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Mödlhammer A, Pfurtscheller S, Feichtner A, Hartl M, Schneider R. The Diarylheptanoid Curcumin Induces MYC Inhibition and Cross-Links This Oncoprotein to the Coactivator TRRAP. Front Oncol 2021; 11:660481. [PMID: 33937075 PMCID: PMC8082493 DOI: 10.3389/fonc.2021.660481] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Accepted: 03/23/2021] [Indexed: 11/13/2022] Open
Abstract
The c-Myc protein (MYC) is a transcription factor with strong oncogenic potential controlling fundamental cellular processes. In most human tumors, MYC is overexpressed by enhanced transcriptional activation, gene amplification, chromosomal rearrangements, or increased protein stabilization. To pharmacologically suppress oncogenic MYC functions, multiple approaches have been applied either to inhibit transcriptional activation of the endogenous MYC gene, or to interfere with biochemical functions of aberrantly activated MYC. Other critical points of attack are targeted protein modification, or destabilization leading to a non-functional MYC oncoprotein. It has been claimed that the natural compound curcumin representing the principal curcumoid of turmeric (Curcuma longa) has anticancer properties although its specificity, efficacy, and the underlying molecular mechanisms have been controversially discussed. Here, we have tested curcumin’s effect on MYC-dependent cell transformation and transcriptional activation, and found that this natural compound interferes with both of these MYC activities. Furthermore, in curcumin-treated cells, the endogenous 60-kDa MYC protein is covalently and specifically cross-linked to one of its transcriptional interaction partners, namely the 434-kDa transformation/transcription domain associated protein (TRRAP). Thereby, endogenous MYC levels are strongly reduced and cells stop to proliferate. TRRAP is a multidomain adaptor protein of the phosphoinositide 3-kinase-related kinases (PIKK) family and represents an important component of many histone acetyltransferase (HAT) complexes. TRRAP is important to mediate transcriptional activation executed by the MYC oncoprotein, but on the other hand TRRAP also negatively regulates protein stability of the tumor suppressor p53 (TP53). Curcumin-mediated covalent binding of MYC to TRRAP reduces the protein amounts of both interaction partners but does not downregulate TP53, so that the growth-arresting effect of wild type TP53 could prevail. Our results elucidate a molecular mechanism of curcumin action that specifically and irreversibly targets two crucial multifunctional cellular players. With regard to their broad impact in cancer, our findings contribute to explain the pleiotropic functions of curcumin, and suggest that this natural spice, or more bioavailable derivatives thereof, may constitute useful adjuvants in the therapy of MYC-dependent and TRRAP-associated human tumors.
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Affiliation(s)
- Alexander Mödlhammer
- Institute of Biochemistry and Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innsbruck, Austria
| | - Sandra Pfurtscheller
- Institute of Biochemistry and Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innsbruck, Austria
| | - Andreas Feichtner
- Institute of Biochemistry and Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innsbruck, Austria
| | - Markus Hartl
- Institute of Biochemistry and Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innsbruck, Austria
| | - Rainer Schneider
- Institute of Biochemistry and Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innsbruck, Austria
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Hartl M, Puglisi K, Nist A, Raffeiner P, Bister K. The brain acid-soluble protein 1 (BASP1) interferes with the oncogenic capacity of MYC and its binding to calmodulin. Mol Oncol 2020; 14:625-644. [PMID: 31944520 PMCID: PMC7053243 DOI: 10.1002/1878-0261.12636] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2019] [Revised: 12/16/2019] [Accepted: 01/09/2020] [Indexed: 12/13/2022] Open
Abstract
The MYC protein is a transcription factor with oncogenic potential controlling fundamental cellular processes such as cell proliferation, metabolism, differentiation, and apoptosis. The MYC gene is a major cancer driver, and elevated MYC protein levels are a hallmark of most human cancers. We have previously shown that the brain acid-soluble protein 1 gene (BASP1) is specifically downregulated by the v-myc oncogene and that ectopic BASP1 expression inhibits v-myc-induced cell transformation. The 11-amino acid effector domain of the BASP1 protein interacts with the calcium sensor calmodulin (CaM) and is mainly responsible for this inhibitory function. We also reported recently that CaM interacts with all MYC variant proteins and that ectopic CaM increases the transactivation and transformation potential of the v-Myc protein. Here, we show that the presence of excess BASP1 or of a synthetic BASP1 effector domain peptide leads to displacement of v-Myc from CaM. The protein stability of v-Myc is decreased in cells co-expressing v-Myc and BASP1, which may account for the inhibition of v-Myc. Furthermore, suppression of v-Myc-triggered transcriptional activation and cell transformation is compensated by ectopic CaM, suggesting that BASP1-mediated withdrawal of CaM from v-Myc is a crucial event in the inhibition. In view of the tumor-suppressive role of BASP1 which was recently also reported for human cancer, small compounds or peptides based on the BASP1 effector domain could be used in drug development strategies aimed at tumors with high MYC expression.
