The RNA helicase DDX39B and its paralog DDX39A regulate androgen receptor splice variant AR-V7 generation

Molecular analysis of archival diagnostic prostate cancer biopsies identifies genomic similarities in cases with progression post-radiotherapy, and those with de novo metastatic disease

BACKGROUND

It is important to identify molecular features that improve prostate cancer (PCa) risk stratification before radical treatment with curative intent. Molecular analysis of historical diagnostic formalin-fixed paraffin-embedded (FFPE) prostate biopsies from cohorts with post-radiotherapy (RT) long-term clinical follow-up has been limited. Utilizing parallel sequencing modalities, we performed a proof-of-principle sequencing analysis of historical diagnostic FFPE prostate biopsies. We compared patients with (i) stable PCa (sPCa) postprimary or salvage RT, (ii) progressing PCa (pPCa) post-RT, and (iii) de novo metastatic PCa (mPCa).

METHODS

A cohort of 19 patients with diagnostic prostate biopsies (n = 6 sPCa, n = 5 pPCa, n = 8 mPCa) and mean 4 years 10 months follow-up (diagnosed 2009-2016) underwent nucleic acid extraction from demarcated malignancy. Samples underwent 3'RNA sequencing (3'RNAseq) (n = 19), nanoString analysis (n = 12), and Illumina 850k methylation (n = 8) sequencing. Bioinformatic analysis was performed to coherently identify differentially expressed genes and methylated genomic regions (MGRs).

RESULTS

Eighteen of 19 samples provided useable 3'RNAseq data. Principal component analysis (PCA) demonstrated similar expression profiles between pPCa and mPCa cases, versus sPCa. Coherently differentially methylated probes between these groups identified ~600 differentially MGRs. The top 50 genes with increased expression in pPCa patients were associated with reduced progression-free survival post-RT (p < 0.0001) in an external cohort.

CONCLUSIONS

3'RNAseq, nanoString and 850k-methylation analyses are each achievable from historical FFPE diagnostic pretreatment prostate biopsies, unlocking the potential to utilize large cohorts of historic clinical samples. Profiling similarities between individuals with pPCa and mPCa suggests biological similarities and historical radiological staging limitations, which warrant further investigation.

Critical Cellular Functions and Mechanisms of Action of the RNA Helicase UAP56

Posttranscriptional maturation and export from the nucleus to the cytoplasm are essential steps in the normal processing of many cellular RNAs. The RNA helicase UAP56 (U2AF associated protein 56; also known as DDX39B) has emerged as a critical player in facilitating and co-transcriptionally linking these steps. Originally identified as a helicase involved in pre-mRNA splicing, UAP56 has been shown to facilitate formation of the A complex during spliceosome assembly. Additionally, it has been found to be critical for interactions between components of the exon junction and transcription and export complexes to promote the loading of export receptors. Although it appears to be structurally similar to other helicase superfamily 2 members, UAP56's ability to interact with multiple different protein partners allows it to perform its various cellular functions. Herein, we describe the structure-activity relationship studies that identified protein interactions of UAP56 and its human paralog URH49 (UAP56-related helicase 49; also known as DDX39A) and are beginning to reveal molecular mechanisms by which interacting proteins and substrate RNAs may regulate these helicases. We also provide an overview of reports that have demonstrated less well-characterized roles for UAP56, including R-loop resolution and telomere maintenance. Finally, we discuss studies that indicate a potential pathogenic effect of UAP56 in the development of autoimmune diseases and cancer, and identify the association of somatic and genetic mutations in UAP56 with neurodevelopmental disorders.

Parsing the roles of DExD-box proteins DDX39A and DDX39B in alternative RNA splicing

DExD-box RNA proteins DDX39A and DDX39B are highly homologous paralogs that are conserved in vertebrates. They are required for energy-driven reactions involved in RNA processing. Although we have some understanding of how their functions overlap in RNA nuclear export, our knowledge of whether or not these proteins have specific or redundant functions in RNA splicing is limited. Our previous work has shown that DDX39B is responsible for regulating the splicing of important immune transcripts IL7R and FOXP3. In this study, we aimed to investigate whether DDX39A, a highly homologous paralog of DDX39B, plays a similar role in regulating alternative RNA splicing. We find that DDX39A and DDX39B have significant redundancy in their gene targets, but there are targets that uniquely require one or the other paralog. For instance, DDX39A is incapable of complementing defective splicing of IL7R exon 6 when DDX39B is depleted. This exon and other cassette exons that specifically depend on DDX39B have U-poor/C-rich polypyrimidine tracts in the upstream intron and this variant polypyrimidine tract is required for DDX39B dependency. This study provides evidence that despite a high degree of functional redundancy, DDX39A and DDX39B are selectively required for the splicing of specific pre-mRNAs.

Constructing lactylation-related genes prognostic model to effectively predict the disease-free survival and treatment responsiveness in prostate cancer based on machine learning

Background: Prostate cancer (PCa) is one of the most common malignancies in men with a poor prognosis. It is therefore of great clinical importance to find reliable prognostic indicators for PCa. Many studies have revealed the pivotal role of protein lactylation in tumor development and progression. This research aims to analyze the effect of lactylation-related genes on PCa prognosis. Methods: By downloading mRNA-Seq data of TCGA PCa, we obtained the differential genes related to lactylation in PCa. Five machine learning algorithms were used to screen for lactylation-related key genes for PCa, then the five overlapping key genes were used to construct a survival prognostic model by lasso cox regression analysis. Furthermore, the relationships between the model and related pathways, tumor mutation and immune cell subpopulations, and drug sensitivity were explored. Moreover, two risk groups were established according to the risk score calculated by the five lactylation-related genes (LRGs). Subsequently, a nomogram scoring system was established to predict disease-free survival (DFS) of patients by combining clinicopathological features and lactylation-related risk scores. In addition, the mRNA expression levels of five genes were verified in PCa cell lines by qPCR. Results: We identified 5 key LRGs (ALDOA, DDX39A, H2AX, KIF2C, RACGAP1) and constructed the LRGs prognostic model. The AUC values for 1 -, 3 -, and 5-year DFS in the TCGA dataset were 0.762, 0.745, and 0.709, respectively. The risk score was found a better predictor of DFS than traditional clinicopathological features in PCa. A nomogram that combined the risk score with clinical variables accurately predicted the outcome of the patients. The PCa patients in the high-risk group have a higher proportion of regulatory T cells and M2 macrophage, a higher tumor mutation burden, and a worse prognosis than those in the low-risk group. The high-risk group had a lower IC50 for certain chemotherapeutic drugs, such as Docetaxel, and Paclitaxel than the low-risk group. Furthermore, five key LRGs were found to be highly expressed in castration-resistant PCa cells. Conclusion: The lactylation-related genes prognostic model can effectively predict the DFS and therapeutic responses in patients with PCa.

The RNA helicase DDX39A binds a conserved structure in chikungunya virus RNA to control infection

Alphaviruses are a large group of re-emerging arthropod-borne RNA viruses. The compact viral RNA genomes harbor diverse structures that facilitate replication. These structures can be recognized by antiviral cellular RNA-binding proteins, including DExD-box (DDX) helicases, that bind viral RNAs to control infection. The full spectrum of antiviral DDXs and the structures that are recognized remain unclear. Genetic screening identified DDX39A as antiviral against the alphavirus chikungunya virus (CHIKV) and other medically relevant alphaviruses. Upon infection, the predominantly nuclear DDX39A accumulates in the cytoplasm inhibiting alphavirus replication, independent of the canonical interferon pathway. Biochemically, DDX39A binds to CHIKV genomic RNA, interacting with the 5' conserved sequence element (5'CSE), which is essential for the antiviral activity of DDX39A. Altogether, DDX39A relocalization and binding to a conserved structural element in the alphavirus genomic RNA attenuates infection, revealing a previously unknown layer to the cellular control of infection.

