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Seo HR, Kim J, Bae S, Soh JW, Lee YS. Cdk5-mediated phosphorylation of c-Myc on Ser-62 is essential in transcriptional activation of cyclin B1 by cyclin G1. J Biol Chem 2008; 283:15601-10. [PMID: 18408012 PMCID: PMC2414302 DOI: 10.1074/jbc.m800987200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2008] [Revised: 04/08/2008] [Indexed: 01/16/2023] Open
Abstract
It has been reported previously that cyclin G1 enables cells to overcome radiation-induced G(2) arrest and increased cell death and that these effects are mediated by transcriptional activation of cyclin B1. In this study, we further investigated the mechanism by which cyclin G1 transcriptionally activates cyclin B1. Deletion or point mutations within the cyclin B1 promoter region revealed that the c-Myc binding site (E-box) is necessary for cyclin G1-mediated transcriptional activation of cyclin B1 to occur. In addition, the kinase activity of Cdk5 was increased by cyclin G1 overexpression, and Cdk5 directly phosphorylated c-Myc on Ser-62. Furthermore, cyclin G1 mediated increased radiosensitivity, and radiation-induced M phase arrest was attenuated when RNA interference of Cdk5 was treated. Taken together, the results of this study indicate that Cdk5 activation in cells that overexpress cyclin G1 leads to c-Myc phosphorylation on Ser-62, which is responsible for cyclin G1-mediated transcriptional activation of cyclin B1.
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Affiliation(s)
- Haeng Ran Seo
- Division of Radiation Effect, Korea
Institute of Radiological and Medical Sciences, Seoul 139-706, Korea,
School of Life Sciences and Biotechnology, Korea
University, Seoul 136-701, Korea, and Laboratory
of Signal Transduction, Department of Chemistry, Inha University, Incheon
402-751, Korea
| | - Joon Kim
- Division of Radiation Effect, Korea
Institute of Radiological and Medical Sciences, Seoul 139-706, Korea,
School of Life Sciences and Biotechnology, Korea
University, Seoul 136-701, Korea, and Laboratory
of Signal Transduction, Department of Chemistry, Inha University, Incheon
402-751, Korea
| | - Sangwoo Bae
- Division of Radiation Effect, Korea
Institute of Radiological and Medical Sciences, Seoul 139-706, Korea,
School of Life Sciences and Biotechnology, Korea
University, Seoul 136-701, Korea, and Laboratory
of Signal Transduction, Department of Chemistry, Inha University, Incheon
402-751, Korea
| | - Jae-Won Soh
- Division of Radiation Effect, Korea
Institute of Radiological and Medical Sciences, Seoul 139-706, Korea,
School of Life Sciences and Biotechnology, Korea
University, Seoul 136-701, Korea, and Laboratory
of Signal Transduction, Department of Chemistry, Inha University, Incheon
402-751, Korea
| | - Yun-Sil Lee
- Division of Radiation Effect, Korea
Institute of Radiological and Medical Sciences, Seoul 139-706, Korea,
School of Life Sciences and Biotechnology, Korea
University, Seoul 136-701, Korea, and Laboratory
of Signal Transduction, Department of Chemistry, Inha University, Incheon
402-751, Korea
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Hann SR. Role of post-translational modifications in regulating c-Myc proteolysis, transcriptional activity and biological function. Semin Cancer Biol 2006; 16:288-302. [PMID: 16938463 DOI: 10.1016/j.semcancer.2006.08.004] [Citation(s) in RCA: 132] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The Myc proteins play a central role in cellular proliferation, differentiation, apoptosis and tumorigenesis. Although it is clear that multiple molecular mechanisms mediate these functions, it is unclear how individual mechanisms contribute and if different mechanisms work in concert or separately in mediating the diverse biological functions of c-Myc. Similarly, the role of post-translational modifications in regulating c-Myc molecular and biological properties has remained uncertain, despite over 20 years of research. In particular, phosphorylation of the N-terminal transcriptional regulatory domain has been shown to have a variety of consequences ranging from dramatic effects on apoptosis, tumorigenesis and c-Myc proteolysis to negligible effects on cellular transformation and transcriptional activity. This review attempts to provide a comprehensive and critical evaluation of the accumulated evidence to address the complex and controversial issues surrounding the role of post-translational modifications in c-Myc function, focusing on phosphorylation and ubiquitination of the N-terminal transcriptional regulatory domain. An overall model emerges that suggests phosphorylation and ubiquitination play critical roles in cell cycle progression, cell growth, apoptosis and tumorigenesis that are mediated by phosphorylation-dependent transcriptional activation of distinct sets of target genes and synchronized proteolysis.
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Affiliation(s)
- Stephen R Hann
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
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Welcker M, Orian A, Jin J, Grim JE, Grim JA, Harper JW, Eisenman RN, Clurman BE. The Fbw7 tumor suppressor regulates glycogen synthase kinase 3 phosphorylation-dependent c-Myc protein degradation. Proc Natl Acad Sci U S A 2004; 101:9085-90. [PMID: 15150404 PMCID: PMC428477 DOI: 10.1073/pnas.0402770101] [Citation(s) in RCA: 715] [Impact Index Per Article: 35.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Myc proteins regulate cell growth and division and are implicated in a wide range of human cancers. We show here that Fbw7, a component of the SCF(Fbw7) ubiquitin ligase and a tumor suppressor, promotes proteasome-dependent c-Myc turnover in vivo and c-Myc ubiquitination in vitro. Phosphorylation of c-Myc on threonine-58 (T58) by glycogen synthase kinase 3 regulates the binding of Fbw7 to c-Myc as well as Fbw7-mediated c-Myc degradation and ubiquitination. T58 is the most frequent site of c-myc mutations in lymphoma cells, and our findings suggest that c-Myc activation is one of the key oncogenic consequences of Fbw7 loss in cancer. Because Fbw7 mediates the degradation of cyclin E, Notch, and c-Jun, as well as c-Myc, the loss of Fbw7 is likely to elicit profound effects on cell proliferation during tumorigenesis.
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Affiliation(s)
- Markus Welcker
- Division of Clinical Research, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA
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Hollander MC, Fornace AJ. Genomic instability, centrosome amplification, cell cycle checkpoints and Gadd45a. Oncogene 2002; 21:6228-33. [PMID: 12214253 DOI: 10.1038/sj.onc.1205774] [Citation(s) in RCA: 108] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Genomic instability has been a recognized feature of many human tumors for decades. Until recently, however, there was little insight into potential mechanisms for this phenomenon. Recent work has shown first, that increased centrosome numbers (also referred to as centrosome amplification) often accompany genomic instability and second, that when centrosome numbers are increased, cells become genetically unstable. Deletion of Gadd45a leads to centrosome amplification and consequent abnormal mitosis and aneuploidy. Gadd45a is known to be involved in a G2 checkpoint and may be involved in the normal progression from G2 to M and its coordination with S phase events. Whether these functions contribute to prevention of centrosome amplification is being investigated. However, potential mechanisms can be proposed based on known protein associations with Gadd45a, as well as proteins that regulate Gadd45a transcription and are also required for efficient coordination of centrosome duplication and DNA synthesis.
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