Musashi1: a stem cell marker no longer in search of a function

Dissecting RNA selectivity mediated by tandem RNA-binding domains

RNA-protein interactions are pivotal to proper gene regulation. Many RNA-binding proteins possess multiple RNA-binding domains; however, how these domains interplay to select and regulate RNA targets remains poorly understood. Here, we investigate three multidomain proteins, Musashi-1, Musashi-2, and unkempt, which share a high degree of RNA specificity, a common feature across RNA-binding proteins. We used massively parallel in vitro assays with unprecedented depth with random or naturally derived RNA sequences and find that individual domains within a protein can have differing affinities, specificities, and motif spacing preferences. We conducted large scale competition assays between these proteins and determined how individual protein specificities and affinities influence competitive binding. Integration of binding and regulation in cells with in vitro specificities showed that target selection involves a combination of the protein intrinsic specificities described here, but cellular context is critical to drive these proteins to motifs in specific transcript regions. Finally, evolutionarily conserved RNA regions displayed evidence of binding multiple RBPs in cultured cells, and these RNA regions represent the highest affinity targets. This work emphasizes the importance of in vitro and in cultured cells studies to fully profile RNA-binding proteins and highlights the complex modes of RNA-protein interactions and the contributing factors in target selection.

Navigating heme pathways: the breach of heme oxygenase and hemin in breast cancer

Breast cancer remains a significant global health challenge, with diverse subtypes and complex molecular mechanisms underlying its development and progression. This review comprehensively examines recent advances in breast cancer research, with a focus on classification, molecular pathways, and the role of heme oxygenases (HO), heme metabolism implications, and therapeutic innovations. The classification of breast cancer subtypes based on molecular profiling has significantly improved diagnosis and treatment strategies, allowing for tailored approaches to patient care. Molecular studies have elucidated key signaling pathways and biomarkers implicated in breast cancer pathogenesis, shedding light on potential targets for therapeutic intervention. Notably, emerging evidence suggests a critical role for heme oxygenases, particularly HO-1, in breast cancer progression and therapeutic resistance, highlighting the importance of understanding heme metabolism in cancer biology. Furthermore, this review highlights recent advances in breast cancer therapy, including targeted therapies, immunotherapy, and novel drug delivery systems. Understanding the complex interplay between breast cancer subtypes, molecular pathways, and innovative therapeutic approaches is essential for improving patient outcomes and developing more effective treatment strategies in the fight against breast cancer.

A novel method for culturing enteric neurons generates neurospheres containing functional myenteric neuronal subtypes

BACKGROUND

The enteric nervous system (ENS) is comprised of neurons, glia, and neural progenitor cells that regulate essential gastrointestinal functions. Advances in high-efficiency enteric neuron culture would facilitate discoveries surrounding ENS regulatory processes, pathophysiology, and therapeutics.

NEW METHOD

Development of a simple, robust, one-step method to culture murine enteric neurospheres in a 3D matrix that supports neural growth and differentiation.

RESULTS

Myenteric plexus cells isolated from the entire length of adult murine small intestine formed ≥3000 neurospheres within 7 days. Matrigel-embedded neurospheres exhibited abundant neural stem and progenitor cells expressing Sox2, Sox10 and Msi1 by day 4. By day 5, neural progenitor cell marker Nestin appeared in the periphery of neurospheres prior to differentiation. Neurospheres produced extensive neurons and neurites, confirmed by Tubulin beta III, PGP9.5, HuD/C, and NeuN immunofluorescence, including neural subtypes Calretinin, ChAT, and nNOS following 8 days of differentiation. Individual neurons within and external to neurospheres generated depolarization induced action potentials which were inhibited in the presence of sodium channel blocker, Tetrodotoxin. Differentiated neurospheres also contained a limited number of glia and endothelial cells.

COMPARISON WITH EXISTING METHODS

This novel one-step neurosphere growth and differentiation culture system, in 3D format (in the presence of GDNF, EGF, and FGF2), allows for ∼2-fold increase in neurosphere count in the derivation of enteric neurons with measurable action potentials.

CONCLUSION

Our method describes a novel, robust 3D culture of electrophysiologically active enteric neurons from adult myenteric neural stem and progenitor cells.

The Potential Reversible Transition between Stem Cells and Transient-Amplifying Cells: The Limbal Epithelial Stem Cell Perspective

Stem cells (SCs) undergo asymmetric division, producing transit-amplifying cells (TACs) with increased proliferative potential that move into tissues and ultimately differentiate into a specialized cell type. Thus, TACs represent an intermediary state between stem cells and differentiated cells. In the cornea, a population of stem cells resides in the limbal region, named the limbal epithelial stem cells (LESCs). As LESCs proliferate, they generate TACs that move centripetally into the cornea and differentiate into corneal epithelial cells. Upon limbal injury, research suggests a population of progenitor-like cells that exists within the cornea can move centrifugally into the limbus, where they dedifferentiate into LESCs. Herein, we summarize recent advances made in understanding the mechanism that governs the differentiation of LESCs into TACs, and thereafter, into corneal epithelial cells. We also outline the evidence in support of the existence of progenitor-like cells in the cornea and whether TACs could represent a population of cells with progenitor-like capabilities within the cornea. Furthermore, to gain further insights into the dynamics of TACs in the cornea, we outline the most recent findings in other organ systems that support the hypothesis that TACs can dedifferentiate into SCs.