DDX39B facilitates the malignant progression of hepatocellular carcinoma via activation of SREBP1-mediated de novo lipid synthesis

PURPOSE

The detailed molecular mechanisms of aberrant lipid metabolism in HCC remain unclear. Herein, we focused on the potential role of DDX39B in aberrant lipogenesis and malignant development in HCC.

METHODS

DDX39B expression in HCC and para-cancer tissues was measured by immunohistochemistry. CCK-8, colony formation and Transwell assays were utilized to detect HCC cell proliferation, migration and invasion in vitro. Oil red O and Nile red staining and triglyceride and cholesterol detection were used to measure lipogenesis. Coimmunoprecipitation was used to detect interactions between DDX39B and SREBP1. Immunofluorescence assays were performed to investigate the impact of DDX39B on SREBP1 nuclear translocation. A luciferase assay was used to explore the transcriptional activity of SREBP1. The subcutaneous and orthotopic xenograft models in nude mice were generated to verify the contribution of the DDX39B/SREBP1 axis to tumor growth, lung metastasis and lipid synthesis in vivo.

RESULTS

DDX39B is upregulated in HCC tissues and predicts a worse prognosis. Upregulated DDX39B contributes to the proliferation, metastasis and lipogenesis of HCC cells. Mechanistically, DDX39B directly interacts with SREBP1, and silencing DDX39B impairs the stabilization of the SREBP1 protein through FBXW7-mediated ubiquitination and degradation of SREBP1. Furthermore, DDX39B deficiency decreases the nuclear translocation and activation of SREBP1 and transcription of SREBP1 downstream genes, resulting in reduced lipid accumulation.

CONCLUSIONS

Our study reveals a novel mechanism by which DDX39B facilitates the malignant progression of HCC via activation of SREBP1-mediated de novo lipogenesis, implicating DDX39B as both a potential predictor of recurrence and prognosis and a promising therapeutic target.

Early Splicing Complexes and Human Disease

Over the last decade, our understanding of spliceosome structure and function has significantly improved, refining the study of the impact of dysregulated splicing on human disease. As a result, targeted splicing therapeutics have been developed, treating various diseases including spinal muscular atrophy and Duchenne muscular dystrophy. These advancements are very promising and emphasize the critical role of proper splicing in maintaining human health. Herein, we provide an overview of the current information on the composition and assembly of early splicing complexes-commitment complex and pre-spliceosome-and their association with human disease.

The RNA helicase DDX39B activates FOXP3 RNA splicing to control T regulatory cell fate

Genes associated with increased susceptibility to multiple sclerosis (MS) have been identified, but their functions are incompletely understood. One of these genes codes for the RNA helicase DExD/H-Box Polypeptide 39B (DDX39B), which shows genetic and functional epistasis with interleukin-7 receptor-α gene (IL7R) in MS-risk. Based on evolutionary and functional arguments, we postulated that DDX39B enhances immune tolerance thereby decreasing MS risk. Consistent with such a role we show that DDX39B controls the expression of many MS susceptibility genes and important immune-related genes. Among these we identified Forkhead Box P3 (FOXP3), which codes for the master transcriptional factor in CD4+/CD25+ T regulatory cells. DDX39B knockdown led to loss of immune-regulatory and gain of immune-effector expression signatures. Splicing of FOXP3 introns, which belong to a previously unrecognized type of introns with C-rich polypyrimidine tracts, was exquisitely sensitive to DDX39B levels. Given the importance of FOXP3 in autoimmunity, this work cements DDX39B as an important guardian of immune tolerance.

Racial Differences in Androgen Receptor (AR) and AR Splice Variants (AR-SVs) Expression in Treatment-Naïve Androgen-Dependent Prostate Cancer

Androgen receptor splice variants (AR-SVs) contribute to the aggressive growth of castration-resistant prostate cancer (CRPC). AR-SVs, including AR-V7, are expressed in ~30% of CRPC, but minimally in treatment-naïve primary prostate cancer (PCa). Compared to Caucasian American (CA) men, African American (AA) men are more likely to be diagnosed with aggressive/potentially lethal PCa and have shorter disease-free survival. Expression of a truncated AR in an aggressively growing patient-derived xenograft developed with a primary PCa specimen from an AA patient led us to hypothesize that the expression of AR-SVs could be an indicator of aggressive growth both in PCa progression and at the CRPC stage in AA men. Tissue microarrays (TMAs) were created from formalin-fixed paraffin-embedded (FFPE) prostatectomy tumor blocks from 118 AA and 115 CA treatment-naïve PCa patients. TMAs were stained with AR-V7-speicifc antibody and with antibodies binding to the N-terminus domain (NTD) and ligand-binding domain (LBD) of the AR. Since over 20 AR-SVs have been identified, and most AR-SVs do not as yet have a specific antibody, we considered a 2.0-fold or greater difference in the NTD vs. LBD staining as indication of potential AR-SV expression. Two AA, but no CA, patient tumors stained positively for AR-V7. AR staining with NTD and LBD antibodies was robust in most patients, with 21% of patients staining at least 2-fold more for NTD than LBD, indicating that AR-SVs other than AR-V7 are expressed in primary treatment-naïve PCa. About 24% of the patients were AR-negative, and race differences in AR expression were not statistically significant. These results indicate that AR-SVs are not restricted to CRPC, but also are expressed in primary PCa at higher rate than previously reported. Future investigation of the relative expression of NTD vs. LBD AR-SVs could guide the use of newly developed treatments targeting the NTD earlier in the treatment paradigm.

The androgen receptor-targeted proteolysis targeting chimera and other alternative therapeutic choices in overcoming the resistance to androgen deprivation treatment in prostate cancer

Androgen receptor (AR) plays a vital role in prostate cancer (PCa), including castration-resistant PCa, by retaining AR signalling. Androgen deprivation treatment (ADT) has been the standard treatment in the past decades. A great number of AR antagonists initially had been found effective in tumour remission; however, most PCa relapsed that caused by pre-translational resistance such as AR mutations to turn antagonist into agonist, and AR variants to bypass the androgen binding. Recently, several alternative therapeutic choices have been proposed. Among them, proteolysis targeting chimera (PROTAC) acts different from traditional drugs that usually function as inhibitors or antagonists, and it degrades oncogenic protein and does not disrupt the transcription of an oncogene. This review first discussed some essential mechanisms of ADT resistance, and then introduced the application of AR-targeted PROTAC in PCa cells, as well as other AR-targeted therapeutic choices.

Androgen Receptor Signaling Inhibition in Advanced Castration Resistance Prostate Cancer: What Is Expected for the Near Future?

The androgen signaling pathway is the cornerstone in the treatment of high risk or advanced prostate cancer patients. However, in recent years, different mechanisms of resistance have been defined in this field, limiting the efficacy of the currently approved antiandrogen drugs. Different therapeutic approaches are under research to assess the role of combination therapies against escape signaling pathways or the development of novel antiandrogen drugs to try to solve the primary or acquired resistance against androgen dependent or independent pathways. The present review aims to summarize the current state of androgen inhibition in the therapeutic algorithm of patients with advanced prostate cancer and the mechanisms of resistance to those available drugs. In addition, this review conducted a comprehensive overview of the main present and future research approaches in the field of androgen receptor inhibition to overcome these resistances and the potential new drugs under research coming into this setting.

