Argonaute Utilization for miRNA Silencing Is Determined by Phosphorylation-Dependent Recruitment of LIM-Domain-Containing Proteins

MicroRNA-320a enhances LRWD1 expression through the AGO2/FXR1-dependent pathway to affect cell behaviors and the oxidative stress response in human testicular embryonic carcinoma cells

BACKGROUND

Testicular cancer is fairly rare but can affect fertility in adult males. Leucine-rich repeats- and WD repeat domain-containing protein 1 (LRWD1) is a sperm-specific marker that mainly affects sperm motility in reproduction. Our previous study demonstrated the impact of LRWD1 on testicular cancer development; however, the underlying mechanisms remain unclear.

METHODS

In this study, various plasmids associated with LRWD1 and miR-320a manipulation were used to explore the roles and regulatory effects of these molecules in NT2D1 cellular processes. A Dual-Glo luciferin-luciferase system was used to investigate LRWD1 transcriptional activity, and qRT-PCR and western blotting were used to determine gene and protein expression.

RESULTS

The results suggested that miR-320a positively regulated LRWD1 and positively correlated with NT2D1 cell proliferation but negatively correlated with cell migration and invasion ability. In addition, the miRNA-ribonucleoprotein complex AGO2/FXR1 was shown to be essential in the mechanism by which miR-320a regulates LRWD1 mRNA expression. As miR-320a was required to regulate LRWD1 expression through the AGO2 and FXR1 complex, eEF2 and eLF4E were also found to be involved in miR-320a increasing LRWD1 expression. Furthermore, miR-320a and LRWD1 were responsive to oxidative stress, and NRF2 was affected by the presence of miR-320a in response to ROS stimulation.

CONCLUSIONS

This is the first study showing the role of miR-320a in upregulating the testicular cancer-specific regulator LRWD1 and the importance of the AGO2/FXR1 complex in miR-320a-mediated upregulation of LRWD1 during testicular cancer progression.

An essential role for the RNA helicase DDX6 in NMDA receptor-dependent gene silencing and dendritic spine shrinkage

MicroRNAs (miRNAs) repress translation of target mRNAs by associating with Argonaute (Ago) proteins in the RNA-induced silencing complex (RISC) to modulate protein expression. Specific miRNAs are required for NMDA receptor (NMDAR)-dependent synaptic plasticity by repressing the translation of proteins involved in dendritic spine morphogenesis. Rapid NMDAR-dependent silencing of Limk1 is essential for spine shrinkage and requires Ago2 phosphorylation at S387. Not all gene silencing events are modulated by S387 phosphorylation, and the mechanisms that govern the selection of specific mRNAs for silencing downstream of S387 phosphorylation are unknown. Here, we show that NMDAR-dependent S387 phosphorylation causes a rapid and transient increase in the association of Ago2 with Limk1, but not Apt1 mRNA. The specific increase in Limk1 mRNA binding to Ago2 requires recruitment of the helicase DDX6 to RISC. Furthermore, we show that DDX6 is required for NMDAR-dependent silencing of Limk1 via miR-134, but not Apt1 via miR-138, and is essential for NMDAR-dependent spine shrinkage. This work defines a novel mechanism for the rapid transduction of NMDAR stimulation into miRNA-mediated translational repression of specific genes to control dendritic spine morphology.

Argonaute3-SF3B3 complex controls pre-mRNA splicing to restrain type 2 immunity

Argonaute (AGO) proteins execute microRNA (miRNA)-mediated gene silencing. However, it is unclear whether all 4 mammalian AGO proteins (AGO1, AGO2, AGO3, and AGO4) are required for miRNA activity. We generate Ago1, Ago3, and Ago4-deficient mice (Ago134Δ) and find AGO1/3/4 to be redundant for miRNA biogenesis, homeostasis, or function, a role that is carried out by AGO2. Instead, AGO1/3/4 regulate the expansion of type 2 immunity via precursor mRNA splicing in CD4+ T helper (Th) lymphocytes. Gain- and loss-of-function experiments demonstrate that nuclear AGO3 interacts directly with SF3B3, a component of the U2 spliceosome complex, to aid global mRNA splicing, and in particular the isoforms of the gene Nisch, resulting in a dysregulated Nisch isoform ratio. This work uncouples AGO1, AGO3, and AGO4 from miRNA-mediated RNA interference, identifies an AGO3:SF3B3 complex in the nucleus, and reveals a mechanism by which AGO proteins regulate inflammatory diseases.

Non-destructive and efficient method for obtaining miRNA information in cells by artificial extracellular vesicles

In recent years, research has explored the use of microRNA (miRNA) analysis in extracellular vesicles (EVs) as a minimally invasive strategy for the diagnosis and prediction of diseases. This is because miRNAs in EVs partly reflect the miRNA information and cellular status of the origin cells. However, not all intracellular miRNAs are internalized into EVs. Therefore, the miRNA information obtained from EVs is limited. To get more miRNA information, we aimed to produce artificial EVs (aEVs) encapsulating Argonaute 2 (Ago2) miRNA-binding protein, which actively incorporate miRNAs within themselves. In this study, we utilized the protein EPN-01, which is capable of releasing aEVs encapsulating it and associated proteins. This system enables us to obtain more miRNA species and increase each miRNA's yield in the EV fraction. Furthermore, we examined whether miRNAs in the EV fraction using our system reflect the cellular condition. In cells treated with CoCl2, a reagent for inducing a hypoxia-mimic state, we detected a change in the level of hypoxia marker miR-210 with aEVs. To the best of our knowledge, this is the first report on a method to increase the yield and variety of endogenous miRNAs in the EV fraction. This approach leads to improved accuracy of cell status assessment using miRNAs in EVs.

Actin-dependent recruitment of AGO2 to the zonula adherens

Adherens junctions are cadherin-based structures critical for cellular architecture. E-cadherin junctions in mature epithelial cell monolayers tether to an apical actomyosin ring to form the zonula adherens (ZA). We have previously shown that the adherens junction protein PLEKHA7 associates with and regulates the function of the core RNA interference (RNAi) component AGO2 specifically at the ZA. However, the mechanism mediating AGO2 recruitment to the ZA remained unexplored. Here, we reveal that this ZA-specific recruitment of AGO2 depends on both the structural and tensile integrity of the actomyosin cytoskeleton. We found that depletion of not only PLEKHA7, but also either of the three PLEKHA7-interacting, LIM-domain family proteins, namely LMO7, LIMCH1, and PDLIM1, results in disruption of actomyosin organization and tension, as well as disruption of AGO2 junctional localization and of its miRNA-binding ability. We also show that AGO2 binds Myosin IIB and that PLEKHA7, LMO7, LIMCH1, and PDLIM1 all disrupt interaction of AGO2 with Myosin IIB at the ZA. These results demonstrate that recruitment of AGO2 to the ZA is sensitive to actomyosin perturbations, introducing the concept of mechanosensitive RNAi machinery, with potential implications in tissue remodeling and in disease.

