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Przanowska RK, Chen Y, Uchida TO, Shibata E, Hao X, Rueda IS, Jensen K, Przanowski P, Trimboli A, Shibata Y, Leone G, Dutta A. DNA replication in primary hepatocytes without the six-subunit ORC. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.04.588006. [PMID: 38617300 PMCID: PMC11014565 DOI: 10.1101/2024.04.04.588006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/16/2024]
Abstract
The six subunit ORC is essential for initiation of DNA replication in eukaryotes. Cancer cell-lines in culture can survive and replicate DNA replication after genetic inactivation of individual ORC subunits, ORC1, ORC2 or ORC5. In primary cells, ORC1 was dispensable in the mouse liver for endo-reduplication, but this could be explained by the ORC1 homolog, CDC6, substituting for ORC1 to restore functional ORC. Here, we have created mice with a conditional deletion of ORC2, which does not have a homolog. Although mouse embryo fibroblasts require ORC2 for proliferation, mouse hepatocytes synthesize DNA in cell culture and endo-reduplicate in vivo without ORC2. Mouse livers endo-reduplicate after simultaneous deletion of ORC1 and ORC2 both during normal development and after partial hepatectomy. Since endo-reduplication initiates DNA synthesis like normal S phase replication these results unequivocally indicate that primary cells, like cancer cell lines, can load MCM2-7 and initiate replication without ORC.
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Ullah R, Naz A, Akram HS, Ullah Z, Tariq M, Mithani A, Faisal A. Transcriptomic analysis reveals differential gene expression, alternative splicing, and novel exons during mouse trophoblast stem cell differentiation. Stem Cell Res Ther 2020; 11:342. [PMID: 32762732 PMCID: PMC7409654 DOI: 10.1186/s13287-020-01848-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Revised: 07/15/2020] [Accepted: 07/22/2020] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND Differentiation of mouse trophoblast stem cells (TSCs) to trophoblast giant cells (TGCs) has been widely used as a model system to study placental development and function. While several differentially expressed genes, including regulators of TSC differentiation, have been identified, a comprehensive analysis of the global expression of genes and splice variants in the two cell types has not been reported. RESULTS Here, we report ~ 7800 differentially expressed genes in TGCs compared to TSCs which include regulators of the cell cycle, apoptosis, cytoskeleton, cell mobility, embryo implantation, metabolism, and various signaling pathways. We show that several mitotic proteins, including Aurora A kinase, were downregulated in TGCs and that the activity of Aurora A kinase is required for the maintenance of TSCs. We also identify hitherto undiscovered, cell-type specific alternative splicing events in 31 genes in the two cell types. Finally, we also report 19 novel exons in 12 genes which are expressed in both TSCs and TGCs. CONCLUSIONS Overall, our results uncover several potential regulators of TSC differentiation and TGC function, thereby providing a valuable resource for developmental and molecular biologists interested in the study of stem cell differentiation and embryonic development.
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Affiliation(s)
- Rahim Ullah
- Department of Biology, Syed Babar Ali School of Science and Engineering, Lahore University of Management Sciences, Lahore, Pakistan
| | - Ambreen Naz
- Department of Biology, Syed Babar Ali School of Science and Engineering, Lahore University of Management Sciences, Lahore, Pakistan
| | - Hafiza Sara Akram
- Department of Biology, Syed Babar Ali School of Science and Engineering, Lahore University of Management Sciences, Lahore, Pakistan
| | - Zakir Ullah
- Virginia Commonwealth University, Richmond, USA
| | - Muhammad Tariq
- Department of Biology, Syed Babar Ali School of Science and Engineering, Lahore University of Management Sciences, Lahore, Pakistan
| | - Aziz Mithani
- Department of Biology, Syed Babar Ali School of Science and Engineering, Lahore University of Management Sciences, Lahore, Pakistan.
| | - Amir Faisal
- Department of Biology, Syed Babar Ali School of Science and Engineering, Lahore University of Management Sciences, Lahore, Pakistan.
