The RNA-binding protein Musashi 1 stabilizes the oncotachykinin 1 mRNA in breast cancer cells to promote cell growth

RNA-binding MSI proteins and their related cancers: A medicinal chemistry perspective

Musashi1 and Musashi2 are RNA-binding proteins originally found in drosophila, in which they play a crucial developmental role. These proteins are pivotal in the maintenance and differentiation of stem cells in other organisms. Research has confirmed that the Musashi proteins are highly involved in cell signal-transduction pathways such as Notch and TGF-β. These signaling pathways are related to the induction and development of cancers, such as breast cancer, leukemia, hepatoma and liver cancer. In this review we focus on how Musashi proteins interact with molecules in different signaling pathways in various cancers and how they affect the physiological functions of these pathways. We further illustrate the status quo of Musashi proteins-targeted therapies and predict the target RNA regions that Musashi proteins interact with, in the hope of exploring the prospect of the design of Musashi protein-targeted medicines.

Short C-terminal Musashi-1 proteins regulate pluripotency states in embryonic stem cells

The RNA-binding protein Musashi-1 (MSI1) regulates the proliferation and differentiation of adult stem cells. However, its role in embryonic stem cells (ESCs) and early embryonic development remains poorly understood. Here, we report the presence of short C-terminal MSI1 (MSI1-C) proteins in early mouse embryos and mouse ESCs, but not in human ESCs, under conventional culture conditions. In mouse embryos and mESCs, deletion of MSI1-C together with full-length MSI1 causes early embryonic developmental arrest and pluripotency dissolution. MSI1-C is induced upon naive induction and facilitates hESC naive pluripotency acquisition, elevating the pluripotency of primed hESCs toward a formative-like state. MSI1-C proteins are nuclear localized and bind to RNAs involved in DNA-damage repair (including MLH1, BRCA1, and MSH2), conferring on hESCs better survival in human-mouse interspecies cell competition and prolonged ability to form blastoids. This study identifies MSI1-C as an essential regulator in ESC pluripotency states and early embryonic development.

The Musashi RNA-binding proteins in female cancers: insights on molecular mechanisms and therapeutic relevance

RNA-binding proteins have increasingly been identified as important regulators of gene expression given their ability to bind distinct RNA sequences and regulate their fate. Mounting evidence suggests that RNA-binding proteins are involved in the onset and progression of multiple malignancies, prompting increasing interest in their potential for therapeutic intervention.The Musashi RNA binding proteins Musashi-1 and Musashi-2 were initially identified as developmental factors of the nervous system but have more recently been found to be ubiquitously expressed in physiological tissues and may be involved in pathological cell behavior. Both proteins are increasingly investigated in cancers given dysregulation in multiple tumor entities, including in female malignancies. Recent data suggest that the Musashi proteins serve as cancer stem cell markers as they contribute to cancer cell proliferation and therapy resistance, prompting efforts to identify mechanisms to target them. However, as the picture remains incomplete, continuous efforts to elucidate their role in different signaling pathways remain ongoing.In this review, we focus on the roles of Musashi proteins in tumors of the female - breast, endometrial, ovarian and cervical cancer - as we aim to summarize current knowledge and discuss future perspectives.

Increased expression of musashi 1 on breast cancer cells has implication to understand dormancy and survival in bone marrow

Breast cancer (BC) stem cells (CSCs) resist treatment and can exist as dormant cells in tissues such as the bone marrow (BM). Years before clinical diagnosis, BC cells (BCCs) could migrate from the primary site where the BM niche cells facilitate dedifferentiation into CSCs. Additionally, dedifferentiation could occur by cell autonomous methods. Here we studied the role of Msi 1, a RNA-binding protein, Musashi I (Msi 1). We also analyzed its relationship with the T-cell inhibitory molecule programmed death-ligand 1 (PD-L1) in CSCs. PD-L1 is an immune checkpoint that is a target in immune therapy for cancers. Msi 1 can support BCC growth through stabilization of oncogenic transcripts and modulation of stem cell-related gene expression. We reported on a role for Msi 1 to maintain CSCs. This seemed to occur by the differentiation of CSCs to more matured BCCs. This correlated with increased transition from cycling quiescence and reduced expression of stem cell-linked genes. CSCs co-expressed Msi 1 and PD-L1. Msi 1 knockdown led to a significant decrease in CSCs with undetectable PD-L1. This study has implications for Msi 1 as a therapeutic target, in combination with immune checkpoint inhibitor. Such treatment could also prevent dedifferentiation of breast cancer to CSCs, and to reverse tumor dormancy. The proposed combined treatment might be appropriate for other solid tumors.

