title: GRK6 deficiency is associated with enhanced CXCR4-mediated neutrophil chemotaxis in vitro and impaired responsiveness to G-CSF in vivo.
abstract: The stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4) signaling pathway is thought to play an important role in the induction of neutrophil mobilization from the bone marrow in response to granulocyte-colony stimulating factor (G-CSF) treatment. CXCR4 belongs to the family of G protein-coupled receptors. Multiple members of this receptor family are desensitized by agonist-induced G protein-coupled receptor kinase (GRK)-mediated phosphorylation. Here, we demonstrate that in vitro SDF-1-induced chemotaxis of bone marrow-derived neutrophils from GRK6-deficient mice is significantly enhanced and that desensitization of the calcium response to SDF-1 is impaired in GRK6-/- neutrophils. CXCR4 activation by SDF-1 provides a key retention signal for hematopoietic cells in the bone marrow. It is interesting that we observed that in the absence of GRK6, the G-CSF-induced increase in circulating neutrophils is profoundly impaired. Three days after injection of pegylated-G-CSF, significantly lower numbers of circulating neutrophils were observed in GRK6-/- as compared with wild-type (WT) mice. In addition, early/acute neutrophil mobilization in response to G-CSF (3 h after treatment) was also impaired in GRK6-/- mice. However, blood neutrophil levels in untreated GRK6-/- and WT mice were not different. Moreover, the percentage of neutrophils in the bone marrow after G-CSF treatment was increased to the same extent in WT and GRK6-/- mice, indicating that neutrophil production is normal in the absence of GRK6. However, the increased chemotactic sensitivity of GRK6-/- neutrophils to SDF-1 was retained after G-CSF treatment. In view of these data, we suggest that the impaired G-CSF-induced neutrophil mobilization in the absence of GRK6 may be a result of enhanced CXCR4-mediated retention of PMN in the bone marrow.
authors.affiliation: Laboratory of Psychoneuroimmunology, University Medical Center Utrecht, The Netherlands.
authors.forename: Anne
authors.initials: A
authors.lastname: Vroon
authors.forename: Cobi J
authors.initials: CJ
authors.lastname: Heijnen
authors.forename: Roel
authors.initials: R
authors.lastname: Raatgever
authors.forename: Ivo P
authors.initials: IP
authors.lastname: Touw
authors.forename: Rob E
authors.initials: RE
authors.lastname: Ploemacher
authors.forename: Richard T
authors.initials: RT
authors.lastname: Premont
authors.forename: Annemieke
authors.initials: A
authors.lastname: Kavelaars
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000276:immunology; D001853:Bone Marrow / Q000187:drug effects / Q000276:immunology; D020013:Calcium Signaling / Q000187:drug effects / Q000276:immunology; D002454:Cell Differentiation / Q000187:drug effects / Q000276:immunology; D002455:Cell Division / Q000187:drug effects / Q000276:immunology; D054377:Chemokine CXCL12; D019743:Chemokines, CXC / Q000494:pharmacology; D002634:Chemotaxis, Leukocyte / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D054768:G-Protein-Coupled Receptor Kinases; D016179:Granulocyte Colony-Stimulating Factor / Q000494:pharmacology*; D006412:Hematopoietic Stem Cells / Q000187:drug effects / Q000276:immunology; D051379:Mice; D018345:Mice, Knockout; D009504:Neutrophils / Q000187:drug effects / Q000276:immunology / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency* / Q000235:genetics; D019718:Receptors, CXCR4 / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects* / Q000235:genetics / Q000276:immunology
chemical_list: D054377:Chemokine CXCL12; D019743:Chemokines, CXC; C515256:Cxcl12 protein, mouse; D019718:Receptors, CXCR4; D016179:Granulocyte Colony-Stimulating Factor; D017346:Protein Serine-Threonine Kinases; D054768:G-Protein-Coupled Receptor Kinases; C089176:G-protein-coupled receptor kinase 6