Coregulation of alternative splicing by hnRNPM and ESRP1 during EMT

ACLY alternative splicing correlates with cancer phenotypes

ATP-citrate lyase (ACLY) links carbohydrate and lipid metabolism and provides nucleocytosolic acetyl-CoA for protein acetylation. ACLY has two major splice isoforms: the full-length canonical "long" isoform and an uncharacterized "short" isoform in which exon 14 is spliced out. Exon 14 encodes 10 amino acids within an intrinsically disordered region and includes at least one dynamically phosphorylated residue. Both isoforms are expressed in healthy tissues to varying degrees. Analysis of human transcriptomic data revealed that the percent spliced in (PSI) of exon 14 is increased in several cancers and correlated with poorer overall survival in a pan-cancer analysis, though not in individual tumor types. This prompted us to explore potential biochemical and functional differences between ACLY isoforms. Here, we show that there are no discernible differences in enzymatic activity or stability between isoforms or phosphomutants of ACLY in vitro. Similarly, both isoforms and phosphomutants were able to rescue ACLY functions, including fatty acid synthesis and bulk histone acetylation, when re-expressed in Acly knockout cells. Deletion of Acly exon 14 in mice did not overtly impact development or metabolic physiology nor did it attenuate tumor burden in a genetic model of intestinal cancer. Notably, expression of epithelial splicing regulatory protein 1 (ESRP1) is highly correlated with ACLY PSI. We report that ACLY splicing is regulated by ESRP1. In turn, both ESRP1 expression and ACLY PSI are correlated with specific immune signatures in tumors. Despite these intriguing patterns of ACLY splicing in healthy and cancer tissues, functional differences between the isoforms remain elusive.

hnRNPM protects against the dsRNA-mediated interferon response by repressing LINE-associated cryptic splicing

RNA splicing is pivotal in post-transcriptional gene regulation, yet the exponential expansion of intron length in humans poses a challenge for accurate splicing. Here, we identify hnRNPM as an essential RNA-binding protein that suppresses cryptic splicing through binding to deep introns, maintaining human transcriptome integrity. Long interspersed nuclear elements (LINEs) in introns harbor numerous pseudo splice sites. hnRNPM preferentially binds at intronic LINEs to repress pseudo splice site usage for cryptic splicing. Remarkably, cryptic exons can generate long dsRNAs through base-pairing of inverted ALU transposable elements interspersed among LINEs and consequently trigger an interferon response, a well-known antiviral defense mechanism. Significantly, hnRNPM-deficient tumors show upregulated interferon-associated pathways and elevated immune cell infiltration. These findings unveil hnRNPM as a guardian of transcriptome integrity by repressing cryptic splicing and suggest that targeting hnRNPM in tumors may be used to trigger an inflammatory immune response, thereby boosting cancer surveillance.

Alternative splicing in EMT and TGF-β signaling during cancer progression

Epithelial to mesenchymal transition (EMT) is a physiological process during development where epithelial cells transform to acquire mesenchymal characteristics, which allows them to migrate and colonize secondary tissues. Many cellular signaling pathways and master transcriptional factors exert a myriad of controls to fine tune this vital process to meet various developmental and physiological needs. Adding to the complexity of this network are post-transcriptional and post-translational regulations. Among them, alternative splicing has been shown to play important roles to drive EMT-associated phenotypic changes, including actin cytoskeleton remodeling, cell-cell junction changes, cell motility and invasiveness. In advanced cancers, transforming growth factor-β (TGF-β) is a major inducer of EMT and is associated with tumor cell metastasis, cancer stem cell self-renewal, and drug resistance. This review aims to provide an overview of recent discoveries regarding alternative splicing events and the involvement of splicing factors in the EMT and TGF-β signaling. It will emphasize the importance of various splicing factors involved in EMT and explore their regulatory mechanisms.

Differential alternative splicing landscape identifies potentially functional RNA binding proteins in early embryonic development in mammals

Alternative splicing (AS) as one of the important post-transcriptional regulatory mechanisms has been poorly studied during embryogenesis. In this study, we comprehensively collected and analyzed the transcriptome data of early embryos from human and mouse. We found that AS plays an important role in this process and predicted candidate RNA binding protein (RBP) regulators that are associated with reproductive development. The predicted RBPs such as EIF4A3, MAK16, SRSF2, and UTP23 were found to be associated with reproductive disorders. By Smart-seq2 sequencing analysis, we identified 5445 aberrant alternative splicing events in Eif4a3-knockdown embryos. These events were preferentially associated with RNA processing. In conclusion, our work on the landscape and potential function of alternative splicing events will boost further investigation of detailed mechanisms and key factors regulating mammalian early embryo development and promote the inspiration of pharmaceutical approaches for disorders in this crucial biology process.

Circular RNA-circLRP6 protects cardiomyocyte from hypoxia-induced apoptosis by facilitating hnRNPM-mediated expression of FGF-9

Coronary atherosclerosis-induced myocardial ischemia leads to cardiomyocyte apoptosis. The regulatory mechanisms for cardiomyocyte apoptosis have not been fully understood. Circular RNAs are non-coding RNAs which play important roles in heart function maintenance and progression of heart diseases by regulating gene transcription and protein translation. Here, we reported a conserved cardiac circular RNA, which is generated from the second exon of LRP6 and named circLRP62-2 . CircLRP62-2 can protect cardiomyocyte from hypoxia-induced apoptosis. The expression of circLRP62-2 in cardiomyocytes was down-regulated under hypoxia, while forced expression of circLRP62-2 inhibited cell apoptosis. Normally, circLRP62-2 was mainly localized in the nucleus. Under hypoxia, circLRP62-2 is associated with heterogeneous nuclear ribonucleoprotein M (hnRNPM) to be translocated into the cytoplasm. It recruited hnRNPM to fibroblast growth factor 9 (FGF9) mRNA to enhance the expression of FGF9 protein, promoting hypoxia-adaption and viability of cardiomyocytes. In summary, this study uncovers a new inhibitor of apoptosis and reveals a novel anti-apoptotic pathway composed of circLRP62-2 , hnRNPM, and FGF9, which may provide therapeutic targets for coronary heart disease and ischemic myocardial injury.

The landscape of alternative polyadenylation during EMT and its regulation by the RNA-binding protein Quaking

Epithelial-mesenchymal transition (EMT) plays important roles in tumour progression and is orchestrated by dynamic changes in gene expression. While it is well established that post-transcriptional regulation plays a significant role in EMT, the extent of alternative polyadenylation (APA) during EMT has not yet been explored. Using 3' end anchored RNA sequencing, we mapped the alternative polyadenylation (APA) landscape following Transforming Growth Factor (TGF)-β-mediated induction of EMT in human mammary epithelial cells and found APA generally causes 3'UTR lengthening during this cell state transition. Investigation of potential mediators of APA indicated the RNA-binding protein Quaking (QKI), a splicing factor induced during EMT, regulates a subset of events including the length of its own transcript. Analysis of QKI crosslinked immunoprecipitation (CLIP)-sequencing data identified the binding of QKI within 3' untranslated regions (UTRs) was enriched near cleavage and polyadenylation sites. Following QKI knockdown, APA of many transcripts is altered to produce predominantly shorter 3'UTRs associated with reduced gene expression. These findings reveal the changes in APA that occur during EMT and identify a potential role for QKI in this process.