AGO2 silences mobile transposons in the nucleus of quiescent cells

Argonaute 2 (AGO2) is a cytoplasmic component of the miRNA pathway, with essential roles in development and disease. Yet little is known about its regulation in vivo. Here we show that in quiescent mouse splenocytes, AGO2 localizes almost exclusively to the nucleus. AGO2 subcellular localization is modulated by the Pi3K-AKT-mTOR pathway, a well-established regulator of quiescence. Signaling through this pathway in proliferating cells promotes AGO2 cytoplasmic accumulation, at least in part by stimulating the expression of TNRC6, an essential AGO2 binding partner in the miRNA pathway. In quiescent cells in which mTOR signaling is low, AGO2 accumulates in the nucleus, where it binds to young mobile transposons co-transcriptionally to repress their expression via its catalytic domain. Our data point to an essential but previously unrecognized nuclear role for AGO2 during quiescence as part of a genome-defense system against young mobile elements and provide evidence of RNA interference in the soma of mammals.

Casein kinase 1 and 2 phosphorylate Argonaute proteins to regulate miRNA-mediated gene silencing

MicroRNAs (miRNAs) together with Argonaute (AGO) proteins form the core of the RNA-induced silencing complex (RISC) to regulate gene expression of their target RNAs post-transcriptionally. Argonaute proteins are subjected to intensive regulation via various post-translational modifications that can affect their stability, silencing efficacy and specificity for targeted gene regulation. We report here that in Caenorhabditis elegans, two conserved serine/threonine kinases - casein kinase 1 alpha 1 (CK1A1) and casein kinase 2 (CK2) - regulate a highly conserved phosphorylation cluster of 4 Serine residues (S988:S998) on the miRNA-specific AGO protein ALG-1. We show that CK1A1 phosphorylates ALG-1 at sites S992 and S995, while CK2 phosphorylates ALG-1 at sites S988 and S998. Furthermore, we demonstrate that phospho-mimicking mutants of the entire S988:S998 cluster rescue the various developmental defects observed upon depleting CK1A1 and CK2. In humans, we show that CK1A1 also acts as a priming kinase of this cluster on AGO2. Altogether, our data suggest that phosphorylation of AGO within the cluster by CK1A1 and CK2 is required for efficient miRISC-target RNA binding and silencing.

Regulation of microRNA expression by the adaptor protein GRB2

Protein interactions with the microRNA (miRNA)-mediated gene silencing protein Argonaute 2 (AGO2) control miRNA expression. miRNA biogenesis starts with the production of precursor transcripts and culminates with the loading of mature miRNA onto AGO2 by DICER1. Here we reveal an additional component to the regulatory mechanism for miRNA biogenesis involving the adaptor protein, growth factor receptor-bound protein 2 (GRB2). The N-terminal SH3 domain of GRB2 is recruited to the PAZ domain of AGO2 forming a ternary complex containing GRB2, AGO2 and DICER1. Using small-RNA sequencing we identified two groups of miRNAs which are regulated by the binding of GRB2. First, mature and precursor transcripts of mir-17~92 and mir-221 miRNAs are enhanced. Second, mature, but not precursor, let-7 family miRNAs are diminished suggesting that GRB2 directly affects loading of these miRNAs. Notably, the resulting loss of let-7 augments expression of oncogenic targets such as RAS. Thus, a new role for GRB2 is established with implications for cancer pathogenesis through regulation of miRNA biogenesis and oncogene expression.

The Multiplicity of Argonaute Complexes in Mammalian Cells

Argonautes (AGOs) are a highly conserved family of proteins found in most eukaryotes and involved in mechanisms of gene regulation, both at the transcriptional and post-transcriptional level. Among other functions, AGO proteins associate with microRNAs (miRNAs) to mediate the post-transcriptional repression of protein-coding genes. In this process, AGOs associate with members of the trinucleotide repeat containing 6 protein (TNRC6) family to form the core of the RNA-induced silencing complex (RISC), the effector machinery that mediates miRNA function. However, the description of the exact composition of the RISC has been a challenging task due to the fact the AGO's interactome is dynamically regulated in a cell type- and condition-specific manner. Here, we summarize some of the most significant studies that have identified AGO complexes in mammalian cells, as well as the approaches used to characterize them. Finally, we discuss possible opportunities to exploit what we have learned on the properties of the RISC to develop novel anti-cancer therapies. SIGNIFICANCE STATEMENT: The RNA-induced silencing complex (RISC) is the molecular machinery that mediates miRNA function in mammals. Studies over the past two decades have shed light on important biochemical and functional properties of this complex. However, many aspects of this complex await further elucidation, mostly due to technical limitations that have hindered full characterization. Here, we summarize some of the most significant studies on the mammalian RISC and discuss possible sources of biases in the approaches used to characterize it.

The Role of microRNA in the Development, Diagnosis, and Treatment of Cardiovascular Disease: Recent Developments

Since their discovery in 1993, microRNAs (miRNAs) have emerged as important regulators of many crucial cellular processes, and their dysregulation have been shown to contribute to multiple pathologic conditions, including cardiovascular disease (CVD). miRNAs have been found to regulate the expression of various genes involved in cardiac development and function and in the development and progression of CVD. Many miRNAs are master regulators fine-tuning the expression of multiple, often interrelated, genes involved in inflammation, apoptosis, fibrosis, senescence, and other processes crucial for the development of different forms of CVD. This article presents a review of recent developments in our understanding of the role of miRNAs in the development of CVD and surveys their potential applicability as therapeutic targets and biomarkers to facilitate CVD diagnosis, prognosis, and treatment. There are currently multiple potential miRNA-based therapeutic agents in different stages of development, which can be grouped into two classes: miRNA mimics (replicating the sequence and activity of their corresponding miRNAs) and antagomiRs (antisense inhibitors of specific miRNAs). However, in spite of promising preliminary data and our ever-increasing knowledge about the mechanisms of action of specific miRNAs, miRNA-based therapeutics and biomarkers have yet to be approved for clinical applications. SIGNIFICANCE STATEMENT: Over the last few years microRNAs have emerged as crucial, specific regulators of the cardiovascular system and in the development of cardiovascular disease, by posttranscriptional regulation of their target genes. The minireview presents the most recent developments in this area of research, including the progress in diagnostic and therapeutic applications of microRNAs. microRNAs seem very promising candidates for biomarkers and therapeutic agents, although some challenges, such as efficient delivery and unwanted effects, need to be resolved.