RNA-binding protein PUM2 promotes T-cell acute lymphoblastic leukemia via competitively binding to RBM5 3'UTR with miR-28-5p

OBJECTIVE

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy, and T-ALL patients are prone to early disease relapse and suffer from poor outcomes. The crucial function of RNA-binding proteins (RBPs) has been reported in the progression of cancers by regulating the expression of transcripts. This study aimed to reveal the role and molecular regulatory mechanism of RBP Pumilio2 (PUM2) in T-ALL.

METHODS

The expression of genes was detected by reverse transcription quantitative polymerase chain reaction (RT-qPCR) and western blot analysis. The viability, proliferation, and apoptosis of T-ALL cells were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, 5-ethynyl-2'-deoxyuridine, and flow cytometry analysis. Luciferase reporter, RNA pulldown, and RNA immunoprecipitation assays were performed to confirm the binding of PUM2 to RBM5. The combination between RNA-binding motif protein 5 (RBM5) and microRNA (miR)-28-5p was validated using luciferase reporter assay.

RESULTS

Our data revealed that PUM2 was highly expressed in T-ALL blood samples and cell lines. PUM2 knockdown suppressed the proliferation but accelerated the apoptosis of T-ALL cells in vitro. Additionally, RBM5 exhibited a low expression level in T-ALL samples and cells. PUM2 negatively regulated RBM5 via targeting its 3'untranslated region (3'UTR). Moreover, PUM2 competitively bound to RBM5 3'UTR with miR-28-5p. Rescue experiments showed that RBM5 knockdown reversed the anti-tumor effects mediated by PUM2 knockdown in T-ALL cells.

CONCLUSION

PUM2 plays as a novel oncogenic RBP in T-ALL by competitively binding to RBM5 mRNA with miR-28-5p.

Research progress on RNA−binding proteins in breast cancer

Breast cancer is the most common malignancy in women and has a high incidence rate and mortality. Abnormal regulation of gene expression plays an important role in breast cancer occurrence and development. RNA-binding proteins (RBPs) are one kind of the key regulators for gene expression. By interacting with RNA, RBPs are widely involved in RNA cutting, transport, editing, intracellular localization, and translation regulation. RBPs are important during breast cancer occurrence and progression by engaging in many aspects, like proliferation, migration, invasion, and stemness. Therefore, comprehensively understanding the role of RBPs in breast cancer progression can facilitate early diagnosis, timely treatment, and long-term survival and quality of life of breast cancer patients.

The Emerging Role of Stress Granules in Hepatocellular Carcinoma

Stress granules (SGs) are small membrane-free cytosolic liquid-phase ordered entities in which mRNAs are protected and translationally silenced during cellular adaptation to harmful conditions (e.g., hypoxia, oxidative stress). This function is achieved by structural and functional SG components such as scaffold proteins and RNA-binding proteins controlling the fate of mRNAs. Increasing evidence indicates that the capacity of cells to assemble/disassemble functional SGs may significantly impact the onset and the development of metabolic and inflammatory diseases, as well as cancers. In the liver, the abnormal expression of SG components and formation of SG occur with chronic liver diseases, hepatocellular carcinoma (HCC), and selective hepatic resistance to anti-cancer drugs. Although, the role of SG in these diseases is still debated, the modulation of SG assembly/disassembly or targeting the expression/activity of specific SG components may represent appealing strategies to treat hepatic disorders and potentially cancer. In this review, we discuss our current knowledge about pathophysiological functions of SGs in HCC as well as available molecular tools and drugs capable of modulating SG formation and functions for therapeutic purposes.

