Inhibition of AMP Kinase by the Protein Phosphatase 2A Heterotrimer, PP2APpp2r2d

Biny K Joseph,Hsing-Yin Liu,Jamie Francisco,Devanshi Pandya,Melissa Donigan,Christina Gallo-Ebert,Caroline Giordano,Adam Bata,Joseph T Nickels

doi:10.1074/jbc.m114.626259

Abstract

AMP kinase is a heterotrimeric serine/threonine protein kinase that regulates a number of metabolic processes, including lipid biosynthesis and metabolism. AMP kinase activity is regulated by phosphorylation, and the kinases involved have been uncovered. The particular phosphatases counteracting these kinases remain elusive. Here we discovered that the protein phosphatase 2A heterotrimer, PP2A(Ppp2r2d), regulates the phosphorylation state of AMP kinase by dephosphorylating Thr-172, a residue that activates kinase activity when phosphorylated. Co-immunoprecipitation and co-localization studies indicated that PP2A(Ppp2r2d) directly interacted with AMP kinase. PP2A(Ppp2r2d) dephosphorylated Thr-172 in rat aortic and human vascular smooth muscle cells. A positive correlation existed between decreased phosphorylation, decreased acetyl-CoA carboxylase Acc1 phosphorylation, and sterol response element-binding protein 1c-dependent gene expression. PP2A(Ppp2r2d) protein expression was up-regulated in the aortas of mice fed a high fat diet, and the increased expression correlated with increased blood lipid levels. Finally, we found that the aortas of mice fed a high fat diet had decreased AMP kinase Thr-172 phosphorylation, and contained an Ampk-PP2A(Ppp2r2d) complex. Thus, PP2A(Ppp2r2d) may antagonize the aortic AMP kinase activity necessary for maintaining normal aortic lipid metabolism. Inhibiting PP2A(Ppp2r2d) or activating AMP kinase represents a potential pharmacological treatment for many lipid-related diseases.

Highlights

AMP kinase is a regulator of lipid metabolism
The addition of 10 nM Okadaic acid (OA) acid, which resulted in an 80% reduction in PP2A activity, caused a significant increase in AMP kinase Thr-172 phosphorylation (Fig. 1B)
AMP kinase substrates include Acc1, Hmgcr, hormone-sensitive lipase, and Srebp1c, all of which are involved in lipogenesis (37, 39 – 41), indicating that proper regulation of AMP kinase activity is necessary to maintain normal lipid metabolism in response to cell energy status

Summary

Background

AMP kinase is a regulator of lipid metabolism. Results: PP2APpp2r2d regulates AMP kinase by dephosphorylating Thr-172, which is required for AMP kinase activation. An increased AMP level stimulates phosphorylation of Thr-172 on the ␣ subunit, which induces kinase activity [11] and stimulates the phosphorylation of factors involved in lipid synthesis, such as acetyl-CoA carboxylase 1 (ACC1)2 [12] and HMG-CoA reductase (HMGCR) [13]. Very few PP2A B subunits have been elucidated that direct AMP kinase dephosphorylation Those that are associated with the A/C dimer and act on AMP kinase include Ppp2r2d [28] and Ppp2r3a [29] (see Table 1). Heterotrimers containing these subunits are activated under conditions of metal excess, calcium release, change in glucose, and heat stress (28 –31). The results suggest that early activation of PPP2APpp2r2d in response to a western style diet may help to initiate aortic plaque formation and atherosclerosis

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION