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Choi S, Cho N, Kim EM, Kim KK. The role of alternative pre-mRNA splicing in cancer progression. Cancer Cell Int 2023; 23:249. [PMID: 37875914 PMCID: PMC10594706 DOI: 10.1186/s12935-023-03094-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Accepted: 10/06/2023] [Indexed: 10/26/2023] Open
Abstract
Alternative pre-mRNA splicing is a critical mechanism that generates multiple mRNA from a single gene, thereby increasing the diversity of the proteome. Recent research has highlighted the significance of specific splicing isoforms in cellular processes, particularly in regulating cell numbers. In this review, we examine the current understanding of the role of alternative splicing in controlling cancer cell growth and discuss specific splicing factors and isoforms and their molecular mechanisms in cancer progression. These isoforms have been found to intricately control signaling pathways crucial for cell cycle progression, proliferation, and apoptosis. Furthermore, studies have elucidated the characteristics and functional importance of splicing factors that influence cell numbers. Abnormal expression of oncogenic splicing isoforms and splicing factors, as well as disruptions in splicing caused by genetic mutations, have been implicated in the development and progression of tumors. Collectively, these findings provide valuable insights into the complex interplay between alternative splicing and cell proliferation, thereby suggesting the potential of alternative splicing as a therapeutic target for cancer.
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Affiliation(s)
- Sunkyung Choi
- Department of Biochemistry, College of Natural Sciences, Chungnam National University, Daejeon, 34134, Republic of Korea
| | - Namjoon Cho
- Department of Biochemistry, College of Natural Sciences, Chungnam National University, Daejeon, 34134, Republic of Korea
| | - Eun-Mi Kim
- Department of Predictive Toxicology, Korea Institute of Toxicology, Daejeon, 34114, Republic of Korea.
| | - Kee K Kim
- Department of Biochemistry, College of Natural Sciences, Chungnam National University, Daejeon, 34134, Republic of Korea.
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2
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Karadkhelkar NM, Lin M, Eubanks LM, Janda KD. Demystifying the Druggability of the MYC Family of Oncogenes. J Am Chem Soc 2023; 145:3259-3269. [PMID: 36734615 PMCID: PMC10182829 DOI: 10.1021/jacs.2c12732] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The MYC family of oncogenes (MYC, MYCN, and MYCL) encodes a basic helix-loop-helix leucine zipper (bHLHLZ) transcriptional regulator that is responsible for moving the cell through the restriction point. Through the HLHZIP domain, MYC heterodimerizes with the bHLHLZ protein MAX, which enables this MYC-MAX complex to bind to E-box regulatory DNA elements thereby controlling transcription of a large group of genes and their proteins. Translationally, MYC is one of the foremost oncogenic targets, and deregulation of expression of the MYC family gene/proteins occurs in over half of all human tumors and is recognized as a hallmark of cancer initiation and maintenance. Additionally, unexpected roles for this oncoprotein have been found in cancers that nominally have a non-MYC etiology. Although MYC is rarely mutated, its gain of function in cancer results from overexpression or from amplification. Moreover, MYC is a pleiotropic transcription factor possessing broad pathogenic prominence making it a coveted cancer target. A widely held notion within the biomedical research community is that the reliable modulation of MYC represents a tremendous therapeutic opportunity given its role in directly potentiating oncogenesis. However, the MYC-MAX heterodimer interaction contains a large surface area with a lack of well-defined binding sites creating the perception that targeting of MYC-MAX is forbidding. Here, we discuss the biochemistry behind MYC and MYC-MAX as it relates to cancer progression associated with these transcription factors. We also discuss the notion that MYC should no longer be regarded as undruggable, providing examples that a therapeutic window is achievable despite global MYC inhibition.
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Affiliation(s)
- Nishant M. Karadkhelkar
- Departments of Chemistry and Immunology, The Skaggs Institute for Chemical Biology, Worm Institute of Research and Medicine (WIRM), The Scripps Research Institute, La Jolla, California 92037, United States
| | - Mingliang Lin
- Departments of Chemistry and Immunology, The Skaggs Institute for Chemical Biology, Worm Institute of Research and Medicine (WIRM), The Scripps Research Institute, La Jolla, California 92037, United States
| | - Lisa M. Eubanks
- Departments of Chemistry and Immunology, The Skaggs Institute for Chemical Biology, Worm Institute of Research and Medicine (WIRM), The Scripps Research Institute, La Jolla, California 92037, United States
| | - Kim D. Janda
- Departments of Chemistry and Immunology, The Skaggs Institute for Chemical Biology, Worm Institute of Research and Medicine (WIRM), The Scripps Research Institute, La Jolla, California 92037, United States
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3
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Carabet LA, Rennie PS, Cherkasov A. Therapeutic Inhibition of Myc in Cancer. Structural Bases and Computer-Aided Drug Discovery Approaches. Int J Mol Sci 2018; 20:E120. [PMID: 30597997 PMCID: PMC6337544 DOI: 10.3390/ijms20010120] [Citation(s) in RCA: 101] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2018] [Revised: 12/08/2018] [Accepted: 12/21/2018] [Indexed: 12/23/2022] Open
Abstract
Myc (avian myelocytomatosis viral oncogene homolog) represents one of the most sought after drug targets in cancer. Myc transcription factor is an essential regulator of cell growth, but in most cancers it is overexpressed and associated with treatment-resistance and lethal outcomes. Over 40 years of research and drug development efforts did not yield a clinically useful Myc inhibitor. Drugging the "undruggable" is problematic, as Myc inactivation may negatively impact its physiological functions. Moreover, Myc is a disordered protein that lacks effective binding pockets on its surface. It is well established that the Myc function is dependent on dimerization with its obligate partner, Max (Myc associated factor X), which together form a functional DNA-binding domain to activate genomic targets. Herein, we provide an overview of the knowledge accumulated to date on Myc regulation and function, its critical role in cancer, and summarize various strategies that are employed to tackle Myc-driven malignant transformation. We focus on important structure-function relationships of Myc with its interactome, elaborating structural determinants of Myc-Max dimer formation and DNA recognition exploited for therapeutic inhibition. Chronological development of small-molecule Myc-Max prototype inhibitors and corresponding binding sites are comprehensively reviewed and particular emphasis is placed on modern computational drug design methods. On the outlook, technological advancements may soon provide the so long-awaited Myc-Max clinical candidate.
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Affiliation(s)
- Lavinia A Carabet
- Vancouver Prostate Centre, University of British Columbia, 2660 Oak Street, Vancouver, BC V6H 3Z6, Canada.
| | - Paul S Rennie
- Vancouver Prostate Centre, University of British Columbia, 2660 Oak Street, Vancouver, BC V6H 3Z6, Canada.
| | - Artem Cherkasov
- Vancouver Prostate Centre, University of British Columbia, 2660 Oak Street, Vancouver, BC V6H 3Z6, Canada.
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Walker CJ, Rush CM, Dama P, O’Hern MJ, Cosgrove CM, Gillespie JL, Zingarelli RA, Smith B, Stein ME, Mutch DG, Shakya R, Chang CW, Selvendiran K, Song JW, Cohn DE, Goodfellow PJ. MAX Mutations in Endometrial Cancer: Clinicopathologic Associations and Recurrent MAX p.His28Arg Functional Characterization. J Natl Cancer Inst 2018; 110:517-526. [PMID: 29155953 PMCID: PMC6279289 DOI: 10.1093/jnci/djx238] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Revised: 08/16/2017] [Accepted: 10/10/2017] [Indexed: 12/30/2022] Open
Abstract
Background Genomic studies have revealed that multiple genes are mutated at varying frequency in endometrial cancer (EC); however, the relevance of many of these mutations is poorly understood. An EC-specific recurrent mutation in the MAX transcription factor p.His28Arg was recently discovered. We sought to assess the functional consequences of this hotspot mutation and determine its association with cancer-relevant phenotypes. Methods MAX was sequenced in 509 endometrioid ECs, and associations between mutation status and clinicopathologic features were assessed. EC cell lines stably expressing MAXH28R were established and used for functional experiments. DNA binding was examined using electrophoretic mobility shift assays and chromatin immunoprecipitation. Transcriptional profiling was performed with microarrays. Murine flank (six to 11 mice per group) and intraperitoneal tumor models were used for in vivo studies. Vascularity of xenografts was assessed by MECA-32 immunohistochemistry. The paracrine pro-angiogenic nature of MAXH28R-expressing EC cells was tested using microfluidic HUVEC sprouting assays and VEGFA enzyme-linked immunosorbent assays. All statistical tests were two-sided. Results Twenty-two of 509 tumors harbored mutations in MAX, including 12 tumors with the p.His28Arg mutation. Patients with a MAX mutation had statistically significantly reduced recurrence-free survival (hazard ratio = 4.00, 95% confidence interval = 1.15 to 13.91, P = .03). MAXH28R increased affinity for canonical E-box sequences, and MAXH28R-expressing EC cells dramatically altered transcriptional profiles. MAXH28R-derived xenografts statistically significantly increased vascular area compared with MAXWT and empty vector tumors (P = .003 and P = .008, respectively). MAXH28R-expressing EC cells secreted nearly double the levels of VEGFA compared with MAXWT cells (P = .03, .005, and .005 at 24, 48, and 72 hours, respectively), and conditioned media from MAXH28R cells increased sprouting when applied to HUVECs. Conclusion These data highlight the importance of MAX mutations in EC and point to increased vascularity as one mechanism contributing to clinical aggressiveness of EC.
