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Contrasting effects of an Mdm2 functional polymorphism on tumor phenotypes. Oncogene 2017; 37:332-340. [PMID: 28925402 DOI: 10.1038/onc.2017.344] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Revised: 07/04/2017] [Accepted: 08/08/2017] [Indexed: 12/18/2022]
Abstract
MDM2, an E3 ubiquitin ligase, is a potent inhibitor of the p53 tumor suppressor and is elevated in many human cancers that retain wild-type p53. MDM2 SNP309G is a functional polymorphism that results in elevated levels of MDM2 (due to enhanced SP1 binding to the MDM2 promoter) thus decreasing p53 activity. Mdm2SNP309G/G mice are more prone to spontaneous tumor formation than Mdm2SNP309T/T mice, providing direct evidence for the impact of this SNP in tumor development. We asked whether environmental factors impact SNP309G function and show that SNP309G cooperates with ionizing radiation to exacerbate tumor development. Surprisingly, ultraviolet B light or Benzo(a)pyrene exposure of skin shows that SNP309G allele actually protects against squamous cell carcinoma susceptibility. These contrasting differences led us to interrogate the mechanism by which Mdm2 SNP309 regulates tumor susceptibility in a tissue-specific manner. Although basal Mdm2 levels were significantly higher in most tissues in Mdm2SNP309G/G mice compared with Mdm2SNP309T/T mice, they were significantly lower in Mdm2SNP309G/G keratinocytes, the cell-type susceptible to squamous cell carcinoma. The assessment of potential transcriptional regulators in ENCODE ChIP-seq database identified transcriptional repressor E2F6 as a possible negative regulator of MDM2 expression. Our data show that E2F6 suppresses Mdm2 expression in cells harboring the SNP309G allele but not the SNP309T allele. Thus, Mdm2 SNP309G exhibits tissue-specific regulation and differentially impacts cancer risk.
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KIM SEONGGON, KIM ANSOOK, JEONG JAEHWAN, CHOI JEYONG, KWEON HAEYONG. 4-hexylresorcinol stimulates the differentiation of SCC-9 cells through the suppression of E2F2, E2F3 and Sp3 expression and the promotion of Sp1 expression. Oncol Rep 2012; 28:677-81. [DOI: 10.3892/or.2012.1845] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2012] [Accepted: 05/14/2012] [Indexed: 11/06/2022] Open
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Hazar-Rethinam M, Endo-Munoz L, Gannon O, Saunders N. The role of the E2F transcription factor family in UV-induced apoptosis. Int J Mol Sci 2011; 12:8947-60. [PMID: 22272113 PMCID: PMC3257110 DOI: 10.3390/ijms12128947] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2011] [Revised: 11/15/2011] [Accepted: 11/30/2011] [Indexed: 11/16/2022] Open
Abstract
The E2F transcription factor family is traditionally associated with cell cycle control. However, recent data has shown that activating E2Fs (E2F1-3a) are potent activators of apoptosis. In contrast, the recently cloned inhibitory E2Fs (E2F7 and 8) appear to antagonize E2F-induced cell death. In this review we will discuss (i) the potential role of E2Fs in UV-induced cell death and (ii) the implications of this to the development of UV-induced cutaneous malignancies.
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Affiliation(s)
- Mehlika Hazar-Rethinam
- Epithelial Pathobiology Group, University of Queensland Diamantina Institute, Princess Alexandra Hospital, Queensland 4102, Australia; E-Mails: (M.H.-R.); (L.E.-M.); (O.G.)
| | - Liliana Endo-Munoz
- Epithelial Pathobiology Group, University of Queensland Diamantina Institute, Princess Alexandra Hospital, Queensland 4102, Australia; E-Mails: (M.H.-R.); (L.E.-M.); (O.G.)
| | - Orla Gannon
- Epithelial Pathobiology Group, University of Queensland Diamantina Institute, Princess Alexandra Hospital, Queensland 4102, Australia; E-Mails: (M.H.-R.); (L.E.-M.); (O.G.)
| | - Nicholas Saunders
- Epithelial Pathobiology Group, University of Queensland Diamantina Institute, Princess Alexandra Hospital, Queensland 4102, Australia; E-Mails: (M.H.-R.); (L.E.-M.); (O.G.)