Pumilio RNA Binding Family Member 2 Promotes the Proliferation and Metastasis of Lung Cancer Cells by Regulating Ca2+ Signaling Pathway via Targeting C-X-C Chemokine Receptor Type 4

The aim of the present study was to investigate the mechanism by which pumilio RNA binding family member 2 (PUM2), an RNA-binding protein (RBP) of C-X-C chemokine receptor type 4 (CXCR4), exerts its effects on the development of lung cancer. RT-qPCR and western blot analysis were utilized to measure the expression of PUM2 in several lung cancer cell lines. Cell Counting Kit-8 (CCK-8), colony formation assay, transwell- and wound healing assays were employed to determine the proliferation, invasion and migration of NCI-H520 cells, respectively. Next, the expression of CXCR4 was measured using western blot analysis, and the combination between PUM2 and CXCR4 was verified by RNA immunoprecipitation (RIP) assay and RNA pull down assay. Finally, whether the expression of PUM2 can affect the Ca2+ signaling pathway was confirmed by western blot assay. Results revealed that the expression level of PUM2 was notably upregulated in lung cancer cells, and knockdown of PUM2 significantly inhibited the proliferation, invasion and migration of NCI-H520 cells. PUM2 was confirmed to be the RBP of CXCR4, and PUM2 knockdown decreased the expression of CXCR4. In addition, PUM2 silencing inhibited the phosphorylation of CaMKII, ERK, and MEK. Taken together, these findings demonstrated that PUM2 could promote the proliferation and metastasis of lung cancer cells by regulating Ca2+ signaling pathway via targeting CXCR4, which may provide a novel insight for the future treatment of lung cancer.

Msi1 promotes breast cancer metastasis by regulating invadopodia-mediated extracellular matrix degradation via the Timp3-Mmp9 pathway

Metastasis is the main cause of death in breast cancer patients. The initial step of metastasis is invadopodia-mediated extracellular matrix (ECM) degradation, which enables local breast tumor cells to invade surrounding tissues. However, the molecular mechanism underlying invadopodia-mediated metastasis remains largely unknown. Here we found that the RNA-binding protein Musashi1 (Msi1) exhibited elevated expression in invasive breast tumors and promoted lung metastasis of mammary cancer cells. Suppression of Msi1 reduced invadopodia formation in mammary cancer cells. Furthermore, Msi1 deficiency decreased the expression and activity of Mmp9, an important enzyme in ECM degradation. Mechanistically, Msi1 directly suppressed Timp3, an endogenous inhibitor of Mmp9. In clinical breast cancer specimens, TIMP3 and MSI1 levels were significantly inversely correlated both in normal breast tissue and breast cancer tissues and associated with overall survival in breast cancer patients. Taken together, our findings demonstrate that the MSI1-TIMP3-MMP9 cascade is critical for invadopodia-mediated onset of metastasis in breast cancer, providing novel insights into a promising therapeutic strategy for breast cancer metastasis.

Musashi-1 promotes cancer stem cell properties of glioblastoma cells via upregulation of YTHDF1

Background

Glioblastoma (GBM) is the most lethal brain tumor characterized by high morbidity and limited treatment options. Tumor malignancy is usually associated with the epigenetic marks, which coordinate gene expression to ascertain relevant phenotypes. One of such marks is m6A modification of RNA, whose functional effects are dependent on the YTH family m6A reader proteins.

Methods and results

In this study, we investigated the expression of five YTH family proteins in different GBM microarray datasets from the Oncomine database, and identified YTHDF1 as the most highly overexpressed member of this family in GBM. By performing the knockdown of YTHDF1 in a GBM cell line, we found that it positively regulates proliferation, chemoresistance and cancer stem cell-like properties. Musashi-1 (MSI1) is a postranscriptional gene expression regulator associated with high oncogenicity in GBM. By knocking down and overexpressing MSI1, we found that it positively regulates YTHDF1 expression. The inhibitory effects imposed on the processes of proliferation and migration by YTHDF1 knockdown were shown to be partially rescued by concomitant overexpression of MSI1. MSI1 and YTHDF1 were shown to be positively correlated in clinical glioma samples, and their concomitant upregulation was associated with decreased survival of glioma patients. We identified the direct regulation of YTHDF1 by MSI1.

