ER chaperone–metal interactions: Links to protein folding disorders

AbstractEndoplasmic reticulum (ER) stress that leads to the accumulation of misfolded proteins in the ER initiates the unfolded protein response (UPR). This homeostatic response activates signaling pathways that seek to reinstate a proper ER protein folding balance or induce apoptosis if ER stress persists. Recently, we and others identified human FICD (Filamentation induced by cyclic AMP domain-containing protein), an enzyme with adenylyltransferase (aka AMPylation) activity, as a new UPR target. Here, we demonstrate that FICD is functionally linked to the UPR, as evidenced by the finding that the adenylyltransferase activity of the protein induces ER stress, while FICD silencing increases sensitivity to ER stress. We identify BiP, an abundant ER chaperone and key regulator of the UPR, as the main substrate of FICD AMPylation in ER-derived microsomes, further emphasizing close functional connection of FICD to the UPR and in line with recent reports that AMPylation inactivates BiP. Notably, BiP overexpression increased the levels of BiP AMPylation as well as FICD auto-AMPylation, suggesting a homeostatic response that balances the pool of active BiP to modulate its functions in protein folding as well as UPR signaling. Finally, we show that overexpressed FICD forms a disulfide-bonded homo-dimer through Cys51 and Cys75 and demonstrate that mutation of these two cysteines in the context of a hyperactive FICD mutant leads to increased BiP AMPylation. This latter finding opens up the possibility that FICD activity is redox regulated and closely connected with ER redox homeostasis.

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Protein Folding Disorders of the Central Nervous System

10.1142/10517 ◽

2017 ◽

Author(s):

Jorge Ghiso ◽

Agueda Rostagno

Keyword(s):

Central Nervous System ◽

Nervous System ◽

Protein Folding ◽

The Central Nervous System ◽

Protein Folding Disorders

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(Glyco)Protein Folding Disorders

Encyclopedia of Biophysics ◽

10.1007/978-3-642-16712-6_102 ◽

2013 ◽

pp. 904-907

Author(s):

Elizabeth Hounsell

Keyword(s):

Protein Folding ◽

Protein Folding Disorders

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Abstract 291: MANF, a Structurally Unique ER Stress-inducible Protein, Restores ER-protein Folding in ER Stressed Cardiac Myocytes and in the Ischemic Heart

Circulation Research ◽

10.1161/res.119.suppl_1.291 ◽

2016 ◽

Vol 119 (suppl_1) ◽

Author(s):

Adrian Arrieta ◽

Winston T Stauffer ◽

Amber N Pentoney ◽

Erik A Blackwood ◽

Shirin Doroudgar ◽

...

Keyword(s):

Protein Folding ◽

Stress Response ◽

Er Stress ◽

Structure And Function ◽

Ischemic Heart ◽

Misfolded Proteins ◽

Er Stress Response ◽

Er Chaperone ◽

And Function

The sarco/endoplasmic reticulum (SR/ER) of cardiomyocytes is a critical site of protein synthesis and folding, as most secreted and membrane proteins including receptors, growth factors, ion channels, and calcium-handling proteins are made at this location. Myocardial ischemia induces ER stress, during which toxic, misfolded proteins accumulate in the SR/ER and contribute to cardiomyocyte death. The branch of the ER stress response mediated by the transcription factor, ATF6, induces ER chaperones that restore SR/ER protein folding. We found that ATF6 also induces mesencephalic astrocyte-derived neurotrophic factor (MANF), a novel, ubiquitously expressed, ER-luminal protein of unknown function. MANF is structurally unique, thus its function cannot be inferred by structural analogy to known proteins. Since it is ATF6-inducible, and resides in the ER lumen, we hypothesized that MANF is an ER chaperone required for optimal viability of cardiac myocytes during ER stresses, including ischemia. The characteristics of MANF gene induction by ER stress, and the effects of MANF knockdown on the ER stress response and cell viability were determined in cultured neonatal rat ventricular myocytes (NRVM). The ability of recombinant MANF to restore structure and function to model misfolded proteins was also examined. Finally, the effects of MANF loss-of-function in the ischemic heart, in vivo , were determined by generating a transgenic mouse model that expresses a cardiomyocyte-specific MANF-targeted microRNA. MANF induction and functional characteristics phenocopied those of a well-studied ER chaperone, glucose-regulated protein 78 (Grp78). Like Grp78, MANF was induced by ER stress in an ATF6-dependent manner. Like knockdown of Grp78, knockdown of MANF in NRVM increased myocyte death in response to ER stress. Like recombinant Grp78, recombinant MANF exhibited a robust ability to restore structure and function to model misfolded proteins, in vitro. Finally, MANF knockdown in the heart, in vivo , increased damage in a mouse model of myocardial infarction. These results suggest that MANF is an SR/ER-resident chaperone required for restoration of SR/ER protein folding during the adaptive ER stress response, and decreasing tissue damage in the ischemic heart.

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