The Musashi proteins MSI1 and MSI2 are required for photoreceptor morphogenesis and vision in mice.

The Musashi family of RNA-binding proteins is known for its role in stem-cell renewal and is a negative regulator of cell differentiation. Interestingly, in the retina, the Musashi proteins MSI1 and MSI2 are differentially expressed throughout the cycle of retinal development, with MSI2 protein displaying robust expression in the adult retinal tissue. In this study, we investigated the importance of Musashi proteins in the development and function of photoreceptor neurons in the retina. We generated a pan-retinal and rod photoreceptor neuron-specific conditional KO mouse lacking MSI1 and MSI2. Independent of the sex, photoreceptor neurons with simultaneous deletion of Msi1 and Msi2 were unable to respond to light and displayed severely disrupted photoreceptor outer segment morphology and ciliary defects. Mice lacking MSI1 and MSI2 in the retina exhibited neuronal degeneration, with complete loss of photoreceptors within 6 months. In concordance with our earlier studies that proposed a role for Musashi proteins in regulating alternative splicing, the loss of MSI1 and MSI2 prevented the use of photoreceptor-specific exons in transcripts critical for outer segment morphogenesis, ciliogenesis, and synaptic transmission. Overall, we demonstrate a critical role for Musashi proteins in the morphogenesis of terminally differentiated photoreceptor neurons. This role is in stark contrast with the canonical function of these two proteins in the maintenance and renewal of stem cells.

Circ_0055625 knockdown inhibits tumorigenesis and improves radiosensitivity by regulating miR-338-3p/MSI1 axis in colon cancer.

BACKGROUND: Radiotherapy is a main therapeutic method for cancers, including colon cancer. In the current study, we aim to explore the effects of circular RNA (circRNA) circ_0055625 in the progression and radiosensitivity of colon cancer and the underlying mechanism. METHODS: The expression of circ_0055625 and musashi homolog 1 (MSI1) mRNA was detected by quantitative real-time polymerase chain reaction (qRT-PCR). MSI1 protein expression was determined by Western blot. Cell proliferation was assessed by cell counting kit-8 (CCK-8) and colony formation assays. Cell survival fraction, apoptosis, and invasion were investigated by colony formation assay, flow cytometry analysis, and transwell invasion assay, respectively. Cell migration was detected by wound-healing and transwell migration assays. The binding relationship between microRNA-338-3p (miR-338-3p) and circ_0055625 or MSI1 was predicted by online databases and identified by Dual-Luciferase Reporter Assay. The effects of circ_0055625 silencing on the tumor formation and radiosensitivity of colon cancer in vivo were explored by in vivo tumor formation assay. RESULTS: Circ_0055625 and MSI1 were upregulated in colon cancer tissues and cells relative to control groups. Radiation treatment apparently increased the expression of circ_0055625 and MSI1 in colon cancer cells. Circ_0055625 knockdown or MSI1 silencing repressed cell proliferation, migration, and invasion and promoted cell apoptosis and radiosensitivity in colon cancer. Also, circ_0055625 silencing-mediated effects were attenuated by MSI1 overexpression. Additionally, circ_0055625 silencing reduced MSI1 expression, which could be attenuated by miR-338-3p inhibitor. Mechanically, circ_0055625 acted as a sponge for miR-338-3p to regulate MSI1. Furthermore, circ_0055625 knockdown hindered tumor growth and improved radiosensitivity in vivo. CONCLUSION: Circ_0055625 repression inhibited the progression and radioresistance of colon cancer by downregulating MSI1 through sponging miR-338-3p. This result might provide a theoretical basis for improving the therapy of colon cancer with radiation.

[Transcription Factors of Direct Neuronal Reprogramming in Ontogenesis and ex vivo].

