RESUMEN
The RAVER1 protein serves as a co-factor in guiding the polypyrimidine tract-binding protein (PTBP)-dependent control of alternative splicing (AS). Whether RAVER1 solely acts in concert with PTBPs and how it affects cancer cell fate remained elusive. Here, we provide the first comprehensive investigation of RAVER1-controlled AS in cancer cell models. This reveals a pro-oncogenic role of RAVER1 in modulating tumor growth and epithelial-mesenchymal-transition (EMT). Splicing analyses and protein-association studies indicate that RAVER1 guides AS in association with other splicing regulators, including PTBPs and SRSFs. In cancer cells, one major function of RAVER1 is the stimulation of proliferation and restriction of apoptosis. This involves the modulation of AS events within the miR/RISC pathway. Disturbance of RAVER1 impairs miR/RISC activity resulting in severely deregulated gene expression, which promotes lethal TGFB-driven EMT. Among others, RAVER1-modulated splicing events affect the insertion of protein interaction modules in factors guiding miR/RISC-dependent gene silencing. Most prominently, in all three human TNRC6 proteins, RAVER1 controls AS of GW-enriched motifs, which are essential for AGO2-binding and the formation of active miR/RISC complexes. We propose, that RAVER1 is a key modulator of AS events in the miR/RISC pathway ensuring proper abundance and composition of miR/RISC effectors. This ensures balanced expression of TGFB signaling effectors and limits TGFB induced lethal EMT.
Asunto(s)
Empalme Alternativo , Transición Epitelial-Mesenquimal , MicroARNs , Transición Epitelial-Mesenquimal/genética , Humanos , MicroARNs/metabolismo , MicroARNs/genética , Línea Celular Tumoral , Proteína de Unión al Tracto de Polipirimidina/metabolismo , Proteína de Unión al Tracto de Polipirimidina/genética , Proteínas de Unión al ARN/metabolismo , Proteínas de Unión al ARN/genética , Factores de Empalme Serina-Arginina/metabolismo , Factores de Empalme Serina-Arginina/genética , Regulación Neoplásica de la Expresión Génica , Proliferación Celular/genética , Apoptosis/genética , Factor de Crecimiento Transformador beta/metabolismo , AnimalesRESUMEN
The stem cell marker Musashi1 (MSI1) is highly expressed during neurogenesis and in glioblastoma (GBM). MSI1 promotes self-renewal and impairs differentiation in cancer and non-malignant progenitor cells. However, a comprehensive understanding of its role in promoting GBM-driving networks remains to be deciphered. We demonstrate that MSI1 is highly expressed in GBM recurrences, an oncologist's major defiance. For the first time, we provide evidence that MSI1 promotes the expression of stem cell markers like CD44, co-expressed with MSI1 within recurrence-promoting cells at the migrating front of primary GBM samples. With GBM cell models of pediatric and adult origin, including isolated primary tumorspheres, we show that MSI1 promotes stem cell-like characteristics. Importantly, it impairs CD44 downregulation in a 3'UTR- and miRNA-dependent manner by controlling mRNA turnover. This regulation is disturbed by the previously reported MSI1 inhibitor luteolin, providing further evidence for a therapeutic target potential of MSI1 in GBM treatment.
RESUMEN
The IGF2 mRNA-binding protein 1 (IGF2BP1) is a non-catalytic post-transcriptional enhancer of tumor growth upregulated and associated with adverse prognosis in solid cancers. However, conserved effector pathway(s) and the feasibility of targeting IGF2BP1 in cancer remained elusive. We reveal that IGF2BP1 is a post-transcriptional enhancer of the E2F-driven hallmark in solid cancers. IGF2BP1 promotes G1/S cell cycle transition by stabilizing mRNAs encoding positive regulators of this checkpoint like E2F1. This IGF2BP1-driven shortening of the G1 cell cycle phase relies on 3'UTR-, miRNA- and m6A-dependent regulation and suggests enhancement of cell cycle progression by m6A-modifications across cancers. In addition to E2F transcription factors, IGF2BP1 also stabilizes E2F-driven transcripts directly indicating post-transcriptional 'super'-enhancer role of the protein in E2F-driven gene expression in cancer. The small molecule BTYNB disrupts this enhancer function by impairing IGF2BP1-RNA association. Consistently, BTYNB interferes with E2F-driven gene expression and tumor growth in experimental mouse tumor models.
Asunto(s)
Factores de Transcripción E2F/genética , Neoplasias/genética , Proteínas de Unión al ARN/genética , Regiones no Traducidas 3'/genética , Animales , Línea Celular Tumoral , Factor de Transcripción E2F1/genética , Regulación Neoplásica de la Expresión Génica/genética , Humanos , Ratones , Neoplasias/patología , Proteínas de Unión al ARN/efectos de los fármacos , Bibliotecas de Moléculas Pequeñas/farmacologíaRESUMEN
Naturally occurring circular RNAs efficiently impair miRNA functions. Synthetic circular RNAs may thus serve as potent agents for miRNA inhibition. Their therapeutic effect critically relies on (i) the identification of optimal miRNA targets, (ii) the optimization of decoy structures and (iii) the development of efficient formulations for their use as drugs. In this study, we extensively explored the functional relevance of miR-21-5p in cancer cells. Analyses of cancer transcriptomes reveal that miR-21-5p is the by far most abundant miRNA in human cancers. Deletion of the MIR21 locus in cancer-derived cells identifies several direct and indirect miR-21-5p targets, including major tumor suppressors with prognostic value across cancers. To impair miR-21-5p activities, we evaluate synthetic, circular RNA decoys containing four repetitive binding elements. In cancer cells, these decoys efficiently elevate tumor suppressor expression and impair tumor cell vitality. For their in vivo delivery, we for the first time evaluate the formulation of decoys in polyethylenimine (PEI)-based nanoparticles. We demonstrate that PEI/decoy nanoparticles lead to a significant inhibition of tumor growth in a lung adenocarcinoma xenograft mouse model via the upregulation of tumor suppressor expression. These findings introduce nanoparticle-delivered circular miRNA decoys as a powerful potential therapeutic strategy in cancer treatment.