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Affiliation(s)
- Markus Hartl
- Institute of Biochemistry and Center for Molecular Biosciences (CMBI), University of Innsbruck, Austria
| | - Kane Puglisi
- Institute of Biochemistry and Center for Molecular Biosciences (CMBI), University of Innsbruck, Austria
| | - Andrea Nist
- Institute of Biochemistry and Center for Molecular Biosciences (CMBI), University of Innsbruck, Austria
| | - Philipp Raffeiner
- Institute of Biochemistry and Center for Molecular Biosciences (CMBI), University of Innsbruck, Austria
| | - Klaus Bister
- Institute of Biochemistry and Center for Molecular Biosciences (CMBI), University of Innsbruck, Austria
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3
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Hartl M, Glasauer S, Gufler S, Raffeiner A, Puglisi K, Breuker K, Bister K, Hobmayer B. Differential regulation of myc homologs by Wnt/β-Catenin signaling in the early metazoan Hydra. FEBS J 2019; 286:2295-2310. [PMID: 30869835 PMCID: PMC6618008 DOI: 10.1111/febs.14812] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Revised: 01/08/2019] [Accepted: 03/12/2019] [Indexed: 12/14/2022]
Abstract
The c‐Myc protein is a transcription factor with oncogenic potential controlling fundamental cellular processes. Homologs of the human c‐myc protooncogene have been identified in the early diploblastic cnidarian Hydra (myc1, myc2). The ancestral Myc1 and Myc2 proteins display the principal design and biochemical properties of their vertebrate derivatives, suggesting that important Myc functions arose very early in metazoan evolution. c‐Myc is part of a transcription factor network regulated by several upstream pathways implicated in oncogenesis and development. One of these signaling cascades is the Wnt/β‐Catenin pathway driving cell differentiation and developmental patterning, but also tumorigenic processes including aberrant transcriptional activation of c‐myc in several human cancers. Here, we show that genetic or pharmacological stimulation of Wnt/β‐Catenin signaling in Hydra is accompanied by specific downregulation of myc1 at mRNA and protein levels. The myc1 and myc2 promoter regions contain consensus binding sites for the transcription factor Tcf, and Hydra Tcf binds to the regulatory regions of both promoters. The myc1 promoter is also specifically repressed in the presence of ectopic Hydra β‐Catenin/Tcf in avian cell culture. We propose that Hydra myc1 is a negative Wnt signaling target, in contrast to vertebrate c‐myc, which is one of the best studied genes activated by this pathway. On the contrary, myc2 is not suppressed by ectopic β‐Catenin in Hydra and presumably represents the structural and functional c‐myc ortholog. Our data implicate that the connection between β‐Catenin‐mediated signaling and myc1 and myc2 gene regulation is an ancestral metazoan feature. Its impact on decision making in Hydra interstitial stem cells is discussed.
