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Anand S, Vikramdeo KS, Sudan SK, Sharma A, Acharya S, Khan MA, Singh S, Singh AP. From modulation of cellular plasticity to potentiation of therapeutic resistance: new and emerging roles of MYB transcription factors in human malignancies. Cancer Metastasis Rev 2024; 43:409-421. [PMID: 37950087 PMCID: PMC11015973 DOI: 10.1007/s10555-023-10153-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/25/2023] [Accepted: 11/05/2023] [Indexed: 11/12/2023]
Abstract
MYB transcription factors are encoded by a large family of highly conserved genes from plants to vertebrates. There are three members of the MYB gene family in human, namely, MYB, MYBL1, and MYBL2 that encode MYB/c-MYB, MYBL1/A-MYB, and MYBL2/B-MYB, respectively. MYB was the first member to be identified as a cellular homolog of the v-myb oncogene carried by the avian myeloblastosis virus (AMV) causing leukemia in chickens. Under the normal scenario, MYB is predominantly expressed in hematopoietic tissues, colonic crypts, and neural stem cells and plays a role in maintaining the undifferentiated state of the cells. Over the years, aberrant expression of MYB genes has been reported in several malignancies and recent years have witnessed tremendous progress in understanding of their roles in processes associated with cancer development. Here, we review various MYB alterations reported in cancer along with the roles of MYB family proteins in tumor cell plasticity, therapy resistance, and other hallmarks of cancer. We also discuss studies that provide mechanistic insights into the oncogenic functions of MYB transcription factors to identify potential therapeutic vulnerabilities.
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Affiliation(s)
- Shashi Anand
- Department of Pathology, Frederick P. Whiddon College of Medicine, University of South Alabama, Mobile, AL, 36617, USA
- Mitchell Cancer Institute, University of South Alabama, Mobile, AL, 36604, USA
| | - Kunwar Somesh Vikramdeo
- Department of Pathology, Frederick P. Whiddon College of Medicine, University of South Alabama, Mobile, AL, 36617, USA
- Mitchell Cancer Institute, University of South Alabama, Mobile, AL, 36604, USA
| | - Sarabjeet Kour Sudan
- Department of Pathology, Frederick P. Whiddon College of Medicine, University of South Alabama, Mobile, AL, 36617, USA
- Mitchell Cancer Institute, University of South Alabama, Mobile, AL, 36604, USA
| | - Amod Sharma
- Department of Pathology, Frederick P. Whiddon College of Medicine, University of South Alabama, Mobile, AL, 36617, USA
- Mitchell Cancer Institute, University of South Alabama, Mobile, AL, 36604, USA
| | - Srijan Acharya
- Department of Pathology, Frederick P. Whiddon College of Medicine, University of South Alabama, Mobile, AL, 36617, USA
- Mitchell Cancer Institute, University of South Alabama, Mobile, AL, 36604, USA
| | - Mohammad Aslam Khan
- Department of Pathology, Frederick P. Whiddon College of Medicine, University of South Alabama, Mobile, AL, 36617, USA
- Mitchell Cancer Institute, University of South Alabama, Mobile, AL, 36604, USA
| | - Seema Singh
- Department of Pathology, Frederick P. Whiddon College of Medicine, University of South Alabama, Mobile, AL, 36617, USA
- Mitchell Cancer Institute, University of South Alabama, Mobile, AL, 36604, USA
- Department of Biochemistry and Molecular Biology, Frederick P. Whiddon College of Medicine, University of South Alabama, Mobile, AL, 36688, USA
| | - Ajay Pratap Singh
- Department of Pathology, Frederick P. Whiddon College of Medicine, University of South Alabama, Mobile, AL, 36617, USA.
- Mitchell Cancer Institute, University of South Alabama, Mobile, AL, 36604, USA.
- Department of Biochemistry and Molecular Biology, Frederick P. Whiddon College of Medicine, University of South Alabama, Mobile, AL, 36688, USA.
