Musashi, a neural RNA-binding protein required for Drosophila adult external sensory organ development

Musashi inhibitor Ro 08-2750 attenuates triple-negative breast cancer cell proliferation and migration and acts as a novel chemo- and radiosensitizer

INTRODUCTION

The Musashi RNA-binding proteins contribute to proliferation, stemness, and therapy resistance in triple-negative breast cancer (TNBC) and have been associated with reduced overall survival in patients.

OBJECTIVES

Leveraging the availability of a Musashi inhibitor, Ro 08-2750, we here aimed to assess the therapeutic potential of Musashi protein inhibition in TNBC.

METHODS

Cell proliferation and clonogenic survival were quantified at different concentrations of the inhibitor in primary, patient-derived breast cancer cultures as well as established TNBC cell lines. Flow cytometry, spheroid formation, MTT assays and digital holographic microscopy were used to assess inhibitor-induced functional effects, while RNA sequencing, dot blot and western blot assays confirmed gene expression changes.

RESULTS

Ro 08-2750 affects cell proliferation and survival in a dose-dependent manner by upregulating apoptosis and inducing a cell cycle arrest. Cell migration was reduced as stemness markers were downregulated. Inhibitor treatment also increased DNA double strand breaks after downregulation of Musashi-associated DNA repair mechanisms. Accordingly, Ro 08-2750 acted as a radio- and chemosensitizer in combined treatment applications. Gene expression findings were consistent with observed functional changes.

CONCLUSION

Our results indicate that Musashi protein inhibition may attenuate tumor progression and sensitize cells to conventional breast cancer therapy, underlining the therapeutic potential of this approach.

Disruption of RNA-binding proteins in neurological disorders

RNA-binding proteins (RBPs) are multifunctional proteins essential for the regulation of RNA processing and metabolism, contributing to the maintenance of cell homeostasis by modulating the expression of target genes. Many RBPs have been associated with neuron-specific processes vital for neuronal development and survival. RBP dysfunction may result in aberrations in RNA processing, which subsequently initiate a cascade of effects. Notably, RBPs are involved in the onset and progression of neurological disorders via diverse mechanisms. Disruption of RBPs not only affects RNA processing, but also promotes the abnormal aggregation of proteins into toxic inclusion bodies, and contributes to immune responses that drive the progression of neurological diseases. In this review, we summarize recent discoveries relating to the roles of RBPs in neurological diseases, discuss their contributions to such conditions, and highlight the unique functions of these RBPs within the nervous system.

Musashi orchestrates melanism in Laodelphax striatellus

In insects, melanism, a fundamental pigmentation process, is of significant importance in evolutionary biology due to its complex genetic foundation. We investigated the role of the RNA-binding gene Musashi (msi) in melanism in Laodelphax striatellus, a Hemiptera species. We identified a single L. striatellus msi homolog, Lsmsi, encoding a 357 amino acid protein with 2 RNA recognition motifs. RNA interference-mediated knockdown of LsMsi resulted in complete body melanism and increased cuticular permeability. Additionally, we found the involvement of G protein-coupled receptor A42 and tyrosine hydroxylase (Th) in L. striatellus melanism. Knockdown of LsTh lightened the epidermis, showing dehydration signs, while LsA42 knockdown enhanced LsTh expression, leading to melanism. Surprisingly, Lsmsi knockdown decreased both LsA42 and LsTh expression, which was expected to cause whitening but resulted in melanism. Further, we found that Lsmsi influenced downstream genes like phenoloxidase homolog LsPo and dopa decarboxylase (Ddc) homolog LsDdc in the tyrosine-mediated melanism pathway. Extending to Nilaparvata lugens and Sogatella furcifera, we demonstrated the conserved role of msi in melanism among Delphacidae. Given MSI proteins' roles in cancer and tumors in vertebrates, our study is the first to link msi in insects to Delphacidae body color melanization via the tyrosine-mediated pathway, offering fresh perspectives on the genetic basis of insect melanism and msi functions.

Update on the Progress of Musashi-2 in Malignant Tumors

Since the discovery of the Musashi (MSI) protein, its ability to affect the mitosis of Drosophila progenitor cells has garnered significant interest among scientists. In the following 20 years, it has lived up to expectations. A substantial body of evidence has demonstrated that it is closely related to the development, metastasis, migration, and drug resistance of malignant tumors. In recent years, research on the MSI protein has advanced, and many novel viewpoints and drug resistance attempts have been derived; for example, tumor protein p53 mutations and MSI-binding proteins lead to resistance to protein arginine N-methyltransferase 5-targeted therapy in lymphoma patients. Moreover, the high expression of MSI2 in pancreatic cancer might suppress its development and progression. As a significant member of the MSI family, MSI2 is closely associated with multiple malignant tumors, including hematological disorders, common abdominal tumors, and other tumor types (e.g., glioblastoma, breast cancer). MSI2 is highly expressed in the majority of tumors and is related to a poor disease prognosis. However, its specific expression levels and regulatory mechanisms may differ based on the tumor type. This review summarizes the research progress related to MSI2 in recent years, including its occurrence, migration mechanism, and drug resistance, as well as the prospect of developing tumor immunosuppressants and biomarkers.

Unraveling the Bivalent and Rapid Interactions Between a Multivalent RNA Recognition Motif and RNA: A Kinetic Approach

The kinetics of the interaction between Musashi-1 (MSI1) and RNA have been characterized using surface plasmon resonance biosensor analysis. Truncated variants of human MSI1 encompassing the two homologous RNA recognition motifs (RRM1 and RRM2) in tandem (aa 1-200), and the two RRMs in isolation (aa 1-103 and aa 104-200, respectively) were produced. The proteins were injected over sensor surfaces with immobilized RNA, varying in sequence and length, and with one or two RRM binding motifs. The interactions of the individual RRMs with all RNA variants were well described by a 1:1 interaction model. The interaction between the MSI1 variant encompassing both RRM motifs was bivalent and rapid for all RNA variants. Due to difficulties in fitting this complex data using standard procedures, we devised a new method to quantify the interactions. It revealed that two RRMs in tandem resulted in a significantly longer residence time than a single RRM. It also showed that RNA with double UAG binding motifs and potential hairpin structures forms less stable bivalent complexes with MSI1 than the single UAG motif containing linear RNA. Substituting the UAG binding motif with a CAG sequence resulted in a reduction of the affinity of the individual RRMs, but for MSI1, this reduction was strongly enhanced, demonstrating the importance of bivalency for specificity. This study has provided new insights into the interaction between MSI1 and RNA and an understanding of how individual domains contribute to the overall interaction. It provides an explanation for why many RNA-binding proteins contain dual RRMs.