The DNA/RNA helicase DHX9 contributes to the transcriptional program of the androgen receptor in prostate cancer

Background

Prostate cancer (PC) is the most commonly diagnosed male malignancy and an important cause of mortality. Androgen deprivation therapy is the first line treatment but, unfortunately, a large part of patients evolves to a castration-resistant stage, for which no effective cure is currently available. The DNA/RNA helicase DHX9 is emerging as an important regulator of cellular processes that are often deregulated in cancer.

Methods

To investigate whether DHX9 modulates PC cell transcriptome we performed RNA-sequencing analyses upon DHX9 silencing in the androgen-responsive cell line LNCaP. Bioinformatics and functional analyses were carried out to elucidate the mechanism of gene expression regulation by DHX9. Data from The Cancer Genome Atlas were mined to evaluate the potential role of DHX9 in PC.

Results

We found that up-regulation of DHX9 correlates with advanced stage and is associated with poor prognosis of PC patients. High-throughput RNA-sequencing analysis revealed that depletion of DHX9 in androgen-sensitive LNCaP cells affects expression of hundreds of genes, which significantly overlap with known targets of the Androgen Receptor (AR). Notably, AR binds to the DHX9 promoter and induces its expression, while Enzalutamide-mediated inhibition of AR activity represses DHX9 expression. Moreover, DHX9 interacts with AR in LNCaP cells and its depletion significantly reduced the recruitment of AR to the promoter region of target genes and the ability of AR to promote their expression in response to 5α-dihydrotestosterone. Consistently, silencing of DXH9 negatively affected androgen-induced PC cell proliferation and migration.

Conclusions

Collectively, our data uncover a new role of DHX9 in the control of the AR transcriptional program and establish the existence of an oncogenic DHX9/AR axis, which may represent a new druggable target to counteract PC progression.

The Crucial Role of AR-V7 in Enzalutamide-Resistance of Castration-Resistant Prostate Cancer

Simple Summary

Androgen receptor splice variant 7 (AR-V7) has always been considered a key driver for triggering enzalutamide resistance of castration-resistant prostate cancer (CRPC). In recent years, both the homeostasis of AR-V7 protein and AR-V7’s relationship with LncRNAs have gained great attention with in-depth studies. Starting from protein stability and LncRNA, the paper discusses and summarizes the mechanisms and drugs that affect the CRPC patients’ sensitivity to enzalutamide by regulating the protein or transcriptional stability of AR-V7, hoping to provide therapeutic ideas for subsequent research to break through the CRPC therapeutic bottleneck.

Abstract

Prostate cancer (PCa) has the second highest incidence of malignancies occurring in men worldwide. The first-line therapy of PCa is androgen deprivation therapy (ADT). Nonetheless, most patients progress to castration-resistant prostate cancer (CRPC) after being treated by ADT. As a second-generation androgen receptor (AR) antagonist, enzalutamide (ENZ) is the current mainstay of new endocrine therapies for CRPC in clinical use. However, almost all patients develop resistance during AR antagonist therapy due to various mechanisms. At present, ENZ resistance (ENZR) has become challenging in the clinical treatment of CRPC. AR splice variant 7 (AR-V7) refers to a ligand-independent and constitutively active variant of the AR and is considered a key driver of ENZR in CRPC. In this review, we summarize the mechanisms and biological behaviors of AR-V7 in ENZR of CRPC to contribute novel insights for CRPC therapy.

DExH/D-box helicases at the frontline of intrinsic and innate immunity against viral infections

DExH/D-box helicases are essential nucleic acid and ribonucleoprotein remodelers involved in all aspects of nucleic acid metabolism including replication, gene expression and post-transcriptional modifications. In parallel to their importance in basic cellular functions, DExH/D-box helicases play multiple roles in viral life cycles, with some of them highjacked by viruses or negatively regulating innate immune activation. However, other DExH/D-box helicases have recurrently been highlighted as direct antiviral effectors or as positive regulators of innate immune activation. Innate immunity relies on the ability of Pathogen Recognition Receptors to recognize viral signatures and trigger the production of interferons (IFNs) and pro-inflammatory cytokines. Secreted IFNs interact with their receptors to establish antiviral cellular reprogramming via expression regulation of the interferon-stimulated genes (ISGs). Several DExH/D-box helicases have been reported to act as viral sensors (DDX3, DDX41, DHX9, DDX1/DDX21/DHX36 complex), and others to play roles in innate immune activation (DDX60, DDX60L, DDX23). In contrast, the DDX39A, DDX46, DDX5 and DDX24 helicases act as negative regulators and impede IFN production upon viral infection. Beyond their role in viral sensing, the ISGs DDX60 and DDX60L act as viral inhibitors. Interestingly, the constitutively expressed DEAD-box helicases DDX56, DDX17, DDX42 intrinsically restrict viral replication. Hence, DExH/D-box helicases appear to form a multilayer network of primary and secondary factors involved in both intrinsic and innate antiviral immunity. In this review, we highlight recent findings on the extent of antiviral defences played by helicases and emphasize the need to better understand their immune functions as well as their complex interplay.

DDX39B contributes to the proliferation of colorectal cancer through direct binding to CDK6/CCND1

DDX39B (also called UAP56 or BAT1) which is a kind of DEAD-box family helicase plays pivotal roles in mRNA binding, splicing, and export. It has been found upregulated in many kinds of tumors as an oncogene. Nevertheless, the underlying molecular mechanisms of DDX39B in the proliferation of human colorectal cancer (CRC) remain fairly elusive. In our study, function experiments including the CCK8 and colony formation assay revealed that DDX39B facilitates CRC proliferation in vitro. DDX39B knockdown cells were administered for the orthotopic CRC tumor xenograft mouse model, after which tumor growth was monitored and immunohistochemistry (IHC) was performed to prove that DDX39B can also facilitates CRC proliferation in vivo. Flow cytometry demonstrated that DDX39B promotes the proliferation of CRC cells by driving the cell cycle from G0/G1 phase to the S phase. Mechanistically, RNA-binding protein immunoprecipitation-sequencing (RIP-seq) confirmed that DDX39B binds directly to the first exon of the CDK6/CCND1 pre-mRNA and upregulates their expression. Splicing experiments in vitro using a RT-PCR and gel electrophoresis assay confirmed that DDX39B promotes CDK6/CCND1 pre-mRNA splicing. Rescue experiments indicated that CDK6/CCND1 is a downstream effector of DDX39B-mediated CRC cell proliferation. Collectively, our results demonstrated that DDX39B and CDK6/CCND1 direct interactions serve as a CRC proliferation promoter, which can accelerate the G1/S phase transition to enhance CRC proliferation, and can offer novel and emerging treatment strategies targeting this cell proliferation-promoting gene.

A Prediction Model Using Alternative Splicing Events and the Immune Microenvironment Signature in Lung Adenocarcinoma

Background

Alternative splicing (AS) is a gene regulatory mechanism that drives protein diversity. Dysregulation of AS is thought to play an essential role in cancer initiation and development. This study aimed to construct a prognostic signature based on AS and explore the role in the tumor immune microenvironment (TIME) in lung adenocarcinoma.

