GRK6 deficiency is associated with enhanced CXCR4-mediated neutrophil chemotaxis in vitro and impaired responsiveness to G-CSF in vivo

J Leukoc Biol. 2004 Apr;75(4):698-704. doi: 10.1189/jlb.0703320. Epub 2004 Jan 2.


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.

MeSH terms

  • Animals
  • Apoptosis / drug effects
  • Apoptosis / immunology
  • Bone Marrow / drug effects
  • Bone Marrow / immunology
  • Calcium Signaling / drug effects
  • Calcium Signaling / immunology
  • Cell Differentiation / drug effects
  • Cell Differentiation / immunology
  • Cell Division / drug effects
  • Cell Division / immunology
  • Chemokine CXCL12
  • Chemokines, CXC / pharmacology
  • Chemotaxis, Leukocyte / drug effects
  • Chemotaxis, Leukocyte / genetics
  • Chemotaxis, Leukocyte / physiology*
  • G-Protein-Coupled Receptor Kinases
  • Granulocyte Colony-Stimulating Factor / pharmacology*
  • Hematopoietic Stem Cells / drug effects
  • Hematopoietic Stem Cells / immunology
  • Mice
  • Mice, Knockout
  • Neutrophils / drug effects
  • Neutrophils / immunology
  • Neutrophils / physiology*
  • Protein Serine-Threonine Kinases / deficiency*
  • Protein Serine-Threonine Kinases / genetics
  • Receptors, CXCR4 / genetics
  • Receptors, CXCR4 / immunology
  • Receptors, CXCR4 / metabolism*
  • Up-Regulation / drug effects*
  • Up-Regulation / genetics
  • Up-Regulation / immunology


  • Chemokine CXCL12
  • Chemokines, CXC
  • Cxcl12 protein, mouse
  • Receptors, CXCR4
  • Granulocyte Colony-Stimulating Factor
  • Protein Serine-Threonine Kinases
  • G-Protein-Coupled Receptor Kinases
  • G-protein-coupled receptor kinase 6