RNA Binding Proteins as Potential Therapeutic Targets in Colorectal Cancer

RNA-binding proteins (RBPs) play critical roles in regulating post-transcriptional gene expression, managing processes such as mRNA splicing, stability, and translation. In normal intestine, RBPs maintain the tissue homeostasis, but when dysregulated, they can drive colorectal cancer (CRC) development and progression. Understanding the molecular mechanisms behind CRC is vital for developing novel therapeutic strategies, and RBPs are emerging as key players in this area. This review highlights the roles of several RBPs, including LIN28, IGF2BP1-3, Musashi, HuR, and CELF1, in CRC. These RBPs regulate key oncogenes and tumor suppressor genes by influencing mRNA stability and translation. While targeting RBPs poses challenges due to their complex interactions with mRNAs, recent advances in drug discovery have identified small molecule inhibitors that disrupt these interactions. These inhibitors, which target LIN28, IGF2BPs, Musashi, CELF1, and HuR, have shown promising results in preclinical studies. Their ability to modulate RBP activity presents a new therapeutic avenue for treating CRC. In conclusion, RBPs offer significant potential as therapeutic targets in CRC. Although technical challenges remain, ongoing research into the molecular mechanisms of RBPs and the development of selective, potent, and bioavailable inhibitors should lead to more effective treatments and improved outcomes in CRC.

Neurobiology of egg-laying behavior in Drosophila: neural control of the female reproductive system

Egg-laying is one of the key aspects of female reproductive behavior in insects. Egg-laying has been studied since the dawn of Drosophila melanogaster as a model organism. The female's internal state, hormones, and external factors, such as nutrition, light, and social environment, affect egg-laying output. However, only recently, neurobiological features of egg-laying behavior have been studied in detail. fruitless and doublesex, two key players in the sex determination pathway, have become focal points in identifying neurons of reproductive significance in both central and peripheral nervous systems. The reproductive tract and external terminalia house sensory neurons that carry the sensory information of egg maturation, mating and egg-laying. These sensory signals include the presence of male accessory gland products and mechanical stimuli. The abdominal neuromere houses neurons that receive information from the reproductive tract, including sex peptide abdominal ganglion neurons (SAGs), and send their information to the brain. In the brain, neuronal groups like aDNs and pC1 clusters modulate egg-laying decision-making, and other neurons like oviINs and oviDNs are necessary for egg-laying itself. Lastly, motor neurons involved in egg-laying, which are mostly octopaminergic, reside in the abdominal neuromere and orchestrate the muscle movements required for laying the egg. Egg-laying neuronal control is important in various evolutionary processes like cryptic female choice, and using different Drosophila species can provide intriguing avenues for the future of the field.

Recent Progress in the Research on RNA-Binding Proteins in Bone Development and Diseases

RNA-binding proteins (RBPs), which regulate gene expression through post-transcriptional modifications of RNAs, play a role in diverse biological processes that include bone cell development and bone tissue formation. RBP dysregulation may result in aberrant bone homeostasis and contribute to various bone diseases. The function of RBPs in bone physiology and pathophysiology and the underlying molecular mechanisms have been extensively studied in recent years. This article provides a review of such studies, highlighting the potential of RBPs as pivotal targets for therapeutic intervention.

Recent progress in hair follicle stem cell markers and their regulatory roles

Hair follicle stem cells (HFSCs) in the bulge are a multipotent adult stem cell population. They can periodically give rise to new HFs and even regenerate the epidermis and sebaceous glands during wound healing. An increasing number of biomarkers have been used to isolate, label, and trace HFSCs in recent years. Considering more detailed data from single-cell transcriptomics technology, we mainly focus on the important HFSC molecular markers and their regulatory roles in this review.

Repurposing the mammalian RNA-binding protein Musashi-1 as an allosteric translation repressor in bacteria

The RNA recognition motif (RRM) is the most common RNA-binding protein domain identified in nature. However, RRM-containing proteins are only prevalent in eukaryotic phyla, in which they play central regulatory roles. Here, we engineered an orthogonal post-transcriptional control system of gene expression in the bacterium Escherichia coli with the mammalian RNA-binding protein Musashi-1, which is a stem cell marker with neurodevelopmental role that contains two canonical RRMs. In the circuit, Musashi-1 is regulated transcriptionally and works as an allosteric translation repressor thanks to a specific interaction with the N-terminal coding region of a messenger RNA and its structural plasticity to respond to fatty acids. We fully characterized the genetic system at the population and single-cell levels showing a significant fold change in reporter expression, and the underlying molecular mechanism by assessing the in vitro binding kinetics and in vivo functionality of a series of RNA mutants. The dynamic response of the system was well recapitulated by a bottom-up mathematical model. Moreover, we applied the post-transcriptional mechanism engineered with Musashi-1 to specifically regulate a gene within an operon, implement combinatorial regulation, and reduce protein expression noise. This work illustrates how RRM-based regulation can be adapted to simple organisms, thereby adding a new regulatory layer in prokaryotes for translation control.

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.

RNA binding proteins in cancer chemotherapeutic drug resistance

Drug resistance has been a major obstacle in the quest for a cancer cure. Many chemotherapeutic treatments fail to overcome chemoresistance, resulting in tumor remission. The exact process that leads to drug resistance in many cancers has not been fully explored or understood. However, the discovery of RNA binding proteins (RBPs) has provided insight into various pathways and post-transcriptional gene modifications involved in drug tolerance. RBPs are evolutionarily conserved proteins, and their abnormal gene expression has been associated with cancer progression. Additionally, RBPs are aberrantly expressed in numerous neoplasms. RBPs have also been implicated in maintaining cancer stemness, epithelial-to-mesenchymal transition, and other processes. In this review, we aim to provide an overview of RBP-mediated mechanisms of drug resistance and their implications in cancer malignancy. We discuss in detail the role of major RBPs and their correlation with noncoding RNAs (ncRNAs) that are associated with the inhibition of chemosensitivity. Understanding and exploring the pathways of RBP-mediated chemoresistance will contribute to the development of improved cancer diagnosis and treatment strategies.

Musashi-2 causes cardiac hypertrophy and heart failure by inducing mitochondrial dysfunction through destabilizing Cluh and Smyd1 mRNA

Regulation of RNA stability and translation by RNA-binding proteins (RBPs) is a crucial process altering gene expression. Musashi family of RBPs comprising Msi1 and Msi2 is known to control RNA stability and translation. However, despite the presence of MSI2 in the heart, its function remains largely unknown. Here, we aim to explore the cardiac functions of MSI2. We confirmed the presence of MSI2 in the adult mouse, rat heart, and neonatal rat cardiomyocytes. Furthermore, Msi2 was significantly enriched in the heart cardiomyocyte fraction. Next, using RNA-seq data and isoform-specific PCR primers, we identified Msi2 isoforms 1, 4, and 5, and two novel putative isoforms labeled as Msi2 6 and 7 to be expressed in the heart. Overexpression of Msi2 isoforms led to cardiac hypertrophy in cultured cardiomyocytes. Additionally, Msi2 exhibited a significant increase in a pressure-overload model of cardiac hypertrophy. We selected isoforms 4 and 7 to validate the hypertrophic effects due to their unique alternative splicing patterns. AAV9-mediated overexpression of Msi2 isoforms 4 and 7 in murine hearts led to cardiac hypertrophy, dilation, heart failure, and eventually early death, confirming a pathological function for Msi2. Using global proteomics, gene ontology, transmission electron microscopy, seahorse, and transmembrane potential measurement assays, increased MSI2 was found to cause mitochondrial dysfunction in the heart. Mechanistically, we identified Cluh and Smyd1 as direct downstream targets of Msi2. Overexpression of Cluh and Smyd1 inhibited Msi2-induced cardiac malfunction and mitochondrial dysfunction. Collectively, we show that Msi2 induces hypertrophy, mitochondrial dysfunction, and heart failure.