Role of epithelial splicing regulatory protein 1 in cancer progression

As aberrant alternative splicing by either dysregulation or mutations of splicing factors contributes to cancer initiation and progression, splicing factors are emerging as potential therapeutic targets for cancer therapy. Therefore, pharmacological modulators targeting splicing factors have been under development. Epithelial splicing regulatory protein 1 (ESRP1) is an epithelial cell-specific splicing factor, whose downregulation is associated with epithelial-mesenchymal transition (EMT) by regulating alternative splicing of multiple genes, such as CD44, CTNND1, ENAH, and FGFR2. Consistent with the downregulation of ESRP1 during EMT, it has been initially revealed that high ESRP1 expression is associated with favorable prognosis and ESRP1 plays a tumor-suppressive role in cancer progression. However, ESRP1 has been found to promote cancer progression in some cancers, such as breast and ovarian cancers, indicating that it plays a dual role in cancer progression depending on the type of cancer. Furthermore, recent studies have reported that ESRP1 affects tumor growth by regulating the metabolism of tumor cells or immune cell infiltration in the tumor microenvironment, suggesting the novel roles of ESRP1 in addition to EMT. ESRP1 expression was also associated with response to anticancer drugs. This review describes current understanding of the roles and mechanisms of ESRP1 in cancer progression, and further discusses the emerging novel roles of ESRP1 in cancer and recent attempts to target splicing factors for cancer therapy.

RNA-binding proteins regulating the CD44 alternative splicing

Alternative splicing is often deregulated in cancer, and cancer-specific isoform switches are part of the oncogenic transformation of cells. Accumulating evidence indicates that isoforms of the multifunctional cell-surface glycoprotein CD44 play different roles in cancer cells as compared to normal cells. In particular, the shift of CD44 isoforms is required for epithelial to mesenchymal transition (EMT) and is crucial for the maintenance of pluripotency in normal human cells and the acquisition of cancer stem cells phenotype for malignant cells. The growing and seemingly promising use of splicing inhibitors for treating cancer and other pathologies gives hope for the prospect of using such an approach to regulate CD44 alternative splicing. This review integrates current knowledge about regulating CD44 alternative splicing by RNA-binding proteins.

Knockdown of HNRNPM inhibits the progression of glioma through inducing ferroptosis

PURPOSE

Ferroptosis acts as an important regulator in diverse human tumors, including the glioma. This study aimed to screen potential ferroptosis-related genes involved in the progression of glioma.

MATERIALS AND METHODS

Differently expressed genes (DEGs) were screened based on GSE31262 and GSE12657 datasets, and ferroptosis-related genes were separated. Among the important hub genes in the protein-protein interaction networks, HNRNPM was selected as a research target. Following the knockdown of HNRNPM, the viability, migration, and invasion were detected by CCK8, wound healing, and transwell assays, respectively. The role of HNRNPM knockdown was also verified in a xenograft tumor model in mice. Immunohistochemistry detected the expression levels of HNRNPM and Ki67. Moreover, the ferroptosis was evaluated according to the levels of iron, glutathione peroxidase (GSH), and malondialdehyde (MDA), as well as the expression of PTGS2, GPX4, and FTH1.

RESULTS

Total 41 overlapping DEGs relating with ferroptosis and glioma were screened, among which 4 up-regulated hub genes (HNRNPM, HNRNPA3, RUVBL1, and SNRPPF) were determined. The up-regulation of HNRNPM presented a certain predictive value for glioma. In addition, knockdown of HNRNPM inhibited the viability, migration, and invasion of glioma cells in vitro, and also the tumor growth in mice. Notably, knockdown of HNRNPM enhanced the ferroptosis in glioma cells. Furthermore, HNRNPM was positively associated with SMARCA4 in glioma.

CONCLUSIONS

Knockdown of HNRNPM inhibits the progression of glioma via inducing ferroptosis. HNRNPM is a promising molecular target for the treatment of glioma via inducing ferroptosis. We provided new insights of glioma progression and potential therapeutic guidance.

Identification of Significant RNA-Binding Proteins in the Process of CD44 Splicing Using the Boosted Beta Regression Algorithm

The expression of RNA-binding proteins and their interaction with the spliced pre-mRNA are the key factors in determining the final isoform profile. Transmembrane protein CD44 is involved in differentiation, invasion, motility, growth and survival of tumor cells, and is also a commonly accepted marker of cancer stem cells and epithelial-mesenchymal transition. However, the functions of the isoforms of this protein differ significantly. In this paper, we developed a method based on the boosted beta regression algorithm for identification of the significant RNA-binding proteins in the splicing process by modeling the isoform ratio. The application of this method to the analysis of CD44 splicing in colorectal cancer cells revealed 20 significant RNA-binding proteins. Many of them were previously shown as EMT regulators, but for the first time presented as potential CD44 splicing factors.

Matrix stiffness regulates tumor cell intravasation through expression and ESRP1-mediated alternative splicing of MENA

During intravasation, cancer cells cross the endothelial barrier and enter the circulation. Extracellular matrix stiffening has been correlated with tumor metastatic potential; however, little is known about the effects of matrix stiffness on intravasation. Here, we utilize in vitro systems, a mouse model, specimens from patients with breast cancer, and RNA expression profiles from The Cancer Genome Atlas Program (TCGA) to investigate the molecular mechanism by which matrix stiffening promotes tumor cell intravasation. Our data show that heightened matrix stiffness increases MENA expression, which promotes contractility and intravasation through focal adhesion kinase activity. Further, matrix stiffening decreases epithelial splicing regulatory protein 1 (ESRP1) expression, which triggers alternative splicing of MENA, decreases the expression of MENA11a, and enhances contractility and intravasation. Altogether, our data indicate that matrix stiffness regulates tumor cell intravasation through enhanced expression and ESRP1-mediated alternative splicing of MENA, providing a mechanism by which matrix stiffness regulates tumor cell intravasation.

LINE-associated cryptic splicing induces dsRNA-mediated interferon response and tumor immunity

RNA splicing plays a critical role in post-transcriptional gene regulation. Exponential expansion of intron length poses a challenge for accurate splicing. Little is known about how cells prevent inadvertent and often deleterious expression of intronic elements due to cryptic splicing. In this study, we identify hnRNPM as an essential RNA binding protein that suppresses cryptic splicing through binding to deep introns, preserving transcriptome integrity. Long interspersed nuclear elements (LINEs) harbor large amounts of pseudo splice sites in introns. hnRNPM preferentially binds at intronic LINEs and represses LINE-containing pseudo splice site usage for cryptic splicing. Remarkably, a subgroup of the cryptic exons can form long dsRNAs through base-pairing of inverted Alu transposable elements scattered in between LINEs and trigger interferon immune response, a well-known antiviral defense mechanism. Notably, these interferon-associated pathways are found to be upregulated in hnRNPM-deficient tumors, which also exhibit elevated immune cell infiltration. These findings unveil hnRNPM as a guardian of transcriptome integrity. Targeting hnRNPM in tumors may be used to trigger an inflammatory immune response thereby boosting cancer surveillance.

Heterogeneity and plasticity of epithelial-mesenchymal transition (EMT) in cancer metastasis: Focusing on partial EMT and regulatory mechanisms

Epithelial-mesenchymal transition (EMT) or mesenchymal-epithelial transition (MET) plays critical roles in cancer metastasis. Recent studies, especially those based on single-cell sequencing, have revealed that EMT is not a binary process, but a heterogeneous and dynamic disposition with intermediary or partial EMT states. Multiple double-negative feedback loops involved by EMT-related transcription factors (EMT-TFs) have been identified. These feedback loops between EMT drivers and MET drivers finely regulate the EMT transition state of the cell. In this review, the general characteristics, biomarkers and molecular mechanisms of different EMT transition states were summarized. We additionally discussed the direct and indirect roles of EMT transition state in tumour metastasis. More importantly, this article provides direct evidence that the heterogeneity of EMT is closely related to the poor prognosis in gastric cancer. Notably, a seesaw model was proposed to explain how tumour cells regulate themselves to remain in specific EMT transition states, including epithelial state, hybrid/intermediate state and mesenchymal state. Additionally, this article also provides a review of the current status, limitations and future perspectives of EMT signalling in clinical applications.