Methods

We analyzed transcriptome profiling and clinical lung adenocarcinoma data from The Cancer Genome Atlas (TCGA) database and lists of AS-related and immune-related signatures from the SpliceSeq. Prognosis-related AS events were analyzed by univariate Cox regression analysis. Gene set enrichment analyses (GSEA) were performed for functional annotation. Prognostic signatures were identified and validated using univariate and multivariate Cox regression, LASSO regression, Kaplan–Meier survival analyses, and proportional hazards model. The context of TIME in lung adenocarcinoma was also analyzed. Gene and protein expression data of Cyclin-Dependent Kinase Inhibitor 2A (CDKN2A) were obtained from ONCOMINE and Human Protein Atlas. Splicing factor (SF) regulatory networks were visualized.

Results

A total of 19,054 survival-related AS events in lung adenocarcinoma were screened in 1,323 genes. Exon skip (ES) and mutually exclusive exons (ME) exhibited the most and fewest AS events, respectively. Based on AS subtypes, eight AS prognostic signatures were constructed. Patients with high-risk scores were associated with poor overall survival. A nomogram with good validity in prognostic prediction was generated. AUCs of risk scores at 1, 2, and 3 years were 0.775, 0.736, and 0.759, respectively. Furthermore, the prognostic signatures were significantly correlated with TIME diversity and immune checkpoint inhibitor (ICI)-related genes. Low-risk patients had a higher StromalScore, ImmuneScore, and ESTIMATEScore. AS-based risk score signature was positively associated with CD8+ T cells. CDKN2A was also found to be a prognostic factor in lung adenocarcinoma. Finally, potential functions of SFs were determined by regulatory networks.

Conclusion

Taken together, our findings show a clear association between AS and immune cell infiltration events and patient outcome, which could provide a basis for the identification of novel markers and therapeutic targets for lung adenocarcinoma. SF networks provide information of regulatory mechanisms.

Genome-wide profiling of alternative splicing in glioblastoma and their clinical value

Background

Alternative splicing (AS), one of the main post-transcriptional biological regulation mechanisms, plays a key role in the progression of glioblastoma (GBM). Systematic AS profiling in GBM is limited and urgently needed.

Methods

TCGA SpliceSeq data and the corresponding clinical data were downloaded from the TCGA data portal. Survival-related AS events were identified through Kaplan–Meier survival analysis and univariate Cox analysis. Then, splicing correlation network was constructed based on these AS events and associated splicing factors. LASSO regression followed by multivariate Cox analysis was performed to validate independent AS biomarkers and to construct a risk prediction model. Enrichment analysis was subsequently conducted to explore potential signaling pathways of these AS events.

Results

A total of 132 TCGA GBM samples and 45,610 AS events were included in our study, among which 416 survival-related AS events were identified. An AS correlation network, including 54 AS events and 94 splicing factors, was constructed, and further functional enrichment was performed. Moreover, the novel risk prediction model we constructed displayed moderate performance (the area under the curves were > 0.7) at both one, two and three years.

Conclusions

Survival-related AS events may be vital factors of both biological function and prognosis. Our findings in this study can deepen the understanding of the complicated mechanisms of AS in GBM and provide novel insights for further study. Moreover, our risk prediction model is ready for preliminary clinical applications. Further verification is required.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08681-z.

DDX39B Predicts Poor Survival and Associated with Clinical Benefit of Anti-PD-L1 Therapy in ccRCC

BACKGROUND

Immune checkpoint inhibitors (ICI) have been shown to improve overall survival (OS) in clear cell renal cell carcinoma (ccRCC) patients. However, less than half of the ccRCC patients have objective response to ICI.

OBJECTIVE

We aim to assess the role of DDX39B in predicting ccRCC patients' OS and ICI therapy response.

METHODS

DDX39B was detected by immunohistochemistry in a tissue microarray of 305 ccRCC patients. DDX39B and its relationship with the prognosis of ccRCC were also evaluated in TCGA set and a RECA-EU set. The expression of DDX39B and patients survival was also analysed in two datasets of ccRCC patients treated with ICI.

RESULTS

Overexpression of DDX39B predicted poor OS of ccRCC patients in SYSU set, TCGA set, and a RECA-EU set. DDX39B expression was significantly positive with the expression of PD-L1 and other immunomodulators., DDX39B negatively correlated with cytotoxic T-lymphocyte and HDAC10 exon 3 inclusion in ccRCC. DDX39B knockdown decreased the expression of PD-L1 and increased the expression of HDAC10 exon 3 in renal cancer ACHN cells. Patients of ccRCC with lower levels of HDAC10 exon 3 inclusion have higher TNM stage, higher Fuhrman grade and poor OS. There was a tendency that patients with DDX39B high expression had longer OS and PFS than patients with DDX39B low expression in ccRCC patients treated with ICI.

CONCLUSION

DDX39B gene is highly expressed in ccRCC and is closely related to patients' OS. DDX39B might increase PD-L1 expression via the enhancement of HDAC10 exon 3 skipping, thereby promoting the ICI therapy response.

Integrated Analysis of the Roles of RNA Binding Proteins and Their Prognostic Value in Clear Cell Renal Cell Carcinoma

Methods

We downloaded the RNA sequencing data of ccRCC from the Cancer Genome Atlas (TCGA) database and identified differently expressed RBPs in different tissues. In this study, we used bioinformatics to analyze the expression and prognostic value of RBPs; then, we performed functional analysis and constructed a protein interaction network for them. We also screened out some RBPs related to the prognosis of ccRCC. Finally, based on the identified RBPs, we constructed a prognostic model that can predict patients' risk of illness and survival time. Also, the data in the HPA database were used for verification.

Results

In our experiment, we obtained 539 ccRCC samples and 72 normal controls. In the subsequent analysis, 87 upregulated RBPs and 38 downregulated RBPs were obtained. In addition, 9 genes related to the prognosis of patients were selected, namely, RPL36A, THOC6, RNASE2, NOVA2, TLR3, PPARGC1A, DARS, LARS2, and U2AF1L4. We further constructed a prognostic model based on these genes and plotted the ROC curve. This ROC curve performed well in judgement and evaluation. A nomogram that can judge the patient's life span is also made.

Conclusion

In conclusion, we have identified differentially expressed RBPs in ccRCC and carried out a series of in-depth research studies, the results of which may provide ideas for the diagnosis of ccRCC and the research of new targeted drugs.

The underlying molecular mechanisms and prognostic factors of RNA binding protein in colorectal cancer: a study based on multiple online databases

BACKGROUND

RNA binding protein (RBP) is an active factor involved in the occurrence and development of colorectal cancer (CRC). Therefore, the potential mechanism of RBP in CRC needs to be clarified by dry-lab analyses or wet-lab experiments.

METHODS

The differential RBP gene obtained from the GEPIA 2 (Gene Expression Profiling Interactive Analysis 2) were performed functional enrichment analysis. Then, the alternative splicing (AS) events related to survival were acquired by univariate regression analysis, and the correlation between RBP and AS was analyzed by R software. The online databases were conducted to analyze the mutation and methylation of RBPs in CRC. Moreover, 5 key RBP signatures were obtained through univariate and multivariate Cox regression analysis and established as RBP prognosis model. Subsequently, the above model was verified through another randomized group of TCGA CRC cohorts. Finally, multiple online databases and qRT-PCR analysis were carried to further confirm the expression of the above 5 RBP signatures in CRC.