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Zybina TG, Zybina EV. Role of cell cycling and polyploidy in placental trophoblast of different mammalian species. Reprod Domest Anim 2020; 55:895-904. [DOI: 10.1111/rda.13732] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2019] [Accepted: 05/07/2020] [Indexed: 12/11/2022]
Affiliation(s)
- Tatiana G. Zybina
- Laboratory of Cell Morphology Institute of Cytology RAS St.‐Petersburg Russia
| | - Eugenia V. Zybina
- Laboratory of Cell Morphology Institute of Cytology RAS St.‐Petersburg Russia
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Champeris Tsaniras S, Delinasios GJ, Petropoulos M, Panagopoulos A, Anagnostopoulos AK, Villiou M, Vlachakis D, Bravou V, Stathopoulos GT, Taraviras S. DNA Replication Inhibitor Geminin and Retinoic Acid Signaling Participate in Complex Interactions Associated With Pluripotency. Cancer Genomics Proteomics 2019; 16:593-601. [PMID: 31659113 PMCID: PMC6885373 DOI: 10.21873/cgp.20162] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2019] [Revised: 09/23/2019] [Accepted: 10/10/2019] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND/AIM Several links between DNA replication, pluripotency and development have been recently identified. The involvement of miRNA in the regulation of cell cycle events and pluripotency factors has also gained attention. MATERIALS AND METHODS In the present study, we used the g:Profiler platform to analyze transcription factor binding sites, miRNA networks and protein-protein interactions to identify novel links among the aforementioned processes. RESULTS AND CONCLUSION A complex circuitry between retinoic acid signaling, SWI/SNF components, pluripotency factors including Oct4, Sox2 and Nanog and cell cycle regulators was identified. It is suggested that the DNA replication inhibitor geminin plays a central role in this circuitry.
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Affiliation(s)
- Spyridon Champeris Tsaniras
- Department of Physiology, Medical School, University of Patras, Patras, Greece
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, U.S.A
| | | | | | | | - Athanasios K Anagnostopoulos
- International Institute of Anticancer Research, Kapandriti, Greece
- Proteomics Research Unit, Biomedical Research Foundation of the Academy of Athens, Athens, Greece
| | - Maria Villiou
- Department of Physiology, Medical School, University of Patras, Patras, Greece
| | - Dimitrios Vlachakis
- Bioinformatics & Medical Informatics Laboratory, Biomedical Research Foundation of the Academy of Athens, Athens, Greece
| | - Vasiliki Bravou
- Department of Anatomy-Histology-Embryology, Faculty of Medicine, University of Patras, Patras, Greece
| | - Georgios T Stathopoulos
- Laboratory for Molecular Respiratory Carcinogenesis, Department of Physiology, Faculty of Medicine, University of Patras, Patras, Greece
| | - Stavros Taraviras
- Department of Physiology, Medical School, University of Patras, Patras, Greece
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CDK1 inhibition facilitates formation of syncytiotrophoblasts and expression of human Chorionic Gonadotropin. Placenta 2018; 66:57-64. [PMID: 29884303 DOI: 10.1016/j.placenta.2018.05.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/11/2018] [Revised: 05/05/2018] [Accepted: 05/09/2018] [Indexed: 11/22/2022]
Abstract
AIMS The human placental syncytiotrophoblast (STB) cells play essential roles in embryo implantation and nutrient exchange between the mother and the fetus. STBs are polyploid which are formed by fusion of diploid cytotrophoblast (CTB) cells. Abnormality in STBs formation can result in pregnancy-related disorders. While a number of genes have been associated with CTB fusion the initial events that trigger cell fusion are not well understood. Primary objective of this study was to enhance our understanding about the molecular mechanism of placental cell fusion. METHODS FACS and microscopic analysis was used to optimize Forskolin-induced fusion of BeWo cells (surrogate of CTBs) and subsequently, changes in the expression of different cell cycle regulator genes were analyzed through Western blotting and qPCR. Immunohistochemistry was performed on the first trimester placental tissue sections to validate the results in the context of placental tissue. Effect of Cyclin Dependent Kinase 1 (CDK1) inhibitor, RO3306, on BeWo cell fusion was studied by microscopy and FACS, and by monitoring the expression of human Chorionic Gonadotropin (hCG) by Western blotting and qPCR. RESULTS The data showed that the placental cell fusion was associated with down regulation of CDK1 and its associated cyclin B, and significant decrease in DNA replication. Moreover, inhibition of CDK1 by an exogenous inhibitor induced placental cell fusion and expression of hCG. CONCLUSION Here, we report that the placental cell fusion can be induced by inhibiting CDK1. This study has a high therapeutic significance to manage pregnancy related abnormalities.