Conclusions

Given the fact that both proteins are master regulators of gene expression, and both of them are unfavorable factors in GBM, we suggest that in any future studies aimed to uncover the prognostic value and therapy potential, these two proteins should be considered together.

Constitutive Musashi1 expression impairs mouse postnatal development and intestinal homeostasis

Evolutionarily conserved RNA-binding protein Musashi1 (Msi1) can regulate developmentally relevant genes. Here we report the generation and characterization of a mouse model that allows inducible Msi1 overexpression in a temporal and tissue-specific manner. We show that ubiquitous Msi1 induction in ∼5-wk-old mice delays overall growth, alters organ-to-body proportions, and causes premature death. Msi1-overexpressing mice had shortened intestines, diminished intestinal epithelial cell (IEC) proliferation, and decreased growth of small intestine villi and colon crypts. Although Lgr5-positive intestinal stem cell numbers remained constant in Msi1-overexpressing tissue, an observed reduction in Cdc20 expression provided a potential mechanism underlying the intestinal growth defects. We further demonstrated that Msi1 overexpression affects IEC differentiation in a region-specific manner, with ileum tissue being influenced the most. Ilea of mutant mice displayed increased expression of enterocyte markers, but reduced expression of the goblet cell marker Mucin2 and fewer Paneth cells. A higher hairy and enhancer of split 1:mouse atonal homolog 1 ratio in ilea from Msi1-overexpressing mice implicated Notch signaling in inducing enterocyte differentiation. Together, this work implicates Msi1 in mouse postnatal development of multiple organs, with Notch signaling alterations contributing to intestinal defects. This new mouse model will be a useful tool to further elucidate the role of Msi1 in other tissue settings.

Stress granules in colorectal cancer: Current knowledge and potential therapeutic applications

Stress granules (SGs) represent important non-membrane cytoplasmic compartments, involved in cellular adaptation to various stressful conditions (e.g., hypoxia, nutrient deprivation, oxidative stress). These granules contain several scaffold proteins and RNA-binding proteins, which bind to mRNAs and keep them translationally silent while protecting them from harmful conditions. Although the role of SGs in cancer development is still poorly known and vary between cancer types, increasing evidence indicate that the expression and/or the activity of several key SGs components are deregulated in colorectal tumors but also in pre-neoplastic conditions (e.g., inflammatory bowel disease), thus suggesting a potential role in the onset of colorectal cancer (CRC). It is therefore believed that SGs formation importantly contributes to various steps of colorectal tumorigenesis but also in chemoresistance. As CRC is the third most frequent cancer and one of the leading causes of cancer mortality worldwide, development of new therapeutic targets is needed to offset the development of chemoresistance and formation of metastasis. Abolishing SGs assembly may therefore represent an appealing therapeutic strategy to re-sensitize colon cancer cells to anti-cancer chemotherapies. In this review, we summarize the current knowledge on SGs in colorectal cancer and the potential therapeutic strategies that could be employed to target them.

Intracellular functions of RNA-binding protein, Musashi1, in stem and cancer cells

RNA-binding protein, musashi1 (MSI1), is a main protein in asymmetric cell division of the sensory organ precursor cells, whereas its expression is reported to be upregulated in cancers. This protein is a critical element in proliferation of stem and cancer stem cells, which acts through Wnt and Notch signaling pathways. Moreover, MSI1 modulates malignancy and chemoresistance of lung cancer cells via activating the Akt signaling. Due to the main role of MSI1 in metastasis and cancer development, MSI1 would be an appropriate candidate for cancer therapy. Downregulation of MSI1 inhibits proliferation of cancer stem cells and reduces the growth of solid tumors in several cancers. On the other hand, MSI1 expression is regulated by microRNAs in such a way that several different tumor suppressor miRNAs negatively regulate oncogenic MSI1 and inhibit migration and tumor metastasis. The aim of this review is summarizing the role of MSI1 in stem cell proliferation and cancer promotion.

