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Role of E2F transcription factor in Oral cancer: Recent Insight and Advancements. Semin Cancer Biol 2023; 92:28-41. [PMID: 36924812 DOI: 10.1016/j.semcancer.2023.03.004] [Citation(s) in RCA: 21] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Revised: 02/27/2023] [Accepted: 03/06/2023] [Indexed: 03/16/2023]
Abstract
The family of mammalian E2F transcription factors (E2Fs) comprise of 8 members (E2F1-E2F8) classified as activators (E2F1-E2F3) and repressors (E2F4-E2F8) primarily regulating the expression of several genes related to cell proliferation, apoptosis and differentiation, mainly in a cell cycle-dependent manner. E2F activity is frequently controlled via the retinoblastoma protein (pRb), cyclins, p53 and the ubiquitin-proteasome pathway. Additionally, genetic or epigenetic changes result in the deregulation of E2F family genes expression altering S phase entry and apoptosis, an important hallmark for the onset and development of cancer. Although studies reveal E2Fs to be involved in several human malignancies, the mechanisms underlying the role of E2Fs in oral cancer lies nascent and needs further investigations. This review focuses on the role of E2Fs in oral cancer and the etiological factors regulating E2Fs activity, which in turn transcriptionally control the expression of their target genes, thus contributing to cell proliferation, metastasis, and drug/therapy resistance. Further, we will discuss therapeutic strategies for E2Fs, which may prevent oral tumor growth, metastasis, and drug resistance.
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Abstract
The cyclin-dependent kinase (CDK)-RB-E2F axis forms the core transcriptional machinery driving cell cycle progression, dictating the timing and fidelity of genome replication and ensuring genetic material is accurately passed through each cell division cycle. The ultimate effectors of this axis are members of a family of eight distinct E2F genes encoding transcriptional activators and repressors. E2F transcriptional activity is tightly regulated throughout the cell cycle via transcriptional and translational regulation, post-translational modifications, protein degradation, binding to cofactors and subcellular localization. Alterations in one or more key components of this axis (CDKs, cyclins, CDK inhibitors and the RB family of proteins) occur in virtually all cancers and result in heightened oncogenic E2F activity, leading to uncontrolled proliferation. In this Review, we discuss the activities of E2F proteins with an emphasis on the newest atypical E2F family members, the specific and redundant functions of E2F proteins, how misexpression of E2F transcriptional targets promotes cancer and both current and developing therapeutic strategies being used to target this oncogenic pathway.
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Affiliation(s)
- Lindsey N Kent
- Department of Biochemistry and Molecular Biology, Hollings Cancer Center, Medical University of South Carolina, Charleston, SC, USA
| | - Gustavo Leone
- Department of Biochemistry and Molecular Biology, Hollings Cancer Center, Medical University of South Carolina, Charleston, SC, USA.
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Garza-Morales R, Yaddanapudi K, Perez-Hernandez R, Riedinger E, McMasters KM, Shirwan H, Yolcu E, Montes de Oca-Luna R, Gomez-Gutierrez JG. Temozolomide renders murine cancer cells susceptible to oncolytic adenovirus replication and oncolysis. Cancer Biol Ther 2018; 19:188-197. [PMID: 29252087 PMCID: PMC5836815 DOI: 10.1080/15384047.2017.1416274] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2017] [Revised: 12/07/2017] [Accepted: 12/07/2017] [Indexed: 12/25/2022] Open
Abstract
The preclinical evaluation of oncolytic adenoviruses (OAds) has been limited to cancer xenograft mouse models because OAds replicate poorly in murine cancer cells. The alkylating agent temozolomide (TMZ) has been shown to enhance oncolytic virotherapy in human cancer cells; therefore, we investigated whether TMZ could increase OAd replication and oncolysis in murine cancer cells. To test our hypothesis, three murine cancer cells were infected with OAd (E1b-deleted) alone or in combination with TMZ. TMZ increased OAd-mediated oncolysis in all three murine cancer cells tested. This increased oncolysis was, at least in part, due to productive virus replication, apoptosis, and autophagy induction. Most importantly, murine lung non-cancerous cells were not affected by OAd+TMZ. Moreover, TMZ increased Ad transduction efficiency. However, TMZ did not increase coxsackievirus and adenovirus receptor; therefore, other mechanism could be implicated on the transduction efficiency. These results showed, for the first time, that TMZ could render murine tumor cells more susceptible to oncolytic virotherapy. The proposed combination of OAds with TMZ presents an attractive approach towards the evaluation of OAd potency and safety in syngeneic mouse models using these murine cancer cell-lines in vivo.
