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Hegde M, Joshi MB. Comprehensive analysis of regulation of DNA methyltransferase isoforms in human breast tumors. J Cancer Res Clin Oncol 2021; 147:937-971. [PMID: 33604794 PMCID: PMC7954751 DOI: 10.1007/s00432-021-03519-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2020] [Accepted: 01/10/2021] [Indexed: 12/14/2022]
Abstract
Significant reprogramming of epigenome is widely described during pathogenesis of breast cancer. Transformation of normal cell to hyperplastic cell and to neoplastic phenotype is associated with aberrant DNA (de)methylation, which, through promoter and enhancer methylation changes, activates oncogenes and silence tumor suppressor genes in variety of tumors including breast. DNA methylation, one of the major epigenetic mechanisms is catalyzed by evolutionarily conserved isoforms namely, DNMT1, DNMT3A and DNMT3B in humans. Over the years, studies have demonstrated intricate and complex regulation of DNMT isoforms at transcriptional, translational and post-translational levels. The recent findings of allosteric regulation of DNMT isoforms and regulation by other interacting chromatin modifying proteins emphasizes functional integrity and their contribution for the development of breast cancer and progression. DNMT isoforms are regulated by several intrinsic and extrinsic parameters. In the present review, we have extensively performed bioinformatics analysis of expression of DNMT isoforms along with their transcriptional and post-transcriptional regulators such as transcription factors, interacting proteins, hormones, cytokines and dietary elements along with their significance during pathogenesis of breast tumors. Our review manuscript provides a comprehensive understanding of key factors regulating DNMT isoforms in breast tumor pathology and documents unsolved issues.
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Affiliation(s)
- Mangala Hegde
- Manipal School of Life Sciences, Manipal Academy of Higher Education, Planetarium Complex, Manipal, 576104, India
| | - Manjunath B Joshi
- Manipal School of Life Sciences, Manipal Academy of Higher Education, Planetarium Complex, Manipal, 576104, India.
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Bernal A, Moltó-Abad M, Domínguez D, Tusell L. Acute telomere deprotection prevents ongoing BFB cycles and rampant instability in p16 INK4a-deficient epithelial cells. Oncotarget 2018; 9:27151-27170. [PMID: 29930757 PMCID: PMC6007466 DOI: 10.18632/oncotarget.25502] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2017] [Accepted: 05/13/2018] [Indexed: 12/12/2022] Open
Abstract
Telomere dysfunction drives chromosome instability through endless breakage-fusion-bridge (BFB) cycles that promote the formation of highly rearranged genomes. However, reactivation of telomerase or ALT-pathway is required for genome stabilisation and full malignant transformation. To allow the unrestricted proliferation of cells at risk of transformation, we have established a conditional system of telomere deprotection in p16INK4a-deficient MCF-10A cells with modified checkpoints. After sustained expression of a dominant negative form of the shelterin protein TRF2 (TRF2ΔBΔM), cells with telomere fusion did progress to anaphase but no signs of ongoing BFB cycles were observed, thus anticipating proliferation defects. Indeed, 96 h TRF2ΔBΔM expression resulted in noticeable growth proliferation defects in the absence of cell cycle disturbances. Further transient periods of 96 h telomere uncapping did not result in cell cycle disturbances either. And reduction of the telomere damage to short acute deprotection periods did not in any case engender cells with a reorganised karyotype. Strikingly, the growth arrest imposed in cells showing dysfunctional telomeres was not accompanied by an activation of the DNA damage response at cellular level, or by the presence of visible markers of senescence or apoptosis. We propose that the deprotection of many telomeres simultaneously, even for a short time, results in a local activation of the cellular stress response which consequently triggers gradual cell withdrawal from cell cycle, restraining the onset of genomic instability.