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Zheng X, Peng Q, Wang L, Zhang X, Huang L, Wang J, Qin Z. Serine/arginine-rich splicing factors: the bridge linking alternative splicing and cancer. Int J Biol Sci 2020; 16:2442-2453. [PMID: 32760211 PMCID: PMC7378643 DOI: 10.7150/ijbs.46751] [Citation(s) in RCA: 51] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Accepted: 06/22/2020] [Indexed: 01/08/2023] Open
Abstract
The serine/arginine-rich splicing factors (SRs) belong to the serine arginine-rich protein family, which plays an extremely important role in the splicing process of precursor RNA. The SRs recognize the splicing elements on precursor RNA, then recruit and assemble spliceosome to promote or inhibit the occurrence of splicing events. In tumors, aberrant expression of SRs causes abnormal splicing of RNA, contributing to proliferation, migration and apoptosis resistance of tumor cells. Here, we reviewed the vital role of SRs in various tumors and discussed the promise of analyzing mRNA alternative splicing events in tumor. Further, we highlight the challenges and discussed the perspectives for the identification of new potential targets for cancer therapy via SRs family members.
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Affiliation(s)
- Xiang Zheng
- Department of Pathology, Affiliated Hospital of Guilin Medical University, Guilin, Guangxi, 541001, China
| | - Qiu Peng
- Cancer Research Institute, School of Basic Medical Science, Central South University, Changsha, Hunan, 410008, China
| | - Lujuan Wang
- Cancer Research Institute, School of Basic Medical Science, Central South University, Changsha, Hunan, 410008, China
| | - Xuemei Zhang
- Department of Pathology, Affiliated Hospital of Guilin Medical University, Guilin, Guangxi, 541001, China
| | - Lili Huang
- Laboratory of Genetics and Metabolism, Maternal and Child Health Hospital of Guangxi Zhuang Autonomous Region; Guangxi Birth Defects Research and Prevention Institute, Nanning, Guangxi, 530003, China
| | - Jia Wang
- Department of Immunology, Changzhi Medical College, Changzhi, Shanxi, 046000 China
| | - Zailong Qin
- Laboratory of Genetics and Metabolism, Maternal and Child Health Hospital of Guangxi Zhuang Autonomous Region; Guangxi Birth Defects Research and Prevention Institute, Nanning, Guangxi, 530003, China
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Nakano K, Uchimaru K, Utsunomiya A, Yamaguchi K, Watanabe T. Dysregulation of c-Myb Pathway by Aberrant Expression of Proto-oncogene MYB Provides the Basis for Malignancy in Adult T-cell Leukemia/lymphoma Cells. Clin Cancer Res 2016; 22:5915-5928. [PMID: 27307595 DOI: 10.1158/1078-0432.ccr-15-1739] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Revised: 05/23/2016] [Accepted: 05/23/2016] [Indexed: 11/16/2022]
Abstract
PURPOSE Adult T-cell leukemia/lymphoma (ATLL) is an aggressive human T-cell malignancy induced by human T-lymphotrophic virus-1 (HTLV-1) infection. The genetic alterations in infected cells that lead to transformation have not been completely elucidated, thus hindering the identification of effective therapeutic targets for ATL. Here, we present the first assessment of MYB proto-oncogene dysregulation in ATL and an exploration of its role in the onset of ATL. EXPERIMENTAL DESIGN We investigated the expression patterns of MYB splicing variants in ATL. The molecular characteristics of the c-Myb-9A isoform, which was overexpressed in ATL cells, were examined using chromatin immunoprecipitation and promoter assays. We further examined the biologic impacts of abnormal c-Myb overexpression in ATL using overall c-Myb knockdown with shRNA or c-Myb-9A knockdown with morpholino oligomers. RESULTS Both total c-Myb and c-Myb-9A, which exhibited strong transforming activity, were overexpressed in ATL cells in a leukemogenesis- and progression-dependent manner. Knockdown of either total c-Myb or c-Myb-9A induced ATL cell death. c-Myb transactivates nine genes that encode essential regulators of cell proliferation and NF-κB signaling. c-Myb-9A induced significantly stronger transactivation of all tested genes and stronger NF-κB activation compared with wild-type c-Myb. CONCLUSIONS Our data demonstrate that c-Myb pathway overactivation caused by unbalanced c-Myb-9A overexpression is associated with disorders in cellular homeostasis and consequently, accelerated transformation, cell proliferation, and malignancy in ATL cells. These data support the notion of the c-Myb pathway as a promising new therapeutic target for ATL. Clin Cancer Res; 22(23); 5915-28. ©2016 AACR.