Perturbations in neural stem cell function during a neurotropic viral infection in juvenile mice

Viral infections of the central nervous system (CNS) often cause worse neurological outcomes in younger hosts. Throughout childhood, the brain undergoes extensive development and refinement to produce functional neural networks. Network function is maintained partly with the help of neural stem cells (NSCs) that replace neuronal and glia subtypes in the two neurogenic niches of the brain (the hippocampus and subventricular zone). Accumulating evidence suggests that viruses disrupt NSC function in adulthood and infancy, but the in vivo impact of childhood infections on acute and long-term NSC function is unknown. Using a juvenile mouse model of measles virus (MeV) infection, where only mature neurons in the brain are infected, we defined the effects of the antiviral immune response on NSCs from juvenile to adult stages of life. We found that (a) virus persists in the brains of survivors despite an anti-viral immune response; (b) NSC numbers decrease dramatically during early infection, but ultimately stabilize in adult survivors; (c) infection is associated with mild apoptosis throughout the juvenile brain, but NSC proliferation is unchanged; (d) the loss of NSC numbers is dependent upon the stage of NSC differentiation; and (e) immature neurons increase early during infection, concurrent with depletion of NSC pools. Collectively, we show that NSCs are exquisitely sensitive to the inflammatory microenvironment created during neuron-restricted MeV infection in juveniles, responding with an early loss of NSCs but increased neurogenesis. These studies provide insight into potential cellular mechanisms associated with long-term neurological deficits in survivors of childhood CNS infections.

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.

Novel therapeutics and drug-delivery approaches in the modulation of glioblastoma stem cell resistance

Glioblastoma (GBM) is a deadly malignancy with a poor prognosis. An important factor contributing to GBM recurrence is high resistance of GBM cancer stem cells (GSCs). While temozolomide (TMZ), has been shown to consistently extend survival, GSCs grow resistant to TMZ through upregulation of DNA damage repair mechanisms and avoidance of apoptosis. Since a single-drug approach has failed to significantly alter prognosis in the past 15 years, unique approaches such as multidrug combination therapy together with distinctive targeted drug-delivery approaches against cancer stem cells are needed. In this review, a rationale for multidrug therapy using a targeted nanotechnology approach that preferentially target GSCs is proposed with discussion and examples of drugs, nanomedicine delivery systems, and targeting moieties.

Glioma Stem Cells in Pediatric High-Grade Gliomas: From Current Knowledge to Future Perspectives

Simple Summary

Pediatric high-grade glioma (pHGG) has a dismal prognosis in which the younger the patient, the more restricted the treatments are, in regard to the incurred risks. Current therapies destroy many tumor cells but fail to target the highly malignant glioma stem cells (GSCs) that adapt quickly to give rise to recurring, treatment-resistant cancers. Despite a lack of consensus around an efficient detection, GSCs are well described in adult brain tumors but remain poorly investigated in pediatric cases, mostly due to their rarity. An improved knowledge about GSC roles in pediatric tumors would provide a key leverage towards the elimination of this sub-population, based on targeted treatments. The aim of this review is to sum up the state of art about GSCs in pHGG.

Abstract

In children, high-grade gliomas (HGG) and diffuse midline gliomas (DMG) account for a high proportion of death due to cancer. Glioma stem cells (GSCs) are tumor cells in a specific state defined by a tumor-initiating capacity following serial transplantation, self-renewal, and an ability to recapitulate tumor heterogeneity. Their presence was demonstrated several decades ago in adult glioblastoma (GBM), and more recently in pediatric HGG and DMG. In adults, we and others have previously suggested that GSCs nest into the subventricular zone (SVZ), a neurogenic niche, where, among others, they find shelter from therapy. Both bench and bedside evidence strongly indicate a role for the GSCs and the SVZ in GBM progression, fostering the development of innovative targeting treatments. Such new therapeutic approaches are of particular interest in infants, in whom standard therapies are often limited due to the risk of late effects. The aim of this review is to describe current knowledge about GSCs in pediatric HGG and DMG, i.e., their characterization, the models that apply to their development and maintenance, the specific signaling pathways that may underlie their activity, and their specific interactions with neurogenic niches. Finally, we will discuss the clinical relevance of these observations and the therapeutic advantages of targeting the SVZ and/or the GSCs in infants.

Expression of Musashi-1 Increases in Bone Healing

Musashi-1 (MSI1) is an RNA-binding protein that regulates progenitor cells in adult and developing organisms to maintain self-renewal capacities. The role of musashi-1 in the bone healing environment and its relation with other osteogenic factors is unknown. In the current study, we analyze the expression of MSI1 in an experimental model of rat femoral bone fractures. We also analyze the relation between MSI1 expression and the expression of two osteogenic markers: periostin (POSTN) and runt-related transcription factor 2 (RUNX2). We use histological, immunohistochemical, and qPCR techniques to evaluate bone healing and the expression of MSI1, POSTN, and RUNX2 over time (4, 7, and 14 days). We compare our findings with non-fractured controls. We find that in bone calluses, the number of cells expressing MSI1 and RUNX2 increase over time and the intensity of POSTN expression decreases over time. Within bone calluses, we find the presence of MSI1 expression in mesenchymal stromal cells, osteoblasts, and osteocytes but not in hypertrophic chondrocytes. After 14 days, the expression of MSI1, POSTN, and RUNX2 was significantly correlated. Thus, we conclude that musashi-1 potentially serves in the osteogenic differentiation of mesenchymal stromal cells and bone healing. Therefore, further studies are needed to determine the possibility of musashi-1′s role as a clinical biomarker of bone healing and therapeutic agent for bone regeneration.

Musashi-1 is the candidate of the regulator of hair cell progenitors during inner ear regeneration

BACKGROUND

Hair cell loss in the cochlea is caused by ototoxic drugs, aging, and environmental stresses and could potentially lead to devastating pathophysiological effects. In adult mammals, hair cell loss is irreversible and may result in hearing and balance deficits. In contrast, nonmammalian vertebrates, including birds, can regenerate hair cells through differentiation of supporting cells and restore inner ear function, suggesting that hair cell progenitors are present in the population of supporting cells.

RESULTS

In the present study, we aimed to identify novel genes related to regeneration in the chicken utricle by gene expression profiling of supporting cell and hair cell populations obtained by laser capture microdissection. The volcano plot identified 408 differentially expressed genes (twofold change, p = 0.05, Benjamini-Hochberg multiple testing correction), 175 of which were well annotated. Among these genes, we focused on Musashi-1 (MSI1), a marker of neural stem cells involved in Notch signaling, and the downstream genes in the Notch pathway. Higher expression of these genes in supporting cells compared with that in hair cells was confirmed by quantitative reverse transcription polymerase chain reaction. Immunohistochemistry analysis demonstrated that MSI1 was mainly localized at the basal side of the supporting cell layer in normal chick utricles. During the regeneration period following aminoglycoside antibiotic-induced damage of chicken utricles, the expression levels of MSI1, hairy and enhancer of split-5, and cyclin D1 were increased, and BrdU labeling indicated that cell proliferation was enhanced.

