The Unfolded Protein Response (UPR)& The Endoplasmic Reticulum

Associated Degradation (ERAD)

Zsuzsa Bebok

Department of Cell Biology

bebok@uab.edu

Ph: 975-5449

1985. Amy Lee: A Calcium ionophore induces the expression of glucose-

regulated genes (GRP78).

1986. John Kearney’s lab : Posttranslational

association of Ig(h) chain binding protein (BiP) with nascent heavy chains in

hybridomas.

1988. Hendershot, L. M.Ting, J.Lee, A. S. Identity

(BiP) with (GRP78)

1990. R. Kaufman’s and lab: The ER stress response.Morimoto, R.I.: Protein conformation (misfolding) and ER stress (UPR)

1996. J.Brodsky: Proteasome-dependent

ERAD: an unconventional route to a familiar fate

UPR&

ERAD

1991. A. Helenius’s lab: Quality control in the ER: misfolding of

the VSV G

1988. Lippincott-Schwartz & Klausner, R. D. Degradation from

the endoplasmicreticulum

The central role of the ER in secretory and membrane protein synthesis(1980s: Tom Rapoport: Protein translocation across and integration into membranes)

Sommer, & Jentsch, A protein translocation defect

linked to ubiquitin conjugation at ER

Tom A. Rapoport, Nature 450, 663-669 (29 November 2007)

How can proteins cross and integrate into the ER membrane?

Tom A. Rapoport, Nature 450, 663-669 (29 November 2007)

Protein translocation across the eukaryotic endoplasmic reticulum membrane

U-turn in the ER – What happens to unwanted or damaged proteins?

• Klausner et al: T-cell receptor complex– non-stoichiometric synthesis of components– forward trafficking of assembled receptors only– Isolated α and μ subunits degraded in non-lysosomal compartments

ER protease Retrotranslocation

•A yeast vacuolar protease carboxypeptidase Y (Cpy*)

•A mammalian ER resident protease (ER60)was isolated and proposed to be the quality-control protease

•Sommer & Jentsch: Sec61 mutation – ubiquitination

•Disruption of UBC6 (yeast) – no degradation

•CFTR degradation by the proteasome

ERAD

Der

lin

Derlin

VCP

AAA

Se

c61S

ec6

1

CYTOSOL

ER

The steps of ERAD

Vembar & BrodskyNat Rev Mol Cell Biol. 2008 December; 9(12): 944–957.

N-linked glycosylation and the degradation of glycosylated proteins

Hydrophobic patches: is being 'oily' sufficient for ERAD?

What happens to to proteins with large cytosolic domains?

Damaged proteins are tagged The ubiquitylation process

What happens when the function of the ER is disturbed?

“perturbation of ER function”

STRESS

What is ER stress?

ERADmRNAdecay

Protein Synthesis

TranscriptionFolding enzymes

Membrane components

Chaperones

2.Decrease load

1.Increase capacity UPR

Recombinant proteins

Hypoxia

Reactive Species

Starvation

ER STRESS

Protein misfolding

Saturated fatty acids

Post-synthetic modifications

Proteasome dysfunction

Cigarette smoke

High cholesterol

Inflammation

ATF6α

UPR target genes

ATF6

IRE1α

PERK

PATP

P

ATP

P

S2P

P

BiP

eIF2αeIF2αP

NUCLEUS

ER LUMEN

CYTOSOL

GOLGI

STRESS

AT

F4

sXBP1mRNA

The Mammalian UPR

XBP1ATF4

ATP

ATP

The adaptive and apoptotic pathways of the UPR

Micro-RNAs????

Adaptation to stress – chronic stress

• Genetic– Insulin secreting β-cells are very sensitive to genetic defects

in PERK, ATF6, Wolframin (Wolfram Syndrome)– Akita mouse – Insulin2 gene mutation prevents oxidative

insulin folding – UPR - diabetes

• Environmental– High cholesterol, alcohol, cigarette smoke…

• Pathogenic– Hepatitis C virus – latent infection and carcinogenesis

• Developmental– B cell development – antibody secretion by plasma cells

Diseases associated with ER stress

• Obesity (leptin signaling)• Type I diabetes (insulin production)• Type II diabetes (insulin receptor signaling)• Necrotizing enterocolitis (?)• Neurological diseases (Alzheimer, Parkinson’s)• Psychiatric disorders (?)• Airway diseases (COPD, asthma, chronic bronchitis..)

The pathomechanism of these diseases varies

Can we modulate the UPR?

ERADmRNAdecay

Protein Synthesis

TranscriptionFolding enzymes

Membrane components

Chaperones

2.Decrease load

1.Increase capacity

•Help to reduce aggregation•Improve trafficking•Reduce toxicity

Reduce toxicity – toxic aggregates

Autophagy

Acute phase of stress - aspecific

You can run from the UPR – ERAD, autophagy

You can hide from ERAD – modulate the UPR and enhance protein folding and rescue proteins

from ERAD

At the end they are still going to get you!

Take home message

Connection of the UPR to other cellular pathways

Proposed models for UPR-mediated JNK and NFκ-B activation

Kezhong Zhang & Randal J. KaufmanNature 454, 455-462(24 July 2008)doi:10.1038/nature07203

(IκB – short half life)

ER-stress-induced

acute-phase response

Kezhong Zhang & Randal J. KaufmanNature 454, 455-462(24 July 2008)doi:10.1038/nature07203

Inflammatory cytokines (TNFα)

CREBH transcription

Questions

• A disease is caused by the misfolding and very efficient ERAD of a membrane protein.– How would you modulate ERAD?

• A disease is caused by the formation of toxic protein aggregates that activate the UPR and apoptosis

– How would you modulate the UPR and ERAD?