Musashi-2 binds with Fbxo6 to induce Rnaset2 ubiquitination and chemokine signaling pathway during vascular smooth muscle cell phenotypic switch in atherosclerosis

OBJECTIVE

The objective of this study is to determine how Musashi-2 (MSI2) affects vascular smooth muscle cell (VSMC) phenotypic switch and contributes to atherosclerosis (AS).

METHODS

Primary mouse VSMCs were transfected with MSI2 specific siRNA and treated with platelet-derived growth factor-BB (PDGF-BB). The proliferation, cell-cycle, and migration of VSMCs were determined by CCK-8, flow cytometry, wound healing, and transwell assays. Western blot and qRT-PCR were conducted to analyze the protein and mRNA expression. Moreover, the correlation between MSI2, Fbxo6, Rnaset2, and chemokine signaling was predicted and verified using RNAct database, KEGG, wiki, RNA-binding protein immunoprecipitation and co-immunoprecipitation. Moreover, H&E and Oil Red O staining were employed for assessing necrotic core and lipid accumulation in AS mouse aorta tissues. The numbers of B lymphocytes and monocytes, and the levels of triglyceride (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDLC), and low-density lipoprotein cholesterol (LDL-C) in AS mice blood were investigated using flow cytometry and corresponding commercial kits, respectively.

RESULTS

MSI2 was up-regulated in the PDGF-BB-treated VSMCs. Knockdown of MSI2 inhibited VSMC proliferation, cell-cycle, and migration. Moreover, MSI2 regulated VSMC phenotypic switch through binding with Fbxo6 to induce Rnaset2 ubiquitination. MSI2 knockdown inhibited chemokine signaling via regulating Fbxo6/Rnaset2 axis. In AS mice, knockdown of MSI2 inhibited the formation of necrotic core and atherosclerotic plaque, and inhibited chemokine signaling via regulating Fbxo6/Rnaset2 axis.

CONCLUSION

Our findings demonstrated that MSI2 could bind with Fbxo6 to induce Rnaset2 ubiquitination and the activation of chemokine signaling pathway during VSMC phenotypic switch in AS.

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.

Musashi-2 (MSI2) promotes neuroblastoma tumorigenesis through targeting MYC-mediated glucose-6-phosphate dehydrogenase (G6PD) transcriptional activation

Neuroblastoma (NB) is the deadliest pediatric solid tumor due to its rapid proliferation. Aberrant expression of MYCN is deemed as the most remarkable feature for the predictive hallmark of NB progression and recurrence. However, the phenomenon that only detection of MYCN in the nearly 20% of NB patients hints that there should be other vital oncogenes in the progression of NB. Here, we firstly show that MSI2 mRNA is augmented by analyzing public GEO datasets in the malignant stage according to International Neuroblastoma Staging System (INSS) stages. Although accumulating evidences uncover the emerging roles of MSI2 in several cancers, the regulatory functions and underlying mechanisms of MSI2 in NB remain under-investigated. Herein, we identified that high-expressed MSI2 and low-expressed n-Myc group account for 43.1% of total NB clinical samples (n = 65). Meanwhile, MSI2 expression is profoundly upregulated along with NB malignancy and negatively associated with the survival outcome of NB patients in the NB tissue microarray (NB: n = 65; Ganglioneuroblastoma: n = 31; Ganglioneuroma: n = 27). In vitro, our results revealed that MSI2 promoted migration, invasion, and proliferation of NB cells via enhancing pentose phosphate pathway. Mechanistically, MSI2 upregulated the key enzyme glucose-6-phosphate dehydrogenase (G6PD) via directly binding to 3'-untranslated regions of c-Myc mRNA to facilitate its stability, resulting in enhancing pentose phosphate pathway. Our findings reveal that MSI2 promotes pentose phosphate pathway via activating c-Myc-G6PD signaling, suggesting that MSI2 exhibits a novel and powerful target for the diagnosis and treatment of NB.

Dysregulated Stem Cell Markers Musashi-1 and Musashi-2 are Associated with Therapy Resistance in Inflammatory Breast Cancer

BACKGROUND AND AIM

While preliminary evidence points to pro-tumorigenic roles for the Musashi (MSI) RNA-binding proteins Musashi-1 (MSI1) and Musashi-2 (MSI2) in some breast cancer subtypes, no data exist for inflammatory breast cancer (IBC).

METHODS

MSI gene expression was quantified in IBC SUM149PT cells. We then used small interfering RNA-based MSI1 and MSI2 double knockdown (DKD) to understand gene expression and functional changes upon MSI depletion. We characterized cancer stem cell characteristics, cell apoptosis and cell cycle progression via flow cytometry, mammospheres via spheroid assays, migration and proliferation via digital holographic microscopy, and cell viability using BrdU assays. Chemoresistance was determined for paclitaxel and cisplatin with MTT assays and radioresistance was assessed with clonogenic analyses. In parallel, we supported our in vitro data by analyzing publicly available patient IBC gene expression datasets.

RESULTS

MSI1 and MSI2 are upregulated in breast cancer generally and IBC specifically. MSI2 is more commonly expressed compared to MSI1. MSI DKD attenuated proliferation, cell cycle progression, migration, and cell viability while increasing apoptosis. Stem cell characteristics CD44(+)/CD24(-), TERT and Oct4 were associated with MSI expression in vivo and were decreased in vitro after MSI DKD as was ALDH expression and mammosphere formation. In vivo, chemoresistant tumors were characterized by MSI upregulation upon chemotherapy application. In vitro, MSI DKD was able to alleviate chemo- and radioresistance.

CONCLUSIONS

The Musashi RNA binding proteins are dysregulated in IBC and associated with tumor proliferation, cancer stem cell phenotype, chemo- and radioresistance. MSI downregulation alleviates therapy resistance and attenuates tumor proliferation in vitro.

Rx and its downstream factor, Musashi1, is required for establishment of the apical organ in sea urchin larvae

Acetylcholine, a vital neurotransmitter, plays a multifarious role in the brain and peripheral nervous system of various organisms. Previous research has demonstrated the proximity of cholinergic neurons to serotonergic neurons in the apical organ of sea urchin embryos. While several transcription factors have been identified as playing a role in the development of serotonergic neurons in this region of a sea urchin, Hemicentrotus pulcherrimus, comparatively little is known about the specific transcription factors and their spatiotemporal expression patterns that regulate the development of cholinergic neurons. In this study, we establish the requirement of the transcription factor Rx for the development of cholinergic neurons in the apical organ of the species. Furthermore, we investigate the role of the RNA-binding protein Musashi1, known to be involved in neurogenesis, including cholinergic neurons in other organisms, and demonstrate that it is a downstream factor of Rx, and that choline acetyltransferase expression is suppressed in Musashi1 downregulated embryos. Our research also highlights the intricate network formed by neurons and other cells in and around the apical organ of sea urchin larvae through axons and dendrites, providing possibility for a systematic and complexed neural pattern like those of the brain in other organisms.

