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

Department of Oncology, Georgetown University, and Lombardi Comprehensive Cancer Center, Washington, DC 20007, USA.
Molecular Cancer (Impact Factor: 4.26). 08/2010; 9(1):221. DOI: 10.1186/1476-4598-9-221
Source: PubMed


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.
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 p21CIP1 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 p21CIP1 expression.
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.

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    • "Other MSI1 functions have been identified including a role in microRNA biogenesis (Kawahara et al., 2011). MSI1 is also overexpressed in a variety of human cancers, including glioblastoma, breast, and colon cancers (Fan et al., 2010; Ma et al., 2008; Potten et al., 2003; Seigel et al., 2007; Sureban et al., 2008; Toda et al., 2001; Wang et al., 2010; Ye et al., 2008; Yokota et al., 2004), with the highest levels occurring in late stage cancers (Fan et al., 2010; Li et al., 2011; Sureban et al., 2008; Wang et al., 2010). Taken together, these data indicate that MSI1 is a cell fate determinant that drives cells toward the less differentiated (more proliferative) fate through maintenance of high levels of Notch and/or Wnt signaling (further discussed below). "
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    ABSTRACT: Musashi-1 (MSI1) is an RNA-binding protein that acts as a translation activator or repressor of target mRNAs. The best-characterized MSI1 target is Numb mRNA, whose encoded protein negatively regulates Notch signaling. Additional MSI1 targets include the mRNAs for the tumor suppressor protein APC that regulates Wnt signaling and the cyclin-dependent kinase inhibitor P21(WAF-1). We hypothesized that increased expression of NUMB, P21 and APC, through inhibition of MSI1 RNA-binding activity might be an effective way to simultaneously downregulate Wnt and Notch signaling, thus blocking the growth of a broad range of cancer cells. We used a fluorescence polarization assay to screen for small molecules that disrupt the binding of MSI1 to its consensus RNA binding site. One of the top hits was (-)-gossypol (Ki = 476 ± 273 nM), a natural product from cottonseed, known to have potent anti-tumor activity and which has recently completed Phase IIb clinical trials for prostate cancer. Surface plasmon resonance and nuclear magnetic resonance studies demonstrate a direct interaction of (-)-gossypol with the RNA binding pocket of MSI1. We further showed that (-)-gossypol reduces Notch/Wnt signaling in several colon cancer cell lines having high levels of MSI1, with reduced SURVIVIN expression and increased apoptosis/autophagy. Finally, we showed that orally administered (-)-gossypol inhibits colon cancer growth in a mouse xenograft model. Our study identifies (-)-gossypol as a potential small molecule inhibitor of MSI1-RNA interaction, and suggests that inhibition of MSI1's RNA binding activity may be an effective anti-cancer strategy. Copyright © 2015 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.
    Full-text · Article · Apr 2015 · Molecular Oncology
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    • "Knockdown of MSI1 has been shown to reduce tumor size and increase overall survival in animal models of several other tumors, including glioblastoma and colorectal cancer (Muto et al. 2012; Sureban et al. 2008). Other tumors have also been shown to overexpress MSI1 in comparison to normal tissue, although the reliance of these tumors on MSI1 expression has in most cases not yet been determined (Li et al., 2011; Liu et al., 2010; Moghbeli et al., 2013; Wang et al., 2010; 2013). "
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    ABSTRACT: Medulloblastoma, the most common malignant brain tumor in children, is a disease whose mechanisms are now beginning to be uncovered by high-throughput studies of somatic mutations, mRNA expression patterns, and epigenetic profiles of patient tumors. One emerging theme from studies that sequenced the tumor genomes of large cohorts of medulloblastoma patients is frequent mutation of RNA binding proteins. Proteins which bind multiple RNA targets can act as master regulators of gene expression at the post-transcriptional level to co-ordinate cellular processes and alter the phenotype of the cell. Identification of the target genes of RNA binding proteins may highlight essential pathways of medulloblastomagenesis that cannot be detected by study of transcriptomics alone.Furthermore, a subset of RNA binding proteins are attractive drug targets. For example, compounds that are under development as anti-viral targets due to their ability to inhibit RNA helicases could also be tested in novel approaches to medulloblastoma therapy by targeting key RNA binding proteins. In this review, we discuss a number of RNA binding proteins, including Musashi1 (MSI1), DEAD (Asp-Glu-Ala-Asp) box helicase 3 X-linked (DDX3X), DDX31, and cell division cycle and apoptosis regulator 1 (CCAR1), which play potentially critical roles in the growth and/or maintenance of medulloblastoma.
    Full-text · Article · Mar 2014 · Moleculer Cells
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    • "A commonly CSCs marker is CD133, also known as prominin-1, a 120 kDa five transmembrane domain cell surface glycoprotein, is originally described as a surface antigen specific for human hematopoietic stem and progenitor cells [14,15]. CD133 is overexpressed in various solid tumors, including brain [16], endometrial cancer [17], kidney [18], lung [19], liver [20], gastric [21,22], colon [23], pancreas [24], breast [25], skin [26] and prostate [27]. "
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    ABSTRACT: Background To investigate on expressions and clinical significances of CD133 protein and vasculogenic mimicry (VM) in primary non-small cell lung cancer (NSCLC). Methods The specimens of NSCLC from 305 Chinese patients with follow-up were analyzed for CD133 protein expression and VM by immunohistochemical and histochemical staining. Results In NSCLC, positive rates of 48.9% and 35.7% were obtained for CD133 and VM, respectively. The VM and expression of CD133 were significantly higher in carcinoma than in normal. There were a positive relationship between the VM and expression of CD133 and the tumor grade, lymph node metastasis and clinical stage (all P<0.05). The overall mean survival time of the patients with CD133 and VM positive expression was lower than that of patients with negative expression. Microvessel density (MVD) was positive corresponded with the grade, lymph node metastasis and clinical stage (all P<0.05). The overall mean survival time of the patients with MVD≥22’s group was shorter than that of patients with MVD<22’s group. Pathological-tumor-node-metastasis (pTNM) stage, positive expression of CD133 and VM, postoperative therapy and MVD were independent prognostic factors of NSCLC (P<0.05). Immunohistochemistry revealed an important intratumoral heterogeneity in all four CD133 expression profiles. Conclusions VM, MVD and expression of CD133 are related to differentiation, lymph node metastasis, clinical stage, and prognosis. It is suggested that CD133, VM and MVD should be considered as a potential marker for the prognosis.
    Full-text · Article · Nov 2012 · BMC Cancer
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