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Wang G, Huang Z, Liu X, Huang W, Chen S, Zhou Y, Li D, Singer RH, Gu W. IMP1 suppresses breast tumor growth and metastasis through the regulation of its target mRNAs. Oncotarget 2016; 7:15690-702. [PMID: 26910917 PMCID: PMC4941270 DOI: 10.18632/oncotarget.7464] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2015] [Accepted: 02/05/2016] [Indexed: 02/05/2023] Open
Abstract
We have previously reported the ability of IMP1 in inhibiting proliferation and invasiveness of breast carcinoma cells in vitro. In the current study, we utilized a mouse xenograft model to further investigate the function of IMP1 in breast tumor progression and its underlying mechanism. We demonstrated that IMP1 expression significantly suppressed the growth of MDA231 cell-derived xenograft tumors and subsequent lung metastasis. Microarray analyses and differential gene expression identified handful mRNAs, many of which were involved in breast tumor-growth and metastasis. Further studies revealed that these mRNAs were directly interacted with the KH34 domain of IMP1 and this interaction post-transcriptionally regulated their corresponding protein expression. Either deletion of the KH34 domain of IMP1 or alteration of the expression of IMP1-bound mRNAs affected cell proliferation and tumor growth, producing the same phenotypes as IMP1 knockdown. Correlation of increased IMP1 expression with the reduced levels of its bound mRNAs, such as PTGS2, GDF15 and IGF-2 transcripts, was also observed in human breast tumors. Our studies provide insights into a molecular mechanism that the positive function of IMP1 to inhibit breast tumor growth and metastasis could be through the regulation of its target mRNAs.
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Affiliation(s)
- Guangli Wang
- Department of Pathophysiology, The Key Immunopathology Laboratory of Guangdong Province, Shantou University Medical College, Shantou, Guangdong Province, 515031, China
| | - Zhenqiang Huang
- Department of Pathophysiology, The Key Immunopathology Laboratory of Guangdong Province, Shantou University Medical College, Shantou, Guangdong Province, 515031, China
| | - Xin Liu
- Department of Pathophysiology, The Key Immunopathology Laboratory of Guangdong Province, Shantou University Medical College, Shantou, Guangdong Province, 515031, China
| | - Wenhe Huang
- Tumor Hospital, Shantou University Medical College, Shantou, Guangdong Province, 515031, China
| | - Shaoying Chen
- Department of Pathophysiology, The Key Immunopathology Laboratory of Guangdong Province, Shantou University Medical College, Shantou, Guangdong Province, 515031, China
| | - Yanchun Zhou
- Department of Pathophysiology, The Key Immunopathology Laboratory of Guangdong Province, Shantou University Medical College, Shantou, Guangdong Province, 515031, China
| | - Deling Li
- Department of Pathophysiology, The Key Immunopathology Laboratory of Guangdong Province, Shantou University Medical College, Shantou, Guangdong Province, 515031, China
| | - Robert H. Singer
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Wei Gu
- Department of Pathophysiology, The Key Immunopathology Laboratory of Guangdong Province, Shantou University Medical College, Shantou, Guangdong Province, 515031, China
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Regulation of Stem Cell Self-Renewal and Oncogenesis by RNA-Binding Proteins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 907:153-88. [PMID: 27256386 DOI: 10.1007/978-3-319-29073-7_7] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Throughout their life span, multicellular organisms rely on stem cell systems. During development pluripotent embryonic stem cells give rise to all cell types that make up the organism. After birth, tissue stem cells maintain properly functioning tissues and organs under homeostasis as well as promote regeneration after tissue damage or injury. Stem cells are capable of self-renewal, which is the ability to divide indefinitely while retaining the potential of differentiation into multiple cell types. The ability to self-renew, however, is a double-edged sword; the molecular mechanisms of self-renewal can be a target of malignant transformation driving tumor development and progression. Growing lines of evidence have shown that RNA-binding proteins (RBPs) play pivotal roles in the regulation of self-renewal by modulating metabolism of coding and non-coding RNAs both in normal tissues and in cancers. In this review, we discuss our current understanding of tissue stem cell systems and how RBPs regulate stem cell fates as well as how the regulatory functions of RBPs contribute to oncogenesis.