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Affiliation(s)
- Kazumi Nakano
- Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Tokyo, Japan.
| | - Kaoru Uchimaru
- Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Tokyo, Japan.,Department of Hematology and Oncology, Research Hospital, Institute of Medical Science, The University of Tokyo, Tokyo, Japan
| | - Atae Utsunomiya
- Department of Hematology, Imamura Bun-in Hospital, Kagoshima, Japan
| | - Kazunari Yamaguchi
- Department of Safety Research on Blood and Biologics, National Institute of Infectious Diseases, Tokyo, Japan
| | - Toshiki Watanabe
- Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Tokyo, Japan. .,Department of Advanced Medical Innovation, Graduate School of Medicine, St. Marianna University, Kawasaki, Japan
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Silipo M, Gautrey H, Tyson-Capper A. Deregulation of splicing factors and breast cancer development. J Mol Cell Biol 2015; 7:388-401. [PMID: 25948865 DOI: 10.1093/jmcb/mjv027] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2014] [Accepted: 02/24/2015] [Indexed: 11/13/2022] Open
Abstract
It is well known that many genes implicated in the development and progression of breast cancer undergo aberrant alternative splicing events to produce proteins with pro-cancer properties. These changes in alternative splicing can arise from mutations or single-nucleotide polymorphisms (SNPs) within the DNA sequences of cancer-related genes, which can strongly affect the activity of splicing factors and influence the splice site choice. However, it is important to note that absence of mutations is not sufficient to prevent misleading choices in splice site selection. There is now increasing evidence to demonstrate that the expression profile of ten splicing factors (including SRs and hnRNPs) and eight RNA-binding proteins changes in breast cancer cells compared with normal cells. These modifications strongly influence the alternative splicing pattern of many cancer-related genes despite the absence of any detrimental mutations within their DNA sequences. Thus, a comprehensive assessment of the splicing factor status in breast cancer is important to provide insights into the mechanisms that lead to breast cancer development and metastasis. Whilst most studies focus on mutations that affect alternative splicing in cancer-related genes, this review focuses on splicing factors and RNA-binding proteins that are themselves deregulated in breast cancer and implicated in cancer-related alternative splicing events.
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Affiliation(s)
- Marco Silipo
- Institute of Cellular Medicine, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
| | - Hannah Gautrey
- Institute of Cellular Medicine, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
| | - Alison Tyson-Capper
- Institute of Cellular Medicine, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
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Manzotti G, Mariani SA, Corradini F, Bussolari R, Cesi V, Vergalli J, Ferrari-Amorotti G, Fragliasso V, Soliera AR, Cattelani S, Raschellà G, Holyoake TL, Calabretta B. Expression of p89(c-Mybex9b), an alternatively spliced form of c-Myb, is required for proliferation and survival of p210BCR/ABL-expressing cells. Blood Cancer J 2012; 2:e71. [PMID: 22829973 PMCID: PMC3366069 DOI: 10.1038/bcj.2012.16] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Accepted: 04/05/2012] [Indexed: 01/04/2023] Open
Abstract
The c-Myb gene encodes the p75c-Myb isoform and less-abundant proteins generated by alternatively spliced transcripts. Among these, the best known is pc-Mybex9b, which contains 121 additional amino acids between exon 9 and 10, in a domain involved in protein–protein interactions and negative regulation. In hematopoietic cells, expression of pc-Mybex9b accounts for 10–15% of total c-Myb; these levels may be biologically relevant because modest changes in c-Myb expression affects proliferation and survival of leukemic cells and lineage choice and frequency of normal hematopoietic progenitors. In this study, we assessed biochemical activities of pc-Mybex9b and the consequences of perturbing its expression in K562 and primary chronic myeloid leukemia (CML) progenitor cells. Compared with p75c-Myb, pc-Mybex9b is more stable and more effective in transactivating Myb-regulated promoters. Ectopic expression of pc-Mybex9b enhanced proliferation and colony formation and reduced imatinib (IM) sensitivity of K562 cells; conversely, specific downregulation of pc-Mybex9b reduced proliferation and colony formation, enhanced IM sensitivity of K562 cells and markedly suppressed colony formation of CML CD34+ cells, without affecting the levels of p75c-Myb. Together, these studies indicate that expression of the low-abundance pc-Mybex9b isoform has an important role for the overall biological effects of c-Myb in BCR/ABL-transformed cells.