Long Non-Coding RNAs as Novel Targets for Phytochemicals to Cease Cancer Metastasis

Metastasis is a multi-step phenomenon during cancer development leading to the propagation of cancer cells to distant organ(s). According to estimations, metastasis results in over 90% of cancer-associated death around the globe. Long non-coding RNAs (LncRNAs) are a group of regulatory RNA molecules more than 200 base pairs in length. The main regulatory activity of these molecules is the modulation of gene expression. They have been reported to affect different stages of cancer development including proliferation, apoptosis, migration, invasion, and metastasis. An increasing number of medical data reports indicate the probable function of LncRNAs in the metastatic spread of different cancers. Phytochemical compounds, as the bioactive agents of plants, show several health benefits with a variety of biological activities. Several phytochemicals have been demonstrated to target LncRNAs to defeat cancer. This review article briefly describes the metastasis steps, summarizes data on some well-established LncRNAs with a role in metastasis, and identifies the phytochemicals with an ability to suppress cancer metastasis by targeting LncRNAs.

RNA binding proteins (RBPs) and their role in DNA damage and radiation response in cancer

Traditionally majority of eukaryotic gene expression is influenced by transcriptional and post-transcriptional events. Alterations in the expression of proteins that act post-transcriptionally can affect cellular signaling and homeostasis. RNA binding proteins (RBPs) are a family of proteins that specifically bind to RNAs and are involved in post-transcriptional regulation of gene expression and important cellular processes such as cell differentiation and metabolism. Deregulation of RNA-RBP interactions and any changes in RBP expression or function can lead to various diseases including cancer. In cancer cells, RBPs play an important role in regulating the expression of tumor suppressors and oncoproteins involved in various cell-signaling pathways. Several RBPs such as HuR, AUF1, RBM38, LIN28, RBM24, tristetrapolin family and Musashi play critical roles in various types of cancers and their aberrant expression in cancer cells makes them an attractive therapeutic target for cancer treatment. In this review we provide an overview of i). RBPs involved in cancer progression and their mechanism of action ii). the role of RBPs, including HuR, in breast cancer progression and DNA damage response and iii). explore RBPs with emphasis on HuR as therapeutic target for breast cancer therapy.

Identifying Hub Genes Associated with Neoadjuvant Chemotherapy Resistance in Breast Cancer and Potential Drug Repurposing for the Development of Precision Medicine

Breast cancer is the second leading cause of morbidity and mortality in women worldwide. Despite advancements in the clinical application of neoadjuvant chemotherapy (NAC), drug resistance remains a major concern hindering treatment efficacy. Thus, identifying the key genes involved in driving NAC resistance and targeting them with known potential FDA-approved drugs could be applied to advance the precision medicine strategy. With this aim, we performed an integrative bioinformatics study to identify the key genes associated with NAC resistance in breast cancer and then performed the drug repurposing to identify the potential drugs which could use in combination with NAC to overcome drug resistance. In this study, we used publicly available RNA-seq datasets from the samples of breast cancer patients sensitive and resistant to chemotherapy and identified a total of 1446 differentially expressed genes in NAC-resistant breast cancer patients. Next, we performed gene co-expression network analysis to identify significantly co-expressed gene modules, followed by MCC (Multiple Correlation Clustering) clustering algorithms and identified 33 key hub genes associated with NAC resistance. mRNA–miRNA network analysis highlighted the potential impact of these hub genes in altering the regulatory network in NAC-resistance breast cancer cells. Further, several hub genes were found to be significantly involved in the poor overall survival of breast cancer patients. Finally, we identified FDA-approved drugs which could be useful for potential drug repurposing against those hub genes. Altogether, our findings provide new insight into the molecular mechanisms of NAC resistance and pave the way for drug repurposing techniques and personalized treatment to overcome NAC resistance in breast cancer.

Dysregulation of splicing variants and spliceosome components in breast cancer

The dysregulation of the splicing process has emerged as a novel hallmark of metabolic and tumor pathologies. In breast cancer (BCa), which represents the most diagnosed cancer type among women worldwide, the generation and/or dysregulation of several oncogenic splicing variants have been described. This is the case of the splicing variants of HER2, ER, BRCA1, or the recently identified by our group, In1-ghrelin and SST5TMD4, which exhibit oncogenic roles, increasing the malignancy, poor prognosis, and resistance to treatment of BCa. This altered expression of oncogenic splicing variants has been closely linked with the dysregulation of the elements belonging to the macromolecular machinery that controls the splicing process (spliceosome components and the associated splicing factors). In this review, we compile the current knowledge demonstrating the altered expression of splicing variants and spliceosomal components in BCa, showing the existence of a growing body of evidence supporting the close implication of the alteration in the splicing process in mammary tumorigenesis.

A Regulatory Axis between Epithelial Splicing Regulatory Proteins and Estrogen Receptor α Modulates the Alternative Transcriptome of Luminal Breast Cancer

Epithelial splicing regulatory proteins 1 and 2 (ESRP1/2) control the splicing pattern during epithelial to mesenchymal transition (EMT) in a physiological context and in cancer, including breast cancer (BC). Here, we report that ESRP1, but not ESRP2, is overexpressed in luminal BCs of patients with poor prognosis and correlates with estrogen receptor α (ERα) levels. Analysis of ERα genome-binding profiles in cell lines and primary breast tumors showed its binding in the proximity of ESRP1 and ESRP2 genes, whose expression is strongly decreased by ERα silencing in hormone-deprived conditions. The combined knock-down of ESRP1/2 in MCF-7 cells followed by RNA-Seq, revealed the dysregulation of 754 genes, with a widespread alteration of alternative splicing events (ASEs) of genes involved in cell signaling, metabolism, cell growth, and EMT. Functional network analysis of ASEs correlated with ESRP1/2 expression in ERα+ BCs showed RAC1 as the hub node in the protein-protein interactions altered by ESRP1/2 silencing. The comparison of ERα- and ESRP-modulated ASEs revealed 63 commonly regulated events, including 27 detected in primary BCs and endocrine-resistant cell lines. Our data support a functional implication of the ERα-ESRP1/2 axis in the onset and progression of BC by controlling the splicing patterns of related genes.

RNA-binding proteins and cancer metastasis

RNA-binding proteins (RBPs) can regulate gene expression through post-transcriptionally influencing all manner of RNA biology, including alternative splicing (AS), polyadenylation, stability, and translation of mRNAs, as well as microRNAs (miRNAs) and circular RNAs (circRNAs) processing. There is accumulating evidence reinforcing the perception that dysregulation or dysfunction of RBPs can lead to various human diseases, including cancers. RBPs influence diverse cancer-associated cellular phenotypes, such as proliferation, apoptosis, senescence, migration, invasion, and angiogenesis, contributing to the initiation and development of tumors, as well as clinical prognosis. Metastasis is the leading cause of cancer-related recurrence and death. Therefore, it is necessary to elucidate the molecular mechanisms behind tumor metastasis. In fact, a growing body of published research has proved that RBPs play pivotal roles in cancer metastasis. In this review, we will summarize the recent advances for helping us understand the role of RBPs in tumor metastasis, and discuss dysfunctions and dysregulations of RBPs affecting metastasis-associated processes including epithelial-mesenchymal transition (EMT), migration, and invasion of cancer cells. Furthermore, we will discuss emerging RBP-based strategy for the treatment of cancer metastasis.

Alternative RNA splicing in tumour heterogeneity, plasticity and therapy

Alternative splicing is a process by which a single gene is able to encode multiple different protein isoforms. It is regulated by the inclusion or exclusion of introns and exons that are joined in different patterns prior to protein translation, thus enabling transcriptomic and proteomic diversity. It is now widely accepted that alternative splicing is dysregulated across nearly all cancer types. This widespread dysregulation means that nearly all cellular processes are affected - these include processes synonymous with the hallmarks of cancer - evasion of apoptosis, tissue invasion and metastasis, altered cellular metabolism, genome instability and drug resistance. Emerging evidence indicates that the dysregulation of alternative splicing also promotes a permissive environment for increased tumour heterogeneity and cellular plasticity. These are fundamental regulators of a patient's response to therapy. In this Review, we introduce the mechanisms of alternative splicing and the role of aberrant splicing in cancer, with particular focus on newfound evidence of alternative splicing promoting tumour heterogeneity, cellular plasticity and altered metabolism. We discuss recent in vivo models generated to study alternative splicing and the importance of these for understanding complex tumourigenic processes. Finally, we review the effects of alternative splicing on immune evasion, cell death and genome instability, and how targeting these might enhance therapeutic efficacy.

