Alternative Polyadenylation: Another Foe in Cancer

Genetic Variants That Impact Alternative Polyadenylation in Cancer Represent Candidate Causal Risk Loci

Alternative polyadenylation (APA) is emerging as a major mechanism of posttranscriptional regulation. APA can impact the development and progression of cancer, suggesting that the genetic determinants of APA might play an important role in regulating cancer risk. Here, we depicted a pan-cancer atlas of human APA quantitative trait loci (apaQTL), containing approximately 0.7 million apaQTLs across 32 cancer types. Systematic multiomics analyses indicated that cancer apaQTLs could contribute to APA regulation by altering poly(A) motifs, RNA-binding proteins (RBP), and chromatin regulatory elements and were preferentially enriched in genome-wide association studies (GWAS)-identified cancer susceptibility loci. Moreover, apaQTL-related genes (aGene) were broadly related to cancer signaling pathways, high mutational burden, immune infiltration, and drug response, implicating their potential as therapeutic targets. Furthermore, apaQTLs were mapped in Chinese colorectal cancer tumor tissues and then screened for functional apaQTLs associated with colorectal cancer risk in 17,789 cases and 19,951 controls using GWAS-ChIP data, with independent validation in a large-scale population consisting of 6,024 cases and 10,022 controls. A multi-ancestry-associated apaQTL variant rs1020670 with a C>G change in DNM1L was identified, and the G allele contributed to an increased risk of colorectal cancer. Mechanistically, the risk variant promoted aberrant APA and facilitated higher usage of DNM1L proximal poly(A) sites mediated by the RBP CSTF2T, which led to higher expression of DNM1L with a short 3'UTR. This stabilized DNM1L to upregulate its expression, provoking colorectal cancer cell proliferation. Collectively, these findings generate a resource for understanding APA regulation and the genetic basis of human cancers, providing insights into cancer etiology.

SIGNIFICANCE

Cancer risk is mediated by alternative polyadenylation quantitative trait loci, including the rs1020670-G variant that promotes alternative polyadenylation of DNM1L and increases colorectal cancer risk.

Differential expression of mRNA 3'-end isoforms in cervical and ovarian cancers

Early diagnosis and therapeutic targeting are continuing challenges for gynecological cancers. Here, we focus on cancer transcriptomes and describe the differential expression of 3'UTR isoforms in patients using an algorithm to detect differential poly(A) site usage. We find primarily 3'UTR shortening cases in cervical cancers compared with the normal cervix. We show differential expression of alternate 3'-end isoforms of FOXP1, VPS4B, and OGT in HPV16-positive patients who develop high-grade cervical lesions compared with the infected but non-progressing group. In contrast, in ovarian cancers, 3'UTR lengthening is more evident compared with normal ovary tissue. Nevertheless, highly malignant ovarian tumors have unique 3'UTR shortening events (e.g., CHRAC1, SLC16A1, and TOP2A), some of which correlate with upregulated protein levels in tumors. Overall, our study shows isoform level deregulation in gynecological cancers and highlights the complexity of the transcriptome. This transcript diversity could help identify novel cancer genes and provide new possibilities for diagnosis and therapy.

Surmounting Cancer Drug Resistance: New Perspective on RNA-Binding Proteins

RNA-binding proteins (RBPs), being pivotal elements in both physiological and pathological processes, possess the ability to directly impact RNA, thereby exerting a profound influence on cellular life. Furthermore, the dysregulation of RBPs not only induces alterations in the expression levels of genes associated with cancer but also impairs the occurrence of post-transcriptional regulatory mechanisms. Consequently, these circumstances can give rise to aberrations in cellular processes, ultimately resulting in alterations within the proteome. An aberrant proteome can disrupt the equilibrium between oncogenes and tumor suppressor genes, promoting cancer progression. Given their significant role in modulating gene expression and post-transcriptional regulation, directing therapeutic interventions towards RBPs represents a viable strategy for combating drug resistance in cancer treatment. RBPs possess significant potential as diagnostic and prognostic markers for diverse cancer types. Gaining comprehensive insights into the structure and functionality of RBPs, along with delving deeper into the molecular mechanisms underlying RBPs in tumor drug resistance, can enhance cancer treatment strategies and augment the prognostic outcomes for individuals afflicted with cancer.

Transcriptome analysis reveals the neuroprotective effect of Dlg4 against fastigial nucleus stimulation-induced ischemia/reperfusion injury in rats

BACKGROUND

Previous studies have demonstrated that electrical stimulation of the cerebellar fastigial nucleus (FNS) can considerably decrease infarction volume and improve neurofunction restoration following cerebral ischemia. Nevertheless, the molecular mechanism of the neuroprotective effect of FNS is still vague.

METHODS

In this study, we developed a rat model of ischemia/reperfusion that included 1 h FNS followed by reperfusion for 3, 6, 12, 24, and 72 h. The expression profile of molecular alterations in brain tissues was obtained by transcriptome sequencing at five different time points. The function and pathway of miRNA expression pattern and core genes were annotated by Allen Brain Atlas, STRING database and Cytoscape software, so as to explore the mechanism of FNS-mediated neuroprotection.

RESULTS

The results indicated that FNS is associated with the neurotransmitter cycle pathway. FNS may regulate the release of monoamine neurotransmitters in synaptic vesicles by targeting the corresponding miRNAs through core Dlg4 gene, stimulate the Alternative polyadenylation (APA) incident's anti -apoptosis effect on the brain, and stimulate the interaction activation of neurons in cerebellum, cortex/thalamus and other brain regions, regulate neurovascular coupling, and reduce cerebral damage.

CONCLUSION

FNS may activate neuronal and neurovascular coupling by regulating the release of neurotransmitters in synaptic vesicles through the methylation of core Dlg4 gene and the corresponding transcription factors and protein kinases, inducing the anti-apoptotic mechanism of APA events. The findings from our investigation offer a new perspective on the way brain tissue responds to FNS-driven neuroprotection.