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Zhou YE, O'Rourke JP, Edwards JS, Ness SA. Single molecule analysis of c-myb alternative splicing reveals novel classifiers for precursor B-ALL. PLoS One 2011; 6:e22880. [PMID: 21853052 PMCID: PMC3154906 DOI: 10.1371/journal.pone.0022880] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Accepted: 07/06/2011] [Indexed: 11/18/2022] Open
Abstract
The c-Myb transcription factor, a key regulator of proliferation and differentiation in hematopoietic and other cell types, has an N-terminal DNA binding domain and a large C-terminal domain responsible for transcriptional activation, negative regulation and determining target gene specificity. Overexpression and rearrangement of the c-myb gene (MYB) has been reported in some patients with leukemias and other types of cancers, implicating activated alleles of c-myb in the development of human tumors. Alternative RNA splicing can produce variants of c-myb with qualitatively distinct transcriptional activities that may be involved in transformation and leukemogenesis. Here, by performing a detailed, single molecule assay we found that c-myb alternative RNA splicing was elevated and much more complex in leukemia samples than in cell lines or CD34+ hematopoietic progenitor cells from normal donors. The results revealed that leukemia samples express more than 60 different c-myb splice variants, most of which have multiple alternative splicing events and were not detectable by conventional microarray or PCR approaches. For example, the single molecule assay detected 21 and 22 splice variants containing the 9B and 9S exons, respectively, most of which encoded unexpected variant forms of c-Myb protein. Furthermore, the detailed analysis identified some splice variants whose expression correlated with poor survival in a small cohort of precursor B-ALL samples. Our findings indicate that single molecule assays can reveal complexities in c-myb alternative splicing that have potential as novel biomarkers and could help explain the role of c-Myb variants in the development of human leukemia.
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Affiliation(s)
- Ye E. Zhou
- Department of Molecular Genetics and Microbiology, University of New Mexico Health Sciences Center, Albuquerque, New Mexico, United States of America
| | - John P. O'Rourke
- Department of Molecular Genetics and Microbiology, University of New Mexico Health Sciences Center, Albuquerque, New Mexico, United States of America
| | - Jeremy S. Edwards
- Department of Molecular Genetics and Microbiology, University of New Mexico Health Sciences Center, Albuquerque, New Mexico, United States of America
| | - Scott A. Ness
- Department of Molecular Genetics and Microbiology, University of New Mexico Health Sciences Center, Albuquerque, New Mexico, United States of America
- * E-mail:
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Zhou Y, Ness SA. Myb proteins: angels and demons in normal and transformed cells. Front Biosci (Landmark Ed) 2011; 16:1109-31. [PMID: 21196221 DOI: 10.2741/3738] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
A key regulator of proliferation, differentiation and cell fate, the c-Myb transcription factor regulates the expression of hundreds of genes and is in turn regulated by numerous pathways and protein interactions. However, the most unique feature of c-Myb is that it can be converted into an oncogenic transforming protein through a few mutations that completely change its activity and specificity. The c-Myb protein is a myriad of interactions and activities rolled up in a protein that controls proliferation and differentiation in many different cell types. Here we discuss the background and recent progress that have led to a better understanding of this complex protein, and outline the questions that have yet to be answered.