A specific type of Argonaute phosphorylation regulates binding to microRNAs during C. elegans development

Argonaute proteins are at the core of the microRNA-mediated gene silencing pathway essential for animals. In C. elegans, the microRNA-specific Argonautes ALG-1 and ALG-2 regulate multiple processes required for proper animal developmental timing and viability. Here we identified a phosphorylation site on ALG-1 that modulates microRNA association. Mutating ALG-1 serine 642 into a phospho-mimicking residue impairs microRNA binding and causes embryonic lethality and post-embryonic phenotypes that are consistent with alteration of microRNA functions. Monitoring microRNA levels in alg-1 phosphorylation mutant animals shows that microRNA passenger strands increase in abundance but are not preferentially loaded into ALG-1, indicating that the miRNA binding defects could lead to microRNA duplex accumulation. Our genetic and biochemical experiments support protein kinase A (PKA) KIN-1 as the putative kinase that phosphorylates ALG-1 serine 642. Our data indicate that PKA triggers ALG-1 phosphorylation to regulate its microRNA association during C. elegans development.

Alu-minating the Mechanisms Underlying Primate Cortex Evolution

The higher-order cognitive functions observed in primates correlate with the evolutionary enhancement of cortical volume and folding, which in turn are driven by the primate-specific expansion of cellular diversity in the developing cortex. Underlying these changes is the diversification of molecular features including the creation of human and/or primate-specific genes, the activation of specific molecular pathways, and the interplay of diverse layers of gene regulation. We review and discuss evidence for connections between Alu elements and primate brain evolution, the evolutionary milestones of which are known to coincide along primate lineages. Alus are repetitive elements that contribute extensively to the acquisition of novel genes and the expansion of diverse gene regulatory layers, including enhancers, alternative splicing, RNA editing, and microRNA pathways. By reviewing the impact of Alus on molecular features linked to cortical expansions or gyrification or implications in cognitive deficits, we suggest that future research focusing on the role of Alu-derived molecular events in the context of brain development may greatly advance our understanding of higher-order cognitive functions and neurologic disorders.

The origin of RNA interference: Adaptive or neutral evolution?

The origin of RNA interference (RNAi) is usually explained by a defense-based hypothesis, in which RNAi evolved as a defense against transposable elements (TEs) and RNA viruses and was already present in the last eukaryotic common ancestor (LECA). However, since RNA antisense regulation and double-stranded RNAs (dsRNAs) are ancient and widespread phenomena, the origin of defensive RNAi should have occurred in parallel with its regulative functions to avoid imbalances in gene regulation. Thus, we propose a neutral evolutionary hypothesis for the origin of RNAi in which qualitative system drift from a prokaryotic antisense RNA gene regulation mechanism leads to the formation of RNAi through constructive neutral evolution (CNE). We argue that RNAi was already present in the ancestor of LECA before the need for a new defense system arose and that its presence helped to shape eukaryotic genomic architecture and stability.

Where does RNA interference come from? This Essay describes a new step-by-step evolutionary model of how RNA interference might have originated in early eukaryotes through neutral events from the molecular machinery present in prokaryotes.

Anatomy of four human Argonaute proteins

MicroRNAs (miRNAs) bind to complementary target RNAs and regulate their gene expression post-transcriptionally. These non-coding regulatory RNAs become functional after loading into Argonaute (AGO) proteins to form the effector complexes. Humans have four AGO proteins, AGO1, AGO2, AGO3 and AGO4, which share a high sequence identity. Since most miRNAs are found across the four AGOs, it has been thought that they work redundantly, and AGO2 has been heavily studied as the exemplified human paralog. Nevertheless, an increasing number of studies have found that the other paralogs play unique roles in various biological processes and diseases. In the last decade, the structural study of the four AGOs has provided the field with solid structural bases. This review exploits the completed structural catalog to describe common features and differences in target specificity across the four AGOs.

The intricate balance between microRNA-induced mRNA decay and translational repression

Post-transcriptional regulation of messenger RNAs (mRNAs) (i.e., mechanisms that control translation, stability and localization) is a critical focal point in spatiotemporal regulation of gene expression in response to changes in environmental conditions. The human genome encodes ~ 2000 microRNAs (miRNAs), each of which could control the expression of hundreds of protein-coding mRNAs by inducing translational repression and/or promoting mRNA decay. While mRNA degradation is a terminal event, translational repression is reversible and can be employed for rapid response to internal or external cues. Recent years have seen significant progress in our understanding of how miRNAs induce degradation or translational repression of the target mRNAs. Here, we review the recent findings that illustrate the cellular machinery that contributes to miRNA-induced silencing, with a focus on the factors that could influence translational repression vs. decay.

Regulation of MicroRNAs

MicroRNAs are RNAs of about 18-24 nucleotides in lengths, which are found in the small noncoding RNA class and have a crucial role in the posttranscriptional regulation of gene expression, cellular metabolic pathways, and developmental events. These small but essential molecules are first processed by Drosha and DGCR8 in the nucleus and then released into the cytoplasm, where they cleaved by Dicer to form the miRNA duplex. These duplexes are bound by the Argonaute (AGO) protein to form the RNA-induced silencing complex (RISC) in a process called RISC loading. Transcription of miRNAs, processing with Drosha and DGCR8 in the nucleus, cleavage by Dicer, binding to AGO proteins and forming RISC are the most critical steps in miRNA biogenesis. Additional molecules involved in biogenesis at these stages can enhance or inhibit these processes, which can radically change the fate of the cell. Biogenesis is regulated by many checkpoints at every step, primarily at the transcriptional level, in the nucleus, cytoplasm, with RNA regulation, RISC loading, miRNA strand selection, RNA methylation/uridylation, and turnover rate. Moreover, in recent years, different regulation mechanisms have been discovered in noncanonical Drosha or Dicer-independent pathways. This chapter seeks answers to how miRNA biogenesis and function are regulated through both canonical and non-canonical pathways.

Interplay between K-RAS and miRNAs

K-RAS is frequently mutated in cancers, and its overactivation can lead to oncogene-induced senescence (OIS), a barrier to cellular transformation. Feedback onto K-RAS limits its signaling to avoid senescence while achieving the appropriate level of activation that promotes proliferation and survival. Such regulation could be mediated by miRNAs, as aberrant RAS signaling and miRNA activity coexist in several cancers, with miRNAs acting both up- and downstream of K-RAS. Several miRNAs both regulate and are regulated by K-RAS, suggesting a noncoding RNA-based feedback mechanism. Functional interactions between K-RAS and the miRNA machinery have also begun to unfold. This review comprehensively surveys the state of knowledge connecting K-RAS to miRNA function and proposes a model for the regulation of K-RAS signaling by noncoding RNAs.