CAFuncAPA: a knowledgebase for systematic functional annotations of APA events in human cancers

Alternative polyadenylation (APA) is a widespread posttranscriptional regulation process. APA generates diverse mRNA isoforms with different 3' UTR lengths, affecting mRNA expression, miRNA binding regulation and alternative splicing events. Previous studies have demonstrated the important roles of APA in tumorigenesis and cancer progression through diverse aspects. Thus, a comprehensive functional landscape of diverse APA events would aid in a better understanding of the underlying mechanisms related to APA in human cancers. Here, we built CAFuncAPA (https://relab.xidian.edu.cn/CAFuncAPA/) to systematically annotate the functions of 15478 APA events in human pan-cancers. Specifically, we first identified APA events associated with cancer survival and tumor progression. We annotated the potential downstream effects of APA on genes/isoforms expression, regulation of miRNAs, RNA binding proteins (RBPs) and alternative splicing events. Moreover, we also identified up-regulators of APA events, including the effects of genetic variants on poly(A) sites and RBPs, as well as the effect of methylation phenotypes on APA events. These findings suggested that CAFuncAPA can be a helpful resource for a better understanding of APA regulators and potential functions in cancer biology.

Novel roles of RNA-binding proteins in drug resistance of breast cancer: from molecular biology to targeting therapeutics

Therapy resistance remains a huge challenge for current breast cancer treatments. Exploring molecular mechanisms of therapy resistance might provide therapeutic targets for patients with advanced breast cancer and improve their prognosis. RNA-binding proteins (RBPs) play an important role in regulating therapy resistance. Here we summarize the functions of RBPs, highlight their tremendously important roles in regulating therapy sensitivity and resistance and we also reveal current therapeutic approaches reversing abnormal functions of RBPs in breast cancer.

Relationship between NUDT21 mediated alternative polyadenylation process and tumor

Alternative polyadenylation (APA) is a molecular process that generates diversity at the 3' end of RNA polymerase II transcripts from over 60% of human genes. APA and microRNA regulation are both mechanisms of post-transcriptional regulation of gene expression. As a key molecular mechanism, Alternative polyadenylation often results in mRNA isoforms with the same coding sequence but different lengths of 3' UTRs, while microRNAs regulate gene expression by binding to specific mRNA 3' UTRs. Nudix Hydrolase 21 (NUDT21) is a crucial mediator involved in alternative polyadenylation (APA). Different studies have reported a dual role of NUDT21 in cancer (both oncogenic and tumor suppressor). The present review focuses on the functions of APA, miRNA and their interaction and roles in development of different types of tumors.NUDT21 mediated 3' UTR-APA changes can be used to generate specific signatures that can be used as potential biomarkers in development and disease. Due to the emerging role of NUDT21 as a regulator of the aforementioned RNA processing events, modulation of NUDT21 levels may be a novel viable therapeutic approach.

Silencing of CPSF7 inhibits the proliferation, migration, and invasion of lung adenocarcinoma cells by blocking the AKT/mTOR signaling pathway

Cleavage and polyadenylation specific factor 7 (CPSF7) is an important participator in the cleavage and polyadenylation of pre-mRNAs. This study aims to uncover the function and underlying mechanism of CPSF7 in lung adenocarcinoma (LUAD). CPSF7 expression in LUAD cells was measured using real time-quantitative polymerase chain reaction and Western blotting. Our results showed that CPSF7 expression was upregulated in LUAD cell lines (A549, H1299, and HCC827). To explore the function of CPSF7 on LUAD, CPSF7 was silenced by the si-CPSF7 transfection and overexpressed by the oe-CPSF7 transfection in A549 cells. Cell proliferation was measured using cell counting kit-8 and colony formation assays. Cell migration and invasion were measured by wound healing and Transwell assays, respectively. Our data revealed that CPSF7 silencing inhibited the viability, colony formation, migration, and invasion of LUAD cells. On the contrary, CPSF7 overexpression enhanced the malignant characteristics of LUAD cells. Additionally, expression of AKT/mTOR pathway-related proteins was detected using Western blotting. CPSF7 silencing blocked the AKT/mTOR signaling pathway. The intervention of SC79 (an activator of the AKT/mTOR pathway) weakened the antitumor effects of CPSF7 silencing in LUAD cells. Silencing of CPSF7 inhibits the malignant characteristics of LUAD cells by blocking the AKT/mTOR signaling pathway.

The function and regulatory mechanism of RNA-binding proteins in breast cancer and their future clinical treatment prospects

Breast cancer is the most common female malignancy, but the mechanisms regulating gene expression leading to its development are complex. In recent years, as epigenetic research has intensified, RNA-binding proteins (RBPs) have been identified as a class of posttranscriptional regulators that can participate in regulating gene expression through the regulation of RNA stabilization and degradation, intracellular localization, alternative splicing and alternative polyadenylation, and translational control. RBPs play an important role in the development of normal mammary glands and breast cancer. Functional inactivation or abnormal expression of RBPs may be closely associated with breast cancer development. In this review, we focus on the function and regulatory mechanisms of RBPs in breast cancer, as well as the advantages and challenges of RBPs as potential diagnostic and therapeutic targets in breast cancer, and discuss the potential of RBPs in clinical treatment.

Advances in nanoparticle mediated targeting of RNA binding protein for cancer

RNA binding proteins (RBPs) enact a very crucial part in the RNA directive processes. Atypical expression of these RBPs affects many steps of RNA metabolism, majorly altering its expression. Altered expression and dysfunction of RNA binding proteins lead to cancer progression and other diseases. We enumerate various available interventions, and recent findings focused on targeting RBPs for cancer therapy and diagnosis. The treatment, sensitization, chemoprevention, gene-mediated, and virus mediated interventions were studied to treat and diagnose cancer. The application of passively and actively targeted lipidic nanoparticles, polymeric nanoparticles, virus-based particles, and vaccine-based immunotherapy for the delivery of therapeutic agent/s against cancer are discussed. We also discuss the formulation aspect of nanoparticles for achieving delivery at the site of action and ongoing clinical trials targeting RBPs.

