FGFR1β is a driver isoform of FGFR1 alternative splicing in breast cancer cells

How Driver Oncogenes Shape and Are Shaped by Alternative Splicing Mechanisms in Tumors

The development of RNA sequencing methods has allowed us to study and better understand the landscape of aberrant pre-mRNA splicing in tumors. Altered splicing patterns are observed in many different tumors and affect all hallmarks of cancer: growth signal independence, avoidance of apoptosis, unlimited proliferation, invasiveness, angiogenesis, and metabolism. In this review, we focus on the interplay between driver oncogenes and alternative splicing in cancer. On one hand, oncogenic proteins-mutant p53, CMYC, KRAS, or PI3K-modify the alternative splicing landscape by regulating expression, phosphorylation, and interaction of splicing factors with spliceosome components. Some splicing factors-SRSF1 and hnRNPA1-are also driver oncogenes. At the same time, aberrant splicing activates key oncogenes and oncogenic pathways: p53 oncogenic isoforms, the RAS-RAF-MAPK pathway, the PI3K-mTOR pathway, the EGF and FGF receptor families, and SRSF1 splicing factor. The ultimate goal of cancer research is a better diagnosis and treatment of cancer patients. In the final part of this review, we discuss present therapeutic opportunities and possible directions of further studies aiming to design therapies targeting alternative splicing mechanisms in the context of driver oncogenes.

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.

The FGF/FGFR signalling mediated anti-cancer drug resistance and therapeutic intervention

ABSTRACT Fibroblast Growth Factor (FGF) ligands and their receptors are crucial factors driving chemoresistance in several malignancies, challenging the efficacy of currently available anti-cancer drugs. The Fibroblast growth factor/receptor (FGF/FGFR) signalling malfunctions in tumor cells, resulting in a range of molecular pathways that may impact its drug effectiveness. Deregulation of cell signalling is critical since it can enhance tumor growth and metastasis. Overexpression and mutation of FGF/FGFR induce regulatory changes in the signalling pathways. Chromosomal translocation facilitating FGFR fusion production aggravates drug resistance. Apoptosis is inhibited by FGFR-activated signalling pathways, reducing multiple anti-cancer medications' destructive impacts. Angiogenesis and epithelial-mesenchymal transition (EMT) are facilitated by FGFRs-dependent signalling, which correlates with drug resistance and enhances metastasis. Further, lysosome-mediated drug sequestration is another prominent method of resistance. Inhibition of FGF/FGFR by following a plethora of therapeutic approaches such as covalent and multitarget inhibitors, ligand traps, monoclonal antibodies, recombinant FGFs, combination therapy, and targeting lysosomes and micro RNAs would be helpful. As a result, FGF/FGFR suppression treatment options are evolving nowadays. To increase positive impacts, the processes underpinning the FGF/FGFR axis' role in developing drug resistance need to be clarified, emphasizing the need for more studies to develop novel therapeutic options to address this significant problem. Communicated by Ramaswamy H. Sarma.

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.

Fibroblast growth factor receptor signalling dysregulation and targeting in breast cancer

Fibroblast Growth Factor Receptor (FGFR) signalling plays a critical role in breast embryonal development, tissue homeostasis, tumorigenesis and metastasis. FGFR, its numerous FGF ligands and signalling partners are often dysregulated in breast cancer progression and are one of the causes of resistance to treatment in breast cancer. Furthermore, FGFR signalling on epithelial cells is affected by signals from the breast microenvironment, therefore increasing the possibility of breast developmental abnormalities or cancer progression. Increasing our understanding of the multi-layered roles of the complex family of FGFRs, their ligands FGFs and their regulatory partners may offer novel treatment strategies for breast cancer patients, as a single agent or rational co-target, which will be explored in depth in this review.