Targeted therapy for LIMD1-deficient non-small cell lung cancer subtypes

An early event in lung oncogenesis is loss of the tumour suppressor gene LIMD1 (LIM domains containing 1); this encodes a scaffold protein, which suppresses tumorigenesis via a number of different mechanisms. Approximately 45% of non-small cell lung cancers (NSCLC) are deficient in LIMD1, yet this subtype of NSCLC has been overlooked in preclinical and clinical investigations. Defining therapeutic targets in these LIMD1 loss-of-function patients is difficult due to a lack of 'druggable' targets, thus alternative approaches are required. To this end, we performed the first drug repurposing screen to identify compounds that confer synthetic lethality with LIMD1 loss in NSCLC cells. PF-477736 was shown to selectively target LIMD1-deficient cells in vitro through inhibition of multiple kinases, inducing cell death via apoptosis. Furthermore, PF-477736 was effective in treating LIMD1-/- tumours in subcutaneous xenograft models, with no significant effect in LIMD1+/+ cells. We have identified a novel drug tool with significant preclinical characterisation that serves as an excellent candidate to explore and define LIMD1-deficient cancers as a new therapeutic subgroup of critical unmet need.

Regulation and different functions of the animal microRNA-induced silencing complex

Among the different types of small RNAs, microRNAs (miRNAs) are key players in controlling gene expression at the mRNA level. To be active, they must associate with an Argonaute protein to form the miRNA induced silencing complex (miRISC) and binds to specific mRNA through complementarity sequences. The miRISC binding to an mRNA can lead to multiple outcomes, the most frequent being inhibition of the translation and/or deadenylation followed by decapping and mRNA decay. In the last years, several studies described different mechanisms modulating miRISC functions in animals. For instance, the regulation of the Argonaute protein through post-translational modifications can change the miRISC gene regulatory activity as well as modulate its binding to proteins, mRNA targets and miRISC stability. Furthermore, the presence of RNA binding proteins and multiple miRISCs at the targeted mRNA 3' untranslated region (3'UTR) can also affect its function through cooperation or competition mechanisms, underlying the importance of the 3'UTR environment in miRNA-mediated repression. Another way to regulate the miRISC function is by modulation of its interactors, forming different types of miRNA silencing complexes that affect gene regulation differently. It is also reported that the subcellular localization of several components of the miRNA pathway can modulate miRISC function, suggesting an important role for vesicular trafficking in the regulation of this essential silencing complex. This article is categorized under: RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes Regulatory RNAs/RNAi/Riboswitches > RNAi: Mechanisms of Action Regulatory RNAs/RNAi/Riboswitches > Biogenesis of Effector Small RNAs.

Emerging Role of isomiRs in Cancer: State of the Art and Recent Advances

The advent of Next Generation Sequencing technologies brought with it the discovery of several microRNA (miRNA) variants of heterogeneous lengths and/or sequences. Initially ascribed to sequencing errors/artifacts, these isoforms, named isomiRs, are now considered non-canonical variants that originate from physiological processes affecting the canonical miRNA biogenesis. To date, accurate IsomiRs abundance, biological activity, and functions are not completely understood; however, the study of isomiR biology is an area of great interest due to their high frequency in the human miRNome, their putative functions in cooperating with the canonical miRNAs, and potential for exhibiting novel functional roles. The discovery of isomiRs highlighted the complexity of the small RNA transcriptional landscape in several diseases, including cancer. In this field, the study of isomiRs could provide further insights into the miRNA biology and its implication in oncogenesis, possibly providing putative new cancer diagnostic, prognostic, and predictive biomarkers as well. In this review, a comprehensive overview of the state of research on isomiRs in different cancer types, including the most common tumors such as breast cancer, colorectal cancer, melanoma, and prostate cancer, as well as in the less frequent tumors, as for example brain tumors and hematological malignancies, will be summarized and discussed.

Genome-wide analysis of the mouse LIM gene family reveals its roles in regulating pathological cardiac hypertrophy

LIM-domain proteins have been shown to be associated with heart development and diseases. Systematic studies of LIM family members at the genome-wide level, which are crucial to further understand their functions in cardiac hypertrophy, are currently lacking. Here, 70 LIM genes were identified and characterised in mice. The expression patterns of LIM genes differ greatly during cardiac development and in the case of hypertrophy. Both Crip2 and Xirp2 are differentially expressed in cardiac hypertrophy and during heart failure. In addition, the hypertrophic state of cardiomyocytes is controlled by the relative expression levels of Crip2 and Xirp2. This study provides a foundation for further understanding of the special roles of LIM proteins in mammalian cardiac development and hypertrophy.

E-cadherin Interacts With Posttranslationally-Modified AGO2 to Enhance miRISC Activity

MicroRNAs (miRNAs) are small non-coding RNAs which post-transcriptionally suppress target mRNAs expression and/or translation to modulate pathophyological processes. Expression and function of miRNAs are fine-tuned by a conserved biogenesis machinery involves two RNase-dependent processing steps of miRNA maturation and the final step of miRNA-induced silencing complex (miRISC)-mediated target silencing. A functional miRISC requires Argonaute 2 (AGO2) as an essential catalytic component which plays central roles in miRISC function. We uncovered a post-translational regulatory mechanism of AGO2 by E-cadherin. Mechanistically, E-cadherin activates ERK to phosphorylate AGO2, along with enhanced protein glycosylation. Consequently, the phosphorylated AGO2 was stabilized and ultimately resulted in induced miRISC activity on gene silencing. This study revealed a novel pathway for miRNA regulation through an E-cadherin-mediated miRISC activation.

Post-transcriptional regulation of MMP2 mRNA by its interaction with miR-20a and Nucleolin in breast cancer cell lines

Matrix-metalloproteinase-2 (MMP2) is a foremost MMP, governing invasion of breast cancer cells during metastasis. miR-20a was reported to induce mesenchymal to epithelial transition in MDA-MB-231 cells and its endogenous expression varies directly with invasiveness of breast cancer cells. The inverse and direct correlation of invasiveness with miR-20a and Nucleolin respectively led us to study the post-transcriptional regulation of MMP2 by miR-20a and mRNA stabilizing protein, Nucleolin. Thus, understanding the mechanism of its regulation will enable modification of the invasion potential. MMP2 was found to be higher in MDA-MB-231 than MCF-7 cells both at RNA and protein levels. RNA-protein co-immunoprecipitation assay with Argonaute 2 revealed that MMP2 undergoes miRNA-mediated post-transcriptional regulation. miR-20a decreased MMP2 expression as well as its enzymatic activity as found by zymogram assay. Reporter assay showed that miR-20a directly binds to its putative binding site in MMP2 3'-UTR as per in silico prediction. miR-20a additionally impeded MMP2 mRNA stability, and binding of stabilizing trans-factor Nucleolin to its 3'-UTR was confirmed by RNA-protein co-immunoprecipitation assay. Partial down-regulation of Nucleolin by Si-RNA resulted in the downregulation of MMP2 and Nucleolin over-expression rescued the inhibitory effect of miR-20a on MMP2 expression. Delineating the mechanism of post-transcriptional regulation of MMP2, two of its potent regulators, miR-20a and Nucleolin were identified. It was established for the first time that MMP2 is a direct target of miR-20a. The results also elucidated that Nucleolin binds to MMP2 3' UTR and its abundance affects MMP2 expression.