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MESH Headings
- Aged
- Aged, 80 and over
- Amino Acid Substitution/genetics
- Animals
- Animals, Outbred Strains
- Arginine/genetics
- Basic Helix-Loop-Helix Leucine Zipper Transcription Factors/genetics
- Carcinoma, Endometrioid/epidemiology
- Carcinoma, Endometrioid/genetics
- Carcinoma, Endometrioid/pathology
- Cells, Cultured
- Codon, Nonsense
- Endometrial Neoplasms/epidemiology
- Endometrial Neoplasms/genetics
- Endometrial Neoplasms/pathology
- Female
- Genetic Association Studies
- Genetic Predisposition to Disease
- HEK293 Cells
- Histidine/genetics
- Humans
- Mice
- Mice, Nude
- Middle Aged
- Neoplasm Invasiveness
- Neovascularization, Pathologic/genetics
- Neovascularization, Pathologic/pathology
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Affiliation(s)
| | - Craig M Rush
- James Comprehensive Cancer Center
- Department of Obstetrics and Gynecology
| | - Paola Dama
- James Comprehensive Cancer Center
- Department of Obstetrics and Gynecology
| | - Matthew J O’Hern
- James Comprehensive Cancer Center
- Department of Obstetrics and Gynecology
| | - Casey M Cosgrove
- James Comprehensive Cancer Center
- Department of Obstetrics and Gynecology
| | | | - Roman A Zingarelli
- James Comprehensive Cancer Center
- Department of Obstetrics and Gynecology
| | - Blair Smith
- James Comprehensive Cancer Center
- Department of Obstetrics and Gynecology
| | - Maggie E Stein
- James Comprehensive Cancer Center
- Department of Obstetrics and Gynecology
| | - David G Mutch
- Siteman Cancer Center and the Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, MO
| | | | | | | | - Jonathan W Song
- James Comprehensive Cancer Center
- Department of Mechanical and Aerospace Engineering The Ohio State University, Columbus, OH
| | - David E Cohn
- James Comprehensive Cancer Center
- Department of Obstetrics and Gynecology
| | - Paul J Goodfellow
- James Comprehensive Cancer Center
- Department of Obstetrics and Gynecology
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5
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MicroRNA Regulation of Glycolytic Metabolism in Glioblastoma. BIOMED RESEARCH INTERNATIONAL 2017; 2017:9157370. [PMID: 28804724 PMCID: PMC5539934 DOI: 10.1155/2017/9157370] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Accepted: 06/22/2017] [Indexed: 12/20/2022]
Abstract
Glioblastoma (GBM) is the most aggressive and common malignant brain tumour in adults. A well-known hallmark of GMB and many other tumours is aerobic glycolysis. MicroRNAs (miRNAs) are a class of short nonprotein coding sequences that exert posttranscriptional controls on gene expression and represent critical regulators of aerobic glycolysis in GBM. In GBM, miRNAs regulate the expression of glycolytic genes directly and via the regulation of metabolism-associated tumour suppressors and oncogenic signalling pathways. This review aims to establish links between miRNAs expression levels, the expression of GBM glycolytic regulatory genes, and the malignant progression and prognosis of GBM. In this review, the involvement of 25 miRNAs in the regulation of glycolytic metabolism of GBM is discussed. Seven of these miRNAs have been shown to regulate glycolytic metabolism in other tumour types. Further eight miRNAs, which are differentially expressed in GBM, have also been reported to regulate glycolytic metabolism in other cancer types. Thus, these miRNAs could serve as potential glycolytic regulators in GBM but will require functional validation. As such, the characterisation of these molecular and metabolic signatures in GBM can facilitate a better understanding of the molecular pathogenesis of this disease.
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6
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Maltais L, Montagne M, Bédard M, Tremblay C, Soucek L, Lavigne P. Biophysical characterization of the b-HLH-LZ of ΔMax, an alternatively spliced isoform of Max found in tumor cells: Towards the validation of a tumor suppressor role for the Max homodimers. PLoS One 2017; 12:e0174413. [PMID: 28350847 PMCID: PMC5370111 DOI: 10.1371/journal.pone.0174413] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Accepted: 03/08/2017] [Indexed: 11/19/2022] Open
Abstract
It is classically recognized that the physiological and oncogenic functions of Myc proteins depend on specific DNA binding enabled by the dimerization of its C-terminal basic-region-Helix-Loop-Helix-Leucine Zipper (b-HLH-LZ) domain with that of Max. However, a new paradigm is emerging, where the binding of the c-Myc/Max heterodimer to non-specific sequences in enhancers and promoters drives the transcription of genes involved in diverse oncogenic programs. Importantly, Max can form a stable homodimer even in the presence of c-Myc and bind DNA (specific and non-specific) with comparable affinity to the c-Myc/Max heterodimer. Intriguingly, alterations in the Max gene by germline and somatic mutations or changes in the gene product by alternative splicing (e.g. ΔMax) were recently associated with pheochromocytoma and glioblastoma, respectively. This has led to the proposition that Max is, by itself, a tumor suppressor. However, the actual mechanism through which it exerts such an activity remains to be elucidated. Here, we show that contrary to the WT motif, the b-HLH-LZ of ΔMax does not homodimerize in the absence of DNA. In addition, although ΔMax can still bind the E-box sequence as a homodimer, it cannot bind non-specific DNA in that form, while it can heterodimerize with c-Myc and bind E-box and non-specific DNA as a heterodimer with high affinity. Taken together, our results suggest that the WT Max homodimer is important for attenuating the binding of c-Myc to specific and non-specific DNA, whereas ΔMax is unable to do so. Conversely, the splicing of Max into ΔMax could provoke an increase in overall chromatin bound c-Myc. According to the new emerging paradigm, the splicing event and the stark reduction in homodimer stability and DNA binding should promote tumorigenesis impairing the tumor suppressor activity of the WT homodimer of Max.
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Affiliation(s)
- Loïka Maltais
- Département de Biochimie, Faculté de Médecine et des Sciences de la Santé, Institut de Pharmacologie de Sherbrooke, Université de Sherbrooke, Sherbrooke, Québec, Canada
- PROTÉO; Regroupement Stratégique sur la Fonction, la Structure et l'Ingénierie des Protéines, Université Laval, Québec, Canada
| | - Martin Montagne
- Département de Biochimie, Faculté de Médecine et des Sciences de la Santé, Institut de Pharmacologie de Sherbrooke, Université de Sherbrooke, Sherbrooke, Québec, Canada
- PROTÉO; Regroupement Stratégique sur la Fonction, la Structure et l'Ingénierie des Protéines, Université Laval, Québec, Canada
| | - Mikaël Bédard
- Département de Biochimie, Faculté de Médecine et des Sciences de la Santé, Institut de Pharmacologie de Sherbrooke, Université de Sherbrooke, Sherbrooke, Québec, Canada
- PROTÉO; Regroupement Stratégique sur la Fonction, la Structure et l'Ingénierie des Protéines, Université Laval, Québec, Canada
| | - Cynthia Tremblay
- Département de Biochimie, Faculté de Médecine et des Sciences de la Santé, Institut de Pharmacologie de Sherbrooke, Université de Sherbrooke, Sherbrooke, Québec, Canada
- PROTÉO; Regroupement Stratégique sur la Fonction, la Structure et l'Ingénierie des Protéines, Université Laval, Québec, Canada
| | - Laura Soucek
- Vall d’Hebron Institute of Oncology (VHIO), Hospital Vall d’Hebron, Barcelona, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
- Department of Biochemistry and Molecular Biology, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - Pierre Lavigne
- Département de Biochimie, Faculté de Médecine et des Sciences de la Santé, Institut de Pharmacologie de Sherbrooke, Université de Sherbrooke, Sherbrooke, Québec, Canada
- PROTÉO; Regroupement Stratégique sur la Fonction, la Structure et l'Ingénierie des Protéines, Université Laval, Québec, Canada
- * E-mail:
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7
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Schwab M, Corvi R, Amler LC. N-MYC Oncogene Amplification: A Consequence of Genomic Instability in Human Neuroblastoma. Neuroscientist 2016. [DOI: 10.1177/107385849500100505] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Increase of the dosage of cellular oncogenes by DNA amplification is a frequent genetic alteration of cancer cells and arises as the consequence of genomic instability. The presence of amplified cellular oncogenes is usually signaled by conspicuous chromosomal abnormalities "double minutes," or "homogeneously staining chromosomal regions." Some human cancers carry a specific amplified oncogene at high incidence. In neuroblastomas, which are tumors of the peripheral nervous system that arise from primitive neuroectodermal cells derived from neural crest, the amplification of the gene N-MYC has been associated with aggressively growing cancers and is an indicator for poor prognosis. N-MYC amplification is of predictive value for iden tifying neuroblastoma patients who either require specific therapeutic regimens or who do not benefit from chemotherapy. The Neuroscientist 1:277-285, 1995
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Affiliation(s)
- Manfred Schwab
- German Cancer Research Center Division of Cytogenetics
Heidelberg, Germany
| | - Raffaella Corvi
- German Cancer Research Center Division of Cytogenetics
Heidelberg, Germany
| | - Lukas C. Amler
- German Cancer Research Center Division of Cytogenetics
Heidelberg, Germany
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8
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Kemmerer K, Weigand JE. Hypoxia reduces MAX expression in endothelial cells by unproductive splicing. FEBS Lett 2014; 588:4784-90. [DOI: 10.1016/j.febslet.2014.11.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2014] [Revised: 10/20/2014] [Accepted: 11/05/2014] [Indexed: 10/24/2022]
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9
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An J, Liu J, Liu L, Liu Y, Pan Y, Huang M, Qi F, Wen J, Xie K, Ma H, Shen H, Hu Z. A genetic variant in primary miR-378 is associated with risk and prognosis of hepatocellular carcinoma in a Chinese population. PLoS One 2014; 9:e93707. [PMID: 24751683 PMCID: PMC3994025 DOI: 10.1371/journal.pone.0093707] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Accepted: 03/05/2014] [Indexed: 01/14/2023] Open
Abstract
Background MiR-378 has been reported to be related to cell survival, tumor growth and angiogenesis and may participate in hepatocellular carcinoma (HCC) development and prognosis. Genetic variants in primary miR-378 (pri-miR-378) may impact miR-378 expression and contribute to HCC risk and survival. This study aimed to assess the associations between a genetic variant in primary miR-378 and HCC susceptibility and prognosis. Methods We conducted a case-control study to analyze the association of rs1076064 in pri-miR-378 with hepatocellular carcinoma risk in 1300 HCC patients with positive hepatitis B virus (HBV) and 1344 HBV carriers. Then, we evaluated the correlation between the polymorphism and hepatocellular carcinoma prognosis in 331 HCC patients at either intermediate or advanced stage without surgical treatment. Results The variant genotypes of rs1076064 were associated with a decreased HCC risk in HBV carriers [Adjusted odds ratio (OR) = 0.90, 95% confidence intervals (CI) = 0.81–1.00, P = 0.047]. Moreover, HCC patients with the variant genotypes were associated with a better survival [Adjusted hazard ratio (HR) = 0.70, 95% CIs = 0.59–0.83, P<0.0001 in an additive genetic model]. The reporter gene assay showed that the variant G allele of rs1076064 exerted higher promoter activity than the A allele. Conclusions These findings indicate that rs1076064 may be a biomarker for HCC susceptibility and prognosis through altering pri-miR-378 transcription.
