title: Functional consequences of perturbed CXCL12 signal processing: analyses of immature hematopoiesis in GRK6-deficient mice.
abstract: Hematopoietic stem and progenitor cells (HSPCs) reside in bone marrow (BM) in an environment rich in CXCL12, the ligand for CXCR4, which is constitutively expressed on all immature hematopoietic cells in BM. This ligand-receptor pair critically controls HSPC retention and (relative) quiescence in BM. Interestingly, in a chemokine-abundant environment, CXCR4 surface expression and CXCL12 sensitivity of BM-residing HSPCs are continuously maintained. The mechanisms underlying this peculiar pattern of G-protein signal integration by BM-HSPCs are unknown. G-protein receptor kinases (GRKs) control receptor function by phosphorylating the intracellular domains upon ligand-induced activation, which results in receptor internalization and transient refractoriness. Using, therefore, a GRK6-deficient (GRK6(-/-)) mouse, we sought to address how perturbed ligand-induced CXCR4 (in)activation affects HSPC behavior in vitro and in vivo. In vitro, GRK6(-/-) HSPCs were characterized by hyper-responsiveness to CXCL12, as expected. In vivo, GRK6(-/-) immature hematopoiesis was characterized by a marked expansion of immature hematopoiesis in spleens and a modest repopulation defect in serial competitive transplantation. Enforced mobilization with granulocyte colony-stimulating factor (G-CSF) and AMD3100 was normal, as was hematopoietic regeneration after noncompetitive transplantation or pharmacological myelosuppression. These observations illustrate that GRK-mediated restriction of CXCR4 signal input after ligand engagement is largely dispensable for BM-resident HSPCs, which may explain how continuous CXCL12 responsiveness of BM-HSPCs can be maintained.
authors.affiliation: 1 German Red Cross Blood Service Baden-Württemberg-Hesse , Frankfurt, Germany .
authors.forename: Doreen
authors.initials: D
authors.lastname: Chudziak
authors.forename: Gabriele
authors.initials: G
authors.lastname: Spohn
authors.forename: Darja
authors.initials: D
authors.lastname: Karpova
authors.forename: Katrin
authors.initials: K
authors.lastname: Dauber
authors.forename: Eliza
authors.initials: E
authors.lastname: Wiercinska
authors.forename: Johanna A
authors.initials: JA
authors.lastname: Miettinen
authors.forename: Thalia
authors.initials: T
authors.lastname: Papayannopoulou
authors.forename: Halvard
authors.initials: H
authors.lastname: Bönig
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D054377:Chemokine CXCL12 / Q000378:metabolism*; D054768:G-Protein-Coupled Receptor Kinases / Q000235:genetics / Q000378:metabolism*; D006410:Hematopoiesis; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D010978:Platelet Factor 4 / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D054377:Chemokine CXCL12; C515256:Cxcl12 protein, mouse; D010978:Platelet Factor 4; D054768:G-Protein-Coupled Receptor Kinases; C089176:G-protein-coupled receptor kinase 6