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Affiliation(s)
- Aina Bernal
- Unitat de Biologia Cel·lular, Facultat de Biociències, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Spain
| | - Marc Moltó-Abad
- Unitat de Biologia Cel·lular, Facultat de Biociències, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Spain.,Current address: Unitat de Malalties Minoritàries, Hospital Universitari de la Vall d'Hebron, 08035 Barcelona, Spain
| | - Daniel Domínguez
- Unitat de Biologia Cel·lular, Facultat de Biociències, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Spain
| | - Laura Tusell
- Unitat de Biologia Cel·lular, Facultat de Biociències, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Spain
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Functional dissection of breast cancer risk-associated TERT promoter variants. Oncotarget 2017; 8:67203-67217. [PMID: 28978027 PMCID: PMC5620167 DOI: 10.18632/oncotarget.18226] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2016] [Accepted: 05/02/2017] [Indexed: 11/25/2022] Open
Abstract
The multi-cancer susceptibility locus at 5p15.33 includes TERT, encoding the telomerase catalytic subunit. Genome-wide association studies (GWAS) have identified six single nucleotide polymorphisms (SNPs) in the TERT promoter associated with decreased breast cancer risk, although the precise causal variants and their mechanisms of action have remained elusive. Luciferase reporter assays indicated that the protective haplotype reduced TERT promoter activity in human mammary epithelial and cancer cells in an estrogen-independent manner. Using single variant constructs, we identified rs3215401 and rs2853669 as likely functional variants. Silencing of MYC decreased TERT promoter activity but neither MYC nor ETS2 silencing conferred allele-specificity. In chromatin immunoprecipitation experiments, the ETS protein GABPA, but not ETS2 or ELF1, bound rs2853669 in an allele-specific manner in mammary epithelial cells. Investigation of open chromatin in mammoplasty samples suggested involvement of three additional variants, though not rs3215401 or rs2853669. Chromosome conformation capture revealed no interaction of the TERT promoter with regulatory elements in the locus, indicating limited local impact of candidate variants on the TERT promoter. Collectively, our functional studies of the TERT-CLPTM1L breast cancer susceptibility locus describe rs2853669 as a functional variant of this association signal among three other potentially causal variants and demonstrate the versatile mechanisms by which TERT promoter variants may affect breast cancer risk.
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Alibek K, Kakpenova A, Mussabekova A, Sypabekova M, Karatayeva N. Role of viruses in the development of breast cancer. Infect Agent Cancer 2013; 8:32. [PMID: 24138789 PMCID: PMC3765990 DOI: 10.1186/1750-9378-8-32] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2013] [Accepted: 08/22/2013] [Indexed: 12/21/2022] Open
Abstract
The most common cancer worldwide among women is breast cancer. The initiation, promotion, and progression of this cancer result from both internal and external factors. The International Agency for Research on Cancer stated that 18-20% of cancers are linked to infection, and the list of definite, probable, and possible carcinogenic agents is growing each year. Among them, biological carcinogens play a significant role. In this review, data covering infection-associated breast and lung cancers are discussed and presented as possible involvements as pathogens in cancer. Because carcinogenesis is a multistep process with several contributing factors, we evaluated to what extent infection is significant, and concluded that members of the herpesvirus, polyomavirus, papillomavirus, and retrovirus families definitely associate with breast cancer. Detailed studies of viral mechanisms support this conclusion, but have presented problems with experimental settings. It is apparent that more effort needs to be devoted to assessing the role of these viruses in carcinogenesis, by characterizing additional confounding and synergistic effects of carcinogenic factors. We propose that preventing and treating infections may possibly stop or even eliminate certain types of cancers.
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Affiliation(s)
- Kenneth Alibek
- Nazarbayev University, 53 Kabanbay Batyr Avenue, Astana 010000, Kazakhstan
- National Medical Holding, 2 Syganak Street, Astana 010000, Kazakhstan
| | - Ainur Kakpenova
- Nazarbayev University, 53 Kabanbay Batyr Avenue, Astana 010000, Kazakhstan
| | - Assel Mussabekova
- Nazarbayev University, 53 Kabanbay Batyr Avenue, Astana 010000, Kazakhstan
| | - Marzhan Sypabekova
- Nazarbayev University, 53 Kabanbay Batyr Avenue, Astana 010000, Kazakhstan
| | - Nargis Karatayeva
- Nazarbayev University, 53 Kabanbay Batyr Avenue, Astana 010000, Kazakhstan
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Crosby LM, Moore TM, George M, Yoon LW, Easton MJ, Ni H, Morgan KT, DeAngelo AB. Transformation of SV40-immortalized human uroepithelial cells by 3-methylcholanthrene increases IFN- and Large T Antigen-induced transcripts. Cancer Cell Int 2010; 10:4. [PMID: 20178601 PMCID: PMC2848030 DOI: 10.1186/1475-2867-10-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2009] [Accepted: 02/23/2010] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Simian Virus 40 (SV40) immortalization followed by treatment of cells with 3-methylcholanthrene (3-MC) has been used to elicit tumors in athymic mice. 3-MC carcinogenesis has been thoroughly studied, however gene-level interactions between 3-MC and SV40 that could have produced the observed tumors have not been explored. The commercially-available human uroepithelial cell lines were either SV40-immortalized (HUC) or SV40-immortalized and then 3-MC-transformed (HUC-TC). RESULTS To characterize the SV40 - 3MC interaction, we compared human gene expression in these cell lines using a human cancer array and confirmed selected changes by RT-PCR. Many viral Large T Antigen (Tag) expression-related changes occurred in HUC-TC, and it is concluded that SV40 and 3-MC may act synergistically to transform cells. Changes noted in IFP 9-27, 2'-5' OAS, IF 56, MxA and MxAB were typical of those that occur in response to viral exposure and are part of the innate immune response. Because interferon is crucial to innate immune host defenses and many gene changes were interferon-related, we explored cellular growth responses to exogenous IFN-gamma and found that treatment impeded growth in tumor, but not immortalized HUC on days 4 - 7. Cellular metabolism however, was inhibited in both cell types. We conclude that IFN-gamma metabolic responses were functional in both cell lines, but IFN-gamma anti-proliferative responses functioned only in tumor cells. CONCLUSIONS Synergism of SV40 with 3-MC or other environmental carcinogens may be of concern as SV40 is now endemic in 2-5.9% of the U.S. population. In addition, SV40-immortalization is a generally-accepted method used in many research materials, but the possibility of off-target effects in studies carried out using these cells has not been considered. We hope that our work will stimulate further study of this important phenomenon.