On the Cutting Edge: Regulation and Therapeutic Potential of the mRNA 3' End Nuclease

Cleavage of nascent transcripts is a fundamental process for eukaryotic mRNA maturation and for the production of different mRNA isoforms. In eukaryotes, cleavage of mRNA precursors by the highly conserved endonuclease CPSF73 is critical for mRNA stability, export from the nucleus, and translation. As an essential enzyme in the cell, CPSF73 surprisingly shows promise as a drug target for specific cancers and for protozoan parasites. In this review, we cover our current understanding of CPSF73 in cleavage and polyadenylation, histone pre-mRNA processing, and transcription termination. We discuss the potential of CPSF73 as a target for novel therapeutics and highlight further research into the regulation of CPSF73 that will be critical to understanding its role in cancer and other diseases.

A computational pipeline to infer alternative poly-adenylation from 3' sequencing data

An increasing number of investigations have established alternative polyadenylation (APA) as a key mechanism of gene regulation through altering the length of 3' untranslated region (UTR) and generating distinct mRNA termini. Further, appreciation for the significance of APA in disease contexts propelled the development of several 3' sequencing techniques. While these RNA sequencing technologies have advanced APA analysis, the intrinsic limitation of 3' read coverage and lack of appropriate computational tools constrain precise mapping and quantification of polyadenylation sites. Notably, Poly(A)-ClickSeq (PAC-seq) overcomes limiting factors such as poly(A) enrichment and 3' linker ligation steps using click-chemistry. Here we provide an updated PolyA-miner protocol, a computational approach to analyze PAC-seq or other 3'-Seq datasets. As a key practical constraint, we also provide a detailed account on the impact of sequencing depth on the number of detected polyadenylation sites and APA changes. This protocol is also updated to handle unique molecular identifiers used to address PCR duplication potentially observed in PAC-seq.

RNA-Binding Proteins Hold Key Roles in Function, Dysfunction, and Disease

RNA-binding proteins (RBPs) are multi-faceted proteins in the regulation of RNA or its RNA splicing, localisation, stability, and translation. Amassing proof from many recent and dedicated studies reinforces the perception of RBPs exerting control through differing expression levels, cellular localization and post-transcriptional alterations. However, since the regulation of RBPs is reliant on the micro-environment and events like stress response and metabolism, their binding affinities and the resulting RNA-RBP networks may be affected. Therefore, any misregulation and disruption in the features of RNA and its related homeostasis can lead to a number of diseases that include diabetes, cardiovascular disease, and other disorders such as cancer and neurodegenerative diseases. As such, correct regulation of RNA and RBPs is crucial to good health as the effect RBPs exert through loss of function can cause pathogenesis. In this review, we will discuss the significance of RBPs and their typical function and how this can be disrupted in disease.

Systemic Multi-Omics Analysis Reveals Amplified P4HA1 Gene Associated With Prognostic and Hypoxic Regulation in Breast Cancer

Breast cancer (BC) is a common malignant tumor in females around the world. While multimodality therapies exist, the mortality rate remains high. The hypoxic condition was one of the potent determinants in BC progression. The molecular mechanisms underpinning hypoxia and their association with BC can contribute to a better understanding of tailored therapies. In this study, two hypoxic induced BC transcriptomic cohorts (GSE27813 and GSE47533) were assessed from the GEO database. The P4HA1 gene was identified as a putative candidate and significantly regulated in hypoxic BC cells compared to normal BC cells at different time intervals (6 h, 9 h, 16 h, 32 h, and 48 h). In patients with Luminal (p < 1E-12), triple-negative subclasses (p = 1.35059E-10), Stage 1 (p = 8.8817E-16), lymph node N1 (p = 1.62436E-12), and in the 40–80 age group (p = 1.62447E-12), the expression of P4HA1 was closely associated with the clinical subtypes of BC. Furthermore, at the 10q22.1 chromosomal band, the P4HA1 gene displayed a high copy number elevation and was associated with a poor clinical regimen with overall survival, relapse-free survival, and distant metastases-free survival in BC patients. In addition, using BioGRID, the protein–protein interaction (PPI) network was built and the cellular metabolic processes, and hedgehog pathways are functionally enriched with GO and KEGG terms. This tentative result provides insight into the molecular function of the P4HA1 gene, which is likely to promote hypoxic-mediated carcinogenesis, which may favor early detection of BC and therapeutic stratification.

RNA-biology ruling cancer progression? Focus on 3'UTRs and splicing

The protein-coding regions of mRNAs have the information to make proteins and hence have been at the center of attention for understanding altered protein functions in disease states, including cancer. Indeed, the discovery of genomic alterations and driver mutations that change protein levels and/or activity has been pivotal in our understanding of cancer biology. However, to better understand complex molecular mechanisms that are deregulated in cancers, we also need to look at non-coding parts of mRNAs, including 3'UTRs (untranslated regions), which control mRNA stability, localization, and translation efficiency. Recently, these rather overlooked regions of mRNAs are gaining attention as mounting evidence provides functional links between 3'UTRs, protein functions, and cancer-related molecular mechanisms. Here, roles of 3'UTRs in cancer biology and mechanisms that result in cancer-specific 3'-end isoform variants will be reviewed. An increased appreciation of 3'UTRs may help the discovery of new ways to explain as of yet unknown oncogene activation and tumor suppressor inactivation cases in cancers, and provide new avenues for diagnostic and therapeutic applications.

Alteration of protein expression and spliceosome pathway activity during Barrett's carcinogenesis

BACKGROUND

Barrett's esophagus (BE) is a known precursor lesion and the strongest risk factor for esophageal adenocarcinoma (EAC), a common and lethal type of cancer. Prediction of risk, the basis for efficient intervention, is commonly solely based on histologic examination. This approach is challenged by problems such as inter-observer variability in the face of the high heterogeneity of dysplastic tissue. Molecular markers might offer an additional way to understand the carcinogenesis and improve the diagnosis-and eventually treatment. In this study, we probed significant proteomic changes during dysplastic progression from BE into EAC.

METHODS

During endoscopic mucosa resection, epithelial and stromal tissue samples were collected by laser capture microdissection from 10 patients with normal BE and 13 patients with high-grade dysplastic/EAC. Samples were analyzed by mass spectrometry-based proteomic analysis. Expressed proteins were determined by label-free quantitation, and gene set enrichment was used to find differentially expressed pathways. The results were validated by immunohistochemistry for two selected key proteins (MSH6 and XPO5).