- School of Biomedical Sciences, University of Queensland, Queensland 4072, Australia
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +61-7-3176-5894; Fax: +61-7-3176-5946
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Loss of E2F7 expression is an early event in squamous differentiation and causes derepression of the key differentiation activator Sp1. J Invest Dermatol 2011; 131:1077-84. [PMID: 21248772 DOI: 10.1038/jid.2010.430] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Squamous differentiation is controlled by key transcription factors such as Sp1 and E2F. We have previously shown that E2F1 can suppress transcription of the differentiation-specific gene, transglutaminase type 1 (TG1), by an indirect mechanism mediated by Sp1. Transient transfection of E2F1-E2F6 indicated that E2F-mediated reduction of Sp1 transcription was not responsible for E2F-mediated suppression of squamous differentiation. However, we found that E2F4 and E2F7, but not E2Fs 1, 2, 3, 5, or 6, could suppress the activation of the Sp1 promoter in differentiated keratinocytes (KCs). E2F4-mediated suppression could not be antagonized by E2Fs 1, 2, 3, 5, or 6 and was localized to a region of the human Sp1 promoter spanning -139 to + 35 bp. Chromatin immunoprecipitation analysis, as well as transient overexpression and short hairpin RNA knockdown experiments indicate that E2F7 binds to a unique binding site located between -139 and -119 bp of the Sp1 promoter, and knockdown of E2F7 in proliferating KCs leads to a derepression of Sp1 expression and the induction of TG1. In contrast, E2F4 knockdown in proliferating KCs did not alter Sp1 expression. These data indicate that loss of E2F7 during the initiation of differentiation leads to the derepression of Sp1 and subsequent transcription of differentiation-specific genes such as TG1.
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Endo-Munoz L, Dahler A, Teakle N, Rickwood D, Hazar-Rethinam M, Abdul-Jabbar I, Sommerville S, Dickinson I, Kaur P, Paquet-Fifield S, Saunders N. E2F7 can regulate proliferation, differentiation, and apoptotic responses in human keratinocytes: implications for cutaneous squamous cell carcinoma formation. Cancer Res 2009; 69:1800-8. [PMID: 19223542 DOI: 10.1158/0008-5472.can-08-2725] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The E2F family of transcription factors plays a crucial role in the regulation of genes involved in cell proliferation, differentiation, and apoptosis. In keratinocytes, the inhibition of E2F is a key step in the control and initiation of squamous differentiation. Because the product of the recently identified E2F7a/E2F7b gene has been shown to repress E2F-regulated promoters, and to be abundant in skin, we examined its role in the epidermis. Our results indicate that E2F7b mRNA expression is selectively associated with proliferation-competent keratinocytes. Moreover, E2F7 was able to antagonize E2F1-induced proliferation and apoptosis. In contrast, although E2F7 was able to inhibit proliferation and initiate differentiation, it was unable to antagonize the differentiation suppression induced by E2F1. These data indicate that E2F7-mediated suppression of proliferation and apoptosis acts through E2F1-dependent pathways, whereas E2F7-induced differentiation acts through an E2F1-independent pathway. These data also suggest that proliferation, differentiation, and survival of primary human keratinocytes can be controlled by the relative ratio of E2F1 to E2F7. Because deregulated proliferation, differentiation, and apoptosis are hallmarks of cancer, we examined the expression levels of E2F1 and E2F7 in cutaneous squamous cell carcinomas (CSCC). We found that both genes were overexpressed in CSCCs compared with normal epidermis. Furthermore, inhibition of E2F7 in a SCC cell line sensitized the cells to UV-induced apoptosis and doxorubicin-induced apoptosis. Combined, these data suggest that the selected disruption of E2F1 and E2F7 in keratinocytes is likely to contribute to CSCC formation and may prove to be a viable therapeutic target.