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Jiang S, Huang Y, Qi Y, He R, Liu Z, Ma Y, Guo X, Shao Y, Sun Z, Ruan Q. Human cytomegalovirus miR-US5-1 inhibits viral replication by targeting Geminin mRNA. Virol Sin 2017; 32:431-439. [PMID: 29116593 DOI: 10.1007/s12250-017-4064-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Accepted: 10/26/2017] [Indexed: 11/25/2022] Open
Abstract
Viruses commonly create favorable cellular conditions for their survival through multiple mechanisms. MicroRNAs (miRNAs), which function as post-transcriptional regulators, are utilized by human cytomegalovirus (HCMV) in its infection and pathogenesis. In the present study, the DNA replication inhibitor Geminin (GMNN) was identified to be a direct target of hcmv-miR-US5-1. Overexpression of hcmv-miR-US5-1 could block the accumulation of GMNN during HCMV infection, and the decrease of GMNN expression caused by hcmv-miR-US5-1 or GMNN specific siRNA reduced HCMV DNA copies in U373 cells. Meanwhile, ectopic expression of hcmv-miR-US5-1 and consequent lower expression of GMNN influenced host cell cycle and proliferation. These results imply that hcmv-miR-US5-1 may affect viral replication and host cellular environment by regulating expression kinetics of GMNN during HCMV infection.
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Affiliation(s)
- Shujuan Jiang
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
- Clinical Genetics, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
| | - Yujing Huang
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
| | - Ying Qi
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
| | - Rong He
- Clinical Genetics, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China.
| | - Zhongyang Liu
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
| | - Yanping Ma
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
| | - Xin Guo
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
| | - Yaozhong Shao
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
| | - Zhengrong Sun
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
| | - Qiang Ruan
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China.
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Jaber M, Sebban S, Buganim Y. Acquisition of the pluripotent and trophectoderm states in the embryo and during somatic nuclear reprogramming. Curr Opin Genet Dev 2017; 46:37-43. [DOI: 10.1016/j.gde.2017.06.012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Revised: 05/08/2017] [Accepted: 06/08/2017] [Indexed: 10/19/2022]
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Links between DNA Replication, Stem Cells and Cancer. Genes (Basel) 2017; 8:genes8020045. [PMID: 28125050 PMCID: PMC5333035 DOI: 10.3390/genes8020045] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2016] [Revised: 01/02/2017] [Accepted: 01/12/2017] [Indexed: 12/31/2022] Open
Abstract
Cancers can be categorized into two groups: those whose frequency increases with age, and those resulting from errors during mammalian development. The first group is linked to DNA replication through the accumulation of genetic mutations that occur during proliferation of developmentally acquired stem cells that give rise to and maintain tissues and organs. These mutations, which result from DNA replication errors as well as environmental insults, fall into two categories; cancer driver mutations that initiate carcinogenesis and genome destabilizing mutations that promote aneuploidy through excess genome duplication and chromatid missegregation. Increased genome instability results in accelerated clonal evolution leading to the appearance of more aggressive clones with increased drug resistance. The second group of cancers, termed germ cell neoplasia, results from the mislocation of pluripotent stem cells during early development. During normal development, pluripotent stem cells that originate in early embryos give rise to all of the cell lineages in the embryo and adult, but when they mislocate to ectopic sites, they produce tumors. Remarkably, pluripotent stem cells, like many cancer cells, depend on the Geminin protein to prevent excess DNA replication from triggering DNA damage-dependent apoptosis. This link between the control of DNA replication during early development and germ cell neoplasia reveals Geminin as a potential chemotherapeutic target in the eradication of cancer progenitor cells.