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Affiliation(s)
- Rodolfo Garza-Morales
- The Hiram C. Polk Jr, MD, Department of Surgery, University of Louisville School of Medicine, Louisville, KY, USA
- Department of Histology, School of Medicine, Autonomous University of Nuevo León, Monterrey, N.L. México
| | - Kavitha Yaddanapudi
- James Graham Brown Cancer Center, University of Louisville School of Medicine, Louisville, KY, USA
| | - Rigoberto Perez-Hernandez
- The Hiram C. Polk Jr, MD, Department of Surgery, University of Louisville School of Medicine, Louisville, KY, USA
| | - Eric Riedinger
- The Hiram C. Polk Jr, MD, Department of Surgery, University of Louisville School of Medicine, Louisville, KY, USA
| | - Kelly M. McMasters
- The Hiram C. Polk Jr, MD, Department of Surgery, University of Louisville School of Medicine, Louisville, KY, USA
- James Graham Brown Cancer Center, University of Louisville School of Medicine, Louisville, KY, USA
| | - Haval Shirwan
- Department of Microbiology and Immunology, Institute for Cellular Therapeutics, University of Louisville, Louisville, KY, USA
| | - Esma Yolcu
- Department of Microbiology and Immunology, Institute for Cellular Therapeutics, University of Louisville, Louisville, KY, USA
| | - Roberto Montes de Oca-Luna
- Department of Histology, School of Medicine, Autonomous University of Nuevo León, Monterrey, N.L. México
| | - Jorge G. Gomez-Gutierrez
- The Hiram C. Polk Jr, MD, Department of Surgery, University of Louisville School of Medicine, Louisville, KY, USA
- James Graham Brown Cancer Center, University of Louisville School of Medicine, Louisville, KY, USA
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Pan J, Zhou S, Xiang R, Zhao Z, Liu S, Ding N, Gong S, Lin Y, Li X, Bai X, Li F, Zhao AZ. An Ω-3 fatty acid desaturase-expressing gene attenuates prostate cancer proliferation by cell cycle regulation. Oncol Lett 2017; 13:3717-3721. [PMID: 28521474 DOI: 10.3892/ol.2017.5880] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Accepted: 10/25/2016] [Indexed: 12/20/2022] Open
Abstract
Previous studies have reported that Ω-6 and Ω-3 fatty acids have opposing effects on cancer development. Consuming high levels of long-chain Ω-3 polyunsaturated fatty acids (PUFAs) has been shown to reduce prostate cancer risk and increase chemotherapy sensitivity. The sdd17 gene encodes an Ω-3 fatty acid desaturase, which converts arachidonic acid into eicosapentaenoic acid (EPA). However, little is known regarding the function of the sdd17 gene in tumor cells in vitro. In the present study, prostate cancer cells were infected with the msdd17 gene, which allowed the endogenous production of Ω-3 PUFAs. The cells that expressed the msdd17 gene had high levels of long-chain Ω-3 PUFAs compared with the control cells. Expression of the msdd17 gene significantly inhibited prostate cancer cell proliferation. EPA exposure and msdd17 gene transfection each induced G2 cell cycle arrest and reduced E2F transcription factor 1 expression in prostate cancer cells. These results suggest that msdd17 gene transfection suppressed prostate cancer cell proliferation and induced G2 cell cycle arrest.