Biological Significance and Targeting of the FGFR Axis in Cancer

The pleiotropic effects of fibroblast growth factors (FGFs), the widespread expression of all seven signalling FGF receptors (FGFRs) throughout the body, and the dramatic phenotypes shown by many FGF/R knockout mice, highlight the diversity, complexity and functional importance of FGFR signalling. The FGF/R axis is critical during normal tissue development, homeostasis and repair. Therefore, it is not surprising that substantial evidence also pinpoints the involvement of aberrant FGFR signalling in disease, including tumourigenesis. FGFR aberrations in cancer include mutations, gene fusions, and amplifications as well as corrupted autocrine/paracrine loops. Indeed, many clinical trials on cancer are focusing on targeting the FGF/FGFR axis, using selective FGFR inhibitors, nonselective FGFR tyrosine kinase inhibitors, ligand traps, and monoclonal antibodies and some have already been approved for the treatment of cancer patients. The heterogeneous tumour microenvironment and complexity of FGFR signalling may be some of the factors responsible for the resistance or poor response to therapy with FGFR axis-directed therapeutic agents. In the present review we will focus on the structure and function of FGF(R)s, their common irregularities in cancer and the therapeutic value of targeting their function in cancer.

Fibroblast Growth Factor Receptor 1 Drives the Metastatic Progression of Prostate Cancer

BACKGROUND

No curative therapy is currently available for metastatic prostate cancer (PCa). The diverse mechanisms of progression include fibroblast growth factor (FGF) axis activation.

OBJECTIVE

To investigate the molecular and clinical implications of fibroblast growth factor receptor 1 (FGFR1) and its isoforms (α/β) in the pathogenesis of PCa bone metastases.

DESIGN, SETTING, AND PARTICIPANTS

In silico, in vitro, and in vivo preclinical approaches were used. RNA-sequencing and immunohistochemical (IHC) studies in human samples were conducted.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

In mice, bone metastases (chi-square/Fisher's test) and survival (Mantel-Cox) were assessed. In human samples, FGFR1 and ladinin 1 (LAD1) analysis associated with PCa progression were evaluated (IHC studies, Fisher's test).

RESULTS AND LIMITATIONS

FGFR1 isoform expression varied among PCa subtypes. Intracardiac injection of mice with FGFR1-expressing PC3 cells reduced mouse survival (α, p < 0.0001; β, p = 0.032) and increased the incidence of bone metastases (α, p < 0.0001; β, p = 0.02). Accordingly, IHC studies of human castration-resistant PCa (CRPC) bone metastases revealed significant enrichment of FGFR1 expression compared with treatment-naïve, nonmetastatic primary tumors (p = 0.0007). Expression of anchoring filament protein LAD1 increased in FGFR1-expressing PC3 cells and was enriched in human CRPC bone metastases (p = 0.005).

CONCLUSIONS

FGFR1 expression induces bone metastases experimentally and is significantly enriched in human CRPC bone metastases, supporting its prometastatic effect in PCa. LAD1 expression, found in the prometastatic PCa cells expressing FGFR1, was also enriched in CRPC bone metastases. Our studies support and provide a roadmap for the development of FGFR blockade for advanced PCa.

PATIENT SUMMARY

We studied the role of fibroblast growth factor receptor 1 (FGFR1) in prostate cancer (PCa) progression. We found that PCa cells with high FGFR1 expression increase metastases and that FGFR1 expression is increased in human PCa bone metastases, and identified genes that could participate in the metastases induced by FGFR1. These studies will help pinpoint PCa patients who use fibroblast growth factor to progress and will benefit by the inhibition of this pathway.

CtIP -mediated alternative mRNA splicing finetunes the DNA damage response

In order to survive to the exposure of DNA damaging agents, cells activate a complex response that coordinates the cellular metabolism, cell cycle progression and DNA repair. Among many other events, recent evidence has described global changes in mRNA splicing in cells treated with genotoxic agents. Here, we explore further this DNA damage-dependent alternative splicing. Indeed, we show that both the splicing factor SF3B2 and the repair protein CtIP contribute to the global pattern of splicing both in cells treated or not to DNA damaging agents. Additionally, we focus on a specific DNA damage- and CtIP-dependent alternative splicing event of the helicase PIF1 and explore its relevance for the survival of cells upon exposure to ionizing radiation. Indeed, we described how the nuclear, active form of PIF1 is substituted by a splicing variant, named vPIF1, in a fashion that requires both the presence of DNA damage and CtIP. Interestingly, timely expression of vPIF1 is required for optimal survival to exposure to DNA damaging agents, but early expression of this isoform delays early events of the DNA damage response. On the contrary, expression of the full length PIF1 facilitates those early events, but increases the sensitivity to DNA damaging agents if the expression is maintained long-term.

