Spliceosome component SF3B1 as novel prognostic biomarker and therapeutic target for prostate cancer

Drosophila as a Promising In Vivo Research Model for the Application and Development of Targeted Protein Inactivation Technologies

Technologies for controlled protein targeting allow the selective manipulations of proteins resulting in their degradation and/or loss of function. Over the past two decades, these technologies have overcome the limitations of genetic methods and have become powerful tools in biological research and the search for new therapeutic approaches to disease treatment. Various methods of protein degradation and inactivation have been successfully applied to a model organism such as Drosophila melanogaster. In this article, we overview the capabilities and prospects of the Drosophila in vivo model for testing and developing modern methods of controlled protein targeting, analyzing their efficacy at the organism level and solving fundamental biological problems.

Targeting RNA splicing modulation: new perspectives for anticancer strategy?

The excision of introns from pre-mRNA is a crucial process in the expression of the majority of genes. Alternative splicing allows a single gene to generate diverse mRNA and protein products. Aberrant RNA splicing is recognized as a molecular characteristic present in almost all types of tumors. Therefore, identifying cancer-specific subtypes from aberrant processing offers new opportunities for therapeutic development. Numerous splicing modulators, each utilizing different mechanisms, have been developed as promising anticancer therapies, some of which are in clinical trials. In this review, we summarize the splice-altered signatures of cancer cell transcriptomes and the contributions of splicing aberrations to tumorigenesis and progression. Especially, we discuss current and emerging RNA splicing-targeted strategies for cancer therapy, including pharmacological approaches and splice-switching antisense oligonucleotides (ASOs). Finally, we address the challenges and opportunities in translating these findings into clinical practice.

The splicing machinery is dysregulated and represents a therapeutic vulnerability in breast cancer

Breast cancer (BCa) is a highly prevalent pathological condition (̴30% in women) with limited and subtype-dependent prognosis and therapeutic options. Therefore, BCa management might benefit from the identification of novel molecular elements with clinical potential. Since splicing process is gaining a great relevance in cancer, this work analysed the expression of multiple Spliceosome Components (SCs = 17) and Splicing Factors (SFs = 26) and found a drastic dysregulation in BCa (n = 69) vs. control (negative biopsies; n = 50) samples. Among all the components analysed, we highlight the upregulation of ESRP1 and down-regulation of PRPF8 and NOVA1 in BCa vs. control samples. Indeed, ESRP1 was specially overexpressed in triple-negative BCa (TNBCa) and associated with worse prognosis (i.e., higher BCa grade and lower overall survival), suggesting an association of ESRP1 with BCa aggressiveness. On the other hand, PRPF8 expression was generally downregulated in BCa with no associations to clinical characteristics, while NOVA1 expression was lower in TNBCa patients and highly aggressive tumours. Consistently, NOVA1 overexpression in vitro reduced functional parameters of aggressiveness in ER-/PR- cell lines (MDA-MB-231 and BT-549) but not in ER+/PR+ cells (MCF7), suggesting a critical role of NOVA1 in subtype-specific BCa. Finally, the in vitro pharmacological inhibition of splicing machinery using pladienolide B decreased aggressiveness features in all the BCa cell lines, showing a subtype-independent inhibitory potential, but being relatively innocuous in normal-like breast cells. These results demonstrate the profound dysregulation of the splicing machinery in BCa and their potential as source of promising diagnosis/prognosis markers, as well as valuable therapeutic targets for BCa.

Clinical value of circulating splicing factors in prostate cancer: SRRM1 as a novel predictive biomarker and therapeutic target

Prostate cancer (PCa) is the second most common cancer among men worldwide. The main screening tool remains the prostate-specific antigen (PSA), which shows significant limitations, including poor sensitivity/specificity. Therefore, establishing accurate non-invasive diagnostic biomarkers remains an unmet clinical need in PCa. In this context, the splicing process dysregulation represents a PCa hallmark. Here, plasma SRRM1, SNRNP200, and SRSF3 levels, previously identified to play a pathophysiological role in PCa, were determined in control individuals (n = 40) and PCa patients (n = 166). We found that plasma SRRM1 and SNRNP200 levels were elevated in PCa patients and discriminated between control individuals and PCa patients. High plasma SRRM1 levels were associated with a shorter castration-resistant PCa-free survival and correlated with androgen-receptor (AR)/AR-splicing variant 7 (AR-V7) expression levels and activity in PCa tissues. Therefore, the functional and molecular effects of in vivo SRRM1 silencing were then tested in 22Rv1-derived xenograft tumors. In vivo SRRM1 silencing reduced aggressiveness features and altered AR/AR-V7 activity. Our data reveal that SRRM1 holds potential as a non-invasive diagnostic and prognostic biomarker and novel therapeutic target in PCa, offering a clinically relevant opportunity worth exploring in humans.

SRSF6 modulates histone-chaperone HIRA splicing to orchestrate AR and E2F activity in prostate cancer

Despite novel therapeutic strategies, advanced-stage prostate cancer (PCa) remains highly lethal, pointing out the urgent need for effective therapeutic strategies. While dysregulation of the splicing process is considered a cancer hallmark, the role of certain splicing factors remains unknown in PCa. This study focuses on characterizing the levels and role of SRSF6 in this disease. Comprehensive analyses of SRSF6 alterations (copy number/mRNA/protein) were conducted across eight well-characterized PCa cohorts and the Hi-MYC transgenic model. SRSF6 was up-regulated in PCa samples, correlating with adverse clinical parameters. Functional assays, both in vitro (cell proliferation, migration, colony, and tumorsphere formation) and in vivo (xenograft tumors), demonstrated the impact of SRSF6 modulation on critical cancer hallmarks. Mechanistically, SRSF6 regulates the splicing pattern of the histone-chaperone HIRA, consequently affecting the activity of H3.3 in PCa and breast cancer cell models and disrupting pivotal oncogenic pathways (AR and E2F) in PCa cells. These findings underscore SRSF6 as a promising therapeutic target for PCa/advanced-stage PCa.

The splicing factor SF3B1 confers ferroptosis resistance and promotes lung adenocarcinoma progression via upregulation of SLC7A11

This study aimed to investigate the expression of SF3B1 in non-small cell lung cancer, and its clinical significance, biological function, and molecular mechanisms. SF3B1 mRNA and protein levels were elevated in both lung squamous cell carcinoma and lung adenocarcinoma (LUAD) tissues based on TCGA data and immunohistochemistry. Notably, high SF3B1 expression in LUAD was significantly associated with increased lymph node metastasis. Functional experiments involving SF3B1 knockdown and overexpression demonstrated that SF3B1 facilitated the proliferation, invasion, and migration of LUAD cells. Additionally, the SF3B1 inhibitor pladienolide-B attenuated the aggressive behavior of LUAD cells both in vitro and in vivo. RNA sequencing analysis indicated that differentially expressed genes in the SF3B1 knockdown and SF3B1 inhibitor groups were enriched in ferroptosis-related pathways compared to their respective control groups. The antiferroptotic role of SF3B1 in LUAD cells was validated by detecting glutathione depletion, lipid peroxidation, and observing morphological changes using transmission electron microscopy. This process was confirmed to be independent of apoptosis and autophagy, as evidenced by the effects of the ferroptosis inducer erastin, the apoptosis inhibitor Z-VAD-FMK, and the autophagy inhibitor 3-methyladenine. Rescue experiments indicated that the antiferroptotic role of SF3B1 in LUAD is partially mediated by upregulating the expression of SLC7A11.

The Protective Effects of an Aged Black Garlic Water Extract on the Prostate

Chronic inflammation is a recognized risk factor for various cancers, including prostate cancer (PCa). We aim to explore the potential protective effects of aged black garlic extract (ABGE) against inflammation-induced prostate damage and its impact on prostate cancer cell lines. We used an ex vivo model of inflammation induced by Escherichia coli lipopolysaccharide (LPS) on C57BL/6 male mouse prostate specimens to investigate the anti-inflammatory properties of ABGE. The gene expression levels of pro-inflammatory biomarkers (COX-2, NF-κB, and TNF-α, IL-6) were measured. Additionally, we evaluated ABGE's therapeutic effects on the prostate cancer cell lines through in vitro functional assays, including colony formation, tumorsphere formation, migration assays, and phosphorylation arrays to assess the signaling pathways (MAPK, AKT, JAK/STAT, and TGF-β). ABGE demonstrated significant anti-inflammatory and antioxidant effects in preclinical models, partly attributed to its polyphenolic content, notably catechin and gallic acid. In the ex vivo model, ABGE reduced the gene expression levels of COX-2, NF-κB, TNF-α, and IL-6. The in vitro studies showed that ABGE inhibited cell proliferation, colony and tumorsphere formation, and cell migration in the prostate cancer cells, suggesting its potential as a therapeutic agent. ABGE exhibits promising anti-inflammatory and anti-cancer properties, supporting further investigation into ABGE as a potential agent for managing inflammation and prostate cancer.