The multifaceted roles of microRNAs in differentiation

MicroRNAs (miRNAs) are major drivers of cell fate specification and differentiation. The post-transcriptional regulation of key molecular factors by microRNAs contributes to the progression of embryonic and postembryonic development in several organisms. Following the discovery of lin-4 and let-7 in Caenorhabditis elegans and bantam microRNAs in Drosophila melanogaster, microRNAs have emerged as orchestrators of cellular differentiation and developmental timing. Spatiotemporal control of microRNAs and associated protein machinery can modulate microRNA activity. Additionally, adaptive modulation of microRNA expression and function in response to changing environmental conditions ensures that robust cell fate specification during development is maintained. Herein, we review the role of microRNAs in the regulation of differentiation during development.

MicroRNAs Responding to Space Radiation

High-energy and high-atom-number (HZE) space radiation poses an inevitable potential threat to astronauts on deep space exploration missions. Compared with low-LET radiation, high-energy and high-LET radiation in space is more efficient in inducing clustered DNA damage with more serious biological consequences, such as carcinogenesis, central nervous system injury and degenerative disease. Space radiation also causes epigenetic changes in addition to inducing damage at the DNA level. Considering the important roles of microRNAs in the regulation of biological responses of radiation, we systematically reviewed both expression profiling and functional studies relating to microRNAs responding to space radiation as well as to space compound environment. Finally, the directions for improvement of the research related to microRNAs responding to space radiation are proposed. A better understanding of the functions and underlying mechanisms of the microRNAs responding to space radiation is of significance to both space radiation risk assessment and therapy development for lesions caused by space radiation.

The CXCR4-Dependent LASP1-Ago2 Interaction in Triple-Negative Breast Cancer

The CXCR4-LASP1 axis is an emerging target in the field of breast cancer metastasis. C-X-C chemokine receptor type 4 (CXCR4) mediates directed cell migration when activated by its cognate ligand CXCL12. LIM and SH3 Protein 1 (LASP1) is a critical node in the CXCR4 signaling pathway, as its deficiency blocks CXCR4-dependent Matrigel invasion. The mechanism by which LASP1 facilitates this invasive ability of tumor cells when CXCR4 is activated is unknown. Our previous proteomics work had revealed several components of the RNA interference (RNAi) machinery as being potential LASP1 interacting proteins. Here we report that argonaute 2 (Ago2), a protein with central involvement in RNAi, associates with LASP1 in triple-negative breast cancer (TNBC) cells. We demonstrate that LASP1 co-immunoprecipitates with Ago2 endogenously in a CXCL12-dependent manner, with further confirmation of this interaction by proximity ligation assay. Furthermore, this association is specific to CXCR4 as it can be abrogated by the CXCR4 antagonist, AMD3465. By GST-pulldown approach, we identify that LASP1 directly binds to Ago2 through its LIM and SH3 domains, and that this binding is dictated by the S146 and Y171 phosphorylation sites of LASP1. Additionally, the phosphorylation status of LASP1 affected tumor suppressor microRNA (miRNA) Let-7a-guided Ago2 activity. Levels of several endogenous targets of Let-7a were found to be altered including C-C chemokine receptor type 7 (CCR7), which is another critical chemokine receptor involved in metastasis to lymph nodes. Our results suggest a novel role for the LASP1-Ago2 module in shaping the RNAi landscape, functionally impacting the invasive ability of cancer cells.

Argonaute proteins: Structural features, functions and emerging roles

Argonaute proteins are highly conserved in almost all organisms. They not only involve in the biogenesis of small regulatory RNAs, but also regulate gene expression and defend against foreign pathogen invasion via small RNA-mediated gene silencing pathways. As a key player in these pathways, the abnormal expression and/or mis-modifications of Argonaute proteins lead to the disorder of small RNA biogenesis and functions, thus influencing multiply biological processes and disease development, especially cancer. In this review, we focus on the post-translational modifications and novel functions of Argonaute proteins in alternative splicing, host defense and genome editing.

Characterization of an MLP Homologue from Haemaphysalis longicornis (Acari: Ixodidae) Ticks

Members of the cysteine-rich protein (CRP) family are known to participate in muscle development in vertebrates. Muscle LIM protein (MLP) belongs to the CRP family and has an important function in the differentiation and proliferation of muscle cells. In this study, the full-length cDNA encoding MLP from Haemaphysalis longicornis (H. longicornis; HLMLP) ticks was obtained by 5' rapid amplification of cDNA ends (RACE). To verify the transcriptional status of MLP in ticks, HLMLP gene expression was assessed during various developmental stages by real-time PCR (RT-PCR). Interestingly, HLMLP expression in the integument was significantly (P < 0.01) higher than that observed in other tested tissues of engorged adult ticks. In addition, HLMLP mRNA levels were significantly downregulated in response to thermal stress at 4 °C for 48 h. Furthermore, recombinant HLMLP was expressed in Escherichia coli, and Western blot analysis showed that rabbit antiserum against H. longicornis adults recognized HLMLP and MLPs from different ticks. Ten 3-month-old rabbits that had never been exposed to ticks were used for the immunization and challenge experiments. The rabbits were divided into two groups of five rabbits each, where rabbits in the first group were immunized with HLMLP, while those in the second group were immunized with phosphate-buffered saline (PBS) diluent as controls. The vaccination of rabbits with the recombinant HLMLP conferred partial protective immunity against ticks, resulting in 20.00% mortality and a 17.44% reduction in the engorgement weight of adult ticks. These results suggest that HLMLP is not ideal as a candidate for use in anti-tick vaccines. However, the results of this study generated novel information on the MLP gene in H. longicornis and provide a basis for further investigation of the function of this gene that could potentially lead to a better understanding of the mechanism of myofiber determination and transformation.

A Requirement for Argonaute 4 in Mammalian Antiviral Defense

While interferon (IFN) responses are critical for mammalian antiviral defense, induction of antiviral RNA interference (RNAi) is evident. To date, individual functions of the mammalian RNAi and micro RNA (miRNA) effector proteins Argonautes 1-4 (AGO1-AGO4) during virus infection remain undetermined. AGO2 was recently implicated in mammalian antiviral defense, so we examined antiviral activity of AGO1, AGO3, or AGO4 in IFN-competent immune cells. Only AGO4-deficient cells are hyper-susceptible to virus infection. AGO4 antiviral function is both IFN dependent and IFN independent, since AGO4 promotes IFN but also maintains antiviral capacity following prevention of IFN signaling or production. We identified AGO-loaded virus-derived short interfering RNAs (vsiRNAs), a molecular marker of antiviral RNAi, in macrophages infected with influenza or influenza lacking the IFN and RNAi suppressor NS1, which are uniquely diminished without AGO4. Importantly, AGO4-deficient influenza-infected mice have significantly higher burden and viral titers in vivo. Together, our data assign an essential role for AGO4 in mammalian antiviral defense.