Direct reprogramming technology allows several specific types of cells, including specialized neurons, to be obtained from readily available autologous somatic cells. It presents unique opportunities for the development of personalized medicine, from in vitro models of hereditary and degenerative neurological diseases to novel neuroregenerative technologies. Over the past decade, a plethora of protocols for primary reprogramming has been published, yet reproducible generation of homogeneous populations of neuronally reprogrammed cells still remains a challenge. All existing protocols, however, use transcription factors that are involved in embryonic neurogenesis. This is presumably be the key issue for obtaining highly efficient and reproducible protocols for ex vivo neurogenesis. Analysis of the functional features of transcription factors in embryonic and adult neurogenesis may not only lead to the improvement of reprogramming protocols, but also, via cell marker analysis, can exactly determine the stage of neurogenesis that a particular protocol will reach. The purpose of this review is to characterize the general factors that play key roles in neurogenesis for the embryonic and adult periods, as well as in cellular reprogramming, and to assess correspondence of cell forms obtained as a result of cellular reprogramming to the ontogenetic series of the nervous system, from pluripotent stem cells to specialized neurons.

Suppression of intestinal tumorigenesis in Apc mutant mice upon Musashi-1 deletion.

Therapeutic strategies based on a specific oncogenic target are better justified when elimination of that particular oncogene reduces tumorigenesis in a model organism. One such oncogene, Musashi-1 (Msi-1), regulates translation of target mRNAs and is implicated in promoting tumorigenesis in the colon and other tissues. Msi-1 targets include the tumor suppressor adenomatous polyposis coli (Apc), a Wnt pathway antagonist lost in ∼80% of all colorectal cancers. Cell culture experiments have established that Msi-1 is a Wnt target, thus positioning Msi-1 and Apc as mutual antagonists in a mutually repressive feedback loop. Here, we report that intestines from mice lacking Msi-1 display aberrant Apc and Msi-1 mutually repressive feedback, reduced Wnt and Notch signaling, decreased proliferation, and changes in stem cell populations, features predicted to suppress tumorigenesis. Indeed, mice with germline Apc mutations (ApcMin ) or with the Apc1322T truncation mutation have a dramatic reduction in intestinal polyp number when Msi-1 is deleted. Taken together, these results provide genetic evidence that Msi-1 contributes to intestinal tumorigenesis driven by Apc loss, and validate the pursuit of Msi-1 inhibitors as chemo-prevention agents to reduce tumor burden.

Musashi1 Promotes Non-Small Cell Lung Carcinoma Malignancy and Chemoresistance via Activating the Akt Signaling Pathway.

BACKGROUND/AIMS: Lung cancer is one of the leading causes for cancer mortality. The poor therapeutic outcome of non-small cell lung carcinoma (NSCLC) is mainly due to late diagnosis and chemoresistance. In this study, we investigated the role of Musashi1 (MSI1) in NSCLC malignancy and chemoresistance. METHODS: Colony formation, MTT, glucose uptake and lactate production assays were employed to study lung cancer cell malignancy and chemoresistance. RT-PCR and Western blotting were performed to detect mRNA and protein expressions of genes. We used immunohistochemistry and Pearson correlation analysis to study the relationship of gene expression. RESULTS: We demonstrated that MSI1 was able to promote the proliferation and glucose metabolism of NSCLC cells, and to mediate the sensitivity to chemotherapy drugs in NSCLC cells. Importantly, we found that MSI1 could regulate the activity of Akt signaling. The regulation of NSCLC proliferation, glucose metabolism and chemoresistance by MSI1 was dependent on the modulation of the activity of the Akt signaling pathway. We also found that MSI1 was a target of miR-181a-5p, a microRNA involved in the regulation of cancer development. The expression levels of MSI1 and miR-181a-5p were negatively correlated in NSCLC. CONCLUSION: MSI1 promotes non-small cell lung carcinoma malignancy and chemoresistance via activating the Akt signaling pathway, which provides a new strategy for the therapy of NSCLC.

Structural Insight into the Recognition of r(UAG) by Musashi-1 RBD2, and Construction of a Model of Musashi-1 RBD1-2 Bound to the Minimum Target RNA.

