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      Haematopoietic stem cells require a highly regulated protein synthesis rate

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          Abstract

          Many aspects of cellular physiology remain unstudied in somatic stem cells. For example, there are almost no data on protein synthesis in any somatic stem cell. We found that the amount of protein synthesized per hour in haematopoietic stem cells (HSCs) in vivo was lower than in most other haematopoietic cells, even if we controlled for differences in cell cycle status or forced HSCs to undergo self-renewing divisions. Reduced ribosome function in Rpl24 Bst/+ mice further reduced protein synthesis in HSCs and impaired HSC function. Pten deletion increased protein synthesis in HSCs but also reduced HSC function. Rpl24 Bst/+ cell-autonomously rescued the effects of Pten deletion in HSCs, blocking the increase in protein synthesis, restoring HSC function, and delaying leukaemogenesis. Pten deficiency thus depletes HSCs and promotes leukaemia partly by increasing protein synthesis. Either increased or decreased protein synthesis impairs HSC function.

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          Most cited references40

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          Tumor spectrum analysis in p53-mutant mice.

          The p53 tumor suppressor gene is mutated in a large percentage of human malignancies, including tumors of the colon, breast, lung and brain. Individuals who inherit one mutant allele of p53 are susceptible to a wide range of tumor types. The gene encodes a transcriptional regulator that may function in the cellular response to DNA damage. The construction of mouse strains carrying germline mutations of p53 facilitates analysis of the function of p53 in normal cells and tumorigenesis. In order to study the effects of p53 mutation in vivo, we have constructed a mouse strain carrying a germline disruption of the gene. This mutation removes approximately 40% of the coding capacity of p53 and completely eliminates synthesis of p53 protein. As observed previously for a different germline mutation of p53, animals homozygous for this p53 deletion mutation are viable but highly predisposed to malignancy. Heterozygous animals also have an increased cancer risk, although the distribution of tumor types in these animals differs from that in homozygous mutants. In most cases, tumorigenesis in heterozygous animals is accompanied by loss of the wild-type p53 allele. We reaffirm that p53 function is not required for normal mouse development and conclude that p53 status can strongly influence tumor latency and tissue distribution.
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            Pten dependence distinguishes haematopoietic stem cells from leukaemia-initiating cells.

            Recent advances have highlighted extensive phenotypic and functional similarities between normal stem cells and cancer stem cells. This raises the question of whether disease therapies can be developed that eliminate cancer stem cells without eliminating normal stem cells. Here we address this issue by conditionally deleting the Pten tumour suppressor gene in adult haematopoietic cells. This led to myeloproliferative disease within days and transplantable leukaemias within weeks. Pten deletion also promoted haematopoietic stem cell (HSC) proliferation. However, this led to HSC depletion via a cell-autonomous mechanism, preventing these cells from stably reconstituting irradiated mice. In contrast to leukaemia-initiating cells, HSCs were therefore unable to maintain themselves without Pten. These effects were mostly mediated by mTOR as they were inhibited by rapamycin. Rapamycin not only depleted leukaemia-initiating cells but also restored normal HSC function. Mechanistic differences between normal stem cells and cancer stem cells can thus be targeted to deplete cancer stem cells without damaging normal stem cells.
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              Ribosomopathies: human disorders of ribosome dysfunction.

              Ribosomopathies compose a collection of disorders in which genetic abnormalities cause impaired ribosome biogenesis and function, resulting in specific clinical phenotypes. Congenital mutations in RPS19 and other genes encoding ribosomal proteins cause Diamond-Blackfan anemia, a disorder characterized by hypoplastic, macrocytic anemia. Mutations in other genes required for normal ribosome biogenesis have been implicated in other rare congenital syndromes, Schwachman-Diamond syndrome, dyskeratosis congenita, cartilage hair hypoplasia, and Treacher Collins syndrome. In addition, the 5q- syndrome, a subtype of myelodysplastic syndrome, is caused by a somatically acquired deletion of chromosome 5q, which leads to haploinsufficiency of the ribosomal protein RPS14 and an erythroid phenotype highly similar to Diamond-Blackfan anemia. Acquired abnormalities in ribosome function have been implicated more broadly in human malignancies. The p53 pathway provides a surveillance mechanism for protein translation as well as genome integrity and is activated by defects in ribosome biogenesis; this pathway appears to be a critical mediator of many of the clinical features of ribosomopathies. Elucidation of the mechanisms whereby selective abnormalities in ribosome biogenesis cause specific clinical syndromes will hopefully lead to novel therapeutic strategies for these diseases.
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                Author and article information

                Journal
                0410462
                6011
                Nature
                Nature
                Nature
                0028-0836
                1476-4687
                5 March 2014
                09 March 2014
                1 May 2014
                01 November 2014
                : 509
                : 7498
                : 49-54
                Affiliations
                [1 ]Howard Hughes Medical Institute, Children’s Research Institute, Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, TX, 75390, USA
                [2 ]Department of Cell Biology, Harvard Medical School, Boston, MA, 02115
                Author notes
                [* ]Correspondence: Children’s Research Institute, UT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, Texas, 75390-8502; Sean.Morrison@ 123456UTSouthwestern.edu
                Article
                NIHMS556876
                10.1038/nature13035
                4015626
                24670665
                e9bf3aa8-3c89-4938-82a0-66b2e217ee15

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