Whole genome sequencing refines stratification and therapy of patients with clear cell renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) is the most common form of kidney cancer, but a comprehensive description of its genomic landscape is lacking. We report the whole genome sequencing of 778 ccRCC patients enrolled in the 100,000 Genomes Project, providing for a detailed description of the somatic mutational landscape of ccRCC. We identify candidate driver genes, which as well as emphasising the major role of epigenetic regulation in ccRCC highlight additional biological pathways extending opportunities for therapeutic interventions. Genomic characterisation identified patients with divergent clinical outcome; higher number of structural copy number alterations associated with poorer prognosis, whereas VHL mutations were independently associated with a better prognosis. The observations that higher T-cell infiltration is associated with better overall survival and that genetically predicted immune evasion is not common supports the rationale for immunotherapy. These findings should inform personalised surveillance and treatment strategies for ccRCC patients.

Splicing Machinery Is Impaired in Oral Squamous Cell Carcinomas and Linked to Key Pathophysiological Features

Alternative splicing dysregulation is an emerging cancer hallmark, potentially serving as a source of novel diagnostic, prognostic, or therapeutic tools. Inhibitors of the activity of the splicing machinery can exert antitumoral effects in cancer cells. We aimed to characterize the splicing machinery (SM) components in oral squamous cell carcinoma (OSCC) and to evaluate the direct impact of the inhibition of SM-activity on OSCC-cells. The expression of 59 SM-components was assessed using a prospective case-control study of tumor and healthy samples from 37 OSCC patients, and the relationship with clinical and histopathological features was assessed. The direct effect of pladienolide-B (SM-inhibitor) on the proliferation rate of primary OSCC cell cultures was evaluated. A significant dysregulation in several SM components was found in OSCC vs. adjacent-healthy tissues [i.e., 12 out of 59 (20%)], and their expression was associated with clinical and histopathological features of less aggressiveness and overall survival. Pladienolide-B treatment significantly decreased OSCC-cell proliferation. Our data reveal a significantly altered expression of several SM-components and link it to pathophysiological features, reinforcing a potential clinical and pathophysiological relevance of the SM dysregulation in OSCC. The inhibition of SM-activity might be a therapeutic avenue in OSCC, offering a clinically relevant opportunity to be explored.

Alternative splicing in prostate cancer progression and therapeutic resistance

Prostate cancer (CaP) remains the second leading cause of cancer deaths in western men. CaP mortality results from diverse molecular mechanisms that mediate resistance to the standard of care treatments for metastatic disease. Recently, alternative splicing has been recognized as a hallmark of CaP aggressiveness. Alternative splicing events cause treatment resistance and aggressive CaP behavior and are determinants of the emergence of the two major types of late-stage treatment-resistant CaP, namely castration-resistant CaP (CRPC) and neuroendocrine CaP (NEPC). Here, we review recent multi-omics data that are uncovering the complicated landscape of alternative splicing events during CaP progression and the impact that different gene transcript isoforms can have on CaP cell biology and behavior. We discuss renewed insights in the molecular machinery by which alternative splicing occurs and contributes to the failure of systemic CaP therapies. The potential for alternative splicing events to serve as diagnostic markers and/or therapeutic targets is explored. We conclude by considering current challenges and promises associated with splicing-modulating therapies, and their potential for clinical translation into CaP patient care.

Exploring the Role of E6 and E7 Oncoproteins in Cervical Oncogenesis through MBD2/3-NuRD Complex Chromatin Remodeling

BACKGROUND

Cervical cancer is among the highest-ranking types of cancer worldwide, with human papillomavirus (HPV) as the agent driving the malignant process. One aspect of the infection's evolution is given by epigenetic modifications, mainly DNA methylation and chromatin alteration. These processes are guided by several chromatin remodeling complexes, including NuRD. The purpose of this study was to evaluate the genome-wide binding patterns of the NuRD complex components (MBD2 and MBD3) in the presence of active HPV16 E6 and E7 oncogenes and to determine the potential of identified genes through an experimental model to differentiate between cervical precursor lesions, with the aim of establishing their utility as biomarkers.

METHODS

The experimental model was built using the CaSki cell line and shRNA for E6 and E7 HPV16 silencing, ChIP-seq, qRT-PCR, and Western blot analyses. Selected genes' expression was also assessed in patients.

RESULTS

Several genes have been identified to exhibit altered transcriptional activity due to the influence of HPV16 E6/E7 viral oncogenes acting through the MBD2/MBD3 NuRD complex, linking them to viral infection and cervical oncogenesis.

CONCLUSIONS

The impacted genes primarily play roles in governing gene transcription, mRNA processing, and regulation of translation. Understanding these mechanisms offers valuable insights into the process of HPV-induced oncogenesis.

Altered CELF4 splicing factor enhances pancreatic neuroendocrine tumors aggressiveness influencing mTOR and everolimus response

Pancreatic neuroendocrine tumors (PanNETs) comprise a heterogeneous group of tumors with growing incidence. Recent molecular analyses provided a precise picture of their genomic and epigenomic landscape. Splicing dysregulation is increasingly regarded as a novel cancer hallmark influencing key tumor features. We have previously demonstrated that splicing machinery is markedly dysregulated in PanNETs. Here, we aimed to elucidate the molecular and functional implications of CUGBP ELAV-like family member 4 (CELF4), one of the most altered splicing factors in PanNETs. CELF4 expression was determined in 20 PanNETs, comparing tumor and non-tumoral adjacent tissue. An RNA sequencing (RNA-seq) dataset was analyzed to explore CELF4-linked interrelations among clinical features, gene expression, and splicing events. Two PanNET cell lines were employed to assess CELF4 function in vitro and in vivo. PanNETs display markedly upregulated CELF4 expression, which is closely associated with malignancy features, altered expression of key tumor players, and distinct splicing event profiles. Modulation of CELF4 influenced proliferation in vitro and reduced in vivo xenograft tumor growth. Interestingly, functional assays and RNA-seq analysis revealed that CELF4 silencing altered mTOR signaling pathway, enhancing the effect of everolimus. We demonstrate that CELF4 is dysregulated in PanNETs, where it influences tumor development and aggressiveness, likely by modulating the mTOR pathway, suggesting its potential as therapeutic target.

The splicing factor SF3B1 is involved in brown adipocyte thermogenic activation

The ability of alternative splicing mechanisms to control gene expression is increasingly being recognized as relevant for adipose tissue function. The expression of SF3B1, a key component of the SF3B complex directly involved in spliceosome formation, was previously reported to be significantly induced in brown adipose tissue under cold-induced thermogenic activation. Here, we identify that noradrenergic cAMP-mediated thermogenic stimulation increases SF3B1 expression in brown and beige adipocytes. We further show that pladienolide-B, a drug that binds SF3B1 to inhibit pre-mRNA splicing by targeting the SF3B complex, down-regulates key components of the thermogenic machinery (e.g., UCP1 gene expression), differentially alters the expression of alternative splicing-regulated transcripts encoding molecular actors involved in the oxidative metabolism of brown adipocytes (e.g., peroxisome proliferator-activated receptor-gamma co-activator-alpha [PGC-1α] and cytochrome oxidase subunit 7a genes), and impairs the respiratory activity of brown adipocytes. Similar alterations were found in brown adipocytes with siRNA-mediated knockdown of SF3B1 protein levels. Our findings collectively indicate that SF3B1 is a key factor in the appropriate thermogenic activation of differentiated brown adipocytes. This work exemplifies the importance of splicing processes in adaptive thermogenesis and suggests that pharmacological tools, such as pladienolide-B, may be used to modulate brown adipocyte thermogenic activity.

Whole genome sequencing refines stratification and therapy of patients with clear cell renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) is the most common form of kidney cancer, but a comprehensive description of its genomic landscape is lacking. We report the whole genome sequencing of 778 ccRCC patients enrolled in the 100,000 Genomes Project, providing the most detailed somatic mutational landscape to date. We identify new driver genes, which as well as emphasising the major role of epigenetic regulation in ccRCC highlight additional biological pathways extending opportunities for drug repurposing. Genomic characterisation identified patients with divergent clinical outcome; higher number of structural copy number alterations associated with poorer prognosis, whereas VHL mutations were independently associated with a better prognosis. The twin observations that higher T-cell infiltration is associated with better outcome and that genetically predicted immune evasion is not common supports the rationale for immunotherapy. These findings should inform personalised surveillance and treatment strategies for ccRCC patients.

The role of alternative pre-mRNA splicing in cancer progression

Alternative pre-mRNA splicing is a critical mechanism that generates multiple mRNA from a single gene, thereby increasing the diversity of the proteome. Recent research has highlighted the significance of specific splicing isoforms in cellular processes, particularly in regulating cell numbers. In this review, we examine the current understanding of the role of alternative splicing in controlling cancer cell growth and discuss specific splicing factors and isoforms and their molecular mechanisms in cancer progression. These isoforms have been found to intricately control signaling pathways crucial for cell cycle progression, proliferation, and apoptosis. Furthermore, studies have elucidated the characteristics and functional importance of splicing factors that influence cell numbers. Abnormal expression of oncogenic splicing isoforms and splicing factors, as well as disruptions in splicing caused by genetic mutations, have been implicated in the development and progression of tumors. Collectively, these findings provide valuable insights into the complex interplay between alternative splicing and cell proliferation, thereby suggesting the potential of alternative splicing as a therapeutic target for cancer.

