Increased Acute Inflammation, Leukotriene B4-Induced Chemotaxis, and Signaling in Mice Deficient for G Protein-Coupled Receptor Kinase 6

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Abstract
Directed migration of polymorphonuclear neutrophils (PMN) is required for adequate host defense against invading organisms and leukotriene B4 (LTB4) is one of the most potent PMN chemoattractants. LTB4 exerts its action via binding to BLT1, a G protein-coupled receptor. G protein-coupled receptors are phosphorylated by G protein-coupled receptor kinases (GRK) in an agonist-dependent manner, resulting in receptor desensitization. Recently, it has been shown that the human BLT1 is a substrate for GRK6. To investigate the physiological importance of GRK6 for inflammation and LTB4 signaling in PMN, we used GRK6-deficient mice. The acute inflammatory response (ear swelling and influx of PMN into the ear) after topical application of arachidonic acid was significantly increased in GRK6−/− mice. In vitro, GRK6−/− PMN showed increased chemokinetic and chemotactic responses to LTB4. GRK6−/− PMN respond to LTB4 with a prolonged increase in intracellular calcium and prolonged actin polymerization, suggesting impaired LTB4 receptor desensitization in the absence of GRK6. However, pre-exposure to LTB4 renders both GRK6−/− as well as wild-type PMN refractory to restimulation with LTB4, indicating that the presence of GRK6 is not required for this process to occur. In conclusion, GRK6 deficiency leads to prolonged BLT1 signaling and increased neutrophil migration.

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