CONCLUSIONS

The findings of this study suggested that MSI1 played an important role in the proliferation of supporting cells in the inner ear during normal and damaged conditions and could be a potential therapeutic target in the treatment of vestibular defects.

Cooperation of Musashi-2, Numb, MDM2, and P53 in drug resistance and malignant biology of pancreatic cancer

Our earlier work showed that Musashi (MSI)-2 promoted the development of pancreatic cancer (PC) by down-regulating Numb, which prevented murine double-minute (MDM)-2-mediated p53 ubiquitin degradation. Thus, we investigate the relationship among MSI2, Numb, MDM2, and p53 in PC in vitro and invivo, an association that has not been reported to our knowledge. MSI2 had no relationship with mutant p53 (mtp53) and wild-type p53 (wtp53) in normal PC cells. However, in response to gemcitabine or cisplatin treatment, MSI2 silencing simultaneously down-regulated MDM2 and up-regulated Numb and wtp53 protein levels. Moreover, these 4 endogenous proteins can be coimmunoprecipitated as a quaternary complex. Numb small interfering RNA (siRNA) reversed the MSI2 silencing-induced p53 increase. During treatment with chemical agents, MSI2 silencing decreased drug resistance and cell motility in vitro and inhibited tumor growth in vivo, all of which were significantly reversed by p53 siRNA. MSI2 was also negatively associated with Numb and positively associated with MDM2 expression in tissue. Overexpression of MSI2, MDM2, and mtp53 and weak expression of Numb were closely associated with aggressive clinicopathologic characteristics and poor prognosis for patients with PC. MSI2 negatively regulates wtp53 protein by up-regulating MDM2 and down-regulating Numb after treatment with chemical agents. MSI2 promotes drug resistance and malignant biology of PC in a p53-dependent manner.-Sheng, W., Dong, M., Chen, C., Wang, Z., Li, Y., Wang, K., Li, Y., Zhou, J. Cooperation of Musashi-2, Numb, MDM2, and P53 in drug resistance and malignant biology of pancreatic cancer.

Musashi2 promotes the development and progression of pancreatic cancer by down-regulating Numb protein

Musashi2-Numb interaction plays a vital role in the progression of myeloid leukemia. However, its potential role in solid cancers has rarely been reported. We investigated the coordinate function of Musashi2-Numb in the development of pancreatic cancer (PC) in vitro and vivo. Both Musashi2 protein and mRNA levels were higher in PC tissues than that in paired normal pancreas (P<0.05). Musashi2 overexpression and Numb positive expression were positively and negatively associated with tumor size and UICC stage, respectively (P<0.05). Multivariate analysis identified Musashi2 and Numb as adverse and favorable independent indicators for the survival of PC patients. Moreover, patients with high Musashi2 expression combining with negative Numb expression had a significantly worse overall survival (P=0.001). The negative relationship between Musashi2 and Numb was found at both PC tissue and cell levels. These two endogenous proteins can be co-immunoprecipitated from PC cell lines, and Musashi2 silence up-regulated Numb protein in vitro and vivo. Meanwhile, its silence decreased cell invasion and migration in vitro and inhibited the growth of subcutaneous tumors and the frequency of liver metastasis in vivo. However, Numb knockdown significantly reversed the decrease of cell invasion and migration induced by Musashi2 silence. Musashi2 promotes the development and progression of pancreatic cancer by down-regulating Numb protein. The interaction of Musashi2-Numb plays a significant role in the development and progression of PC.

Msi1 promotes tumor progression by epithelial-to-mesenchymal transition in cervical cancer

Musashi1 (Msi1) is an RNA-binding protein that has been reported to be a pivotal regulator in tumorigenesis and progression in several cancers. However, its function and mechanism in cervical cancer is still unknown. In this study, Msi1 expression was found elevated in cervical cancers by immunohistochemistry and correlated with poor outcomes. Then, endogenous Msi1 was silenced in cervical cancer cell lines by short hairpin RNA, and its function and mechanism were determined. The results showed that the silencing of Msi1 in SiHa and HeLa cells inhibited the cells' migratory and invasive abilities in vitro and tumor progression in vivo. Epithelial-to-mesenchymal transition (EMT) markers were down-regulated, and Wnt activity was inhibited by the silencing of Msi1. In clinical tissues, positive correlations between Msi1 and EMT markers were found. In conclusion, Msi1, a diagnostic marker and potential therapeutic target, promoted the EMT progression through activation of the Wnt signaling pathway in cervical cancers, thereby contributing to poor prognosis.

Role of Msi1 and PYGO2 in esophageal squamous cell carcinoma depth of invasion

Deregulation of developmental signaling pathways such as Wnt/b-catenin and NOTCH are commonly observed in different cancers. A normal wnt pathway is essential for development and tissue homeostasis to preserve a normal balance between the differentiation and proliferation. PYGO2 is the main transcription factor of wnt pathway, while Msi1 is one of the wnt inhibitors. In this study we assessed the correlation between Msi1 and PYGO2 mRNA expression using Real time polymerase chain reaction in 48 esophageal squamous cell carcinoma (ESCC) patients. Although, there was not any significant correlation between the levels of Msi1 and PYGO2 mRNA expression, we observed a significant correlation between the Msi1 and PYGO2 overexpressed cases and depth of tumor invasion (p = 0.05). In conclusion, despite the role of these markers in tumor depth of invasion there is not any feedback between Msi1 and PYGO2 gene expression in ESCC.

Musashi2 as a novel predictive biomarker for liver metastasis and poor prognosis in colorectal cancer

Aberrant expression of musashi2 (MSI-2) has been detected in several malignancies. However, its role in the progression of colorectal cancer (CRC) remains unknown. Our study was designed to investigate the expression and prognostic significance of MSI-2 protein in patients with colorectal cancer. The expression of MSI-2 was detected in 164 patients' colorectal cancer and control specimens by the tissue microarray technique and immunohistochemical staining. The correlations between MSI-2 expression and clinicopathological variables including overall survival were analyzed. The prognostic value of liver metastasis is evaluated by logistic regression and receiver operating characteristic (ROC) analysis. MSI-2 was highly expressed in 32.9% (54/164) of the colorectal cancer. Overexpression of MSI-2 was associated with depth of invasion, lymph node metastasis, distant metastasis, liver metastasis, Tumor Node Metastasis (TNM) clinical stage, and Carcinoembryonicantigen (CEA) level (P = 0.040, 0.014, <0.001, <0.001, 0.003, and 0.002, respectively). In the Cox multivariate test, MSI-2 overexpression, lymph node metastasis, and distant metastasis were found to be the independent prognostic factors (P = 0.027, 0.010, and 0.001, respectively). Further logistic regression suggested that TNM stage and MSI-2 high expression were related to liver metastasis in colorectal cancer patients. Conclusively, our study indicates that MSI-2 overexpression is associated with an unfavorable prognosis and may be a potential biomarker for liver metastasis in colorectal cancer patients.

Putative stem cell markers in cervical squamous cell carcinoma are correlated with poor clinical outcome

Background

The aim of this study was to elucidate the value of putative cancer stem cell markers Musashi-1, ALDH1, Sox2, and CD49f in predicting the prognosis in cervical squamous cell carcinoma (CSCC).

Methods

Real-time PCR and immunohistochemistry staining was performed to examine Musashi-1, ALDH1, Sox2, and CD49f expression in archived specimens of CSCC patients with postoperative chemotherapy. Kaplan–Meier analysis and Cox proportional hazards model were used to assess the prognostic impact of CSC markers for overall survival (OS) and recurrent-free survival (RFS).

Results

The Real-time PCR data showed that the expression of all markers were increased in CSCC tissues compared with in paired normal cervical tissues (P < 0.05). The IHC result showed that high expression of Msi1, ALDH1, Sox2, and CD49f was found in 25.7 %, 43.0 %, 62.0 % and 29.0 % CSCC samples, respectively. Moreover, high expression of Msi1 (P = 0.033 and P = 0.003, respectively), ALDH1 (P = 0.015 and P = 0.002, respectively), and Sox2 (P = 0.005 and P = 0.003, respectively), and low expression of CD49f (P = 0.027 and P = 0.025, respectively) were correlated with poor OS and PFS in CSCC patients. Interestingly, tumors with Msi1_high/CD49f_low expression had the poorest prognosis according to Msi1/CD49f stratification. In multivariate Cox regression analysis, Sox2 expression (P = 0.047 and P = 0.018, respectively), ALDH1 expression (P = 0.013 and P = 0.003, respectively), and CD49f expression (P = 0.008 and P = 0.003, respectively) were independent prognostic markers for both OS and RFS.

Conclusions

Our results suggest that cancer stem cell markers are linked with poor prognosis of CSCC patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1826-4) contains supplementary material, which is available to authorized users.

A Mouse Model of Targeted Musashi1 Expression in Whole Intestinal Epithelium Suggests Regulatory Roles in Cell Cycle and Stemness

The intestinal epithelium is very peculiar for its continuous cell renewal, fuelled by multipotent stem cells localized within the crypts of Lieberkühn. Several lines of evidence have established the evolutionary conserved RNA-binding protein Musashi1 as a marker of adult stem cells, including those of the intestinal epithelium, and revealed its roles in stem cell self-renewal and cell fate determination. Previous studies from our laboratories have shown that Musashi1 controls stem cell-like features in medulloblastoma, glioblastoma, and breast cancer cells, and has pro-proliferative and pro-tumorigenic properties in intestinal epithelial progenitor cells in vitro. To undertake a detailed study of Musashi1's function in the intestinal epithelium in vivo, we have generated a mouse model, referred to as v-Msi, overexpressing Musashi1 specifically in the entire intestinal epithelium. Compared with wild type litters, v-Msi1 mice exhibited increased intestinal crypt size accompanied by enhanced proliferation. Comparative transcriptomics by RNA-seq revealed Musashi1's association with gut stem cell signature, cell cycle, DNA replication, and drug metabolism. Finally, we identified and validated three novel mRNA targets that are stabilized by Musashi1, Ccnd1 (Cyclin D1), Cdk6, and Sox4. In conclusion, the targeted expression of Musashi1 in the intestinal epithelium in vivo increases the cell proliferation rate and strongly suggests its action on stem cells activity. This is due to the modulation of a complex network of gene functions and pathways including drug metabolism, cell cycle, and DNA synthesis and repair.

Heterogeneous generation of new cells in the adult echinoderm nervous system

Adult neurogenesis, generation of new functional cells in the mature central nervous system (CNS), has been documented in a number of diverse organisms, ranging from humans to invertebrates. However, the origin and evolution of this phenomenon is still poorly understood for many of the key phylogenetic groups. Echinoderms are one such phylum, positioned as a sister group to chordates within the monophyletic clade Deuterostomia. They are well known for the ability of their adult organs, including the CNS, to completely regenerate after injury. Nothing is known, however, about production of new cells in the nervous tissue under normal physiological conditions in these animals. In this study, we show that new cells are continuously generated in the mature radial nerve cord (RNC) of the sea cucumber Holothuria glaberrima. Importantly, this neurogenic activity is not evenly distributed, but is significantly more extensive in the lateral regions of the RNC than along the midline. Some of the new cells generated in the apical region of the ectoneural neuroepithelium leave their place of origin and migrate basally to populate the neural parenchyma. Gene expression analysis showed that generation of new cells in the adult sea cucumber CNS is associated with transcriptional activity of genes known to be involved in regulation of various aspects of neurogenesis in other animals. Further analysis of one of those genes, the transcription factor Myc, showed that it is expressed, in some, but not all radial glial cells, suggesting heterogeneity of this CNS progenitor cell population in echinoderms.