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Affiliation(s)
- Ye Zhou
- Department of Molecular Genetics and Microbiology, University of New Mexico Health Sciences Center, Albuquerque, NM 87131-0001, USA
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Verduci L, Simili M, Rizzo M, Mercatanti A, Evangelista M, Mariani L, Rainaldi G, Pitto L. MicroRNA (miRNA)-mediated interaction between leukemia/lymphoma-related factor (LRF) and alternative splicing factor/splicing factor 2 (ASF/SF2) affects mouse embryonic fibroblast senescence and apoptosis. J Biol Chem 2010; 285:39551-63. [PMID: 20923760 DOI: 10.1074/jbc.m110.114736] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Leukemia/lymphoma-related factor (LRF) is a transcriptional repressor, which by recruiting histone deacetylases specifically represses p19/ARF expression, thus behaving as an oncogene. Conversely, in mouse embryonic fibroblasts (MEF), LRF inhibition causes aberrant p19ARF up-regulation resulting in proliferative defects and premature senescence. We have recently shown that LRF is controlled by microRNAs. Here we show that LRF acts on MEF proliferation and senescence/apoptosis by repressing miR-28 and miR-505, revealing a regulatory circuit where microRNAs (miRNAs) work both upstream and downstream of LRF. By analyzing miRNA expression profiles of MEF transfected with LRF-specific short interfering RNAs, we found that miR-28 and miR-505 are modulated by LRF. Both miRNAs are predicted to target alternative splicing factor/splicing factor 2 (ASF/SF2), a serine/arginine protein essential for cell viability. In vertebrates, loss or inactivation of ASF/SF2 may result in genomic instability and induce G(2) cell cycle arrest and apoptosis. We showed that miR-28 and miR-505 modulate ASF/SF2 by directly binding ASF/SF2 3'-UTR. Decrease in LRF causes a decrease in ASF/SF2, which depends on up-regulation of miR-28 and miR-505. Alteration of each of the members of the LRF/miR-28/miR-505/ASF/SF2 axis affects MEF proliferation and the number of senescent and apoptotic cells. Consistently, the axis is coordinately modulated as cell senescence increases with passages in MEF culture. In conclusion, we show that LRF-dependent miRNAs miR-28 and miR-505 control MEF proliferation and survival by targeting ASF/SF2 and suggest a central role of LRF-related miRNAs, in addition to the role of LRF-dependent p53 control, in cellular homeostasis.
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Affiliation(s)
- Lorena Verduci
- Laboratory of Gene and Molecular Therapy, Institute of Clinical Physiology, Consiglio Nazionale delle Ricerche, 56124 Pisa, Italy
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Exploiting the balance between life and death: Targeted cancer therapy and “oncogenic shock”. Biochem Pharmacol 2010; 80:666-73. [DOI: 10.1016/j.bcp.2010.03.001] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2009] [Revised: 02/24/2010] [Accepted: 03/01/2010] [Indexed: 01/05/2023]
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Abstract
The c-myb gene encodes two proteins, termed p75 and p89. Of these, the larger isoform is transcribed from an alternatively spliced message that contains an additional exon, exon 9A. Disruption of the c-myb locus in mice results in embryonic lethality due to defective hematopoiesis and in the adult, tissue-specific inactivation of c-myb in hematopoietic tissues blocks differentiation along several lineages. The c-myb knock-out mouse models described thus far result in the disruption of both the p75 and p89 isoforms, making it impossible to assign a definitive role to p89(c-Myb) in development and hematopoiesis. We have therefore generated a null-mutant mouse where exon 9A has been systemically deleted that results in the absence of only the p89-myb transcript and protein. Unlike disruption of both forms of the c-myb gene, loss of only the p89-encoding isoform does not have any deleterious effects on mammalian hematopoiesis and development.
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MYB suppresses differentiation and apoptosis of human breast cancer cells. Breast Cancer Res 2010; 12:R55. [PMID: 20659323 PMCID: PMC2949644 DOI: 10.1186/bcr2614] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2010] [Revised: 06/25/2010] [Accepted: 07/26/2010] [Indexed: 11/10/2022] Open
Abstract
INTRODUCTION MYB is highly expressed in estrogen receptor positive (ER + ve) breast tumours and tumour cell lines. We recently demonstrated that MYB is essential for the proliferation of ER + ve breast cancer cells, and have now investigated its role in mammary epithelial differentiation. METHODS MCF-7 breast cancer cells were treated with sodium butyrate, vitamin E succinate or 12-O-tetradecanoylphorbol-13-acetate to induce differentiation as measured by Nile Red staining of lipid droplets and β-casein expression. The non-tumorigenic murine mammary epithelial cell (MEC) line, HC11, was induced to differentiate with lactogenic hormones. MYB levels were manipulated by inducible lentiviral shRNA-mediated knockdown and retroviral overexpression. RESULTS We found that MYB expression decreases following chemically-induced differentiation of the human breast cancer cell line MCF-7, and hormonally-induced differentiation of a non-tumorigenic murine mammary epithelial cell (MEC) line, HC11. We also found that shRNA-mediated MYB knockdown initiated differentiation of breast cancer cells, and greatly sensitised them to the differentiative and pro-apoptotic effects of differentiation-inducing agents (DIAs). Sensitisation to the pro-apoptotic effects DIAs is mediated by decreased expression of BCL2, which we show here is a direct MYB target in breast cancer cells. Conversely, enforced expression of MYB resulted in the cells remaining in an undifferentiated state, with concomitant suppression of apoptosis, in the presence of DIAs. CONCLUSIONS Taken together, these data imply that MYB function is critical in regulating the balance between proliferation, differentiation, and apoptosis in MECs. Moreover, our findings suggest MYB may be a viable therapeutic target in breast cancer and suggest specific approaches for exploiting this possibility.