SF3B1-dependent alternative splicing is critical for maintaining endometrial homeostasis and the establishment of pregnancy

The remarkable potential of human endometrium to undergo spontaneous remodeling is shaped by controlled spatiotemporal gene expression patterns. Although hormone-driven transcription shown to govern these patterns, the post-transcriptional processing of these mRNA transcripts, including the mRNA splicing in the endometrium is not studied yet. Here, we report that the splicing factor, SF3B1 is central in driving alternative splicing (AS) events that are vital for physiological responses of the endometrium. We show that loss of SF3B1 splicing activity impairs stromal cell decidualization as well as embryo implantation. Transcriptomic analysis revealed that SF3B1 depletion decidualizing stromal cells led to differential mRNA splicing. Specifically, a significant upregulation in mutually exclusive AS events (MXEs) with SF3B1 loss resulted in the generation of aberrant transcripts. Further, we found that some of these candidate genes phenocopy SF3B1 function in decidualization. Importantly, we identify progesterone as a potential upstream regulator of SF3B1-mediated functions in endometrium possibly via maintaining its persistently high levels, in coordination with deubiquitinating enzymes. Collectively, our data suggest that SF3B1-driven alternative splicing plays a critical role in mediating the endometrial-specific transcriptional paradigms. Thus, the identification of novel mRNA variants associated with successful pregnancy establishment may help to develop new strategies to diagnose or prevent early pregnancy loss.

Alternative splicing in bladder cancer: potential strategies for cancer diagnosis, prognosis, and treatment

Bladder cancer is the most common malignancy of the urinary tract worldwide. The therapeutic options to tackle this disease comprise surgery, intravesical or systemic chemotherapy, and immunotherapy. Unfortunately, a wide number of patients ultimately become resistant to these treatments and develop aggressive metastatic disease, presenting a poor prognosis. Therefore, the identification of novel therapeutic approaches to tackle this devastating pathology is urgently needed. However, a significant limitation is that the progression and drug response of bladder cancer is strongly associated with its intrinsic molecular heterogeneity. In this sense, RNA splicing is recently gaining importance as a critical hallmark of cancer since can have a significant clinical value. In fact, a profound dysregulation of the splicing process has been reported in bladder cancer, especially in the expression of certain key splicing variants and circular RNAs with a potential clinical value as diagnostic/prognostic biomarkers or therapeutic targets in this pathology. Indeed, some authors have already evidenced a profound antitumor effect by targeting some splicing factors (e.g., PTBP1), mRNA splicing variants (e.g., PKM2, HYAL4-v1), and circular RNAs (e.g., circITCH, circMYLK), which illustrates new possibilities to significantly improve the management of this pathology. This review represents the first detailed overview of the splicing process and its alterations in bladder cancer, and highlights opportunities for the development of novel diagnostic/prognostic biomarkers and their clinical potential for the treatment of this devastating cancer type. This article is categorized under: RNA Processing > Splicing Regulation/Alternative Splicing RNA in Disease and Development > RNA in Disease.

Molecular predictors of metastasis in patients with prostate cancer

INTRODUCTION

Prostate cancer is a serious threat to the health of older adults worldwide. The quality of life and survival time of patients sharply decline once metastasis occurs. Thus, early screening for prostate cancer is very advanced in developed countries. The detection methods used include Prostate-specific antigen (PSA) detection and digital rectal examination. However, the lack of universal access to early screening in some developing countries has resulted in an increased number of patients presenting with metastatic prostate cancer. In addition, the treatment methods for metastatic and localized prostate cancer are considerably different. In many patients, early-stage prostate cancer cells often metastasize due to delayed observation, negative PSA results, and delay in treatment time. Therefore, the identification of patients who are prone to metastasis is important for future clinical studies.

AREAS COVERED

this review introduced a large number of predictive molecules related to prostate cancer metastasis. These molecules involve the mutation and regulation of tumor cell genes, changes in the tumor microenvironment, and the liquid biopsy.

EXPERT OPINION

In next decade, PSMA PET/CT and liquid biopsy will be the excellent predicting tools, while ¹⁷⁷ Lu- PSMA-RLT will be showed excellent anti-tumor efficacy in mPCa patients.

Tumor suppressor role of RBM22 in prostate cancer acting as a dual-factor regulating alternative splicing and transcription of key oncogenic genes

Prostate cancer (PCa) is one of the leading causes of cancer-related deaths among men. Consequently, the identification of novel molecular targets for treatment is urgently needed to improve patients' outcomes. Our group recently reported that some elements of the cellular machinery controlling alternative-splicing might be useful as potential novel therapeutic tools against advanced PCa. However, the presence and functional role of RBM22, a key spliceosome component, in PCa remains unknown. Therefore, RBM22 levels were firstly interrogated in 3 human cohorts and 2 preclinical mouse models (TRAMP/Pbsn-Myc). Results were validated in in silico using 2 additional cohorts. Then, functional effects in response to RBM22 overexpression (proliferation, migration, tumorspheres/colonies formation) were tested in PCa models in vitro (LNCaP, 22Rv1, and PC-3 cell-lines) and in vivo (xenograft). High throughput methods (ie, RNA-seq, nCounter PanCancer Pathways Panel) were performed in RBM22 overexpressing cells and xenograft tumors. We found that RBM22 levels were down-regulated (mRNA and protein) in PCa samples, and were inversely associated with key clinical aggressiveness features. Consistently, a gradual reduction of RBM22 from non-tumor to poorly differentiated PCa samples was observed in transgenic models (TRAMP/Pbsn-Myc). Notably, RBM22 overexpression decreased aggressiveness features in vitro, and in vivo. These actions were associated with the splicing dysregulation of numerous genes and to the downregulation of critical upstream regulators of cell-cycle (i.e., CDK1/CCND1/EPAS1). Altogether, our data demonstrate that RBM22 plays a critical pathophysiological role in PCa and invites to suggest that targeting negative regulators of RBM22 expression/activity could represent a novel therapeutic strategy to tackle this disease.

Metformin inhibits oral squamous cell carcinoma progression through regulating RNA alternative splicing

AIMS

Oral squamous cell carcinoma (OSCC) is considered as the sixth most common cancer worldwide characterized by high invasiveness, high metastasis rate and high mortality. It is urgent to explore novel therapeutic strategies to overcome this feature. Metformin is currently a strong candidate anti-tumor drug in multiple cancers. However, whether metformin could inhibit cancer progression by regulating RNA alternative splicing remains largely unknown.

MAIN METHODS

Cell proliferation and growth ability of CAL-27 and UM-SCC6 were analyzed by CCK8 and colony formation assays. Cell migration was judged by wound healing assay. Mechanistically, RNA-seq was applied to systematically identify genes that are regulated by metformin. The expression of metformin-regulated genes was determined by real-time quantitative PCR (RT-qPCR). Metformin-regulated alternative splicing events were confirmed by RT-PCR.

KEY FINDINGS

We demonstrated that metformin could significantly inhibit the proliferation and migration of oral squamous cell carcinoma cells. Mechanistically, in addition to transcriptional regulation, metformin induces a wide range of alternative splicing alteration, including genes involved in centrosome, cellular response to DNA damage stimulus, GTPase binding, histone modification, catalytic activity, regulation of cell cycle process and ATPase complex. Notably, metformin specifically modulates the splicing of NUBP2, a component of the cytosolic iron-sulfur (Fe/S) protein assembly (CIA). Briefly, metformin favors the production of NUBP2-L, the long splicing isoform of NUBP2, thereby inhibiting cancer cell proliferation.

SIGNIFICANCE

Our findings provide mechanistic insights of metformin on RNA alternative splicing regulation, thus to offer a potential novel route for metformin to inhibit cancer progression.

Splicing machinery is profoundly altered in systemic lupus erythematosus and antiphospholipid syndrome and directly linked to key clinical features

OBJECTIVES

To characterize the splicing machinery (SM) of leukocytes from primary antiphospholipid syndrome (APS), systemic lupus erythematosus (SLE) and antiphospholipid syndrome with lupus (APS + SLE) patients, and to assess its clinical involvement.

METHODS

Monocytes, lymphocytes and neutrophils from 80 patients (22 APS, 35 SLE and 23 APS + SLE) and 50 HD were purified, and 45 selected SM components were evaluated by qPCR-microfluidic array. Relationship with clinical features and underlying regulatory mechanisms were assessed.

RESULTS

APS, SLE and APS + SLE leukocytes displayed significant and specific alterations in SM-components (SMC), associated with clinical features [autoimmune profiles, disease activity, lupus nephritis (LN), and CV-risk markers]. A remarkable relationship among dysregulated SMC in monocytes and the presence of LN in SLE was highlighted, revealing a novel pathological mechanism, which was further explored. Immunohistology analysis of renal biopsies highlighted the pathological role of the myeloid compartment in LN. Transcriptomic analysis of monocytes from SLE-LN(+) vs SLE-LN(-) identified 271 genes differentially expressed, mainly involved in inflammation and IFN-signaling. Levels of IFN-related genes correlated with those of SMC in SLE-LN(+). These results were validated in two external SLE-LN(+) datasets of whole-blood and kidney biopsies. In vitro, SLE-LN(+)-serum promoted a concomitant dysregulation of both, the IFN signature and several SMC, further reversed by JAKinibs treatment. Interestingly, IFNs, key inflammatory cytokines in SLE pathology, also altered SMC. Lastly, the over/down-expression of selected SMC in SLE-monocytes reduced the release of inflammatory cytokines and their adhesion capacity.

CONCLUSION

Overall, we have identified, for the first time, a specific alteration of SMC in leukocytes from APS, SLE and APS + SLE patients that would be responsible for the development of distinctive clinical profiles.

PRPF8 increases the aggressiveness of hepatocellular carcinoma by regulating FAK/AKT pathway via fibronectin 1 splicing

Hepatocellular carcinoma (HCC) pathogenesis is associated with alterations in splicing machinery components (spliceosome and splicing factors) and aberrant expression of oncogenic splice variants. We aimed to analyze the expression and potential role of the spliceosome component PRPF8 (pre-mRNA processing factor 8) in HCC. PRPF8 expression (mRNA/protein) was analyzed in a retrospective cohort of HCC patients (n = 172 HCC and nontumor tissues) and validated in two in silico cohorts (TCGA and CPTAC). PRPF8 expression was silenced in liver cancer cell lines and in xenograft tumors to understand the functional and mechanistic consequences. In silico RNAseq and CLIPseq data were also analyzed. Our results indicate that PRPF8 is overexpressed in HCC and associated with increased tumor aggressiveness (patient survival, etc.), expression of HCC-related splice variants, and modulation of critical genes implicated in cancer-related pathways. PRPF8 silencing ameliorated aggressiveness in vitro and decreased tumor growth in vivo. Analysis of in silico CLIPseq data in HepG2 cells demonstrated that PRPF8 binds preferentially to exons of protein-coding genes, and RNAseq analysis showed that PRPF8 silencing alters splicing events in multiple genes. Integrated and in vitro analyses revealed that PRPF8 silencing modulates fibronectin (FN1) splicing, promoting the exclusion of exon 40.2, which is paramount for binding to integrins. Consistent with this finding, PRPF8 silencing reduced FAK/AKT phosphorylation and blunted stress fiber formation. Indeed, HepG2 and Hep3B cells exhibited a lower invasive capacity in membranes treated with conditioned medium from PRPF8-silenced cells compared to medium from scramble-treated cells. This study demonstrates that PRPF8 is overexpressed and associated with aggressiveness in HCC and plays important roles in hepatocarcinogenesis by altering FN1 splicing, FAK/AKT activation and stress fiber formation.

Spliceosomal profiling identifies EIF4A3 as a novel oncogene in hepatocellular carcinoma acting through the modulation of FGFR4 splicing

INTRODUCTION

Altered splicing landscape is an emerging cancer hallmark; however, the dysregulation and implication of the cellular machinery controlling this process (spliceosome components and splicing factors) in hepatocellular carcinoma (HCC) is poorly known. This study aimed to comprehensively characterize the spliceosomal profile and explore its role in HCC.

METHODS

Expression levels of 70 selected spliceosome components and splicing factors and clinical implications were evaluated in two retrospective and six in silico HCC cohorts. Functional, molecular and mechanistic studies were implemented in three cell lines (HepG2, Hep3B and SNU-387) and preclinical Hep3B-induced xenograft tumours.

RESULTS

Spliceosomal dysregulations were consistently found in retrospective and in silico cohorts. EIF4A3, RBM3, ESRP2 and SRPK1 were the most dysregulated spliceosome elements in HCC. EIF4A3 expression was associated with decreased survival and greater recurrence. Plasma EIF4A3 levels were significantly elevated in HCC patients. In vitro EIF4A3-silencing (or pharmacological inhibition) resulted in reduced aggressiveness, and hindered xenograft-tumours growth in vivo, whereas EIF4A3 overexpression increased tumour aggressiveness. EIF4A3-silencing altered the expression and splicing of key HCC-related genes, specially FGFR4. EIF4A3-silencing blocked the cellular response to the natural ligand of FGFR4, FGF19. Functional consequences of EIF4A3-silencing were mediated by FGFR4 splicing as the restoration of non-spliced FGFR4 full-length version blunted these effects, and FGFR4 inhibition did not exert further effects in EIF4A3-silenced cells.

CONCLUSIONS

Splicing machinery is strongly dysregulated in HCC, providing a source of new diagnostic, prognostic and therapeutic options in HCC. EIF4A3 is consistently elevated in HCC patients and associated with tumour aggressiveness and mortality, through the modulation of FGFR4 splicing.

Somatostatin, Cortistatin and Their Receptors Exert Antitumor Actions in Androgen-Independent Prostate Cancer Cells: Critical Role of Endogenous Cortistatin

Somatostatin (SST), cortistatin (CORT), and their receptors (SSTR1-5/sst5TMD4-TMD5) comprise a multifactorial hormonal system involved in the regulation of numerous pathophysiological processes. Certain components of this system are dysregulated and play critical roles in the development/progression of different endocrine-related cancers. However, the presence and therapeutic role of this regulatory system in prostate cancer (PCa) remain poorly explored. Accordingly, we performed functional (proliferation/migration/colonies-formation) and mechanistic (Western-blot/qPCR/microfluidic-based qPCR-array) assays in response to SST and CORT treatments and CORT-silencing (using specific siRNA) in different PCa cell models [androgen-dependent (AD): LNCaP; androgen-independent (AI)/castration-resistant PCa (CRPC): 22Rv1 and PC-3], and/or in the normal-like prostate cell-line RWPE-1. Moreover, the expression of SST/CORT system components was analyzed in PCa samples from two different patient cohorts [internal (n = 69); external (Grasso, n = 88)]. SST and CORT treatment inhibited key functional/aggressiveness parameters only in AI-PCa cells. Mechanistically, antitumor capacity of SST/CORT was associated with the modulation of oncogenic signaling pathways (AKT/JNK), and with the significant down-regulation of critical genes involved in proliferation/migration and PCa-aggressiveness (e.g., MKI67/MMP9/EGF). Interestingly, CORT was highly expressed, while SST was not detected, in all prostate cell-lines analyzed. Consistently, endogenous CORT was overexpressed in PCa samples (compared with benign-prostatic-hyperplasia) and correlated with key clinical (i.e., metastasis) and molecular (i.e., SSTR2/SSTR5 expression) parameters. Remarkably, CORT-silencing drastically enhanced proliferation rate and blunted the antitumor activity of SST-analogues (octreotide/pasireotide) in AI-PCa cells. Altogether, we provide evidence that SST/CORT system and SST-analogues could represent a potential therapeutic option for PCa, especially for CRPC, and that endogenous CORT could act as an autocrine/paracrine regulator of PCa progression.

Dysregulation of splicing variants and spliceosome components in breast cancer

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

SF3B1 facilitates HIF1-signaling and promotes malignancy in pancreatic cancer

Mutations in the splicing factor SF3B1 are frequently occurring in various cancers and drive tumor progression through the activation of cryptic splice sites in multiple genes. Recent studies also demonstrate a positive correlation between the expression levels of wild-type SF3B1 and tumor malignancy. Here, we demonstrate that SF3B1 is a hypoxia-inducible factor (HIF)-1 target gene that positively regulates HIF1 pathway activity. By physically interacting with HIF1α, SF3B1 facilitates binding of the HIF1 complex to hypoxia response elements (HREs) to activate target gene expression. To further validate the relevance of this mechanism for tumor progression, we show that a reduction in SF3B1 levels via monoallelic deletion of Sf3b1 impedes tumor formation and progression via impaired HIF signaling in a mouse model for pancreatic cancer. Our work uncovers an essential role of SF3B1 in HIF1 signaling, thereby providing a potential explanation for the link between high SF3B1 expression and aggressiveness of solid tumors.