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Affiliation(s)
- Markus Hartl
- Institute of Biochemistry, University of Innsbruck, Austria.,Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Austria
| | - Stella Glasauer
- Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Austria.,Institute of Zoology, University of Innsbruck, Austria
| | - Sabine Gufler
- Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Austria.,Institute of Zoology, University of Innsbruck, Austria
| | - Andrea Raffeiner
- Institute of Biochemistry, University of Innsbruck, Austria.,Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Austria
| | - Kane Puglisi
- Institute of Biochemistry, University of Innsbruck, Austria.,Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Austria
| | - Kathrin Breuker
- Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Austria.,Institute of Organic Chemistry, University of Innsbruck, Austria
| | - Klaus Bister
- Institute of Biochemistry, University of Innsbruck, Austria.,Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Austria
| | - Bert Hobmayer
- Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Austria.,Institute of Zoology, University of Innsbruck, Austria
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Raffeiner P, Schraffl A, Schwarz T, Röck R, Ledolter K, Hartl M, Konrat R, Stefan E, Bister K. Calcium-dependent binding of Myc to calmodulin. Oncotarget 2018; 8:3327-3343. [PMID: 27926480 PMCID: PMC5356885 DOI: 10.18632/oncotarget.13759] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Accepted: 11/21/2016] [Indexed: 12/13/2022] Open
Abstract
The bHLH-LZ (basic region/helix-loop-helix/leucine zipper) oncoprotein Myc and the bHLH-LZ protein Max form a binary transcription factor complex controlling fundamental cellular processes. Deregulated Myc expression leads to neoplastic transformation and is a hallmark of most human cancers. The dynamics of Myc transcription factor activity are post-translationally coordinated by defined protein-protein interactions. Here, we present evidence for a second messenger controlled physical interaction between the Ca2+ sensor calmodulin (CaM) and all Myc variants (v-Myc, c-Myc, N-Myc, and L-Myc). The predominantly cytoplasmic Myc:CaM interaction is Ca2+-dependent, and the binding site maps to the conserved bHLH domain of Myc. Ca2+-loaded CaM binds the monomeric and intrinsically disordered Myc protein with high affinity, whereas Myc:Max heterodimers show less, and Max homodimers no affinity for CaM. NMR spectroscopic analyses using alternating mixtures of 15N-labeled and unlabeled preparations of CaM and a monomeric Myc fragment containing the bHLH-LZ domain corroborate the biochemical results on the Myc:CaM interaction and confirm the interaction site mapping. In electrophoretic mobility shift assays, addition of CaM does not affect high-affinity DNA-binding of Myc:Max heterodimers. However, cell-based reporter analyses and cell transformation assays suggest that increasing CaM levels enhance Myc transcriptional and oncogenic activities. Our results point to a possible involvement of Ca2+ sensing CaM in the fine-tuning of Myc function.
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Affiliation(s)
- Philipp Raffeiner
- Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, A-6020 Innsbruck, Austria.,Present address: Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Andrea Schraffl
- Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, A-6020 Innsbruck, Austria
| | - Thomas Schwarz
- Max F. Perutz Laboratories, Department of Structural and Computational Biology, University of Vienna, A-1030 Vienna, Austria
| | - Ruth Röck
- Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, A-6020 Innsbruck, Austria
| | - Karin Ledolter
- Max F. Perutz Laboratories, Department of Structural and Computational Biology, University of Vienna, A-1030 Vienna, Austria
| | - Markus Hartl
- Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, A-6020 Innsbruck, Austria
| | - Robert Konrat
- Max F. Perutz Laboratories, Department of Structural and Computational Biology, University of Vienna, A-1030 Vienna, Austria
| | - Eduard Stefan
- Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, A-6020 Innsbruck, Austria
| | - Klaus Bister
- Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, A-6020 Innsbruck, Austria
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Hartl M. The Quest for Targets Executing MYC-Dependent Cell Transformation. Front Oncol 2016; 6:132. [PMID: 27313991 PMCID: PMC4889588 DOI: 10.3389/fonc.2016.00132] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2016] [Accepted: 05/20/2016] [Indexed: 12/26/2022] Open
Abstract
MYC represents a transcription factor with oncogenic potential converting multiple cellular signals into a broad transcriptional response, thereby controlling the expression of numerous protein-coding and non-coding RNAs important for cell proliferation, metabolism, differentiation, and apoptosis. Constitutive activation of MYC leads to neoplastic cell transformation, and deregulated MYC alleles are frequently observed in many human cancer cell types. Multiple approaches have been performed to isolate genes differentially expressed in cells containing aberrantly activated MYC proteins leading to the identification of thousands of putative targets. Functional analyses of genes differentially expressed in MYC-transformed cells had revealed that so far more than 40 upregulated or downregulated MYC targets are actively involved in cell transformation or tumorigenesis. However, further systematic and selective approaches are required for determination of the known or yet unidentified targets responsible for processing the oncogenic MYC program. The search for critical targets in MYC-dependent tumor cells is exacerbated by the fact that during tumor development, cancer cells progressively evolve in a multistep process, thereby acquiring their characteristic features in an additive manner. Functional expression cloning, combinatorial gene expression, and appropriate in vivo tests could represent adequate tools for dissecting the complex scenario of MYC-specified cell transformation. In this context, the central goal is to identify a minimal set of targets that suffices to phenocopy oncogenic MYC. Recently developed genomic editing tools could be employed to confirm the requirement of crucial transformation-associated targets. Knowledge about essential MYC-regulated genes is beneficial to expedite the development of specific inhibitors to interfere with growth and viability of human tumor cells in which MYC is aberrantly activated. Approaches based on the principle of synthetic lethality using MYC-overexpressing cancer cells and chemical or RNAi libraries have been employed to search for novel anticancer drugs, also leading to the identification of several druggable targets. Targeting oncogenic MYC effector genes instead of MYC may lead to compounds with higher specificities and less side effects. This class of drugs could also display a wider pharmaceutical window because physiological functions of MYC, which are important for normal cell growth, proliferation, and differentiation would be less impaired.