Musashi-1 (Msi1) controls the maintenance of stem cells and tumorigenesis through binding to its target mRNAs and subsequent translational regulation. Msi1 has two RNA-binding domains (RBDs), RBD1 and RBD2, which recognize r(GUAG) and r(UAG), respectively. These minimal recognition sequences are connected by variable linkers in the Msi1 target mRNAs, however, the molecular mechanism by which Msi1 recognizes its targets is not yet understood. We previously determined the solution structure of the Msi1 RBD1:r(GUAGU) complex. Here, we determined the first structure of the RBD2:r(GUAGU) complex. The structure revealed that the central trinucleotide, r(UAG), is specifically recognized by the intermolecular hydrogen-bonding and aromatic stacking interactions. Importantly, the C-terminal region, which is disordered in the free form, took a certain conformation, resembling a helix. The observation of chemical shift perturbation and intermolecular NOEs, together with increases in the heteronuclear steady-state {¹H}-15N NOE values on complex formation, indicated the involvement of the C-terminal region in RNA binding. On the basis of the two complex structures, we built a structural model of consecutive RBDs with r(UAGGUAG) containing both minimal recognition sequences, which resulted in no steric hindrance. The model suggests recognition of variable lengths (n) of the linker up to n = 50 may be possible.

RNA binding protein Musashi-1 directly targets Msi2 and Erh during early testis germ cell development and interacts with IPO5 upon translocation to the nucleus.

Controlled gene regulation during gamete development is vital for maintaining reproductive potential. During the process of gamete development, male germ cells experience extended periods of inactive transcription despite requirements for continued growth and differentiation. Spermatogenesis therefore provides an ideal model to study the effects of posttranscriptional control on gene regulation. During spermatogenesis posttranscriptional regulation is orchestrated by abundantly expressed RNA-binding proteins. One such group of RNA-binding proteins is the Musashi family, previously identified as a critical regulator of testis germ cell development and meiosis in Drosophila and also shown to be vital to sperm development and reproductive potential in the mouse. We focus in depth on the role and function of the vertebrate Musashi ortholog Musashi-1 (MSI1). Through detailed expression studies and utilizing our novel transgenic Msi1 testis-specific overexpression model, we have identified 2 unique RNA-binding targets of MSI1 in spermatogonia, Msi2 and Erh, and have demonstrated a role for MSI1 in translational regulation. We have also provided evidence to suggest that nuclear import protein, IPO5, facilitates the nuclear translocation of MSI1 to the transcriptionally silenced XY chromatin domain in meiotic pachytene spermatocytes, resulting in the release of MSI1 RNA-binding targets. This firmly establishes MSI1 as a master regulator of posttranscriptional control during early spermatogenesis and highlights the significance of the subcellular localization of RNA binding proteins in relation to their function.

Musashi1 regulates survival of hepatoma cell lines by activation of Wnt signalling pathway.

BACKGROUND & AIMS: Musashi1 (MSI1) belongs to the RNA-binding protein (RBP) family, with functions as translational activator or suppressor of specifically bound mRNA. However, its function in hepatocellular carcinoma (HCC) has been deeply unexplored. Here, we investigated the role of MSI1 for proliferation and tumourigenesis in HCC. METHODS: The expression of MSI1 in HCC tissues was examined by immunohistochemistry and western blotting. The effects of MSI1 overexpression and silencing on cell proliferation, cell viability, tumoursphere and tumour formation of HCC were explored. RESULTS: In this study, we initially reported that MSI1 was upregulated in HCC. Overexpression of MSI1 in HepG2 cell lines resulted in significantly promoted cell growth, tumour formation and cell cycle progression. Consistently, knockdown of MSI1 in Huh7 cell lines remarkably inhibited cell growth and tumour formation, and caused cell cycle arrest at the G1/S transition. Dual-luciferase assays indicated that MSI1 activated Wnt signal pathway, and APC and DKK1 were direct targets of MSI1. CONCLUSION: Taken together, these findings indicate that an oncogenic role of MSI1 in HCC may be through modulation of cell growth and cell cycle by activating Wnt pathway via direct downregulation of APC and DKK1.

Mir-23a and mir-125b regulate neural stem/progenitor cell proliferation by targeting Musashi1.

Musashi1 is an RNA binding protein that controls the neural cell fate, being involved in maintaining neural progenitors in their proliferative state. In particular, its downregulation is needed for triggering early neural differentiation programs. In this study, we profiled microRNA expression during the transition from neural progenitors to differentiated astrocytes and underscored 2 upregulated microRNAs, miR-23a and miR-125b, that sinergically act to restrain Musashi1 expression, thus creating a regulatory module controlling neural progenitor proliferation.