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Koltsova EK, Grivennikov SI. IMPlicating Mesenchymal Imp1 in Colitis-Associated Cancer. Mol Cancer Res 2015; 13:1452-4. [PMID: 26452664 DOI: 10.1158/1541-7786.mcr-15-0385] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2015] [Accepted: 10/01/2015] [Indexed: 11/16/2022]
Abstract
Chronic inflammation and associated pathways are significant facilitators of many disease states, including malignancies. In the context of cancer, fibroblasts can actively regulate both inflammation and carcinogenesis. In this issue, Hamilton and colleagues describe a fibroblast-specific role of the RNA binding protein Imp1 in suppression of intestinal inflammatory responses and development of colitis-associated cancer.
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Affiliation(s)
- Ekaterina K Koltsova
- Blood Cell Development and Host Defense Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania
| | - Sergei I Grivennikov
- Cancer Prevention and Control Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania.
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Madison BB, Jeganathan AN, Mizuno R, Winslow MM, Castells A, Cuatrecasas M, Rustgi AK. Let-7 Represses Carcinogenesis and a Stem Cell Phenotype in the Intestine via Regulation of Hmga2. PLoS Genet 2015; 11:e1005408. [PMID: 26244988 PMCID: PMC4526516 DOI: 10.1371/journal.pgen.1005408] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2015] [Accepted: 07/01/2015] [Indexed: 11/18/2022] Open
Abstract
Let-7 miRNAs comprise one of the largest and most highly expressed family of miRNAs among vertebrates, and is critical for promoting differentiation, regulating metabolism, inhibiting cellular proliferation, and repressing carcinogenesis in a variety of tissues. The large size of the Let-7 family of miRNAs has complicated the development of mutant animal models. Here we describe the comprehensive repression of all Let-7 miRNAs in the intestinal epithelium via low-level tissue-specific expression of the Lin28b RNA-binding protein and a conditional knockout of the MirLet7c-2/Mirlet7b locus. This ablation of Let-7 triggers the development of intestinal adenocarcinomas concomitant with reduced survival. Analysis of both mouse and human intestinal cancer specimens reveals that stem cell markers were significantly associated with loss of Let-7 miRNA expression, and that a number of Let-7 targets were elevated, including Hmga1 and Hmga2. Functional studies in 3-D enteroids revealed that Hmga2 is necessary and sufficient to mediate many characteristics of Let-7 depletion, namely accelerating cell cycle progression and enhancing a stem cell phenotype. In addition, inactivation of a single Hmga2 allele in the mouse intestine epithelium significantly represses tumorigenesis driven by Lin28b. In aggregate, we conclude that Let-7 depletion drives a stem cell phenotype and the development of intestinal cancer, primarily via Hmga2. Cancer develops following multiple genetic mutations (i.e. in tumor suppressors and oncogenes), and mutations that cooperate or synergize are often advantageous to cancer cell growth. To study how multiple genes might cooperate, it is usually informative to generate candidate mutations in cells or in mice. Large gene families, such as the Let-7 family, are difficult to silence or mutate because of the large amount of redundancy that exists between similar copies of the same gene; the mutation of one will often be masked or compensated by the continued function of others. In the mouse intestine we have achieved comprehensive depletion of all Let-7 miRNAs in this large multi-genic family through use of an inhibitory protein, called LIN28B, that specifically represses Let-7, and genetic inactivation of another gene cluster called MirLet7c-2/Mirlet7b. Mice with this comprehensive depletion of Let-7 develop intestinal cancers that resemble human colon cancers. Our further analysis identified another gene, HMGA2, downstream of this pathway that is critical to this outcome.