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Patmanidi AL, Champeris Tsaniras S, Karamitros D, Kyrousi C, Lygerou Z, Taraviras S. Concise Review: Geminin-A Tale of Two Tails: DNA Replication and Transcriptional/Epigenetic Regulation in Stem Cells. Stem Cells 2016; 35:299-310. [DOI: 10.1002/stem.2529] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2016] [Revised: 09/18/2016] [Accepted: 10/01/2016] [Indexed: 12/14/2022]
Affiliation(s)
| | | | - Dimitris Karamitros
- Department of Physiology; Medical School, University of Patras; Rio Patras Greece
| | - Christina Kyrousi
- Department of Physiology; Medical School, University of Patras; Rio Patras Greece
| | - Zoi Lygerou
- Department of Biology; Medical School, University of Patras; Rio Patras Greece
| | - Stavros Taraviras
- Department of Physiology; Medical School, University of Patras; Rio Patras Greece
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Adler-Wailes DC, Kramer JA, DePamphilis ML. Geminin Is Essential for Pluripotent Cell Viability During Teratoma Formation, but Not for Differentiated Cell Viability During Teratoma Expansion. Stem Cells Dev 2016; 26:285-302. [PMID: 27821018 DOI: 10.1089/scd.2016.0260] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Pluripotent embryonic stem cells (ESCs) are unusual in that geminin has been reported to be essential either to prevent differentiation by maintaining expression of pluripotency genes or to prevent DNA rereplication-dependent apoptosis. To distinguish between these two incompatible hypotheses, immune-compromised mice were inoculated subcutaneously with ESCs harboring conditional Gmnn alleles alone or together with a tamoxifen-dependent Cre recombinase gene. Mice were then injected with tamoxifen at various times during which the ESCs proliferated and differentiated into a teratoma. For comparison, the same ESCs were cultured in vitro in the presence of monohydroxytamoxifen. The results revealed that geminin is a haplosufficient gene that is essential for ESC viability before they differentiate into a teratoma, but once a teratoma is established, the differentiated cells can continue to proliferate in the absence of Gmnn alleles, geminin protein, and pluripotent stem cells. Thus, differentiated cells did not require geminin for efficient proliferation within the context of a solid tissue, although they did when teratoma cells were cultured in vitro. These results provide proof-of-principle that preventing geminin function could prevent malignancy in tumors derived from pluripotent cells by selectively eliminating the progenitor cells with little harm to normal cells.
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Affiliation(s)
- Diane C Adler-Wailes
- 1 Eunice Kennedy Shriver National Institute of Child Health and Human Development , Bethesda, Maryland
| | - Joshua A Kramer
- 2 Laboratory Animal Sciences Program, Leidos Biomedical Research, Inc. , Bethesda, Maryland
| | - Melvin L DePamphilis
- 1 Eunice Kennedy Shriver National Institute of Child Health and Human Development , Bethesda, Maryland
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Kushwaha PP, Rapalli KC, Kumar S. Geminin a multi task protein involved in cancer pathophysiology and developmental process: A review. Biochimie 2016; 131:115-127. [PMID: 27702582 DOI: 10.1016/j.biochi.2016.09.022] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Accepted: 09/29/2016] [Indexed: 02/05/2023]
Abstract
DNA replicates in a timely manner with each cell division. Multiple proteins and factors are involved in the initiation of DNA replication including a dynamic interaction between Cdc10-dependent transcript (Cdt1) and Geminin (GMNN). A conformational change between GMNN-Cdt1 heterotrimer and heterohexamer complex is responsible for licensing or inhibition of the DNA replication. This molecular switch ensures a faithful DNA replication during each S phase of cell cycle. GMNN inhibits Cdt1-mediated minichromosome maintenance helicases (MCM) loading onto the chromatin-bound origin recognition complex (ORC) which results in the inhibition of pre-replication complex assembly. GMNN modulates DNA replication by direct binding to Cdt1, and thereby alters its stability and activity. GMNN is involved in various stages of development such as pre-implantation, germ layer formation, cell commitment and specification, maintenance of genome integrity at mid blastula transition, epithelial to mesenchymal transition during gastrulation, neural development, organogenesis and axis patterning. GMNN interacts with different proteins resulting in enhanced hematopoietic stem cell activity thereby activating the development-associated genes' transcription. GMNN expression is also associated with cancer pathophysiology and development. In this review we discussed the structure and function of GMNN in detail. Inhibitors of GMNN and their role in DNA replication, repair, cell cycle and apoptosis are reviewed. Further, we also discussed the role of GMNN in virus infected host cells.
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Affiliation(s)
- Prem Prakash Kushwaha
- School of Basic and Applied Sciences, Centre for Biochemistry and Microbial Sciences, Central University of Punjab, Bathinda, 151001, India
| | - Krishna Chaitanya Rapalli
- School of Basic and Applied Sciences, Centre for Animal Sciences, Central University of Punjab, Bathinda, 151001, India
| | - Shashank Kumar
- School of Basic and Applied Sciences, Centre for Biochemistry and Microbial Sciences, Central University of Punjab, Bathinda, 151001, India.
