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.

Leukocyte analysis from WHIM syndrome patients reveals a pivotal role for GRK3 in CXCR4 signaling

“…14). However, to date, the GRKs responsible for agonist-promoted phosphorylation, desensitization, and/ or endocytosis of CXCR4 remain to be characterized, although some alterations of CXCR4 functions have been revealed in mice lacking Grk6 (10,15). In this work, we identify GRK3 as a key regulator of CXCR4 attenuation, the impaired activity of which in WHIM WT cells accounts for the enhancement of CXCR4-mediated G protein-dependent responses.…”

“…Recent findings indicate that different GRKs may set in motion distinct functions of GPCR-bound β-arrestin (26,27,37,38), opening the possibility that a specialization of GRKs also takes place in the regulation of β-arrestin2-dependent CXCR4 signaling. For instance, studies from Grk6-deficient mice suggest a positive contribution of this kinase to the CXCL12-induced chemotaxis of T cells, whereas Grk6 appears to play an opposite role in neutrophils (10,15). These results, if extended to the regulation of CXCR4-mediated signaling in human cells, would open the possibility that GRK6 and GRK3 differentially regulate CXCR4 activities.…”

Multiple roles of chemokine CXCL12 in the central nervous system: A migration from immunology to neurobiology

“…1). CXCL12 activation of CXCR4 desensitizes CXCR4 though GRKmediated receptor phosphorylation and β-arrestin binding (Cheng ZJ et al, 2000;Fong AM et al, 2002;Vroon A, 2004). β-Arrestin2 enhances CXCR4-mediated activation of p38 MAPK that is critically involved in CXCR4-mediated chemotaxis (Sun Y, et al, 2002).…”

G Protein-Coupled Receptor Kinase 6 Acts as a Critical Regulator of Cytokine-Induced Hyperalgesia by Promoting Phosphatidylinositol 3-Kinase and Inhibiting p38 Signaling

“…Although most of the substrates of GRK6 are probably still unknown, it has been shown that GRK6 regulates desensitization of the chemokine receptor CXCR4, the BLT1 receptor for the leukotriene B4 (LTB4) and the calcitonin gene-related peptide (CGRP) receptor (13)(14)(15)(16). Furthermore, GRK6 binds and phosphorylates PDZ domains in Na + /H + exchanger regulatory factor (NHERF) and binds to downstream regulatory element antagonistic modulator (DREAM), both regulators of ion channels, indicating that GRK6 can also regulate cellular signaling via mechanisms independent of GPCR desensitization (17,18).…”