Functional Role of RBP in Osteosarcoma: Regulatory Mechanism and Clinical Therapy

Malignant bone neoplasms can be represented by osteosarcoma (OS), which accounts for 36% of all sarcomas. To reduce tumor malignancy, extensive efforts have been devoted to find an ideal target from numerous candidates, among which RNA-binding proteins (RBPs) have shown their unparalleled competitiveness. With the special structure of RNA-binding domains, RBPs have the potential to establish relationships with RNAs or small molecules and are considered regulators of different sections of RNA processes, including splicing, transport, translation, and degradation of RNAs. RBPs have considerable significant roles in various cancers, and experiments revealed that there was a strong association of RBPs with tumorigenesis and tumor cell progression. Regarding OS, RBPs are a new orientation, but achievements in hand are noteworthy. Higher or lower expression of RBPs was first found in tumor cells compared to normal tissue. By binding to different molecules, RBPs are capable of influencing tumor cell phenotypes through different signaling pathways or other axes, and researches on medical treatment have been largely inspired. Exploring the prognostic and therapeutic values of RBPs in OS is a hotspot where diverse avenues on regulating RBPs have achieved dramatical effects. In this review, we briefly summarize the contribution of RBPs and their binding molecules to OS oncogenicity and generally introduce distinctive RBPs as samples. Moreover, we focus on the attempts to differentiate RBP's opposite functions in predicting prognosis and collect possible strategies for treatment. Our review provides forwards insight into improving the understanding of OS and suggests RBPs as potential biomarkers for therapies.

Identification of ecdysone receptor target genes in the worker honey bee brains during foraging behavior

Ecdysone signaling plays central roles in morphogenesis and female ovarian development in holometabolous insects. In the European honey bee (Apis mellifera L.), however, ecdysone receptor (EcR) is expressed in the brains of adult workers, which have already undergone metamorphosis and are sterile with shrunken ovaries, during foraging behavior. Aiming at unveiling the significance of EcR signaling in the worker brain, we performed chromatin-immunoprecipitation sequencing of EcR to search for its target genes using the brains of nurse bees and foragers. The majority of the EcR targets were common between the nurse bee and forager brains and some of them were known ecdysone signaling-related genes. RNA-sequencing analysis revealed that some EcR target genes were upregulated in forager brains during foraging behavior and some were implicated in the repression of metabolic processes. Single-cell RNA-sequencing analysis revealed that EcR and its target genes were expressed mostly in neurons and partly in glial cells in the optic lobes of the forager brain. These findings suggest that in addition to its role during development, EcR transcriptionally represses metabolic processes during foraging behavior in the adult worker honey bee brain.

New insights into the ambivalent role of YAP/TAZ in human cancers

Hippo signaling was first identified in Drosophila as a key controller of organ size by regulating cell proliferation and anti-apoptosis. Subsequent studies have shown that this pathway is highly conserved in mammals, and its dysregulation is implicated in multiple events of cancer development and progression. Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) (hereafter YAP/TAZ) are the downstream effectors of the Hippo pathway. YAP/TAZ overexpression or activation is sufficient to induce tumor initiation and progression, as well as recurrence and therapeutic resistance. However, there is growing evidence that YAP/TAZ also exert a tumor-suppressive function in a context-dependent manner. Therefore, caution should be taken when targeting Hippo signaling in clinical trials in the future. In this review article, we will first give an overview of YAP/TAZ and their oncogenic roles in various cancers and then systematically summarize the tumor-suppressive functions of YAP/TAZ in different contexts. Based on these findings, we will further discuss the clinical implications of YAP/TAZ-based tumor targeted therapy and potential future directions.

Zika virus RNA structure controls its unique neurotropism by bipartite binding to Musashi-1

Human RNA binding protein Musashi-1 (MSI1) plays a critical role in neural progenitor cells (NPCs) by binding to various host RNA transcripts. The canonical MSI1 binding site (MBS), A/GU_(1-3)AG single-strand motif, is present in many RNA virus genomes, but only Zika virus (ZIKV) genome has been demonstrated to bind MSI1. Herein, we identified the AUAG motif and the AGAA tetraloop in the Xrn1-resistant RNA 2 (xrRNA2) as the canonical and non-canonical MBS, respectively, and both are crucial for ZIKV neurotropism. More importantly, the unique AGNN-type tetraloop is evolutionally conserved, and distinguishes ZIKV from other known viruses with putative MBSs. Integrated structural analysis showed that MSI1 binds to the AUAG motif and AGAA tetraloop of ZIKV in a bipartite fashion. Thus, our results not only identified an unusual viral RNA structure responsible for MSI recognition, but also revealed a role for the highly structured xrRNA in controlling viral neurotropism.

Distinct but interchangeable subpopulations of colorectal cancer cells with different growth fates and drug sensitivity

Dynamic changes in cell properties lead to intratumor heterogeneity; however, the mechanisms of nongenetic cellular plasticity remain elusive. When the fate of each cell from colorectal cancer organoids was tracked through a clonogenic growth assay, the cells showed a wide range of growth ability even within the clonal organoids, consisting of distinct subpopulations; the cells generating large spheroids and the cells generating small spheroids. The cells from the small spheroids generated only small spheroids (S-pattern), while the cells from the large spheroids generated both small and large spheroids (D-pattern), both of which were tumorigenic. Transition from the S-pattern to the D-pattern occurred by various extrinsic triggers, in which Notch signaling and Musashi-1 played a key role. The S-pattern spheroids were resistant to chemotherapy and transited to the D-pattern upon drug treatment through Notch signaling. As the transition is linked to the drug resistance, it can be a therapeutic target.

Rationally designed inhibitors of the Musashi protein-RNA interaction by hotspot mimicry

RNA-binding proteins (RBPs) are key post-transcriptional regulators of gene expression, and thus underlie many important biological processes. Here, we developed a strategy that entails extracting a "hotspot pharmacophore" from the structure of a protein-RNA complex, to create a template for designing small-molecule inhibitors and for exploring the selectivity of the resulting inhibitors. We demonstrate this approach by designing inhibitors of Musashi proteins MSI1 and MSI2, key regulators of mRNA stability and translation that are upregulated in many cancers. We report this novel series of MSI1/MSI2 inhibitors is specific and active in biochemical, biophysical, and cellular assays. This study extends the paradigm of "hotspots" from protein-protein complexes to protein-RNA complexes, supports the "druggability" of RNA-binding protein surfaces, and represents one of the first rationally-designed inhibitors of non-enzymatic RNA-binding proteins. Owing to its simplicity and generality, we anticipate that this approach may also be used to develop inhibitors of many other RNA-binding proteins; we also consider the prospects of identifying potential off-target interactions by searching for other RBPs that recognize their cognate RNAs using similar interaction geometries. Beyond inhibitors, we also expect that compounds designed using this approach can serve as warheads for new PROTACs that selectively degrade RNA-binding proteins.

