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.

Abstract 1396: Musashi 1 stabilizes TAC1 transcript in breast cancer cells to increase the production of onco-substance P

Despite improved education and aggressive treatments, the mortality of breast cancer (BC) remains high. The TAC1 gene exerts oncogenic effects partly due to its major peptide, substance P, inducing the production of cytokines, which facilitate expression of the tumor-promoting truncated neurokinin-1 receptor. In turn, TAC1 facilitates metastasis to bone marrow and brain. TAC1 expression in BC cells (BCCs) occurs partly through increased translation of its mRNA. Cytosolic extracts from TAC1-expressing cells (BCCs and ectopic expression in non-tumorigenic breast cells) were analyzed for the candidate RNA-binding protein. In vitro translational, RNA stabilization, RNA shift and proteomic analyses identified a 40 kDa binding protein, which interacted with Exon 7 of the 3′ UTR of TAC1. Western blots and RNA supershift assay identified musashi 1 (Msi1) as the TAC1 mRNA binding protein. The data also indicated that TAC1 expression was sufficient for an increase in Msi1. A reporter gene system utilizing the TAC1 3′ UTR indicated that Msi1 competed with the endogenous translational suppressors, miR-130a and -206 for the same interacting site. Use of anti-miRs, Msi1 shRNA and the reporter gene system confirmed Msi1 as the stabilizer of TAC1 mRNA to increase the production of substance P. In vivo studies with nude mice showed reduced tumor growth with Msi1 knockdown BCCs compared to control. Msi1 knockdown retracted the tumor, indicating a role in tumor initiation. These findings correlated with a loss of two stem cell genes, REST and Oct4. In summary, this study identified Msi1 as a central RNA binding protein, which enhanced expression of the oncogenic TAC1 in BCCs. The data also suggested that Msi1, through TAC1 might be important in tumor initiation. These findings have clinical implications as a new drug target to reverse the oncogenic effects of TAC1. Furthermore, the feasibility of targeting TAC1 is evident since its receptor antagonist such as aprepitant are already approved by the FDA.

Citation Format: George R. Nahas, Raghav G. Murthy, Shyam A. Patel, Steven J. Greco, Pranela Rameshwar. Musashi 1 stabilizes TAC1 transcript in breast cancer cells to increase the production of onco-substance P. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1396. doi:10.1158/1538-7445.AM2014-1396

Abstract 3198: The RNA-binding protein Musashi-1 stabilizes TAC1 mRNA in breast cancer cells

Breast cancer (BC) remains a major public health challenge in the United States. Prognosis for metastatic cancer is poor with nearly all deaths from BC due to metastatic disease. Upon discovery in bone, the five year survival rate of BC patients is approximately eight percent. The tachykinin gene, TAC1, has been implicated in facilitating metastasis of BC to the bone marrow. The predominant product of TAC1 is the neuropeptide, substance P (SP). We have previously demonstrated that in non-malignant cells, TAC1 translation is suppressed by miRNAs. Stimulation with specific cytokines decreased these miRNA to allow synthesis of SP. BC cells (BCCs) lack endogenous expression of the TAC1-specific miRNA, which is consistent with the increased levels of SP in these cells. Herein the present study investigated the translational control of TAC1 mRNA in BCCs. Cytoplasmic extracts from BCCs showed an increase in TAC1 translation and stabilization of its mRNA. These findings led us to bioinformatic analyses of the secondary structure of TAC1 mRNA, which predicted candidate interacting sites in Exons 3 and 7. These predictions were further refined by results from an RNA shift assay that indicated an RNA-binding protein specifically targeting Exon 7. Through western blots and proteomic analysis we identified the RNA-binding protein, Musashi-1 (Msi1), as a putative candidate. Identity was confirmed by RNA supershift assay utilizing an antibody specific for Msi1. Gain-of-function and reporter gene assays utilizing the Msi1 expression vector co-transfected with a luciferase reporter gene linked to the 3′UTR of TAC1, including Exon 7, confirmed a stabilizing role for Msi1 in TAC1 mRNA regulation, concomitant with an increase in substance P. In summary, we identified Msi1 as a novel binding protein for the oncogenic TAC1 mRNA. These findings have implications for the identification of novel targets to treat BC.

