Expression control of the AMPK regulatory subunit and its functional significance in yeast ER stress response

Yuichi Kimura,Tomoaki Mizuno,Kenji Irie

doi:10.1038/srep46713

Abstract

AMP-activated protein kinase (AMPK) is an evolutionarily conserved heterotrimeric kinase complex consisting of a catalytic subunit, α, and two regulatory subunits, β and γ. Previously, we demonstrated that Snf1, the Saccharomyces cerevisiae ortholog of AMPK, negatively regulates the unfolded protein response (UPR) pathway and the Hog1 MAP kinase pathway in ER stress response. However, it remains unclear how the alternate three β subunits, Sip1, Sip2, and Gal83, of the Snf1 complex participate in ER stress response. Here, we show that Gal83 plays a major role in Snf1-mediated downregulation of the UPR and Hog1 pathways. Gal83 is the most abundant β subunit in the normal state and further induced by ER stress. This induction is mediated via activation of the GAL83 promoter by the UPR. When expressed under the control of the GAL83 promoter, Sip2 exhibits potent functional activity equivalent to Gal83. Our results suggest that the functional significance of the β subunit of Snf1 AMPK in ER stress response is defined by modulation of the expression level through regulation of the promoter activity.

Highlights

Synthesized secretory or membrane proteins are folded and glycosylated in the endoplasmic reticulum (ER)
These results suggest that the functional significance of Gal[83] as the AMPK βsubunit in ER stress response is defined by its promoter
To investigate which βsubunits are involved in regulation of the unfolded protein response (UPR) and Hog[1] pathways, we employed reg[1] mutation which causes Snf[1] hyperactivation

Summary

Introduction

Synthesized secretory or membrane proteins are folded and glycosylated in the endoplasmic reticulum (ER). The gene expression program activated by Hac[1] increases ER-resident chaperones and proteins functioning ER-associated degradation, alleviating ER stress. The βsubunits are encoded by three genes, SIP1, SIP2, and GAL83, and one of them is utilized in each complex[7,11,12,13] These βsubunits share overlapping functions, they display distinctive features[14]. We found that Gal[83] plays a major role in Snf1-mediated downregulation of the UPR and Hog[1] during ER stress response. When SIP2 was expressed from the GAL83 promoter, loss of Gal[83] could be effectively complemented These results suggest that the functional significance of Gal[83] as the AMPK βsubunit in ER stress response is defined by its promoter

Methods

Results

Conclusion