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Affiliation(s)
- Lynn M Crosby
- Environmental Carcinogenesis Division, National Health Effects and Environmental Research Laboratory, US Environmental Protection Agency, Research Triangle Park, USA.
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Huschtscha LI, Moore JD, Noble JR, Campbell HG, Royds JA, Braithwaite AW, Reddel RR. Normal human mammary epithelial cells proliferate rapidly in the presence of elevated levels of the tumor suppressors p53 and p21(WAF1/CIP1). J Cell Sci 2009; 122:2989-95. [PMID: 19638413 DOI: 10.1242/jcs.044107] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
In normal cells, p53 protein is maintained at low levels, but the levels increase after stress or inappropriate growth signals to coordinate growth arrest or apoptosis. Human mammary epithelial cells (HMECs) are unusual in that they exhibit two phases of growth. The second growth phase, referred to as post-selection, follows a period of temporary growth arrest and is characterized by the absence of p16(INK4a) (also known as CDK4I and p16-INK4a) expression. Previously, we observed that post-selection HMECs have elevated levels of p53. Exogenous p16(INK4a) expression decreased levels of both p53 transcript and protein, and this effect was inhibited by nutlin-3a, indicating that p16(INK4a) can regulate p53 expression by affecting both p53 transcription and Mdm2-dependent degradation of p53. The p53 in post-selection HMECs was wild type and, as expected, increased p53 expression was associated with elevated p21(WAF1/CIP1) and Mdm2 levels; the p53 response to DNA damage seemed normal. Despite elevated levels of wild-type p53 and p21(WAF1/CIP1), post-selection cells grew more rapidly than their pre-selection HMEC precursors. We found that the post-selection HMECs contain a truncated Mdm2 protein (p60), which presumably lacks the p53 ubiquitylation domain. We propose that the increased levels of p53 in post-selection HMECs are due to the presence of an Mdm2 fragment that binds p53 but does not result in its degradation.
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Affiliation(s)
- Lily I Huschtscha
- Children's Medical Research Institute, Westmead, New South Wales 2145, Australia
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Hinshelwood RA, Melki JR, Huschtscha LI, Paul C, Song JZ, Stirzaker C, Reddel RR, Clark SJ. Aberrant de novo methylation of the p16INK4A CpG island is initiated post gene silencing in association with chromatin remodelling and mimics nucleosome positioning. Hum Mol Genet 2009; 18:3098-109. [PMID: 19477956 DOI: 10.1093/hmg/ddp251] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Changes in the epigenetic landscape are widespread in neoplasia, with de novo methylation and histone repressive marks commonly enriched in CpG island associated promoter regions. DNA hypermethylation and histone repression correlate with gene silencing, however, the dynamics of this process are still largely unclear. The tumour suppressor gene p16(INK4A) is inactivated in association with CpG island methylation during neoplastic progression in a variety of cancers, including breast cancer. Here, we investigated the temporal progression of DNA methylation and histone remodelling in the p16(INK4A) CpG island in primary human mammary epithelial cell (HMEC) strains during selection, as a model for early breast cancer. Silencing of p16(INK4A) has been previously shown to be necessary before HMECs can escape from selection. Here, we demonstrate that gene silencing occurs prior to de novo methylation and histone remodelling. An increase in DNA methylation was associated with a rapid loss of both histone H3K27 trimethylation and H3K9 acetylation and a gradual gain of H3K9 dimethylation. Interestingly, we found that regional-specific 'seeding' methylation occurs early after post-selection and that the de novo methylation pattern observed in HMECs correlates with the apparent footprint of nucleosomes across the p16(INK4A) CpG island. Our results demonstrate for the first time that p16(INK4A) gene silencing is a precursor to epigenetic suppression and that subsequent de novo methylation initially occurs in nucleosome-free regions across the p16(INK4A) CpG island and this is associated with a dynamic change in histone modifications.