RESULTS

Comparing dysplastic/EAC to non-dysplastic BE, we found in equal volumes of epithelial tissue an overall up-regulation in terms of protein abundance and diversity, and determined a set of 226 differentially expressed proteins. Significantly higher expressions of MSH6 and XPO5 were validated orthogonally and confirmed by immunohistochemistry.

CONCLUSIONS

Our results demonstrate that disease-related proteomic alterations can be determined by analyzing minute amounts of cell-type-specific collected tissue. Further analysis indicated that alterations of certain pathways associated with carcinogenesis, such as micro-RNA trafficking, DNA damage repair, and spliceosome activity, exist in dysplastic/EAC.

Alternative Polyadenylation: a new frontier in post transcriptional regulation

Polyadenylation of pre-messenger RNA (pre-mRNA) specific sites and termination of their downstream transcriptions are signaled by unique sequence motif structures such as AAUAAA and its auxiliary elements. Alternative polyadenylation (APA) is an important post-transcriptional regulatory mechanism that processes RNA products depending on its 3'-untranslated region (3'-UTR) specific sequence signal. APA processing can generate several mRNA isoforms from a single gene, which may have different biological functions on their target gene. As a result, cellular genomic stability, proliferation capability, and transformation feasibility could all be affected. Furthermore, APA modulation regulates disease initiation and progression. APA status could potentially act as a biomarker for disease diagnosis, severity stratification, and prognosis forecast. While the advance of modern throughout technologies, such as next generation-sequencing (NGS) and single-cell sequencing techniques, have enriched our knowledge about APA, much of APA biological process is unknown and pending for further investigation. Herein, we review the current knowledge on APA and how its regulatory complex factors (CFI/IIm, CPSF, CSTF, and RBPs) work together to determine RNA splicing location, cell cycle velocity, microRNA processing, and oncogenesis regulation. We also discuss various APA experiment strategies and the future direction of APA research.

Poly(A)-DG: A deep-learning-based domain generalization method to identify cross-species Poly(A) signal without prior knowledge from target species

In eukaryotes, polyadenylation (poly(A)) is an essential process during mRNA maturation. Identifying the cis-determinants of poly(A) signal (PAS) on the DNA sequence is the key to understand the mechanism of translation regulation and mRNA metabolism. Although machine learning methods were widely used in computationally identifying PAS, the need for tremendous amounts of annotation data hinder applications of existing methods in species without experimental data on PAS. Therefore, cross-species PAS identification, which enables the possibility to predict PAS from untrained species, naturally becomes a promising direction. In our works, we propose a novel deep learning method named Poly(A)-DG for cross-species PAS identification. Poly(A)-DG consists of a Convolution Neural Network-Multilayer Perceptron (CNN-MLP) network and a domain generalization technique. It learns PAS patterns from the training species and identifies PAS in target species without re-training. To test our method, we use four species and build cross-species training sets with two of them and evaluate the performance of the remaining ones. Moreover, we test our method against insufficient data and imbalanced data issues and demonstrate that Poly(A)-DG not only outperforms state-of-the-art methods but also maintains relatively high accuracy when it comes to a smaller or imbalanced training set.

RNA-Binding Proteins in Cancer: Functional and Therapeutic Perspectives

Simple Summary

RNA-binding proteins (RBPs) play central roles in regulating posttranscriptional expression of genes. Many of them are known to be deregulated in a wide variety of cancers. Dysregulated RBPs influence the expression levels of target RNAs related to cancer phenotypes, such as proliferation, apoptosis, angiogenesis, senescence, and EMT/invasion/metastasis. Thus, understanding the molecular functions of RBPs and their roles in cancer-related phenotypes can lead to improved therapeutic strategies.

Abstract

RNA-binding proteins (RBPs) crucially regulate gene expression through post-transcriptional regulation, such as by modulating microRNA (miRNA) processing and the alternative splicing, alternative polyadenylation, subcellular localization, stability, and translation of RNAs. More than 1500 RBPs have been identified to date, and many of them are known to be deregulated in cancer. Alterations in the expression and localization of RBPs can influence the expression levels of oncogenes, tumor-suppressor genes, and genome stability-related genes. RBP-mediated gene regulation can lead to diverse cancer-related cellular phenotypes, such as proliferation, apoptosis, angiogenesis, senescence, and epithelial-mesenchymal transition (EMT)/invasion/metastasis. This regulation can also be associated with cancer prognosis. Thus, RBPs can be potential targets for the development of therapeutics for the cancer treatment. In this review, we describe the molecular functions of RBPs, their roles in cancer-related cellular phenotypes, and various approaches that may be used to target RBPs for cancer treatment.

PolyA-miner: accurate assessment of differential alternative poly-adenylation from 3'Seq data using vector projections and non-negative matrix factorization

Almost 70% of human genes undergo alternative polyadenylation (APA) and generate mRNA transcripts with varying lengths, typically of the 3′ untranslated regions (UTR). APA plays an important role in development and cellular differentiation, and its dysregulation can cause neuropsychiatric diseases and increase cancer severity. Increasing awareness of APA’s role in human health and disease has propelled the development of several 3′ sequencing (3′Seq) techniques that allow for precise identification of APA sites. However, despite the recent data explosion, there are no robust computational tools that are precisely designed to analyze 3′Seq data. Analytical approaches that have been used to analyze these data predominantly use proximal to distal usage. With about 50% of human genes having more than two APA isoforms, current methods fail to capture the entirety of APA changes and do not account for non-proximal to non-distal changes. Addressing these key challenges, this study demonstrates PolyA-miner, an algorithm to accurately detect and assess differential alternative polyadenylation specifically from 3′Seq data. Genes are abstracted as APA matrices, and differential APA usage is inferred using iterative consensus non-negative matrix factorization (NMF) based clustering. PolyA-miner accounts for all non-proximal to non-distal APA switches using vector projections and reflects precise gene-level 3′UTR changes. It can also effectively identify novel APA sites that are otherwise undetected when using reference-based approaches. Evaluation on multiple datasets—first-generation MicroArray Quality Control (MAQC) brain and Universal Human Reference (UHR) PolyA-seq data, recent glioblastoma cell line NUDT21 knockdown Poly(A)-ClickSeq (PAC-seq) data, and our own mouse hippocampal and human stem cell-derived neuron PAC-seq data—strongly supports the value and protocol-independent applicability of PolyA-miner. Strikingly, in the glioblastoma cell line data, PolyA-miner identified more than twice the number of genes with APA changes than initially reported. With the emerging importance of APA in human development and disease, PolyA-miner can significantly improve data analysis and help decode the underlying APA dynamics.