RESULTS

Through a comprehensive bioinformatics analysis, it was revealed that RBPs had genetic and epigenetic changes in CRC. We obtained 300 differentially expressed RBPs in CRC samples. The functional analysis suggested that they mainly participated in spliceosome. Then, a regulatory network for RBP was established to participate in AS and DDX39B was detected to act as a potentially essential factor in the regulation of AS in CRC. Our analysis discovered that 11 differentially expressed RBPs with a mutation frequency higher than 5%. Furthermore, we found that 10 differentially expressed RBPs had methylation sites related to the prognosis of CRC, and a prognostic model was constructed by the 5 RBP signatures. In another randomized group of TCGA CRC cohorts, the prognostic performance of the 5 RBP signatures was verified.

CONCLUSION

The potential mechanisms that regulate the aberrant expression of RBPs in the development of CRC was explored, a network that regulated AS was established, and the RBP-related prognosis model was constructed and verified, which could improve the individualized prognosis prediction of CRC.

The Mammalian Ecdysoneless Protein Interacts with RNA Helicase DDX39A To Regulate Nuclear mRNA Export

The mammalian orthologue of ecdysoneless (ECD) protein is required for embryogenesis, cell cycle progression, and mitigation of endoplasmic reticulum stress. Here, we identified key components of the mRNA export complexes as binding partners of ECD and characterized the functional interaction of ECD with key mRNA export-related DEAD BOX protein helicase DDX39A. We find that ECD is involved in RNA export through its interaction with DDX39A. ECD knockdown (KD) blocks mRNA export from the nucleus to the cytoplasm, which is rescued by expression of full-length ECD but not an ECD mutant that is defective in interaction with DDX39A. We have previously shown that ECD protein is overexpressed in ErbB2⁺ breast cancers (BC). In this study, we extended the analyses to two publicly available BC mRNA The Cancer Genome Atlas (TCGA) and Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) data sets. In both data sets, ECD mRNA overexpression correlated with short patient survival, specifically ErbB2⁺ BC. In the METABRIC data set, ECD overexpression also correlated with poor patient survival in triple-negative breast cancer (TNBC). Furthermore, ECD KD in ErbB2⁺ BC cells led to a decrease in ErbB2 mRNA level due to a block in its nuclear export and was associated with impairment of oncogenic traits. These findings provide novel mechanistic insight into the physiological and pathological functions of ECD.

Biology of the mRNA Splicing Machinery and Its Dysregulation in Cancer Providing Therapeutic Opportunities

Dysregulation of messenger RNA (mRNA) processing—in particular mRNA splicing—is a hallmark of cancer. Compared to normal cells, cancer cells frequently present aberrant mRNA splicing, which promotes cancer progression and treatment resistance. This hallmark provides opportunities for developing new targeted cancer treatments. Splicing of precursor mRNA into mature mRNA is executed by a dynamic complex of proteins and small RNAs called the spliceosome. Spliceosomes are part of the supraspliceosome, a macromolecular structure where all co-transcriptional mRNA processing activities in the cell nucleus are coordinated. Here we review the biology of the mRNA splicing machinery in the context of other mRNA processing activities in the supraspliceosome and present current knowledge of its dysregulation in lung cancer. In addition, we review investigations to discover therapeutic targets in the spliceosome and give an overview of inhibitors and modulators of the mRNA splicing process identified so far. Together, this provides insight into the value of targeting the spliceosome as a possible new treatment for lung cancer.

A functional LSD1 coregulator screen reveals a novel transcriptional regulatory cascade connecting R-loop homeostasis with epigenetic regulation

The lysine specific demethylase 1 (LSD1) plays a pivotal role in cellular differentiation by regulating the expression of key developmental genes in concert with different coregulatory proteins. This process is impaired in different cancer types and incompletely understood. To comprehensively identify functional coregulators of LSD1, we established a novel tractable fluorescent reporter system to monitor LSD1 activity in living cells. Combining this reporter system with a state-of-the-art multiplexed RNAi screen, we identify the DEAD-box helicase 19A (DDX19A) as a novel coregulator and demonstrate that suppression of Ddx19a results in an increase of R-loops and reduced LSD1-mediated gene silencing. We further show that DDX19A binds to tri-methylated lysine 27 of histone 3 (H3K27me3) and it regulates gene expression through the removal of transcription promoting R-loops. Our results uncover a novel transcriptional regulatory cascade where the downregulation of genes is dependent on the LSD1 mediated demethylation of histone H3 lysine 4 (H3K4). This allows the polycomb repressive complex 2 (PRC2) to methylate H3K27, which serves as a binding site for DDX19A. Finally, the binding of DDX19A leads to the efficient removal of R-loops at active promoters, which further de-represses LSD1 and PRC2, establishing a positive feedback loop leading to a robust repression of the target gene.

U2AF2 binds IL7R exon 6 ectopically and represses its inclusion

Interleukin 7 receptor α-chain is crucial for the development and maintenance of T cells and is genetically associated with autoimmune disorders including multiple sclerosis (MS), a demyelinating disease of the CNS. Exon 6 of IL7R encodes for the transmembrane domain of the receptor and is regulated by alternative splicing: inclusion or skipping of IL7R exon 6 results in membrane-bound or soluble IL7R isoforms, respectively. We previously identified a SNP (rs6897932) in IL7R exon 6, strongly associated with MS risk and showed that the risk allele (C) increases skipping of the exon, resulting in elevated levels of sIL7R. This has important pathological consequences as elevated levels of sIL7R has been shown to exacerbate the disease in the experimental autoimmune encephalomyelitis mouse model of MS. Understanding the regulation of exon 6 splicing provides important mechanistic insights into the pathogenesis of MS. Here we report two mechanisms by which IL7R exon 6 is controlled. First, a competition between PTBP1 and U2AF2 at the polypyrimidine tract (PPT) of intron 5, and second, an unexpected U2AF2-mediated assembly of spicing factors in the exon. We noted the presence of a branchpoint sequence (BPS) (TACTAAT or TACTAAC) within exon 6, which is stronger with the C allele. We also noted that the BPS is followed by a PPT and conjectured that silencing could be mediated by the binding of U2AF2 to that tract. In support of this model, we show that evolutionary conservation of the exonic PPT correlates well with the degree of alternative splicing of exon 6 in two non-human primate species and that U2AF2 binding to this PPT recruits U2 snRNP components to the exon. These observations provide the first explanation for the stronger silencing of IL7R exon 6 with the disease associated C allele at rs6897932.

Identification of RNA-binding protein SNRPA1 for prognosis in prostate cancer

Prostate cancer is one of the deadliest cancers in men. RNA-binding proteins play a critical role in human cancers; however, whether they have a significant effect on the prognosis of prostate cancer has yet to be elucidated. In the present study, we performed a comprehensive analysis of RNA sequencing and clinical data from the Cancer Genome Atlas dataset and obtained differentially expressed RNA-binding proteins between prostate cancer and benign tissues. We constructed a protein-protein interaction network and Cox regression analyses were conducted to identify prognostic hub RNA-binding proteins. SNRPA1 was associated with the highest risk of poor prognosis and was therefore selected for further analysis. SNRPA1 expression was positively correlated with Gleason score and pathological TNM stage in prostate cancer patients. Furthermore, the expression profile of SNRPA1 was validated using the Oncomine, Human Protein Atlas, and Cancer Cell Line Encyclopedia databases. Meanwhile, the prognostic profile of SNRPA1 was successfully verified in GSE70769. Additionally, the results of molecular experiments revealed the proliferative role of SNRPA1 in prostate cancer cells. In summary, our findings evidenced a relationship between RNA-binding proteins and prostate cancer and indicated the prognostic significance of SNRPA1 in prostate cancer.

