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Jun SY, Brown AJ, Chua NK, Yoon JY, Lee JJ, Yang JO, Jang I, Jeon SJ, Choi TI, Kim CH, Kim NS. Reduction of Squalene Epoxidase by Cholesterol Accumulation Accelerates Colorectal Cancer Progression and Metastasis. Gastroenterology 2021; 160:1194-1207.e28. [PMID: 32946903 DOI: 10.1053/j.gastro.2020.09.009] [Citation(s) in RCA: 57] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Revised: 09/03/2020] [Accepted: 09/05/2020] [Indexed: 02/07/2023]
Abstract
BACKGROUND & AIMS Squalene epoxidase (SQLE), a rate-limiting enzyme in cholesterol biosynthesis, is suggested as a proto-oncogene. Paradoxically, SQLE is degraded by excess cholesterol, and low SQLE is associated with aggressive colorectal cancer (CRC). Therefore, we studied the functional consequences of SQLE reduction in CRC progression. METHODS Gene and protein expression data and clinical features of CRCs were obtained from public databases and 293 human tissues, analyzed by immunohistochemistry. In vitro studies showed underlying mechanisms of CRC progression mediated by SQLE reduction. Mice were fed a 2% high-cholesterol or a control diet before and after cecum implantation of SQLE genetic knockdown/control CRC cells. Metastatic dissemination and circulating cancer stem cells were demonstrated by in vivo tracking and flow cytometry analysis, respectively. RESULTS In vitro studies showed that SQLE reduction helped cancer cells overcome constraints by inducing the epithelial-mesenchymal transition required to generate cancer stem cells. Surprisingly, SQLE interacted with GSK3β and p53. Active GSK3β contributes to the stability of SQLE, thereby increasing cell cholesterol content, whereas SQLE depletion disrupted the GSK3β/p53 complex, resulting in a metastatic phenotype. This was confirmed in a spontaneous CRC metastasis mice model, where SQLE reduction, by a high-cholesterol regimen or genetic knockdown, strikingly promoted CRC aggressiveness through the production of migratory cancer stem cells. CONCLUSIONS We showed that SQLE reduction caused by cholesterol accumulation aggravates CRC progression via the activation of the β-catenin oncogenic pathway and deactivation of the p53 tumor suppressor pathway. Our findings provide new insights into the link between cholesterol and CRC, identifying SQLE as a key regulator in CRC aggressiveness and a prognostic biomarker.
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Affiliation(s)
- Soo Young Jun
- Medical Genomics Research Center, Daejon, Korea; Functional Genomics, University of Science and Technology, Daejeon, Korea
| | - Andrew J Brown
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, New South Wales, Australia
| | - Ngee Kiat Chua
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, New South Wales, Australia
| | | | | | - Jin Ok Yang
- Korean Bioinformation Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, Korea
| | - InSu Jang
- Korean Bioinformation Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, Korea
| | - Su-Jin Jeon
- Medical Genomics Research Center, Daejon, Korea; Functional Genomics, University of Science and Technology, Daejeon, Korea
| | - Tae-Ik Choi
- Department of Biology, Chungnam National University, Daejeon, Korea
| | - Cheol-Hee Kim
- Department of Biology, Chungnam National University, Daejeon, Korea
| | - Nam-Soon Kim
- Medical Genomics Research Center, Daejon, Korea; Functional Genomics, University of Science and Technology, Daejeon, Korea.
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Samassekou O, Bastien N, Yan J, Mai S, Drouin R. Study of Telomere Dysfunction in TP53 Mutant LoVo Cell Lines as a Model for Genomic Instability. Methods Mol Biol 2018; 1769:209-230. [PMID: 29564827 DOI: 10.1007/978-1-4939-7780-2_14] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
Telomere restriction fragment, 3D quantitative FISH on nuclei, and quantitative FISH on metaphases are complementary approaches that explore telomere dysfunction genomically, cellularly, and chromosomally, respectively. We used these approaches to study association between telomere dysfunction and degree of genomic instability related to TP53 mutations in LoVo isogenic cell lines. We found a strong correlation between degree of genomic instability, telomere dysfunction, and specific mutations of TP53. The use of complementary approaches to study telomere biology is essential to have a comprehensive understanding of telomere involvement in genomic instability.