SNP2APA: a database for evaluating effects of genetic variants on alternative polyadenylation in human cancers

Alternative polyadenylation (APA) is an important post-transcriptional regulation that recognizes different polyadenylation signals (PASs), resulting in transcripts with different 3' untranslated regions, thereby influencing a series of biological processes and functions. Recent studies have revealed that some single nucleotide polymorphisms (SNPs) could contribute to tumorigenesis and development through dysregulating APA. However, the associations between SNPs and APA in human cancers remain largely unknown. Here, using genotype and APA data of 9082 samples from The Cancer Genome Atlas (TCGA) and The Cancer 3'UTR Altas (TC3A), we systematically identified SNPs affecting APA events across 32 cancer types and defined them as APA quantitative trait loci (apaQTLs). As a result, a total of 467 942 cis-apaQTLs and 30 721 trans-apaQTLs were identified. By integrating apaQTLs with survival and genome-wide association studies (GWAS) data, we further identified 2154 apaQTLs associated with patient survival time and 151 342 apaQTLs located in GWAS loci. In addition, we designed an online tool to predict the effects of SNPs on PASs by utilizing PAS motif prediction tool. Finally, we developed SNP2APA, a user-friendly and intuitive database (http://gong_lab.hzau.edu.cn/SNP2APA/) for data browsing, searching, and downloading. SNP2APA will significantly improve our understanding of genetic variants and APA in human cancers.

HPV shapes tumor transcriptome by globally modifying the pool of RNA binding protein-binding motif

Human papillomavirus (HPV) positive head and neck cancer displayed specific transcription landscape but the underlying molecular mechanisms are not fully determined. Here, we interestingly found that HPV infection could globally elongate the 3’-untranslated regions (3’UTRs) in the majority of alternative polyadenylation (APA)-containing genes. Counterintuitively, the 3’UTR elongation does not affect their resident gene expression. Rather, they significantly increase the number of binding sites for RNA-binding proteins (RBPs) and subsequently upregulate a group of oncogenic genes by absorbing RBPs. A significant fraction of HPV affected genes are regulated through such mechanism that is 3’UTR-mediated recruitment of RBPs. As an example, we observed that HPV infection increases the length of 3’UTR of RBM25 transcript and hence recruits much more RNA binding protein including FUS and DGCR8. Consequently, in the absence of FUS and DGCR8 regulation, PD-1 was rescued and up-regulated after HPV infection. Taken together, our findings not only suggest a novel paradigm of how oncogenic viruses shape tumor transcriptome by modifying the 3’UTR, but also present a previously unrecognized layer of APA—RBP interplay in this molecular hierarchy. Modification of the pool of RBP-binding motif might expand our understandings into virus-associated carcinogenesis.

Alternative polyadenylation drives oncogenic gene expression in pancreatic ductal adenocarcinoma

Alternative polyadenylation (APA) is a gene regulatory process that dictates mRNA 3'-UTR length, resulting in changes in mRNA stability and localization. APA is frequently disrupted in cancer and promotes tumorigenesis through altered expression of oncogenes and tumor suppressors. Pan-cancer analyses have revealed common APA events across the tumor landscape; however, little is known about tumor type-specific alterations that may uncover novel events and vulnerabilities. Here, we integrate RNA-sequencing data from the Genotype-Tissue Expression (GTEx) project and The Cancer Genome Atlas (TCGA) to comprehensively analyze APA events in 148 pancreatic ductal adenocarcinomas (PDACs). We report widespread, recurrent, and functionally relevant 3'-UTR alterations associated with gene expression changes of known and newly identified PDAC growth-promoting genes and experimentally validate the effects of these APA events on protein expression. We find enrichment for APA events in genes associated with known PDAC pathways, loss of tumor-suppressive miRNA binding sites, and increased heterogeneity in 3'-UTR forms of metabolic genes. Survival analyses reveal a subset of 3'-UTR alterations that independently characterize a poor prognostic cohort among PDAC patients. Finally, we identify and validate the casein kinase CSNK1A1 (also known as CK1alpha or CK1a) as an APA-regulated therapeutic target in PDAC. Knockdown or pharmacological inhibition of CSNK1A1 attenuates PDAC cell proliferation and clonogenic growth. Our single-cancer analysis reveals APA as an underappreciated driver of protumorigenic gene expression in PDAC via the loss of miRNA regulation.

Post-Transcriptional Dysregulation of microRNA and Alternative Polyadenylation in Colorectal Cancer

Background

Colorectal cancer (CRC) is one of the leading causes of cancer death worldwide. microRNAs (miRNAs) repress gene expression by binding to complementary sequences in the 3' untranslated region (3'UTR) of target mRNAs. Alternative polyadenylation (APA) are relevant to the variability of the 3'UTR of mRNA. However, the posttranscriptional dysregulation of miRNAs and APA in CRC are poorly understood.

Method

In this study, we conducted small RNA sequencing to identify differentially expressed miRNAs (DERs) and their target genes. Function analysis on DER-target genes can explain the regulation roles of miRNAs in CRC. The mutual regulation of miRNAs and APA was analyzed by combining miRNA data to 3'UTR alteration using 3' termini of polyadenylated RNAs sequencing (3T-seq) technique, and this was validated using TCGA gene expression data.