The Role of Dynamic miRISC During Neuronal Development

Activity-dependent protein synthesis plays an important role during neuronal development by fine-tuning the formation and function of neuronal circuits. Recent studies have shown that miRNAs are integral to this regulation because of their ability to control protein synthesis in a rapid, specific and potentially reversible manner. miRNA mediated regulation is a multistep process that involves inhibition of translation before degradation of targeted mRNA, which provides the possibility to store and reverse the inhibition at multiple stages. This flexibility is primarily thought to be derived from the composition of miRNA induced silencing complex (miRISC). AGO2 is likely the only obligatory component of miRISC, while multiple RBPs are shown to be associated with this core miRISC to form diverse miRISC complexes. The formation of these heterogeneous miRISC complexes is intricately regulated by various extracellular signals and cell-specific contexts. In this review, we discuss the composition of miRISC and its functions during neuronal development. Neurodevelopment is guided by both internal programs and external cues. Neuronal activity and external signals play an important role in the formation and refining of the neuronal network. miRISC composition and diversity have a critical role at distinct stages of neurodevelopment. Even though there is a good amount of literature available on the role of miRNAs mediated regulation of neuronal development, surprisingly the role of miRISC composition and its functional dynamics in neuronal development is not much discussed. In this article, we review the available literature on the heterogeneity of the neuronal miRISC composition and how this may influence translation regulation in the context of neuronal development.

Argonaute Proteins: From Structure to Function in Development and Pathological Cell Fate Determination

The highly conserved Argonaute protein family members play a central role in the regulation of gene expression networks, orchestrating the establishment and the maintenance of cell identity throughout the entire life cycle, as well as in several human disorders, including cancers. Four functional Argonaute proteins (AGO1-4), with high structure similarity, have been described in humans and mice. Interestingly, only AGO2 is robustly expressed during human and mouse early development, in contrast to the other AGOs. Consequently, AGO2 is indispensable for early development in vivo and in vitro. Here, we review the roles of Argonaute proteins during early development by focusing on the interplay between specific domains of the protein and their function. Moreover, we report recent works highlighting the importance of AGO posttranslational modifications in cancer.

AGO unchained: Canonical and non-canonical roles of Argonaute proteins in mammals

Argonaute (AGO) proteins play key roles in animal physiology by binding to small RNAs and regulating the expression of their targets. In mammals, they do so through two distinct pathways: the miRNA pathway represses genes through a multiprotein complex that promotes both decay and translational repression; the siRNA pathway represses transcripts through direct Ago2-mediated cleavage. Here, we review our current knowledge of mechanistic details and physiological requirements of both these pathways and briefly discuss their implications to human disease.

Ajuba: An emerging signal transducer in oncogenesis

The LIM protein Ajuba contains an unstructured proline/glycine-rich preLIM region in the N terminus and conserved tandem LIM motifs in the C terminus. Additionally, Ajuba contains both nuclear export sequences (NES) and nuclear localization sequences (NLS), which enable Ajuba shuttle between the cytoplasm and the nucleus. Thus, Ajuba can act as a versatile scaffold participating in assembly of variety of protein complexes to execute multiple cellular functions including cell adhesion, motility, mitosis, survival, gene expression, microRNA processing and mechanical force sensing. Numerous studies have demonstrated that Ajuba plays important roles in oncogenesis and progression by regulating major signalling pathways such as Wnt, RAS/ERK, JAK/STAT and Hippo, and by acting as a co-regulator of key transcription factors such as Snail, Sp1 and nuclear hormone receptors. Clinically, Ajuba is highly expressed in various types of tumors and can be a marker for prognosis and diagnosis. In this review, we aim to summarize the up-to-date literatures on the signaling pathways mediated by Ajuba and its associated protein complexes in oncogenesis, and to discuss Ajuba as a potential target for new therapeutics to treat cancers.

A Systems-level Characterization of the Differentiation of Human Embryonic Stem Cells into Mesenchymal Stem Cells

Mesenchymal stem/stromal cells (MSCs) are self-renewing multipotent cells with regenerative, secretory and immunomodulatory capabilities that are beneficial for the treatment of various diseases. To avoid the issues that come with using tissue-derived MSCs in therapy, MSCs may be generated by the differentiation of human embryonic stems cells (hESCs) in culture. However, the changes that occur during the differentiation process have not been comprehensively characterized. Here, we combined transcriptome, proteome and phosphoproteome profiling to perform an in-depth, multi-omics study of the hESCs-to-MSCs differentiation process. Based on RNA-to-protein correlation, we determined a set of high confidence genes that are important to differentiation. Among the earliest and strongest induced proteins with extensive differential phosphorylation was AHNAK, which we hypothesized to be a defining factor in MSC biology. We observed two distinct expression waves of developmental HOX genes and an AGO2-to-AGO3 switch in gene silencing. Exploring the kinetic of noncoding ORFs during differentiation, we mapped new functions to well annotated long noncoding RNAs (CARMN, MALAT, NEAT1, LINC00152) as well as new candidates which we identified to be important to the differentiation process. Phosphoproteome analysis revealed ESC and MSC-specific phosphorylation motifs with PAK2 and RAF1 as top predicted upstream kinases in MSCs. Our data represent a rich systems-level resource on ESC-to-MSC differentiation that will be useful for the study of stem cell biology.

Biphasic regulation of RNA interference during rotavirus infection by modulation of Argonaute2

RNA interference (RNAi) is an evolutionary ancient innate immune response in plants, nematodes, and arthropods providing natural protection against viral infection. Viruses have also gained counter‐defensive measures by producing virulence determinants called viral‐suppressors‐of‐RNAi (VSRs). Interestingly, in spite of dominance of interferon‐based immunity over RNAi in somatic cells of higher vertebrates, recent reports are accumulating in favour of retention of the antiviral nature of RNAi in mammalian cells. The present study focuses on the modulation of intracellular RNAi during infection with rotavirus (RV), an enteric virus with double‐stranded RNA genome. Intriguingly, a time point‐dependent bimodal regulation of RNAi was observed in RV‐infected cells, where short interfering RNA (siRNA)‐based RNAi was rendered non‐functional during early hours of infection only to be reinstated fully beyond that early infection stage. Subsequent investigations revealed RV nonstructural protein 1 to serve as a putative VSR by associating with and triggering degradation of Argonaute2 (AGO2), the prime effector of siRNA‐mediated RNAi, via ubiquitin–proteasome pathway. The proviral significance of AGO2 degradation was further confirmed when ectopic overexpression of AGO2 significantly reduced RV infection. Cumulatively, the current study presents a unique modulation of host RNAi during RV infection, highlighting the importance of antiviral RNAi in mammalian cells.

