In contrast, in MEFDKO barr2, PAR2 stimulated AMPK phosphory lation was inhibited. Furthermore, when flag b arrestin 2 was over expressed in NIH3T3 cells, PAR2 stimulated AMPK phosphorylation was abolished. In NIH3T3 cells over expressing b arrestin 2, we observe a small selleck chemical Trichostatin A increase in base line pAMPK. We do not yet know the significance of this alteration in basal AMPK phosphorylation but may reflect a PAR 2 independent effect of b arrestin on AMPK phosphorylation. b arrestins are involved in ter minating the signals of a number of receptors known to activate AMPK. PAR2 is relatively unusual in that it pro motes a number of b arrestin dependent signaling events, while its G protein signal is being dampened. We conclude that b arrestins can inhibit PAR2 stimu lated AMPK phosphorylation.

PAR2 promotes b arrestin dependent inhibition of AMPK in primary fat To confirm the inhibitory role of b arrestin 2 on AMPK phosphorylation in primary cells, we investigated PAR2 stimulated AMPK phosphorylation in adipose tissue from wild type and either b arrestin 1 or b arrestin 2 mice. AMPK activity in adipose plays a key role in modulating the metabolic state of the animal and we observe high levels of b arrestin expression in primary fat as well as differentiated 3T3L1 adipocytes. Isolated epididymal fat was incubated with or without 2fAP for 5 and 120 minutes, then homogenized and analyzed by SDS PAGE followed by western blotting for phospho AMPK. In wt and b arr1 fat, no significant increase in AMPK activity was observed in response to PAR2 activa tion.

However, in b arr2 fat, PAR2 promoted a 5 fold increase in AMPK phosphorylation, and a 1. 5 2. 5 fold increase in AMPK activity. Similar results were observed in liver from wt, b arr 1 and b arr2 animals. Pretreatment with STO 609 abolished PAR2 stimulated AMPK phosphory lation in b arr2 fat, suggesting that AMPK phosphorylation by CAMKKb is inhibited by b arrestin 2. Consistent with these observations, PAR2 stimulated phosphorylation of the AMPK substrate, ACC, was only observed in b arr2 mice. We conclude that PAR2 can promote CAMKKb depen dent AMPK activation in primary fat, but under normal conditions this activity is suppressed by an inhibitory PAR2 pathway through b arrestin 2. AMPK and CAMKKb associate with b arrestin 2 Our studies on PI3K suggest that b arrestins can form inhibitory scaffolds leading to decreased kinase activity.

To examine whether b arrestins similarly associate with AMPK and CAMKKb, we performed co immunopreci pitations in NIH3T3 cells transfected with flag tagged b arrestin 1 or b arrestin 2, treated with and without 2fAP. Both AMPK and CAMKKb could be co precipi tated with b arrestin 2 and to a lesser extent, b arrestin 1. Only b arrestin 2 increased association GSK-3 with AMPK and CAMKKb upon PAR2 activation. Furthermore, a greater amount of both proteins asso ciated with b arrestin 2 relative to its expression level, than with b arrestin 1.