MHC Class III RNA Binding Proteins and Immunity

Here we review data suggestive of a role for RNA-binding proteins in vertebrate immunity. We focus on the products of genes found in the class III region of the Major Histocompatibility Complex. Six of these genes, DDX39B (aka BAT1), DXO, LSM2, NELFE, PRRC2A (aka BAT2), and SKIV2L, encode RNA-binding proteins with clear roles in post-transcriptional gene regulation and RNA surveillance. These genes are likely to have important functions in immunity and are associated with autoimmune diseases.

Molecular Origin, Expression Regulation, and Biological Function of Androgen Receptor Splicing Variant 7 in Prostate Cancer

The problem of resistance to therapy in prostate cancer (PCa) is multifaceted. Key determinants of drug resistance include tumor burden and growth kinetics, tumor heterogeneity, physical barriers, immune system and microenvironment, undruggable cancer drivers, and consequences of therapeutic pressures. With regard to the fundamental importance of the androgen receptor (AR) in all stages of PCa from tumorigenesis to progression, AR is postulated to have a continued critical role in castration-resistant prostate cancer (CRPC). Suppression of AR signaling mediated by the full-length AR (AR-FL) is the therapeutic goal of all AR-directed therapies. However, AR-targeting agents ultimately lead to AR aberrations that promote PCa progression and drug resistance. Among these AR aberrations, androgen receptor variant 7 (AR-V7) is gaining attention as a potential predictive marker for as well as one of the resistance mechanisms to the most current anti-AR therapies in CRPC. Meanwhile, development of next-generation drugs that directly or indirectly target AR-V7 signaling is urgently needed. In the present review of the current literature, we have summarized the origin, alternative splicing, expression induction, protein conformation, interaction with coregulators, relationship with AR-FL, transcriptional activity, and biological function of AR-V7 in PCa development and therapeutic resistance. We hope this review will help further understand the molecular origin, expression regulation, and role of AR-V7 in the progression of PCa and provide insight into the design of novel selective inhibitors of AR-V7 in PCa treatment.

DDX39 Overexpression Predicts a Poor Prognosis and Promotes Aggressiveness of Melanoma by Cooperating With SNAIL

This study aimed to investigate the prognostic value and molecular mechanism of DDX39 and its effector SNAIL in melanoma. First, overexpression of DDX39 in melanoma, which was identified by database analysis, was further validated in patient tissues. Cell growth, cell cycle, cell migration, and cell invasion assays were then performed to evaluate the effects of downregulated DDX39 on the melanoma cell proliferation and aggressiveness. The same approaches were also used to reveal the cooperation of the transcription factor SNAIL with DDX39 to promote the aggressiveness of melanoma cells. We found that the expression of DDX39 was significantly upregulated in melanoma tissue compared to pigmented nevus tissue, and it was positively correlated with the clinical stage defined by the American Joint Committee on Cancer (AJCC) and the prognosis. Downregulation of DDX39 in melanoma cells was found to significantly inhibit cell proliferation, increase G2/M cell cycle arrest, enhance caspase-mediated cell apoptosis, and suppress cell invasion and migration. In addition, we demonstrated that the overexpression of SNAIL could restore the cell growth and aggressiveness impaired by DDX39 RNA interference. Immunohistochemical staining also showed a positive correlation between DDX39 overexpression and SNAIL overexpression in melanoma tissues, suggesting that SNAIL is one of the effectors activated by DDX39. In summary, the overexpression of DDX39 and SNAIL was positively related to the poor prognosis of melanoma patients and the increased aggressiveness of melanoma cells. Our study provides valuable evidence regarding the prognostic value of DDX39 and SNAIL as well as their potential as novel therapeutic targets for treating melanoma patients.

Intrinsic Regulatory Role of RNA Structural Arrangement in Alternative Splicing Control

Alternative splicing is a highly sophisticated process, playing a significant role in posttranscriptional gene expression and underlying the diversity and complexity of organisms. Its regulation is multilayered, including an intrinsic role of RNA structural arrangement which undergoes time- and tissue-specific alterations. In this review, we describe the principles of RNA structural arrangement and briefly decipher its cis- and trans-acting cellular modulators which serve as crucial determinants of biological functionality of the RNA structure. Subsequently, we engage in a discussion about the RNA structure-mediated mechanisms of alternative splicing regulation. On one hand, the impairment of formation of optimal RNA structures may have critical consequences for the splicing outcome and further contribute to understanding the pathomechanism of severe disorders. On the other hand, the structural aspects of RNA became significant features taken into consideration in the endeavor of finding potential therapeutic treatments. Both aspects have been addressed by us emphasizing the importance of ongoing studies in both fields.

Prognostic role of alternative splicing events in head and neck squamous cell carcinoma

Background

Aberrant alternative splicing (AS) is implicated in biological processes of cancer. This study aims to reveal prognostic AS events and signatures that may serve as prognostic predictors for head and neck squamous cell carcinoma (HNSCC).

Methods

Prognostic AS events in HNSCC were identified by univariate COX analysis. Prognostic signatures comprising prognostic AS events were constructed for prognosis prediction in patients with HNSCC. The correlation between the percent spliced in (PSI) values of AS events and the expression of splicing factors (SFs) was analyzed by Pearson correlation analysis. Gene functional annotation analysis was performed to reveal pathways in which prognostic AS is enriched.

Results

A total of 27,611 AS events in 15,873 genes were observed, and there were 3433 AS events in 2624 genes significantly associated with overall survival (OS) for HNSCC. Moreover, we found that AS prognostic signatures could accurately predict HNSCC prognosis. SF-AS regulatory networks were constructed according to the correlation between PSI values of AS events and the expression levels of SFs.

Conclusions

Our study identified prognostic AS events and signatures. Furthermore, it established SF-AS networks in HNSCC that were valuable in predicting the prognosis of patients with HNSCC and elucidating the regulatory mechanisms underlying AS in HNSCC.

Identification and validation of an alternative splicing-based prognostic signature for head and neck squamous cell carcinoma

Increasing evidence has demonstrated that changes in alternative splicing (AS) events are closely associated with the initiation and progression of cancer. However, the concrete role of AS in tumorigenesis of head and neck squamous cell carcinoma (HNSCC) is poorly known. In this study, we aimed to investigate the AS profile in HNSCC, and build up a robust AS-based prognostic signature for HNSCC. Our results revealed a total of 4068 overall survival (OS) associated AS events in the TCGA HNSCC cohort. The whole TCGA HNSCC cohort was randomly divided into discovery cohort and validation cohort. A prognostic signature including five AS events was developed with the discovery cohort based on the most significant OS-associated AS events. Then it was further successfully validated in the validation cohort. The AS-based risk signature was an independent prognostic indicator in both discovery cohort and validation cohort. This prognostic signature-based nomogram model showed excellent performance for predicting the OS of HNSCC. Splicing network analysis have identified the most correlated splicing factor-AS network in HNSCC. Collectively, we have constructed a robust AS-based prognostic signature which might contribute to improve the clinical outcome of HNSCC.

Androgen receptor variant-driven prostate cancer II: advances in laboratory investigations

Background:

The androgen receptor (AR) is a key prostate cancer drug target. Suppression of AR signaling mediated by the full-length AR (AR-FL) is the therapeutic goal of all existing AR-directed therapies. AR-targeting agents impart therapeutic benefit, but lead to AR aberrations that underlie disease progression and therapeutic resistance. Among the AR aberrations specific to castration-resistant prostate cancer (CRPC), AR variants (AR-Vs) have emerged as important indicators of disease progression and therapeutic resistance.