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Affiliation(s)
- Markus Hartl
- Institute of Biochemistry and Center of Molecular Biosciences (CMBI), University of Innsbruck , Innsbruck , Austria
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Raffeiner P, Röck R, Schraffl A, Hartl M, Hart JR, Janda KD, Vogt PK, Stefan E, Bister K. In vivo quantification and perturbation of Myc-Max interactions and the impact on oncogenic potential. Oncotarget 2015; 5:8869-78. [PMID: 25326649 PMCID: PMC4253403 DOI: 10.18632/oncotarget.2588] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
The oncogenic bHLH-LZ transcription factor Myc forms binary complexes with its binding partner Max. These and other bHLH-LZ-based protein-protein interactions (PPI) in the Myc-Max network are essential for the physiological and oncogenic activities of Myc. We have generated a genetically determined and highly specific protein-fragment complementation assay based on Renilla luciferase to analyze the dynamic interplay of bHLH-LZ transcription factors Myc, Max, and Mxd1 in vivo. We also applied this PPI reporter to quantify alterations of nuclear Myc-Max complexes in response to mutational events, competitive binding by the transcriptional repressor Mxd1, or perturbations by small-molecule Myc inhibitors, including recently identified potent PPI inhibitors from a Kröhnke pyridine library. We show that the specificity of Myc-Max PPI reduction by the pyridine inhibitors directly correlates with their efficient and highly specific potential to interfere with the proliferation of human and avian tumor cells displaying deregulated Myc expression. In a direct comparison with known Myc inhibitors using human and avian cell systems, the pyridine compounds reveal a unique inhibitory potential even at sub-micromolar concentrations combined with remarkable specificity for the inhibition of Myc-driven tumor cell proliferation. Furthermore, we show in direct comparisons using defined avian cell systems that different Max PPI profiles for the variant members of the Myc protein family (c-Myc, v-Myc, N-Myc, L-Myc) correlate with their diverse oncogenic potential and their variable sensitivity to the novel pyridine inhibitors.
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Affiliation(s)
- Philipp Raffeiner
- Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, Innsbruck, Austria
| | - Ruth Röck
- Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, Innsbruck, Austria
| | - Andrea Schraffl
- Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, Innsbruck, Austria
| | - Markus Hartl
- Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, Innsbruck, Austria
| | - Jonathan R Hart
- Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, CA
| | - Kim D Janda
- Department of Chemistry, The Scripps Research Institute, La Jolla, CA
| | - Peter K Vogt
- Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, CA
| | - Eduard Stefan
- Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, Innsbruck, Austria
| | - Klaus Bister
- Institute of Biochemistry and Center for Molecular Biosciences, University of Innsbruck, Innsbruck, Austria
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Hartl M, Glasauer S, Valovka T, Breuker K, Hobmayer B, Bister K. Hydra myc2, a unique pre-bilaterian member of the myc gene family, is activated in cell proliferation and gametogenesis. Biol Open 2014; 3:397-407. [PMID: 24771621 PMCID: PMC4021362 DOI: 10.1242/bio.20147005] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The myc protooncogene encodes the Myc transcription factor which is the essential part of the Myc–Max network controlling fundamental cellular processes. Deregulation of myc leads to tumorigenesis and is a hallmark of many human cancers. We have recently identified homologs of myc (myc1, myc2) and max in the early diploblastic cnidarian Hydra and have characterized myc1 in detail. Here we show that myc2 is transcriptionally activated in the interstitial stem cell system. Furthermore, in contrast to myc1, myc2 expression is also detectable in proliferating epithelial stem cells throughout the gastric region. myc2 but not myc1 is activated in cycling precursor cells during early oogenesis and spermatogenesis, suggesting that the Hydra Myc2 protein has a possible non-redundant function in cell cycle progression. The Myc2 protein displays the principal design and properties of vertebrate Myc proteins. In complex with Max, Myc2 binds to DNA with similar affinity as Myc1–Max heterodimers. Immunoprecipitation of Hydra chromatin revealed that both Myc1 and Myc2 bind to the enhancer region of CAD, a classical Myc target gene in mammals. Luciferase reporter gene assays showed that Myc1 but not Myc2 transcriptionally activates the CAD promoter. Myc2 has oncogenic potential when tested in primary avian fibroblasts but to a lower degree as compared to Myc1. The identification of an additional myc gene in Cnidaria, a phylum that diverged prior to bilaterians, with characteristic expression patterns in tissue homeostasis and developmental processes suggests that principle functions of myc genes have arisen very early in metazoan evolution.