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Affiliation(s)
- Jinshun Pan
- Department of Biotherapy, The Second Affiliated Hospital, Nanjing Medical University, Nanjing, Jiangsu 210029, P.R. China
| | - Sujin Zhou
- Collaborative Innovation Center for Cancer Medicine, The Institute of Biomedical and Pharmaceutical Sciences, Guangdong University of Technology, Guangzhou, Guangdong 510006, P.R. China
| | - Rong Xiang
- The Center of Metabolic Disease Research, Nanjing Medical University, Nanjing, Jiangsu 210029, P.R. China
| | - Zhenggang Zhao
- Collaborative Innovation Center for Cancer Medicine, The Institute of Biomedical and Pharmaceutical Sciences, Guangdong University of Technology, Guangzhou, Guangdong 510006, P.R. China
| | - Shanshan Liu
- The Center of Metabolic Disease Research, Nanjing Medical University, Nanjing, Jiangsu 210029, P.R. China
| | - Ning Ding
- The Center of Metabolic Disease Research, Nanjing Medical University, Nanjing, Jiangsu 210029, P.R. China
| | - Sijia Gong
- The Center of Metabolic Disease Research, Nanjing Medical University, Nanjing, Jiangsu 210029, P.R. China
| | - Yan Lin
- The Center of Metabolic Disease Research, Nanjing Medical University, Nanjing, Jiangsu 210029, P.R. China
| | - Xiaoxi Li
- The Center of Metabolic Disease Research, Nanjing Medical University, Nanjing, Jiangsu 210029, P.R. China
| | - Xiaoming Bai
- Cancer Center, Department of Pathology, Nanjing Medical University, Nanjing, Jiangsu 210029, P.R. China
| | - Fanghong Li
- Collaborative Innovation Center for Cancer Medicine, The Institute of Biomedical and Pharmaceutical Sciences, Guangdong University of Technology, Guangzhou, Guangdong 510006, P.R. China
| | - Allan Z Zhao
- Collaborative Innovation Center for Cancer Medicine, The Institute of Biomedical and Pharmaceutical Sciences, Guangdong University of Technology, Guangzhou, Guangdong 510006, P.R. China
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Cyclooxygenase-2 induced β1-integrin expression in NSCLC and promoted cell invasion via the EP1/MAPK/E2F-1/FoxC2 signal pathway. Sci Rep 2016; 6:33823. [PMID: 27654511 PMCID: PMC5031967 DOI: 10.1038/srep33823] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2016] [Accepted: 09/02/2016] [Indexed: 12/28/2022] Open
Abstract
Cyclooxygenase-2 (COX-2) has been implicated in cell invasion in non-small-cell lung cancer (NSCLC). However, the mechanism is unclear. The present study investigated the effect of COX-2 on β1-integrin expression and cell invasion in NSCLC. COX-2 and β1-integrin were co-expressed in NSCLC tissues. COX-2 overexpression or Prostaglandin E2 (PGE2) treatment increased β1-integrin expression in NSCLC cell lines. β1-integrin silencing suppressed COX-2-mediated tumour growth and cancer cell invasion in vivo and in vitro. Prostaglandin E Receptor EP1 transfection or treatment with EP1 agonist mimicked the effect of PGE2 treatment. EP1 siRNA blocked PGE2-mediated β1-integrin expression. EP1 agonist treatment promoted Erk1/2, p38 phosphorylation and E2F-1 expression. MEK1/2 and p38 inhibitors suppressed EP1-mediated β1-integrin expression. E2F-1 silencing suppressed EP1-mediated FoxC2 and β1-integrin upregulation. ChIP and Luciferase Reporter assays identified that EP1 agonist treatment induced E2F-1 binding to FoxC2 promotor directly and improved FoxC2 transcription. FoxC2 siRNA suppressed β1-integrin expression and EP1-mediated cell invasion. Immunohistochemistry showed E2F-1, FoxC2, and EP1R were all highly expressed in the NSCLC cases. This study suggested that COX-2 upregulates β1-integrin expression and cell invasion in NSCLC by activating the MAPK/E2F-1 signalling pathway. Targeting the COX-2/EP1/PKC/MAPK/E2F-1/FoxC2/β1-integrin pathway might represent a new therapeutic strategy for the prevention and treatment of this cancer.