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Affiliation(s)
- Jiaze An
- Department of Hepatobiliary Surgery, Xijing Hospital, Fourth Military Medical University, Xi’an, China
| | - Jibin Liu
- Department of Hepatobiliary Surgery, Nantong Tumor Hospital, Nantong, Nantong, Jiangsu, China
| | - Li Liu
- Digestive Endoscopy Center, the First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu, China
| | - Yao Liu
- Pathology Center and Department of Pathology, Soochow University, Suzhou, Jiangsu, China
| | - Yun Pan
- Department of Epidemiology and Biostatistics, Jiangsu Key Lab of Cancer Biomarkers, Prevention and Treatment, Cancer Center, School of Public Health, Nanjing Medical University, Nanjing, Jiangsu, China
| | - Mingde Huang
- Department of Oncology, Huai’an First People’s Hospital, Nanjing Medical University, Huai’an, Jiangsu, China
| | - Fuzhen Qi
- Department of Hepatopancreatobiliary Surgery, Huai’an First People’s Hospital, Nanjing Medical University, Huai’an, Jiangsu, China
| | - Juan Wen
- Department of Epidemiology and Biostatistics, Jiangsu Key Lab of Cancer Biomarkers, Prevention and Treatment, Cancer Center, School of Public Health, Nanjing Medical University, Nanjing, Jiangsu, China
| | - Kaipeng Xie
- Department of Epidemiology and Biostatistics, Jiangsu Key Lab of Cancer Biomarkers, Prevention and Treatment, Cancer Center, School of Public Health, Nanjing Medical University, Nanjing, Jiangsu, China
| | - Hongxia Ma
- Department of Epidemiology and Biostatistics, Jiangsu Key Lab of Cancer Biomarkers, Prevention and Treatment, Cancer Center, School of Public Health, Nanjing Medical University, Nanjing, Jiangsu, China
- State Key Laboratory of Reproductive Medicine, Nanjing Medical University, Nanjing, Jiangsu, China
| | - Hongbing Shen
- Department of Epidemiology and Biostatistics, Jiangsu Key Lab of Cancer Biomarkers, Prevention and Treatment, Cancer Center, School of Public Health, Nanjing Medical University, Nanjing, Jiangsu, China
- State Key Laboratory of Reproductive Medicine, Nanjing Medical University, Nanjing, Jiangsu, China
| | - Zhibin Hu
- Department of Epidemiology and Biostatistics, Jiangsu Key Lab of Cancer Biomarkers, Prevention and Treatment, Cancer Center, School of Public Health, Nanjing Medical University, Nanjing, Jiangsu, China
- State Key Laboratory of Reproductive Medicine, Nanjing Medical University, Nanjing, Jiangsu, China
- * E-mail:
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10
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Conacci-Sorrell M, McFerrin L, Eisenman RN. An overview of MYC and its interactome. Cold Spring Harb Perspect Med 2014; 4:a014357. [PMID: 24384812 DOI: 10.1101/cshperspect.a014357] [Citation(s) in RCA: 291] [Impact Index Per Article: 29.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
This review is intended to provide a broad outline of the biological and molecular functions of MYC as well as of the larger protein network within which MYC operates. We present a view of MYC as a sensor that integrates multiple cellular signals to mediate a broad transcriptional response controlling many aspects of cell behavior. We also describe the larger transcriptional network linked to MYC with emphasis on the MXD family of MYC antagonists. Last, we discuss evidence that the network has evolved for millions of years, dating back to the emergence of animals.
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11
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Babic I, Anderson ES, Tanaka K, Guo D, Masui K, Li B, Zhu S, Gu Y, Villa GR, Akhavan D, Nathanson D, Gini B, Mareninov S, Li R, Camacho CE, Kurdistani SK, Eskin A, Nelson SF, Yong WH, Cavenee WK, Cloughesy TF, Christofk HR, Black DL, Mischel PS. EGFR mutation-induced alternative splicing of Max contributes to growth of glycolytic tumors in brain cancer. Cell Metab 2013; 17:1000-1008. [PMID: 23707073 PMCID: PMC3679227 DOI: 10.1016/j.cmet.2013.04.013] [Citation(s) in RCA: 117] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/05/2012] [Revised: 03/03/2013] [Accepted: 04/08/2013] [Indexed: 12/26/2022]
Abstract
Alternative splicing contributes to diverse aspects of cancer pathogenesis including altered cellular metabolism, but the specificity of the process or its consequences are not well understood. We characterized genome-wide alternative splicing induced by the activating EGFRvIII mutation in glioblastoma (GBM). EGFRvIII upregulates the heterogeneous nuclear ribonucleoprotein (hnRNP) A1 splicing factor, promoting glycolytic gene expression and conferring significantly shorter survival in patients. HnRNPA1 promotes splicing of a transcript encoding the Myc-interacting partner Max, generating Delta Max, an enhancer of Myc-dependent transformation. Delta Max, but not full-length Max, rescues Myc-dependent glycolytic gene expression upon induced EGFRvIII loss, and correlates with hnRNPA1 expression and downstream Myc-dependent gene transcription in patients. Finally, Delta Max is shown to promote glioma cell proliferation in vitro and augment EGFRvIII expressing GBM growth in vivo. These results demonstrate an important role for alternative splicing in GBM and identify Delta Max as a mediator of Myc-dependent tumor cell metabolism.
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Affiliation(s)
- Ivan Babic
- Ludwig Institute for Cancer Research, University of California, San Diego, La Jolla, CA 92093, USA
| | - Erik S Anderson
- Department of Microbiology, Immunology, and Molecular Genetics, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA; UCLA Molecular Biology Interdepartmental Graduate Program, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA; UCLA Medical Scientist Training Program, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Kazuhiro Tanaka
- Department of Neurosurgery, Kobe University, Kobe 650-0017, Japan
| | - Deliang Guo
- Department of Radiation Oncology, James Comprehensive Cancer Center, The Ohio State University Medical Center, Columbus, OH 43210, USA
| | - Kenta Masui
- Ludwig Institute for Cancer Research, University of California, San Diego, La Jolla, CA 92093, USA
| | - Bing Li
- Department of Biological Chemistry, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Shaojun Zhu
- Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Yuchao Gu
- Ludwig Institute for Cancer Research, University of California, San Diego, La Jolla, CA 92093, USA; Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Genaro R Villa
- Ludwig Institute for Cancer Research, University of California, San Diego, La Jolla, CA 92093, USA; Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA; UCLA Medical Scientist Training Program, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - David Akhavan
- Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA; UCLA Medical Scientist Training Program, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - David Nathanson
- Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Beatrice Gini
- Ludwig Institute for Cancer Research, University of California, San Diego, La Jolla, CA 92093, USA
| | - Sergey Mareninov
- Department of Pathology and Laboratory Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Rui Li
- Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Carolina Espindola Camacho
- Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Siavash K Kurdistani
- Department of Biological Chemistry, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Ascia Eskin
- Department of Human Genetics, David Geffen School of Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Stanley F Nelson
- Department of Human Genetics, David Geffen School of Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - William H Yong
- Department of Pathology and Laboratory Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Webster K Cavenee
- Ludwig Institute for Cancer Research, University of California, San Diego, La Jolla, CA 92093, USA; Moores Cancer Center, University of California, San Diego, La Jolla, CA 92093, USA
| | - Timothy F Cloughesy
- Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Heather R Christofk
- Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Douglas L Black
- Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA; Department of Microbiology, Immunology, and Molecular Genetics, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Paul S Mischel
- Ludwig Institute for Cancer Research, University of California, San Diego, La Jolla, CA 92093, USA; Moores Cancer Center, University of California, San Diego, La Jolla, CA 92093, USA; Department of Pathology, University of California, San Diego, La Jolla, CA 92093, USA.