Resveratrol Inhibits Colorectal Cancer Cell Tumor Property by Activating the miR-769-5p/MSI1 Pathway.

Resveratrol exhibits inhibitory effects on the progression of various cancers including colorectal cancer (CRC), however, the underlying mechanism in regulating CRC development remains elusive. The present study aims to uncover the role and molecular mechanism of resveratrol in modulating CRC cell tumor properties. NCM460 cells, LoVo cells, SW480 cells, and BALB/c nude mice were utilized in this study. RNA levels of miR-769-5p and musashi RNA-binding protein 1 (MSI1) were detected by quantitative real-time polymerase chain reaction (qRT-PCR). Protein expression was assessed by western blotting or immunohistochemistry assay. Cell viability was analyzed by CCK-8 assay, while cell proliferation and apoptosis were evaluated by 5-Ethynyl-2'-deoxyuridine assay and flow cytometry analysis. Cell migration was investigated by transwell and wound-healing assays. The association between miR-769-5p and MSI1 was identified by a dual-luciferase reporter assay. Tumor formation was analyzed using a xenograft mouse model assay. Compared to control groups, miR-769-5p expression was downregulated, while MSI1 expression was upregulated in CRC tissues and cells. Resveratrol treatment led to increased miR-769-5p expression and decreased MSI1 expression in CRC cells. Resveratrol treatment or miR-769-5p upregulation inhibited CRC cell proliferation and migration, and induced apoptosis. These effects were enhanced after combined treatment with resveratrol and miR-769-5p mimics. MSI1 was identified as a target of miR-769-5p, and its overexpression attenuated the effects of miR-769-5p mimics on cell proliferation, migration, and apoptosis. Moreover, miR-769-5p overexpression enhanced the inhibitory effects of resveratrol on tumor growth in vivo. Resveratrol inhibited colorectal cancer cell tumor properties by activating the miR-769-5p/MSI1 pathway.

MSI1 Stabilizes MACF1 to Inhibit Apoptosis of MC3T3-E1 Cells Induced by High Glucose and Promote Osteogenic Differentiation Through Wnt/ß-Catenin Signaling Pathway.

Diabetes mellitus (DM) affects bone metabolism and causes osteoporosis. Musashi 1 (MSI1), a member of the Musashi family, regulates protein expression by targeting protein mRNA and has been reported to play an important role in osteogenic differentiation. Therefore, this paper attempts to explore the role of MSI1 in diabetic osteoporosis and discussing its specific mechanism. The glucose concentration for high glucose (HG) and control MC3T3-E1 cells were 30 and 5.5 mM. MC3T3-E1 cells induced by high glucose (HG) were used to simulate diabetic osteoporosis in vivo. The interaction between MSI1 and microtubule actin crosslinking factor 1 (MACF1) was confirmed by RNA Immunoprecipitation (RIP). The mRNA and protein expressions of MSI1 and MACF1 in MC3T3-E1 cells and HG-induced MC3T3-E1 cells after indicated transfection were tested by Real-time quantitative polymerase chain reaction (RT-qPCR) assay and western blot. After transfection, the proliferation, apoptosis, and osteogenic differentiation of HG-induced MC3T3-E1 cells were detected by cell counting kit (CCK)-8, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), alkaline phosphatase (ALP) activity assay, and alizarin red staining. The expression of Wnt/ß-catenin signaling pathway-related proteins in HG-induced MC3T3-E1 cells after transfection was detected by western blot. This work shows that MSI1 can combine with MACF1. The expression of MSI1 and MACF1 was increased in HG-induced MC3T3-E1 cells. Upregulation of MSI1 promoted the proliferative and differentiative capabilities, but inhibited the apoptosis of HG-insulted MC3T3-E1 cells, which could be reversed by MACF1 knockdown. MSI1 stabilizes MACF1 to suppress apoptosis and promote osteogenic differentiation in HG-induced MC3T3-E1 cells by inhibiting Wnt/ß-catenin signaling pathway.

Sonic Hedgehog and WNT Signaling Regulate a Positive Feedback Loop Between Intestinal Epithelial and Stromal Cells to Promote Epithelial Regeneration.

