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The Src Homology 2 Protein Shb Promotes Cell Cycle Progression In Murine Hematopoietic Stem Cells By Regulation Of Focal Adhesion Kinase Activity
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Cell Biology.
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2013 (English)In: Experimental Cell Research, ISSN 0014-4827, E-ISSN 1090-2422, Vol. 319, no 12, 1852-1864 p.Article in journal (Refereed) Published
Abstract [en]

The widely expressed adaptor protein Shb has previously been reported to contribute to T cell function due to its association with the T cell receptor and furthermore, several of Shb's known interaction partners are established regulators of blood cell development and function. In addition, Shb deficient embryonic stem cells displayed reduced blood cell colony formation upon differentiation in vitro. The aim of the current study was therefore to explore hematopoietic stem and progenitor cell function in the Shb knockout mouse. Shbdeficient bone marrow contained reduced relative numbers of long-term hematopoietic stem cells (LT-HSCs) that exhibited lower proliferation rates. Despite this, Shb knockout LT-HSCs responded promptly by entering the cell cycle in response to genotoxic stress by 5-fluorouracil treatment. In competitive LT-HSC transplantations, Shb null cells initially engrafted as well as the wild-type cells but provided less myeloid expansion over time. Moreover, Shb knockout bone marrow cells exhibited elevated basal activities of focal adhesion kinase/Rac1/p21-activated kinase signaling and reduced responsiveness to Stem Cell Factor stimulation. Consequently, treatment with a focal adhesion kinase inhibitor increased Shb knockout LT-HSC proliferation. The altered signaling characteristics thus provide a plausible mechanistic explanation for the changes in LT-HSC proliferation since these signaling intermediates have all been shown to participate in LT-HSC cell cycle control. In summary, the loss of Shb dependent signaling in bone marrow cells, resulting in elevated focal adhesion kinase activity and reduced proliferative responses in LT-HSCs under steady state hematopoiesis, confers a disadvantage to the maintenance of LT-HSCs over time.

Place, publisher, year, edition, pages
2013. Vol. 319, no 12, 1852-1864 p.
National Category
Medical and Health Sciences
URN: urn:nbn:se:uu:diva-197537DOI: 10.1016/j.yexcr.2013.03.020ISI: 000322055700015OAI: oai:DiVA.org:uu-197537DiVA: diva2:613303
Available from: 2013-03-27 Created: 2013-03-27 Last updated: 2014-01-23Bibliographically approved
In thesis
1. Consequences of Shb Deficiency on Hematopoietic Cell Function
Open this publication in new window or tab >>Consequences of Shb Deficiency on Hematopoietic Cell Function
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The adaptor protein Shb has been implicated in the signaling of several tyrosine kinase receptors and previous studies have suggested a role for Shb in the signal transduction of T cells. Shb associates with the T cell receptor (TCR) and partakes in the signal propagation of activated T lymphocytes. In order to explore Shb’s influence on TCR signaling in vivo, T cell development and function was studied in a Shb knockout mouse. The loss of Shb led to aberrant TCR signaling in both thymocytes and peripheral CD4+ TH cells, with elevated basal phosphorylation of key components in the signal cascade. Shb was found to be dispensable for thymocyte development, but its absence resulted in a TH2 bias in in vitro stimulated peripheral CD4+ TH cells. As imbalances in TH2 responses are linked to allergic diseases, we further explored Shb’s role in immune regulation in a mouse model of atopic dermatitis. Shb knockout mice exhibit more aggravated signs of atopic dermatitis, including increased immune cell recruitment to the affected areas and elevated mRNA levels of typical TH2 cytokines.

The effect of Shb on hematopoiesis in general was determined by examining populations of long-term hematopoietic stem cells (LT-HSCs) and hematopoietic progenitor cells in bone marrow of Shb knockout and wild type mice. Shb deficient bone marrow was found to contain significantly fewer relative numbers of LT-HSCs due to a proliferative defect. The reduced cell cycle activity of Shb LT-HSCs could further be linked to an abnormal regulation of the focal adhesion kinase/Rac1/p21-activated kinase pathway. Since alterations in LT-HSC proliferative abilities may have implications for leukemia development, BCR-Abl induced myeloid neoplasia was investigated in the absence of Shb. Shb deficiency confers a more aggressive progression of BCR-Abl induced myeloid neoplasia characterized by an increased peripheral blood neutrophilia and a deregulated cytokine profile. In addition, focal adhesion kinase and STAT3 signaling is hyperactivated in Shb knockout leukemic cells.

In conclusion, Shb appears to be a multifunctional signaling mediator that controls several responses in hematopoietic cells, under homeostatic as well as disease conditions.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 81 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 937
hematopoiesis, hematopoietic stem cells, myeloid neoplasia, T cells, atopic dermatitis, cell signaling
National Category
Cell and Molecular Biology
Research subject
Medical Cell Biology
urn:nbn:se:uu:diva-209339 (URN)978-91-554-8780-5 (ISBN)
Public defence
2013-11-30, A1:107a, BMC, Husargatan 3, Uppsala, 09:15 (English)
Available from: 2013-11-08 Created: 2013-10-17 Last updated: 2014-01-23

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