Cells 2012, 1(4), 926-950; doi:10.3390/cells1040926
Review

Unfolded Protein Responses With or Without Unfolded Proteins?

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Received: 17 September 2012; in revised form: 15 October 2012 / Accepted: 22 October 2012 / Published: 1 November 2012
(This article belongs to the Special Issue Cellular Stress Response)
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Abstract: The endoplasmic reticulum (ER) is the site of secretory protein biogenesis. The ER quality control (QC) machinery, including chaperones, ensures the correct folding of secretory proteins. Mutant proteins and environmental stresses can overwhelm the available QC machinery. To prevent and resolve accumulation of misfolded secretory proteins in the ER, cells have evolved integral membrane sensors that orchestrate the Unfolded Protein Response (UPR). The sensors, Ire1p in yeast and IRE1, ATF6, and PERK in metazoans, bind the luminal ER chaperone BiP during homeostasis. As unfolded secretory proteins accumulate in the ER lumen, BiP releases, and the sensors activate. The mechanisms of activation and attenuation of the UPR sensors have exhibited unexpected complexity. A growing body of data supports a model in which Ire1p, and potentially IRE1, directly bind unfolded proteins as part of the activation process. However, evidence for an unfolded protein-independent mechanism has recently emerged, suggesting that UPR can be activated by multiple modes. Importantly, dysregulation of the UPR has been linked to human diseases including Type II diabetes, heart disease, and cancer. The existence of alternative regulatory pathways for UPR sensors raises the exciting possibility for the development of new classes of therapeutics for these medically important proteins.
Keywords: unfolded protein response; endoplasmic reticulum; misfolded protein; BIP; stress; Ire1; inositol
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Snapp, E.L. Unfolded Protein Responses With or Without Unfolded Proteins? Cells 2012, 1, 926-950.

AMA Style

Snapp EL. Unfolded Protein Responses With or Without Unfolded Proteins? Cells. 2012; 1(4):926-950.

Chicago/Turabian Style

Snapp, Erik L. 2012. "Unfolded Protein Responses With or Without Unfolded Proteins?" Cells 1, no. 4: 926-950.


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