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Abstract
The mechanism that duplicates the nuclear genome during the trillions of cell divisions required to develop from zygote to adult is the same throughout the eukarya, but the mechanisms that determine where, when and how much nuclear genome duplication occur regulate development and differ among the eukarya. They allow organisms to change the rate of cell proliferation during development, to activate zygotic gene expression independently of DNA replication, and to restrict nuclear DNA replication to once per cell division. They allow specialized cells to exit their mitotic cell cycle and differentiate into polyploid cells, and in some cases, to amplify the number of copies of specific genes. It is genome duplication that drives evolution, by virtue of the errors that inevitably occur when the same process is repeated trillions of times. It is, unfortunately, the same errors that produce age-related genetic disorders such as cancer.
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Affiliation(s)
- Melvin L DePamphilis
- National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA.
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14
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Huang YY, Kaneko KJ, Pan H, DePamphilis ML. Geminin is Essential to Prevent DNA Re-Replication-Dependent Apoptosis in Pluripotent Cells, but not in Differentiated Cells. Stem Cells 2015; 33:3239-53. [PMID: 26140583 DOI: 10.1002/stem.2092] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2015] [Accepted: 06/11/2015] [Indexed: 01/17/2023]
Abstract
Geminin is a dual-function protein unique to multicellular animals with roles in modulating gene expression and preventing DNA re-replication. Here, we show that geminin is essential at the beginning of mammalian development to prevent DNA re-replication in pluripotent cells, exemplified by embryonic stem cells, as they undergo self-renewal and differentiation. Embryonic stem cells, embryonic fibroblasts, and immortalized fibroblasts were characterized before and after geminin was depleted either by gene ablation or siRNA. Depletion of geminin under conditions that promote either self-renewal or differentiation rapidly induced DNA re-replication, followed by DNA damage, then a DNA damage response, and finally apoptosis. Once differentiation had occurred, geminin was no longer essential for viability, although it continued to contribute to preventing DNA re-replication induced DNA damage. No relationship was detected between expression of geminin and genes associated with either pluripotency or differentiation. Thus, the primary role of geminin at the beginning of mammalian development is to prevent DNA re-replication-dependent apoptosis, a role previously believed essential only in cancer cells. These results suggest that regulation of gene expression by geminin occurs only after pluripotent cells differentiate into cells in which geminin is not essential for viability.
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Affiliation(s)
- Yi-Yuan Huang
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA
| | - Kotaro J Kaneko
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA
| | - Haiyan Pan
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA
| | - Melvin L DePamphilis
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA
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de Renty C, DePamphilis ML, Ullah Z. Cytoplasmic localization of p21 protects trophoblast giant cells from DNA damage induced apoptosis. PLoS One 2014; 9:e97434. [PMID: 24848107 PMCID: PMC4029599 DOI: 10.1371/journal.pone.0097434] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2014] [Accepted: 04/17/2014] [Indexed: 01/05/2023] Open
Abstract
Proliferating trophoblast stem cells (TSCs) can differentiate into nonproliferating but viable trophoblast giant cells (TGCs) that are resistant to DNA damage induced apoptosis. Differentiation is associated with selective up-regulation of the Cip/Kip cyclin-dependent kinase inhibitors p57 and p21; expression of p27 remains constant. Previous studies showed that p57 localizes to the nucleus in TGCs where it is essential for endoreplication. Here we show that p27 also remains localized to the nucleus during TSC differentiation where it complements the role of p57. Unexpectedly, p21 localized to the cytoplasm where it was maintained throughout both the G- and S-phases of endocycles, and where it prevented DNA damage induced apoptosis. This unusual status for a Cip/Kip protein was dependent on site-specific phosphorylation of p21 by the Akt1 kinase that is also up-regulated in TGCs. Although cytoplasmic p21 is widespread among cancer cells, among normal cells it has been observed only in monocytes. The fact that it also occurs in TGCs reveals that p57 and p21 serve nonredundant functions, and suggests that the role of p21 in suppressing apoptosis is restricted to terminally differentiated cells.
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Affiliation(s)
- Christelle de Renty
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Melvin L. DePamphilis
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Zakir Ullah
- Department of Biology, School of Science and Engineering, Lahore University of Management Sciences, Lahore, Pakistan
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