Regulation of Alternative Splicing during Epithelial-Mesenchymal Transition

Alternative splicing is an essential mechanism of gene regulation, giving rise to remarkable protein diversity in higher eukaryotes. Epithelial-mesenchymal transition (EMT) is a developmental process that plays an essential role in metazoan embryogenesis. Recent studies have revealed that alternative splicing serves as a fundamental layer of regulation that governs cells to undergo EMT. In this review, we summarize recent findings on the functional impact of alternative splicing in EMT and EMT-associated activities. We then discuss the regulatory mechanisms that control alternative splicing changes during EMT.

The ubiquitin E3 ligase ARIH1 regulates hnRNP E1 protein stability, EMT and breast cancer progression

The epithelial to mesenchymal transition (EMT), a process that is aberrantly activated in cancer and facilitates metastasis to distant organs, requires coordinated transcriptional and post-transcriptional control of gene expression. The tumor-suppressive RNA binding protein, hnRNP-E1, regulates splicing and translation of EMT-associated transcripts and it is thought that it plays a major role in the control of epithelial cell plasticity during cancer progression. We have utilized yeast 2 hybrid screening to identify novel hnRNP-E1 interactors that play a role in regulating hnRNP-E1; this approach led to the identification of the E3 ubiquitin ligase ARIH1. Here, we demonstrate that hnRNP-E1 protein stability is increased upon ARIH1 silencing, whereas, overexpression of ARIH1 leads to a reduction in hnRNP-E1. Reduced ubiquitination of hnRNP-E1 detected in ARIH1 knockdown (KD) cells compared to control suggests a role for ARIH1 in hnRNP-E1 degradation. The identification of hnRNP-E1 as a candidate substrate of ARIH1 led to the characterization of a novel function for this ubiquitin ligase in EMT induction and cancer progression. We demonstrate a delayed induction of EMT and reduced invasion in mammary epithelial cells silenced for ARIH1. Conversely, ARIH1 overexpression promoted EMT induction and invasion. ARIH1 silencing in breast cancer cells significantly attenuated cancer cell stemness in vitro and tumor formation in vivo. Finally, we utilized miniTurboID proximity labeling to identify novel ARIH1 interactors that may contribute to ARIH1's function in EMT induction and cancer progression.

Multifunctional RNA-binding proteins influence mRNA abundance and translational efficiency of distinct sets of target genes

RNA-binding proteins (RBPs) can regulate more than a single aspect of RNA metabolism. We searched for such previously undiscovered multifunctionality within a set of 143 RBPs, by defining the predictive value of RBP abundance for the transcription and translation levels of known RBP target genes across 80 human hearts. This led us to newly associate 27 RBPs with cardiac translational regulation in vivo. Of these, 21 impacted both RNA expression and translation, albeit for virtually independent sets of target genes. We highlight a subset of these, including G3BP1, PUM1, UCHL5, and DDX3X, where dual regulation is achieved through differential affinity for target length, by which separate biological processes are controlled. Like the RNA helicase DDX3X, the known splicing factors EFTUD2 and PRPF8—all identified as multifunctional RBPs by our analysis—selectively influence target translation rates depending on 5’ UTR structure. Our analyses identify dozens of RBPs as being multifunctional and pinpoint potential novel regulators of translation, postulating unanticipated complexity of protein-RNA interactions at consecutive stages of gene expression.

The lifecycle of an RNA molecule is controlled by hundreds of proteins that can bind RNA, also known as RNA-binding proteins (RBPs). These proteins recognize landing sites within the RNA and guide the RNA’s transcription from DNA, its processing into a mature messenger RNA, its translation into protein, or its degradation once the RNA is no longer needed. Although we now mechanistically understand how certain RBPs regulate these processes, for many RBP-target interactions the consequences imposed by RNA binding are not well understood. For 143 RBPs with known RNA binding positions, the authors of the current study investigated how RNA molecules responded to fluctuations in the expression levels of these RBPs, across each of 80 human hearts. Using statistical approaches, they could show that many RBPs influenced stages of the RNA lifecycle that they were not known to be involved in. Some RBPs turned out to be true "all-rounders" of RNA metabolism: they controlled the RNA transcript levels of some genes, whereas they influenced the translation rates of others. This unexpected multifunctionality unveiled previously hidden aspects of the everyday RNA-binding protein working life.

Matrix factorization-based data fusion for the prediction of RNA-binding proteins and alternative splicing event associations during epithelial-mesenchymal transition

MOTIVATION

The epithelial-mesenchymal transition (EMT) is a cellular-developmental process activated during tumor metastasis. Transcriptional regulatory networks controlling EMT are well studied; however, alternative RNA splicing also plays a critical regulatory role during this process. Unfortunately, a comprehensive understanding of alternative splicing (AS) and the RNA-binding proteins (RBPs) that regulate it during EMT remains largely unknown. Therefore, a great need exists to develop effective computational methods for predicting associations of RBPs and AS events. Dramatically increasing data sources that have direct and indirect information associated with RBPs and AS events have provided an ideal platform for inferring these associations.

RESULTS

In this study, we propose a novel method for RBP-AS target prediction based on weighted data fusion with sparse matrix tri-factorization (WDFSMF in short) that simultaneously decomposes heterogeneous data source matrices into low-rank matrices to reveal hidden associations. WDFSMF can select and integrate data sources by assigning different weights to those sources, and these weights can be assigned automatically. In addition, WDFSMF can identify significant RBP complexes regulating AS events and eliminate noise and outliers from the data. Our proposed method achieves an area under the receiver operating characteristic curve (AUC) of $90.78\%$, which shows that WDFSMF can effectively predict RBP-AS event associations with higher accuracy compared with previous methods. Furthermore, this study identifies significant RBPs as complexes for AS events during EMT and provides solid ground for further investigation into RNA regulation during EMT and metastasis. WDFSMF is a general data fusion framework, and as such it can also be adapted to predict associations between other biological entities.

Impact of alternative splicing on mechanisms of resistance to anticancer drugs

A shared characteristic of many tumors is the lack of response to anticancer drugs. Multiple mechanisms of pharmacoresistance (MPRs) are involved in permitting cancer cells to overcome the effect of these agents. Pharmacoresistance can be primary (intrinsic) or secondary (acquired), i.e., triggered or enhanced in response to the treatment. Moreover, MPRs usually result in the lack of sensitivity to several agents, which accounts for diverse multidrug-resistant (MDR) phenotypes. MPRs are based on the dynamic expression of more than one hundred genes, constituting the so-called resistome. Alternative splicing (AS) during pre-mRNA maturation results in changes affecting proteins involved in the resistome. The resulting splicing variants (SVs) reduce the efficacy of anticancer drugs by lowering the intracellular levels of active agents, altering molecular targets, enhancing both DNA repair ability and defensive mechanism of tumors, inducing changes in the balance between pro-survival and pro-apoptosis signals, modifying interactions with the tumor microenvironment, and favoring malignant phenotypic transitions. Reasons accounting for cancer-associated aberrant splicing include mutations that create or disrupt splicing sites or splicing enhancers or silencers, abnormal expression of splicing factors, and impaired signaling pathways affecting the activity of the splicing machinery. Here we have reviewed the impact of AS on MPR in cancer cells.