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

Substance P and its truncated receptor exert oncogenic effects. The high production of substance P in breast cancer cells (BCCs) is caused by the enhancement of tachykinin (TAC)1 translation by cytosolic factor. In vitro translational studies and mRNA stabilization analyses indicate that BCCs contain the factor needed to increase TAC1 translation and to stabilize the mRNA. Prediction of protein folding, RNA-shift analysis, and proteomic analysis identified a 40 kDa molecule that interacts with the noncoding exon 7. Western blot analysis and RNA supershift identified Musashi 1 (Msi1) as the binding protein. Ectopic expression of TAC1 in nontumorigenic breast cells (BCs) indicates that TAC1 regulates its stability by increasing Msi1. Using a reporter gene system, we showed that Msi1 competes with microRNA (miR)130a and -206 for the 3' UTR of exon 7/TAC1. In the absence of Msi1 and miR130a and -206, reporter gene activity decreased, indicating that Msi1 expression limits TAC1 expression. Tumor growth was significantly decreased when nude BALB/c mice were injected with Msi1-knockdown BCCs. In summary, the RNA-binding protein Msi1 competes with miR130a and -206 for interaction with TAC1 mRNA, to stabilize and increase its translation. Consequently, these interactions increase tumor growth.

Msi1 promotes tumor growth and cell proliferation by targeting cell cycle checkpoint proteins p21, p27 and p53 in cervical carcinomas

Musashi RNA-binding protein1 (Msi1), a member of the RNA-binding protein family, has been reported to be a diagnostic marker and potential therapeutic target in some cancers, its function in cervical cancer remains unknown. In this study, we found Msi1 was highly expressed in cervical cancer tissues, and over-expressing Msi1 in cervical cancer cells enhanced tumor formation and cell proliferation and accelerated cells into the S phase. Whereas, down-regulating Msi1 by shRNA in cervical cancer cells inhibited tumor formation and cell proliferation and slowed cell into the S phase, suggesting that Msi1 might act as cell cycle regulator. Immunohistochemistry assay showed the negative correlation between Msi1 and p21, p27 and p53, suggesting that Msi1 might regulate these cycle regulators in cervical cancer. Moreover, the expression of the p21, p27 and p53 proteins were down-regulated in Msi1 overexpressing cervical cancer cells and up-regulated in shMsi1 cervical cancer cells. Luciferase assays and RNA-protein binding assays confirmed that Msi1 could bind to the mRNA 3′UTRs of p21, p27 and p53 and suppress the translation of these proteins. Our findings provide new evidence that Msi1 might promote cell proliferation by accelerating the cell cycle by directly targeting p21, p27 and p53.

The Musashi family RNA-binding proteins in stem cells

The Musashi family is an evolutionarily conserved group of RNA-binding proteins. In mammal, two members of the group, Msi1 and Msi2, have been identified to date. Msi1 is considered to play roles in maintaining the stem cell status (stemness) of neural stem/progenitor cells in adults and in the development of central nervous system through translational regulation of its target mRNAs, which encode regulators of signal transduction and the cell cycle. Recently, strong expression of Msi1 in various somatic stem/progenitor cells of adult tissues, such as eye, gut, stomach, breast, and hair follicle, has been reported. The protein is also expressed in various cancer cells, and ectopically emerging cells have been found in neural tissues of patients with diseases involving neural disorder, including epilepsy. Many novel target mRNAs and regulatory pathways of Msi1 have been reported in recent years. Here, we present a review of the functions and action mechanisms of Msi1 protein and discuss possible directions for further study.

Up-regulated MSI2 is associated with more aggressive chronic myeloid leukemia

A better understanding of events triggering chronic myeloid leukemia progression is critical for optimized clinical management of chronic myeloid leukemia (CML). We sought to validate that increased expression of Musashi 2 (MSI2), a post-transcription regulator, is associated with progression and prognosis. Screening of 152 patients with CML showed that MSI2 was significantly decreased among patients with CML in chronic phase (CP) at diagnosis (p < 0.0001), but found no significant difference between the normal control group and treated patients with CML in CP. Moreover MSI2 was significantly increased (p < 0.0001) in patients with advance disease (AD) CML. Furthermore, our human hematopoietic cell line data imply that MSI2 and BCR-ABL1 mRNA expression are correlated. However, these data cast a doubt on earlier reports that MSI2 effects HES1 expression via NUMB-NOTCH signaling.

The RNA-binding protein Musashi-1 regulates proteasome subunit expression in breast cancer- and glioma-initiating cells

Cancer stem cells (CSCs) or tumor-initiating cells, similar to normal tissue stem cells, rely on developmental pathways, such as the Notch pathway, to maintain their stem cell state. One of the regulators of the Notch pathway is Musashi-1, a mRNA-binding protein. Musashi-1 promotes Notch signaling by binding to the mRNA of Numb, the negative regulator of Notch signaling, thus preventing its translation. CSCs have also been shown to downregulate their 26S proteasome activity in several types of solid tumors, thus making them resistant to proteasome-inhibitors used as anticancer agents in the clinic. Interestingly, the Notch pathway can be inhibited by proteasomal degradation of the Notch intracellular domain (Notch-ICD); therefore, downregulation of the 26S proteasome activity can lead to stabilization of Notch-ICD. Here, we present evidence that the downregulation of the 26S proteasome in CSCs constitutes another level of control by which Musashi-1 promotes signaling through the Notch pathway and maintenance of the stem cell phenotype of this subpopulation of cancer cells. We demonstrate that Musashi-1 mediates the downregulation of the 26S proteasome by binding to the mRNA of NF-YA, the transcriptional factor regulating 26S proteasome subunit expression, thus providing an additional route by which the degradation of Notch-ICD is prevented, and Notch signaling is sustained.