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12
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Weigand JE, Boeckel JN, Gellert P, Dimmeler S. Hypoxia-induced alternative splicing in endothelial cells. PLoS One 2012; 7:e42697. [PMID: 22876330 PMCID: PMC3411717 DOI: 10.1371/journal.pone.0042697] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2012] [Accepted: 07/11/2012] [Indexed: 01/12/2023] Open
Abstract
Background Adaptation to low oxygen by changing gene expression is vitally important for cell survival and tissue development. The sprouting of new blood vessels, initiated from endothelial cells, restores the oxygen supply of ischemic tissues. In contrast to the transcriptional response induced by hypoxia, which is mainly mediated by members of the HIF family, there are only few studies investigating alternative splicing events. Therefore, we performed an exon array for the genome-wide analysis of hypoxia-related changes of alternative splicing in endothelial cells. Methodology/Principal findings Human umbilical vein endothelial cells (HUVECs) were incubated under hypoxic conditions (1% O2) for 48 h. Genome-wide transcript and exon expression levels were assessed using the Affymetrix GeneChip Human Exon 1.0 ST Array. We found altered expression of 294 genes after hypoxia treatment. Upregulated genes are highly enriched in glucose metabolism and angiogenesis related processes, whereas downregulated genes are mainly connected to cell cycle and DNA repair. Thus, gene expression patterns recapitulate known adaptations to low oxygen supply. Alternative splicing events, until now not related to hypoxia, are shown for nine genes: six which are implicated in angiogenesis-mediated cytoskeleton remodeling (cask, itsn1, larp6, sptan1, tpm1 and robo1); one, which is involved in the synthesis of membrane-anchors (pign) and two universal regulators of gene expression (cugbp1 and max). Conclusions/Significance For the first time, this study investigates changes in splicing in the physiological response to hypoxia on a genome-wide scale. Nine alternative splicing events, until now not related to hypoxia, are reported, considerably expanding the information on splicing changes due to low oxygen supply. Therefore, this study provides further knowledge on hypoxia induced gene expression changes and presents new starting points to study the hypoxia adaptation of endothelial cells.
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Affiliation(s)
- Julia E Weigand
- Institute for Cardiovascular Regeneration, Center of Molecular Medicine, Johann Wolfgang Goethe University Frankfurt, Frankfurt am Main, Germany.
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13
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Theodorou E, Dalembert G, Heffelfinger C, White E, Weissman S, Corcoran L, Snyder M. A high throughput embryonic stem cell screen identifies Oct-2 as a bifunctional regulator of neuronal differentiation. Genes Dev 2009; 23:575-88. [PMID: 19270158 DOI: 10.1101/gad.1772509] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Neuronal differentiation is a complex process that involves a plethora of regulatory steps. To identify transcription factors that influence neuronal differentiation we developed a high throughput screen using embryonic stem (ES) cells. Seven-hundred human transcription factor clones were stably introduced into mouse ES (mES) cells and screened for their ability to induce neuronal differentiation of mES cells. Twenty-four factors that are capable of inducing neuronal differentiation were identified, including four known effectors of neuronal differentiation, 11 factors with limited evidence of involvement in regulating neuronal differentiation, and nine novel factors. One transcription factor, Oct-2, was studied in detail and found to be a bifunctional regulator: It can either repress or induce neuronal differentiation, depending on the particular isoform. Ectopic expression experiments demonstrate that isoform Oct-2.4 represses neuronal differentiation, whereas Oct-2.2 activates neuron formation. Consistent with a role in neuronal differentiation, Oct-2.2 expression is induced during differentiation, and cells depleted of Oct-2 and its homolog Oct-1 have a reduced capacity to differentiate into neurons. Our results reveal a number of transcription factors potentially important for mammalian neuronal differentiation, and indicate that Oct-2 may serve as a binary switch to repress differentiation in precursor cells and induce neuronal differentiation later during neuronal development.
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Affiliation(s)
- Elias Theodorou
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520, USA
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14
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Proszkowiec-Weglarz M, Humphrey BD, Richards MP. Molecular cloning and expression of chicken carbohydrate response element binding protein and Max-like protein X gene homologues. Mol Cell Biochem 2008; 312:167-84. [DOI: 10.1007/s11010-008-9732-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2007] [Accepted: 02/25/2008] [Indexed: 12/30/2022]
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15
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Faiola F, Wu YT, Pan S, Zhang K, Farina A, Martinez E. Max is acetylated by p300 at several nuclear localization residues. Biochem J 2007; 403:397-407. [PMID: 17217336 PMCID: PMC1876387 DOI: 10.1042/bj20061593] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Max is a ubiquitous transcription factor with a bHLHZip [basic HLH (helix-loop-helix) leucine zipper] DNA-binding/dimerization domain and the central component of the Myc/Max/Mad transcription factor network that controls cell growth, proliferation, differentiation and apoptotic cell death in metazoans. Max is the obligatory DNA-binding and dimerization partner for all the bHLHZip regulators of the Myc/Max/Mad network, including the Myc family of oncoproteins and the Mad family of Myc antagonists, which recognize E-box DNA elements in the regulatory regions of target genes. Max lacks a transcription regulatory domain and is the only member of the network that efficiently homodimerizes. Binding of Max homodimers to E-box elements suppresses the transcription regulatory functions of its network partners and of other non-network E-box-binding regulators. In contrast with its highly regulated partners, Max is a constitutively expressed and phosphorylated protein. Phosphorylation is, however, the only Max post-translational modification identified so far. In the present study, we have analysed Max posttranslational modifications by MS. We have found that Max is acetylated at several lysine residues (Lys-57, Lys-144 and Lys-145) in mammalian cells. Max acetylation is stimulated by inhibitors of histone deacetylases and by overexpression of the p300 co-activator/HAT (histone acetyltransferase). The p300 HAT also directly acetylates Max in vitro at these three residues. Interestingly, the three Max residues acetylated in vivo and in vitro by p300 are important for Max nuclear localization and Max-mediated suppression of Myc transactivation. These results uncover novel post-translational modifications of Max and suggest the potential regulation of specific Max complexes by p300 and reversible acetylation.
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Affiliation(s)
- Francesco Faiola
- *Department of Biochemistry, University of California Riverside, Riverside, CA 92521, U.S.A
| | - Yi-Ting Wu
- *Department of Biochemistry, University of California Riverside, Riverside, CA 92521, U.S.A
| | - Songqin Pan
- †W.M. Keck Proteomics Laboratory, Center for Plant Cell Biology, University of California Riverside, Riverside, CA 92521, U.S.A
| | - Kangling Zhang
- ‡Department of Chemistry, University of California Riverside, Riverside, CA 92521, U.S.A
| | - Anthony Farina
- *Department of Biochemistry, University of California Riverside, Riverside, CA 92521, U.S.A
| | - Ernest Martinez
- *Department of Biochemistry, University of California Riverside, Riverside, CA 92521, U.S.A
- To whom correspondence should be addressed (email )
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16
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Abstract
The small bHLHZip protein MAX functions at the center of a transcription factor network that governs many aspects of cell behavior, including cell proliferation and tumorigenesis. MAX serves as a cofactor for DNA binding by the various members of this network, which include the MYC family of oncoproteins and a group of putative MYC antagonists that include MNT, MXD1-4 (formerly MAD1, MXI1, MAD3 and MAD4) and MGA. The many heterodimerization partners of MAX raises questions concerning the dynamics of MAX interactions and the functional consequences of the switching of Max partners. Here we review the activities of MAX, its interaction partners, and recent results showing that tissues lacking the MAX-interacting protein MNT are predisposed to tumor formation.
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Affiliation(s)
- Peter J Hurlin
- Shriners Hospitals for Children and Department of Cell and Developmental Biology, Oregon Health & Science University, Portland, OR 97201, USA.
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17
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Abstract
The Myc proto-oncogenes, their binding partner Max and their antagonists from the Mad family of transcriptional repressors have been extensively analysed in vertebrates. However, members of this network are found in all animals examined so far. Several recent studies have addressed the physiological function of these proteins in invertebrate model organisms, in particular Drosophila melanogaster. This review describes the structure of invertebrate Myc/Max/Mad genes and it discusses their regulation and physiological functions, with special emphasis on their essential role in the control of cellular growth and proliferation.
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Affiliation(s)
- P Gallant
- Universität Zürich, Zoologisches Institut, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
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18
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19
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Pursglove SE, Fladvad M, Bellanda M, Moshref A, Henriksson M, Carey J, Sunnerhagen M. Biophysical properties of regions flanking the bHLH-Zip motif in the p22 Max protein. Biochem Biophys Res Commun 2004; 323:750-9. [PMID: 15381064 DOI: 10.1016/j.bbrc.2004.08.166] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2004] [Indexed: 11/23/2022]
Abstract
The Max protein is the central dimerization partner in the Myc-Max-Mad network of transcriptional regulators, and a founding structural member of the family of basic-helix-loop-helix (bHLH)-leucine zipper (Zip) proteins. Biologically important regions flanking its bHLH-Zip motif have been disordered or absent in crystal structures. The present study shows that these regions are resistant to proteolysis in both the presence and absence of DNA, and that Max dimers containing both flanking regions have significantly higher helix content as measured by circular dichroism than that predicted from the crystal structures. Nuclear magnetic resonance measurements in the absence of DNA also support the inferred structural order. Deletion of both flanking regions is required to achieve maximal DNA affinity as measured by EMSA. Thus, the previously observed functionalities of these Max regions in DNA binding, phosphorylation, and apoptosis are suggested to be linked to structural properties.
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Affiliation(s)
- Sharon E Pursglove
- Medical Biochemistry and Biophysics, Karolinska Institutet, 171 77 Stockholm, Sweden
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20
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Farina A, Faiola F, Martinez E. Reconstitution of an E box-binding Myc:Max complex with recombinant full-length proteins expressed in Escherichia coli. Protein Expr Purif 2004; 34:215-22. [PMID: 15003254 PMCID: PMC4004042 DOI: 10.1016/j.pep.2003.11.021] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2003] [Revised: 11/12/2003] [Indexed: 11/26/2022]
Abstract
The c-Myc oncoprotein (Myc) is a DNA sequence-specific transcription factor that regulates transcription of a wide variety of genes involved in the control of cell growth, proliferation, differentiation, and apoptosis and its deregulated expression is implicated in many types of human cancer. Myc has an N-terminal transcription activation domain (TAD) that interacts with various coactivators and a C-terminal basic-helix-loop-helix-leucine zipper (bHLHZip) domain required for E box-specific DNA-binding and heterodimerization with its obligatory bHLHZip protein partner Max. The analysis of the mechanisms by which the Myc:Max complex regulates transcription at the molecular level in vitro has been hampered by the difficulty in obtaining highly pure recombinant Myc:Max heterodimers that contain full-length Myc with its complete TAD domain and that have sequence-specific DNA-binding activity. Here, we describe a simple method to reconstitute recombinant Myc:Max complexes from highly purified full-length proteins expressed in Escherichia coli that are soluble and highly active in E box-specific DNA-binding in vitro. The reconstituted Myc:Max complexes are stable and lack Max:Max homodimers. This procedure should facilitate the characterization of the DNA-binding and transcription activation functions of full-length Myc:Max complexes in vitro and in particular the role of Myc TAD-interacting cofactors and Myc:Max post-translational modifications.