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Egger ME, McNally LR, Nitz J, McMasters KM, Gomez-Gutierrez JG. Adenovirus-mediated FKHRL1/TM sensitizes melanoma cells to apoptosis induced by temozolomide. HUM GENE THER CL DEV 2015; 25:186-95. [PMID: 25238278 DOI: 10.1089/humc.2014.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Melanoma exhibits variable resistance to the alkylating agent temozolomide (TMZ). We evaluated the potential of adenovirus expressing forkhead human transcription factor like 1 triple mutant (Ad-FKHRL1/TM) to sensitize melanoma cells to TMZ. Four melanoma cell lines were treated with Ad-FKHRL1/TM and TMZ, alone or in combination. Apoptosis was assessed by activation and inhibition of caspase pathway, nuclei fragmentation, and annexin V staining. The potential therapeutic efficacy of Ad-FKHRL1/TM with TMZ was also assessed in a mouse melanoma xenograft model. Combination therapy of Ad-FKHRL1/TM and TMZ resulted in greater cell killing (<20% cell viability) compared with single therapy and controls (p<0.05). Combination indices of Ad-FKHRL1/TM and TMZ therapy indicated significant (p<0.05) synergistic killing effect. Greater apoptosis induction was found in cells treated with Ad-FKHRL1/TM and TMZ than with Ad-FKHRL1/TM or TMZ-treated cells alone. Treatment with TMZ enhanced adenovirus transgene expression in a cell type-dependent manner. In an in vivo model, combination therapy of Ad-FKHRL1/TM with TMZ results in greater tumor growth reduction in comparison with single treatments. We suggest that Ad-FKHRL1/TM is a promising vector to sensitize melanoma cells to TMZ, and that a combination of both approaches would be effective in the clinical setting.
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Affiliation(s)
- Michael E Egger
- 1 The Hiram C. Polk Jr., MD, Department of Surgery, University of Louisville School of Medicine , Louisville, KY 40292
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Meng P, Ghosh R. Transcription addiction: can we garner the Yin and Yang functions of E2F1 for cancer therapy? Cell Death Dis 2014; 5:e1360. [PMID: 25101673 PMCID: PMC4454301 DOI: 10.1038/cddis.2014.326] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Revised: 06/24/2014] [Accepted: 06/26/2014] [Indexed: 12/29/2022]
Abstract
Classically, as a transcription factor family, the E2Fs are known to regulate the expression of various genes whose products are involved in a multitude of biological functions, many of which are deregulated in diseases including cancers. E2F is deregulated and hyperactive in most human cancers with context dependent, dichotomous and contradictory roles in almost all cancers. Cancer cells have an insatiable demand for transcription to ensure that gene products are available to sustain various biological processes that support their rapid growth and survival. In this context, cutting-off hyperactivity of transcription factors that support transcription dependence could be a valuable therapeutic strategy. However, one of the greatest challenges of targeting a transcription factor is the global effects on non-cancerous cells given that they control cellular functions in general. Recently, there is growing realization regarding the possibility to target the oncogenic activation of transcription factors to modulate transcription addiction without affecting the normal activity required for cell functions. In this review, we used E2F1 as a prototype transcription factor to address transcription factor activity in cancer cell functions. We focused on melanoma considering that E2F1 executes critical functions in response to UV, an etiological factor of cutaneous melanoma and lies immediately downstream of the CDKN2A/pRb axis, which is frequently deregulated in melanoma. Further, activation of E2F1 in melanomas can also occur independent of loss of CDKN2A. Given its activated status and the ability to transcriptionally control a plethora of genes involved in regulating melanoma development and progression, we review the current literature on its differential role in controlling signaling pathways involved in melanoma as well as therapeutic resistance, and discuss the practical value of weaning melanoma cells from E2F1-mediated transcription dependence for melanoma management.
