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

Abstract

BackgroundProteinase-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.ResultsHere 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.ConclusionsStudies 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.

Role for β-arrestin in mediating paradoxical β2AR and PAR2 signaling in asthma

“…β-arrestins can serve as scaffolds for signaling complexes that then promote G-protein-independent signals. Most of these signals are positive, in that they facilitate activation of the proteins they scaffold, but there are also examples of β-arrestin-dependent inhibition of the enzymatic activity of kinases and GTPases [7,14,15]. A common result of β-arrestin-dependent signaling is cell migration and actin reorganization, as well as transcription of specific genes not targeted by the G-protein pathway [13,16–18].…”

“…First, cytoskeletal reorganization and chemotaxis, which are the main cellular processes underlying the pro-inflammatory effects of PAR 2 , do not require Gαq/Ca 2+ signaling, but rather utilize β-arrestins [7,14,45,46]. β-arrestins can signal to various actin assembly pathways to promote chemotaxis, but a major player in PAR 2 /β-arrestin signaling is the actin filament severing protein, cofilin [7,47].…”

Inflammation, obesity, and thrombosis

“…In addition to signaling through G proteins, PAR2 also signals in a G protein-independent manner through cytosolic recruitment of b-arrestin 2. In adipocytes, PAR2 signaling through b-arrestin suppresses AMPK activation, 73 but the significance of this pathway remains to be fully elucidated.…”

“…PAR2 may also have an opposing effect through G protein-mediated activation of AMPK in the absence of b-arrestin. 73 In adipose tissue, TF-FVIIa-PAR2 signaling may regulate macrophage recruitment and/or retention via phosphorylation-dependent crosstalk between integrins and the cytoplasmic domain of TF. TF-FVIIa-PAR2 signaling and/or TFintegrin interactions activate and sustain M1 polarization of ATMs, contributing to insulin resistance.…”

Tissue factor pathways linking obesity and inflammation

“…These gene expression changes in adipocytes are prevented by an antibody that blocks FVIIa binding to TF, data confirmed by treatment experiments in vivo (3). Since weight control by adiponectin is linked to the regulation of AMP-activated protein kinase (AMPK) activation and PAR2 signals in a G protein-independent manner through cytosolic recruitment of β-arrestin 2 leading to inhibition of AMPK in adipocytes (24), suppression of AMPK signaling may be another component of the obesity promoting effects of TF-PAR2 signaling.…”