MANF regulates unfolded protein response and neuronal survival through its ER-located receptor IRE1α

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum (ER)-located protein with cytoprotective effects in numerous cell types in vitro and in models of neurodegeneration and diabetes in vivo. So far, the exact mode of its action has remained elusive and plasma membrane or ER-located receptors of MANF have not been identified. We have found that MANF can directly interact with transmembrane unfolded protein response (UPR) receptor IRE1α and compete with the major ER chaperone BiP (GRP78) for the interaction with IRE1α. With lower affinities MANF can also interact with other UPR receptors, PERK and ATF6. Using molecular modeling and mutagenesis analysis, we have identified the exact structural MANF regions involved in its binding to the luminal domain of IRE1α. MANF attenuates UPR signaling by decreasing IRE1α oligomerization and IRE1α phosphorylation. MANF mutant deficient in IRE1α binding cannot regulate IRE1α oligomerization and fails to protect neurons from ER stress induced death. Importantly, we found that MANF-IRE1α interaction is also crucial for the survival promoting action of MANF for dopamine neurons in an animal model of Parkinson9s disease. Our data reveal a novel mechanism of IRE1α regulation during ER stress and demonstrate the intracellular mode of action of MANF as a modulator of UPR and neuronal cell survival through the direct interaction with IRE1α and regulation of its activity. Furthermore, our data explain why MANF in contrast to other growth factors has no effects on naive cells and rescues only ER stressed or injured cells.