Methods:

We conducted a systemic review of the literature focusing on recent laboratory studies on AR-Vs following our last review article published in 2016. Topics ranged from measurement and detection, molecular origin, regulation, genomic function, and preclinical therapeutic targeting of AR-Vs. We provide expert opinions and perspectives on these topics.

Results:

Transcript sequences for 22 AR-Vs have been reported in the literature. Different AR-Vs may arise through different mechanisms, and can be regulated by splicing factors and dictated by genomic rearrangements, but a low-androgen environment is a prerequisite for generation of AR-Vs. The unique transcript structures allowed development of in-situ and in-solution measurement and detection methods, including mRNA and protein detection, in both tissue and blood specimens. AR variant-7 (AR-V7) remains the main measurement target and the most extensively characterized AR-V. Although AR-V7 co-exists with AR-FL, genomic functions mediated by AR-V7 do not require the presence of AR-FL. The distinct cistromes and transcriptional programs directed by AR-V7 and their co-regulators are consistent with genomic features of progressive disease in a low-androgen environment. Preclinical development of AR-V-directed agents currently focuses on suppression of mRNA expression and protein degradation as well as targeting of the amino-terminal domain.

Conclusions:

Current literature continues to support AR-Vs as biomarkers and therapeutic targets in prostate cancer. Laboratory investigations reveal both challenges and opportunities in targeting AR-Vs to overcome resistance to current AR-directed therapies.

Risk score based on expression of five novel genes predicts survival in soft tissue sarcoma

In this study, The Cancer Genome Atlas and Genotype-Tissue Expression databases were used to identify potential biomarkers of soft tissue sarcoma (STS) and construct a prognostic model. The model was used to calculate risk scores based on the expression of five key genes, among which MYBL2 and FBN2 were upregulated and TSPAN7, GCSH, and DDX39B were downregulated in STS patients. We also examined gene signatures associated with the key genes and evaluated the model’s clinical utility. The key genes were found to be involved in the cell cycle, DNA replication, and various cancer pathways, and gene alterations were associated with a poor prognosis. According to the prognostic model, risk scores negatively correlated with infiltration of six types of immune cells. Furthermore, age, margin status, presence of metastasis, and risk score were independent prognostic factors for STS patients. A nomogram that incorporated the risk score and other independent prognostic factors accurately predicted survival in STS patients. These findings may help to improve prognostic prediction and aid in the identification of effective treatments for STS patients.

Regulation of androgen receptor variants in prostate cancer

Aberrant activation of androgen receptor (AR) signaling occurs in patients treated with AR-targeted therapies, contributing to the development of castration-resistant prostate cancer (CRPC) and therapeutic resistance. Over the past decade, many AR variants (AR-Vs) have been identified in prostate cancer cell lines and clinical CRPC specimens. These AR-Vs lack the COOH-terminal ligand-binding domain (LBD), and may mediate constitutively active AR signaling acquired following AR-targeting therapies. AR splice variant-7 (AR-V7), one of the most well characterized AR-Vs, can be reliably measured in tissue and liquid biopsy specimens, and blood-based detection of AR-V7 is a reliable indicator of poor outcome to relatively novel hormonal therapies (NHT) such as abiraterone and enzalutamide in men with metastatic CRPC (mCRPC). Given the important clinical implication of AR-Vs, this short review will focus on studies addressing how AR-Vs are regulated in prostate cancer. With regard to the molecular origin of AR-Vs, it is established that expression of AR-Vs is highly correlated with androgen deprivation and suppression of AR signaling. Therapeutic targeting of the AR axis may result in active transcription of the AR gene, elevated activities of certain components of the mRNA splicing machinery, as well as AR genomic alterations, all of which may explain the molecular origin of AR-Vs. Although a unified hypothesis is currently lacking, existing data suggest that elevated expression of AR-Vs, which in general occurs quite specifically in a cellular environment where the canonical AR signaling is suppressed, is driven by both genomic and epigenomic features acquired in the development of CRPC.

Comparative Analysis of Putative Prognostic and Predictive Markers in Neuroblastomas: High Expression of PBX1 Is Associated With a Poor Response to Induction Therapy

The survival rate for patients with high-risk neuroblastomas remains poor despite new improvements in available therapeutic modalities. A detailed understanding of the mechanisms underlying clinical responses to multimodal treatment is one of the important aspects that may provide precision in the prediction of a patient's clinical outcome. Our study was designed as a detailed comparative analysis of five selected proteins (DDX39A, HMGA1, HOXC9, NF1, and PBX1) in one cohort of patients using the same methodical approaches. These proteins were already reported separately as related to the resistance or sensitivity to retinoids and as useful prognostic markers of survival probability. In the cohort of 19 patients suffering from high-risk neuroblastomas, we analyzed initial immunohistochemistry samples obtained by diagnostic biopsy and post-induction samples taken after the end of induction therapy. The expression of DDX39A, HMGA1, HOXC9, and NF1 showed varied patterns with almost no differences between responders and non-responders. Nevertheless, we found very interesting results for PBX1: non-responders had significantly higher expression levels of this protein in the initial tumor samples when compared with responders; this expression pattern changed inversely in the post-induction samples, and this change was also statistically significant. Moreover, our results from survival analyses reveal the prognostic value of PBX1, NF1, and HOXC9 expression in neuroblastoma tissue. In addition to the prognostic importance of PBX1, NF1, and HOXC9 proteins, our results demonstrated that PBX1 could be used for the prediction of the clinical response to induction chemotherapy in patients suffering from high-risk neuroblastoma.

TCF3 mutually exclusive alternative splicing is controlled by long-range cooperative actions between hnRNPH1 and PTBP1

TCF3, also known as E2A, is a well-studied transcription factor that plays an important role in stem cell maintenance and hematopoietic development. The TCF3 gene encodes two related proteins, E12 and E47, which arise from mutually exclusive alternative splicing (MEAS). Since these two proteins have different DNA binding and dimerization domains, this AS event must be strictly regulated to ensure proper isoform ratios. Previously, we found that heterogeneous nuclear ribonucleoprotein (hnRNP) H1/F regulates TCF3 AS by binding to exonic splicing silencers (ESSs) in exon 18b. Here, we identify conserved intronic splicing silencers (ISSs) located between, and far from, the two mutually exclusive exons, and show that they are essential for MEAS. Further, we demonstrate that the hnRNP PTBP1 binds the ISS and is a regulator of TCF3 AS. We also demonstrate that hnRNP H1 and PTBP1 regulate TCF3 AS reciprocally, and that position-dependent interactions between these factors are essential for proper TCF3 MEAS. Our study provides a new model in which MEAS is regulated by cooperative actions of distinct hnRNPs bound to ISSs and ESSs.