Comprehensive Characterization of RNA-Binding Proteins in Colon Adenocarcinoma Identifies a Novel Prognostic Signature for Predicting Clinical Outcomes and Immunotherapy Responses Based on Machine Learning

BACKGROUND

RNA-binding proteins (RBPs) are crucial factors that function in the posttranscriptional modification process and are significant in cancer.

OBJECTIVE

This research aimed for a multigene signature to predict the prognosis and immunotherapy response of patients with colon adenocarcinoma (COAD) based on the expression profile of RNA-binding proteins (RBPs).

METHODS

COAD samples retrieved from the TCGA and GEO datasets were utilized for a training dataset and a validation dataset. Totally, 14 shared RBP genes with prognostic significance were identified. Non-negative matrix factorization clusters defined by these RBPs could stratify COAD patients into two molecular subtypes. Cox regression analysis and identification of 8-gene signature categorized COAD patients into high- and low-risk populations with significantly different prognosis and immunotherapy responses.

RESULTS

Our prediction signature was superior to another five well-established prediction models. A nomogram was generated to quantificationally predict the overall survival (OS) rate, validated by calibration curves. Our findings also indicated that high-risk populations possessed an enhanced immune evasion capacity and low-risk populations might benefit immunotherapy, especially for the joint combination of PD-1 and CTLA4 immunosuppressants. DHX15 and LARS2 were detected with significantly different expressions in both datasets, which were further confirmed by qRTPCR and immunohistochemical staining.

CONCLUSION

Our observations supported an eight-RBP-related signature that could be applied for survival prediction and immunotherapy response of patients with COAD.

MiMIC analysis reveals an isoform specific role for Drosophila Musashi in follicle stem cell maintenance and escort cell function

The Drosophila ovary is regenerated from germline and somatic stem cell populations that have provided fundamental conceptual understanding on how adult stem cells are regulated within their niches. Recent ovarian transcriptomic studies have failed to identify mRNAs that are specific to follicle stem cells (FSCs), suggesting that their fate may be regulated post-transcriptionally. We have identified that the RNA-binding protein, Musashi (Msi) is required for maintaining the stem cell state of FSCs. Loss of msi function results in stem cell loss, due to a change in differentiation state, indicated by upregulation of Lamin C in the stem cell population. In msi mutant ovaries, Lamin C upregulation was also observed in posterior escort cells that interact with newly formed germ cell cysts. Mutant somatic cells within this region were dysfunctional, as evidenced by the presence of germline cyst collisions, fused egg chambers and an increase in germ cell cyst apoptosis. The msi locus produces two classes of mRNAs (long and short). We show that FSC maintenance and escort cell function specifically requires the long transcripts, thus providing the first evidence of isoform-specific regulation in a population of Drosophila epithelial cells. We further demonstrate that although male germline stem cells have previously been shown to require Msi function to prevent differentiation this is not the case for female germline stem cells, indicating that these similar stem cell types have different requirements for Msi, in addition to the differential use of Msi isoforms between soma and germline. In summary, we show that different isoforms of the Msi RNA-binding protein are expressed in specific cell populations of the ovarian stem cell niche where Msi regulates stem cell differentiation, niche cell function and subsequent germ cell survival and differentiation.

The Role of RNA-Binding Proteins in Hematological Malignancies

Hematological malignancies comprise a plethora of different neoplasms, such as leukemia, lymphoma, and myeloma, plus a myriad of dysplasia, such as myelodysplastic syndromes or anemias. Despite all the advances in patient care and the development of new therapies, some of these malignancies remain incurable, mainly due to resistance and refractoriness to treatment. Therefore, there is an unmet clinical need to identify new biomarkers and potential therapeutic targets that play a role in treatment resistance and contribute to the poor outcomes of these tumors. RNA-binding proteins (RBPs) are a diverse class of proteins that interact with transcripts and noncoding RNAs and are involved in every step of the post-transcriptional processing of transcripts. Dysregulation of RBPs has been associated with the development of hematological malignancies, making them potential valuable biomarkers and potential therapeutic targets. Although a number of dysregulated RBPs have been identified in hematological malignancies, there is a critical need to understand the biology underlying their contribution to pathology, such as the spatiotemporal context and molecular mechanisms involved. In this review, we emphasize the importance of deciphering the regulatory mechanisms of RBPs to pinpoint novel therapeutic targets that could drive or contribute to hematological malignancy biology.

Theoretical studies on RNA recognition by Musashi 1 RNA-binding protein

The Musashi (MSI) family of RNA-binding proteins, comprising the two homologs Musashi-1 (MSI1) and Musashi-2 (MSI2), typically regulates translation and is involved in cell proliferation and tumorigenesis. MSI proteins contain two ribonucleoprotein-like RNA-binding domains, RBD1 and RBD2, that bind single-stranded RNA motifs with a central UAG trinucleotide with high affinity and specificity. The finding that MSI also promotes the replication of Zika virus, a neurotropic Flavivirus, has triggered further investigations of the biochemical principles behind MSI–RNA interactions. However, a detailed molecular understanding of the specificity of MSI RBD1/2 interaction with RNA is still missing. Here, we performed computational studies of MSI1–RNA association complexes, investigating different RNA pentamer motifs using molecular dynamics simulations with binding free energy calculations based on the solvated interaction energy method. Simulations with Alphafold2 suggest that predicted MSI protein structures are highly similar to experimentally determined structures. The binding free energies show that two out of four RNA pentamers exhibit a considerably higher binding affinity to MSI1 RBD1 and RBD2, respectively. The obtained structural information on MSI1 RBD1 and RBD2 will be useful for a detailed functional and mechanistic understanding of this type of RNA–protein interactions.

Emerging Proteins in CRPC: Functional Roles and Clinical Implications

Prostate cancer (PCa) is the most common cancer in men in the western world, but the lack of specific and sensitive markers often leads to overtreatment of prostate cancer which eventually develops into castration-resistant prostate cancer (CRPC). Novel protein markers for diagnosis and management of CRPC will be promising. In this review, we systematically summarize and discuss the expression pattern of emerging proteins in tissue, cell lines, and serum when castration-sensitive prostate cancer (CSPC) progresses to CRPC; focus on the proteins involved in CRPC growth, invasion, metastasis, metabolism, and immune microenvironment; summarize the current understanding of the regulatory mechanisms of emerging proteins in CSPC progressed to CRPC at the molecular level; and finally summarize the clinical applications of emerging proteins as diagnostic marker, prognostic marker, predictive marker, and therapeutic marker.

Emerging Roles of RNA-Binding Proteins in Neurodevelopment

Diverse cell types in the central nervous system (CNS) are generated by a relatively small pool of neural stem cells during early development. Spatial and temporal regulation of stem cell behavior relies on precise coordination of gene expression. Well-studied mechanisms include hormone signaling, transcription factor activity, and chromatin remodeling processes. Much less is known about downstream RNA-dependent mechanisms including posttranscriptional regulation, nuclear export, alternative splicing, and transcript stability. These important functions are carried out by RNA-binding proteins (RBPs). Recent work has begun to explore how RBPs contribute to stem cell function and homeostasis, including their role in metabolism, transport, epigenetic regulation, and turnover of target transcripts. Additional layers of complexity are provided by the different target recognition mechanisms of each RBP as well as the posttranslational modifications of the RBPs themselves that alter function. Altogether, these functions allow RBPs to influence various aspects of RNA metabolism to regulate numerous cellular processes. Here we compile advances in RNA biology that have added to our still limited understanding of the role of RBPs in neurodevelopment.