Emerging Multi-cancer Regulatory Role of ESRP1: Orchestration of Alternative Splicing to Control EMT

RNA binding proteins (RBPs) associate with nascent and mature RNAs to perform biological functions such as alternative splicing and RNA stability. Having unique RNA recognition binding motifs, RBPs form complexes with RNA in a sequence- and structure-based manner. Aberrant expressions of several RBPs have been identified in tumorigenesis and cancer progression. These uncontrolled RBPs affect several mechanisms, including cell proliferation, tumor growth, invasion, metastasis and chemoresistance. Epithelial splicing regulatory protein 1 (ESRP1) is a member of the hnRNP family of proteins that play a crucial role in regulating numerous cellular processes, including alternative splicing and translation of multiple genes during organogenesis. Abnormal expression of ESRP1 alters the cell morphology, and leads to cell proliferation and tumor growth during cancer progression. ESRP1 mediated alternative splicing of target genes, including CD44, FGFR, PTBP1, LYN, ENAH, SPAG1 and ZMYND8, results in cancer progression. In addition, ESRP1 also regulates circularization and biogenesis of circular RNAs such as circUHRF1, circNOL10 and circANKS1B, whose expressions have been identified as key factors in various cancers. This multi-functional protein is also involved in imposing stability of target mRNAs such as cyclin A2, and thereby cell cycle regulation. The scope of this review is to examine recent scientific data, outcomes of the up- and down-regulated proteins, and the role of ESRP1 in various cancers. We conclude by summarizing ESRP1 dysregulation and its consequences on target genes in various human cancers. Collectively, the consequences of ESRP1 mediated splicing in cancer cells suggest the role of ESRP1 in cell proliferation and chemoresistance via apoptosis and autophagy modulation, which could, therefore, be potential targets for cancer therapeutics.

The RNA-Binding Protein ESRP1 Modulates the Expression of RAC1b in Colorectal Cancer Cells

Simple Summary

Colorectal cancer (CRC) ranks third for incidence and second for number of deaths among cancer types worldwide. Poor patient survival due to inadequate response to currently available treatment regimens points to the urgent requirement for personalized therapy in CRC patients. Our aim was to provide mechanistic insights into the pro-tumorigenic role of the RNA-binding protein ESRP1, which is highly expressed in a subset of CRC patients. We show that, in CRC cells, ESRP1 binds to and has the same trend in expression as RAC1b, a well-known tumor promoter. Thus, RAC1b may be a potential therapeutic target in ESRP1-overexpressing CRC.

Abstract

RNA binding proteins are well recognized as critical regulators of tumorigenic processes through their capacity to modulate RNA biogenesis, including alternative splicing, RNA stability and mRNA translation. The RNA binding protein Epithelial Splicing Regulatory Protein 1 (ESRP1) can act as a tumor suppressor or promoter in a cell type- and disease context-dependent manner. We have previously shown that elevated expression of ESRP1 in colorectal cancer cells can drive tumor progression. To gain further insights into the pro-tumorigenic mechanism of action of ESRP1, we performed cDNA microarray analysis on two colorectal cells lines modulated for ESRP1 expression. Intriguingly, RAC1b was highly expressed, both at mRNA and protein levels, in ESRP1-overexpressing cells, while the opposite trend was observed in ESRP1-silenced CRC cells. Moreover, RAC1 and RAC1b mRNA co-immunoprecipitate with ESRP1 protein. Silencing of RAC1b expression significantly reduced the number of soft agar colonies formed by ESRP1-overexpressing cells, suggesting that ESRP1 acted, at least partially, through RAC1b in its tumor-promoting activities in CRC cells. Thus, our data provide molecular cues on targetable candidates in CRC cases with high ESRP1 expression.

E2F1 and epigenetic modifiers orchestrate breast cancer progression by regulating oxygen-dependent ESRP1 expression

Epithelial splicing regulatory protein 1 (ESRP1) is an RNA binding protein that governs the alternative splicing events related to epithelial phenotypes. ESRP1 contributes significantly at different stages of cancer progression. ESRP1 expression is substantially elevated in carcinoma in situ compared to the normal epithelium, whereas it is drastically ablated in cancer cells within hypoxic niches, which promotes epithelial to mesenchymal transition (EMT). Although a considerable body of research sought to understand the EMT-associated ESRP1 downregulation, the regulatory mechanisms underlying ESRP1 upregulation in primary tumors remained largely uncharted. This study seeks to unveil the regulatory mechanisms that spatiotemporally fine-tune the ESRP1 expression during breast carcinogenesis. Our results reveal that an elevated expression of transcription factor E2F1 and increased CpG hydroxymethylation of the E2F1 binding motif conjointly induce ESRP1 expression in breast carcinoma. However, E2F1 fails to upregulate ESRP1 despite its abundance in oxygen-deprived breast cancer cells. Mechanistically, impelled by the hypoxia-driven reduction of tet methylcytosine dioxygenase 3 (TET3) activity, CpG sites across the E2F1 binding motif lose the hydroxymethylation marks while gaining the de novo methyltransferase-elicited methylation marks. These two oxygen-sensitive epigenetic events work in concert to repel E2F1 from the ESRP1 promoter, thereby diminishing ESRP1 expression under hypoxia. Furthermore, E2F1 skews the cancer spliceome by upregulating splicing factor SRSF7 in hypoxic breast cancer cells. Our findings provide previously unreported mechanistic insights into the plastic nature of ESRP1 expression and insinuate important implications in therapeutics targeting breast cancer progression.

Identification of prognostic and bone metastasis​-related alternative splicing signatures in mesothelioma

Mesothelioma (MESO) is an infrequent tumor derived from mesothelial cells of pleura, peritoneum, pericardium, and tunica vaginalis testis. Despite advancement in technologies and better understanding of tumor progression mechanism, the prognosis of MESO remains poor. The role of alternative splicing events (ASEs) in the oncogenesis, tumor metastasis and drug resistance has been widely discussed in multiple cancers. But the prognosis and potential therapeutic value of ASEs in MESO were not clearly studied by now. We constructed a prognostic model using RNA sequencing data and matched ASE data of MESO patients obtained from the TCGA and TCGASpliceSeq database. A total of 3,993 ASEs were identified associated with overall survival using Cox regression analysis. Eight of them were finally figured out to institute the model by lasso regression analysis. The risk score of the model can predict the prognosis independently. Among the identified 390 splicing factors (SF), HSPA1A and DDX3Y was significantly associated with 43 OS-SEs. Among these OS-SEs, SNX5-58744-AT (p = 0.048) and SNX5-58745-AT (p = 0.048) were significantly associated with bone metastasis. Co-expression analysis of signal pathways and SNX5-58744-AT, SNX5-58745-AT was also depicted using GSVA. Finally, we proposed that splicing factor (SF) HSPA1A could regulate SNX5-58744-AT (R = -0.414) and SNX5-58745-AT (R = 0.414) through the pathway "Class I MHC mediated antigen processing and presentation" (R = 0.400). In this way, tumorigenesis and bone metastasis of MESO were controlled.

A prometastatic splicing program regulated by SNRPA1 interactions with structured RNA elements

Aberrant alternative splicing is a hallmark of cancer, yet the underlying regulatory programs that control this process remain largely unknown. Here, we report a systematic effort to decipher the RNA structural code that shapes pathological splicing during breast cancer metastasis. We discovered a previously unknown structural splicing enhancer that is enriched near cassette exons with increased inclusion in highly metastatic cells. We show that the spliceosomal protein small nuclear ribonucleoprotein polypeptide A' (SNRPA1) interacts with these enhancers to promote cassette exon inclusion. This interaction enhances metastatic lung colonization and cancer cell invasion, in part through SNRPA1-mediated regulation of PLEC alternative splicing, which can be counteracted by splicing modulating morpholinos. Our findings establish a noncanonical regulatory role for SNRPA1 as a prometastatic splicing enhancer in breast cancer.