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21
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Hurlin PJ, Dezfouli S. Functions of myc:max in the control of cell proliferation and tumorigenesis. INTERNATIONAL REVIEW OF CYTOLOGY 2004; 238:183-226. [PMID: 15364199 DOI: 10.1016/s0074-7696(04)38004-6] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Deregulation and elevated expression of members of the Myc family of bHLHZip transcription factors are observed in a high percentage of tumors. This close association with human cancers has led to a tremendous effort to define their biological and biochemical activities. Although Myc family proteins have the capacity to elicit a wide range of cell behaviors, their principal function appears to be to drive cells into the cell cycle and to keep them there. However, forced expression of Myc profoundly sensitizes normal cells to apoptosis. Therefore, tumor formation caused by deregulated Myc expression requires cooperating events that disrupt pathways that mediate apoptosis. Myc-dependent tumor formation may also be impeded by a set of related bHLHZip proteins with the demonstrated potential to act as Myc antagonists in cell culture experiments. In this review, we examine the complex activities of Myc family proteins and how their actions might be regulated in the context of a network of bHLHZip proteins.
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Affiliation(s)
- Peter J Hurlin
- Portland Shriners Hospitals for Children and Department of Cell and Developmental Biology Oregon Health Sciences University, Portland, Oregon 97201, USA
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22
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Auvinen M, Järvinen K, Hotti A, Okkeri J, Laitinen J, Jänne OA, Coffino P, Bergman M, Andersson LC, Alitalo K, Hölttä E. Transcriptional regulation of the ornithine decarboxylase gene by c-Myc/Max/Mad network and retinoblastoma protein interacting with c-Myc. Int J Biochem Cell Biol 2003; 35:496-521. [PMID: 12565711 DOI: 10.1016/s1357-2725(02)00305-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
c-Myc is an oncogenic transcription factor involved in the regulation of cell proliferation, differentiation and apoptosis. The direct targets of c-Myc mediating these various processes are slowly being unravelled. This study indicates that the ornithine decarboxylase (ODC) gene is a physiological transcriptional target of c-Myc in association with induction of cell proliferation and transformation, but not with induction of apoptosis. In addition to the two conserved CACGTG c-Myc-binding sites in the first intron, the CATGTG motif in the 5'-flanking region of the murine odc is also shown to be a functional c-Myc response element. odc is thus a c-Myc target with three binding sites a distance apart. Transient transfection studies with different c-Myc, Max and Mad constructs in COS-7 cells showed that the balance between c-Myc/Max, Max/Max and Max/Mad complexes is crucial for the regulation, resulting in either transactivation or transrepression of an ODC-CAT reporter gene. Transcription of both ODC-CAT and endogenous odc was strongly induced in HeLa cells expressing tetracycline-regulated c-Myc, concomitant with c-Myc promoting the S-phase entry of the cells. Transformation of NIH3T3 cells by c-Ha-ras-(Val12) oncogene was reversed by expression of transcriptionally inactive c-Myc, which was associated with repression of ODC-CAT expression. Further, the c-Myc-induced transactivation of ODC-CAT in COS-7 cells was suppressed by co-expression of the retinoblastoma tumor suppresser pRb, evidently as a result of pRb directly or indirectly interacting with c-Myc. Importantly, the endogenous c-Myc and pRb proteins were also found to associate in Colo 320HSR cells under physiological conditions. These results suggest that c-Myc and pRb can interact in vivo, and may in part control some aspects of cell proliferation and transformation through modulation of odc expression.
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Affiliation(s)
- Merja Auvinen
- Department of Pathology, Haartman Institute and Helsinki University Central Hospital, University of Helsinki, P.O. Box 21, 00014, Helsinki, Finland
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23
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Abstract
Although cell death once was viewed exclusively as the disordered, chaotic outcome of metabolic catastrophe, apoptosis now is recognized as a highly ordered, evolutionarily conserved, and genetically selected program that is essential for normal development. The death receptor pathway of apoptosis, cytotoxic T cells, prolife survival signals, Bcl-2 family of regulators, p53 and regulated cell death in cancer, and oncogenes are reviewed. Future prospects in this arena also are discussed.
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Affiliation(s)
- D E Fisher
- Division of Pediatric Hematology and Oncology, Children's Hospital, Dana-Farber Cancer Institute, Boston, Massachusetts, USA
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24
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Affiliation(s)
- T A Baudino
- Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA
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25
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Meroni G, Cairo S, Merla G, Messali S, Brent R, Ballabio A, Reymond A. Mlx, a new Max-like bHLHZip family member: the center stage of a novel transcription factors regulatory pathway? Oncogene 2000; 19:3266-77. [PMID: 10918583 DOI: 10.1038/sj.onc.1203634] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The Myc proto-oncogene family members have been identified as the cellular homologs of the transforming oncogene of avian retroviruses. They encode central regulators of mammalian cell proliferation and apoptosis, and they associate with the bHLHZip protein Max to bind specific DNA sequences and regulate the expression of genes important for cell cycle progression. The other family members, Mad1, Mxi1, Mad3, Mad4 and Rox (Mnt) antagonize their activities. The Mads and Rox compete with Myc in heterodimerizing with Max and in binding to the same specific target sequences. These Mads:Max and Rox:Max dimers repress transcription through binding to the mSIN3 corepressor protein and by tethering histone deacetylase-containing complexes to the DNA. In a screen for Rox interactors we isolated Mlx, a bHLHZip protein previously identified in a screen for Mad1 interactors. In the present work we extend the known dimerization partners of Mlx by demonstrating its ability to interact with Rox. Moreover, we show that contrary to previous reports Mlx is able to homodimerize and to bind E-box sequences at low concentration levels. The possible role of Mlx in an emerging regulatory pathway and acting parallel to the Max driven network is discussed.
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Affiliation(s)
- G Meroni
- Telethon Institute of Genetics and Medicine, Milan, Italy
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26
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Kivinen L, Tsubari M, Haapajärvi T, Datto MB, Wang XF, Laiho M. Ras induces p21Cip1/Waf1 cyclin kinase inhibitor transcriptionally through Sp1-binding sites. Oncogene 1999; 18:6252-61. [PMID: 10597223 DOI: 10.1038/sj.onc.1203000] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
p21Cip1/Waf1 cyclin-dependent kinase inhibitor (p21) is inducible by Raf and mitogen-activated protein kinase kinase (MAPKK), but the level of regulation is unknown. We show here by conditional and transient Ras-expression models that Ras induces p21. Induction of p21 in conditionally Ras-expressing cells is posttranscriptional utilizing mitogen-activated protein kinase (MAPK) pathway. Transient, high-level Ras-expression induces transcriptional activation of p21 mediated by a GC-rich region in p21 promoter -83-54 bp relative to the transcription initiation site containing binding sites for Sp1-family transcription factors. Mutation of either Sp1-binding site 2 or 4 in this region decreases the magnitude of induction of promoter activity by Ras, but only the simultaneous mutation of both sites abolishes fully the induction. Electrophoretic mobility shift assays using an oligonucleotide corresponding to Sp1-binding site 2 indicate that both Sp1 and Sp3 transcription factors bind to this region. The results demonstrate that the central cytosolic growth regulator Ras is a potent transcriptional and posttranscriptional inducer of the nuclear growth inhibitor p21.
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Affiliation(s)
- L Kivinen
- Haartman Institute, Department of Virology, University of Helsinki, Finland
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27
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Abstract
The cell proliferative activity of the Myc family of basic helix-loop-helix/leucine zipper (bHLHZip) transcription factors is dependent upon binding to the ubiquitous Max protein. In the absence of heterodimerization with Max, Myc protein is unable to efficiently bind to DNA and activate transcription. Members of the Mad family of transcription factors are thought to modulate the cell proliferative effects of the c-myc proto-oncogene by binding to Max, directly competing with the Myc protein for both heterodimerization and DNA binding. Consistent with a role in down-regulating cell division, the murine mad genes are expressed in embryonic tissues undergoing differentiation, often during or shortly after the down-regulation of myc gene expression. Here, we report the isolation and characterization of the first Xenopus mad family member, Xmad4. Maternal Xmad4 transcripts are present at high levels in the oocyte and in the cleavage stage embryo, but almost disappear by the neurula stage. Zygotic expression of the Xmad4 gene is initiated in the epidermis of the late neurula stage, and shortly thereafter, Xmad4 is transiently detectable in the cement and hatching glands. At later stages, expression is also observed in the developing pronephros and liver. Unlike the murine mad4 gene, we find that multiple Xmad4 splice variants exist in Xenopus and that these variants are differentially expressed in both the embryo and the adult. Despite the demonstrated antagonistic role of Mad proteins in the regulation of Myc activity, we show that the over-expression of Xmad4 in the cleavage-stage embryo has no detectable phenotypic effect, suggesting that Myc function is dispensable during early embryonic development.