Results

Our results showed 64 significant differentially expressed miRNAs (DERs) in CRC patients. Their target genes were related to cell adhesion and transcription regulation and were prevailingly involved in the CRC-related pathway. Integrative analysis of the miRNA and APA profile revealed 16 DERs were correlated with 12 polyadenylation factors, and six of them were significantly differently expressed in CRC. We also found four DERs that lost binding sites due to APA and showed a positive correlation between the miRNA and gene expression.

Conclusion

Our study found that miRNAs regulated APA by modulating key polyadenylation factors, and several miRNAs lost their suppression on mRNA due to APA. Associating this with gene expression may provide some important clues for a deeper study of posttranscriptional cellular regulation and biomarker research in CRC. Our data provided the first evidence that the interaction between miRNAs and APA associated with gene expression could serve as biomarkers for CRC, suggesting that hsa-miR-133a-3p and MLEC, hsa-miR-145-5p and SET, hsa-miR-1-3p and PPIA, and hsa-miR-378d and YY1 might be novel and potential biomarkers in improving the diagnosis of CRC.

Genome-wide profiling reveals alternative polyadenylation of mRNA in human non-small cell lung cancer

BACKGROUND

Lung cancer is the second most common cancer with an extremely poor overall survival rate. Post-transcriptional regulation of gene expression play many important roles in human cancer, and one of the potential mechanisms underlying this is alternative mRNA maturation at its 3' untranslated regions (3'-UTRs).

METHODS

Cancer tissues and paired adjacent normal lung tissues from 26 patients diagnosed with non-small cell lung cancer (NSCLC) were analyzed by in vitro transcription-sequencing alternative polyadenylation sites (IVT-SAPAS). 41,773,101 reads in average were obtained from each paired sample. A potential regulation of Cleavage Stimulation Factor Subunit 2 (CSTF2) on 3'UTR length of genes was tested in H460 cells.

RESULTS

1439 (10.26%) genes showed up-regulated expression and 1364 (9.72%) genes showed down-regulated expression in lung cancer tissue versus normal lung tissue, and shorten 3'UTR in cancer tissue was detected in cancer tissues collected from 96.2% (25/26) patients, indicating lung cancer tend to have shortened 3'UTRs of these identified genes. KEGG analysis showed 1855 genes with shorten 3'UTR were enriched in mTOR signaling, ubiquitin mediated proteolysis and RNA degradation. Knocking down CSTF2 expression in H460 cells results in 3'UTR elongation of genes that was identified to be with shortened length in cancer tissues.

CONCLUSION

Alternative polyadenylation (APA) site-switching of 3'UTRs is prevalent in NSCLC, and CSTF2 may serve as an oncogene regulates the 3'UTR length of cancer related genes in NSCLC.

A comprehensive analysis of core polyadenylation sequences and regulation by microRNAs in a set of cancer predisposition genes

Two core polyadenylation elements (CPE) located in the 3' untranslated region of eukaryotic pre-mRNAs play an essential role in their processing: the polyadenylation signal (PAS) AAUAAA and the cleavage site (CS), preferentially a CA dinucleotide. Herein, we characterized PAS and CS sequences in a set of cancer predisposition genes (CPGs) and performed an in silico investigation of microRNAs (miRNAs) regulation to identify potential tumor-suppressive and oncogenic miRNAs. NCBI and alternative polyadenylation databases were queried to characterize CPE sequences in 117 CPGs, including 81 and 17 known tumor suppressor genes and oncogenes, respectively. miRNA-mediated regulation analysis was performed using predicted and validated data sources. Based on NCBI analyses, we did not find an established PAS in 21 CPGs, and verified that the majority of PAS already described (74.4%) had the canonical sequence AAUAAA. Interestingly, "AA" dinucleotide was the most common CS (37.5%) associated with this set of genes. Approximately 90% of CPGs exhibited evidence of alternative polyadenylation (more than one functional PAS). Finally, the mir-192 family was significantly overrepresented as regulator of tumor suppressor genes (P < 0.01), which suggests a potential oncogenic function. Overall, this study provides a landscape of CPE in CPGs, which might be useful in development of future molecular analyses covering these frequently neglected regulatory sequences.

No association between G1359A CB1 polymorphisms and pain in young northeastern Mexicans

AIM

Recent studies show an association between the endocannabinoid system and pain. In this study, we analyzed the association between two CNR1 gene polymorphisms and pain perception in a northeast Mexican population.

METHODS

Genotypic and allelic frequencies were obtained for both polymorphisms. Pain threshold, tolerance and perception were measured using the cold pressor task.

RESULTS

No significant association between the polymorphisms and pain perception was found (p > 0.05).

CONCLUSION

Genotypic and allelic frequencies for both polymorphisms were reported for the first time in a Mexican population; however, our results suggest that there is not a significant association between these and pain.

Alternative polyadenylation factors link cell cycle to migration

Background

In response to a wound, fibroblasts are activated to migrate toward the wound, to proliferate and to contribute to the wound healing process. We hypothesize that changes in pre-mRNA processing occurring as fibroblasts enter the proliferative cell cycle are also important for promoting their migration.

Results

RNA sequencing of fibroblasts induced into quiescence by contact inhibition reveals downregulation of genes involved in mRNA processing, including splicing and cleavage and polyadenylation factors. These genes also show differential exon use, especially increased intron retention in quiescent fibroblasts compared to proliferating fibroblasts. Mapping the 3′ ends of transcripts reveals that longer transcripts from distal polyadenylation sites are more prevalent in quiescent fibroblasts and are associated with increased expression and transcript stabilization based on genome-wide transcript decay analysis. Analysis of dermal excisional wounds in mice reveals that proliferating cells adjacent to wounds express higher levels of cleavage and polyadenylation factors than quiescent fibroblasts in unwounded skin. Quiescent fibroblasts contain reduced levels of the cleavage and polyadenylation factor CstF-64. CstF-64 knockdown recapitulates changes in isoform selection and gene expression associated with quiescence, and results in slower migration.

Conclusions

Our findings support cleavage and polyadenylation factors as a link between cellular proliferation state and migration.

Electronic supplementary material

The online version of this article (10.1186/s13059-018-1551-9) contains supplementary material, which is available to authorized users.