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Affiliation(s)
- Markus Hartl
- Institute of Biochemistry, University of Innsbruck, A-6020 Innsbruck, Austria Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, A-6020 Innsbruck, Austria
| | - Stella Glasauer
- Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, A-6020 Innsbruck, Austria Institute of Zoology, University of Innsbruck, A-6020 Innsbruck, Austria Present address: Institute of Molecular Life Sciences, University of Zurich, CH-8057 Zurich, Switzerland
| | - Taras Valovka
- Institute of Biochemistry, University of Innsbruck, A-6020 Innsbruck, Austria Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, A-6020 Innsbruck, Austria
| | - Kathrin Breuker
- Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, A-6020 Innsbruck, Austria Institute of Organic Chemistry, University of Innsbruck, A-6020 Innsbruck, Austria
| | - Bert Hobmayer
- Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, A-6020 Innsbruck, Austria Institute of Zoology, University of Innsbruck, A-6020 Innsbruck, Austria
| | - Klaus Bister
- Institute of Biochemistry, University of Innsbruck, A-6020 Innsbruck, Austria Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, A-6020 Innsbruck, Austria
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Transcriptional control of DNA replication licensing by Myc. Sci Rep 2013; 3:3444. [PMID: 24309437 PMCID: PMC3853707 DOI: 10.1038/srep03444] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2013] [Accepted: 11/21/2013] [Indexed: 01/12/2023] Open
Abstract
The c-myc protooncogene encodes the Myc transcription factor, a global regulator of fundamental cellular processes. Deregulation of c-myc leads to tumorigenesis, and c-myc is an important driver in human cancer. Myc and its dimerization partner Max are bHLH-Zip DNA binding proteins involved in transcriptional regulation of target genes. Non-transcriptional functions have also been attributed to the Myc protein, notably direct interaction with the pre-replicative complex (pre-RC) controlling the initiation of DNA replication. A key component of the pre-RC is the Cdt1 protein, an essential factor in origin licensing. Here we present data suggesting that the CDT1 gene is a transcriptional target of the Myc-Max complex. Expression of the CDT1 gene in v-myc-transformed cells directly correlates with myc expression. Also, human tumor cells with elevated c-myc expression display increased CDT1 expression. Occupation of the CDT1 promoter by Myc-Max is demonstrated by chromatin immunoprecipitation, and transactivation by Myc-Max is shown in reporter assays. Ectopic expression of CDT1 leads to cell transformation. Our results provide a possible direct mechanistic link of Myc's canonical function as a transcription factor to DNA replication. Furthermore, we suggest that aberrant transcriptional activation of CDT1 by deregulated myc alleles contributes to the genomic instabilities observed in tumor cells.
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Abstract
The myc oncogene was originally identified as a transduced allele (v-myc) in the genome of a highly oncogenic avian retrovirus. The protein product (Myc) of the cellular c-myc proto-oncogene represents the key component of a transcription factor network controlling the expression of a large fraction of all human genes. Myc regulates fundamental cellular processes like growth, metabolism, proliferation, differentiation, and apoptosis. Mutational deregulation of c-myc leading to increased levels of the Myc protein is a frequent event in the etiology of human cancers. In this chapter, we describe cell systems and experimental strategies to monitor and quantify the oncogenic potential of myc alleles and to isolate and characterize transcriptional targets of Myc that are relevant for the cell transformation process. We also describe experimental procedures to study the evolutionary origin of myc and to analyze structure and function of the ancestral myc proto-oncogenes.