BACKGROUND AND AIMS: Active intestinal stem cells are prone to injury by ionizing radiation. We previously showed that upon radiation-induced injury, normally quiescent reserve intestinal stem cells (rISCs) (marked by BMI1) are activated by Musashi-1 (MSI1) and exit from the quiescent state to regenerate the intestinal epithelium. This study aims to further establish the mechanism that regulates activation of Bmi1-CreER;Rosa26eYFP (Bmi1-CreER) rISCs following γ radiation-induced injury. METHODS: Bmi1-CreER mice were treated with tamoxifen to initiate lineage tracing of BMI1 (eYFP+) cells and exposed to 12 Gy of total body γ irradiation or sham. Intestinal tissues were collected and analyzed by immunofluorescence, Western blot, reverse-transcription quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, and chromatin immunoprecipitation real-time polymerase chain reaction. RESULTS: After irradiation, increased expression of Msi1 in eYFP+ cells was accompanied by increased expression of Axin2, a WNT marker. Promoter studies of the Msi1 gene indicated that Msi1 is a WNT target gene. Coculture of stromal cells isolated from irradiated mice stimulated Bmi1-CreER-derived organoid regeneration more effectively than those from sham mice. Expression of WNT ligands, including Wnt2b, Wnt4, Wnt5a, and Rspo3, was increased in irradiated stromal cells compared with sham-treated stromal cells. Moreover, expression of the Sonic hedgehog (SHH) effector Gli1 was increased in stromal cells from irradiated mice. This was correlated with an increased expression of SHH in epithelial cells postirradiation, indicating epithelial-stromal interaction. Finally, preinjury treatment with SHH inhibitor cyclopamine significantly reduced intestinal epithelial regeneration and Msi1 expression postirradiation. CONCLUSIONS: Upon ionizing radiation-induced injury, intestinal epithelial cells increase SHH secretion, stimulating stromal cells to secrete WNT ligands. WNT activators induce Msi1 expression in the Bmi1-CreER cells. This stromal-epithelial interaction leads to Bmi1-CreER rISCs induction and epithelial regeneration.

Exosomal Circ_FMN2 Derived from the Serum of Colorectal Cancer Patients Promotes Cancer Progression by miR-338-3p/MSI1 Axis.

BACKGROUND: Colorectal cancer (CRC) is a common malignancy of the gastrointestinal tract with high incidence and mortality. Exosomal circular RNA (circRNA) has been shown to be associated with the malignant progression of cancers, including CRC. Circ_0005100 (named as circ_FMN2) has been shown to promote CRC cell proliferation and migration. However, whether exosomal circ_FMN2 participated in CRC progression remains unclear. METHODS: Exosomes were isolated from the serum of CRC patients and then identified using transmission electron microscope. Western blot assay was used to test the protein levels of exosome markers, proliferation-related marker, metastasis-related markers and musashi-1 (MSI1). The expression levels of circ_FMN2, microRNA (miR)-338-3p and MSI1 were detected by qPCR. Flow cytometry, colony formation assay, MTT assay, and transwell assay were employed to measure cell cycle, apoptosis, colony formation ability, viability, migration and invasion. Dual-luciferase reporter assay was performed to assess the interaction between miR-338-3p and circ_FMN2 or MSI1. BALB/c nude mice was used to conduct animal experiments. RESULTS: Circ_FMN2 was overexpressed in the exosomes of CRC patient's serums and CRC cells. Overexpressed exosomal circ_FMN2 could promote CRC cell proliferation, metastasis, and suppress apoptosis. Circ_FMN2 acted as miR-338-3p sponge. MiR-338-3p overexpression reversed the promotion effect of circ_FMN2 on CRC progression. MSI1 was found to be a target of miR-338-3p, and its overexpression revoked the inhibitory effect of miR-338-3p on CRC progression. Furthermore, exosomal circ_FMN2 overexpression also could facilitate CRC tumor growth in vivo. CONCLUSION: Exosomal circ_FMN2 accelerated CRC progression through miR-338-3p/MSI1 axis, revealing that exosomal circ_FMN2 might be a target for CRC treatment.

