G-Protein Coupled Receptor Kinase 5 Mediates Lipopolysaccharide-Induced NFκB Activation in Primary Macrophages and Modulates Inflammation In Vivo in Mice

G-protein coupled receptor kinase-5 (GRK5) is a serine/threonine kinase discovered for its role in the regulation of G-protein coupled receptor signaling. Recent studies have shown that GRK5 is also an important regulator of signaling pathways stimulated by non-GPCRs. This study was undertaken to determine the physiological role of GRK5 in Toll-like receptor-4-induced inflammatory signaling pathways in vivo and in vitro. Using mice genetically deficient in GRK5 (GRK5(-/-)) we demonstrate here that GRK5 is an important positive regulator of lipopolysaccharide (LPS, a TLR4 agonist)-induced inflammatory cytokine and chemokine production in vivo. Consistent with this role, LPS-induced neutrophil infiltration in the lungs (assessed by myeloperoxidase activity) was markedly attenuated in the GRK5(-/-) mice compared to the GRK5(+/+) mice. Similar to the in vivo studies, primary macrophages from GRK5(-/-) mice showed attenuated cytokine production in response to LPS. Our results also identify TLR4-induced NF kappa B pathway in macrophages to be selectively regulated by GRK5. LPS-induced I kappa B alpha phosphorylation, NF kappa B p65 nuclear translocation, and NF kappa B binding were markedly attenuated in GRK5(-/-) macrophages. Together, our findings demonstrate that GRK5 is a positive regulator of TLR4-induced I kappa B alpha-NF kappa B pathway as well as a key modulator of LPS-induced inflammatory response. J. Cell. Physiol. 226: 1323-1333, 2011. (C) 2010 Wiley-Liss, Inc.