ABSTRACT
Chemokine receptor interactions coordinate leukocyte migration in inflammation. Chemokine receptors are GPCRs that when activated, are phosphorylated by GRKs to turn off G protein-mediated signaling yet recruit additional signaling machinery. Recently, GRK3 was identified as a negative regulator of CXCL12/CXCR4 signaling that is defective in human WHIM syndrome. Here, we report that GRK3-/- mice exhibit numerous features of human WHIM, such as impaired CXCL12-mediated desensitization, enhanced CXCR4 signaling to ERK activation, altered granulocyte migration, and a mild myelokathexis. Moreover, GRK3-/- protects mice from two acute models of inflammatory arthritis (K/BxN serum transfer and CAIA). In these granulocyte-dependent disease models, protection of GRK3-/- mice is mediated by retention of cells in the marrow, fewer circulating granulocytes in the peripheral blood, and reduced granulocytes in the joints during active inflammation. In contrast to WHIM, GRK3-/- mice have minimal hypogammaglobulinemia and a peripheral leukocytosis with increased lymphocytes and absent neutropenia. Thus, we conclude that the loss of GRK3-mediated regulation of CXCL12/CXCR4 signaling contributes to some, but not all, of the complete WHIM phenotype and that GRK3 inhibition may be beneficial in the treatment of inflammatory arthritis.
Subject(s)
G-Protein-Coupled Receptor Kinase 3/immunology , Immunologic Deficiency Syndromes/immunology , MAP Kinase Signaling System/immunology , Warts/immunology , Animals , Cell Line, Transformed , Chemokine CXCL12/genetics , Chemokine CXCL12/immunology , Chemokine CXCL12/metabolism , Disease Models, Animal , G-Protein-Coupled Receptor Kinase 3/genetics , G-Protein-Coupled Receptor Kinase 3/metabolism , Granulocytes/enzymology , Granulocytes/immunology , Granulocytes/pathology , Humans , Immunologic Deficiency Syndromes/enzymology , Immunologic Deficiency Syndromes/genetics , Immunologic Deficiency Syndromes/pathology , Inflammation/enzymology , Inflammation/genetics , Inflammation/immunology , Inflammation/pathology , MAP Kinase Signaling System/genetics , Mice , Mice, Knockout , Primary Immunodeficiency Diseases , Receptors, CXCR4/genetics , Receptors, CXCR4/immunology , Receptors, CXCR4/metabolism , Warts/enzymology , Warts/genetics , Warts/pathologyABSTRACT
The interaction between mycobacteria and epithelium is unexplored, but may determine the outcome of the infection. We have analyzed the role of two G protein-coupled receptors, CXCR1 and CXCR2 that are important regulators of many pulmonary diseases. We found that mycobacteria significantly increased the expression of both CXCR1 and CXCR2 on alveolar epithelial cells and both receptors were found to be important for neutrophil diapedesis across primary endothelial cells towards infected mucosa. Mycobacteria, lipoarabinomannan or 19-kDa glycolipoprotein up-regulated the inhibitory G protein-coupled receptor kinase (GRK)2, while GRK3 was less affected. Mycobacteria-induced GRK2 up-regulation decreased chemokine transcription and secretion thereby affecting the neutrophil recruitment to infected mucosa. These events were completely abolished by blocking these receptors prior to infection as the blocking increased epithelial immune responses. We have identified novel interactions occurring in the initial phase of mycobacterial infections by which mycobacterial manipulate epithelial inflammatory responses.
