title: The Src homology 2 protein Shb promotes cell cycle progression in murine hematopoietic stem cells by regulation of focal adhesion kinase activity.
abstract: 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. Shb deficient 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.
authors.affiliation: Department of Medical Cell Biology, Uppsala University, Uppsala 751 23, Sweden.
authors.forename: Karin
authors.initials: K
authors.lastname: Gustafsson
authors.affiliation: HHMI, Children's Hospital Boston, Harvard Medical School, Boston, 02115 MA, USA.
authors.forename: Garrett
authors.initials: G
authors.lastname: Heffner
authors.affiliation: HHMI, Children's Hospital Boston, Harvard Medical School, Boston, 02115 MA, USA.
authors.forename: Pamela L
authors.initials: PL
authors.lastname: Wenzel
authors.affiliation: HHMI, Children's Hospital Boston, Harvard Medical School, Boston, 02115 MA, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Curran
authors.affiliation: Department of Genetics and Pathology, Uppsala University, Uppsala 75185, Sweden.
authors.forename: Jan
authors.initials: J
authors.lastname: Grawé
authors.affiliation: Department of Hematology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.
authors.forename: Shannon L
authors.initials: SL
authors.lastname: McKinney-Freeman
authors.affiliation: HHMI, Children's Hospital Boston, Harvard Medical School, Boston, 02115 MA, USA.
authors.forename: George Q
authors.initials: GQ
authors.lastname: Daley
authors.affiliation: Department of Medical Cell Biology, Uppsala University, Uppsala 751 23, Sweden. Electronic address: michael.welsh@mcb.uu.se.
authors.forename: Michael
authors.initials: M
authors.lastname: Welsh
mesh_terms: D000818:Animals; D002453:Cell Cycle; D049109:Cell Proliferation; D004249:DNA Damage; D005472:Fluorouracil / Q000633:toxicity; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000378:metabolism*; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009479:Neuropeptides / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D019089:Stem Cell Factor / Q000378:metabolism; D054462:p21-Activated Kinases / Q000378:metabolism; D020744:rac GTP-Binding Proteins / Q000378:metabolism; D020830:rac1 GTP-Binding Protein
chemical_list: D009479:Neuropeptides; D011518:Proto-Oncogene Proteins; C484602:Rac1 protein, mouse; C085634:Shb protein, mouse; D019089:Stem Cell Factor; D051416:Focal Adhesion Protein-Tyrosine Kinases; D054462:p21-Activated Kinases; D020744:rac GTP-Binding Proteins; D020830:rac1 GTP-Binding Protein; D005472:Fluorouracil