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Abstract
The transcription factor MYB has a key role as a regulator of stem and progenitor cells in the bone marrow, colonic crypts and a neurogenic region of the adult brain. It is in these compartments that a deficit in MYB activity leads to severe or lethal phenotypes. As was predicted from its leukaemogenicity in several animal species, MYB has now been identified as an oncogene that is involved in some human leukaemias. Moreover, recent evidence has strengthened the case that MYB is activated in colon and breast cancer: a block to MYB expression is overcome by mutation of the regulatory machinery in the former disease and by oestrogen receptor-alpha (ERalpha) in the latter.
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Affiliation(s)
- Robert G Ramsay
- Peter MacCallum Cancer Centre, St Andrew's Place, Melbourne, Victoria 3002, Australia
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Alternative RNA splicing produces multiple forms of c-Myb with unique transcriptional activities. Mol Cell Biol 2008; 28:2091-101. [PMID: 18195038 DOI: 10.1128/mcb.01870-07] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The c-Myb transcription factor regulates the proliferation and differentiation of hematopoietic cells, and activated alleles of c-myb induce leukemias and lymphomas in animals. Relatively minor changes in the structure of c-Myb protein change the genes that it regulates and can unleash its latent transforming activities. Here, quantitative assays were used to analyze the alternative splicing of human c-myb transcripts. We identified an array of variant transcripts, expressed in highly regulated, lineage-specific patterns, that were formed through the use of alternate exons 8A, 9A, 9B, 10A, 13A, and 14A. Expression levels of the different splice variant transcripts were regulated independently of one another during human hematopoietic cell differentiation, and the alternative splicing of c-myb mRNAs was increased in primary leukemia samples. The alternatively spliced c-myb transcripts were associated with polysomes and encoded a series of c-Myb proteins with identical DNA binding domains but unique C-terminal domains. In several types of assays, the variant c-Myb proteins exhibited quantitative and qualitative differences in transcriptional activities and specificities. The results suggest that the human c-myb gene encodes a family of related proteins with different transcriptional activities. Enhanced alternative splicing may be a mechanism for unmasking the transforming activity of c-myb in human leukemias.
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Hwang IK, Moon SM, Yoo KY, Li H, Kwon HD, Hwang HS, Choi SK, Lee BH, Kim JD, Won MH. c-Myb immunoreactivity, protein and mRNA levels significantly increase in the aged hippocampus proper in gerbils. Neurochem Res 2007; 32:1091-7. [PMID: 17401667 DOI: 10.1007/s11064-006-9278-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2006] [Accepted: 12/28/2006] [Indexed: 11/28/2022]
Abstract
Myb genes are a family of transcription factors and have been implicated in the control of the proliferation and differentiation of normal and transformed cells. c-Myb is the best characterized member of the myb family. In the present study, we investigated age-dependent changes of c-myb immunoreactivity, its protein and mRNA level in the hippocampus proper (CA1-3 regions) at various age stages in gerbils. In the postnatal month 1 (PM 1) group, c-myb immunoreactivity was detected in non-pyramidal neurons of the strata oriens and radiatum as well as in pyramidal neurons of the stratum pyramidale. At PM 3, c-myb immunoreactivity and its protein level were similar to those at PM 1. Thereafter, c-myb immunoreactivity and its protein level were increased with time. In the PM 24 group, c-myb immunoreactivity, its protein and mRNA levels were highest. These results suggest that the significant increase of c-myb immunoreactivity, protein and mRNA levels in the aged hippocampus may be associated with neuronal aging.