Global proteomic analysis of insulin receptor interactors in glomerular podocytes

Background: Insulin signalling contributes to diverse cellular activities including protein synthesis, proliferation and cell survival. Insulin resistance describes the inability of cells to activate the insulin signalling pathway effectively; leading to pathological effects in multiple organ systems including the kidney. In diabetic kidney disease, there is progressive glomerular dysfunction and recent studies have demonstrated that the kidney podocyte is a direct target for insulin action. In this study we defined the literature-based insulin receptor (INSR) interactome and utilised an unbiased proteomic approach to examine INSR interactors in podocytes. Methods: Human podocytes expressing the INSR were characterised under basal and insulin resistant conditions. The INSR was isolated by whole cell immunoprecipitation following a time course stimulation of 2, 7, and 15 minutes with of 100nM insulin. The resulting INSR complexes were analysed by label-free mass spectrometry (MS) to detect protein interactors. Results: We identified 27 known, direct INSR interactors in addition to novel interactors including doublecortin domain-containing protein 2 (DCDC2). The interaction of DCDC2 with the INSR was confirmed by immunoprecipitation and immunofluorescence, and under insulin resistant conditions, DCDC2 had increased association with the INSR. siRNA knockdown of DCDC2 in podocytes resulted in cell morphological change and altered INSR localisation. Conclusion: This study provides insight into the complexity of INSR interactors in podocytes and highlights DCDC2 as a novel INSR binding protein. Involvement of this novel interactor in insulin signalling and podocyte biology may explain how insulin resistance alters morphology and integrity of the glomerular filtration barrier.

Application of Genome-Wide Association Studies in Coronary Artery Disease

Coronary artery disease (CAD) is a complex disease caused by the combination of environmental and genetic factors. It is one of the leading causes of death and disability in the world. Much research has been focussed on CAD genetic mechanism. In recent years, genome-wide association study (GWAS) has developed rapidly around the world. Medical researchers around the world have successfully discovered a series of CAD genetic susceptibility genes or susceptible loci using medical research strategies, leading CAD research toward a new stage. This paper briefly summarizes the important progress made by GWAS for CAD in the world in recent years, and then analyzes the challenges faced by GWAS at this stage and the development trend of future research, to promote the transformation of genetic research results into clinical practice and provide guidance for further exploration of the genetic mechanism of CAD.

Roles of PTBP1 in alternative splicing, glycolysis, and oncogensis

Polypyrimidine tract-binding protein 1 (PTBP1) plays an essential role in splicing and is expressed in almost all cell types in humans, unlike the other proteins of the PTBP family. PTBP1 mediates several cellular processes in certain types of cells, including the growth and differentiation of neuronal cells and activation of immune cells. Its function is regulated by various molecules, including microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and RNA-binding proteins. PTBP1 plays roles in various diseases, particularly in some cancers, including colorectal cancer, renal cell cancer, breast cancer, and glioma. In cancers, it acts mainly as a regulator of glycolysis, apoptosis, proliferation, tumorigenesis, invasion, and migration. The role of PTBP1 in cancer has become a popular research topic in recent years, and this research has contributed greatly to the formulation of a useful therapeutic strategy for cancer. In this review, we summarize recent findings related to PTBP1 and discuss how it regulates the development of cancer cells.

Alternative Splicing in Angiogenesis

Alternative splicing of pre-mRNA allows the generation of multiple splice isoforms from a given gene, which can have distinct functions. In fact, splice isoforms can have opposing functions and there are many instances whereby a splice isoform acts as an inhibitor of canonical isoform function, thereby adding an additional layer of regulation to important processes. Angiogenesis is an important process that is governed by alternative splicing mechanisms. This review focuses on the alternative spliced isoforms of key genes that are involved in the angiogenesis process; VEGF-A, VEGFR1, VEGFR2, NRP-1, FGFRs, Vasohibin-1, Vasohibin-2, HIF-1α, Angiopoietin-1 and Angiopoietin-2.