Signature of gene aberrant alternative splicing events in pancreatic adenocarcinoma prognosis

Alternative splicing (AS), as an effective and universal mechanism of transcriptional regulation, is involved in the development and progression of cancer. Therefore, systematic analysis of alternative splicing in pancreatic adenocarcinoma (PAAD) is warranted. The corresponding clinical information of the RNA-Seq data and PAAD cohort was downloaded from the TCGA data portal. Then, a java application, SpliceSeq, was used to evaluate the RNA splicing pattern and calculate the splicing percentage index (PSI). Differentially expressed AS events (DEAS) were identified based on PSI values between PAAD cancer samples and normal samples of adjacent tissues. Kaplan-Meier and Cox regression analyses were used to assess the association between DEAS and patient clinical characteristics. Unsupervised cluster analysis used to reveal four clusters with different survival patterns. At the same time, GEO and TCGA combined with GTEx to verify the differential expression of AS gene and splicing factor. After rigorous filtering, a total of 45,313 AS events were identified, 1,546 of which were differentially expressed AS events. Nineteen DEAS were found to be associated with OS with a five-year overall survival rate of 0.946. And the subtype clusters results indicate that there are differences in the nature of individual AS that affect clinical outcomes. Results also identified 15 splicing factors associated with the prognosis of PAAD. And the splicing factors ESRP1 and RBM5 played an important role in the PAAD-associated AS events. The PAAD-associated AS events, splicing networks, and clusters identified in this study are valuable for deciphering the underlying mechanisms of AS in PAAD and may facilitate the establishment of therapeutic goals for further validation.

Alternative splicing and cancer: a systematic review

The abnormal regulation of alternative splicing is usually accompanied by the occurrence and development of tumors, which would produce multiple different isoforms and diversify protein expression. The aim of the present study was to conduct a systematic review in order to describe the regulatory mechanisms of alternative splicing, as well as its functions in tumor cells, from proliferation and apoptosis to invasion and metastasis, and from angiogenesis to metabolism. The abnormal splicing events contributed to tumor progression as oncogenic drivers and/or bystander factors. The alterations in splicing factors detected in tumors and other mis-splicing events (i.e., long non-coding and circular RNAs) in tumorigenesis were also included. The findings of recent therapeutic approaches targeting splicing catalysis and splicing regulatory proteins to modulate pathogenically spliced events (including tumor-specific neo-antigens for cancer immunotherapy) were introduced. The emerging RNA-based strategies for the treatment of cancer with abnormally alternative splicing isoforms were also discussed. However, further studies are still required to address the association between alternative splicing and cancer in more detail.

Prediction of RNA-binding protein and alternative splicing event associations during epithelial-mesenchymal transition based on inductive matrix completion

MOTIVATION

The developmental process of epithelial-mesenchymal transition (EMT) is abnormally activated during breast cancer metastasis. Transcriptional regulatory networks that control EMT have been well studied; however, alternative RNA splicing plays a vital regulatory role during this process and the regulating mechanism needs further exploration. Because of the huge cost and complexity of biological experiments, the underlying mechanisms of alternative splicing (AS) and associated RNA-binding proteins (RBPs) that regulate the EMT process remain largely unknown. Thus, there is an urgent need to develop computational methods for predicting potential RBP-AS event associations during EMT.

RESULTS

We developed a novel model for RBP-AS target prediction during EMT that is based on inductive matrix completion (RAIMC). Integrated RBP similarities were calculated based on RBP regulating similarity, and RBP Gaussian interaction profile (GIP) kernel similarity, while integrated AS event similarities were computed based on AS event module similarity and AS event GIP kernel similarity. Our primary objective was to complete missing or unknown RBP-AS event associations based on known associations and on integrated RBP and AS event similarities. In this paper, we identify significant RBPs for AS events during EMT and discuss potential regulating mechanisms. Our computational results confirm the effectiveness and superiority of our model over other state-of-the-art methods. Our RAIMC model achieved AUC values of 0.9587 and 0.9765 based on leave-one-out cross-validation (CV) and 5-fold CV, respectively, which are larger than the AUC values from the previous models. RAIMC is a general matrix completion framework that can be adopted to predict associations between other biological entities. We further validated the prediction performance of RAIMC on the genes CD44 and MAP3K7. RAIMC can identify the related regulating RBPs for isoforms of these two genes.

AVAILABILITY AND IMPLEMENTATION

The source code for RAIMC is available at https://github.com/yushanqiu/RAIMC.

CONTACT

zouquan@nclab.net online.

ESRP1 regulates alternative splicing of CARM1 to sensitize small cell lung cancer cells to chemotherapy by inhibiting TGF-β/Smad signaling

Epithelial splicing regulatory protein 1 (ESRP1) is an RNA-binding protein that regulates alternative splicing of mRNA. ESRP1 plays an important role in chemoresistance of various cancers, including breast cancer, colon cancer and non-small cell lung cancer. However, the role of ESRP1 and its mechanism in small cell lung cancer (SCLC) chemoresistance remains unclear. In this study, we found that ESRP1 is significantly downregulated in SCLC chemo-resistant cells compared with chemo-sensitive cells. Moreover, the expression of ESRP1 was significantly lower in SCLC tissues than that in normal adjacent tissues and positively correlated with overall survival. Overexpression of ESRP1 increased SCLC chemosensitivity, and induced cell apoptosis and cell cycle arrest, whereas knockdown of ESRP1 induced the opposite effects. ESRP1 could inhibit the growth of SCLC in vivo. Through mRNA transcriptome sequencing, we found that ESRP1 regulates coactivator-associated arginine methyltransferase 1 (CARM1) to produce two different transcripts CARM1FL and CARM1ΔE15 by alternative splicing. ESRP1 affects the chemoresistance of SCLC by changing the content of different transcripts of CARM1. Furthermore, CARM1 regulates arginine methylation of Smad7, activates the TGF-β/Smad pathway and induces epithelial-to-mesenchymal transition (EMT), thereby promoting SCLC chemoresistance. Collectively, our study firstly demonstrates that ESRP1 inhibits the TGF-β/Smad signaling pathway by regulating alternative splicing of CARM1, thereby reversing chemoresistance of SCLC. The splicing factor ESRP1 may serve as a new drug resistance marker molecule and a potential therapeutic target in SCLC patients.

Alternative splicing modulates cancer aggressiveness: role in EMT/metastasis and chemoresistance

Enhanced metastasis and disease recurrence accounts for the high mortality rates associated with cancer. The process of Epithelial-Mesenchymal Transition (EMT) contributes towards the augmentation of cancer invasiveness along with the gain of stem-like and the subsequent drug-resistant behavior. Apart from the well-established transcriptional regulation, EMT is also controlled post-transcriptionally by virtue of alternative splicing (AS). Numerous genes including Fibroblast Growth Factor receptor (FGFR) as well as CD44 are differentially spliced during this trans-differentiation process which, in turn, governs cancer progression. These splicing alterations are controlled by various splicing factors including ESRP, RBFOX2 as well as hnRNPs. Here, we have depicted the mechanisms governing the splice isoform switching of FGFR and CD44. Moreover, the role of the splice variants generated by AS of these gene transcripts in modulating the metastatic potential and stem-like/chemoresistant behavior of cancer cells has also been highlighted. Additionally, the involvement of splicing factors in regulating EMT/invasiveness along with drug-resistance as well as the metabolic properties of the cells has been emphasized. Tumorigenesis is accompanied by a remodeling of the cellular splicing profile generating diverse protein isoforms which, in turn, control the cancer-associated hallmarks. Therefore, we have also briefly discussed about a wide variety of genes which are differentially spliced in the tumor cells and promote cancer progression. We have also outlined different strategies for targeting the tumor-associated splicing events which have shown promising results and therefore this approach might be useful in developing therapies to reduce cancer aggressiveness in a more specific manner.