Dysregulation of the miRNome unveils a crosstalk between obesity and prostate cancer: miR-107 asa personalized diagnostic and therapeutic tool

Prostate-specific antigen (PSA) is the gold-standard marker to screen prostate cancer (PCa) nowadays. Unfortunately, its lack of specificity and sensitivity makes the identification of novel tools to diagnose PCa an urgent medical need. In this context, microRNAs (miRNAs) have emerged as potential sources of non-invasive diagnostic biomarkers in several pathologies. Therefore, this study was aimed at assessing for the first time the dysregulation of the whole plasma miRNome in PCa patients and its putative implication in PCa from a personalized perspective (i.e., obesity condition). Plasma miRNome from a discovery cohort (18 controls and 19 PCa patients) was determined using an Affymetrix-miRNA array, showing that the expression of 104 miRNAs was significantly altered, wherein six exhibited a significant receiver operating characteristic (ROC) curve to distinguish between control and PCa patients (area under the curve [AUC] = 1). Then, a systematic validation using an independent cohort (135 controls and 160 PCa patients) demonstrated that miR-107 was the most profoundly altered miRNA in PCa (AUC = 0.75). Moreover, miR-107 levels significantly outperformed the ability of PSA to distinguish between control and PCa patients and correlated with relevant clinical parameters (i.e., PSA). These differences were more pronounced when considering only obese patients (BMI > 30). Interestingly, miR-107 levels were reduced in PCa tissues versus non-tumor tissues (n = 84) and in PCa cell lines versus non-tumor cells. In vitro miR-107 overexpression altered key aggressiveness features in PCa cells (i.e., proliferation, migration, and tumorospheres formation) and modulated the expression of important genes involved in PCa pathophysiology (i.e., lipid metabolism [i.e., FASN] and splicing process). Altogether, miR-107 might represent a novel and useful personalized diagnostic and prognostic biomarker and a potential therapeutic tool in PCa, especially in obese patients.

SF3B1 inhibition disrupts malignancy and prolongs survival in glioblastoma patients through BCL2L1 splicing and mTOR/ß-catenin pathways imbalances

BACKGROUND

Glioblastoma is one of the most devastating cancer worldwide based on its locally aggressive behavior and because it cannot be cured by current therapies. Defects in alternative splicing process are frequent in cancer. Recently, we demonstrated that dysregulation of the spliceosome is directly associated with glioma development, progression, and aggressiveness.

METHODS

Different human cohorts and a dataset from different glioma mouse models were analyzed to determine the mutation frequency as well as the gene and protein expression levels between tumor and control samples of the splicing-factor-3B-subunit-1 (SF3B1), an essential and druggable spliceosome component. SF3B1 expression was also explored at the single-cell level across all cell subpopulations and transcriptomic programs. The association of SF3B1 expression with relevant clinical data (e.g., overall survival) in different human cohorts was also analyzed. Different functional (proliferation/migration/tumorspheres and colonies formation/VEGF secretion/apoptosis) and mechanistic (gene expression/signaling pathways) assays were performed in three different glioblastomas cell models (human primary cultures and cell lines) in response to SF3B1 blockade (using pladienolide B treatment). Moreover, tumor progression and formation were monitored in response to SF3B1 blockade in two preclinical xenograft glioblastoma mouse models.

RESULTS

Our data provide novel evidence demonstrating that the splicing-factor-3B-subunit-1 (SF3B1, an essential and druggable spliceosome component) is low-frequency mutated in human gliomas (~ 1 %) but widely overexpressed in glioblastoma compared with control samples from the different human cohorts and mouse models included in the present study, wherein SF3B1 levels are associated with key molecular and clinical features (e.g., overall survival, poor prognosis and/or drug resistance). Remarkably, in vitro and in vivo blockade of SF3B1 activity with pladienolide B drastically altered multiple glioblastoma pathophysiological processes (i.e., reduction in proliferation, migration, tumorspheres formation, VEGF secretion, tumor initiation and increased apoptosis) likely by suppressing AKT/mTOR/ß-catenin pathways, and an imbalance of BCL2L1 splicing.

CONCLUSIONS

Together, we highlight SF3B1 as a potential diagnostic and prognostic biomarker and an efficient pharmacological target in glioblastoma, offering a clinically relevant opportunity worth to be explored in humans.

The SF3B1R625H mutation promotes prolactinoma tumor progression through aberrant splicing of DLG1

Background

Recently, a hotspot mutation in prolactinoma was observed in splicing factor 3b subunit 1 (SF3B1^R625H), but its functional effects and underlying molecular mechanisms remain largely unexplored.

Methods

Using the CRISPR/Cas9 genome editing system and rat pituitary GH3 cells, we generated heterozygous Sf3b1^R625H mutant cells. Sanger and whole-genome sequencing were conducted to verify the introduction of this mutation. Transcriptome analysis was performed in SF3B1-wild-type versus mutant human prolactinoma samples and GH3 cells. RT-PCR and minigene reporter assays were conducted to verify aberrant splicing. The functional consequences of SF3B1^R625H were evaluated in vitro and in vivo. Critical makers of epithelial-mesenchymal transition and key components were detected using western blot, immunohistochemistry, and immunofluorescence. Suppressing proteins was achieved using siRNA.

Results

Transcriptomic analysis of prolactinomas and heterozygous mutant cells revealed that the SF3B1^R625H allele led to different alterations in splicing properties, affecting different genes in different species. SF3B1^R625H promoted aberrant splicing and DLG1 suppression in both rat cells and human tumors. In addition, SF3B1^R625H and knocking down DLG1 promoted cell migration, invasion, and epithelial-mesenchymal transition through PI3K/Akt pathway.

Conclusions

Our findings elucidate a mechanism through which mutant SF3B1 promotes tumor progression and may provide a potent molecular therapeutic target for prolactinomas with the SF3B1^R625H mutation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-022-02245-0.

Splicing machinery is impaired in rheumatoid arthritis, associated with disease activity and modulated by anti-TNF therapy

OBJECTIVES

To characterise splicing machinery (SM) alterations in leucocytes of patients with rheumatoid arthritis (RA), and to assess its influence on their clinical profile and therapeutic response.

METHODS

Leucocyte subtypes from 129 patients with RA and 29 healthy donors (HD) were purified, and 45 selected SM elements (SME) were evaluated by quantitative PCR-array based on microfluidic technology (Fluidigm). Modulation by anti-tumour necrosis factor (TNF) therapy and underlying regulatory mechanisms were assessed.

RESULTS

An altered expression of several SME was found in RA leucocytes. Eight elements (SNRNP70, SNRNP200, U2AF2, RNU4ATAC, RBM3, RBM17, KHDRBS1 and SRSF10) were equally altered in all leucocytes subtypes. Logistic regressions revealed that this signature might: discriminate RA and HD, and anti-citrullinated protein antibodies (ACPAs) positivity; classify high-disease activity (disease activity score-28 (DAS28) >5.1); recognise radiological involvement; and identify patients showing atheroma plaques. Furthermore, this signature was altered in RA synovial fluid and ankle joints of K/BxN-arthritic mice. An available RNA-seq data set enabled to validate data and identified distinctive splicing events and splicing variants among patients with RA expressing high and low SME levels. 3 and 6 months anti-TNF therapy reversed their expression in parallel to the reduction of the inflammatory profile. In vitro, ACPAs modulated SME, at least partially, by Fc Receptor (FcR)-dependent mechanisms. Key inflammatory cytokines further altered SME. Lastly, induced SNRNP70-overexpression and KHDRBS1-overexpression reversed inflammation in lymphocytes, NETosis in neutrophils and adhesion in RA monocytes and influenced activity of RA synovial fibroblasts.

CONCLUSIONS

Overall, we have characterised for the first time a signature comprising eight dysregulated SME in RA leucocytes from both peripheral blood and synovial fluid, linked to disease pathophysiology, modulated by ACPAs and reversed by anti-TNF therapy.

Impact of Alternative Splicing Variants on Liver Cancer Biology

Simple Summary

Among the top ten deadly solid tumors are the two most frequent liver cancers, hepatocellular carcinoma, and intrahepatic cholangiocarcinoma, whose development and malignancy are favored by multifactorial conditions, which include aberrant maturation of pre-mRNA due to abnormalities in either the machinery involved in the splicing, i.e., the spliceosome and associated factors, or the nucleotide sequences of essential sites for the exon recognition process. As a consequence of cancer-associated aberrant splicing in hepatocytes- and cholangiocytes-derived cancer cells, abnormal proteins are synthesized. They contribute to the dysregulated proliferation and eventually transformation of these cells to phenotypes with enhanced invasiveness, migration, and multidrug resistance, which contributes to the poor prognosis that characterizes these liver cancers.

Abstract

The two most frequent primary cancers affecting the liver, whose incidence is growing worldwide, are hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (iCCA), which are among the five most lethal solid tumors with meager 5-year survival rates. The common difficulty in most cases to reach an early diagnosis, the aggressive invasiveness of both tumors, and the lack of favorable response to pharmacotherapy, either classical chemotherapy or modern targeted therapy, account for the poor outcome of these patients. Alternative splicing (AS) during pre-mRNA maturation results in changes that might affect proteins involved in different aspects of cancer biology, such as cell cycle dysregulation, cytoskeleton disorganization, migration, and adhesion, which favors carcinogenesis, tumor promotion, and progression, allowing cancer cells to escape from pharmacological treatments. Reasons accounting for cancer-associated aberrant splicing include mutations that create or disrupt splicing sites or splicing enhancers or silencers, abnormal expression of splicing factors, and impaired signaling pathways affecting the activity of the splicing machinery. Here we have reviewed the available information regarding the impact of AS on liver carcinogenesis and the development of malignant characteristics of HCC and iCCA, whose understanding is required to develop novel therapeutical approaches aimed at manipulating the phenotype of cancer cells.

Dysregulated splicing factor SF3B1 unveils a dual therapeutic vulnerability to target pancreatic cancer cells and cancer stem cells with an anti-splicing drug

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal cancer, requiring novel treatments to target both cancer cells and cancer stem cells (CSCs). Altered splicing is emerging as both a novel cancer hallmark and an attractive therapeutic target. The core splicing factor SF3B1 is heavily altered in cancer and can be inhibited by Pladienolide-B, but its actionability in PDAC is unknown. We explored the presence and role of SF3B1 in PDAC and interrogated its potential as an actionable target.

METHODS

SF3B1 was analyzed in PDAC tissues, an RNA-seq dataset, and publicly available databases, examining associations with splicing alterations and key features/genes. Functional assays in PDAC cell lines and PDX-derived CSCs served to test Pladienolide-B treatment effects in vitro, and in vivo in zebrafish and mice.

RESULTS

SF3B1 was overexpressed in human PDAC and associated with tumor grade and lymph-node involvement. SF3B1 levels closely associated with distinct splicing event profiles and expression of key PDAC players (KRAS, TP53). In PDAC cells, Pladienolide-B increased apoptosis and decreased multiple tumor-related features, including cell proliferation, migration, and colony/sphere formation, altering AKT and JNK signaling, and favoring proapoptotic splicing variants (BCL-XS/BCL-XL, KRASa/KRAS, Δ133TP53/TP53). Importantly, Pladienolide-B similarly impaired CSCs, reducing their stemness capacity and increasing their sensitivity to chemotherapy. Pladienolide-B also reduced PDAC/CSCs xenograft tumor growth in vivo in zebrafish and in mice.

CONCLUSION

SF3B1 overexpression represents a therapeutic vulnerability in PDAC, as altered splicing can be targeted with Pladienolide-B both in cancer cells and CSCs, paving the way for novel therapies for this lethal cancer.

Prostate cancer: Alternatively spliced mRNA transcripts in tumor progression and their uses as therapeutic targets

Prostate cancer is the most frequently diagnosed cancer and second leading cause of cancer deaths among American men. Current therapies show early antitumor responses, but ultimately lead to treatment resistance, relapse and poorer survival in patients. Alternative RNA splicing, a cell mechanism increasing the proteome diversity by producing multiple transcripts from a single gene, has been associated with prostate cancer development/progression. Reports showed that many aberrant mRNA splice variants are upregulated in prostate cancer, promoting malignancy through enhanced proliferation, metastasis, tumor growth, anti-apoptosis, and/or treatment resistance. Here, we discuss the oncogenic properties of aberrant splicing mechanisms underlying prostate cancer pathogenesis, as well as the uses of the splicing variants as potential diagnostics and treatment targets. Finally, we discuss the pharmacologic and molecular approaches for targeting aberrant splicing mechanisms as effective therapies to correct the splicing errors and overcome the drug resistance, ultimately improving the clinical outcome of prostate cancer patients.

Epigenetic and post-transcriptional regulation of somatostatin receptor subtype 5 (SST5 ) in pituitary and pancreatic neuroendocrine tumors

Somatostatin receptor subtype 5 (SST₅) is an emerging biomarker and actionable target in pituitary (PitNETs) and pancreatic (PanNETs) neuroendocrine tumors. Transcriptional and epigenetic regulation of SSTR5 gene expression and mRNA biogenesis is poorly understood. Recently, an overlapping natural antisense transcript, SSTR5‐AS1, potentially regulating SSTR5 expression, was identified. We aimed to elucidate whether epigenetic processes contribute to the regulation of SSTR5 expression in PitNETs (somatotropinomas) and PanNETs. We analyzed the SSTR5/SSTR5‐AS1 human locus in silico to identify CpG islands. SSTR5 and SSTR5‐AS1 expression was assessed by quantitative real‐time PCR (qPCR) in 27 somatotropinomas, 11 normal pituitaries (NPs), and 15 PanNETs/paired adjacent (control) samples. We evaluated methylation grade in four CpG islands in the SSTR5/SSTR5‐AS1 genes. Results revealed that SSTR5 and SSTR5‐AS1 were directly correlated in NP, somatotropinoma, and PanNET samples. Interestingly, selected CpG islands were differentially methylated in somatotropinomas compared with NPs. In PanNETs cell lines, SSTR5‐AS1 silencing downregulated SSTR5 expression, altered aggressiveness features, and influenced pasireotide response. These results provide evidence that SSTR5 expression in PitNETs and PanNETs can be epigenetically regulated by the SSTR5‐AS1 antisense transcript and, indirectly, by DNA methylation, which may thereby impact tumor behavior and treatment response.

Total Syntheses of Pladienolide-Derived Spliceosome Modulators

Pladienolides, an emerging class of naturally occurring spliceosome modulators, exhibit interesting structural features, such as highly substituted 12-membered macrocycles and epoxide-containing diene side chains. The potential of pladienolides as anti-cancer agents is confirmed by H3B-8800, a synthetic analog of this natural product class, which is currently under Phase I clinical trials. Since its isolation in 2004 and the first total synthesis in 2007, a dozen total syntheses and synthetic approaches toward the pladienolide class have been reported to date. This review focuses on the eight completed total syntheses of naturally occurring pladienolides or their synthetic analogs, in addition to a synthetic approach to the main framework of the natural product.

Impaired mRNA splicing and proteostasis in preadipocytes in obesity-related metabolic disease

Preadipocytes are crucial for healthy adipose tissue expansion. Preadipocyte differentiation is altered in obese individuals, which has been proposed to contribute to obesity-associated metabolic disturbances. Here, we aimed at identifying the pathogenic processes underlying impaired adipocyte differentiation in obese individuals with insulin resistance (IR)/type 2 diabetes (T2D). We report that down-regulation of a key member of the major spliceosome, PRFP8/PRP8, as observed in IR/T2D preadipocytes from subcutaneous (SC) fat, prevented adipogenesis by altering both the expression and splicing patterns of adipogenic transcription factors and lipid droplet-related proteins, while adipocyte differentiation was restored upon recovery of PRFP8/PRP8 normal levels. Adipocyte differentiation was also compromised under conditions of endoplasmic reticulum (ER)-associated protein degradation (ERAD) hyperactivation, as occurs in SC and omental (OM) preadipocytes in IR/T2D obesity. Thus, targeting mRNA splicing and ER proteostasis in preadipocytes could improve adipose tissue function and thus contribute to metabolic health in obese individuals.

Comparative Cytotoxic Activity of Hydroxytyrosol and Its Semisynthetic Lipophilic Derivatives in Prostate Cancer Cells

A high adherence to a Mediterranean diet has been related to numerous beneficial effects in human health, including a lower incidence and mortality of prostate cancer (PCa). Olive oil is an important source of phenolic bioactive compounds, mainly hydroxytyrosol (HT), of this diet. Because of the growing interest of this compound and its derivatives as a cancer chemopreventive agent, we aimed to compare the in vitro effect of HT isolated from olive mill wastewaters and five semisynthetic alkyl ether, ester, and nitro-derivatives against prostate cancer (PCa) cell lines. The effect in cell proliferation was determined in RWPE-1, LNCaP, 22Rv1, and PC-3 cells by resazurin assay, the effect in cell migration by wound healing assay, and tumorsphere and colony formation were evaluated. The changes in key signaling pathways involved in carcinogenesis were assessed by using a phosphorylation pathway profiling array and by Western blotting. Antiproliferative effects of HT and two lipophilic derivatives [hydroxytyrosyl acetate (HT-Ac)/ethyl hydroxytyrosyl ether (HT-Et)] were significantly higher in cancerous PC-3 and 22Rv1 cells than in non-malignant RWPE-1 cells. HT/HT-Ac/HT-Et significantly reduced migration capacity in RWPE-1 and PC-3 and prostatosphere size and colony formation in 22Rv1, whereas only HT-Ac and HT-Et reduced these functional parameters in PC-3. The cytotoxic effect in 22Rv1 cells was correlated with modifications in the phosphorylation pattern of key proteins, including ERK1/2 and AKT. Consistently, HT-Ac and HT-Et decreased p-AKT levels in PC-3. In sum, our results suggest that HT and its lipophilic derivatives could be considered as potential therapeutic tools in PCa.

A PROTAC targets splicing factor 3B1

The proteolysis-targeting chimeras (PROTACs) are a new technology to degrade target proteins. However, their clinical application is limited currently by lack of chemical binders to target proteins. For instance, it is still unknown whether splicing factor 3B subunit 1 (SF3B1) is targetable by PROTACs. We recently identified a 2-aminothiazole derivative (herein O4I2) as a promoter in the generation of human pluripotent stem cells. In this work, proteomic analysis on the biotinylated O4I2 revealed that O4I2 targeted SF3B1 and positively regulated RNA splicing. Fusing thalidomide-the ligand of the cereblon ubiquitin ligase-to O4I2 led to a new PROTAC-O4I2, which selectively degraded SF3B1 and induced cellular apoptosis in a CRBN-dependent manner. In a Drosophila intestinal tumor model, PROTAC-O4I2 increased survival by interference with the maintenance and proliferation of stem cell. Thus, our finding demonstrates that SF3B1 is PROTACable by utilizing noninhibitory chemicals, which expands the list of PROTAC target proteins.