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Affiliation(s)
- Oumar Samassekou
- 3D Signatures Holdings Inc. MaRS Centre, South Tower, Toronto, ON, Canada
| | - Nathalie Bastien
- Laboratoire d'Anatomopathologie et de Cytologie, Laboratoires médicaux de la Capitale Nationale et des Îles, site IUCPQ-UL, 2725 Chemin Sainte-Foy, Québec, QC, Canada
| | - Ju Yan
- Cytogenetics and Molecular Cytogenetics laboratory, Beijing Boren Hospital, Beijing, China
| | - Sabine Mai
- Department of Physiology and Pathophysiology, Cell Biology, University of Manitoba, Research Institute of Oncology and Hematology, CancerCare Manitoba, Winnipeg, MB, Canada
| | - Régen Drouin
- Division of Medical Genetics, Department of Pediatrics, Laval University and Centre Hospitalier Universitaire de Québec, Quebec City, QC, Canada.
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Samassekou O, Bastien N, Lichtensztejn D, Yan J, Mai S, Drouin R. DifferentTP53mutations are associated with specific chromosomal rearrangements, telomere length changes, and remodeling of the nuclear architecture of telomeres. Genes Chromosomes Cancer 2014; 53:934-50. [DOI: 10.1002/gcc.22205] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2014] [Accepted: 07/02/2014] [Indexed: 02/06/2023] Open
Affiliation(s)
- Oumar Samassekou
- Division of Genetics; Department of Pediatrics; Faculty of Medicine and Health Sciences; Université de Sherbrooke; Sherbrooke QC Canada
- Manitoba Institute of Cell Biology; CancerCare Manitoba; Department of Physiology; Faculty of Medicine, University of Manitoba; Winnipeg MB Canada
| | - Nathalie Bastien
- Division of Genetics; Department of Pediatrics; Faculty of Medicine and Health Sciences; Université de Sherbrooke; Sherbrooke QC Canada
| | - Daniel Lichtensztejn
- Manitoba Institute of Cell Biology; CancerCare Manitoba; Department of Physiology; Faculty of Medicine, University of Manitoba; Winnipeg MB Canada
| | - Ju Yan
- Division of Genetics; Department of Pediatrics; Faculty of Medicine and Health Sciences; Université de Sherbrooke; Sherbrooke QC Canada
| | - Sabine Mai
- Manitoba Institute of Cell Biology; CancerCare Manitoba; Department of Physiology; Faculty of Medicine, University of Manitoba; Winnipeg MB Canada
| | - Régen Drouin
- Division of Genetics; Department of Pediatrics; Faculty of Medicine and Health Sciences; Université de Sherbrooke; Sherbrooke QC Canada
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Leandro J, Leandro P, Flatmark T. Heterotetrameric forms of human phenylalanine hydroxylase: Co-expression of wild-type and mutant forms in a bicistronic system. Biochim Biophys Acta Mol Basis Dis 2011; 1812:602-12. [DOI: 10.1016/j.bbadis.2011.02.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2010] [Revised: 01/19/2011] [Accepted: 02/03/2011] [Indexed: 11/28/2022]
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Intrinsic radiosensitivity correlated with radiation-induced ROS and cell cycle regulation. Mol Cell Toxicol 2010. [DOI: 10.1007/s13273-010-0001-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Gupta V, Kalaiarasan P, Faheem M, Singh N, Iqbal MA, Bamezai RNK. Dominant negative mutations affect oligomerization of human pyruvate kinase M2 isozyme and promote cellular growth and polyploidy. J Biol Chem 2010; 285:16864-73. [PMID: 20304929 DOI: 10.1074/jbc.m109.065029] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
This study was designed to understand the mechanism and functional implication of the two heterozygous mutations (H391Y and K422R) of human pyruvate kinase M2 isozyme (PKM(2)) observed earlier in a Bloom syndrome background. The co-expression of homotetrameric wild type and mutant PKM(2) in the cellular milieu resulting in the interaction between the two at the monomer level was substantiated further by in vitro experiments. The cross-monomer interaction significantly altered the oligomeric state of PKM(2) by favoring dimerization and heterotetramerization. In silico study provided an added support in showing that hetero-oligomerization was energetically favorable. The hetero-oligomeric populations of PKM(2) showed altered activity and affinity, and their expression resulted in an increased growth rate of Escherichia coli as well as mammalian cells, along with an increased rate of polyploidy. These features are known to be essential to tumor progression. This study provides insight in understanding the modulated role of large oligomeric multifunctional proteins such as PKM(2) by affecting cellular behavior, which is an essential observation to understand tumor sustenance and progression and to design therapeutic intervention in future.