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Affiliation(s)
- P Meng
- Department of Urology, School of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
| | - R Ghosh
- 1] Department of Urology, School of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA [2] Department of Pharmacology, School of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA [3] Department of Molecular Medicine, School of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA [4] Cancer Therapy and Research Center, School of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
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8
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Gomez-Gutierrez JG, Rao XM, Zhou HS, McMasters KM. Enhanced cancer cell killing by truncated E2F-1 used in combination with oncolytic adenovirus. Virology 2012; 433:538-47. [PMID: 23021422 PMCID: PMC3494286 DOI: 10.1016/j.virol.2012.09.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Revised: 08/27/2012] [Accepted: 09/07/2012] [Indexed: 12/26/2022]
Abstract
Adenovirus-mediated gene transfer into a tumor mass can be improved by combining it with conditionally-replicating adenovirus (CRAd) when both vectors co-infect the same cancer cell. We investigated the efficiency of enhancing transgene expression and effectiveness of cancer killing of two advenoviruses (Ads), one expressing E2F-1 (AdE2F-1) and another expressing a truncated form of E2F-1 that lacks the transactivation domain (AdE2Ftr), when combined with oncolytic Adhz60. We found that AdE2F-1 with Adhz60 actually decreased E2F-1 expression and viral replication through a mechanism apparently involving repression of the cyclin-E promoter and decreased expression of early and late structural proteins necessary for viral replication. In contrast, AdE2Ftr with Adhz60 resulted in increased E2Ftr expression, AdE2Ftr replication, and cancer cell death both in vitro and in vivo. These results indicate that AdE2Ftr coupled with a CRAd enhances AdE2Ftr-mediated cancer cell death.
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Affiliation(s)
- Jorge G. Gomez-Gutierrez
- Department of Surgery, University of Louisville School of Medicine, Louisville, Kentucky 40292, USA
| | - Xiao-Mei Rao
- Department of Surgery, University of Louisville School of Medicine, Louisville, Kentucky 40292, USA
- James Graham Brown Cancer Center, University of Louisville School of Medicine, Louisville, Kentucky 40292, USA
| | - Heshan Sam Zhou
- Department of Surgery, University of Louisville School of Medicine, Louisville, Kentucky 40292, USA
- James Graham Brown Cancer Center, University of Louisville School of Medicine, Louisville, Kentucky 40292, USA
| | - Kelly M. McMasters
- Department of Surgery, University of Louisville School of Medicine, Louisville, Kentucky 40292, USA
- James Graham Brown Cancer Center, University of Louisville School of Medicine, Louisville, Kentucky 40292, USA
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Gomez-Gutierrez JG, Egger ME, Hao H, Zhou HS, McMasters KM. Adenovirus-mediated expression of mutated forkhead human transcription like-1 suppresses tumor growth in a mouse melanoma xenograft model. Cancer Biol Ther 2012; 13:1195-204. [PMID: 22892845 DOI: 10.4161/cbt.21349] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Melanoma is generally resistant to chemotherapy, which may be related to defects in death receptor signaling and to defects in induction of apoptosis. Forkhead family transcription factors induce the expression of death receptor ligands such as Fas ligand (Fas-L) resulting in apoptosis. We therefore investigated whether a triple mutant form of forkhead transcription factor FKHRL1 (FKHRL1/TM) can enhance Fas-L mediated-apoptosis in melanoma cells. Two melanoma cells A2058 or DM6 were tested for their sensitivity to agonistic anti-Fas antibody (CH-11); adenovirus expressing FKHRL1/TM (Ad-FKHRL1/TM) was assessed for its capability to induce activation of the caspase pathway; the role of Fas-L in the Ad-FKHRL1/TM mediated-cell death was also assessed in vitro. Ad-FKHRL1/TM antitumor activity in vivo was also evaluated in a mouse melanoma xenograft model. We found that DM6 melanoma cells were more resistant to Fas/Fas-L-mediated apoptosis induced by agonistic anti-Fas antibody than A2058 melanoma cells. Ectopic expression of FKHRL1/TM in melanoma cells upregulated Fas-L expression, decreased procaspase-8 levels, and significantly increased Fas/FasL-mediated cell death in both cells lines; this induced cell death was partially blocked by a Fas/Fas-L antagonist. Importantly, Ad-FKHRL1/TM treatment of subcutaneous melanoma xenografts in mice resulted in approximately 70% decrease in tumor size compared with controls. These data indicate that overexpression of FKHRL1/TM can induce the Fas-L pathway in melanoma cells. Ad-FKHRL1/TM therefore might represent a promising vector for melanoma treatment.
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Affiliation(s)
- Jorge G Gomez-Gutierrez
- Department of Surgery, James Graham Brown Cancer Center, University of Louisville School of Medicine, Louisville, KY, USA.