Knockdown of NUDT21 inhibits proliferation and promotes apoptosis of human K562 leukemia cells through ERK pathway

Background

NUDT21 is a mammalian precursor mRNA(pre-mRNA) 3’ end processing factor and plays an important role in the selection of poly(A) sites in 3’-untranslated region (3’-UTR). NUDT21 links alternative polyadenylation with regulation of glioblastoma and osteosarcoma progression and is found to be related to drug resistance in childhood acute leukemia. However, the effect of NUDT21 on leukemia cells and the underlying mechanism are unknown.

Methods

We knocked down NUDT21 in K562 cells and applied qRT-PCR and western blotting to quantitate the mRNA and protein expression. Cell proliferating and apoptosis were investigated subsequently by flow cytometry, BrdU, Caspase3/7. RNA microarray and intracellular signaling array were used to determine the important cell signaling pathways.

Results

We clarified that the mRNA expression levels of NUDT21 are higher in primary chronic myelocytic leukemia patients and K562 leukemic cells compared with healthy controls and PBMCs. Downregulation of NUDT21 expression in K562 cells inhibits proliferation and promotes apoptosis. Screening by mRNA chip and intracellular signaling array, we found that MAPK/ERK pathway represented the main molecular mechanism underlying the effects of NUDT21 knockdown in K562 cells.

Conclusion

NUDT21 played an important role in promoting proliferation and inhibiting apoptosis in leukemia K562 cells. The underlying mechanisms involved the modulation of PTEN and a set of downstream molecules including ERK1/2.

Impact statement

The present work shows that the expression of NUDT21 was upregulated in chronic myelocytic leukemia and K562 cells. Silencing NUDT21 inhibited the proliferation and promoted the apoptosis of K562 cells. Subsequent experiments confirmed that NUDT21 promoted K562 proliferation through regulating the expression of p-ERK. Our findings may provide insights into the molecular mechanism underlying the effects of NUDT21 on leukemia cells and a novel strategy for the treatment of leukemia.

Recurrent tumor-specific regulation of alternative polyadenylation of cancer-related genes

Background

Alternative polyadenylation (APA) results in messenger RNA molecules with different 3′ untranslated regions (3’ UTRs), affecting the molecules’ stability, localization, and translation. APA is pervasive and implicated in cancer. Earlier reports on APA focused on 3’ UTR length modifications and commonly characterized APA events as 3’ UTR shortening or lengthening. However, such characterization oversimplifies the processing of 3′ ends of transcripts and fails to adequately describe the various scenarios we observe.

Results

We built a cloud-based targeted de novo transcript assembly and analysis pipeline that incorporates our previously developed cleavage site prediction tool, KLEAT. We applied this pipeline to elucidate the APA profiles of 114 genes in 9939 tumor and 729 tissue normal samples from The Cancer Genome Atlas (TCGA). The full set of 10,668 RNA-Seq samples from 33 cancer types has not been utilized by previous APA studies. By comparing the frequencies of predicted cleavage sites between normal and tumor sample groups, we identified 77 events (i.e. gene-cancer type pairs) of tumor-specific APA regulation in 13 cancer types; for 15 genes, such regulation is recurrent across multiple cancers. Our results also support a previous report showing the 3’ UTR shortening of FGF2 in multiple cancers. However, over half of the events we identified display complex changes to 3’ UTR length that resist simple classification like shortening or lengthening.

Conclusions

Recurrent tumor-specific regulation of APA is widespread in cancer. However, the regulation pattern that we observed in TCGA RNA-seq data cannot be described as straightforward 3’ UTR shortening or lengthening. Continued investigation into this complex, nuanced regulatory landscape will provide further insight into its role in tumor formation and development.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4903-7) contains supplementary material, which is available to authorized users.

NUDT21 negatively regulates PSMB2 and CXXC5 by alternative polyadenylation and contributes to hepatocellular carcinoma suppression

Alternative polyadenylation (APA) is an important post-transcriptional regulatory mechanism and involved in many diseases, including cancer. CFIm25, a subunit of the cleavage factor I encoded by NUDT21, is required for 3'RNA cleavage and polyadenylation. Although it has been recently reported to be involved in glioblastoma tumor suppression, its roles and the underlying functional mechanism remain unclear in other types of cancer. In this study, we characterized NUDT21 in hepatocellular carcinoma (HCC). Reduced expression of NUDT21 was observed in HCC tissue compared to adjacent non-tumorous compartment. HCC patients with lower NUDT21 expression have shorter overall and disease-free survival times than those with higher NUDT21 expression after surgery. Knockdown of NUDT21 promotes HCC cell proliferation, metastasis, and tumorigenesis, whereas forced expression of NUDT21 exhibits the opposite effects. We then performed global APA site profiling analysis in HCC cells and identified considerable number of genes with shortened 3'UTRs upon the modulation of NUDT21 expression. In particular, we further characterized the NUDT21-regulated genes PSMB2 and CXXC5. We found NUDT21 knockdown increases usage of the proximal polyadenylation site in the PSMB2 and CXXC5 3' UTRs, resulting in marked increase in the expression of PSMB2 and CXXC5. Moreover, knockdown of PSMB2 or CXXC5 suppresses HCC cell proliferation and invasion. Taken together, our study demonstrated that NUDT21 inhibits HCC proliferation, metastasis and tumorigenesis, at least in part, by suppressing PSMB2 and CXXC5, and thereby provided a new insight into understanding the connection of HCC suppression and APA machinery.

Aberrant Ki-67 expression through 3'UTR alternative polyadenylation in breast cancers

Ki‐67 (MKI67) is a marker of cellular proliferation of cancer. Here, we show that Ki‐67 is post‐transcriptionally regulated through alternative polyadenylation (APA) and microRNAs in breast cancer. We show that shortening of the Ki‐67 3′UTR results in the loss of the binding sites for the suppressive miRNAs and thus renders the transcript with a shortened 3′UTR insusceptible to miRNA‐mediated suppression. This APA‐mediated shortening of the Ki‐67 3′UTR contributes to increased mRNA stability and enhanced translational efficiency. In summary, our results not only highlight the post‐transcriptional regulation of Ki‐67 involving APA and microRNAs but also suggest that Ki‐67 3′UTR disruption could serve as a molecular marker in breast cancer.