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Affiliation(s)
- Liliana Endo-Munoz
- Translational Research Unit, Cancer Collaborative Group, Princess Alexandra Hospital, Wooloongabba, Queensland 4102, Australia
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Kozaki KI, Imoto I, Mogi S, Omura K, Inazawa J. Exploration of tumor-suppressive microRNAs silenced by DNA hypermethylation in oral cancer. Cancer Res 2008; 68:2094-105. [PMID: 18381414 DOI: 10.1158/0008-5472.can-07-5194] [Citation(s) in RCA: 473] [Impact Index Per Article: 29.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In the last few years, microRNAs (miRNA) have started a revolution in molecular biology and emerged as key players in the carcinogenesis. They have been identified in various tumor types, showing that different sets of miRNAs are usually deregulated in different cancers. To identify the miRNA signature that was specific for oral squamous cell carcinoma (OSCC), we first examined expression profiles of 148 miRNAs in a panel of 18 OSCC cell lines and the immortalized oral keratinocyte line RT7 as a control. Compared with RT7, the expression of 54 miRNAs (36.5%) was frequently down-regulated in OSCC lines (<0.5-fold expression, >or=66.7% of 18 lines). Among these 54 miRNAs, we further analyzed four of these miRNAs (i.e., miR-34b, miR-137, miR-193a, and miR-203), located around CpG islands, to identify tumor-suppressive miRNAs silenced through aberrant DNA methylation. The expression of those four genes was restored by treatment with 5-aza-2'-deoxycytidine in OSCC cells lacking their expression. In addition, expression levels of the four miRNAs were inversely correlated with their DNA methylation status in the OSCC lines. In primary tumors of OSCC with paired normal oral mucosa, down-regulation of miRNA expression through tumor-specific hypermethylation was more frequently observed for miR-137 and miR-193a than for miR-34b and miR-203. Moreover, the ectopic transfection of miR-137 or miR-193a into OSCC lines lacking their expressions significantly reduced cell growth, with down-regulation of the translation of cyclin-dependent kinase 6 or E2F transcription factor 6, respectively. Taken together, our results clearly show that miR-137 and miR-193a are tumor suppressor miRNAs epigenetically silenced during oral carcinogenesis.
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Affiliation(s)
- Ken-ichi Kozaki
- Department of Genome Medicine, Tokyo Medical and Dental University, Tokyo, Japan
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Wong CF, Tellam RL. MicroRNA-26a targets the histone methyltransferase Enhancer of Zeste homolog 2 during myogenesis. J Biol Chem 2008; 283:9836-43. [PMID: 18281287 DOI: 10.1074/jbc.m709614200] [Citation(s) in RCA: 245] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
MicroRNA (miRNA) are important regulators of many biological processes, but the targets for most miRNA are still poorly defined. In this study, we profiled the expression of miRNA during myogenesis, from proliferating myoblasts through to terminally differentiated myotubes. Microarray results identified six significantly differentially expressed miRNA that were more than 2-fold different in myotubes. From this list, miRNA-26a (miR-26a), an up-regulated miRNA, was further examined. Overexpression of miR-26a in murine myogenic C2C12 cells induced creatine kinase activity, an enzyme that markedly increases during myogenesis. Further, myoD and myogenin mRNA expression levels were also up-regulated. These results suggest that increased expression of miR-26a promotes myogenesis. Through a bioinformatics approach, we identified the histone methyltransferase, Enhancer of Zeste homolog 2 (Ezh2), as a potential target of miR-26a. Overexpression of miR-26a suppressed the activity of a luciferase reporter construct fused with the 3'-untranslated region of Ezh2. In addition, miR-26a overexpression decreased Ezh2 mRNA expression. These results reveal a model of regulation during myogenesis whereby the up-regulation of miR-26a acts to post-transcriptionally repress Ezh2, a known suppressor of skeletal muscle cell differentiation.
