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Sustained PU.1 levels balance cell-cycle regulators to prevent exhaustion of adult hematopoietic stem cells.

ABSTRACT: To provide a lifelong supply of blood cells, hematopoietic stem cells (HSCs) need to carefully balance both self-renewing cell divisions and quiescence. Although several regulators that control this mechanism have been identified, we demonstrate that the transcription factor PU.1 acts upstream of these regulators. So far, attempts to uncover PU.1's role in HSC biology have failed because of the technical limitations of complete loss-of-function models. With the use of hypomorphic mice with decreased PU.1 levels specifically in phenotypic HSCs, we found reduced HSC long-term repopulation potential that could be rescued completely by restoring PU.1 levels. PU.1 prevented excessive HSC division and exhaustion by controlling the transcription of multiple cell-cycle regulators. Levels of PU.1 were sustained through autoregulatory PU.1 binding to an upstream enhancer that formed an active looped chromosome architecture in HSCs. These results establish that PU.1 mediates chromosome looping and functions as a master regulator of HSC proliferation.

SUBMITTER: Staber PB

PROVIDER: S-EPMC3644723 | biostudies-literature | 2013 Mar

REPOSITORIES: biostudies-literature

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Sustained PU.1 levels balance cell-cycle regulators to prevent exhaustion of adult hematopoietic stem cells.

Staber Philipp B PB Zhang Pu P Ye Min M Welner Robert S RS Nombela-Arrieta César C Bach Christian C Kerenyi Marc M Bartholdy Boris A BA Zhang Hong H Alberich-Jordà Meritxell M Lee Sanghoon S Yang Henry H Ng Felicia F Zhang Junyan J Leddin Mathias M Silberstein Leslie E LE Hoefler Gerald G Orkin Stuart H SH Göttgens Berthold B Rosenbauer Frank F Huang Gang G Tenen Daniel G DG

Molecular cell 20130208 5

To provide a lifelong supply of blood cells, hematopoietic stem cells (HSCs) need to carefully balance both self-renewing cell divisions and quiescence. Although several regulators that control this mechanism have been identified, we demonstrate that the transcription factor PU.1 acts upstream of these regulators. So far, attempts to uncover PU.1's role in HSC biology have failed because of the technical limitations of complete loss-of-function models. With the use of hypomorphic mice with decre ...[more]

PMID: 23395001

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Project description:To guarantee blood supply throughout adult life hematopoietic stem cells (HSCs) need to carefully balance between self-renewing cell divisions and quiescence. Identification of genes controlling HSC self-renewal is of utmost importance given that HSCs are the only stem cells with broad clinical applications. Transcription factor PU.1 is one of the major regulators of myeloid and lymphoid development. Recent reports suggest that PU.1 mediates its functions via gradual expression level changes rather than binary on/off states. So far, this has not been considered in any study of HSCs and thus, PU.1’s role in HSC function has remained largely unclear. Here we demonstrate using hypomorphic mice with an engineered disruption of an autoregulatory feedback loop that decreased PU.1 levels resulted in loss of key HSC functions, all of which could be fully rescued by restoration of proper PU.1 levels via a human PU.1 transgene. Mechanistically, we found excessive HSC cell divisions and altered expression of cell cycle regulators whose promoter regions were bound by PU.1 in normal HSCs. Adequate PU.1 levels were maintained by a mechanism of direct autoregulation restricted to HSCs through a physical interaction of a -14kb enhancer with the proximal promoter. Our findings identify PU.1 as novel regulator controling the switch between cell division and quiescence in order to prevent exhaustion of HSCs. Given that even moderate level changes greatly impact stem cell function, our data suggest important therapeutic implications for leukemic patients with reduced PU.1 levels. Moreover, we provide first proof, that autoregulation of a transcription factor, PU.1, has a crucial function in vivo. We anticipate that our concept of how autoregulation forms an active chromosomal conformation will impact future research on transcription factor networks regulating stem cell fate. HSCs of Pu.1 knock-in (PU.1ki/ki) mice were used for RNA extraction and hybridization on Affymetrix microarrays. We compared these microarray samples with the corresponding wild type.

Dataset Information

Sustained PU.1 levels balance cell-cycle regulators to prevent exhaustion of adult hematopoietic stem cells.

Publications

Sustained PU.1 levels balance cell-cycle regulators to prevent exhaustion of adult hematopoietic stem cells.

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