Identification of Prognostic and Metastatic Alternative Splicing Signatures in Kidney Renal Clear Cell Carcinoma

Background: Kidney renal clear cell carcinoma (KIRC) is the malignancy originated from the renal epithelium, with a high rate of distant metastasis. Aberrant alternative splicing (AS) of pre-mRNA are widely reported to be involved in the tumorigenesis and metastasis of multiple cancers. The aim of this study is to explore the mechanism of alternative splicing events (ASEs) underlying tumorigenesis and metastasis of KIRC. Methods: RNA-seq of 537 KIRC samples downloaded from the TCGA database and ASEs data from the TCGASpliceSeq database were used to identify ASEs in patients with KIRC. The univariate and Lasso regression analysis were used to screen the most significant overall survival-related ASEs (OS-SEs). Based on those, the OS-SEs model was proposed. The interaction network of OS-SEs and splicing factors (SFs) with absolute value of correlation coefficient value >0.750 was constructed by Pearson correlation analysis. The OS-SEs significantly related to distant metastasis and clinical stage were identified by non-parametric test, and those were also integrated into co-expression analysis with prognosis-related Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways identified by Gene Set Variation Analysis (GSVA). ASEs with significance were selected for multiple online database validation. Results: A total of prognostic 6,081 overall survival-related ASEs (OS-SEs) were identified by univariate Cox regression analysis and a prediction model was constructed based on 5 OS-SEs screened by Lasso regression with the Area Under Curve of 0.788. Its risk score was also illustrated to be an independent predictor, which the good reliability of the model. Among 390 identified candidate SFs, DExD-Box Helicase 39B (DDX39B) was significantly correlated with OS and metastasis. After external database validation, Retained Intron of Ras Homolog Family Member T2 (RHOT2) and T-Cell Immune Regulator 1 (TCIRG1) were identified. In the co-expression analysis, overlapped co-expression signal pathways for RHOT2 and TCIRG1 were sphingolipid metabolism and N-glycan biosynthesis. Conclusions: Based on the results of comprehensive bioinformatic analysis, we proposed that aberrant DDX39B regulated RHOT2-32938-RI and TCIRG1-17288-RI might be associated with the tumorigenesis, metastasis, and poor prognosis of KIRC via sphingolipid metabolism or N-glycan biosynthesis pathway.

Cigarette smoking augments androgen receptor activity and promotes resistance to antiandrogen therapy

BACKGROUND

Cigarette smoking is associated with worse outcomes in prostate cancer, whose growth is dependent on androgen receptor (AR) signaling. We aimed to elucidate the biological effect of cigarette smoking on AR signaling and its clinical influence on oncological outcome.

METHODS

Gene expression levels after exposure to tobacco smoke condensate (TSC) were evaluated by quantitative real-time polymerase chain reaction and Western blot analysis in prostate cancer cells. Cellular sensitivities to enzalutamide and docetaxel after TSC exposure were evaluated using a prostate cancer cell proliferation assay. Prognosis was compared between current smokers and nonsmokers when treated with AR-axis-targeting (ARAT) agent enzalutamide and docetaxel.

RESULTS

Expression of AR variants as well as prostate-specific antigen was augmented after TSC exposure, which occurred after Akt phosphorylation. These inductions were suppressed by Akt inhibitor LY294002 as well as antioxidant N-acetylcysteine. Consistently, TSC exposure augmented cellular resistance to enzalutamide. In clinical data, cigarette smoking was associated with worse progression-free survival and cancer-specific survival when patients with prostate cancer were treated with ARAT agents but not docetaxel.

CONCLUSIONS

It was suggested that cigarette smoking leads to detrimental oncological outcome when prostate cancer patients are treated with ARAT agents through induction of aberrant AR signaling. Accordingly, we recommend that patients with advanced prostate cancer should refrain from cigarette smoking.

Splicing Factors Have an Essential Role in Prostate Cancer Progression and Androgen Receptor Signaling

Although inhibition of the androgen–androgen receptor (AR) axis effectively represses the growth of prostate cancer, most of all cases eventually become castration-resistant prostate cancers (CRPCs). Enhancement of the expression of AR and its variants along with the downstream signals is important for disease progression. AR-V7, a constitutive active form of AR, is generated as a result of RNA splicing. RNA splicing creates multiple transcript variants from one pre-messenger RNA (mRNA) by removing introns/exons to allow mRNA translation. The molecular mechanisms leading to marked increases of AR and generation of AR-V7 have been unclear. However, recent papers highlighted the roles of RNA splicing factors which promote AR expression and production of variants. Notably, a broad range of splicing components were aberrantly regulated in CRPC tissues. Interestingly, expression of various spliceosome genes is enhanced by RNA-binding protein splicing factor proline- and glutamine-rich (PSF/SFPQ), leading to changes in the expression of AR transcript variants. Moreover, inhibition of several splicing factors repressed tumor growth in vivo. Altered expression of splicing factors is correlated to biochemical recurrence in prostate cancer patients. Thus, these findings suggest that splicing factors would be a potential therapeutic target. This review focuses on the emerging roles of splicing factors in prostate cancer progression and AR signaling.

The potential of AR-V7 as a therapeutic target

INTRODUCTION

The androgen receptor variant AR-V7 is gaining attention as a potential predictive marker for as well as one of the resistance mechanisms to the most current anti-androgen receptor (AR) therapies in castration-resistant prostate cancer (CRPC). Accordingly, development of next-generation drugs that directly or indirectly target AR-V7 signaling is urgently needed. Areas covered: We review proposed mechanisms of drug resistance in relation to AR-V7 status, the mechanisms of generation of AR-V7, and its transcriptome, cistrome, and interactome. Pharmacological agents that interfere with these processes are being developed to counteract pan AR and AR-V7-specific signaling. Also, we address the current status of the preclinical and clinical studies targeting AR-V7 signaling. Expert opinion: AR-V7 is considered a true therapeutic target, however, it remains to be determined if AR-V7 is a principal driver or merely a bystander requiring heterodimerization with co-expressed full-length AR or other variants to drive CRPC progression. While untangling AR-V7 biology, multiple strategies are being developed to counteract drug resistance, including selective blockade of AR-V7 signaling as well as inhibition of pan-AR signaling. Ideally anti-AR therapies will be combined with agents preventing activation and enrichment of AR negative tumor cells that are otherwise depressed by AR activity axis.

Long non-coding RNA GAS5 and ZFAS1 are prognostic markers involved in translation targeted by miR-940 in prostate cancer

Identification of prognostic biomarkers helps facilitate the prediction of patient outcomes as well as guide treatments. Accumulating evidence now suggests that long non-coding RNAs (lncRNAs) play key roles in tumor progression with diagnostic and prognostic values. However, little is known about the biological functions of lncRNAs and how they contribute to the pathogenesis of cancer. Herein, we performed weighted correlation network analysis (WGCNA) on 380 RNA-seq samples from prostate cancer patients to create networks comprising of microRNAs, lncRNAs, and protein-coding genes. Our analysis revealed expression modules that associated with pathological parameters. More importantly, we identified a gene module that is involved in protein translation and is associated with patient survival. In this gene module, we explored the regulation axis involving GAS5, ZFAS1, and miR-940. We show that GAS5, ZFAS1, and miR-940 are up-regulated in tumors relative to normal prostate tissues, and high expression of either lncRNA is an indicator of poor patient outcome. Finally, we constructed a co-expression network involving GAS5, ZFAS1, and miR-940, as well as the targets of miR-940. Our results show that GAS5 and ZFAS1 are targeted by miR-940 via NAA10 and RPL28. Taken together, co-expression analysis of gene expression profiling from RNA-seq can accelerate the identification and functional characterization of novel prognostic markers in prostate cancer.

[Androgen receptor variants in prostate cancer]

Prostate cancer is a public health concern as it currently represents the most frequent malignancy in men in Europe. Progression of this hormone-dependent cancer is driven by androgens. Thus, the most common treatment for patients with advanced prostate cancer consists in an androgen ablation by castration therapy. However, the majority of patients relapses and develops a castration-resistant prostate cancer. This failure of androgen deprivation is related to the emergence of mutant and splice variants of the androgen receptor. Indeed, androgen receptor variants are ligand-independent, constitutively active and thus able to induce resistance to castration. This review focuses on AR variants signaling pathways and their role in resistance to castration and prostate cancer progression.