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Affiliation(s)
- In Koo Hwang
- Department of Anatomy and Neurobiology, College of Medicine, Hallym University, Chuncheon, South Korea
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Karni R, de Stanchina E, Lowe SW, Sinha R, Mu D, Krainer AR. The gene encoding the splicing factor SF2/ASF is a proto-oncogene. Nat Struct Mol Biol 2007; 14:185-93. [PMID: 17310252 PMCID: PMC4595851 DOI: 10.1038/nsmb1209] [Citation(s) in RCA: 698] [Impact Index Per Article: 41.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2006] [Accepted: 01/25/2007] [Indexed: 01/05/2023]
Abstract
Alternative splicing modulates the expression of many oncogene and tumor-suppressor isoforms. We have tested whether some alternative splicing factors are involved in cancer. We found that the splicing factor SF2/ASF is upregulated in various human tumors, in part due to amplification of its gene, SFRS1. Moreover, slight overexpression of SF2/ASF is sufficient to transform immortal rodent fibroblasts, which form sarcomas in nude mice. We further show that SF2/ASF controls alternative splicing of the tumor suppressor BIN1 and the kinases MNK2 and S6K1. The resulting BIN1 isoforms lack tumor-suppressor activity; an isoform of MNK2 promotes MAP kinase-independent eIF4E phosphorylation; and an unusual oncogenic isoform of S6K1 recapitulates the transforming activity of SF2/ASF. Knockdown of either SF2/ASF or isoform-2 of S6K1 is sufficient to reverse transformation caused by the overexpression of SF2/ASF in vitro and in vivo. Thus, SF2/ASF can act as an oncoprotein and is a potential target for cancer therapy.
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Affiliation(s)
- Rotem Karni
- Cold Spring Harbor Laboratory, PO Box 100, Cold Spring Harbor, New York 11724, USA
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Deniaud E, Baguet J, Mathieu AL, Pagès G, Marvel J, Leverrier Y. Overexpression of Sp1 transcription factor induces apoptosis. Oncogene 2006; 25:7096-105. [PMID: 16715126 DOI: 10.1038/sj.onc.1209696] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Transcription factor Sp1 has recently been shown to be overexpressed in a number of human cancers and its overexpression contributes to malignant transformation. Sp1 regulates the expression of a number of genes participating in multiple aspects of tumorigenesis such as angiogenesis, cell growth and apoptosis resistance. To better understand the role of increased Sp1 levels on apoptosis regulation we have used retroviruses to overexpress this protein in haematopoietic Baf-3 cells and in 3T3 fibroblasts. We have also used inducible expression systems to control ectopic Sp1 levels in different cell types. Surprisingly, Sp1 overexpression on its own induces apoptosis in all the cellular models tested. The apoptotic pathways induced by Sp1 overexpression are cell type specific. Finally, using a truncated form of Sp1, we show that Sp1-induced apoptosis requires its DNA-binding domain. Our results highlight that Sp1 levels in untransformed cells must be tightly regulated as Sp1 overexpression leads to the induction of apoptosis. Our results also suggest that cancer cells overexpressing Sp1 can avoid Sp1-induced apoptosis.
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Corradini F, Cesi V, Bartella V, Pani E, Bussolari R, Candini O, Calabretta B. Enhanced proliferative potential of hematopoietic cells expressing degradation-resistant c-Myb mutants. J Biol Chem 2005; 280:30254-62. [PMID: 15927960 DOI: 10.1074/jbc.m504703200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The c-myb gene encodes a transcription factor required for proliferation, differentiation, and survival of hematopoietic cells. Expression of c-Myb is often increased in hematological malignancies, but the underlying mechanisms are poorly understood. We show here that c-Myb has a longer half-life (at least 2-fold) in BCR/ABL-expressing than in normal hematopoietic cells. Such enhanced stability was dependent on a phosphatidylinositol 3-kinase (PI-3K)/Akt/GSKIIIbeta pathway(s) as indicated by the suppression of c-Myb expression upon treatment with PI-3K inhibitors or co-expression with dominant negative Akt or constitutively active GSKIIIbeta. Moreover, inhibition of GSKIIIbeta by LiCl enhanced c-Myb expression in parental 32Dcl3 cells. Compared with wild type c-Myb, three mutants (delta(358-452), delta(389-418), and L389A/L396A c-Myb) of the leucine zipper domain had increased stability. However, only expression of delta(358-452) was not affected by inhibition of the PI-3K/Akt pathway and was not enhanced by a proteasome inhibitor, suggesting that leucine zipper-dependent and -independent mechanisms are involved in the regulation of c-Myb stability. Indeed, delta(389-418) carrying four lysine-to-alanine substitutions (delta(389-418) K387A/K428A/K442A/K445A) was as stable as delta(358-452) c-Myb. Compared with full-length c-Myb, constitutive expression of delta(358-452) and delta(389-418) c-Myb in Lin-Sca-1+ mouse marrow cells increased cytokine-dependent primary and secondary colony formation. In K562 cells, expression of delta(358-452), delta(389-418), and L389A/L396A c-Myb led to enhanced proliferation after STI571 treatment. Thus, enhanced stability of c-Myb by activation of PI-3K-dependent pathway(s) might contribute to the higher proliferative potential of BCR/ABL-expressing and, perhaps, other leukemic cells.