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Affiliation(s)
- C S Newman
- Institute for Cellular and Molecular Biology and Department of Zoology, University of Texas at Austin, 78712, USA
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28
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Abstract
Much recent research on c-Myc has focused on how it drives apoptosis. c-Myc is widely known as a crucial regulator of cell proliferation in normal and neoplastic cells, but until relatively recently its apoptotic properties, which appear to be intrinsic, were not fully appreciated. Its death-dealing aspects have gained wide attention in part because of their potential therapeutic utility in advanced malignancy, where c-Myc is frequently deregulated and where novel modalities are badly needed. Although its exact function remains obscure, c-Myc is a transcription factor and advances have been made in characterizing target genes which may mediate its apoptotic properties. Candidate regulators and effectors are also emerging. Among recent findings are connections to the CD95/Fas and TNF pathways and roles for the tumor suppressor p19ARF and the c-Myc-interacting adaptor protein Binl in mediating cell death. In this review I summarize the data establishing a role for c-Myc in apoptosis in diverse settings and present a modified dual signal model for c-Myc function. It is proposed that c-Myc induces apoptosis through separate 'death priming' and 'death triggering' mechanisms in which 'death priming' and mitogenic signals are coordinated. Investigation of the mechanisms that underlie the triggering steps may offer new therapeutic opportunities.
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29
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Lüscher B, Larsson LG. The basic region/helix-loop-helix/leucine zipper domain of Myc proto-oncoproteins: function and regulation. Oncogene 1999; 18:2955-66. [PMID: 10378692 DOI: 10.1038/sj.onc.1202750] [Citation(s) in RCA: 156] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
A large body of evidence has been accumulated that demonstrates dominant effects of Myc proto-oncoproteins on different aspects of cellular growth. Myc is one of the few proteins that is sufficient to drive resting cells into the cell cycle and promote DNA synthesis. In line with this finding is that the constitutive expression of Myc in cells blocks their differentiation. These growth stimulating properties are most likely responsible for Myc's ability to initiate and promote tumor formation. Interestingly Myc can also sensitize cells to apoptosis, suggesting that this protein is part of a life-and-death switch. Molecularly Myc functions as a transcriptional regulator that needs to heterodimerize with Max to exert the biological activities described above and to regulate gene transcription. Myc and Max are just two members of a growing family of proteins referred to as the Myc/Max/Mad network. A hallmark of these proteins is that they possess a C-terminal basic region/helix-loop-helix/leucine zipper domain (bHLHZip). The bHLHZip domain specifies dimerization within the network and determines sequence specific DNA binding. Importantly this domain together with the N-terminal transactivation domain is essential for Myc biology. Here we have summarized the structural, functional, and regulatory aspects of the bHLHZip domain of Myc proteins.
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Affiliation(s)
- B Lüscher
- Institut für Molekularbiologie, Medizinische Hochschule Hannover, Germany.
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30
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Abstract
Despite its intensive investigation for almost two decades, c-Myc remains a fascinating and enigmatic subject. A large and compelling body of evidence indicates that c-Myc is a transcription factor with central roles in the regulation of cell proliferation, differentiation, and apoptosis, but its exact function has remained elusive. In this review we survey recent advances in the identification and analysis of c-Myc-binding proteins, which suggest insights into the transcriptional roles of c-Myc but which also extend the existing functional paradigms. The C-terminal domain (CTD) of c-Myc mediates interaction with Max and physiological recognition of DNA target sequences, events needed for all biological actions. Recently described interactions between the CTD and other cellular proteins, including YY-1, AP-2, BRCA-1, TFII-I, and Miz-1, suggest levels of regulatory complexity beyond Max in controlling DNA recognition by c-Myc. The N-terminal domain (NTD), which includes the evolutionarily conserved and functionally crucial Myc Box sequences (MB1 and MB2), contains the transcription activation domain (TAD) of c-Myc as well as regions required for transcriptional repression, cell cycle regulation, transformation, and apoptosis. In addition to interaction with the retinoblastoma family protein p107, the NTD has been shown to interact with alpha-tubulin and the novel adaptor proteins Binl, MM-1, Pam, TRRAP, and AMY-1. The structure of these proteins and their effects on c-Myc actions suggest links to the transcriptional regulatory machinery as well as to cell cycle regulation, chromatin modeling, and apoptosis. Investigations of this emerging NTD-based network may reveal how c-Myc is regulated and how it affects cell fate, as well as providing tools to distinguish the physiological roles of various Myc target genes.
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Affiliation(s)
- D Sakamuro
- The Wistar Institute, Philadelphia, Pennsylvania 19104-4268, USA
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31
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Abstract
MYCN amplification in neuroblastomas is strongly associated with advanced stages of disease and a poor prognosis. We have recently defined a 130 kb core region of the MYCN amplicon that is consistently amplified in neuroblastomas. However, it has been argued that other expressed sequences were coamplified with MYCN and, as a result, might contribute to the aggressive phenotype of MYCN-amplified neuroblastomas. Therefore, we have screened cosmids representing the core MYCN-amplified domain and surrounding DNA by using a differential hybridization approach to detect other amplified, highly expressed genes from this region. Our results suggest that MYCN is the only highly expressed gene consistently amplified in human neuroblastomas, and that the MYCN gene is likely to be the only selective marker for genomic amplification in these tumors.
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Affiliation(s)
- J L Reiter
- Division of Oncology, The Children's Hospital of Philadelphia and the University of Pennsylvania 19104-4318, USA
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32
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Schreiber-Agus N, Alland L, Muhle R, Goltz J, Chen K, Stevens L, Stein D, DePinho RA. A biochemical and biological analysis of Myc superfamily interactions. Curr Top Microbiol Immunol 1997; 224:159-68. [PMID: 9308239 DOI: 10.1007/978-3-642-60801-8_16] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- N Schreiber-Agus
- Dept. of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY, USA
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33
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Krylov D, Echlin DR, Taparowsky EJ, Vinson C. Design of dominant negatives to bHLHZip proteins that inhibit DNA binding. Curr Top Microbiol Immunol 1997; 224:169-77. [PMID: 9308240 DOI: 10.1007/978-3-642-60801-8_17] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- D Krylov
- Laboratory of Biochemistry, National Cancer Institute, National Institutes of Health Bethesda, Maryland 20892, USA
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34
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Joshi VV, Tsongalis GJ. Correlation between morphologic and nonmorphologic prognostic markers of neuroblastoma. Ann N Y Acad Sci 1997; 824:71-83. [PMID: 9382456 DOI: 10.1111/j.1749-6632.1997.tb46210.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Morphologic (Shimada classification--SC, original and modified histologic grades--OHG and MHG) and nonmorphologic (serum LDH, 1 p del, DNA index, N-myc copy number, telomerase activity, and expression of MRP, MDR1, and TRK) prognostic markers for NB have been reviewed. The functional role of these nonmorphologic markers in the development and progression of this disease include abnormal cell proliferation, resistance to chemotherapeutic agents, and induction of apoptosis. A statistically significant association between high OHG/MHG (grade 3), DNA index of 1 (diploidy), > 1 copy of N-myc per haploid genome and serum LDH of > or = 1500 IU/1 (p < 0.001 for each) has been described. In SC, undifferentiated histology and high MKI are associated with N-myc amplification. However, a lack of correlation between morphology and N-myc amplification has been found in localized NB. Confirmation of these observations must now be obtained on larger numbers of prospectively studied cases. Data on correlation for various prognostic markers could provide guidelines for identification of subsets of NB having strongly significant, readily determinable, reproducible, and relatively inexpensive prognostic markers that could ultimately be used to design an algorithm for risk-specific therapy.
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Affiliation(s)
- V V Joshi
- Department of Pathology, Connecticut Children's Medical Center, Hartford, Connecticut, USA
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35
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Brownlie P, Ceska T, Lamers M, Romier C, Stier G, Teo H, Suck D. The crystal structure of an intact human Max-DNA complex: new insights into mechanisms of transcriptional control. Structure 1997; 5:509-20. [PMID: 9115440 DOI: 10.1016/s0969-2126(97)00207-4] [Citation(s) in RCA: 117] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
BACKGROUND Max belongs to the basic helix-loop-helix leucine zipper (bHLHZ) family of transcription factors. Max is able to form homodimers and heterodimers with other members of this family, which include Mad, Mxi1 and Myc; Myc is an oncoprotein implicated in cell proliferation, differentiation and apoptosis. The homodimers and heterodimers compete for a common DNA target site (the E box) and rearrangement amongst these dimer forms provides a complex system of transcriptional regulation. Max is also regulated by phosphorylation at a site preceding the basic region. We report here the first crystal structure of an intact bHLHZ protein bound to its target site. RESULTS The X-ray crystal structure of the intact human Max protein homodimer in complex with a 13-mer DNA duplex was determined to 2.8 A resolution and refined to an R factor of 0.213. The C-terminal domains in both chains of the Max dimer are disordered. In contrast to the DNA observed in complex with other bHLH and bHLHZ proteins, the DNA in the Max complex is bent by about 25 degrees, directed towards the protein. Intimate contacts with interdigitating sidechains give rise to the formation of tetramers in the crystal. CONCLUSIONS The structure confirms the importance of the HLH and leucine zipper motifs in dimerization as well as the mode of E box recognition which was previously analyzed by X-ray crystallography of shortened constructs. The disorder observed in the C-terminal domain suggests that contacts with additional protein components of the transcription machinery are necessary for ordering the secondary structure. The tetramers seen in the crystal are consistent with the tendency of Max and other bHLHZ and HLH proteins to form higher order oligomers in solution and may play a role in DNA looping. The location of the two phosphorylation sites at Ser1 and Ser10 (the latter is the N-cap of the basic helix) suggests how phosphorylation could disrupt DNA binding.