Citation Format: George R. Nahas, Raghav G. Murthy, Steven J. Greco, Pranela Rameshwar. The RNA-binding protein Musashi-1 stabilizes TAC1 mRNA in breast cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3198. doi:10.1158/1538-7445.AM2013-3198

An indirect role for oncomir-519b in the expression of truncated neurokinin-1 in breast cancer cells

Neurokinin 1 (NK1) encodes full-length (NK1-FL) and truncated (NK1-Tr) receptors, with distinct 3' UTR. NK1-Tr exerts oncogenic functions and is increased in breast cancer (BC). Enhanced transcription of NK1 resulted in higher level of NK1-Tr. The 3' UTR of these two transcripts are distinct with NK1-Tr terminating at a premature stop codon. NK1-Tr mRNA gained an advantage over NK1-FL with regards to translation. This is due to the ability of miR519B to interact with sequences within the 3' UTR of NK1-FL, but not NK1-Tr since the corresponding region is omitted. MiR519b suppressed the translation of NK1-FL in T47D and MDA-MB-231 resulting in increased NK1-Tr protein. Cytokines can induce the transcription of NK1. However, our studies indicated that translation appeared to be independent of cytokine production by the BC cells (BCCs). This suggested that transcription and translation of NK1 might be independent. The findings were validated in vivo. MiR-519b suppressed the growth of MDA-MB-231 in 7/10 nude BALB/c. In total, increased NK1-Tr in BCCs is due to enhanced transcription and suppressed translation of NK1-FL by miR-519b to reduced tumor growth. In summary, we report on miRNA as a method to further regulate the expression of a spiced variant to promote oncogenesis. In addition, the findings have implications for therapy with NK1 antagonists. The oncogenic effect of NK1-Tr must be considered to improve the efficacy of current drugs to NK1.

Metastatic breast cancer cells in the bone marrow microenvironment: novel insights into oncoprotection

Among all cancers, malignancies of the breast are the second leading cause of cancer death in the United States after carcinoma of the lung. One of the major factors considered when assessing the prognosis of breast cancer patients is whether the tumor has metastasized to distant organs. Although the exact phenotype of the malignant cells responsible for metastasis and dormancy is still unknown, growing evidence has revealed that they may have stem cell-like properties that may account for resistance to chemotherapy and radiation. One process that has been attributed to primary tumor metastasis is the epithelial- to-mesenchymal transition. In this review, we specifically discuss breast cancer dissemination to the bone marrow and factors that ultimately serve to shelter and promote tumor growth, including the complex relationship between mesenchymal stem cells (MSCs) and various aspects of the immune system, carcinoma-associated fibroblasts, and the diverse components of the tumor microenvironment. A better understanding of the journey from the primary tumor site to the bone marrow and subsequently the oncoprotective role of MSCs and other factors within that microenvironment can potentially lead to development of novel therapeutic targets.

Metastatic breast cancer cells in the bone marrow microenvironment: novel insights into oncoprotection

Among all cancers, malignancies of the breast are the second leading cause of cancer death in the United States after carcinoma of the lung. One of the major factors considered when assessing the prognosis of breast cancer patients is whether the tumor has metastasized to distant organs. Although the exact phenotype of the malignant cells responsible for metastasis and dormancy is still unknown, growing evidence has revealed that they may have stem cell-like properties that may account for resistance to chemotherapy and radiation. One process that has been attributed to primary tumor metastasis is the epithelial- to-mesenchymal transition. In this review, we specifically discuss breast cancer dissemination to the bone marrow and factors that ultimately serve to shelter and promote tumor growth, including the complex relationship between mesenchymal stem cells (MSCs) and various aspects of the immune system, carcinoma-associated fibroblasts, and the diverse components of the tumor microenvironment. A better understanding of the journey from the primary tumor site to the bone marrow and subsequently the oncoprotective role of MSCs and other factors within that microenvironment can potentially lead to development of novel therapeutic targets.