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Affiliation(s)
- Francesca Corradini
- Department of Microbiology and Immunology, Kimmel Cancer Center, Thomas Jefferson Medical College, Philadelphia, Pennsylvania 19107, USA
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Lang G, White JR, Argent-Katwala MJG, Allinson CG, Weston K. Myb proteins regulate the expression of diverse target genes. Oncogene 2005; 24:1375-84. [PMID: 15608679 DOI: 10.1038/sj.onc.1208301] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Hematopoiesis, the process by which mature blood cells arise, is controlled by multiple transcription factors, which act in stage- and lineage-specific complexes. It is a major goal to elucidate the genes regulated by these transcription factors, in order to obtain a full understanding of the process and its malignant counterpart, leukemia. Myb family transcription factors play a central role in hematopoiesis. To identify new Myb family target genes, we have used an inducible dominant-negative protein for a subtraction cloning protocol in a model cell system (FDCP-Mix) with many characteristics of normal hematopoiesis. We present here a novel group of 29 validated Myb family target genes of diverse functions.
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Affiliation(s)
- Georgina Lang
- CRUK Centre for Cell and Molecular Biology, Institute of Cancer Research, 237 Fulham Road, London SW3 6JB, UK
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Gumireddy K, Baker SJ, Cosenza SC, John P, Kang AD, Robell KA, Reddy MVR, Reddy EP. A non-ATP-competitive inhibitor of BCR-ABL overrides imatinib resistance. Proc Natl Acad Sci U S A 2005; 102:1992-7. [PMID: 15677719 PMCID: PMC546016 DOI: 10.1073/pnas.0408283102] [Citation(s) in RCA: 174] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Imatinib, which is an inhibitor of the BCR-ABL tyrosine kinase, has been a remarkable success for the treatment of Philadelphia chromosome-positive (Ph+) chronic myelogenous leukemias (CMLs). However, a significant proportion of patients chronically treated with imatinib develop resistance because of the acquisition of mutations in the kinase domain of BCR-ABL. Mutations occur at residues directly implicated in imatinib binding or, more commonly, at residues important for the ability of the kinase to adopt the specific closed (inactive) conformation to which imatinib binds. In our quest to develop new BCR-ABL inhibitors, we chose to target regions outside the ATP-binding site of this enzyme because these compounds offer the potential to be unaffected by mutations that make CML cells resistant to imatinib. Here we describe the activity of one compound, ON012380, that can specifically inhibit BCR-ABL and induce cell death of Ph+ CML cells at a concentration of <10 nM. Kinetic studies demonstrate that this compound is not ATP-competitive but is substrate-competitive and works synergistically with imatinib in wild-type BCR-ABL inhibition. More importantly, ON012380 was found to induce apoptosis of all of the known imatinib-resistant mutants at concentrations of <10 nM concentration in vitro and cause regression of leukemias induced by i.v. injection of 32Dcl3 cells expressing the imatinib-resistant BCR-ABL isoform T315I. Daily i.v. dosing for up to 3 weeks with a >100 mg/kg concentration of this agent is well tolerated in rodents, without any hematotoxicity.
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Affiliation(s)
- Kiranmai Gumireddy
- The Fels Institute for Cancer Research and Molecular Biology, Temple University School of Medicine, 3307 North Broad Street, Philadelphia, PA 19140, USA
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