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Affiliation(s)
- P Brownlie
- EMBL Structural Biology Programme, Meyerhofstrasse 1, 69117, Heidelberg, Germany
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36
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Peters MA, Sollenberger KG, Kao TL, Taparowsky EJ. A minimal regulatory region maintains constitutive expression of the max gene. Mol Cell Biol 1997; 17:1037-48. [PMID: 9032230 PMCID: PMC231828 DOI: 10.1128/mcb.17.3.1037] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Max is a basic helix-loop-helix/leucine zipper protein that forms heterodimers with the Myc family of proteins to promote cell growth and with the Mad/Mxi1 family of proteins to inhibit cell growth. The role of Max as the obligate binding partner for these two protein families necessitates the observed constitutive expression and relatively long half-life of the max mRNA under a variety of growth conditions. In this study, we have used the chicken max gene to map DNA elements maintaining max gene expression in vertebrate cells. We have identified a minimal regulatory region (MRR) that resides within 115 bp of the max translation initiation site and that possesses an overall structure typical of TATA-less promoters. Within the MRR are two consensus binding sites for Sp1, a ubiquitously expressed transcription factor that plays a role in the expression of many constitutive genes. Interestingly, we show that direct binding by Sp1 to these sites is not required for MRR-mediated transcription. Instead, the integrity of a 20-bp DNA element in the MRR is required for transcriptional activity, as is the interaction of this DNA element with a 90-kDa cellular protein. Our data suggest that it is the persistence of this 90-kDa protein in vertebrate cells which drives max gene expression, insulates the max promoter from the dramatic changes in transcription that accompany cell growth and development, and ensures that adequate levels of Max will be available to facilitate the function of the Myc, Mad, and Mxi1 families of proteins.
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Affiliation(s)
- M A Peters
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907-1392, USA
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37
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Hurlin PJ, Quéva C, Eisenman RN. Mnt, a novel Max-interacting protein is coexpressed with Myc in proliferating cells and mediates repression at Myc binding sites. Genes Dev 1997; 11:44-58. [PMID: 9000049 DOI: 10.1101/gad.11.1.44] [Citation(s) in RCA: 195] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The small constitutively expressed bHLHZip protein Max is known to form sequence-specific DNA binding heterodimers with members of both the Myc and Mad families of bHLHZip proteins. Myc:Max complexes activate transcription, promote proliferation, and block terminal differentiation. In contrast, Mad:Max heterodimers act as transcriptional repressors, have an antiproliferative effect, and are induced upon differentiation in a wide variety of cell types. We have identified a novel bHLHZip Max-binding protein, Mnt, which belongs to neither the Myc nor the Mad families and which is coexpressed with Myc in a number of proliferating cell types. Mnt:Max heterodimers act as transcriptional repressors and efficiently suppress Myc-dependent activation from a promoter containing proximal CACGTG sites. Transcription repression by Mnt maps to a 13-amino-acid amino-terminal region related to the Sin3 interaction domain (SID) of Mad proteins. We show that this region of Mnt mediates interaction with mSin3 corepressor proteins and that its deletion converts Mnt from a repressor to an activator. Furthermore, wild-type Mnt suppresses Myc+Ras cotransformation of primary cells, whereas Mnt containing a SID deletion cooperates with Ras in the absence of Myc to transform cells. This suggests that Mnt and Myc regulate an overlapping set of target genes in vivo. When mnt is expressed as a transgene under control of the beta-actin promoter in mice the transgenic embryos exhibit a delay in development and die during mid-gestation, when c- and N-Myc functions are critical. We propose that Mnt:Max:Sin3 complexes normally function to restrict Myc:Max activities associated with cell proliferation.
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Affiliation(s)
- P J Hurlin
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98104, USA
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38
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Chen TH, Brody JR, Romantsev FE, Yu JG, Kayler AE, Voneiff E, Kuhajda FP, Pasternack GR. Structure of pp32, an acidic nuclear protein which inhibits oncogene-induced formation of transformed foci. Mol Biol Cell 1996; 7:2045-56. [PMID: 8970164 PMCID: PMC276049 DOI: 10.1091/mbc.7.12.2045] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
pp32 is a nuclear protein found highly expressed in normal tissues in those cells capable of self-renewal and in neoplastic cells. We report the cloning of cDNAs encoding human and murine pp32. The clones encode a 28.6-kDa protein; approximately two-thirds of the N-terminal predicts an amphipathic alpha helix containing two possible nuclear localization signals and a potential leucine zipper motif. The C-terminal third is exceptionally acidic, comprised of approximately 70% aspartic and glutamic acid residues; the predicted pI of human pp32 is 3.81. Human and murine pp32 cDNAs are 88% identical; the predicted proteins are 89% identical and 95% similar. Although the structure of pp32 is suggestive of a transcription factor, pp32 did not significantly modulate transcription of a reporter construct when fused to the Gal4 DNA-binding domain. In contrast, in cotransfection experiments, pp32 inhibited the ability of a broad assortment of oncogene pairs to transform rat embryo fibroblasts, including ras + myc, ras + jun, ras + E1a, ras + mutant p53, and E6 + E7. In related experiments, pp32 inhibited the ability of Rat 1a-myc cells to grow in soft agar, whereas it failed to affect ras-induced focus formation in NIH3T3 cells. These results suggest that pp32 may play a key role in self-renewing cell populations where it may act in the nucleus to limit their sensitivity to transformation.
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Affiliation(s)
- T H Chen
- Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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39
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de la Luna S, Burden MJ, Lee CW, La Thangue NB. Nuclear accumulation of the E2F heterodimer regulated by subunit composition and alternative splicing of a nuclear localization signal. J Cell Sci 1996; 109 ( Pt 10):2443-52. [PMID: 8923205 DOI: 10.1242/jcs.109.10.2443] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The cellular transcription factor E2F plays a critical role in integrating cell cycle progression with the transcription apparatus by virtue of a physical interaction and control by key regulators of the cell cycle, such as pRb, cyclins and cyclin-dependent kinases. Generic E2F DNA binding activity arises when a member of two families of proteins, E2F and DP, form heterodimeric complexes, an interaction which results in co-operative transcriptional and DNA binding activity. Here, we characterise a new and hitherto unexpected mechanism of control influencing the activity of E2F which is mediated at the level of intracellular location through a dependence on heterodimer formation for nuclear translocation. Nuclear accumulation is dramatically influenced by two distinct processes: alternative splicing of a nuclear localization signal and subunit composition of the E2F heterodimer. These data define a new level of control in the E2F transcription factor whereby interplay between subunits dictates the levels of nuclear DNA binding activity.
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Affiliation(s)
- S de la Luna
- Division of Biochemistry and Molecular Biology, University of Glasgow, UK
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40
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Harper SE, Qiu Y, Sharp PA. Sin3 corepressor function in Myc-induced transcription and transformation. Proc Natl Acad Sci U S A 1996; 93:8536-40. [PMID: 8710905 PMCID: PMC38707 DOI: 10.1073/pnas.93.16.8536] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Many basic-helix-loop-helix-leucine zipper (b-HLH-LZ) proteins, including the Myc family and non-Myc family, bind a common DNA sequence CACGTG, yet have quite different biological actions. Myc binds this sequence as a heterodimer with Max in the activation of both transcription and transformation. The Myc family members Mad and Mxi1 are known to suppress Myc-induced transcription and transformation and to dimerize with Max to form ternary complexes with the mammalian Sin3 transcriptional corepressor (mSin3). The b-HLH-LZ domain of TFEB, which cannot heterodimerize within the Myc family, does not suppress Myc-induced transcription or transformation. However, transfer of a 25- to 36-aa region from Mad or Mxi1, which interacts with mSin3, to the b-HLH-LZ of TFEB, mediated profound suppression of Myc-induced transcription and transformation. These results suggest that the DNA binding specificities of the Myc family and non-Myc family b-HLH-LZ proteins, in the context of the cellular genes involved in Myc-induced transformation, are shared. The results also demonstrate that targeting mSin3 to CACGTG sites via a non-Myc family DNA binding domain is sufficient to oppose Myc activity in growth regulation.
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Affiliation(s)
- S E Harper
- Department of Biology, Massachusetts Institute of Technology, Cambridge 02139, USA
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41
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Luo X, Sawadogo M. Antiproliferative properties of the USF family of helix-loop-helix transcription factors. Proc Natl Acad Sci U S A 1996; 93:1308-13. [PMID: 8577760 PMCID: PMC40076 DOI: 10.1073/pnas.93.3.1308] [Citation(s) in RCA: 98] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
USF is a family of transcription factors characterized by a highly conserved basic-helix-loop-helix-leucine zipper (bHLH-zip) DNA-binding domain. Two different USF genes, termed USF1 and USF2, are ubiquitously expressed in both humans and mice. The USF1 and USF2 proteins contain highly divergent transcriptional activation domains but share extensive homologies in the bHLH-zip region and recognize the same CACGTG DNA motifs. Although the DNA-binding and transcriptional activities of these proteins have been characterized, the biological function of USF is not well understood. Here, focus- and colony-formation assays were used to investigate the potential involvement of USF in the regulation of cellular transformation and proliferation. Both USF1 and USF2 inhibited the transformation of rat embryo fibroblasts mediated by Ras and c-Myc, a bHLH-zip transcription factor that also binds CACGTG motifs. DNA binding was required but not fully sufficient for inhibition of Myc-dependent transformation by USF, since deletion mutants containing only the DNA-binding domains of USF1 or USF2 produced partial inhibition. While the effect of USF1 was selective for Myc-dependent transformation, wild-type USF2 exerted in addition a strong inhibition of E1A-mediated transformation and a strong suppression of HeLa cell colony formation. These results suggest that members of the USF family may serve as negative regulators of cellular proliferation in two ways, one by antagonizing the transforming function of Myc, the other through a more general growth-inhibitory effect.
