[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Cell injury, adaptation and death](https://durgical.com/en/general-pathology/#a-injury) › Endoplasmic reticulum stress and the unfolded protein response

[General pathology](https://durgical.com/en/general-pathology/) · [Cell injury, adaptation and death](https://durgical.com/en/general-pathology/#a-injury)

# Endoplasmic reticulum stress and the unfolded protein response

- Mechanism

When too many proteins fold badly inside the ER, the cell slows production and makes more helpers; if that fails, it kills itself.

Updated 2026-11-01

## Key points

- Three ER sensors: IRE1 (splices XBP1), PERK (phosphorylates eIF2α to slow translation) and ATF6.
- Adaptive phase: less translation, more chaperones, more degradation through ER-associated degradation (ERAD) and the proteasome.
- Persistent stress: CHOP and other signals trigger the intrinsic apoptosis pathway.
- Alpha-1 antitrypsin Z protein is retained in hepatocytes: PAS-positive, diastase-resistant globules and liver injury.
- CFTR ΔF508 misfolds and is degraded before reaching the membrane.

## What it is

Secreted and membrane proteins fold in the endoplasmic reticulum with the help of chaperones. Misfolded proteins pile up with mutations, oxidative stress, heat, lack of glucose or simply high secretory demand. The unfolded protein response first tries to restore balance; if the stress lasts, it triggers apoptosis. Misfolded proteins also injure by aggregating or by losing their normal function.

## Step by step

- Unfolded proteins accumulate in the ER lumen.
- The chaperone BiP binds them and releases the sensors IRE1, PERK and ATF6.
- PERK phosphorylates eIF2α and slows general protein synthesis.
- IRE1 and ATF6 increase genes for chaperones and for ER-associated degradation.
- Misfolded proteins are exported to the cytosol, tagged with ubiquitin and destroyed by the proteasome.
- If balance returns, the cell survives; if not, CHOP and BH3-only proteins trigger apoptosis.

## Diseases of protein misfolding

| Disease | Protein | Main effect |
| --- | --- | --- |
| Alpha-1 antitrypsin deficiency | Alpha-1 antitrypsin (Z variant) | ER retention in hepatocytes (liver injury) and lack in lung (emphysema) |
| Cystic fibrosis | CFTR ΔF508 | Misfolded channel degraded; loss of chloride transport |
| Alzheimer disease | Amyloid beta, tau | Aggregates, neuron loss |
| Parkinson disease | Alpha-synuclein | Lewy bodies, loss of dopaminergic neurons |
| Prion disease | Prion protein | Misfolded form converts normal protein; spongiform change |
| Type 2 diabetes | Proinsulin, islet amyloid | Beta-cell ER stress and loss |

## Clinical notes

- Liver disease in alpha-1 antitrypsin deficiency comes from accumulation (toxic gain), lung disease from deficiency (loss of protease inhibition).
- CFTR correctors are drugs designed to help misfolded CFTR fold and reach the membrane.

## Memory aid

A jammed factory first slows the line, hires more helpers and scraps faulty parts; if the jam persists, it closes for good.

## Test yourself

Think of the answer, then tap the question to see it.

## What are the three sensors of the unfolded protein response?

IRE1, PERK and ATF6.

## Why does alpha-1 antitrypsin deficiency damage the liver?

The misfolded Z protein is retained in the hepatocyte ER, causing ER stress, cell injury and eventually cirrhosis.

## How does PERK reduce the protein load in the ER?

It phosphorylates eIF2α, which slows overall translation.

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## Related

- [Apoptosis: the intrinsic and extrinsic pathways](https://durgical.com/en/general-pathology/apoptosis-the-intrinsic-and-extrinsic-pathways/)
- [Autophagy](https://durgical.com/en/general-pathology/autophagy/)
- [Intracellular accumulations: cholesterol, proteins, hyaline, glycogen](https://durgical.com/en/general-pathology/intracellular-accumulations-cholesterol-proteins-hyaline-glycogen/)
- [Mechanisms of cell injury: ATP, mitochondria, calcium, membranes and DNA](https://durgical.com/en/general-pathology/mechanisms-of-cell-injury-atp-mitochondria-calcium-membranes-and-dna/)
- [Cellular aging: telomeres, DNA damage, senescence and proteostasis](https://durgical.com/en/general-pathology/cellular-aging-telomeres-dna-damage-senescence-and-proteostasis/)

## Related conditions

- [Alzheimer disease](https://durgical.com/en/conditions/alzheimer-disease/)
- [α1-antitrypsin deficiency](https://durgical.com/en/conditions/1-antitrypsin-deficiency/)
- [Cystic fibrosis](https://durgical.com/en/conditions/cystic-fibrosis/)
- [Parkinson disease](https://durgical.com/en/conditions/parkinson-disease/)
- [Huntington disease](https://durgical.com/en/conditions/huntington-disease/)
- [Prion diseases (Creutzfeldt–Jakob)](https://durgical.com/en/conditions/prion-diseases/)
- [Type 2 diabetes mellitus](https://durgical.com/en/conditions/type-2-diabetes-mellitus/)
- [Amyloidosis](https://durgical.com/en/conditions/amyloidosis/)

## Elsewhere in DurgiPedia

- [Molecular chaperones and heat shock proteins](https://durgical.com/en/biochemistry/topics/molecular-chaperones-and-heat-shock-proteins/)
- [Protein structure and folding](https://durgical.com/en/biochemistry/topics/protein-structure-and-folding/)
- [Ubiquitin–proteasome system](https://durgical.com/en/biochemistry/topics/ubiquitin-proteasome-system/)
- [Proteasome (26S, β5 subunit)](https://durgical.com/en/biochemistry/enzymes/proteasome/)
- [α1-antitrypsin](https://durgical.com/en/biochemistry/enzymes/1-antitrypsin/)
- [Protein targeting and signal sequences](https://durgical.com/en/biochemistry/topics/protein-targeting-and-signal-sequences/)
- [Organelles: nucleus, ER, Golgi, mitochondria, lysosomes, peroxisomes](https://durgical.com/en/histology/organelles-nucleus-er-golgi-mitochondria-lysosomes-peroxisomes/)

[← All of general pathology](https://durgical.com/en/general-pathology/)

Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Alpha-1 antitrypsin deficiency: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/alpha-1-antitrypsin-deficiency/) (MedlinePlus, US National Library of Medicine, 2024); [Alzheimer Disease](https://www.ncbi.nlm.nih.gov/books/NBK499922/) (StatPearls (NCBI Bookshelf), 2024).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/general-pathology/endoplasmic-reticulum-stress-and-the-unfolded-protein-response/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/endoplasmic-reticulum-stress-and-the-unfolded-protein-response/