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Affiliation(s)
- Vibhor Gupta
- National Centre of Applied Human Genetics, School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
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Millau JF, Bastien N, Drouin R. P53 transcriptional activities: a general overview and some thoughts. Mutat Res 2008; 681:118-133. [PMID: 18639648 DOI: 10.1016/j.mrrev.2008.06.002] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2007] [Revised: 05/05/2008] [Accepted: 06/19/2008] [Indexed: 12/20/2022]
Abstract
P53 is a master transcriptional regulator controlling several main cellular pathways. Its role is to adapt gene expression programs in order to maintain cellular homeostasis and genome integrity in response to stresses. P53 is found mutated in about half of human cancers and most mutations are clustered within the DNA-binding domain of the protein resulting in altered p53 transcriptional activity. This illustrates the importance of the gene regulations achieved by p53. The aim of this review is to provide a global overview of the current understanding of p53 transcriptional activities and to discuss some ongoing questions and unresolved points about p53 transcriptional activity.
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Affiliation(s)
- Jean-François Millau
- Service of Genetics, Department of Pediatrics, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3001, 12th Avenue North, Sherbrooke J1H 5N4, QC, Canada
| | - Nathalie Bastien
- Service of Genetics, Department of Pediatrics, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3001, 12th Avenue North, Sherbrooke J1H 5N4, QC, Canada
| | - Régen Drouin
- Service of Genetics, Department of Pediatrics, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3001, 12th Avenue North, Sherbrooke J1H 5N4, QC, Canada.
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Vidaurreta M, Maestro ML, Sanz-Casla MT, Rafael S, Veganzones S, de la Orden V, Cerdán J, Arroyo M, Torres A. Colorectal carcinoma prognosis can be predicted by alterations in gene p53 exons 5 and 8. Int J Colorectal Dis 2008; 23:581-6. [PMID: 18322661 DOI: 10.1007/s00384-008-0454-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 02/12/2008] [Indexed: 02/04/2023]
Abstract
BACKGROUND AND AIMS Gene p53 alteration is a genetic event described in the progression from adenoma to colorectal carcinoma. Most of the p53 mutations occur in exons 5 to 8 in highly preserved regions and in the three main structural domains of the p53 protein. It is possible that mutations affecting different structural regions may present different effects on the p53 protein function and, due to this, they may have different prognostic meaning. MATERIALS AND METHODS The study population consisted of 353 patients diagnosed with sporadic colorectal cancer. Mutations in 5-8 exons of p53 gene were detected by means of single strand conformation polymorphism (SSCP). All samples that showed different migration bands in SSCP were confirmed by sequencing. RESULTS A total of 69 patients (19.7%) showed alterations of the gene p53. It was observed that mutation in codon 175 in exon 5 was related to tumors located in the colon (p = 0.01) and the mutation in the codon 288 in exon 8 was related to rectal tumors (p = 0.02). In the study of overall survival, mutation in codon 175 of exon 5 conferred a better prognosis and alterations of exon 8 were related to a worse prognosis in different population subgroups: in men, in patients younger than 71 years old, in the tumors located in the proximal colon, the ones moderately differentiated, and those that are mucinous. CONCLUSION According to this study, mutations in different exons of p53 are related to different phenotypes in colorectal cancer. These phenotypes could mean differences in the clinical evolution of the patients.
