Exploring the Conserved Role of MANF in the Unfolded Protein Response in Drosophila melanogaster.

Riitta Lindström,Päivi Lindholm,Mari Palgi,Jukka Kallijärvi,Tapio I Heino,Mart Saarma,Andreas Bergmann

doi:10.1371/journal.pone.0151550

Abstract

Disturbances in the homeostasis of endoplasmic reticulum (ER) referred to as ER stress is involved in a variety of human diseases. ER stress activates unfolded protein response (UPR), a cellular mechanism the purpose of which is to restore ER homeostasis. Previous studies show that Mesencephalic Astrocyte-derived Neurotrophic Factor (MANF) is an important novel component in the regulation of UPR. In vertebrates, MANF is upregulated by ER stress and protects cells against ER stress-induced cell death. Biochemical studies have revealed an interaction between mammalian MANF and GRP78, the major ER chaperone promoting protein folding. In this study we discovered that the upregulation of MANF expression in response to drug-induced ER stress is conserved between Drosophila and mammals. Additionally, by using a genetic in vivo approach we found genetic interactions between Drosophila Manf and genes encoding for Drosophila homologues of GRP78, PERK and XBP1, the key components of UPR. Our data suggest a role for Manf in the regulation of Drosophila UPR.

Highlights

The accumulation of unfolded or misfolded proteins causes disturbances in endoplasmic reticulum (ER) homeostasis, a phenomenon referred to as ER stress
The induction of ER stress was monitored by measuring the mRNA levels of Drosophila GRP78 homologue Hsc3 and Xbp1 [total (Xbp1t) and spliced (Xbp1s) forms separately] by qPCR analysis and by evaluating the proportions of unspliced and spliced transcripts of Xbp1 (Xbp1u and Xbp1s, respectively) by agarose gel electrophoresis
We found that DmManf mRNA levels were increased in response to drug-induced ER stress (Fig 1A)

Summary

Introduction

The accumulation of unfolded or misfolded proteins causes disturbances in endoplasmic reticulum (ER) homeostasis, a phenomenon referred to as ER stress. In order to overcome ER stress, UPR leads to attenuation of protein synthesis, enhancement of degradation of unfolded proteins, and activation of specific signalling cascades. These events aim to reduce the overall protein load in the ER and to enhance the protein folding capacity by selective transcription of chaperones. UPR is activated through three signalling cascades by ER transmembrane sensor proteins PERK (PRKR-like endoplasmic reticulum kinase), IRE1 (inositol requiring enzyme 1), and ATF6 (activating transcription factor 6). All of these three proteins are maintained inactive in PLOS ONE | DOI:10.1371/journal.pone.0151550. All of these three proteins are maintained inactive in PLOS ONE | DOI:10.1371/journal.pone.0151550 March 14, 2016

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