Y-Box Binding Protein-1 Promotes Epithelial-Mesenchymal Transition in Sorafenib-Resistant Hepatocellular Carcinoma Cells

Hepatocellular carcinoma is one of the most common cancer types worldwide. In cases of advanced-stage disease, sorafenib is considered the treatment of choice. However, resistance to sorafenib remains a major obstacle for effective clinical application. Based on integrated phosphoproteomic and The Cancer Genome Atlas (TCGA) data, we identified a transcription factor, Y-box binding protein-1 (YB-1), with elevated phosphorylation of Ser102 in sorafenib-resistant HuH-7^R cells. Phosphoinositide-3-kinase (PI3K) and protein kinase B (AKT) were activated by sorafenib, which, in turn, increased the phosphorylation level of YB-1. In functional analyses, knockdown of YB-1 led to decreased cell migration and invasion in vitro. At the molecular level, inhibition of YB-1 induced suppression of zinc-finger protein SNAI1 (Snail), twist-related protein 1 (Twist1), zinc-finger E-box-binding homeobox 1 (Zeb1), matrix metalloproteinase-2 (MMP-2) and vimentin levels, implying a role of YB-1 in the epithelial-mesenchymal transition (EMT) process in HuH-7^R cells. Additionally, YB-1 contributes to morphological alterations resulting from F-actin rearrangement through Cdc42 activation. Mutation analyses revealed that phosphorylation at S102 affects the migratory and invasive potential of HuH-7^R cells. Our collective findings suggest that sorafenib promotes YB-1 phosphorylation through effect from the EGFR/PI3K/AKT pathway, leading to significant enhancement of hepatocellular carcinoma (HCC) cell metastasis. Elucidation of the specific mechanisms of action of YB-1 may aid in the development of effective strategies to suppress metastasis and overcome resistance.

RNA editing in cancer impacts mRNA abundance in immune response pathways

BACKGROUND

RNA editing generates modifications to the RNA sequences, thereby increasing protein diversity and shaping various layers of gene regulation. Recent studies have revealed global shifts in editing levels across many cancer types, as well as a few specific mechanisms implicating individual sites in tumorigenesis or metastasis. However, most tumor-associated sites, predominantly in noncoding regions, have unknown functional relevance.

RESULTS

Here, we carry out integrative analysis of RNA editing profiles between epithelial and mesenchymal tumors, since epithelial-mesenchymal transition is a key paradigm for metastasis. We identify distinct editing patterns between epithelial and mesenchymal tumors in seven cancer types using TCGA data, an observation further supported by single-cell RNA sequencing data and ADAR perturbation experiments in cell culture. Through computational analyses and experimental validations, we show that differential editing sites between epithelial and mesenchymal phenotypes function by regulating mRNA abundance of their respective genes. Our analysis of RNA-binding proteins reveals ILF3 as a potential regulator of this process, supported by experimental validations. Consistent with the known roles of ILF3 in immune response, epithelial-mesenchymal differential editing sites are enriched in genes involved in immune and viral processes. The strongest target of editing-dependent ILF3 regulation is the transcript encoding PKR, a crucial player in immune and viral response.

CONCLUSIONS

Our study reports widespread differences in RNA editing between epithelial and mesenchymal tumors and a novel mechanism of editing-dependent regulation of mRNA abundance. It reveals the broad impact of RNA editing in cancer and its relevance to cancer-related immune pathways.

MYCT1 inhibits the EMT and migration of laryngeal cancer cells via the SP1/miR-629-3p/ESRP2 pathway

MYCT1 has an inhibitory effect on the migration of laryngeal cancer cells, although the underlying molecular mechanism remains unknown. In this study, we aimed to explore the mechanism of MYCT1 in the epithelial-mesenchymal transition (EMT) and migration of laryngeal cancer cells. We found that MYCT1 significantly decreased the expression of miR-629-3p but increased the expression of ESRP2 in laryngeal cancer cells. The expression of miR-629-3p and ESRP2 in laryngeal cancer tissues showed significantly positive and negative correlations with patient metastasis, respectively. miR-629-3p was confirmed to repress the expression of ESRP2 by targeting its 3'UTR. SP1 was verified to be a direct transcription factor for miR-629-3p and a downstream target of MYCT1. Moreover, MYCT1 inhibited the EMT and migration of laryngeal cancer cells through the SP1/miR-629-3p/ESRP2 pathway. Taken together, our results establish a novel MYCT1 signaling pathway in the EMT and migration of laryngeal cancer cells, thus providing important insights for further studying the pathway in the diagnosis and treatment of laryngeal cancer.

RNA-recognition motif in Matrin-3 mediates neurodegeneration through interaction with hnRNPM

Background

Amyotrophic lateral sclerosis (ALS) is an adult-onset, fatal neurodegenerative disease characterized by progressive loss of upper and lower motor neurons. While pathogenic mutations in the DNA/RNA-binding protein Matrin-3 (MATR3) are linked to ALS and distal myopathy, the molecular mechanisms underlying MATR3-mediated neuromuscular degeneration remain unclear.

Methods

We generated Drosophila lines with transgenic insertion of human MATR3 wildtype, disease-associated variants F115C and S85C, and deletion variants in functional domains, ΔRRM1, ΔRRM2, ΔZNF1 and ΔZNF2. We utilized genetic, behavioral and biochemical tools for comprehensive characterization of our models in vivo and in vitro. Additionally, we employed in silico approaches to find transcriptomic targets of MATR3 and hnRNPM from publicly available eCLIP datasets.

Results

We found that targeted expression of MATR3 in Drosophila muscles or motor neurons shorten lifespan and produces progressive motor defects, muscle degeneration and atrophy. Strikingly, deletion of its RNA-recognition motif (RRM2) mitigates MATR3 toxicity. We identified rump, the Drosophila homolog of human RNA-binding protein hnRNPM, as a modifier of mutant MATR3 toxicity in vivo. Interestingly, hnRNPM physically and functionally interacts with MATR3 in an RNA-dependent manner in mammalian cells. Furthermore, common RNA targets of MATR3 and hnRNPM converge in biological processes important for neuronal health and survival.

Conclusions

We propose a model of MATR3-mediated neuromuscular degeneration governed by its RNA-binding domains and modulated by interaction with splicing factor hnRNPM.

Electronic supplementary material

The online version of this article (10.1186/s40478-020-01021-5) contains supplementary material, which is available to authorized users.

Targeting QKI-7 in vivo restores endothelial cell function in diabetes

Vascular endothelial cell (EC) dysfunction plays a key role in diabetic complications. This study discovers significant upregulation of Quaking-7 (QKI-7) in iPS cell-derived ECs when exposed to hyperglycemia, and in human iPS-ECs from diabetic patients. QKI-7 is also highly expressed in human coronary arterial ECs from diabetic donors, and on blood vessels from diabetic critical limb ischemia patients undergoing a lower-limb amputation. QKI-7 expression is tightly controlled by RNA splicing factors CUG-BP and hnRNPM through direct binding. QKI-7 upregulation is correlated with disrupted cell barrier, compromised angiogenesis and enhanced monocyte adhesion. RNA immunoprecipitation (RIP) and mRNA-decay assays reveal that QKI-7 binds and promotes mRNA degradation of downstream targets CD144, Neuroligin 1 (NLGN1), and TNF-α-stimulated gene/protein 6 (TSG-6). When hindlimb ischemia is induced in diabetic mice and QKI-7 is knocked-down in vivo in ECs, reperfusion and blood flow recovery are markedly promoted. Manipulation of QKI-7 represents a promising strategy for the treatment of diabetic vascular complications.

The RNA-binding protein AKAP8 suppresses tumor metastasis by antagonizing EMT-associated alternative splicing

Alternative splicing has been shown to causally contribute to the epithelial–mesenchymal transition (EMT) and tumor metastasis. However, the scope of splicing factors that govern alternative splicing in these processes remains largely unexplored. Here we report the identification of A-Kinase Anchor Protein (AKAP8) as a splicing regulatory factor that impedes EMT and breast cancer metastasis. AKAP8 not only is capable of inhibiting splicing activity of the EMT-promoting splicing regulator hnRNPM through protein–protein interaction, it also directly binds to RNA and alters splicing outcomes. Genome-wide analysis shows that AKAP8 promotes an epithelial cell state splicing program. Experimental manipulation of an AKAP8 splicing target CLSTN1 revealed that splice isoform switching of CLSTN1 is crucial for EMT. Moreover, AKAP8 expression and the alternative splicing of CLSTN1 predict breast cancer patient survival. Together, our work demonstrates the essentiality of RNA metabolism that impinges on metastatic breast cancer.