Phase separation driven by interchangeable properties in the intrinsically disordered regions of protein paralogs

Paralogs, arising from gene duplications, increase the functional diversity of proteins. Protein functions in paralog families have been extensively studied, but little is known about the roles that intrinsically disordered regions (IDRs) play in their paralogs. Without a folded structure to restrain them, IDRs mutate more diversely along with evolution. However, how the diversity of IDRs in a paralog family affects their functions is unexplored. Using the RNA-binding protein Musashi family as an example, we applied multiple structural techniques and phylogenetic analysis to show how members in a paralog family have evolved their IDRs to different physicochemical properties but converge to the same function. In this example, the lower prion-like tendency of Musashi-1's IDRs, rather than Musashi-2's, is compensated by its higher α-helical propensity to assist their assembly. Our work suggests that, no matter how diverse they become, IDRs could evolve different traits to a converged function, such as liquid-liquid phase separation.

[Advances in research of Musashi2 in solid tumors]

RNA binding protein (RBP) plays a key role in gene regulation and participate in RNA translation, modification, splicing, transport and other important biological processes. Studies have shown that abnormal expression of RBP is associated with a variety of diseases. The Musashi (Msi) family of mammals is an evolutionarily conserved and powerful RBP, whose members Msi1 and Msi2 play important roles in the regulation of stem cell activity and tumor development. The Msi family members regulate a variety of biological processes by binding and regulating mRNA translation, stability and downstream cell signaling pathways, and among them, Msi2 is closely related to embryonic growth and development, maintenance of tumor stem cells and development of hematological tumors. Accumulating evidence has shown that Msi2 also plays a crucial role in the development of solid tumors, mainly by affecting the proliferation, invasion, metastasis and drug resistance of tumors, involving Wnt/β-catenin, TGF-β/SMAD3, Akt/mTOR, JAK/STAT, Numb and their related signaling pathways (Notch, p53, and Hedgehog pathway). Preclinical studies of Msi2 gene as a therapeutic target for tumor have achieved preliminary results. This review summarizes the molecular structure, physiological function, role of Msi2 in the development and progression of various solid tumors and the signaling pathways involved.

Small Molecule Palmatine Targeting Musashi-2 in Colorectal Cancer

Musashi-2 (MSI2) is an evolutionally conserved RNA-binding protein and recently considered as an attractive therapeutic target in a wide spectrum of malignancies. However, MSI2-engaged mRNAs are not well profiled, and no MSI2-dependent antagonist is available so far. In the study, we created MSI2 knockout cancer cells and demonstrated that MSI2 is required for the survival of colorectal cancer HCT116 cells but not non-small cell lung cancer A549 cells. In addition, the global profiling of the transcriptome and proteomics of MSI2 knockout colorectal cells revealed 38 candidate MSI2-targeted genes. In a loss–rescue screening, palmatine was identified as a functional MSI2 antagonist inhibiting the MSI2-dependent growth of colorectal cancer cells. Finally, we confirmed that palmatine is directly bound to MSI2 at its C-terminal. Our findings not only indicated MSI2 as a promising therapeutic target of colorectal cancer but also provided a small molecule palmatine as a direct and functional MSI2 antagonist for cancer therapy.

Tau mRNA Metabolism in Neurodegenerative Diseases: A Tangle Journey

Tau proteins are known to be mainly involved in regulation of microtubule dynamics. Besides this function, which is critical for axonal transport and signal transduction, tau proteins also have other roles in neurons. Moreover, tau proteins are turned into aggregates and consequently trigger many neurodegenerative diseases termed tauopathies, of which Alzheimer’s disease (AD) is the figurehead. Such pathological aggregation processes are critical for the onset of these diseases. Among the various causes of tau protein pathogenicity, abnormal tau mRNA metabolism, expression and dysregulation of tau post-translational modifications are critical steps. Moreover, the relevance of tau function to general mRNA metabolism has been highlighted recently in tauopathies. In this review, we mainly focus on how mRNA metabolism impacts the onset and development of tauopathies. Thus, we intend to portray how mRNA metabolism of, or mediated by, tau is associated with neurodegenerative diseases.

The RNA-Binding Protein Musashi1 Regulates a Network of Cell Cycle Genes in Group 4 Medulloblastoma

Medulloblastoma is the most common malignant brain tumor in children. Treatment with surgery, irradiation, and chemotherapy has improved survival in recent years, but patients are frequently left with devastating neurocognitive and other sequelae. Patients in molecular subgroups 3 and 4 still experience a high mortality rate. To identify new pathways contributing to medulloblastoma development and create new routes for therapy, we have been studying oncogenic RNA-binding proteins. We defined Musashi1 (Msi1) as one of the main drivers of medulloblastoma development. The high expression of Msi1 is prevalent in Group 4 and correlates with poor prognosis while its knockdown disrupted cancer-relevant phenotypes. Genomic analyses (RNA-seq and RIP-seq) indicated that cell cycle and division are the main biological categories regulated by Msi1 in Group 4 medulloblastoma. The most prominent Msi1 targets include CDK2, CDK6, CCND1, CDKN2A, and CCNA1. The inhibition of Msi1 with luteolin affected the growth of CHLA-01 and CHLA-01R Group 4 medulloblastoma cells and a synergistic effect was observed when luteolin and the mitosis inhibitor, vincristine, were combined. These findings indicate that a combined therapeutic strategy (Msi1 + cell cycle/division inhibitors) could work as an alternative to treat Group 4 medulloblastoma.

The Fine Art of Writing a Message: RNA Metabolism in the Shaping and Remodeling of the Nervous System

Neuronal morphogenesis, integration into circuits, and remodeling of synaptic connections occur in temporally and spatially defined steps. Accordingly, the expression of proteins and specific protein isoforms that contribute to these processes must be controlled quantitatively in time and space. A wide variety of post-transcriptional regulatory mechanisms, which act on pre-mRNA and mRNA molecules contribute to this control. They are thereby critically involved in physiological and pathophysiological nervous system development, function, and maintenance. Here, we review recent findings on how mRNA metabolism contributes to neuronal development, from neural stem cell maintenance to synapse specification, with a particular focus on axon growth, guidance, branching, and synapse formation. We emphasize the role of RNA-binding proteins, and highlight their emerging roles in the poorly understood molecular processes of RNA editing, alternative polyadenylation, and temporal control of splicing, while also discussing alternative splicing, RNA localization, and local translation. We illustrate with the example of the evolutionary conserved Musashi protein family how individual RNA-binding proteins are, on the one hand, acting in different processes of RNA metabolism, and, on the other hand, impacting multiple steps in neuronal development and circuit formation. Finally, we provide links to diseases that have been associated with the malfunction of RNA-binding proteins and disrupted post-transcriptional regulation.