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Affiliation(s)
- Chung Fai Wong
- CSIRO Livestock Industries, Queensland Bioscience Precinct, 306 Carmody Road, St. Lucia 4067, QLD, Australia
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Dahler AL, Rickwood D, Guminski A, Teakle N, Saunders NA. Indole-3-carbinol - induced growth inhibition can be converted to a cytotoxic response in the presence of TPA+Ca(2+) in squamous cell carcinoma cell lines. FEBS Lett 2007; 581:3839-47. [PMID: 17659285 DOI: 10.1016/j.febslet.2007.07.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2007] [Revised: 07/04/2007] [Accepted: 07/05/2007] [Indexed: 10/23/2022]
Abstract
We examined the possibility that I3C, when combined with a differentiation stimulus (TPA+CaCl(2)), would sensitise SCC cells to a differentiation stimulus. We report that I3C induces a profound growth inhibition in SCC cells that is dissimilar to the growth inhibition required to initiate differentiation. Moreover, we report that I3C, when combined with TPA+CaCl(2) treatment, induces a loss of colony forming ability that was differentiation and senescence - independent but was due to delayed cytotoxicity. This study shows that I3C in combination with a PKC activator+Ca(2+) may be a useful therapeutic strategy for treating oral SCC.
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Affiliation(s)
- A L Dahler
- Epithelial Pathobiology Group, Cancer Biology Programme, Diamantina Institute for Cancer, Immunology and Metabolic Medicine, University of Queensland, Princess Alexandra Hospital, Queensland, Australia
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Wong CF, Barnes LM, Dahler AL, Smith L, Popa C, Serewko-Auret MM, Saunders NA. E2F suppression and Sp1 overexpression are sufficient to induce the differentiation-specific marker, transglutaminase type 1, in a squamous cell carcinoma cell line. Oncogene 2005; 24:3525-34. [PMID: 15735752 DOI: 10.1038/sj.onc.1208372] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Recently, E2F function has expanded to include the regulation of differentiation in human epidermal keratinocytes (HEKs). We extend these findings to report that in HEKs, Sp1 is a differentiation-specific activator and a downstream target of E2F-mediated suppression of the differentiation-specific marker, transglutaminase type 1 (TG-1). Deletion of elements between -0.084 to -0.034 kb of the TG-1 promoter disabled E2F1-induced suppression of promoter activity. Electrophoretic mobility shift assays (EMSAs) demonstrated that Sp1 and Sp3 bound this region. Protein expression analysis suggested that squamous differentiation was accompanied by increased Sp1/Sp3 ratio. Cotransfection of proliferating HEKs or the squamous cell carcinoma (SCC) cell line, KJD-1/SV40, with an E2F inhibitor (E2Fd/n) and Sp1 expression plasmid was sufficient to activate the TG-1 promoter. The suppression of Sp1 activity by E2F in differentiated cells appeared to be indirect since we found no evidence of an Sp1/E2F coassociation on the TG-1 promoter fragment. Moreover, E2F inhibition in the presence of a differentiation stimulus induced Sp1 protein. These data demonstrate that (i) Sp1 can act as a differentiation stimulus, (ii) E2F-mediated suppression of differentiation-specific markers is indirect via Sp1 inhibition and (iii) a combination of E2F inhibition and Sp1 activation could form the basis of a differentiation therapy for SCCs.
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Affiliation(s)
- Chung Fai Wong
- Epithelial Pathobiology Group, Cancer Biology Programme, Centre for Immunology and Cancer Research, University of Queensland, Princess Alexandra Hospital, Woolloongabba, Queensland 4102, Australia
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