Regulation of the Proteasome by AMPK in Endothelial Cells: The Role of O-GlcNAc Transferase (OGT)

Abstract

26S proteasome is a macromolecular multi-subunit complex responsible for recognizing, unfolding, and ultimately destroying proteins. It remains poorly understood how 26S proteasome activity is regulated. The present study was to investigate if AMP-activated protein kinase (AMPK) functions as a physiological suppressor of the 26S proteasome in endothelial cells. 26S proteasome assembly, activity, and O-GlcNAcylation of P700 were assayed in cultured human umbilical vein endothelial cells (HUVEC) and mouse aortas isolated from C57BL6 wild type and AMPKα2 knockout mice with or without being exposed to selective AMPK activators or inhibitors. Pharmacological and genetic activation of AMPK effectively suppresses 26S proteasomes in endothelial cells. Conversely, inactivation of AMPK either pharmacologically or genetically increases 26S proteasome activity; furthermore, the inactivation decreases the O-GlcNAcylation of PA700/S10B (the regulatory complex in 26S proteasomes) and increases the assembly of 26S proteasomes. In contrast, AMPK activation increases levels of O-GlcNAcylated PA700/S10B, likely through enhanced association of PA700 with O-GlcNAc transferase (OGT), the enzyme that catalyzes protein O-GlcNAcylation. Finally, aortas from AMPK-KO vs wild type mice exhibit elevated 26S proteasome activity in parallel with decreased PA700/S10B O-GlcNAcylation and PA700/S10B-OGT association. Taken together, we conclude that AMPK functions as a physiological suppressor of 26S proteasomes.

Protein Expression of Proteasome Subunits in Elderly Patients with Schizophrenia

“…Additionally, the three proteolytic activities of the proteasome, trypsin-like, chymotrypsin-like, and peptidylglutamyl-peptide hydrolyzing (or caspase-like), work in concert, but can be independently regulated by different modifications, including the ones investigated in this study and others. For example, posttranslational modifications including phosphorylation, O-GlcNAcylation, and S-glutathionylation have been shown to alter proteasome function without necessarily affecting subunit abundance (Ishii et al, 2005;Aiken et al, 2011;Xu et al, 2012). Further analysis in patients with schizophrenia on the state of different proteasome complexes, posttranslational modifications, and assays of trypsin-, chymotrypsin-, and caspase-like activity will be necessary to fully understand how these protein abnormalities affect cellular function and potentially contribute to the pathophysiology of schizophrenia.…”

Proteasome inhibitors induce AMPK activation via CaMKKβ in human breast cancer cells

“…Indeed, while either AMPK or UPS signaling is well understood, their crosstalk is still unclear. Also, the AMPK regulation by the UPS and vice versa forms the basis of an integrated system that connects proteasome-mediated protein degradation and cellular energetics [34,35]. It should be noted that, depending on the target protein or context, a significant amount of cellular energy is spent by the UPS in regulating protein turnover [36][37][38].…”

Participation of proteasome-ubiquitin protein degradation in autophagy and the activation of AMP-activated protein kinase

“…AMPK modulates protein turnover at several levels, including mTOR-dependent protein synthesis, transcriptional regulation, and affecting 26S proteasome function [26, 70]. AMPK can also activate alternative protein degradative pathways, including autophagy and mitophagy [9, 41].…”