RNA-Binding Proteins in Acute Leukemias

Acute leukemias are genetic diseases caused by translocations or mutations, which dysregulate hematopoiesis towards malignant transformation. However, the molecular mode of action is highly versatile and ranges from direct transcriptional to post-transcriptional control, which includes RNA-binding proteins (RBPs) as crucial regulators of cell fate. RBPs coordinate RNA dynamics, including subcellular localization, translational efficiency and metabolism, by binding to their target messenger RNAs (mRNAs), thereby controlling the expression of the encoded proteins. In view of the growing interest in these regulators, this review summarizes recent research regarding the most influential RBPs relevant in acute leukemias in particular. The reported RBPs, either dysregulated or as components of fusion proteins, are described with respect to their functional domains, the pathways they affect, and clinical aspects associated with their dysregulation or altered functions.

New insight into the role of substance P/neurokinin-1 receptor system in breast cancer progression and its crosstalk with microRNAs

The neuropeptide substance P (SP) triggers a variety of tumor-promoting signaling pathways through the activation of neurokinin-1receptor (NK1R), a class of neurokinin G protein-coupled receptors superfamily. Recent researches in our and other laboratories have shown the overexpression of both SP and NK1R in breast cancer (BC) patients. SP/NK1R signaling is strongly implicated in the pathogenesis of BC through affecting cell proliferation, migration, metastasis, angiogenesis, and resistance. Therefore, SP/NK1R signaling responses must be rigorously regulated; otherwise, they would contribute to a more aggressive BC phenotype. Recently, microRNAs (miRNAs) as a specific class of epigenetic regulators have been shown to regulate NK1R and thus, controlling SP/NK1R signaling responses in BC. This review summarizes the current knowledge of the role of SP/NK1R signaling and its therapeutic potentials in BC. We also provide an overview regarding the effects of miRNA-mediated NK1R regulatory mechanisms in controlling BC tumorigenesis to gain a clearer view and thus better management of cancer.

RNA binding protein PUM2 promotes the stemness of breast cancer cells via competitively binding to neuropilin-1 (NRP-1) mRNA with miR-376a

Others and ours studies have established the promoting roles of NRP-1 (neuropilin-1) in breast cancer, however, the underlying mechanisms by which NRP-1 is regulated are still confused. Here, bioinformatics analysis indicated that RNA binding protein PUM2 could bind to NRP-1 mRNA. Clinical samples showed that PUM2 expression was significantly increased in breast cancer tissues, negatively correlated with the overall survival and relapse-free survival of breast cancer patients, and positively correlated with NRP-1 expression. Meanwhile, PUM2 expression was remarkably increased in non-adherent spheroids. in vitro experiments demonstrated that PUM2 knockdown attenuated the stemness of breast cancer cells, evident by the decrease of spheroid formation capacity, ALDH1 activity and stemness marker expression. Mechanistically, RNA immunoprecipitation (RIP) and luciferase reporter analysis indicated that PUM2 competitively bound to NRP 3'UTR with miR-376a, which had been previously confirmed by us to suppress the stemness of breast cancer cells, and increased NRP-1 mRNA stability and expression. Furthermore, ectopic expression of NRP-1 or miR-376a knockdown rescued the inhibitory effects of NRP-1 knockdown on the stemness of breast cancer cells. Thus, our results suggest that PUM2 could facilitate the stemness of breast cancer cells by competitively binding to NRP-1 3'UTR with miR-376a.

RNA-binding protein PUM2 suppresses osteosarcoma progression via partly and competitively binding to STARD13 3'UTR with miRNAs

OBJECTIVES

This work aims to reveal the roles and related mechanisms of RNA binding protein PUM2 in osteosarcoma progression.

MATERIALS AND METHODS

Transcriptome analysis based on RNA sequencing data, real-time quantitative PCR (RT-qPCR), and western blot analysis were used to detect the expression of RBPs and miRNAs in OS and normal adjacent tissues, and the correlation between them in OS tissues. RT-qPCR, western blot, cell viability, transwell migration, tumour spheres formation and in vivo tumour formation assays were used to examine the effects of RBP PUM2 on OS progression. Additionally, RNA immunoprecipitation (RIP) assay combined with RNA sequencing was performed to determine the binding site of RBP PUM2 on STARD13 3'UTR. Luciferase reporter and RIP assays were used to confirm the binding of miRNAs or PUM2 on STARD13 3'UTR.