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Affiliation(s)
- Blair B. Madison
- Division of Gastroenterology, Washington University School of Medicine, Saint Louis, Missouri, United States of America
- Department of Medicine, Washington University School of Medicine, Saint Louis, Missouri, United States of America
| | - Arjun N. Jeganathan
- Division of Gastroenterology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, United States of America
- Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, United States of America
- Department of Surgery, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, United States of America
| | - Rei Mizuno
- Division of Gastroenterology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, United States of America
- Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, United States of America
| | - Monte M. Winslow
- Department of Genetics, Stanford University School of Medicine, Stanford, California, United States of America
| | - Antoni Castells
- Gastroenterology Department, Hospital Clínic, CIBERehd, IDIBAPS, Barcelona, Catalonia, Spain
| | - Miriam Cuatrecasas
- Department of Pathology, Pharmacology and Microbiology, Hospital Clínic, CDB, University of Barcelona, Barcelona, Catalonia, Spain
| | - Anil K. Rustgi
- Division of Gastroenterology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, United States of America
- Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, United States of America
- Department of Genetics, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, United States of America
- Abramson Cancer Center, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, United States of America
- * E-mail:
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Hamilton KE, Chatterji P, Lundsmith ET, Andres SF, Giroux V, Hicks PD, Noubissi FK, Spiegelman VS, Rustgi AK. Loss of Stromal IMP1 Promotes a Tumorigenic Microenvironment in the Colon. Mol Cancer Res 2015; 13:1478-86. [PMID: 26194191 DOI: 10.1158/1541-7786.mcr-15-0224] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2015] [Accepted: 07/08/2015] [Indexed: 12/26/2022]
Abstract
UNLABELLED The colon tumor microenvironment is becoming increasingly recognized as a complex but central player in the development of many cancers. Previously, we identified an oncogenic role for the mRNA-binding protein IMP1 (IGF2BP1) in the epithelium during colon tumorigenesis. In the current study, we reveal the contribution of stromal IMP1 in the context of colitis-associated colon tumorigenesis. Interestingly, stromal deletion of Imp1 (Dermo1Cre;Imp1(LoxP/LoxP), or Imp1(ΔMes)) in the azoxymethane/dextran sodium sulfate (AOM/DSS) model of colitis-associated cancer resulted in increased tumor numbers of larger size and more advanced histologic grade than controls. In addition, Imp1(ΔMes) mice exhibited a global increase in protumorigenic microenvironment factors, including enhanced inflammation and stromal components. Evaluation of purified mesenchyme from AOM/DSS-treated Imp1(ΔMes) mice demonstrated an increase in hepatocyte growth factor (HGF), which has not been associated with regulation via IMP1. Genetic knockdown of Imp1 in human primary fibroblasts confirmed an increase in HGF with Imp1 loss, demonstrating a specific, cell-autonomous role for Imp1 loss to increase HGF expression. Taken together, these data demonstrate a novel tumor-suppressive role for IMP1 in colon stromal cells and underscore an exquisite, context-specific function for mRNA-binding proteins, such as IMP1, in disease states. IMPLICATIONS The tumor-suppressive role of stromal IMP1 and its ability to modulate protumorigenic factors suggest that IMP1 status is important for the initiation and growth of epithelial tumors.
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Affiliation(s)
- Kathryn E Hamilton
- Division of Gastroenterology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania. Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania
| | - Priya Chatterji
- Division of Gastroenterology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania. Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania
| | - Emma T Lundsmith
- Division of Gastroenterology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania. Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania
| | - Sarah F Andres
- Division of Gastroenterology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania. Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania
| | - Veronique Giroux
- Division of Gastroenterology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania. Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania
| | - Philip D Hicks
- Division of Gastroenterology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania. Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania
| | - Felicite K Noubissi
- Department of Pediatrics, Pennsylvaia State University, College of Medicine, Hershey, Pennsylvania. Division of Pediatric Hematology/Oncology, Pennsylvaia State University, College of Medicine, Hershey, Pennsylvania. Department of Biomedical Engineering, University of Minnesota Twin Cities, Minneapolis, Minnesota
| | - Vladimir S Spiegelman
- Department of Pediatrics, Pennsylvaia State University, College of Medicine, Hershey, Pennsylvania. Division of Pediatric Hematology/Oncology, Pennsylvaia State University, College of Medicine, Hershey, Pennsylvania
| | - Anil K Rustgi
- Division of Gastroenterology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania. Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania. Department of Genetics, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania. Abramson Cancer Center, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania.
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Barnes M, van Rensburg G, Li WM, Mehmood K, Mackedenski S, Chan CM, King DT, Miller AL, Lee CH. Molecular insights into the coding region determinant-binding protein-RNA interaction through site-directed mutagenesis in the heterogeneous nuclear ribonucleoprotein-K-homology domains. J Biol Chem 2014; 290:625-39. [PMID: 25389298 DOI: 10.1074/jbc.m114.614735] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ability of its four heterogeneous nuclear RNP-K-homology (KH) domains to physically associate with oncogenic mRNAs is a major criterion for the function of the coding region determinant-binding protein (CRD-BP). However, the particular RNA-binding role of each of the KH domains remains largely unresolved. Here, we mutated the first glycine to an aspartate in the universally conserved GXXG motif of the KH domain as an approach to investigate their role. Our results show that mutation of a single GXXG motif generally had no effect on binding, but the mutation in any two KH domains, with the exception of the combination of KH3 and KH4 domains, completely abrogated RNA binding in vitro and significantly retarded granule formation in zebrafish embryos, suggesting that any combination of at least two KH domains cooperate in tandem to bind RNA efficiently. Interestingly, we found that any single point mutation in one of the four KH domains significantly impacted CRD-BP binding to mRNAs in HeLa cells, suggesting that the dynamics of the CRD-BP-mRNA interaction vary over time in vivo. Furthermore, our results suggest that different mRNAs bind preferentially to distinct CRD-BP KH domains. The novel insights revealed in this study have important implications on the understanding of the oncogenic mechanism of CRD-BP as well as in the future design of inhibitors against CRD-BP function.