Metastatic breast cancer cells in the bone marrow microenvironment: novel insights into oncoprotection

Among all cancers, malignancies of the breast are the second leading cause of cancer death in the United States after carcinoma of the lung. One of the major factors considered when assessing the prognosis of breast cancer patients is whether the tumor has metastasized to distant organs. Although the exact phenotype of the malignant cells responsible for metastasis and dormancy is still unknown, growing evidence has revealed that they may have stem cell-like properties that may account for resistance to chemotherapy and radiation. One process that has been attributed to primary tumor metastasis is the epithelial-to-mesenchymal transition. In this review, we specifically discuss breast cancer dissemination to the bone marrow and factors that ultimately serve to shelter and promote tumor growth, including the complex relationship between mesenchymal stem cells (MSCs) and various aspects of the immune system, carcinoma-associated fibroblasts, and the diverse components of the tumor microenvironment. A better understanding of the journey from the primary tumor site to the bone marrow and subsequently the oncoprotective role of MSCs and other factors within that microenvironment can potentially lead to development of novel therapeutic targets.

Neurokinin receptors as potential targets in breast cancer treatment

Despite recent advances in the diagnoses and treatment of breast cancer, this disease continues to be a major cause of death. One of the biggest challenges in breast cancer treatment is bone metastasis. Breast cancer cells (BCCs) are capable of migrating to the bone marrow and utilizing the marrow microenvironment to remain quiescent. While exhibiting quiescence in the marrow, BCCs can evade the effects of conventional cancer treatments such as chemotherapy. Therefore, scientists must find a new paradigm to target these quiescent BCCs. The development of potential targets may require a more comprehensive understanding of the marrow microenvironment and its regulators. The preprotachykinin-1 (PPT-I) gene encodes for the tachykinin peptides, which interact with neurokinin (NK) receptors. Studies have correlated this interaction with BCC integration into the bone marrow and breast cancer progression. In this review, we discuss the roles that different factors of the marrow microenvironment play in breast cancer and targets of NK receptors as potential treatment options.

Tachykinins and Hematopoiesis

Originally discovered in the 1930s, tachykinins have been a subject of renewed interest. Antagonists to the tachykinin receptors have shown potential in the treatment of a variety of maladies including neurodegenerative disorders, heart disease, pain perception and malignancies. Tachykinins have been the subject of intense studies due to their impact on hematopoiesis that has significant effects on endothelial tissue and vascular conditions. Hematopoiesis relies on a relatively small subset of bone marrow-resident hematopoietic stem cells. This review discusses the network developed by cytokines and the tachykinins to regulate hematopoiesis. An understanding of tachykinin effect on normal hematopoietic functions and their involvement in hematological disorders could lead to new treatments for bone marrow disorders such as fibrosis, leukemia and anemia.

Synergy between the RE-1 Silencer of Transcription and NFκB in the Repression of the Neurotransmitter Gene TAC1 in Human Mesenchymal Stem Cells