RESULTS

PUM2 and STARD13 expression was significantly decreased in OS tissues, and positively correlated. Overexpression of PUM2 or STARD13 3'UTR inhibited OS cells proliferation, migration, and stemness. Mechanistically, PUM2 competitively bound to STARD13 3'UTR with miR-590-3p and miR-9. The inhibition of PUM2 on OS cells progression was attenuated by STARD13 knockdown or related miRNAs overexpression.

CONCLUSION

PUM2 suppresses OS progression via partly and competitively binding to STARD13 3'UTR with miRNAs.

RNA binding protein HuR promotes osteosarcoma cell progression via suppressing the miR-142-3p/HMGA1 axis

The present study aimed to study the roles and underlying mechanisms of human antigen R (HuR) in osteosarcoma (OS) cell progression. It was determined that the HuR mRNA and protein levels were significantly upregulated in OS tissues, compared with that in normal adjacent tissues. HuR expression was negatively associated with miR-142-3p expression, but positively with High Mobility Group AT-Hook 1 (HMGA1). Additionally, knockdown of HuR inhibited OS cells viability, epithelial-mesenchymal transition and promoted cell apoptosis. HuR was determined to harbor binding sites on HMGA1, directly binding to HMGA1, increasing HMGA1 mRNA stability and expression. Notably, the promotion of HuR on HMGA1 expression was attenuated via miR-142-3p overexpression, and miR-142-3p could directly bind to HMGA1 3'untranslated region (UTR). Furthermore, HMGA1 3'UTR with a mutated miR-142-3p binding site did not respond to HuR alterations. Finally, the inhibition of HuR knockdown was attenuated or even reversed via HMGA1 overexpression; therefore, the results of the present study indicated that RNA binding protein HuR may facilitate OS cell progression via competitively binding to HMGA1 with miR-142-3p.

RNA binding protein Lin28B confers gastric cancer cells stemness via directly binding to NRP-1

This work aims to explore the roles and related mechanisms of RNA binding protein Lin28B in gastric cancer cells stemness. We found that Lin28B expression was negatively correlated with the overall survival (OS) of gastric cancer patients, and significantly increased in gastric cancer cells compared with that in gastric epithelial cells. Lin28B overexpression increased spheroid formation, expression of gastric cancer stemness-related markers, and decreased cisplatin sensitivity in gastric cancer cells. Mechanistically, Lin28B could directly bind to NRP-1 3'UTR, thus increasing NRP-1 mRNA stability and expression, and activate the downstream Wnt/β-catenin signaling. Knockdown of NRP-1 or treatment with Wnt/β-catenin antagonist could rescue the promotive effects of Lin28B on gastric cancer stemness. Thus, thes results indicate that Lin28B could facilitate gastric cancer stemness via directly binding to NRP-1 3'UTR and activating the downstream Wnt/β-catenin signaling.

An Update on the Therapeutic Potential of Stem Cells

The seeming setbacks noted for stem cells underscore the need for experimental studies for safe and efficacious application to patients. Both clinical and experimental researchers have gained valuable knowledge on the characteristics of stem cells, and their behavior in different microenvironment. This introductory chapter focuses on adult mesenchymal stem cells (MSCs) based on the predominance in the clinic. MSCs can be influenced by inflammatory mediators to exert immune suppressive properties, commonly referred to as "licensing." Interestingly, while there are questions if other stem cells can be delivered across allogeneic barrier, there is no question on the ability of MSCs to provide this benefit. This property has been a great advantage since MSCs could be available for immediate application as "off-the-shelf" stem cells for several disorders, tissue repair and gene/drug delivery. Despite the benefit of MSCs, it is imperative that research continues with the various types of stem cells. The method needed to isolate these cells is outlined in this book. In parallel, safety studies are needed; particularly links to oncogenic event. In summary, this introductory chapter discusses several potential areas that need to be addressed for safe and efficient delivery of stem cells, and argue for the incorporation of microenvironmental factors in the studies. The method described in this chapter could be extrapolated to the field of chimeric antigen receptor T-cells (CAR-T). This will require application to stem cell hierarchy of memory T-cells.