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Affiliation(s)
- M Vidaurreta
- Department of Clinical Analysis, Hospital Clínico San Carlos, Madrid, Spain
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Gorlov IP, Gorlova OY, Amos CI. Predicting the oncogenicity of missense mutations reported in the International Agency for Cancer Research (IARC) mutation database on p53. Hum Mutat 2006; 26:446-54. [PMID: 16173033 DOI: 10.1002/humu.20242] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Many mutation databases, comprising thousands of reported mutations, are available. Often the clinical significance of the reported mutations is unknown. In this study we developed an algorithm that allows prediction of the clinical significance of missense mutations reported in a mutation database. Nonsense mutations are used as a referent group for this assessment. We used the International Association for Research on Cancer (IARC) mutation database on TP53 to implement the algorithm. First, on the basis of published data [Nachman MW, Crowell SL. 2000. Genetics 156:297-304], we ascribed mutation rates to every single nucleotide substitution (SNS) in the core domain of the TP53 gene. Second, for every possible SNS we computed the expected number of missense mutations, under the assumption that missense mutations are as oncogenic as nonsense ones. The natural logarithm of the ratio of the observed to the expected number of missense mutations (LR) was used as a quantitative measure of oncogenicity (i.e., the ability of a mutation to produce cancer). We estimated the relative oncogenicity of all missense mutations reported in the IARC p53 mutation database, and constructed a profile of oncogenicity of the missense mutations along the DNA-binding region of p53.
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Affiliation(s)
- Ivan P Gorlov
- Department of Epidemiology, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030., USA.
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Dridi W, Krabchi K, Gadji M, Lavoie J, Bronsard M, Fetni R, Drouin R. Activité dominante négative des protéines p53 mutées. Med Sci (Paris) 2006; 22:301-7. [PMID: 16527213 DOI: 10.1051/medsci/2006223301] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Tumor suppressor gene inactivation as proposed by the Knudson model implies a sequential inactivation of two alleles of a gene. For example, the first allele is inactivated by a missense mutation, and the second one is inactivated by a deletion or insertion. The alteration of the p53 tumor suppressor gene is far to correspond only to this model. In the great majority of cancers, the mutated allele of p53 coexists with the normal allele. It is well known that the transcriptional activity is one of the most important functions of p53. The p53 protein is active as a tetramer (this complex activates the expression of targeted genes by binding to its consensus DNA sequence called the p53 response element). Experimental evidence shows that wild-type p53 interacts with mutant proteins to form heterotetramers. In association with wild-type proteins, mutant proteins drive the wild-type subunits into a mutant conformation. This association leads to a loss of trans-activating function. The capacity of mutant subunits to form heterotetramers with wild-type subunits and to commit them into a mutant conformation is called << dominant negative effect >>. Many p53 mutant proteins possess this dominant negative activity. Recently, several factors, which are implicated in the control of the dominant negative activity of p53 mutants, have been identified. The elucidation of these complex molecular functions, which are implicated in the dominant negative activity of the p53 mutated protein represents an important aspect in the comprehension of the biological mechanisms involved in carcinogenesis.
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Affiliation(s)
- Walid Dridi
- Service de Génétique, Département de Pédiatrie, Faculté de médecine et des sciences de la santé, Université de Sherbrooke, 3001, 12e avenue Nord, Sherbrooke (Québec), J1H 5N4, Canada
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Rosenke K, Samuel MA, McDowell ET, Toerne MA, Fortunato EA. An intact sequence-specific DNA-binding domain is required for human cytomegalovirus-mediated sequestration of p53 and may promote in vivo binding to the viral genome during infection. Virology 2006; 348:19-34. [PMID: 16455125 DOI: 10.1016/j.virol.2005.12.013] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2005] [Revised: 08/12/2005] [Accepted: 12/12/2005] [Indexed: 11/23/2022]
Abstract
The p53 protein is stabilized during infection of primary human fibroblasts with human cytomegalovirus (HCMV). However, the p53 in HCMV-infected cells is unable to activate its downstream targets. HCMV accomplishes this inactivation, at least in part, by sequestering p53 into viral replication centers within the cell's nucleus soon after they are established. In order to better understand the interplay between HCMV and p53 and the mechanism of sequestration, we constructed a panel of mutant p53-GFP fusion constructs for use in transfection/infection experiments. These mutants affected several post-translational modification sites and several sites within the central sequence-specific DNA-binding domain of the protein. Two categories of p53 sequestration were observed when the mutant constructs were transfected into primary fibroblasts and then infected at either high or low multiplicity. The first category, including all of the post-translational modification mutants, showed sequestration comparable to a wild-type (wt) control, while the second category, mutants affecting the DNA-binding core, were not specifically sequestered above control GFP levels. This suggested that the DNA-binding ability of the protein was required for sequestration. When the HCMV genome was analyzed for p53 consensus binding sites, 21 matches were found, which localized either to the promoters or the coding regions of viral proteins involved in DNA replication and processing as well as structural proteins. An analysis of in vivo binding to these identified sites via chromatin immunoprecipitation assays revealed differential binding to several of the sites over the course of infection.