Paths and pathways that generate cell-type heterogeneity and developmental progression in hematopoiesis

Mechanistic studies of Drosophila lymph gland hematopoiesis are limited by the availability of cell-type-specific markers. Using a combination of bulk RNA-Seq of FACS-sorted cells, single-cell RNA-Seq, and genetic dissection, we identify new blood cell subpopulations along a developmental trajectory with multiple paths to mature cell types. This provides functional insights into key developmental processes and signaling pathways. We highlight metabolism as a driver of development, show that graded Pointed expression allows distinct roles in successive developmental steps, and that mature crystal cells specifically express an alternate isoform of Hypoxia-inducible factor (Hif/Sima). Mechanistically, the Musashi-regulated protein Numb facilitates Sima-dependent non-canonical, and inhibits canonical, Notch signaling. Broadly, we find that prior to making a fate choice, a progenitor selects between alternative, biologically relevant, transitory states allowing smooth transitions reflective of combinatorial expressions rather than stepwise binary decisions. Increasingly, this view is gaining support in mammalian hematopoiesis.

Asymmetric cell division of mammary stem cells

Somatic stem cells are distinguished by their capacity to regenerate themselves and also to produce daughter cells that will differentiate. Self-renewal is achieved through the process of asymmetric cell division which helps to sustain tissue morphogenesis as well as maintain homeostasis. Asymmetric cell division results in the development of two daughter cells with different fates after a single mitosis. Only one daughter cell maintains "stemness" while the other differentiates and achieves a non-stem cell fate. Stem cells also have the capacity to undergo symmetric division of cells that results in the development of two daughter cells which are identical. Symmetric division results in the expansion of the stem cell population. Imbalances and deregulations in these processes can result in diseases such as cancer. Adult mammary stem cells (MaSCs) are a group of cells that play a critical role in the expansion of the mammary gland during puberty and any subsequent pregnancies. Furthermore, given the relatively long lifespans and their capability to undergo self-renewal, adult stem cells have been suggested as ideal candidates for transformation events that lead to the development of cancer. With the possibility that MaSCs can act as the source cells for distinct breast cancer types; understanding their regulation is an important field of research. In this review, we discuss asymmetric cell division in breast/mammary stem cells and implications on further research. We focus on the background history of asymmetric cell division, asymmetric cell division monitoring techniques, identified molecular mechanisms of asymmetric stem cell division, and the role asymmetric cell division may play in breast cancer.

The RNA-binding protein Musashi controls axon compartment-specific synaptic connectivity through ptp69D mRNA poly(A)-tailing

Synaptic targeting with subcellular specificity is essential for neural circuit assembly. Developing neurons use mechanisms to curb promiscuous synaptic connections and to direct synapse formation to defined subcellular compartments. How this selectivity is achieved molecularly remains enigmatic. Here, we discover a link between mRNA poly(A)-tailing and axon collateral branch-specific synaptic connectivity within the CNS. We reveal that the RNA-binding protein Musashi binds to the mRNA encoding the receptor protein tyrosine phosphatase Ptp69D, thereby increasing poly(A) tail length and Ptp69D protein levels. This regulation specifically promotes synaptic connectivity in one axon collateral characterized by a high degree of arborization and strong synaptogenic potential. In a different compartment of the same axon, Musashi prevents ectopic synaptogenesis, revealing antagonistic, compartment-specific functions. Moreover, Musashi-dependent Ptp69D regulation controls synaptic connectivity in the olfactory circuit. Thus, Musashi differentially shapes synaptic connectivity at the level of individual subcellular compartments and within different developmental and neuron type-specific contexts.

Overview of the molecular mechanisms of migration and invasion in glioblastoma multiforme

Glioblastoma (GBM) is one of the most devastating cancers, with an approximate median survival of only 16 months. Although some new insights into the fantastic heterogeneity of this kind of brain tumor have been revealed in recent studies, all subclasses of GBM still demonstrate highly aggressive invasion properties to the surrounding parenchyma. This behavior has become the main obstruction to current curative therapies as invasive GBM cells migrate away from these foci after surgical therapies. Therefore, this review aimed to provide a relatively comprehensive study of GBM invasion mechanisms, which contains an intricate network of interactions and signaling pathways with the extracellular matrix (ECM). Among these related molecules, TGF-β, the ECM, Akt, and microRNAs are most significant in terms of cellular procedures related to GBM motility and invasion. Moreover, we also review data indicating that Musashi-1 (MSI1), a neural RNA-binding protein (RBP), regulates GBM motility and invasion, maintains stem cell populations in GBM, and promotes drug-resistant GBM phenotypes by stimulating necessary oncogenic signaling pathways through binding and regulating mRNA stability. Importantly, these necessary oncogenic signaling pathways have a close connection with TGF-β, ECM, and Akt. Thus, it appears promising to find MSI-specific inhibitors or RNA interference-based treatments to prevent the actions of these molecules despite using RBPs, which are known as hard therapeutic targets. In summary, this review aims to provide a better understanding of these signaling pathways to help in developing novel therapeutic approaches with better outcomes in preclinical studies.

Interplay of RNA-Binding Proteins and microRNAs in Neurodegenerative Diseases

The number of patients with neurodegenerative diseases (NDs) is increasing, along with the growing number of older adults. This escalation threatens to create a medical and social crisis. NDs include a large spectrum of heterogeneous and multifactorial pathologies, such as amyotrophic lateral sclerosis, frontotemporal dementia, Alzheimer’s disease, Parkinson’s disease, Huntington’s disease and multiple system atrophy, and the formation of inclusion bodies resulting from protein misfolding and aggregation is a hallmark of these disorders. The proteinaceous components of the pathological inclusions include several RNA-binding proteins (RBPs), which play important roles in splicing, stability, transcription and translation. In addition, RBPs were shown to play a critical role in regulating miRNA biogenesis and metabolism. The dysfunction of both RBPs and miRNAs is often observed in several NDs. Thus, the data about the interplay among RBPs and miRNAs and their cooperation in brain functions would be important to know for better understanding NDs and the development of effective therapeutics. In this review, we focused on the connection between miRNAs, RBPs and neurodegenerative diseases.

Musashi-1-A Stemness RBP for Cancer Therapy?

The RNA-binding protein Musashi-1 (MSI1) promotes stemness during development and cancer. By controlling target mRNA turnover and translation, MSI1 is implicated in the regulation of cancer hallmarks such as cell cycle or Notch signaling. Thereby, the protein enhanced cancer growth and therapy resistance to standard regimes. Due to its specific expression pattern and diverse functions, MSI1 represents an interesting target for cancer therapy in the future. In this review we summarize previous findings on MSI1's implications in developmental processes of other organisms. We revisit MSI1's expression in a set of solid cancers, describe mechanistic details and implications in MSI1 associated cancer hallmark pathways and highlight current research in drug development identifying the first MSI1-directed inhibitors with anti-tumor activity.