WT1-interacting protein inhibits cell proliferation and tumorigenicity in non-small-cell lung cancer via the AKT/FOXO1 axis

Lung cancer is the most common cancer and the leading cause of cancer‐related death worldwide; hence, it is imperative that the mechanisms underlying the malignant properties of lung cancer be uncovered in order to efficiently treat this disease. Increasing evidence has shown that WT1‐interacting protein (WTIP) plays important roles both physiologically and pathologically in humans; however, the role of WTIP in cancer is unknown. Here, we investigated the role and mechanism of WTIP in cell proliferation and tumorigenesis of non‐small‐cell lung cancer (NSCLC). We report that WTIP is a tumor suppressor in human NSCLC. We found that WTIP expression was significantly reduced in both NSCLC cell lines and clinical specimens compared to that in normal controls; this reduction was largely attributed to promoter hypermethylation. Downregulation of WTIP significantly correlates with poor prognosis and predicts a shorter overall survival and progression‐free survival among NSCLC patients. Moreover, ectopic overexpression of WTIP dramatically inhibits cell proliferation and tumorigenesis in vitro and in vivo; conversely, depletion of WTIP expression shows the opposite effects. Mechanistically, WTIP impairs AKT phosphorylation and activation, leading to enhanced expression and transcriptional activity of FOXO1, which further increases p21Cip1 and p27Kip1, and decreases cyclin D1, which consequently results in cell cycle arrest. Collectively, the results of the current study indicate that WTIP is an important proliferation‐related gene and that WTIP expression may represent a novel prognostic biomarker for NSCLC.

LIMD1 phosphorylation in mitosis is required for mitotic progression and its tumor-suppressing activity

LIM domains containing 1 (LIMD1) is a member of the Zyxin family proteins and functions as a tumor suppressor in lung cancer. LIMD1 has been shown to regulate Hippo-YAP signaling activity. Here, we report a novel regulatory mechanism for LIMD1. We found that cyclin-dependent kinase 1 (CDK1) and c-Jun NH2-terminal kinases 1/2 (JNK1/2) phosphorylate LIMD1 in vitro and in cells during anti-tubulin drug-induced mitotic arrest. Phosphorylation also occurs during normal mitosis. S272, S277, S421, and S424 were identified as the main phosphorylation sites in LIMD1. Deletion of LIMD1 resulted in a shortened mitotic cell cycle and phosphorylation of LIMD1 is required for proper mitotic progression. We further showed that the phosphorylation-deficient mutant LIMD1-4A is less active in suppressing cell proliferation, anchorage-independent growth, cell migration, and invasion in lung cancer cells. Together, our findings suggest that LIMD1 is a key regulator of mitotic progression, and that dysregulation of LIMD1 contributes to tumorigenesis.

Regulation of microRNA function in animals

Since their serendipitous discovery in nematodes, microRNAs (miRNAs) have emerged as key regulators of biological processes in animals. These small RNAs form complex networks that regulate cell differentiation, development and homeostasis. Deregulation of miRNA function is associated with an increasing number of human diseases, particularly cancer. Recent discoveries have expanded our understanding of the control of miRNA function. Here, we review the mechanisms that modulate miRNA activity, stability and cellular localization through alternative processing and maturation, sequence editing, post-translational modifications of Argonaute proteins, viral factors, transport from the cytoplasm and regulation of miRNA-target interactions. We conclude by discussing intriguing, unresolved research questions.

Acetylation of AGO2 promotes cancer progression by increasing oncogenic miR-19b biogenesis

Argonaute2 (AGO2) is an effector of small RNA mediated gene silencing. Increasing evidence show that post-translational modifications of AGO2 can change miRNA activity at specific or global levels. Among the six mature miRNAs that are encoded by miR-17-92, miR-19b1 is the most powerful to exert the oncogenic properties of the entire cluster. Here we identify that AGO2 can be acetylated by P300/CBP and deacetylated by HDAC7, and that acetylation occurs at three sites K720, K493, and K355. Mutation of K493R/K720R, but not K355R at AGO2, inhibits miR-19b biogenesis. We demonstrate that acetylation of AGO2 specifically increases its recruiting pre-miR-19b1 to form the miPDC (miRNA precursor deposit complex), thereby to enhance miR-19b maturation. The motif UGUGUG in the terminal-loop of pre-miR-19b1, as a specific processing feature that is recognized and bound by acetylated AGO2, is essential for the assembly of miRISC (miRNA-induced silencing complex) loading complex. Analyses on public clinical data, xenograft mouse models, and IHC and ISH staining of lung cancer tissues, further confirm that the high levels of both AGO2 acetylation and miR-19b correlate with poor prognosis in lung cancer patients. Our finding reveals a novel function of AGO2 acetylation in increasing oncogenic miR-19b biogenesis and suggests that modulation of AGO2 acetylation has potential clinical implications.

Identification of the UBA2-WTIP fusion gene in acute myeloid leukemia

Identifying and targeting oncogenic fusion genes have revolutionized the treatment of leukemia, such as PML-RARα fusion gene in acute promyelocytic leukemia. Here we identified an intrachromosomal fusion gene located on chromosome 19q.13 between UBA2 and WTIP gene in a case of acute myeloid leukemia. The UBA2-WTIP fusion gene contains the N-terminal E1_enzyme_family, VAE_Ubl domains of UBA2, and the C-terminal LIM domains of WTIP. The UBA2-WTIP fusion was detected by reverse transcriptase polymerase chain reaction and Sanger sequencing in 19 of 56 acute myeloid leukemia samples (33.9%). Ectopic expression of the UBA2-WTIP fusion in human acute myeloid leukemia KG-1a cells showed enhanced cell proliferation both in vitro and in vivo. The UBA2-WTIP fusion induced phosphorylation of STAT3, STAT5 and ERK1/2, and abrogates WTIP-mediated mammalian processing body formation. Finally, triptolide displayed selective cytotoxicity against KG-1a cells harboring the UBA2-WTIP fusion. Collectively, our findings suggest that the UBA2-WTIP fusion is an oncogenic fusion gene, as well as a promising therapeutic target for the treatment of acute myeloid leukemia.