SF3B1 mutation in pancreatic cancer contributes to aerobic glycolysis and tumor growth through a PP2A-c-Myc axis

Hot spot gene mutations in splicing factor 3b subunit 1 (SF3B1) are observed in many types of cancer and create abundant aberrant mRNA splicing, which is profoundly implicated in tumorigenesis. Here, we identified that the SF3B1 K700E (SF3B1^K700E) mutation is strongly associated with tumor growth in pancreatic ductal adenocarcinoma (PDAC). Knockdown of SF3B1 significantly retarded cell proliferation and tumor growth in a cell line (Panc05.04) with the SF3B1^K700E mutation. However, SF3B1 knockdown had no notable effect on cell proliferation in two cell lines (BxPC3 and AsPC1) carrying wild‐type SF3B1. Ectopic expression of SF3B1^K700E but not SF3B1^WT in SF3B1‐knockout Panc05.04 cells largely restored the inhibitory role induced by SF3B1 knockdown. Introduction of the SF3B1^K700E mutation in BxPC3 and AsPC1 cells also boosted cell proliferation. Gene set enrichment analysis demonstrated a close correlation between SF3B1 mutation and aerobic glycolysis. Functional analyses showed that the SF3B1^K700E mutation promoted tumor glycolysis, as evidenced by glucose consumption, lactate release, and extracellular acidification rate. Mechanistically, the SF3B1 mutation promoted the aberrant splicing of PPP2R5A and led to the activation of the glycolytic regulator c‐Myc via post‐translational regulation. Pharmacological activation of PP2A with FTY‐720 markedly compromised the growth advantage induced by the SF3B1^K700E mutation in vitro and in vivo. Taken together, our data suggest a novel function for SF3B1 mutation in the Warburg effect, and this finding may offer a potential therapeutic strategy against PDAC with the SF3B1^K700E mutation.

Novel Single Inhibitor of HDAC6/8 and Dual Inhibitor of PI3K/HDAC6 as Potential Alternative Treatments for Prostate Cancer

Background: Prostate cancer is the second most frequently diagnosed malignancy worldwide. Here, the cytotoxic and antimetastatic effects of a new HDAC6/8 inhibitor, LASSBio-1911, and a new dual-PI3K/HDAC6 inhibitor, LASSBio-2208, were evaluated against PC3 prostate cancer cell line. Methods: A MTT assay was used to assess the cell viability. Annexin V/propidium iodide (PI) was used to detect apoptotic cell death and to analyze the cell cycle distribution. Interleukin 6 (IL-6) levels were measured by ELISA. A cell scratch assay was performed to assess cell migration, and the expression of proteins was estimated by Western blotting. Results: LASSBio-1911 and LASSBio-2208 exert cytotoxic effects against PC3 cells. However, LASSBio-2208 was demonstrated to be more potent than LASSBio-1911. The apoptosis assays showed that both compounds trigger apoptotic processes and cause the arrest of cells in the G2/M phase of the cell cycle. The Western blot analysis revealed that LASSBio-2208 significantly decreased the expression of p-JNK and JAK2. However, both compounds reduced the expression of p-STAT3, IL-6 secretion, and cell migration. Conclusions: LASSBio-1911 and LASSBio-2208 demonstrated significant activity in reducing cell viability and migration. These compounds can be further used as prototypes for the development of new potential anticancer alternative treatments.

Clinical, Cellular, and Molecular Evidence of the Additive Antitumor Effects of Biguanides and Statins in Prostate Cancer

CONTEXT

Prostate cancer (PCa) is one of the leading causes of cancer-related death among the male population worldwide. Unfortunately, current medical treatments fail to prevent PCa progression in a high percentage of cases; therefore, new therapeutic tools to tackle PCa are urgently needed. Biguanides and statins have emerged as antitumor agents for several endocrine-related cancers.

OBJECTIVE

To evaluate: (1) the putative in vivo association between metformin and/or statins treatment and key tumor and clinical parameters and (2) the direct effects of different biguanides (metformin/buformin/phenformin), statins (atorvastatin/simvastatin/lovastatin), and their combination, on key functional endpoints and associated signalling mechanisms.

METHODS

An exploratory/observational retrospective cohort of patients with PCa (n = 75) was analyzed. Moreover, normal and tumor prostate cells (normal [RWPE-cells/primary prostate cell cultures]; tumor [LNCaP/22RV1/PC3/DU145 cell lines]) were used to measure proliferation/migration/tumorsphere-formation/signalling pathways.

RESULTS

The combination of metformin+statins in vivo was associated to lower Gleason score and longer biochemical recurrence-free survival. Moreover, biguanides and statins exerted strong antitumor actions (ie, inhibition of proliferation/migration/tumorsphere formation) on PCa cells, and that their combination further decreased; in addition, these functional parameters compared with the individual treatments. These actions were mediated through modulation of key oncogenic and metabolic signalling pathways (ie, AR/mTOR/AMPK/AKT/ERK) and molecular mediators (MKI67/cMYC/androgen receptor/cell-cycle inhibitors).

CONCLUSIONS

Biguanides and statins significantly reduced tumor aggressiveness in PCa, with this effect being more potent (in vitro and in vivo) when both compounds are combined. Therefore, given the demonstrated clinical safety of biguanides and statins, our results suggest a potential therapeutic role of these compounds, especially their combination, for the treatment of PCa.

Influence of Obesity in the miRNome: miR-4454, a Key Regulator of Insulin Response Via Splicing Modulation in Prostate

CONTEXT

Obesity is a major health problem associated with severe comorbidities, including type 2 diabetes and cancer, wherein microRNAs (miRNAs) might be useful as diagnostic/prognostic tools or therapeutic targets.

OBJECTIVE

To explore the differential expression pattern of miRNAs in obesity and their putative role in obesity-related comorbidities such as insulin resistance.

METHODS

An Affymetrix-miRNA array was performed in plasma samples from normoweight (n = 4/body mass index < 25) and obese subjects (n = 4/body mass index > 30). The main changes were validated in 2 independent cohorts (n = 221/n = 18). Additionally, in silico approaches were performed and in vitro assays applied in tissue samples and prostate (RWPE-1) and liver (HepG2) cell-lines.

RESULTS

A total of 26 microRNAs were altered (P < 0.01) in plasma of obese subjects compared to controls using the Affymetrix-miRNA array. Validation in ampler cohorts revealed that miR-4454 levels were consistently higher in obesity, associated with insulin-resistance (Homeostatic Model Assessment of Insulin Resistance/insulin) and modulated by medical (metformin/statins) and surgical (bariatric surgery) strategies. miR-4454 was highly expressed in prostate and liver tissues and its expression was increased in prostate and liver cells by insulin. In vitro, overexpression of miR-4454 in prostate cells resulted in decreased expression levels of INSR, GLUT4, and phosphorylation of AMPK/AKT/ERK, as well as in altered expression of key spliceosome components (ESRP1/ESRP2/RBM45/RNU2) and insulin-receptor splicing variants.

CONCLUSIONS

Obesity was associated to an alteration of the plasmatic miRNA landscape, wherein miR-4454 levels were higher, associated with insulin-resistance and modulated by obesity-controlling interventions. Insulin regulated miR-4454, which, in turn may impair the cellular response to insulin, in a cell type-dependent manner (i.e., prostate gland), by modulating the splicing process.

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.

Splicing machinery dysregulation drives glioblastoma development/aggressiveness: oncogenic role of SRSF3

Glioblastomas remain the deadliest brain tumour, with a dismal ∼12–16-month survival from diagnosis. Therefore, identification of new diagnostic, prognostic and therapeutic tools to tackle glioblastomas is urgently needed. Emerging evidence indicates that the cellular machinery controlling the splicing process (spliceosome) is altered in tumours, leading to oncogenic splicing events associated with tumour progression and aggressiveness. Here, we identify for the first time a profound dysregulation in the expression of relevant spliceosome components and splicing factors (at mRNA and protein levels) in well characterized cohorts of human high-grade astrocytomas, mostly glioblastomas, compared to healthy brain control samples, being SRSF3, RBM22, PTBP1 and RBM3 able to perfectly discriminate between tumours and control samples, and between proneural-like or mesenchymal-like tumours versus control samples from different mouse models with gliomas. Results were confirmed in four additional and independent human cohorts. Silencing of SRSF3, RBM22, PTBP1 and RBM3 decreased aggressiveness parameters in vitro (e.g. proliferation, migration, tumorsphere-formation, etc.) and induced apoptosis, especially SRSF3. Remarkably, SRSF3 was correlated with patient survival and relevant tumour markers, and its silencing in vivo drastically decreased tumour development and progression, likely through a molecular/cellular mechanism involving PDGFRB and associated oncogenic signalling pathways (PI3K-AKT/ERK), which may also involve the distinct alteration of alternative splicing events of specific transcription factors controlling PDGFRB (i.e. TP73). Altogether, our results demonstrate a drastic splicing machinery-associated molecular dysregulation in glioblastomas, which could potentially be considered as a source of novel diagnostic and prognostic biomarkers as well as therapeutic targets for glioblastomas. Remarkably, SRSF3 is directly associated with glioblastoma development, progression, aggressiveness and patient survival and represents a novel potential therapeutic target to tackle this devastating pathology.