Musashi 2 influences chronic lymphocytic leukemia cell survival and growth making it a potential therapeutic target

Progression of chronic lymphocytic leukemia (CLL) results from the expansion of a small fraction of proliferating leukemic B cells. When comparing the global gene expression of recently divided CLL cells with that of previously divided cells, we found higher levels of genes involved in regulating gene expression. One of these was the oncogene Musashi 2 (MSI2), an RNA-binding protein that induces or represses translation. While there is an established role for MSI2 in normal and malignant stem cells, much less is known about its expression and role in CLL. Here we report for the first time ex vivo and in vitro experiments that MSI2 protein levels are higher in dividing and recently divided leukemic cells and that downregulating MSI2 expression or blocking its function eliminates primary human and murine CLL and mature myeloid cells. Notably, mature T cells and hematopoietic stem and progenitor cells are not affected. We also confirm that higher MSI2 levels correlate with poor outcome markers, shorter time-to-first-treatment, and overall survival. Thus, our data highlight an important role for MSI2 in CLL-cell survival and proliferation and associate MSI2 with poor prognosis in CLL patients. Collectively, these findings pinpoint MSI2 as a potentially valuable therapeutic target in CLL.

Deciphering the Role of Intestinal Crypt Cell Populations in Resistance to Chemotherapy

Intestinal crypts are composed of heterogeneous and highly plastic cell populations. Lgr5^high-stem cells (SC) are responsible for homeostatic renewal, but other cells can revert to an SC-like phenotype to maintain epithelial integrity. Despite their distinct roles in orchestrating homeostasis, both populations have been designated as the putative "cell-of-origin" of colorectal cancer. However, their respective involvement in the emergence of drug-resistant cancer SCs (CSC), responsible for tumor relapse and associated with poor outcome of colorectal cancer, remains elusive. In this context, the intestinal SC/progenitor-marker Musashi1 (MSI1) is interesting as it plays important functions in intestinal homeostasis and is frequently overexpressed in human colorectal cancer. Therefore, our aims were: (i) to study the impact of chemotherapy on Lgr5-expressing and MSI1-expressing cell populations, (ii) to explore the effect of increased MSI1 levels in response to treatment, and (iii) to evaluate the relevance in human colorectal cancer. Engineered mouse models treated with the therapeutic agent 5-fluorouracil showed that upon increased MSI1 levels, Lgr5^high SCs remain sensitive while Lgr5^low progenitors reprogram to a drug-resistant phenotype. This resulted in the expansion of an MSI1-expressing cell subpopulation with improved resistance to DNA damage and increased detoxification, typical properties of dormant-CSCs that can reactivate after chemotherapy. Analysis in patients with colorectal cancer revealed a correlation between MSI1 levels and tumor grading, CSC phenotype, and chemoresistance. Altogether, these results shed new light on the biology and plasticity of normal crypt and cancer cell populations and also open new perspectives to target MSI1 to improve chemotherapy outcome. SIGNIFICANCE: This study unveils paradoxical roles for MSI1, underlining its importance in facilitating intestinal regeneration upon injury but also unraveling its new function in drug-resistant colorectal cancer stem cells.

Potential Role of Musashi-2 RNA-Binding Protein in Cancer EMT

Local invasion and distant metastasis are the key hallmarks in the aggressive progression of malignant tumors, including the ability of cancer cells to detach from the extracellular matrix overcome apoptosis, and disseminate into distant sites. It is generally believed that this malignant behavior is stimulated by epithelial-mesenchymal transition (EMT). Musashi (MSI) RNA-binding proteins, belonging to the evolutionarily conserved RNA-binding proteins (RBP) family, were originally discovered to regulate asymmetric cell division during embryonic development. Recently, Musashi-2 (MSI2), as a key member of MSI family, has been prevalently reported to be tightly associated with the advanced clinical stage of several cancers. Multiple oncogenic signaling pathways mediated by MSI2 play vital roles in EMT. Here, we systematically reviewed the detailed role and signal networks of MSI2 in regulating cancer development, especially in EMT signal transduction, involving EGF, TGF-β, Notch, and Wnt pathways.

Musashi1 inhibit the release of Newcastle disease viruses through preventing apoptosis of DF-1 cells

The efficient proliferation of Newcastle disease virus (NDV) depends on its inhibition of host cell innate immunity. V protein acts as a nonstructural protein which plays a significant role in virus replication, whereas its function remains to be further explored. In this study, Musashi RNA binding protein 1 (MSI1) was selected and its interaction with V protein was further verified by Co-immunoprecipitation (Co-IP) and Immuno-colocalization test. Through the transfection of pCMV-HA-MSI1 in DF-1 cells, the overexpression of MSI1 reduced virus particles in the cell supernatant but not reduced mRNA and virus protein in cells pellet, which suggests that MSI1may act as a new antiviral molecule by inhibiting viral release. Cell early apoptosis was detected by flow cytometry (FCM), the result shows that overexpression of MSI1 inhibit cell apoptosis, implying MSI1 Inhibit virus release may through this way. Taken together, MSI1 and NDV V protein has a detectable interaction, and may block apoptosis to inhibit the release of NDV. However, this is the first report about the interaction between MSI1 and V protein of NDV that can inhibit the NDV replicated.

The RNA-binding protein Quaking regulates multiciliated and basal cell abundance in the developing lung

RNA-binding proteins (RBPs) form complexes with RNA, changing how the RNA is processed and thereby regulating gene expression. RBPs are important sources of gene regulation during organogenesis, including the development of lungs. The RBP called Quaking (QK) is critical for embryogenesis, yet it has not been studied in the developing lung. Here, we show that QK is widely expressed during rat lung development and into adulthood. The QK isoforms QK5 and QK7 colocalize to the nuclei of nearly all lung cells. QK6 is present in the nuclei and cytoplasm of mesenchymal cells and is only present in the epithelium during branching morphogenesis. QK knockdown in embryonic lung explants caused a greater number of multiciliated cells to appear in the airways, at the expense of basal cells. The mRNA of multiciliated cell genes and the abundance of FOXJ1/SOX2+ cells increased after knockdown, whereas P63/SOX2+ cells decreased. The cytokine IL-6, a known regulator of multiciliated cell differentiation, had increased mRNA levels after QK knockdown, although protein levels remained unchanged. Further studies are necessary to confirm whether QK acts as a blocker for the IL-6-induced differentiation of basal cells into multiciliated cells, and a conditional QK knockout would likely lead to additional discoveries on QK's role during lung development.

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.

Musashi expression in intestinal stem cells attenuates radiation-induced decline in intestinal permeability and survival in Drosophila

Exposure to genotoxic stress by environmental agents or treatments, such as radiation therapy, can diminish healthspan and accelerate aging. We have developed a Drosophila melanogaster model to study the molecular effects of radiation-induced damage and repair. Utilizing a quantitative intestinal permeability assay, we performed an unbiased GWAS screen (using 156 strains from the Drosophila Genetic Reference Panel) to search for natural genetic variants that regulate radiation-induced gut permeability in adult D. melanogaster. From this screen, we identified an RNA binding protein, Musashi (msi), as one of the possible genes associated with changes in intestinal permeability upon radiation. The overexpression of msi promoted intestinal stem cell proliferation, which increased survival after irradiation and rescued radiation-induced intestinal permeability. In summary, we have established D. melanogaster as an expedient model system to study the effects of radiation-induced damage to the intestine in adults and have identified msi as a potential therapeutic target.