Splice isoform switching regulated by the heterogeneous nuclear ribonucleoprotein M (hnRNPM) induces EMT and metastasis. Here, the authors report that AKAP8 is a metastasis suppressor that inhibits the splicing activity of hnRNPM and antagonizes genome-wide EMT-associated alternative splicing to maintain epithelial cell state.

Differential Functions of Splicing Factors in Mammary Transformation and Breast Cancer Metastasis

Misregulation of alternative splicing is a hallmark of human tumors, yet to what extent and how it contributes to malignancy are only beginning to be unraveled. Here, we define which members of the splicing factor SR and SR-like families contribute to breast cancer and uncover differences and redundancies in their targets and biological functions. We identify splicing factors frequently altered in human breast tumors and assay their oncogenic functions using breast organoid models. We demonstrate that not all splicing factors affect mammary tumorigenesis in MCF-10A cells. Specifically, the upregulation of SRSF4, SRSF6, or TRA2β disrupts acinar morphogenesis and promotes cell proliferation and invasion in MCF-10A cells. By characterizing the targets of these oncogenic splicing factors, we identify shared spliced isoforms associated with well-established cancer hallmarks. Finally, we demonstrate that TRA2β is regulated by the MYC oncogene, plays a role in metastasis maintenance in vivo, and its levels correlate with breast cancer patient survival.

Splicing regulatory factors in breast cancer hallmarks and disease progression

By regulating transcript isoform expression levels, alternative splicing provides an additional layer of protein control. Recent studies show evidence that cancer cells use different splicing events to fulfill their requirements in order to develop, progress and metastasize. However, there has been less attention for the role of the complex catalyzing the complicated multistep splicing reaction: the spliceosome. The spliceosome consists of multiple sub-complexes in total comprising 244 proteins or splice factors and 5 associated RNA molecules. Here we discuss the role of splice factors in the oncogenic processes tumors cells need to fulfill their oncogenic properties (the so-called the hallmarks of cancer). Despite the fact that splice factors have been investigated only recently, they seem to play a prominent role in already five hallmarks of cancer: angiogenesis, resisting cell death, sustaining proliferation, deregulating cellular energetics and invasion and metastasis formation by affecting major signaling pathways such as epithelial-to-mesenchymal transition, the Warburg effect, DNA damage response and hormone receptor dependent proliferation. Moreover, we could relate expression of representative genes of four other hallmarks (enabling replicative mortality, genomic instability, avoiding immune destruction and evading growth suppression) to splice factor levels in human breast cancer tumors, suggesting that also these hallmarks could be regulated by splice factors. Since many splice factors are involved in multiple hallmarks of cancer, inhibiting splice factors might provide a new layer of oncogenic control and a powerful method to combat breast cancer progression.

Splicing factor derived circular RNA circUHRF1 accelerates oral squamous cell carcinoma tumorigenesis via feedback loop

Emerging evidences have suggested the vital roles of circular RNA (circRNA) in the human cancers. However, the underlying biological functions and biogenesis of circRNA in the oral squamous cell carcinoma (OSCC) is still ambiguous. Here, we investigate the oncogenic roles and biogenesis of the novel identified circRNA, circUHRF1 (hsa_circ_0002185), in the OSCC tumorigenesis. Results showed that circUHRF1 was markedly upregulated in the OSCC cells and tissue, besides, the overexpression was closely correlated with the poor prognosis of OSCC patients. Functionally, circUHRF1 promoted the proliferation, migration, invasion, and epithelial mesenchymal transformation (EMT) in vitro and the tumor growth in vivo. Mechanically, circUHRF1 acted as the sponge of miR-526b-5p, thereby positively regulating c-Myc. Transcription factor c-Myc could accelerate the transcription of TGF-β1 and ESRP1. Moreover, splicing factor ESRP1 promoted the circularization and biogenesis of circUHRF1 by targeting the flanking introns, forming the circUHRF1/miR-526b-5p/c-Myc/TGF-β1/ESRP1 feedback loop. In conclusion, our research identified the oncogenic roles of circUHRF1 in the OSCC tumorigenesis and EMT via circUHRF1/miR-526b-5p/c-Myc/TGF-β1/ESRP1 feedback loop, shedding light on the pathogenic mechanism of circUHRF1 for OSCC and providing the potential therapeutic target.

Cancer the'RBP'eutics-RNA-binding proteins as therapeutic targets for cancer

RNA-binding proteins (RBPs) play a critical role in the regulation of various RNA processes, including splicing, cleavage and polyadenylation, transport, translation and degradation of coding RNAs, non-coding RNAs and microRNAs. Recent studies indicate that RBPs not only play an instrumental role in normal cellular processes but have also emerged as major players in the development and spread of cancer. Herein, we review the current knowledge about RNA binding proteins and their role in tumorigenesis as well as the potential to target RBPs for cancer therapeutics.

Identification of Upregulated HNRNPs Associated with Poor Prognosis in Pancreatic Cancer

Heterogeneous nuclear ribonucleoproteins (HNRNPs) are reported to play a crucial role in the pathogenic process of multiple malignancies. However, the expression patterns and prognostic values of HNRNPs in pancreatic cancer (PC) are lacking. In this study, several public databases were explored to identify the commonly upregulated HNRNPs in PC. The clinical significance of HNRNPL (heterogeneous nuclear ribonucleoproteins L) in PC was analyzed. We further performed a series of experiments to elucidate the biological functions of HNRNPL. Bioinformatics analysis including pathway enrichment and interactors with HNRNPL was used to explain the potential mechanisms of HNRNPL in PC pathogenesis. Herein, we reported that HNRNPL was commonly overexpressed in public databases and that high expression of HNRNPL in PC was positively associated with aggressive disease and poor overall survival. Downregulation of HNRNPL suppressed the abilities of migration and epithelial mesenchymal transition of PC cells in vitro, while depletion of HNRNPL did not affect the proliferation rate of PC cells. We further showed that HNRNPL might combine with RNA-binding protein, PTBP1, and function as a part of the spliceosome to regulate alternative splicing of target genes in the occurrence and development of PC. HNRNPL could be employed as an innovative prognostic biomarker and therapeutic target for PC.

Contribution of alternative splicing to breast cancer metastasis

Alternative splicing is a major contributor to transcriptome and proteome diversity in eukaryotes. Comparing to normal samples, about 30% more alternative splicing events were recently identified in 32 cancer types included in The Cancer Genome Atlas database. Some alternative splicing isoforms and their encoded proteins contribute to specific cancer hallmarks. In this review, we will discuss recent progress regarding the contributions of alternative splicing to breast cancer metastasis. We plan to dissect the role of MTDH, CD44 and their interaction with other mRNA splicing factors. We believe an in-depth understanding of the mechanism underlying the contribution of splicing to breast cancer metastasis will provide novel strategies to the management of breast cancer.

Splicing and cancer: Challenges and opportunities

Cancer arises from alterations in several metabolic processes affecting proliferation, growth, replication and death of cells. A fundamental challenge in the study of cancer biology is to uncover molecular mechanisms that lead to malignant cellular transformation. Recent genomic analyses revealed that many molecular alterations observed in cancers come from modifications in the splicing process, including mutations in pre-mRNA regulatory sequences, mutations in spliceosome components, and altered ratio of specific splicing regulators. While alterations in splice site preferences might generate alternative isoforms enabling different biological functions, these might also be responsible for nonfunctional isoforms that can eventually cause dysregulation in cellular processes. Molecular characteristics of regulatory sequences and proteins might also be important prognostic tools revealing a cancer-specific splicing pattern and linking splicing control to cancer development. The connection between cancer biology and splicing regulation is of primary importance to understand the mechanisms leading to disease and also to improve development of therapeutic approaches. Splicing modulation is being explored in new anti-cancer therapies and further investigation of targeted splicing factors is critical for the success of these strategies. This article is categorized under: RNA Processing > Splicing Mechanisms RNA-Based Catalysis > RNA Catalysis in Splicing and Translation RNA Processing > Splicing Regulation/Alternative Splicing RNA in Disease and Development > RNA in Disease.