The RE-1 silencer of transcription (REST) is a transcriptional regulator that represses neuron-specific genes in non-neuronal tissues by remodeling chromatin structure. We have utilized human mesenchymal stem cells (MSCs) as a research tool to understand the molecular mechanisms that regulate a neurogenic program of differentiation in non-neuronal tissue. MSCs are mesoderm-derived cells that generate specialized cells such as stroma, fat, bone, and cartilage. We have reported previously the transdifferentiation of MSCs into functional neuronal cells (Cho, K. J., Trzaska, K. A., Greco, S. J., McArdle, J., Wang, F. S., Ye, J.-H., and Rameshwar, P. (2005) Stem Cells 23, 383-391). Expression of the neurotransmitter gene TAC1 was detected only in neuronal cells and thus served as a model to study transcriptional regulation of neuron-specific genes in undifferentiated MSCs. Bone marrow stromal cells are known to transiently express TAC1 following stimulation with the microenvironmental factor interleukin-1alpha. We thus compared the effects of interleukin-1alpha stimulation and neuronal induction of MSCs on TAC1 regulation. Transcription factor mapping of the 5'-flanking region of the TAC1 promoter predicted two REST-binding sites adjacent to one NFkappaB site within exon 1. Chromatin immunoprecipitation, mutagenesis, and loss-of-function studies showed that both transcription factors synergistically mediated repression of TAC1 in the neurogenic and microenvironmental models. Together, the results support the novel finding of synergism between REST and NFkappaB in the suppression of TAC1 in non-neuronal cells.

Tachykinins and hematopoietic stem cell functions: implications in clinical disorders and tissue regeneration

Hematopoiesis is the process by which a limited number of hematopoietic stem cells (HSCs) maintain a functioning blood and immune system. In adults, hematopoiesis occurs in bone marrow and is supported by the microenvironment. The tachykinin family of peptides regulates hematopoiesis. Tachykinins can be released in bone marrow as neurotransmitters from innervating fibers, and from resident bone marrow cells. The hematopoietic effects by tachykinins involve four tachykinin genes, Tac1-Tac4. The latter is the most recently discovered member and encodes hemokinin-1, endokinin A, endokinin B, and two orphan peptides, endokinin C, and endokinin D. The alteration of normal hematopoietic functions by the tachykinins may result in the development of various pathologies. For example, Tac1 is involved in myelofibrosis and in leukemia, both of which are dysfunction of hematopoietic stem cells. A comprehensive understanding of dysfunctions caused by the tachykinins requires further research since other cells, such as stromal cells and factors including cytokines, chemokines, and endopeptidases, are involved in a network in which the tachykinins have critical roles. Studies into the properties and functions of tachykinins, the biology of their receptors, and related molecules would provide insights into the development of aging disorders, hematopoiesis, other dysfunction, and may also lead to the discovery of novel and effective clinical therapies. Controversies on applications for hematopoietic stem cells in regenerative medicine are discussed. Despite these controversies, a detailed understanding on how the bone marrow microenvironment maintains pluripotency of hematopoietic stem cells would be useful to manipulate the system to acquire specialized cells for tissue repair.

Immunological study of typhoid: immunoglobulins, C3, antibodies, and leukocyte migration inhibition in patients with typhoid fever and TAB-vaccinated individuals

The development of humoral and cell-mediated immune responses to Salmonella typhi antigens and immunoglobulin and C(3) levels were determined in patients suffering from typhoid fever, TAB-vaccinated individuals, and appropriate controls. In 45 patients with typhoid, a significant elevation of immunoglobulin M (IgM) level was noted from the first week of illness onwards. Eighteen TAB-vaccinated persons also showed a significant elevation of IgM levels. In typhoid sera, the anti-O and anti-H antibodies were mostly 2-mercaptoethanol (2-ME) sensitive. The rise of IgM level correlated well with the 2-ME-sensitive anti-O and anti-H antibodies seen in typhoid patients. The anti-O antibodies in the TAB-vaccinated group were almost entirely 2-ME sensitive, but both 2-ME-sensitive and -resistant anti-H antibodies were detected in the TAB group. A marked increas in C(3) level was also noted in patients with typhoid. The cell-mediated immunity (CMI), as measured by leukocyte migration inhibition tests, was demonstrable in 15 of 22 patients with typhoid. On the other hand, only 8 of the 20 normal subjects, 5 of the 16 fever control cases, and 6 of the 18 TAB-vaccinated individuals gave a positive CMI. The latter three groups were comparable with each other but were significantly different from the typhoid patients. It was concluded that TAB-vaccination did not induce CMI even though it induced the development of antibodies, the latter being comparable with those of the patients with typhoid. The significance of these findings is discussed.