A HIF-LIMD1 negative feedback mechanism mitigates the pro-tumorigenic effects of hypoxia

The adaptive cellular response to low oxygen tensions is mediated by the hypoxia-inducible factors (HIFs), a family of heterodimeric transcription factors composed of HIF-α and HIF-β subunits. Prolonged HIF expression is a key contributor to cellular transformation, tumorigenesis and metastasis. As such, HIF degradation under hypoxic conditions is an essential homeostatic and tumour-suppressive mechanism. LIMD1 complexes with PHD2 and VHL in physiological oxygen levels (normoxia) to facilitate proteasomal degradation of the HIF-α subunit. Here, we identify LIMD1 as a HIF-1 target gene, which mediates a previously uncharacterised, negative regulatory feedback mechanism for hypoxic HIF-α degradation by modulating PHD2-LIMD1-VHL complex formation. Hypoxic induction of LIMD1 expression results in increased HIF-α protein degradation, inhibiting HIF-1 target gene expression, tumour growth and vascularisation. Furthermore, we report that copy number variation at the LIMD1 locus occurs in 47.1% of lung adenocarcinoma patients, correlates with enhanced expression of a HIF target gene signature and is a negative prognostic indicator. Taken together, our data open a new field of research into the aetiology, diagnosis and prognosis of LIMD1-negative lung cancers.

P-Bodies: Cytosolic Droplets for Coordinated mRNA Storage

P-bodies (PBs) are cytosolic RNP granules that are conserved among eukaryotic organisms. In the past few years, major progress has been made in understanding the biochemical and biophysical mechanisms that lead to their formation. However, whether they play a role in mRNA storage or decay remains actively debated. P-bodies were recently isolated from human cells by a novel fluorescence-activated particle sorting (FAPS) approach that enabled the characterization of their protein and RNA content, providing new insights into their function. Together with recent innovative imaging studies, these new data show that mammalian PBs are primarily involved not in RNA decay but rather in the coordinated storage of mRNAs encoding regulatory functions. These small cytoplasmic droplets could thus be important for cell adaptation to the environment.

NMDAR-dependent Argonaute 2 phosphorylation regulates miRNA activity and dendritic spine plasticity

MicroRNAs (miRNAs) repress translation of target mRNAs by associating with Argonaute (Ago) proteins to form the RNA-induced silencing complex (RISC), underpinning a powerful mechanism for fine-tuning protein expression. Specific miRNAs are required for NMDA receptor (NMDAR)-dependent synaptic plasticity by modulating the translation of proteins involved in dendritic spine morphogenesis or synaptic transmission. However, it is unknown how NMDAR stimulation stimulates RISC activity to rapidly repress translation of synaptic proteins. We show that NMDAR stimulation transiently increases Akt-dependent phosphorylation of Ago2 at S387, which causes an increase in binding to GW182 and a rapid increase in translational repression of LIMK1 via miR-134. Furthermore, NMDAR-dependent down-regulation of endogenous LIMK1 translation in dendrites and dendritic spine shrinkage requires phospho-regulation of Ago2 at S387. AMPAR trafficking and hippocampal LTD do not involve S387 phosphorylation, defining this mechanism as a specific pathway for structural plasticity. This work defines a novel mechanism for the rapid transduction of NMDAR stimulation into miRNA-mediated translational repression to control dendritic spine morphology.

GTSF-1 is required for formation of a functional RNA-dependent RNA Polymerase complex in Caenorhabditis elegans

Argonaute proteins and their associated small RNAs (sRNAs) are evolutionarily conserved regulators of gene expression. Gametocyte-specific factor 1 (Gtsf1) proteins, characterized by two tandem CHHC zinc fingers and an unstructured C-terminal tail, are conserved in animals and have been shown to interact with Piwi clade Argonautes, thereby assisting their activity. We identified the Caenorhabditis elegans Gtsf1 homolog, named it gtsf-1 and characterized it in the context of the sRNA pathways of C. elegans We report that GTSF-1 is not required for Piwi-mediated gene silencing. Instead, gtsf-1 mutants show a striking depletion of 26G-RNAs, a class of endogenous sRNAs, fully phenocopying rrf-3 mutants. We show, both in vivo and in vitro, that GTSF-1 interacts with RRF-3 via its CHHC zinc fingers. Furthermore, we demonstrate that GTSF-1 is required for the assembly of a larger RRF-3 and DCR-1-containing complex (ERIC), thereby allowing for 26G-RNA generation. We propose that GTSF-1 homologs may act to drive the assembly of larger complexes that act in sRNA production and/or in imposing sRNA-mediated silencing activities.

Differential transmission of the molecular signature of RBSP3, LIMD1 and CDC25A in basal/ parabasal versus spinous of normal epithelium during head and neck tumorigenesis: A mechanistic study

Head and neck squamous cell carcinoma (HNSCC) is a global disease and mortality burden, necessitating the elucidation of its molecular progression for effective disease management. The study aims to understand the molecular profile of three candidate cell cycle regulatory genes, RBSP3, LIMD1 and CDC25A in the basal/ parabasal versus spinous layer of normal oral epithelium and during head and neck tumorigenesis. Immunohistochemical expression and promoter methylation was used to determine the molecular signature in normal oral epithelium. The mechanism of alteration transmission of this profile during tumorigenesis was then explored through additional deletion and mutation in HPV/ tobacco etiological groups, followed byclinico-pathological correlation. In basal/parabasal layer, the molecular signature of the genes was low protein expression/ high promoter methylation of RBSP3, high expression/ low methylation of LIMD1 and high expression of CDC25A. Dysplastic epithelium maintained the signature of RBSP3 through high methylation/ additional deletion with loss of the signatures of LIMD1 and CDC25A via deletion/ additional methylation. Similarly, maintenance and / or loss of signature in invasive tumors was by recurrent deletion/ methylation. Thus, differential patterns of alteration of the genes might be pre-requisite for the development of dysplastic and invasive lesions. Etiological factors played a key role in promoting genetic alterations and determining prognosis. Tobacco negative HNSCC patients had significantly lower alterations of LIMD1 and CDC25A, along with better survival among tobacco negative/ HPV positive patients. Our data suggests the necessity for perturbation of normal molecular profile of RBSP3, LIMD1 and CDC25A in conjunction with etiological factors for head and neck tumorigenesis, implying their diagnostic and prognostic significance.

Phase Transitions in the Assembly and Function of Human miRISC

miRISC is a multi-protein assembly that uses microRNAs (miRNAs) to identify mRNAs targeted for repression. Dozens of miRISC-associated proteins have been identified, and interactions between many factors have been examined in detail. However, the physical nature of the complex remains unknown. Here, we show that two core protein components of human miRISC, Argonaute2 (Ago2) and TNRC6B, condense into phase-separated droplets in vitro and in live cells. Phase separation is promoted by multivalent interactions between the glycine/tryptophan (GW)-rich domain of TNRC6B and three evenly spaced tryptophan-binding pockets in the Ago2 PIWI domain. miRISC droplets formed in vitro recruit deadenylation factors and sequester target RNAs from the bulk solution. The condensation of miRISC is accompanied by accelerated deadenylation of target RNAs bound to Ago2. The combined results may explain how miRISC silences mRNAs of varying size and structure and provide experimental evidence that protein-mediated phase separation can facilitate an RNA processing reaction.