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      Protein post-translational modifications and regulation of pluripotency in human stem cells

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          Abstract

          Post-translational modifications (PTMs) are known to be essential mechanisms used by eukaryotic cells to diversify their protein functions and dynamically coordinate their signaling networks. Defects in PTMs have been linked to numerous developmental disorders and human diseases, highlighting the importance of PTMs in maintaining normal cellular states. Human pluripotent stem cells (hPSCs), including embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs), are capable of self-renewal and differentiation into a variety of functional somatic cells; these cells hold a great promise for the advancement of biomedical research and clinical therapy. The mechanisms underlying cellular pluripotency in human cells have been extensively explored in the past decade. In addition to the vast amount of knowledge obtained from the genetic and transcriptional research in hPSCs, there is a rapidly growing interest in the stem cell biology field to examine pluripotency at the protein and PTM level. This review addresses recent progress toward understanding the role of PTMs (glycosylation, phosphorylation, acetylation and methylation) in the regulation of cellular pluripotency.

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          Most cited references139

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          Genome-wide mapping of HATs and HDACs reveals distinct functions in active and inactive genes.

          Histone acetyltransferases (HATs) and deacetylases (HDACs) function antagonistically to control histone acetylation. As acetylation is a histone mark for active transcription, HATs have been associated with active and HDACs with inactive genes. We describe here genome-wide mapping of HATs and HDACs binding on chromatin and find that both are found at active genes with acetylated histones. Our data provide evidence that HATs and HDACs are both targeted to transcribed regions of active genes by phosphorylated RNA Pol II. Furthermore, the majority of HDACs in the human genome function to reset chromatin by removing acetylation at active genes. Inactive genes that are primed by MLL-mediated histone H3K4 methylation are subject to a dynamic cycle of acetylation and deacetylation by transient HAT/HDAC binding, preventing Pol II from binding to these genes but poising them for future activation. Silent genes without any H3K4 methylation signal show no evidence of being bound by HDACs.
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            Induction of pluripotent stem cells by defined factors is greatly improved by small-molecule compounds.

            Reprogramming of mouse and human somatic cells can be achieved by ectopic expression of transcription factors, but with low efficiencies. We report that DNA methyltransferase and histone deacetylase (HDAC) inhibitors improve reprogramming efficiency. In particular, valproic acid (VPA), an HDAC inhibitor, improves reprogramming efficiency by more than 100-fold, using Oct4-GFP as a reporter. VPA also enables efficient induction of pluripotent stem cells without introduction of the oncogene c-Myc.
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              EZH1 mediates methylation on histone H3 lysine 27 and complements EZH2 in maintaining stem cell identity and executing pluripotency.

              Trimethylation on H3K27 (H3K27me3) mediated by Polycomb repressive complex 2 (PRC2) has been linked to embryonic stem cell (ESC) identity and pluripotency. EZH2, the catalytic subunit of PRC2, has been reported as the sole histone methyltransferase that methylates H3K27 and mediates transcriptional silencing. Analysis of Ezh2(-/-) ESCs suggests existence of an additional enzyme(s) catalyzing H3K27 methylation. We have identified EZH1, a homolog of EZH2 that is physically present in a noncanonical PRC2 complex, as an H3K27 methyltransferase in vivo and in vitro. EZH1 colocalizes with the H3K27me3 mark on chromatin and preferentially preserves this mark on development-related genes in Ezh2(-/-) ESCs. Depletion of Ezh1 in cells lacking Ezh2 abolishes residual methylation on H3K27 and derepresses H3K27me3 target genes, demonstrating a role of EZH1 in safeguarding ESC identity. Ezh1 partially complements Ezh2 in executing pluripotency during ESC differentiation, suggesting that cell-fate transitions require epigenetic specificity.
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                Author and article information

                Journal
                Cell Res
                Cell Res
                Cell Research
                Nature Publishing Group
                1001-0602
                1748-7838
                February 2014
                12 November 2013
                1 February 2014
                : 24
                : 2
                : 143-160
                Affiliations
                [1 ]Department of Chemical Physiology, Center for Regenerative Medicine, The Scripps Research Institute , 10550 N. Torrey Pines Rd., La Jolla, CA 92037, USA
                Author notes
                [* ]Tel: +1-858-784 7139; Fax: +1-858-784 7211 E-mail: ycwang@ 123456scripps.edu
                [* ]Tel: +1-858-784 7362; Fax: +1-858-784 7211 E-mail: jloring@ 123456scripps.edu
                Article
                cr2013151
                10.1038/cr.2013.151
                3915910
                24217768
                7ec87245-ae85-4fb5-b7d8-67daec06c616
                Copyright © 2014 Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences

                This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/3.0

                History
                Categories
                Review

                Cell biology
                pluripotency-associated signaling,hescs,hipscs,post-translational modifications
                Cell biology
                pluripotency-associated signaling, hescs, hipscs, post-translational modifications

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