The Unfolded Protein Response (UPR)
& The Endoplasmic Reticulum
Associated Degradation (ERAD)
Zsuzsa Bebok
Department of Cell Biology
bebok@uab.edu
Ph: 975-5449
The central role of the ER in secretory and membrane protein synthesis
(1980s: Tom Rapoport: Protein translocation across and integration into membranes)
1988. Lippincott-Schwartz &
Klausner, R. D. Degradation from the
endoplasmic
reticulum
1985. Amy Lee: A Calcium
ionophore induces the
expression of glucoseregulated 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)
UPR
&
ERAD
1991. A. Helenius’s lab: Quality
control in the ER: misfolding of
the VSV G
Sommer, & Jentsch, A protein
translocation defect
linked to ubiquitin conjugation
at ER
1996. J.Brodsky:
Proteasome-dependent
ERAD: an unconventional
route to a familiar fate
1990. R. Kaufman’s and lab: The ER stress response.
Morimoto, R.I.: Protein conformation (misfolding) and ER stress (UPR)
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
Tom A. Rapoport, Nature 450, 663-669 (29 November 2007)
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*)
•Sommer & Jentsch: Sec61
mutation – ubiquitination
•A mammalian ER resident
protease (ER60)
was isolated and proposed to
be the quality-control protease
•Disruption of UBC6 (yeast) –
no degradation
•CFTR degradation by the
proteasome
ERAD
Derlin
AAA
CYTOSOL
VCP
Derlin
Sec61
Sec61
ER
The steps of ERAD
Vembar & Brodsky
Nat 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?
Proteasome dysfunction
Hypoxia
Post-synthetic
modifications
Reactive Species
Saturated fatty
acids
ER
STRESS
Recombinant
proteins
Inflammation
Starvation
Cigarette
smoke
1.
Increase capacity
Membrane
components
Folding
enzymes
Chaperones
High
cholesterol
UPR
ERAD
Protein misfolding
2.
Decrease load
Protein
Synthesis
mRNA
decay
Transcription
The Mammalian UPR
NUCLEUS
UPR target genes
ATF4
ATF6α
XBP1
STRESS
BiP
ER LUMEN
P
ATP
P
ATP
GOLGI
PeIF2α
CYTOSOL
eIF2α
P
P
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?
2.
Decrease load
1.
Increase capacity
Autophagy
Membrane
components
Folding
enzymes
Chaperones
ERAD
Protein
Synthesis
mRNA
decay
Transcription
Acute phase of stress - aspecific
•Help to reduce aggregation
•Improve trafficking
•Reduce toxicity
Reduce toxicity – toxic aggregates
Take home message
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!
Connection of the UPR to
other cellular pathways
Proposed models for UPR-mediated JNK
and NFκ-B activation
(IκB – short half life)
Kezhong Zhang & Randal J. Kaufman
Nature 454, 455-462(24 July 2008)
doi:10.1038/nature07203
ER-stressinduced
acute-phase
response
Inflammatory
cytokines (TNFα)
CREBH
transcription 
Kezhong Zhang & Randal J. Kaufman
Nature 454, 455-462(24 July 2008)
doi:10.1038/nature07203
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?