Physiological changes in GRK2 regulate CCL2-induced signaling to ERK1/2 and Akt but not to MEK1/2 and calcium.

G protein-coupled receptor (GPCR) kinase 2 (GRK2) regulates G protein-coupled receptor signaling via agonist-induced receptor phosphorylation and desensitization. GRK2 can also modulate cellular activation by interacting with downstream signaling molecules. The intracellular GRK2 level changes during inflammatory conditions. We investigated how IL-1beta-induced changes in endogenous GRK2 expression influence chemokine receptor signaling in primary astrocytes. Culturing astrocytes with IL-1beta for 24 h induced a 2-3-fold increase in GRK2 and decreased C-C chemokine ligand 2 (CCL2)-induced ERK1/2 activation. Conversely, the 45% decrease in GRK2 expression in astrocytes from GRK2+/- animals resulted in a more pronounced CCL2-induced ERK1/2 phosphorylation. Increased GRK2 inhibited CCL2-induced Akt phosphorylation at Thr308 and Ser473 as well as pPDK-1 translocation. In contrast, altered GRK2 levels did not change the CCL2-induced increase in intracellular calcium or MEK1/2 phosphorylation. These data suggest that altered GRK2 expression modulates chemokine signaling downstream of the receptor. We found that GRK2 kinase activity was not required to decrease chemokine-induced ERK1/2 phosphorylation, whereas regulation of CCL2-induced Akt phosphorylation did require an active GRK2 kinase domain. Collectively, these data suggest that changes in endogenous GRK2 expression in primary astrocytes regulate chemokine receptor signaling to ERK1/2 and to PDK-1-Akt downstream of receptor coupling via kinase-dependent and kinase-independent mechanisms, respectively.