Alternative Polyadenylation of PRELID1 Regulates Mitochondrial ROS Signaling and Cancer Outcomes

Disruption of posttranscriptional gene regulation is a critical step in oncogenesis that can be difficult to observe using traditional molecular techniques. To overcome this limitation, a modified polyadenylation site sequencing (PAS-seq) protocol was used to generate a genome-wide map of alternative polyadenylation (APA) events in human primary breast tumor specimens and matched normal tissue. This approach identified an APA event in the PRELID1 mRNA that enhances its steady-state level and translational efficiency, and is a strong breast cancer subtype-dependent predictor of patient clinical outcomes. Furthermore, it has been demonstrated that PRELID1 regulates stress response and mitochondrial reactive oxygen species (ROS) production in a cell type-specific manner. Modulation of PRELID1 expression, including its posttranscriptional control, appears to be a common stress response across different cancer types. These data reveal that PRELID1 mRNA processing is an important regulator of cell type-specific responses to stress used by multiple cancers and is associated with patient outcomes.Implications: This study suggests that the regulation of PRELID1 expression, by APA and other mechanisms, plays a role in mitochondrial ROS signaling and represents a novel prognostic factor and therapeutic target in cancer. Mol Cancer Res; 15(12); 1741-51. ©2017 AACR.

Post-transcriptional regulation of ERBB2 by miR26a/b and HuR confers resistance to tamoxifen in estrogen receptor-positive breast cancer cells

Tamoxifen-resistant (TAMR) estrogen receptor-positive (ER+) breast cancer is characterized by elevated Erb-B2 receptor tyrosine kinase 2 (ERBB2) expression. However, the underlying mechanisms responsible for the increased ERBB2 expression in the TAMR cells remain poorly understood. Herein, we reported that the ERBB2 expression is regulated at the post-transcriptional level by miR26a/b and the RNA-binding protein human antigen R (HuR), both of which associate with the 3'-UTR of the ERBB2 transcripts. We demonstrated that miR26a/b inhibits the translation of ERBB2 mRNA, whereas HuR enhances the stability of the ERBB2 mRNA. In TAMR ER+ breast cancer cells with elevated ERBB2 expression, we observed a decrease in the level of miR26a/b and an increase in the level of HuR. The forced expression of miR26a/b or the depletion of HuR decreased ERBB2 expression in the TAMR cells, resulting in the reversal of tamoxifen resistance. In contrast, the inactivation of miR26a/b or forced expression of HuR decreased tamoxifen responsiveness of the parental ER+ breast cancer cells. We further showed that the increase in HuR expression in the TAMR ER+ breast cancer cells is attributable to an increase in the HuR mRNA isoform with shortened 3'-UTR, which exhibits increased translational activity. This shortening of the HuR mRNA 3'-UTR via alternative polyadenylation (APA) was observed to be dependent on cleavage stimulation factor subunit 2 (CSTF2/CstF-64), which is up-regulated in the TAMR breast cancer cells. Taken together, we have characterized a model in which the interplay between miR26a/b and HuR post-transcriptionally up-regulates ERBB2 expression in TAMR ER+ breast cancer cells.

Alternative Polyadenylation Patterns for Novel Gene Discovery and Classification in Cancer

Certain aspects of diagnosis, prognosis, and treatment of cancer patients are still important challenges to be addressed. Therefore, we propose a pipeline to uncover patterns of alternative polyadenylation (APA), a hidden complexity in cancer transcriptomes, to further accelerate efforts to discover novel cancer genes and pathways. Here, we analyzed expression data for 1045 cancer patients and found a significant shift in usage of poly(A) signals in common tumor types (breast, colon, lung, prostate, gastric, and ovarian) compared to normal tissues. Using machine-learning techniques, we further defined specific subsets of APA events to efficiently classify cancer types. Furthermore, APA patterns were associated with altered protein levels in patients, revealed by antibody-based profiling data, suggesting functional significance. Overall, our study offers a computational approach for use of APA in novel gene discovery and classification in common tumor types, with important implications in basic research, biomarker discovery, and precision medicine approaches.

Polyadenylation site selection: linking transcription and RNA processing via a conserved carboxy-terminal domain (CTD)-interacting protein

Despite the fact that the process of mRNA polyadenylation has been known for more than 40 years, a detailed understating of the mechanism underlying polyadenylation site selection is still far from complete. As 3' end processing is intimately associated with RNA polymerase II (RNAPII) transcription, factors that can successively interact with the transcription machinery and recognize cis-acting sequences on the nascent pre-mRNA would be well suited to contribute to poly(A) site selection. Studies using the fission yeast Schizosaccharomyces pombe have recently identified Seb1, a protein that shares homology with Saccharomyces cerevisiae Nrd1 and human SCAF4/8, and that is critical for poly(A) site selection. Seb1 binds to the C-terminal domain (CTD) of RNAPII via a conserved CTD-interaction domain and recognizes specific sequence motifs clustered downstream of the polyadenylation site on the uncleaved pre-mRNA. In this short review, we summarize insights into Seb1-dependent poly(A) site selection and discuss some unanswered questions regarding its molecular mechanism and conservation.

Alternative polyadenylation and RNA-binding proteins

Our understanding of the extent of microRNA-based gene regulation has expanded in an impressive pace over the past decade. Now, we are beginning to better appreciate the role of 3'-UTR (untranslated region) cis-elements which harbor not only microRNA but also RNA-binding protein (RBP) binding sites that have significant effect on the stability and translational rate of mRNAs. To add further complexity, alternative polyadenylation (APA) emerges as a widespread mechanism to regulate gene expression by producing shorter or longer mRNA isoforms that differ in the length of their 3'-UTRs or even coding sequences. Resulting shorter mRNA isoforms generally lack cis-elements where trans-acting factors bind, and hence are differentially regulated compared with the longer isoforms. This review focuses on the RBPs involved in APA regulation and their action mechanisms on APA-generated isoforms. A better understanding of the complex interactions between APA and RBPs is promising for mechanistic and clinical implications including biomarker discovery and new therapeutic approaches.