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Affiliation(s)
- Kyle Rosenke
- University of Idaho, Department of Microbiology, Molecular Biology and Biochemistry and Center for Reproductive Biology, Moscow, ID 83844-3052, USA
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Rochette PJ, Bastien N, Lavoie J, Guérin SL, Drouin R. SW480, a p53 Double-mutant Cell Line Retains Proficiency for Some p53 Functions. J Mol Biol 2005; 352:44-57. [PMID: 16061257 DOI: 10.1016/j.jmb.2005.06.033] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2004] [Revised: 06/08/2005] [Accepted: 06/09/2005] [Indexed: 01/19/2023]
Abstract
During certain types of cellular stress, the p53 tumor suppressor protein binds to DNA and transactivates a variety of genes that regulate critical responses including apoptosis, cell cycle checkpoints, differentiation, and angiogenesis. In addition, functional p53 is known to be required for efficient nucleotide excision repair (NER) of bulky DNA adducts generated through exposure to environmental mutagens such as UV light. Nonetheless, we previously showed that the model p53-mutated human adenocarcinoma strain SW480 is proficient in the removal of UV-induced cyclobutane pyrimidine dimers (CPD) via NER. We undertook the present study to begin probing the molecular basis for this unexpected repair phenotype. Cytogenetic analysis indicated that SW480 is stable at the chromosomal level, i.e. manifests a karyotypic profile very similar to that revealed for this line as far back as 14 years ago. After fluorescence in situ hybridization (FISH), using a probe complementary to the p53 gene, we found that 98% of the SW480 interphase nuclei contains three copies of the gene, later revealed to be localized on intact short arms of three chromosomes 17. DNA sequence analysis further showed that all three p53 copies in SW480 carry two point mutations (R273H and P309S), and levels of the corresponding mutated p53 protein are about 20-fold higher than in the closely related p53 wild-type strain LoVo. Using an electrophoretic mobility shift assay (EMSA), we demonstrated that R273H/P309S p53 is able to bind with wild-type affinity to its consensus DNA sequence in vitro. Analysis of p21(Cip1/WAF1) expression and in vivo footprinting by ligation-mediated PCR (LMPCR) showed that, in wild-type LoVo cells, an exposure to cellular stress (e.g. UV or ionizing radiation) is necessary for p53 activation of the p21(Cip1/WAF1) promoter. In contrast, the R273H/P309S-mutated p53 protein in SW480 constitutively activates p21(Cip1/WAF1) in the absence of stress through an unknown mechanism. A similar phenomenon whereby mutated p53 in SW480 is able to induce NER-related proteins might explain the normal DNA repair phenotype previously observed in this strain. For now we conclude that, in general, results obtained using SW480 as a p53-deficient cell line should be interpreted very cautiously.