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Affiliation(s)
- Mark Barnes
- From the Chemistry Program, University of Northern British Columbia, Prince George, British Columbia V2N 4Z9, Canada
| | - Gerrit van Rensburg
- From the Chemistry Program, University of Northern British Columbia, Prince George, British Columbia V2N 4Z9, Canada
| | - Wai-Ming Li
- From the Chemistry Program, University of Northern British Columbia, Prince George, British Columbia V2N 4Z9, Canada
| | - Kashif Mehmood
- From the Chemistry Program, University of Northern British Columbia, Prince George, British Columbia V2N 4Z9, Canada
| | - Sebastian Mackedenski
- From the Chemistry Program, University of Northern British Columbia, Prince George, British Columbia V2N 4Z9, Canada
| | - Ching-Man Chan
- the Division of Life Science and The Key State Laboratory for Molecular Neuroscience, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, and
| | - Dustin T King
- From the Chemistry Program, University of Northern British Columbia, Prince George, British Columbia V2N 4Z9, Canada
| | - Andrew L Miller
- the Division of Life Science and The Key State Laboratory for Molecular Neuroscience, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, and the Marine Biological Laboratory, Woods Hole, Massachusetts 02543
| | - Chow H Lee
- From the Chemistry Program, University of Northern British Columbia, Prince George, British Columbia V2N 4Z9, Canada,
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57
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Colvin HS, Nishida N, Koseki J, Konno M, Kawamoto K, Tsunekuni K, Doki Y, Mori M, Ishii H. Cancer Stem Cells of the Digestive System. Jpn J Clin Oncol 2014; 44:1141-9. [DOI: 10.1093/jjco/hyu146] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
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Faye MD, Holcik M. The role of IRES trans-acting factors in carcinogenesis. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2014; 1849:887-97. [PMID: 25257759 DOI: 10.1016/j.bbagrm.2014.09.012] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Revised: 09/09/2014] [Accepted: 09/14/2014] [Indexed: 02/06/2023]
Abstract
Regulation of protein expression through RNA metabolism is a key aspect of cellular homeostasis. Upon specific cellular stresses, distinct transcripts are selectively controlled to modify protein output in order to quickly and appropriately respond to stress. Reprogramming of the translation machinery is one node of this strict control that typically consists of an attenuation of the global, cap-dependent translation and accompanying switch to alternative mechanisms of translation initiation, such as internal ribosome entry site (IRES)-mediated initiation. In cancer, many aspects of the RNA metabolism are frequently misregulated to provide cancer cells with a growth and survival advantage. This includes changes in the expression and function of RNA binding proteins termed IRES trans-acting factors (ITAFs) that are central to IRES translation. In this review, we will examine select emerging, as well as established, ITAFs with important roles in cancer initiation and progression, and in particular their role in IRES-mediated translation. This article is part of a Special Issue entitled: Translation and Cancer.
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Affiliation(s)
- Mame Daro Faye
- Apoptosis Research Centre, Children's Hospital of Eastern Ontario Research Institute, 401 Smyth Road, Ottawa K1H 8L1, Canada; Department of Biochemistry, Microbiology and Immunology, University of Ottawa, 451 Smyth Road, Ottawa K1H 8M5, Canada
| | - Martin Holcik
- Apoptosis Research Centre, Children's Hospital of Eastern Ontario Research Institute, 401 Smyth Road, Ottawa K1H 8L1, Canada; Department of Biochemistry, Microbiology and Immunology, University of Ottawa, 451 Smyth Road, Ottawa K1H 8M5, Canada; Department of Pediatrics, University of Ottawa, 451 Smyth Road, Ottawa K1H 8M5, Canada.
