The Unfolded Protein Response (UPR) & The Endoplasmic Reticulum Associated Degradation (ERAD) Zsuzsa...
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Transcript of The Unfolded Protein Response (UPR) & The Endoplasmic Reticulum Associated Degradation (ERAD) Zsuzsa...
The Unfolded Protein Response (UPR)& The Endoplasmic Reticulum
Associated Degradation (ERAD)
Zsuzsa Bebok
Department of Cell Biology
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?