Beta-arrestin inhibits CAMKKbeta-dependent AMPK activation downstream of protease-activated-receptor-2

BACKGROUND: Proteinase-activated-receptor-2 (PAR(2)) is a seven transmembrane receptor that can activate two separate signaling arms: one through Gαq and Ca(2+ )mobilization, and a second through recruitment of β-arrestin scaffolds. In some cases downstream targets of the Gαq/Ca(2+ )signaling arm are directly inhibited by β-arrestins, while in other cases the two pathways are synergistic; thus β-arrestins act as molecular switches capable of modifying the signal generated by the receptor. RESULTS: Here we demonstrate that PAR(2 )can activate adenosine monophosphate-activated protein kinase (AMPK), a key regulator of cellular energy balance, through Ca(2+)-dependent Kinase Kinase β (CAMKKβ), while inhibiting AMPK through interaction with β-arrestins. The ultimate outcome of PAR(2 )activation depended on the cell type studied; in cultured fibroblasts with low endogenous β-arrestins, PAR(2 )activated AMPK; however, in primary fat and liver, PAR(2 )only activated AMPK in β-arrestin-2(-/- )mice. β-arrestin-2 could be co-immunoprecipitated with AMPK and CAMKKβ under baseline conditions from both cultured fibroblasts and primary fat, and its association with both proteins was increased by PAR(2 )activation. Addition of recombinant β-arrestin-2 to in vitro kinase assays directly inhibited phosphorylation of AMPK by CAMKKβ on Thr172. CONCLUSIONS: Studies have shown that decreased AMPK activity is associated with obesity and Type II Diabetes, while AMPK activity is increased with metabolically favorable conditions and cholesterol lowering drugs. These results suggest a role for β-arrestin in the inhibition of AMPK signaling, raising the possibility that β-arrestin-dependent PAR(2 )signaling may act as a molecular switch turning a positive signal to AMPK into an inhibitory one.