PP2A Mediated AMPK Inhibition Promotes HSP70 Expression in Heat Shock Response

Abstract

BackgroundUnder stress, AMP-activated protein kinase (AMPK) plays a central role in energy balance, and the heat shock response is a protective mechanism for cell survival. The relationship between AMPK activity and heat shock protein (HSP) expression under stress is unclear.Methodology/Principal FindingsWe found that heat stress induced dephosphorylation of AMPKα subunit (AMPKα) in various cell types from human and rodent. In HepG2 cells, the dephosphorylation of AMPKα under heat stress in turn caused dephosphorylation of acetyl-CoA carboxylase and upregulation of phosphoenolpyruvate carboxykinase, two downstream targets of AMPK, confirming the inhibition of AMPK activity by heat stress. Treatment of HepG2 cells with phosphatase 2A (PP2A) inhibitor okadaic acid or inhibition of PP2A expression by RNA interference efficiently reversed heat stress-induced AMPKα dephosphorylation, suggesting that heat stress inhibited AMPK through activation of PP2A. Heat stress- and other HSP inducer (CdCl2, celastrol, MG132)-induced HSP70 expression could be inhibited by AICAR, an AMPK specific activator. Inhibition of AMPKα expression by RNA interference reversed the inhibitory effect of AICAR on HSP70 expression under heat stress. These results indicate that AMPK inhibition under stress contribute to HSP70 expression. Mechanistic studies showed that activation of AMPK by AICAR had no effect on heat stress-induced HSF1 nuclear translocation, phosphorylation and binding with heat response element in the promoter region of HSP70 gene, but significantly decreased HSP70 mRNA stability.Conclusions/SignificanceThese results demonstrate that during heat shock response, PP2A mediated AMPK inhibition upregulates HSP70 expression at least partially through stabilizing its mRNA, which suggests a novel mechanism for HSP induction under stress.

Nilotinib Induces Autophagy in Hepatocellular Carcinoma through AMPK Activation

“…Recently, AMPK inhibition induced by glucose, palmitate, or ethanol was also found to be mediated by PP2A activation (39 -41). One previous finding also revealed that PP2A mediates AMPK inhibition to upregulate heat shock protein (HSP) 70 expression during stress (26). Exploration of the AMPK-downstream signaling cascades revealed that nilotinib-mediated AMPK activation to induce autophagy is via an mTOR-independent pathway.…”

“…PP2A Mediates the Effect of Nilotinib on AMPK Activation and Autophagy-Protein phosphatase PP2A is an essential serine/threonine phosphatase ubiquitously expressed in eukaryotic cells that is known to mediate AMPK inhibition to induce heat shock proteins under stress (26). PP2A exists as a heterotrimeric enzyme composed of a 36-kDa catalytic subunit or C subunit, a 64-kDa scaffolding A subunit, and multiple regulatory B subunits that are thought to influence enzyme activity, substrate specificity, and subcellular localization (17).…”

Heat stress induces mitochondrial adaptations in skeletal muscle

“…Interestingly, it was shown that heat stress suppresses the activity of AMPK. Some studies in vitro demonstrated that responses of these kinases are required for HSF1 activation or HSP induction [34][35][36] . Importantly, there is no unified view on the effect of heat stress on AMPK.…”

“…Previous studies on isolated muscles have been reported to activate AMPK by heat stress (42ºC, 10 min) 37) . In addition, opinions are divided on research targeting cultured cells (Activation 18) : 40ºC, 30 min; Inactivation 34) : 42ºC, 30 min). It is notable that AMPK can be both activated or inactivated by heat stress not only in muscle tissues, but also in cultured cells.…”

AICAR-induced activation of AMPK negatively regulates myotube hypertrophy through the HSP72-mediated pathway in C2C12skeletal muscle cells

“…Interestingly, some recent studies revealed that inhibition of AMPK upregulated HSP72 expression in a human hepatoma cell line (40) and that activation of AMPK downregulated HSP72 expression in a human malignant epithelial cell line (16). Therefore, we hypothesized that AMPK negatively controls skeletal muscle mass by modulating HSP expression.…”