Musashi-1 Enhances Glioblastoma Cell Migration and Cytoskeletal Dynamics through Translational Inhibition of Tensin3

The RNA-binding protein Musashi-1 (MSI1) exerts essential roles in multiple cellular functions, such as maintenance of self-renewal and pluripotency of stem cells. MSI1 overexpression has been observed in several tumor tissues, including glioblastoma (GBM), and is considered as a well-established marker for tumor metastasis and recurrence. However, the molecular mechanisms by which MSI1 regulates cell migration are still undetermined. Here we reported that MSI1 alters cell morphology, promotes cell migration, and increases viscoelasticity of GBM cells. We also found that MSI1 directly binds to the 3′UTR of Tensin 3 (TNS3) mRNA, a negative regulator of cell migration, to inhibit its translation. Additionally, we identified that RhoA-GTP could be a potential regulator in MSI1/TNS3-mediated cell migration and morphological changes. In a xenograft animal model, high expression ratio of MSI1 to TNS3 enhanced GBM tumor migration. We also confirmed that MSI1 and TNS3 expressions are mutually exclusive in migratory tumor lesions, and GBM patients with MSI1^high/TNS3^low pattern tend to have poor clinical outcome. Taken together, our findings suggested a critical role of MSI1-TNS3 axis in regulating GBM migration and highlighted that the ratio of MSI1/TNS3 could predict metastatic and survival outcome of GBM patients.

Metabolic labeling and recovery of nascent RNA to accurately quantify mRNA stability

Changes in the rate of mRNA decay are closely coordinated with transcriptional changes and together these events have profound effects on gene expression during development and disease. Traditional approaches to assess mRNA decay have relied on inhibition of transcription, which can alter mRNA decay rates and confound interpretation. More recently, metabolic labeling combined with chemical modification and fractionation of labeled RNAs has allowed the isolation of nascent transcripts and the subsequent calculation of mRNA decay rates. This approach has been widely adopted for measuring mRNA half-lives on a global scale, but has proven challenging to use for analysis of single genes. We present a series of normalization and quality assurance steps to be used in combination with 4-thiouridine pulse labeling of cultured eukaryotic cells. Importantly, we demonstrate how the relative amount of 4sU-labeled nascent RNA influences accurate quantification. The approach described facilitates reproducible measurement of individual mRNA half-lives using 4-thiouridine and could be adapted for use with other nucleoside analogs.

Musashi RNA-Binding Proteins as Cancer Drivers and Novel Therapeutic Targets

Aberrant gene expression that drives human cancer can arise from epigenetic dysregulation. Although much attention has focused on altered activity of transcription factors and chromatin-modulating proteins, proteins that act posttranscriptionally can potently affect expression of oncogenic signaling proteins. The RNA-binding proteins (RBP) Musashi-1 (MSI1) and Musashi-2 (MSI2) are emerging as regulators of multiple critical biological processes relevant to cancer initiation, progression, and drug resistance. Following identification of Musashi as a regulator of progenitor cell identity in Drosophila, the human Musashi proteins were initially linked to control of maintenance of hematopoietic stem cells, then stem cell compartments for additional cell types. More recently, the Musashi proteins were found to be overexpressed and prognostic of outcome in numerous cancer types, including colorectal, lung, and pancreatic cancers; glioblastoma; and several leukemias. MSI1 and MSI2 bind and regulate the mRNA stability and translation of proteins operating in essential oncogenic signaling pathways, including NUMB/Notch, PTEN/mTOR, TGFβ/SMAD3, MYC, cMET, and others. On the basis of these activities, MSI proteins maintain cancer stem cell populations and regulate cancer invasion, metastasis, and development of more aggressive cancer phenotypes, including drug resistance. Although RBPs are viewed as difficult therapeutic targets, initial efforts to develop MSI-specific inhibitors are promising, and RNA interference-based approaches to inhibiting these proteins have had promising outcomes in preclinical studies. In the interim, understanding the function of these translational regulators may yield insight into the relationship between mRNA expression and protein expression in tumors, guiding tumor-profiling analysis. This review provides a current overview of Musashi as a cancer driver and novel therapeutic target. Clin Cancer Res; 23(9); 2143-53. ©2017 AACR.