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Affiliation(s)
- Patrick J Rochette
- Department of Medical Biology, Faculty of Medicine, Laval University and Unité de Recherche en Génétique Humaine et Moléculaire, Research Center, Hôpital St-François d'Assise, Centre Hospitalier Universitaire de Québec, Québec, Canada G1L 3L5
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Abstract
We performed a systematic review of studies that investigated the effect of abnormalities of the tumour suppressor gene p53 upon prognosis in patients with colorectal cancer. The methods used to assess p53 status were immunohistochemistry (IHC), indicating abnormal accumulation of p53, and sequence analysis, indicating presence of p53 mutations (mut). We identified 168 reports, with 241 comparisons of relevant end points and survival data on 18 766 patients. We found evidence of both publication bias and heterogeneity of results. Our analysis was hampered by variability in both the assessment of p53 status and the reporting of results. We used a trim and fill method to correct for publication bias and minimised heterogeneity by using well-defined clinical subgroups for the assessment of outcomes. Overall, patients with abnormal p53 were at increased risk of death: relative risk (RR) with IHC 1.32 (95% confidence interval (c.i.) 1.23–1.42) and with mutation analysis 1.31 (95% c.i. 1.19–1.45). The adverse impact of abnormal p53 was greater in patients with lower baseline risk of dying: good prognosis RR (mut) 1.63 (95% c.i. 1.40–1.90) and poor prognosis RR (mut) 1.04 (95% c.i. 0.91–1.19). We found no effect of abnormal p53 on outcome in patients treated with chemotherapy. Abnormal p53 was associated with failure of response to radiotherapy in patients with rectal cancer: RR (mut) 1.49 (95% c.i. 1.25–1.77).
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Affiliation(s)
- A J Munro
- Department of Surgery and Molecular Oncology, University of Dundee, Ninewells Hospital and Medical School, Dundee DD1 9SY, UK.
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Shih KN, Chuang YT, Liu H, Lo SJ. Hepatitis D virus RNA editing is inhibited by a GFP fusion protein containing a C-terminally deleted delta antigen. J Gen Virol 2004; 85:947-957. [PMID: 15039537 DOI: 10.1099/vir.0.19661-0] [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] [Indexed: 11/18/2022] Open
Abstract
During its life cycle, hepatitis D virus (HDV) produces two forms of delta antigen (HDAg), small delta antigen (SDAg) and large delta antigen (LDAg), which differ in their C-terminal 19 amino acids. Host enzymes termed ADARs (adenosine deaminases that act on double-stranded RNA) are required for LDAg production. These enzymes change the stop codon (UAG) of SDAg to a tryptophan codon (UGG). However, the temporal and spatial regulation of HDV RNA editing is largely unknown. In this study, we constructed three GFP fusion proteins containing different lengths of SDAg and characterized their cellular localization and effects on HDV replication. One of these fusion proteins, designated D(1–88)-GFP, inhibited LDAg but not SDAg production, suggesting that D(1–88)-GFP inhibits HDV RNA editing. Two experiments further supported this supposition: (i) RT-PCR analysis combined with NcoI restriction enzyme digestion revealed that HDV RNA editing was reduced by 42 % in HeLa-D(1–88)-GFP when compared with HeLa cells; and (ii) the ratio of SDAg/LDAg production from the reporter RNAs was reduced in cells co-transfected with ADAR-expressing and reporter plasmids in the presence of D(1–88)-GFP. Double fluorescence microscopy found that D(1–88)-GFP was either associated with SC-35 or was adjacent to PML (premyelocytic leukaemia antigen) at nuclear speckles, but D(1–88)-GFP was not co-localized with ADAR, which was mainly located in the nucleolus. In situ hybridization showing co-localization of HDV RNA with D(1–88)-GFP at nuclear speckles suggested that HDV RNA editing might occur in the nuclear speckles and require other nuclear factor(s), in addition to ADAR.
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Affiliation(s)
- Ko-Nien Shih
- Institute of Microbiology and Immunology, National Yang-Ming University, Taipei, Taiwan 112
| | - Ya-Ting Chuang
- Institute of Microbiology and Immunology, National Yang-Ming University, Taipei, Taiwan 112
| | - Hsuan Liu
- Department of Life Science, National Yang-Ming University, Taipei, Taiwan 112
| | - Szecheng J Lo
- Department of Life Science, School of Medicine, Chang Gung University, TaoYun, Taiwan 333
- Department of Life Science, National Yang-Ming University, Taipei, Taiwan 112
- Institute of Microbiology and Immunology, National Yang-Ming University, Taipei, Taiwan 112
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