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Assessing specific oligonucleotides and small molecule antibiotics for the ability to inhibit the CRD-BP-CD44 RNA interaction. PLoS One 2014; 9:e91585. [PMID: 24622399 PMCID: PMC3951440 DOI: 10.1371/journal.pone.0091585] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2013] [Accepted: 02/12/2014] [Indexed: 11/19/2022] Open
Abstract
Studies on Coding Region Determinant-Binding Protein (CRD-BP) and its orthologs have confirmed their functional role in mRNA stability and localization. CRD-BP is present in extremely low levels in normal adult tissues, but it is over-expressed in many types of aggressive human cancers and in neonatal tissues. Although the exact role of CRD-BP in tumour progression is unclear, cumulative evidence suggests that its ability to physically associate with target mRNAs is an important criterion for its oncogenic role. CRD-BP has high affinity for the 3′UTR of the oncogenic CD44 mRNA and depletion of CRD-BP in cells led to destabilization of CD44 mRNA, decreased CD44 expression, reduced adhesion and disruption of invadopodia formation. Here, we further characterize the CRD-BP-CD44 RNA interaction and assess specific antisense oligonucleotides and small molecule antibiotics for their ability to inhibit the CRD-BP-CD44 RNA interaction. CRD-BP has a high affinity for binding to CD44 RNA nts 2862–3055 with a Kd of 645 nM. Out of ten antisense oligonucleotides spanning nts 2862–3055, only three antisense oligonucleotides (DD4, DD7 and DD10) were effective in competing with CRD-BP for binding to 32P-labeled CD44 RNA. The potency of DD4, DD7 and DD10 in inhibiting the CRD-BP-CD44 RNA interaction in vitro correlated with their ability to specifically reduce the steady-state level of CD44 mRNA in cells. The aminoglycoside antibiotics neomycin, paramomycin, kanamycin and streptomycin effectively inhibited the CRD-BP-CD44 RNA interaction in vitro. Assessing the potential inhibitory effect of aminoglycoside antibiotics including neomycin on the CRD-BP-CD44 mRNA interaction in cells proved difficult, likely due to their propensity to non-specifically bind nucleic acids. Our results have important implications for future studies in finding small molecules and nucleic acid-based inhibitors that interfere with protein-RNA interactions.
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Madison BB, Liu Q, Zhong X, Hahn CM, Lin N, Emmett MJ, Stanger BZ, Lee JS, Rustgi AK. LIN28B promotes growth and tumorigenesis of the intestinal epithelium via Let-7. Genes Dev 2013; 27:2233-45. [PMID: 24142874 PMCID: PMC3814644 DOI: 10.1101/gad.224659.113] [Citation(s) in RCA: 99] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The RNA-binding proteins LIN28A and LIN28B have diverse functions in cellular reprogramming, growth, and oncogenesis. Madison et al. discover that intestine targeted expression of LIN28B causes intestinal hypertrophy, crypt expansion, and adenocarcinoma formation. Modulation of Let-7 levels via deletion of the mirLet7c2/mirLet7b genes recapitulated these effects, and intestine-specific Let-7 expression reversed the hypertrophy and Paneth cell depletion caused by Lin28b. These results demonstrate that Let-7 miRNAs are critical for repressing intestinal tissue growth and that LIN28B can act as an oncogene. The RNA-binding proteins LIN28A and LIN28B have diverse functions in embryonic stem cells, cellular reprogramming, growth, and oncogenesis. Many of these effects occur via direct inhibition of Let-7 microRNAs (miRNAs), although Let-7-independent effects have been surmised. We report that intestine targeted expression of LIN28B causes intestinal hypertrophy, crypt expansion, and Paneth cell loss. Furthermore, LIN28B fosters intestinal polyp and adenocarcinoma formation. To examine potential Let-7-independent functions of LIN28B, we pursued ribonucleoprotein cross-linking, immunoprecipitation, and high-throughput sequencing (CLIP-seq) to identify direct RNA targets. This revealed that LIN28B bound a substantial number of mRNAs and modestly augmented protein levels of these target mRNAs in vivo. Conversely, Let-7 had a profound effect; modulation of Let-7 levels via deletion of the mirLet7c2/mirLet7b genes recapitulated effects of Lin28b overexpression. Furthermore, intestine-specific Let-7 expression could reverse hypertrophy and Paneth cell depletion caused by Lin28b. This was independent of effects on insulin–PI3K–mTOR signaling. Our study reveals that Let-7 miRNAs are critical for repressing intestinal tissue growth and promoting Paneth cell differentiation. Let-7-dependent effects of LIN28B may supersede Let-7-independent effects on intestinal tissue growth. In summary, LIN28B can definitively act as an oncogene in the absence of canonical genetic alterations.
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Affiliation(s)
- Blair B Madison
- Division of Gastroenterology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania 19104, USA
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