Prognostic significance of neural stem cell markers, Nestin and Musashi-1, in oral squamous cell carcinoma: expression pattern of Nestin in the precancerous stages of oral squamous epithelium

BACKGROUND

Besides the tissue-specific stem cell markers, neural and hematopoietic stem cell markers were found to play an important role in carcinogenesis. Based on this background, we have investigated the expression pattern and prognostic significance of neural stem cell markers, Nestin and Musashi-1, in oral cancer.

METHODS

We used immunohistochemistry and immunofluorescence analyses to study the expression pattern and correlation between Nestin and Musashi-1 in oral squamous cell carcinoma. The Kaplan-Meier method was used to construct overall and disease-free survival curves, and the differences were calculated using log-rank test.

RESULTS

Nestin expression was gradually increased in the transformation stages of oral cancer. Both Nestin and Musashi-1 expressions were associated with higher stage and poorly differentiated status of oral carcinoma. Interestingly, Nestin and Musashi-1 double positive cases showed statistically highly significant correlation with poorer survival of oral carcinoma patients.

CONCLUSIONS

Expression of Nestin in the preneoplastic lesions indicates its role in the transformation of oral squamous epithelium. Clinicopathological and survival analyses suggest that Nestin and Musashi-1 might be associated with invasion, differentiation and poorer survival in oral squamous cell carcinoma. In addition to their role as independent prognostic indicators, Nestin and Musashi-1 double positivity can be used to select high-risk cases for effective therapy and this is the novel finding of this study.

CLINICAL RELEVANCE

Nestin and Musashi-1 are found to be independent prognostic markers of oral cancer, and they might be used as molecular targets for effective therapy.

Blast crisis Ph+ chronic myeloid leukemia with NUP98/HOXA13 up-regulating MSI2

Background

Musashi2(Msi2)-Numb pathway de-regulation is a molecular mechanism underlying the transition of chronic phase Ph + CML to deadly blast crisis, particularly in cases with a NUP98/HOXA9 fusion from a t(7;11)(p15;p15). This study provides new insights on the mechanisms cooperating in driving MSI2 over-expression and progression of Ph-positive CML.

Results

Herein we describe a t(7;11)(p15;p15) originating a NUP98 fusion with HOXA13, at 7p15, in a 39 year-old man in blast crisis of Ph-positive CML. Both MSI2 and HOXA9 were evaluated by quantitative RT-PCR in our patient and in a series of haematological malignancies. Up-regulation of both genes emerged only in the presence of NUP98/HOXA13 gene fusion. However, over-expression of MSI2, but not HOXA9, was found in 2 cases of Ph + blast crisis with additional chromosome aberrations other than t(7;11). To determine the mechanisms underlying MSI2 over-expression in our patient we performed Chromatin Immunoprecipitation and found that NUP98/HOXA13 fusion protein deregulates MSI2 gene by binding its promoter.

Conclusions

To the best of our knowledge, this is the first molecular characterization of NUP98/HOXA13 fusion in blast crisis of Ph + CML. Our findings suggest cooperative mechanisms of MSI2 over-expression driven by HOXA proteins and strongly supports MSI2 as a prognostic marker and a candidate in target treatment of CML.

Musashi1 as a potential therapeutic target and diagnostic marker for lung cancer

Lung cancer remains one of the leading causes of cancer-related deaths worldwide with a 5-year survival rate of less than 20%. One approach to improving survival is the identification of biomarkers to detect early stage disease. In this study, we investigated the potential of the stem cell and progenitor cell marker, Musashi1 (Msi1), as a diagnostic marker and potential therapeutic target for lung cancer. Functional studies in A549 bronchioalveolar carcinoma and NCI-H520 squamous cell carcinoma cells revealed that Msi1 was enriched in spheroid cultures of tumor cells and in the CD133+ cell population. Downregulation of Msi1 by lentivirus-mediated expression of an Msi1 shRNA reduced spheroid colony proliferation. Growth inhibition was associated with reduced nuclear localization of β-catenin and inhibition of the processing of intracellular Notch. In primary lung cancer, Msi1 protein expression was elevated in 86% of 202 tissue microarray specimens, and Msi1 mRNA was increased in 80% of 118 bronchoscopic biopsies, including metastatic disease, but was rarely detected in adjacent normal lung tissue and in non-malignant diseased tissue. Msi1 was expressed in a diffuse pattern in most tumor subtypes, except in squamous cell carcinomas, where it appeared in a focal pattern in 50% of specimens. Thus, Msi1 is a sensitive and specific diagnostic marker for all lung cancer subtypes.

Musashi2 predicts poor prognosis and invasion in hepatocellular carcinoma by driving epithelial-mesenchymal transition

The high incidence of recurrence and the poor prognosis of hepatocellular carcinoma (HCC) necessitate the discovery of new predictive markers of HCC invasion and prognosis. In this study, we evaluated the expression pattern of two members of a novel oncogene family, Musashi1 (MSI1) and Musashi2 (MSI2) in 40 normal hepatic tissue specimens, 149 HCC specimens and their adjacent non-tumourous tissues. We observed that MSI1 and MSI2 were significantly up-regulated in HCC tissues. High expression levels of MSI1 and MSI2 were detectable in 37.6% (56/149) and 49.0% (73/149) of the HCC specimens, respectively, but were rarely detected in adjacent non-tumourous tissues and were never detected in normal hepatic tissue specimens. Nevertheless, only high expression of MSI2 correlated with poor prognosis. In addition, MSI2 up-regulation correlated with clinicopathological parameters representative of highly invasive HCC. Further study indicated that MSI2 might enhance invasion of HCC by inducing epithelial–mesenchymal transition (EMT). Knockdown of MSI2 significantly decreased the invasion of HCC cells and changed the expression pattern of EMT markers. Moreover, immunohistochemistry assays of 149 HCC tissue specimens further confirmed this correlation. Taken together, the results of our study demonstrated that MSI2 correlates with EMT and has the potential to be a new predictive biomarker of HCC prognosis and invasion to help guide diagnosis and treatment of post-operative HCC patients.