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Affiliation(s)
- Rebecca A Hinshelwood
- Cancer Program, Garvan Institute of Medical Research, 384 Victoria St, Darlinghurst, NSW 2010, Australia
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Beauséjour CM, Krtolica A, Galimi F, Narita M, Lowe SW, Yaswen P, Campisi J. Reversal of human cellular senescence: roles of the p53 and p16 pathways. EMBO J 2003; 22:4212-22. [PMID: 12912919 PMCID: PMC175806 DOI: 10.1093/emboj/cdg417] [Citation(s) in RCA: 943] [Impact Index Per Article: 44.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Telomere erosion and subsequent dysfunction limits the proliferation of normal human cells by a process termed replicative senescence. Replicative senescence is thought to suppress tumorigenesis by establishing an essentially irreversible growth arrest that requires activities of the p53 and pRB tumor suppressor proteins. We show that, depending on expression of the pRB regulator p16, replicative senescence is not necessarily irreversible. We used lentiviruses to express specific viral and cellular proteins in senescent human fibroblasts and mammary epithelial cells. Expression of telomerase did not reverse the senescence arrest. However, cells with low levels of p16 at senescence resumed robust growth upon p53 inactivation, and limited growth upon expression of oncogenic RAS. In contrast, cells with high levels of p16 at senescence failed to proliferate upon p53 inactivation or RAS expression, although they re-entered the cell cycle without growth after pRB inactivation. Our results indicate that the senescence response to telomere dysfunction is reversible and is maintained primarily by p53. However, p16 provides a dominant second barrier to the unlimited growth of human cells.
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Affiliation(s)
- Christian M Beauséjour
- Lawrence Berkeley National Laboratory, MS 84-171, 1 Cyclotron Road, Berkeley, CA 94720, USA
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Nahreini P, Andreatta C, Kumar B, Hanson A, Edwards-Prasad J, Freed CR, Prasad KN. Distinct patterns of gene expression induced by viral oncogenes in human embryonic brain cells. Cell Mol Neurobiol 2003; 23:27-42. [PMID: 12701882 DOI: 10.1023/a:1022541017085] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
1. The limited lifespan of human embryonic brain (HEB) cells hampers their therapeutic use for the treatment of neurodegenerative diseases. 2. Stable expression of SV40 large T antigen (LTA) or E6E7 genes of human papillomavirus type 16 significantly increased the lifespan of HEB cells, but did not induce transformation. 3. The extended lifespan was triggered by changes in the expression of antiproliferative genes. We found that changes in the expression of p16 (INK4a), p21 (WAFI), p14ARF, and p53 tumor suppressor gene, but not p27 (Kip1), differed between the LTA- and E6E7-HEB cells. 4. Despite the induction of p53 RNA, p53 protein was undetectable in HEB-E6E7 cells. In contrast, p53 protein was increased in HEB-LTA cells as compared with the parental cells. Expression of p21 was, however, reduced in both cell lines. 5. While p16 was decreased in HEB-E6E7 cells, its expression was increased in HEB-LTA cells. 6. Despite these changes, HEB cell lines showed neuron-like morphological differentiation when the intracellular level of cAMP was elevated. 7. This suggests that the mechanisms for inducing neuronal differentiation are still intact in HEB-E6E7 and HEB-LTA cells. More importantly, differentiation signals can override the effects of viral oncogenes in HEB cells.
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Affiliation(s)
- Piruz Nahreini
- Department of Radiology, Center for Vitamins and Cancer Research, School of Medicine, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
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Toouli CD, Huschtscha LI, Neumann AA, Noble JR, Colgin LM, Hukku B, Reddel RR. Comparison of human mammary epithelial cells immortalized by simian virus 40 T-Antigen or by the telomerase catalytic subunit. Oncogene 2002; 21:128-39. [PMID: 11791183 DOI: 10.1038/sj.onc.1205014] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2001] [Revised: 09/29/2001] [Accepted: 10/01/2001] [Indexed: 12/17/2022]
Abstract
We directly compared two methods of immortalizing human mammary epithelial cells (HMECs). Cells were transfected with an expression plasmid either for hTERT, the catalytic subunit of telomerase, or for the simian virus 40 (SV40) early region genes. Under standard culture conditions, HMECs were not immortalized by hTERT unless they had spontaneously ceased expression of the p16(INK4a) tumor suppressor gene. Untransfected HMECs had low levels of telomerase expression, and immortalization by both methods was associated with an increase in telomerase activity and prevention of telomere shortening. SV40-induced immortalization was accompanied by aberrant differentiation, loss of DNA damage response, karyotypic instability and, in some cases, tumorigenicity. hTERT-immortalized cells had fewer karyotypic changes, but had intact DNA damage responses, and features of normal differentiation. Although SV40-immortalized cells are useful for studies of carcinogenesis, hTERT-immortalized cells retain more properties of normal cells.
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Affiliation(s)
- Christian D Toouli
- Children's Medical Research Institute, 214 Hawkesbury Road, Westmead 2145, Australia
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