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Garcia-Garcia A, Rodriguez-Rocha H, Tseng MT, Montes de Oca-Luna R, Zhou HS, McMasters KM, Gomez-Gutierrez JG. E2F-1 lacking the transcriptional activity domain induces autophagy. Cancer Biol Ther 2012; 13:1091-101. [PMID: 22825328 DOI: 10.4161/cbt.21143] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The transcription factor E2F-1 plays a crucial role in the control of cell proliferation. E2F-1 has tumor suppressive properties by inducing apoptosis and autophagy. In this study, E2F-1 and its truncated form (E2Ftr), lacking the transactivation domain (TAD), were compared for their ability to induce autophagy. In Gaussia luciferase-based assays, both E2F-1 and E2Ftr induced the proteolytic cleavage of the autophagic marker LC3. In addition, LC3 and autophagy protein 5 (Atg5) were upregulated by E2F-1 and E2Ftr. Likewise, both E2F proteins induced a punctate pattern of GFP-tagged LC3, indicating autophagosome formation. The presence of double-membrane autophagic vesicles induced by E2F-1 and E2Ftr was confirmed by transmission electron microscopy (TEM). The application of z-VAD-fmk, a caspase inhibitor, partially blocked both E2F-1 and E2Ftr-mediated cytotoxicity. Moreover, Atg5 (-/-) cells were more resistant to the E2F-1 or E2Ftr-induced cell killing effect than Atg5 wt cells. The TAD of E2F-1 is not essential for induction of autophagy; apoptosis and autophagy cooperate for an efficient cancer cell killing effect induced by E2F-1 or E2Ftr. E2Ftr-induced autophagy is a promising approach to destroy tumors that are resistant to conventional treatments.
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Hao H, Chen C, Rao XM, Gomez-Gutierrez JG, Zhou HS, McMasters KM. E2F-1- and E2Ftr-mediated apoptosis: the role of DREAM and HRK. J Cell Mol Med 2012; 16:605-15. [PMID: 21564512 PMCID: PMC3822935 DOI: 10.1111/j.1582-4934.2011.01338.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
E2F-1-deleted mutant, ‘truncated E2F’ (E2Ftr, E2F-1[1–375]), lacking the carboxy-terminal transactivation domain, was shown to be more potent at inducing cancer cell apoptosis than wild-type E2F-1 (wtE2F-1; full-length E2F-1). Mechanisms by which wtE2F-1 and E2Ftr induce apoptosis, however, are not fully elucidated. Our study demonstrates molecular effects of pro-apoptotic BH3-only Bcl-2 family member Harakiri (Hrk) in wtE2F-1- and E2Ftr-induced melanoma cell apoptosis. We found that Hrk mRNA and Harakiri (HRK) protein expression was highly up-regulated in melanoma cells in response to wtE2F-1 and E2Ftr overexpression. HRK up-regulation did not require the E2F-1 transactivation domain. In addition, Hrk gene up-regulation and HRK protein expression did not require p53 in cancer cells. Hrk knockdown by Hrk siRNA was associated with significantly reduced wtE2F-1- and E2Ftr-induced apoptosis. We also found that an upstream factor, ‘downstream regulatory element antagonist modulator’ (DREAM), may be involved in HRK-mediated apoptosis in response to wtE2F-1 and E2Ftr overexpression. DREAM expression levels increased following wtE2F-1 and E2Ftr overexpression. Western blotting detected increased DREAM primarily in dimeric form. The homodimerization of DREAM resulting from wtE2F-1 and E2Ftr overexpression may contribute to the decreased binding activity of DREAM to the 3′-untranslated region of the Hrk gene as shown by electromobility shift assay. Results showed wtE2F-1- and E2Ftr-induced apoptosis is partially mediated by HRK. HRK function is regulated in response to DREAM. Our findings contribute to understanding the mechanisms that regulate wtE2F-1- and E2Ftr-induced apoptosis and provide insights into the further evaluation of how E2Ftr-induced apoptosis may be used for therapeutic gain.
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Affiliation(s)
- Hongying Hao
- Department of Surgery, University of Louisville School of Medicine, and J. Graham Brown Cancer Center, Louisville, KY, USA
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