Clinicopathological sex- related relevance of musashi1 mRNA expression in esophageal squamous cell carcinoma patients

The cancer stem cell theory is considered as the spotlight of cancer biology, in which a subpopulation of tumor cells show unlimited proliferative and self renewal capacities. Post-transcriptional regulation is involved in different cellular functions such as cell differentiation and proliferation which results in cellular diversity. Musashi1 (Msi1) is one of the most important RNA-binding proteins (RBPs) which are involved in translational inhibition. Although, Msi1 targets are largely unknown, p21WAF-1, a cell cycle regulator, and Numb, inhibitor of notch signaling pathway, are well-known factors which are suppressed by the Msi1 in normal and cancer stem cells. Msi1 expression in tumor tissues from 53 ESCC patients was compared to normal tissues using real-time polymerase chain reaction (PCR). Msi1 was significantely overexpressed in 41.5 % of tumor samples and we observed a significant correlation between Msi1 expression and sex, in which the males had shown a higher level of Msi1 expression in comparison with the females (2.00 Vs 0.78 fold changes, p = 0.05). In this study, we assessed whether Msi1 is expressed in ESCC samples suggesting this protein as a novel cancer stem cell marker which requires further studies.

The Musashi family of RNA binding proteins: master regulators of multiple stem cell populations

In order to maintain their unlimited capacity to divide, stem cells require controlled temporal and spatial protein expression. The Musashi family of RNA-binding proteins have been shown to exhibit this necessary translational control through both repression and activation in order to regulate multiple stem cell populations. This chapter looks in depth at the initial discovery and characterisation of Musashi in the model organism Drosophila, and its subsequent emergence as a master regulator in a number of stem cell populations. Furthermore the unique roles for mammalian Musashi-1 and Musashi-2 in different stem cell types are correlated with the perceived diagnostic power of Musashi expression in specific stem cell derived oncologies. In particular the potential role for Musashi in the identification and treatment of human cancer is considered, with a focus on the role of Musashi-2 in leukaemia. Finally, the manipulation of Musashi expression is proposed as a potential avenue towards the targeted treatment of specific aggressive stem cell cancers.

Mammary stem cell research in veterinary science: an update

The mammary gland is an organ with a remarkable regenerative capacity that can undergo multiple cycles of proliferation, lactation, and involution. Growing evidence suggests that these changes are driven by the coordinated division and differentiation of mammary stem cell populations (MaSC). Whereas information regarding MaSC and their role in comparative mammary gland physiology is readily available in human and mice, such information remains scarce in most veterinary mammal species such as cows, horses, sheep, goats, pigs, and dogs. We believe that a better knowledge on the MaSC in these species will not only help to gain more insights into mammary gland (patho) physiology in veterinary medicine, but will also be of value for human medicine. Therefore, this review summarizes the current knowledge on stem cell isolation and characterization in different mammals of veterinary importance.

Mammalian cells acquire epigenetic hallmarks of human cancer during immortalization

Progression to malignancy requires that cells overcome senescence and switch to an immortal phenotype. Thus, exploring the genetic and epigenetic changes that occur during senescence/immortalization may help elucidate crucial events that lead to cell transformation. In the present study, we have globally profiled DNA methylation in relation to gene expression in primary, senescent and immortalized mouse embryonic fibroblasts. Using a high-resolution genome-wide mapping technique, followed by extensive locus-specific validation assays, we have identified 24 CpG islands that display significantly higher levels of CpG methylation in immortalized cell lines as compared to primary murine fibroblasts. Several of these hypermethylated CpG islands are associated with genes involved in the MEK–ERK pathway, one of the most frequently disrupted pathways in cancer. Approximately half of the hypermethylated targets are developmental regulators, and bind to the repressive Polycomb group (PcG) proteins, often in the context of bivalent chromatin in mouse embryonic stem cells. Because PcG-associated aberrant DNA methylation is a hallmark of several human malignancies, our methylation data suggest that epigenetic reprogramming of pluripotency genes may initiate cell immortalization. Consistent with methylome alterations, global gene expression analysis reveals that the vast majority of genes dysregulated during cell immortalization belongs to gene families that converge into the MEK–ERK pathway. Additionally, several dysregulated members of the MAP kinase network show concomitant hypermethylation of CpG islands. Unlocking alternative epigenetic routes for cell immortalization will be paramount for understanding crucial events leading to cell transformation. Unlike genetic alterations, epigenetic changes are reversible events, and as such, can be amenable to pharmacological interventions, which makes them appealing targets for cancer therapy when genetic approaches prove inadequate.

The oncogenic RNA-binding protein Musashi1 is regulated by HuR via mRNA translation and stability in glioblastoma cells

Musashi1 (Msi1) is an evolutionarily conserved RNA-binding protein (RBP) that has profound implications in cellular processes such as stem cell maintenance, nervous system development, and tumorigenesis. Msi1 is highly expressed in many cancers, including glioblastoma, whereas in normal tissues, its expression is restricted to stem cells. Unfortunately, the factors that modulate Msi1 expression and trigger high levels in tumors are largely unknown. The Msi1 mRNA has a long 3' untranslated region (UTR) containing several AU- and U-rich sequences. This type of sequence motif is often targeted by HuR, another important RBP known to be highly expressed in tumor tissue such as glioblastoma and to regulate a variety of cancer-related genes. In this report, we show an interaction between HuR and the Msi1 3'-UTR, resulting in a positive regulation of Msi1 expression. We show that HuR increased MSI1 mRNA stability and promoted its translation. We also present evidence that expression of HuR and Msi1 correlate positively in clinical glioblastoma samples. Finally, we show that inhibition of cell proliferation, increased apoptosis, and changes in cell-cycle profile as a result of silencing HuR are partially rescued when Msi1 is ectopically expressed. In summary, our results suggest that HuR is an important regulator of Msi1 in glioblastoma and that this regulation has important biological consequences during gliomagenesis.

