title: Beta-arrestin inhibits CAMKKbeta-dependent AMPK activation downstream of protease-activated-receptor-2.
abstract: BACKGROUND
  Proteinase-activated-receptor-2 (PAR2) is a seven transmembrane receptor that can activate two separate signaling arms: one through Gαq and Ca2+ mobilization, and a second through recruitment of β-arrestin scaffolds. In some cases downstream targets of the Gαq/Ca2+ 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 PAR2 can activate adenosine monophosphate-activated protein kinase (AMPK), a key regulator of cellular energy balance, through Ca2+-dependent Kinase Kinase β (CAMKKβ), while inhibiting AMPK through interaction with β-arrestins. The ultimate outcome of PAR2 activation depended on the cell type studied; in cultured fibroblasts with low endogenous β-arrestins, PAR2 activated AMPK; however, in primary fat and liver, PAR2 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 PAR2 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 PAR2 signaling may act as a molecular switch turning a positive signal to AMPK into an inhibitory one.
authors.affiliation: Division of Biomedical Sciences University of California Riverside, California, USA.
authors.forename: Ping
authors.initials: P
authors.lastname: Wang
authors.forename: Yong
authors.initials: Y
authors.lastname: Jiang
authors.forename: Yinsheng
authors.initials: Y
authors.lastname: Wang
authors.forename: John Y
authors.initials: JY
authors.lastname: Shyy
authors.forename: Kathryn A
authors.initials: KA
authors.lastname: DeFea
mesh_terms: D000091162:AMP-Activated Protein Kinase Kinases; D000818:Animals; D019390:Arrestins / Q000502:physiology*; D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase / Q000378:metabolism*; D051379:Mice; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D011494:Protein Kinases / Q000737:chemistry / Q000378:metabolism*; D044464:Receptor, PAR-2 / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins
chemical_list: C000605258:Arrb2 protein, mouse; D019390:Arrestins; D044464:Receptor, PAR-2; D011994:Recombinant Proteins; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins; D011494:Protein Kinases; D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase; D000091162:AMP-Activated Protein Kinase Kinases