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

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

The MSI1 member OsRBAP1 gene, identified by a modified MutMap method, is required for rice height and spikelet fertility.

To explore the molecular mechanisms underlying plant height regulation, we isolated and characterized a stably inherited semi-dwarf mutant bgsd-2 from the ethane methyl sulfonate (EMS) mutant progeny of 'Ping Tang Wild-type (PTWT)', a rice (Oryza sativa ssp. japonica) landrace in Guizhou. Transcriptome sequencing and qRT-PCR analyses showed that a number of cellulose and lignin-related genes involved in cell wall biogenesis were substantially downregulated in bgsd-2. MutMap-based cloning revealed the occurrence of a single amino acid substitution in the LOC_Os01g51300 gene, belonging to the MSI1 (multicopy suppressor of IRA1) member OsRBAP1. The bgsd-2 mutation occurred in the 3rd exon of OsRBAP1, resulting in a nonsense mutation of a codon shift from glycine (G) to glutamic acid (E) at residue 65. Protein localization analysis uncovered that the OsRBAP1 gene encodes a nuclear-localized protein and that the mutation in bgsd-2 may affect the stability of the OsRBAP1 protein. The CRISPR/Cas9 system was used to switch off OsRBAP1 in PTWT to obtain the knockout mutant osrbap1, which exhibited a severe reduction in height and fertility. Cytological observations suggest that the dwarfism of osrabp1 may be caused by reduced cell size and numbers, and that male sterility may be due to abnormal microspore development. Transcriptome analysis revealed that OsRBAP1 defects can repress the expression of numerous essential genes, which regulate multiple developmental processes in plants. Altogether, our results suggest that OsRBAP1 plays an important role in the regulation of rice height and spikelet fertility.

Strategic Decoy Peptides Interfere with MSI1/AGO2 Interaction to Elicit Tumor Suppression Effects.

Peptide drugs that target protein-protein interactions have attracted mounting research efforts towards clinical developments over the past decades. Increasing reports have indicated that expression of Musashi 1 (MSI1) is tightly correlated to high grade of cancers as well as enrichment of cancer stem cells. Treatment failure in malignant tumors glioblastoma multiform (GBM) had also been correlated to CSC-regulating properties of MSI1. It is thus imperative to develop new therapeutics that could effectively improve current regimens used in clinics. MSI1 and AGO2 are two emerging oncogenic molecules that both contribute to GBM tumorigenesis through mRNA regulation of targets involved in apoptosis and cell cycle. In this study, we designed peptide arrays covering the C-terminus of MSI1 and identified two peptides (Pep#11 and Pep#26) that could specifically interfere with the binding with AGO2. Our Biacore analyses ascertained binding between the identified peptides and AGO2. Recombinant reporter system Gaussian luciferase and fluorescent bioconjugate techniques were employed to determine biological functions and pharmacokinetic characteristics of these two peptides. Our data suggested that Pep#11 and Pep#26 could function as decoy peptides by mimicking the interaction function of MSI1 with its binding partner AGO2 in vitro and in vivo. Further experiments using GMB animal models corroborated the ability of Pep#11 and Pep#26 in disrupting MSI1/AGO2 interaction and consequently anti-tumorigenicity and prolonged survival rates. These striking therapeutic efficacies orchestrated by the synthetic peptides were attributed to the decoy function to C-terminal MSI1, especially in malignant brain tumors and glioblastoma.

Msi1 inhibits cervical cancer cell apoptosis by downregulating BAK through AKT signaling.

Musashi-1 (Msi1) is an RNA binding protein that functions as a regulator in multiple carcinomas. Our previous study demonstrated that Msi1 could promote the proliferation of cervical cancer cells by targeting the cell cycle proteins P21, P27 and P53. However, the mechanisms by which Msi1 affects the survival of cervical cancer cells, such as apoptosis, are still unclear. In this study, we found that the expression of Msi1 inhibited cervical cancer cell apoptosis in vitro and in vivo. Furthermore, the expression of Msi1 downregulated the expression of PTEN, while AKT signaling was activated, which resulted in a reduction in the proapoptotic protein BAK. In addition, rescue the expression of BAK in Msi1 expressing cervical cancer cells induced the increase of apoptosis cells. These findings indicate that Msi1 regulates cervical cancer cell apoptosis by inhibiting PTEN and activating AKT signaling, which leads to the downregulation of BAK.