Aberrant expression of CD133 and musashi-1 in preneoplastic and neoplastic human oral squamous epithelium and their correlation with clinicopathological factors

BACKGROUND

The present study focuses on the expression pattern of the stem cell markers CD133 and Musashi-1 in precancerous and cancerous tissues of oral epithelium. The study also aims to investigate the correlation of CD133 and Musashi-1 expression with clinicopathological factors.

METHODS

Immunohistochemical analysis was done to investigate the expression pattern of CD133 and Musashi-1, whereas, the coexpression of CD133 and Musashi-1 was studied using immunofluorescence analysis.

RESULTS

A gradual increase in the expression of CD133 and Musashi-1 was observed from normal to dysplasia to carcinoma. In addition, the expression of CD133 and Musashi-1 shows significant difference between the stages and histological types of oral carcinoma. Interestingly, coexpression of CD133 and Musashi-1 was observed in oral carcinoma and CAL27 cells.

CONCLUSIONS

A gradual increase in the expression of CD133 and Musashi-1 from normal to dysplasia to carcinoma suggests the possible involvement of these 2 proteins in oral carcinogenesis. The overexpression of CD133 and Musashi-1 in advanced stages and also in poorly differentiated tumors reveals their relationship with invasion and differentiation status of oral carcinoma cells. Moreover, the significant positive correlation between CD133 and Musashi-1 expression suggests that they might have a functional relationship in oral carcinoma cells, which needs further investigation.

Expression of a Musashi-like gene in sexual and asexual development of the colonial chordate Botryllus schlosseri and phylogenetic analysis of the protein group

Tunicates are the unique chordates to possess species reproducing sexually and asexually. Among them, the colonial ascidian Botryllus schlosseri is a reference model for the study of similarities and differences in these two developmental pathways. We here illustrate the characterization and expression pattern during both pathways of a transcript for a gene orthologous to Dazap1. Dazap1 genes encode for RNA-binding proteins and fall into the Musashi-like (Msi-like) group. Our phylogenetic analysis shows that these are related to other RNA-binding proteins (Tardbp and several heterogeneous nuclear ribonucleoproteins types) that share the same modular domain structure of conserved tandem RNA Recognition Motifs (RRMs). We also classify the whole group as derived from a single ancient duplication of the RRM. Our results also show that Dazap1 is expressed with discrete spatiotemporal pattern during embryogenesis and blastogenesis of B. schlosseri. It is never expressed in wholly differentiated tissues, but it is located in all bud tissues and in different spatiotemporally defined territories of embryos and larva. These expression patterns could indicate different roles in the two processes, but an intriguing relationship appears if aspects of cell division dynamics are taken into account, suggesting that it is related to the proliferative phases in all tissues, and raising a similarity with known Dazap1 orthologs in other metazoans.

Visual activity regulates neural progenitor cells in developing xenopus CNS through musashi1

Regulation of progenitor cell fate determines the numbers of neurons in the developing brain. While proliferation of neural progenitors predominates during early central nervous system (CNS) development, progenitor cell fate shifts toward differentiation as CNS circuits develop, suggesting that signals from developing circuits may regulate proliferation and differentiation. We tested whether activity regulates neurogenesis in vivo in the developing visual system of Xenopus tadpoles. Both cell proliferation and the number of musashi1-immunoreactive progenitors in the optic tectum decrease as visual system connections become stronger. Visual deprivation for 2 days increased proliferation of musashi1-immunoreactive radial glial progenitors, while visual experience increased neuronal differentiation. Morpholino-mediated knockdown and overexpression of musashi1 indicate that musashi1 is necessary and sufficient for neural progenitor proliferation in the CNS. These data demonstrate a mechanism by which increased brain activity in developing circuits decreases cell proliferation and increases neuronal differentiation through the downregulation of musashi1 in response to circuit activity.

Musashi1 regulates breast tumor cell proliferation and is a prognostic indicator of poor survival

Background

Musashi1 (Msi1) is a conserved RNA-binding protein that regulates the Notch and Wnt pathways, and serves as a stem cell marker in the breast and other tissues. It is unknown how Msi1 relates to other breast cancer markers, whether it denotes tumor initiating cells (TICs), and how it affects gene expression and tumor cell survival in breast cancer cells.

Results

Msi1 expression was analyzed in 20 breast cancer cell lines and in 140 primary breast tumors by western blotting and immunohistochemistry, respectively. Lentivirus RNA interference was used to reduce Msi1 expression in breast cancer cell lines MCF-7 and T47D grown as spheroid cultures and to assess stem cell gene expression and the growth of these cell lines as xenografts. In normal human breast tissue, Msi1 was expressed in 10.6% of myoepithelum and 1.2% of ductal epithelium in the terminal ductal lobular unit (TDLU), whereas, less than 0.05% of ductal epithelium and myoepithelium in large ducts outside the TDLU expressed Msi1. Msi1 was expressed in 55% of the breast cancer cell lines and correlated with ErbB2 expression in 50% of the cell lines. Msi1 was expressed in 68% of primary tumors and in 100% of lymph node metastases, and correlated with 5 year survival. Msi1 was enriched in CD133⁺ MCF-7 and T47D cells and in spheroid cultures of these cells, and Msi1 'knockdown' (KD) with a lentivirus-expressed shRNA decreased the number and size of spheroid colonies. Msi1 KD reduced Notch1, c-Myc, ErbB2 and pERK1/2 expression, and increased p21^CIP1 expression, which is consistent with known Msi1 target mRNAs. Msi1 KD also reduced the expression of the somatic and embryonic stem cell markers, CD133, Bmi1, Sox2, Nanog and Oct4. Xenografts of MCF-7 and T47D Msi1 KD cells resulted in a marked reduction of tumor growth, reduced Msi1 and Notch1 expression and increased p21^CIP1 expression.

Conclusion

Msi1 is a negative prognostic indicator of breast cancer patient survival, and is indicative of tumor cells with stem cell-like characteristics. Msi1 KD reduces tumor cell survival and tumor xenograft growth, suggesting that it may represent a novel target for drug discovery.