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Affiliation(s)
- X Luo
- Department of Molecular Genetics, University of Texas M.D. Anderson Cancer Center, Houston 77030, USA
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42
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Henriksson M, Lüscher B. Proteins of the Myc network: essential regulators of cell growth and differentiation. Adv Cancer Res 1996; 68:109-82. [PMID: 8712067 DOI: 10.1016/s0065-230x(08)60353-x] [Citation(s) in RCA: 583] [Impact Index Per Article: 20.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- M Henriksson
- Institute for Molecular Biology, Hannover Medical School, Germany
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43
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Lemaitre JM, Buckle RS, Méchali M. c-Myc in the control of cell proliferation and embryonic development. Adv Cancer Res 1996; 70:95-144. [PMID: 8902055 DOI: 10.1016/s0065-230x(08)60873-8] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
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44
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Arsura M, Deshpande A, Hann SR, Sonenshein GE. Variant Max protein, derived by alternative splicing, associates with c-Myc in vivo and inhibits transactivation. Mol Cell Biol 1995; 15:6702-9. [PMID: 8524235 PMCID: PMC230923 DOI: 10.1128/mcb.15.12.6702] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Max (Myc-associated factor X) is a basic helix-loop-helix/leucine zipper protein that has been shown to play a central role in the functional activity of c-Myc as a transcriptional activator. Max potentiates the binding of Myc-Max heterodimers through its basic region to its specific E-box Myc site (EMS), enabling c-Myc to transactivate effectively. In addition to the alternatively spliced exon a, several naturally occurring forms of alternatively spliced max mRNAs have been reported, but variant protein products from these transcripts have not been detected. Using Western blot (immunoblot) and immunoprecipitation analysis, we have identified a variant form of Max protein (16 to 17 kDa), termed dMax, in detergent nuclear extracts of murine B-lymphoma cells, normal B lymphocytes, and NIH 3T3 fibroblasts. Cloning and sequencing revealed that dMax contains a deletion spanning the basic region and helix 1 and the loop of the helix-loop-helix region, presumably as a result of alternative splicing of max RNA. S1 nuclease analysis confirmed the presence of the mRNA for dMax in cells. The dMax protein, prepared via in vitro transcription and translation, associated with bacterially synthesized Myc-glutathione S-transferase. Coimmunoprecipitation of dMax and c-Myc indicated their intracellular association. In vitro-synthesized dMax failed to bind EMS DNA, presumably because of the absence of the basic region. Coexpression of dMax inhibited EMS-mediated transactivation by c-Myc. Thus dMax, which can interact with c-Myc, appears to function as a dominant negative regulator, providing an additional level of regulation to the transactivation potential of c-Myc.
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Affiliation(s)
- M Arsura
- Department of Biochemistry, Boston University School of Medicine, Massachusetts 02118-2394, USA
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45
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Affiliation(s)
- G Packham
- Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, TN 38105, USA
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46
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Schreiber-Agus N, Chin L, Chen K, Torres R, Rao G, Guida P, Skoultchi AI, DePinho RA. An amino-terminal domain of Mxi1 mediates anti-Myc oncogenic activity and interacts with a homolog of the yeast transcriptional repressor SIN3. Cell 1995; 80:777-86. [PMID: 7889571 DOI: 10.1016/0092-8674(95)90356-9] [Citation(s) in RCA: 302] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Documented interactions among members of the Myc superfamily support a yin-yang model for the regulation of Myc-responsive genes in which transactivation-competent Myc-Max heterodimers are opposed by repressive Mxi1-Max or Mad-Max complexes. Analysis of mouse mxi1 has led to the identification of two mxi1 transcript forms possessing open reading frames that differ in their capacity to encode a short amino-terminal alpha-helical domain. The presence of this segment dramatically augments the suppressive potential of Mxi1 and allows for association with a mammalian protein that is structurally homologous to the yeast transcriptional repressor SIN3. These findings provide a mechanistic basis for the antagonistic actions of Mxi1 on Myc activity that appears to be mediated in part through the recruitment of a putative transcriptional repressor.
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Affiliation(s)
- N Schreiber-Agus
- Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York 10461
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47
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Västrik I, Kaipainen A, Penttilä TL, Lymboussakis A, Alitalo R, Parvinen M, Alitalo K. Expression of the mad gene during cell differentiation in vivo and its inhibition of cell growth in vitro. J Biophys Biochem Cytol 1995; 128:1197-208. [PMID: 7896882 PMCID: PMC2120421 DOI: 10.1083/jcb.128.6.1197] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Mad is a basic region helix-loop-helix leucine zipper transcription factor which can dimerize with the Max protein and antagonize transcriptional activation by the Myc-Max transcription factor heterodimer. While the expression of Myc is necessary for cell proliferation, the expression of Mad is induced upon differentiation of at least some leukemia cell lines. Here, the expression of the mad gene has been explored in developing mouse tissues. During organogenesis in mouse embryos mad mRNA was predominantly expressed in the liver and in the mantle layer of the developing brain. At later stages mad expression was detected in neuroretina, epidermis, and whisker follicles, and in adult mice mad was expressed at variable levels in most organs analyzed. Interestingly, in the skin mad was highly expressed in the differentiating epidermal keratinocytes, but not in the underlying proliferating basal keratinocyte layer. Also, in the gut mad mRNA was abundant in the intestinal villi, where cells cease proliferation and differentiate, but not in the crypts, where the intestinal epithelial cells proliferate. In the testis, mad expression was associated with the completion of meiosis and early development of haploid cells. In cell culture, Mad inhibited colony formation of a mouse keratinocyte cell line and rat embryo fibroblast transformation by Myc and Ras. The pattern of mad expression in tissues and its ability to inhibit cell growth in vitro suggests that Mad can cause the cessation of cell proliferation associated with cell differentiation in vivo.
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Affiliation(s)
- I Västrik
- Molecular/Cancer Biology Laboratory, Haartman Institute, University of Helsinki, Finland
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48
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Shimizu E, Shirasawa H, Kodama K, Koseki K, Sato T, Simizu B. Cloning and sequencing of the murine Mxi1 cDNA. Gene 1995; 152:283-4. [PMID: 7835718 DOI: 10.1016/0378-1119(94)00722-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The cloning and sequencing of the murine Mxi1 gene encoding Mxi1, one of Max-associated proteins, is described. Murine and human sequences showed 87.9% nucleotide (nt) and 90.3% amino acid (aa) sequence homology, whereas murine and zebra fish sequences showed 67.2% nt and 67.8% aa sequence homology.
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Affiliation(s)
- E Shimizu
- Department of Microbiology, School of Medicine, Chiba University, Japan
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49
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Hann SR. Methionine deprivation regulates the translation of functionally-distinct c-Myc proteins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1995; 375:107-16. [PMID: 7645422 DOI: 10.1007/978-1-4899-0949-7_10] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Numerous studies have demonstrated a critical role for the c-myc gene in the control of cellular growth. Alterations of the c-myc gene have been found associated with many different types of tumors in several species, including humans. The increased synthesis of one of the major forms of c-Myc protein, c-Myc 1, upon methionine deprivation provides a link between the regulation of oncogenes and the nutritional status of the cell. While deregulation or overexpression of the other major form, c-Myc 2, has been shown to cause tumorigenesis, the synthesis of c-Myc 1 protein is lost in many tumors. This suggests that the c-Myc 1 protein is necessary to keep the c-Myc 2 protein "in check" and prevent certain cells from becoming tumorigenic. Indeed, we have shown that overproduction of c-Myc 1 can inhibit cell growth. We have also shown that c-Myc 1 and 2 proteins have a differential molecular function in the regulation of transcription through a new binding site of Myc/Max heterodimers. We have also recently identified new translational forms of the c-Myc protein which we term delta-c-Myc. These proteins arise from translational initiation at downstream start sites which yield N-terminally-truncated c-Myc proteins. Since these proteins lack a significant portion of the transactivation domain of c-Myc, they behave as dominant-negative inhibitors of the full-length c-Myc 1 and 2 proteins. The synthesis of delta-c-Myc proteins is also regulated during cell growth and is repressed by methionine deprivation. Therefore, the synthesis of c-Myc 1 and delta-c-Myc proteins are reciprocally regulated by methionine availability. We have also found some tumor cell lines which synthesize high levels of the delta-c-Myc proteins. Taken together, our data suggest that c-Myc function is dependent on the levels of these different translational forms of c-Myc protein which are regulated by the nutritional status of the cell during growth. Numerous reports have demonstrated a fundamental and diverse role for the myc gene in cellular events, including proliferation, differentiation and apoptosis (Cole 1986; Spencer and Groudine 1991; Askew et al. 1991; Evan et al. 1992). This is dramatically illustrated by the frequent occurrence of a variety of tumors in many species having alterations of myc genes and the transduction of c-myc sequences by retroviruses (Spencer and Groudine 1991).4+ Eisenman 1990).(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- S R Hann
- Department of Cell Biology, Vanderbilt Univeristy, School of Medicine, Nashville, Tennessee 37232-2175, USA
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50
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Abstract
The oncogenic activation by amplification of the MYCN gene is frequently observed in human neuroblastomas and occasionally in other tumours with neuronal qualities. As a consequence of amplification, elevated levels of the mycN protein are expressed. mycN contains a C-terminal basic region (BR) that can bind to DNA, and a helix-loop-helix (HLH)-leucine zipper (Zip) domain, which is responsible for the physical interaction with another HLH-Zip protein, max. This principle structure is conserved among all members of the MYC gene family. The resulting dimers can bind to the DNA sequence CACGTG. The mycN protein, but not max, contains, near the N-terminus, a region conferring the ability to activate the transcription of genes. mycN/max heterodimers probably activate and max/max homodimers repress transcription of, as yet, unidentified target genes. In neuroblastoma cells, where mycN is deregulated, the balanced interaction of BR-HLH-Zip proteins is probably perturbed, and, therefore, genes controlled by mycN might be abnormally expressed and thereby alter normal cell growth with the consequence of tumorigenesis.
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Affiliation(s)
- A Wenzel
- Department of Cytogenetics, German Cancer Research Center, Heidelberg, Germany
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