Deconstructing Sonic Hedgehog Medulloblastoma: Molecular Subtypes, Drivers, and Beyond

Medulloblastoma (MB) is a highly malignant cerebellar tumor predominantly diagnosed during childhood. Driven by pathogenic activation of sonic hedgehog (SHH) signaling, SHH subgroup MB (SHH-MB) accounts for nearly one-third of diagnoses. Extensive molecular analyses have identified biologically and clinically relevant intertumoral heterogeneity among SHH-MB tumors, prompting the recognition of novel subtypes. Beyond germline and somatic mutations promoting constitutive SHH signaling, driver alterations affect a multitude of pathways and molecular processes, including TP53 signaling, chromatin modulation, and post-transcriptional gene regulation. Here, we review recent advances in the underpinnings of SHH-MB in the context of molecular subtypes, clarify novel somatic and germline drivers, highlight cellular origins and developmental hierarchies, and describe the composition of the tumor microenvironment and its putative role in tumorigenesis.

Dietary Intervention Modulates the Expression of Splicing Machinery in Cardiovascular Patients at High Risk of Type 2 Diabetes Development: From the CORDIOPREV Study

Type-2 diabetes mellitus (T2DM) has become a major health problem worldwide. T2DM risk can be reduced with healthy dietary interventions, but the precise molecular underpinnings behind this association are still incompletely understood. We recently discovered that the expression profile of the splicing machinery is associated with the risk of T2DM development. Thus, the aim of this work was to evaluate the influence of 3-year dietary intervention in the expression pattern of the splicing machinery components in peripheral blood mononuclear cells (PBMCs) from patients within the CORDIOPREV study. Expression of splicing machinery components was determined in PBMCs, at baseline and after 3 years of follow-up, from all patients who developed T2DM (Incident-T2DM, n = 107) and 108 randomly selected non-T2DM subjects, who were randomly enrolled in two healthy dietary patterns (Mediterranean or low-fat diets). Dietary intervention modulated the expression of key splicing machinery components (i.e., up-regulation of SPFQ/RMB45/RNU6, etc., down-regulation of RNU2/SRSF6) after three years, independently of the type of healthy diet. Some of these changes (SPFQ/RMB45/SRSF6) were associated with key clinical features and were differentially induced in Incident-T2DM patients and non-T2DM subjects. This study reveals that splicing machinery can be modulated by long-term dietary intervention, and could become a valuable tool to screen the progression of T2DM.

Splicing factor SF3B1 promotes endometrial cancer progression via regulating KSR2 RNA maturation

Although endometrial cancer is the most common cancer of the female reproductive tract, we have little understanding of what controls endometrial cancer beyond the transcriptional effects of steroid hormones such as estrogen. As a result, we have limited therapeutic options for the ~62,000 women diagnosed with endometrial cancer each year in the United States. Here, in an attempt to identify new prognostic and therapeutic targets, we focused on a new area for this cancer—alternative mRNA splicing—and investigated whether splicing factor, SF3B1, plays an important role in endometrial cancer pathogenesis. Using a tissue microarray, we found that human endometrial tumors expressed more SF3B1 protein than non-cancerous tissues. Furthermore, SF3B1 knockdown reduced in vitro proliferation, migration, and invasion of the endometrial cancer cell lines Ishikawa and AN3CA. Similarly, the SF3B1 inhibitor, Pladienolide-B (PLAD-B), reduced the Ishikawa and AN3CA cell proliferation and invasion in vitro. Moreover, PLAD-B reduced tumor growth in an orthotopic endometrial cancer mouse model. Using RNA-Seq approach, we identified ~2000 differentially expressed genes (DEGs) with SF3B1 knockdown in endometrial cancer cells. Additionally, alternative splicing (AS) events analysis revealed that SF3B1 depletion led to alteration in multiple categories of AS events including alternative exon skipping (ES), transcript start site usage (TSS), and transcript termination site (TTS) usage. Subsequently, bioinformatics analysis showed KSR2 as a potential candidate for SF3B1-mediated functions in endometrial cancer. Specifically, loss of SF3B1 led to decrease in KSR2 expression, owing to reduced maturation of KSR2 pre-mRNA to a mature RNA. Importantly, we found rescuing the KSR2 expression with SF3B1 knockdown partially restored the cell growth of endometrial cancer cells. Taken together, our data suggest that SF3B1 plays a crucial oncogenic role in the tumorigenesis of endometrial cancer and hence may support the development of SF3B1 inhibitors to treat this disease.

The biological function and clinical significance of SF3B1 mutations in cancer

Spliceosome mutations have become the most interesting mutations detected in human cancer in recent years. The spliceosome, a large, dynamic multimegadalton small nuclear ribonucleoprotein composed of small nuclear RNAs associated with proteins, is responsible for removing introns from precursor mRNA (premRNA) and generating mature, spliced mRNAs. SF3B1 is the largest subunit of the spliceosome factor 3b (SF3B) complex, which is a core component of spliceosomes. Recurrent somatic mutations in SF3B1 have been detected in human cancers, including hematological malignancies and solid tumors, and indicated to be related to patient prognosis. This review summarizes the research progress of SF3B1 mutations in cancer, including SF3B1 mutations in the HEAT domain, the multiple roles and aberrant splicing events of SF3B1 mutations in the pathogenesis of tumors, and changes in mutated cancer cells regarding sensitivity to SF3B small-molecule inhibitors. In addition, the potential of SF3B1 or its mutations to serve as biomarkers or therapeutic targets in cancer is discussed. The accumulated knowledge about SF3B1 mutations in cancer provides critical insight into the integral role the SF3B1 protein plays in mRNA splicing and suggests new targets for anticancer therapy.

Unleashing the Diagnostic, Prognostic and Therapeutic Potential of the Neuronostatin/GPR107 System in Prostate Cancer

Certain components of the somatostatin-system play relevant roles in Prostate Cancer (PCa), whose most aggressive phenotype (Castration-Resistant-PCa (CRPC)) remains lethal nowadays. However, neuronostatin and the G protein-coupled receptor 107 (GPR107), two novel members of the somatostatin-system, have not been explored yet in PCa. Consequently, we investigated the pathophysiological role of NST/GPR107-system in PCa. GPR107 expression was analyzed in well-characterized PCa patient's cohorts, and functional/mechanistic assays were performed in response to GPR107-silencing and NST-treatment in PCa cells (androgen-dependent (AD: LNCaP) and androgen-independent (AI: 22Rv1/PC-3), which are cell models of hormone-sensitive and CRPC, respectively), and normal prostate cells (RWPE-1 cell-line). GPR107 was overexpressed in PCa and associated with key clinical parameters (e.g., advance stage of PCa, presence of vascular invasion and metastasis). Furthermore, GPR107-silencing inhibited proliferation/migration rates in AI-PCa-cells and altered key genes and oncogenic signaling-pathways involved in PCa aggressiveness (i.e., KI67/CDKN2D/MMP9/PRPF40A, SST5TMD4/AR-v7/In1-ghrelin/EZH2 splicing-variants and AKT-signaling). Interestingly, NST treatment inhibited proliferation/migration only in AI-PCa cells and evoked an identical molecular response than GPR107-silencing. Finally, NST decreased GPR107 expression exclusively in AI-PCa-cells, suggesting that part of the specific antitumor effects of NST could be mediated through a GPR107-downregulation. Altogether, NST/GPR107-system could represent a valuable diagnostic and prognostic tool and a promising novel therapeutic target for PCa and CRPC.

Targeting the spliceosome machinery: A new therapeutic axis in cancer?

Pre-mRNA splicing is the removal of introns and ligation of exons to form mature mRNAs, and it provides a critical mechanism by which eukaryotic cells can regulate their gene expression. Strikingly, more than 90% of protein-encoding transcripts are alternatively spliced, through exon inclusion/skipping, differential use of 5' or 3' alternative splice sites, intron retention or selection of an alternative promoter, thereby drastically increasing protein diversity. Splicing is altered in various pathological conditions, including cancers. In the last decade, high-throughput transcriptomic analyses have identified thousands of splice variants in cancers, which can distinguish between tumoral and normal tissues as well as identify tumor types, subtypes and clinical stages. These abnormal or aberrantly expressed splice variants, found in all cancer hallmarks, can result from mutations in splice sites, deregulated expression or even somatic mutations of components of the spliceosome machinery. Therefore, and based on these recent observations, a new anti-cancer strategy of targeting the spliceosome machinery with small molecules has emerged; however, the potential for these therapies is still a matter of great debate. Notably, more preclinical studies are needed to clarify which splicing patterns are mainly affected by these compounds, which cancer patients could be the most eligible for these treatments and whether using these spliceosome inhibitors alone or in combination with chemotherapies or targeted therapies would provide better therapeutic benefits. In this commentary, I will discuss all of these aspects.