Control of the Anterior Pituitary Cell Lineage Regulator POU1F1 by the Stem Cell Determinant Musashi.

The adipokine leptin regulates energy homeostasis through ubiquitously expressed leptin receptors. Leptin has a number of major signaling targets in the brain, including cells of the anterior pituitary (AP). We have previously reported that mice lacking leptin receptors in AP somatotropes display growth hormone (GH) deficiency, metabolic dysfunction, and adult-onset obesity. Among other targets, leptin signaling promotes increased levels of the pituitary transcription factor POU1F1, which in turn regulates the specification of somatotrope, lactotrope, and thyrotrope cell lineages within the AP. Leptin's mechanism of action on somatotropes is sex dependent, with females demonstrating posttranscriptional control of Pou1f1 messenger RNA (mRNA) translation. Here, we report that the stem cell marker and mRNA translational control protein, Musashi1, exerts repression of the Pou1f1 mRNA. In female somatotropes, Msi1 mRNA and protein levels are increased in the mouse model that lacks leptin signaling (Gh-CRE Lepr-null), coincident with lack of POU1f1 protein, despite normal levels of Pou1f1 mRNA. Single-cell RNA sequencing of pituitary cells from control female animals indicates that both Msi1 and Pou1f1 mRNAs are expressed in Gh-expressing somatotropes, and immunocytochemistry confirms that Musashi1 protein is present in the somatotrope cell population. We demonstrate that Musashi interacts directly with the Pou1f1 mRNA 3' untranslated region and exerts translational repression of a Pou1f1 mRNA translation reporter in a leptin-sensitive manner. Musashi immunoprecipitation from whole pituitary reveals coassociated Pou1f1 mRNA. These findings suggest a mechanism in which leptin stimulation is required to reverse Musashi-mediated Pou1f1 mRNA translational control to coordinate AP somatotrope function with metabolic status.

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.

Exosomal circ_IFT80 Enhances Tumorigenesis and Suppresses Radiosensitivity in Colorectal Cancer by Regulating miR-296-5p/MSI1 Axis.

BACKGROUND: Exosomal circular RNAs (circRNAs) can act as biomarkers and play crucial roles in colorectal cancer (CRC) and radiosensitivity. The aim of this study was to explore the functions and regulatory mechanism of exosomal circRNA intraflagellar transport 80 (circ_IFT80) in tumorigenesis and radiosensitivity of CRC. METHODS: Exosomes were detected using transmission electron microscopy (TEM). Protein levels were determined by Western blot assay. The expression of circ_IFT80, microRNA-296-5p (miR-296-5p) and musashi1 (MSI1) was measured by quantitative real-time polymerase chain reaction (qRT-PCR). Cell cycle distribution, cell apoptosis, and cell proliferation were detected by flow cytometry and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, respectively. Colony formation assay was used to determine the radiosensitivity of cells. The interaction between miR-296-5p and circ_IFT80 or MSI1 was verified by dual-luciferase reporter assay. A xenograft tumor model was established to explore the role of exosomal circ_IFT80 in vivo. RESULTS: Circ_IFT80 was upregulated in exosomes derived from CRC patient serum and CRC cells. Exosomal circ_IFT80 or circ_IFT80 overexpression facilitated tumorigenesis by increasing cell proliferation and reducing apoptosis, and inhibited radiosensitivity via promoting colony formation and inhibiting apoptosis. Additionally, circ_IFT80 acted as a sponge of miR-296-5p, and miR-296-5p reversed the effects of circ_IFT80 on tumorigenesis and radiosensitivity. Moreover, MSI1 was a direct target of miR-296-5p. Furthermore, miR-296-5p overexpression inhibited tumorigenesis and promoted radiosensitivity by downregulating MSI1. Exosomal circ_IFT80 also accelerated tumor growth in vivo. CONCLUSION: Exosomal circ_IFT80 promoted tumorigenesis and reduced radiosensitivity by regulating miR-296-5p/MSI1 axis, which might provide a novel avenue for treatment of CRC.