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Affiliation(s)
- Markus Hartl
- Center for Chemistry and Biomedicine, Institute of Biochemistry, University of Innsbruck, Innsbruck, Austria
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v-Myc inhibits C/EBPβ activity by preventing C/EBPβ-induced phosphorylation of the co-activator p300. Oncogene 2009; 28:2446-55. [DOI: 10.1038/onc.2009.90] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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Inhibition of Myc-induced cell transformation by brain acid-soluble protein 1 (BASP1). Proc Natl Acad Sci U S A 2009; 106:5604-9. [PMID: 19297618 DOI: 10.1073/pnas.0812101106] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cell transformation by the Myc oncoprotein involves transcriptional activation or suppression of specific target genes with intrinsic oncogenic or tumor-suppressive potential, respectively. We have identified the BASP1 (CAP-23, NAP-22) gene as a novel target suppressed by Myc. The acidic 25-kDa BASP1 protein was originally isolated as a cortical cytoskeleton-associated protein from rat and chicken brain, but has also been found in other tissues and subcellular locations. BASP1 mRNA and protein expression is specifically suppressed in fibroblasts transformed by the v-myc oncogene, but not in cells transformed by other oncogenic agents. The BASP1 gene encompasses 2 exons separated by a 58-kbp intron and a Myc-responsive regulatory region at the 5' boundary of untranslated exon 1. Bicistronic expression of BASP1 and v-myc from a retroviral vector blocks v-myc-induced cell transformation. Furthermore, ectopic expression of BASP1 renders fibroblasts resistant to subsequent cell transformation by v-myc, and exogenous delivery of the BASP1 gene into v-myc-transformed cells leads to significant attenuation of the transformed phenotype. The inhibition of v-myc-induced cell transformation by BASP1 also prevents the transcriptional activation or repression of known Myc target genes. Mutational analysis showed that the basic N-terminal domain containing a myristoylation site, a calmodulin binding domain, and a putative nuclear localization signal is essential for the inhibitory function of BASP1. Our results suggest that down-regulation of the BASP1 gene is a necessary event in myc-induced oncogenesis and define the BASP1 protein as a potential tumor suppressor.
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TOJ3, a v-jun target with intrinsic oncogenic potential, is directly regulated by Jun via a novel AP-1 binding motif. Virology 2008; 378:371-6. [PMID: 18603277 DOI: 10.1016/j.virol.2008.06.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2008] [Revised: 05/20/2008] [Accepted: 06/02/2008] [Indexed: 01/09/2023]
Abstract
The TOJ3 gene was originally identified on the basis of its specific activation in avian fibroblasts transformed by the v-jun oncogene of avian sarcoma virus 17 (ASV17). Overexpression of TOJ3 induces cellular transformation of embryonic avian fibroblasts, revealing an intrinsic oncogenic potential. Transforming activity has also been demonstrated for MSP58, the human homolog of TOJ3, and oncogenic cell transformation by MSP58 is specifically inhibited by the tumor suppressor PTEN. To investigate the mechanism of aberrant TOJ3 gene activation in jun-transformed fibroblasts, the entire quail TOJ3 gene including 13 exons and the 5' regulatory region was isolated. Functional analyses of the promoter by transcriptional transactivation assays revealed that the specific induction of TOJ3 is mediated by a cluster of three noncanonical AP-1 binding motifs (5'-CAGCTCA-3' or 5'-CACCTCA-3') which share the 3' half-site with the consensus motif (5'-TGA(C)/(G)TCA-3'). Electrophoretic mobility shift assays and chromatin immunoprecipitation analyses showed that Jun binds to these motifs with an affinity similar to that observed for binding to an AP-1 consensus site. Noncanonical binding sites are also present in the chicken and human TOJ3/MSP58 promoter regions. These results confirm and extend the previous observation that TOJ3 represents an immediate effector gene of Jun and may point to an essential role of TOJ3/MSP58 in carcinogenesis involving aberrant AP-1 expression.
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