CHMI 4237 E
Special topics in Biochemistry
Stress signaling
Eric R. Gauthier, Ph.D.
Dept. Chemistry-Biochemistry
Laurentian University
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Cell stresses
Hypoxia
Mechanical
Oxidative
Viruses
Chemicals
Nutrient
Radiation
Heat
Osmotic
pressure
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Cellular responses to stress
?
Cell cycle
arrest
Adaptation
Death
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Cellular responses to stress
?
- Metabolic
rewiring
- Differentiation
Cell cycle
arrest
Adaptation
- Plasticity
- Motility
Death
- Defense
- Aging
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Cellular responses to stress
Stress
Adaptation
Example
Oxidative stress
Metabolic rewiring
Increase in NAPHproducing pathways
Hypoxia
Differentiation
Increase in red
blood cells
Increased exercise
Plasticity
Change in muscle
fiber type
Wound
Motility
Wound closure
Foreign RNA
Translation arrest
Viral infection
Food shortage
Lifespan increase
Caloric restriction
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1. Response to nutrient starvation
Food shortage
Cell cycle
Protein synthesis
Alternative food source
OR
Commit suicide
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1. Response to nutrient starvation
 Blocking ATP-vorous processes
http://8e.devbio.com/image.php?id=187
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http://8e.devbio.com/image.php?id=188
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http://8e.devbio.com/image.php?id=188
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eIF2 phosphorylation leads to
translation arrest
http://deverlab.nichd.nih.gov/graphics/fig3a.gif
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GCN2 – linking amino acid
availability with translation
http://deverlab.nichd.nih.gov/sub_rec.htm
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The EMBO Journal Vol. 20 No. 6 pp. 1425-1438, 2001
ATF4 translation is INCREASED
when eIF2 is phosphorylated…
Trends in Endocrinology & Metabolism
Volume 20, Issue 9, November 2009, Pages 436-443
uORF = - upstream open reading frame (i.e. upstream of the ATF4 ORF)
- uORF1 encodes for a 3-amino acid protein
- uORF2 overlaps with the ATF4 ORF but is out of frame.
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ATF4 translation is limited when
amino acids are plentyful
Trends in Endocrinology & Metabolism
Volume 20, Issue 9, November 2009, Pages 436-443
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ATF4 translation is limited when
amino acids are plentyful
Trends in Endocrinology & Metabolism
Volume 20, Issue 9, November 2009, Pages 436-443
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ATF4 gene targets
Trends in Endocrinology & Metabolism
Volume 20, Issue 9, November 2009, Pages 436-443
Transcription
Initiation machinery
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ATF4 gene targets
Function
ASNS
Amino acid
synthesis
SNAT2
CAT-1
Amino acid
transporters
4EBP-1
Translation
arrest
ATF3
CHOP
Transcription
factors
TRB3
AKT inhibitor
Trends in Endocrinology & Metabolism
Volume 20, Issue 9, November 2009, Pages 436-443
Gene
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Molecular Cell, Vol. 18, 141–148, April 15, 2005
GCN2/eIF2 and feeding behavior
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mTOR: the art of sensing nutrients

mTOR:

NATURE REvIEWS | Molecular cell Biology vOlUME 10 | MAy
2009 | 307
◦ Protein serine kinase
◦ Same family as ATM
Inhibited by Rapamycin
◦ Rapamycin: secreted by
Streptomyces hygroscopicus
◦ From Rapa Nui
(aka Easter Island)

Senses:
◦ Glucose
◦ Amino acids
◦ Energy levels

Triggers:
◦ AKT activation
◦ Translation
◦ Proliferation
HEAT repeats: protein interaction domain
FAT domain: domain structure shared by FRAP,
ATM and TRRAP
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mTORC1: targeting translation
Oncogene (2006) 25, 6416–6422
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mTORC1: targeting translation
mTORC1
p70 S6K
S6
ribosomal
protein
NATURE REvIEWS | Molecular cell Biology vOlUME
10 | MAy 2009 | 307
↑ translation
efficiency
eIF4B
↑ eIF4A
helicase
activity
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mTORC1: wide ranging effects
http://www.cellsignal.com/reference/pathway/mTor.html
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mTORC1 regulation


TSC 1/2:

◦ GTPase activating enzyme
 targets Rheb
◦ Mutated in patients with
Tuberous Sclerosis
PRAS40
◦ Binds mTORC and inhibits
it;
◦ Dissociates form mTORC
upon phosphorylation by
AKT
AKT
Rheb:
◦ small G protein
◦ In GTP-bound form:
activates mTOR
PRAS40
mTOR
GbL
Raptor
PO4
PRAS40
mTOR
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NATURE REVIEWS | DRUG DISCOVERY VOLUME 4 | DECEMBER 2005 | 989
GbL
Raptor
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mTORC1 regulation
NATURE REvIEWS | Molecular cell Biology vOlUME 10 | MAy 2009 | 307
http://www.lsi.umich.edu/files/ken_research_fig1.jpg
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Glucose and mTORC1
NATURE REvIEWS | Molecular cell Biology vOlUME 10 | MAy 2009 | 307
http://www.lsi.umich.edu/files/ken_research_fig1.jpg
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When glucose in plenty…
GLUCOSE
Glycogen
Glycolysis
ATP
Acetyl-CoA
Citrate
NADH
ETC
ATP
Energy
reserves
Fatty acids
Cellular
processes
TCA
CO2
ATP
ATP
ADP
ETC
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When glucose in scarce…
GLUCOSE
Glycogen
Glycolysis
ATP
Acetyl-CoA
ATP
Energy
reserves
Citrate
NADH
ETC
Fatty acids
TCA
Glutamine
CO2
ATP
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But, how are glucose levels
sensed?
AMP
ATP
ADP Kinase
ADP
ADP
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But, how are glucose levels
sensed?
AMP
ADP Kinase
ADP
AMPK
ATP
ADP
Adaptation
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AMPK and mTORC1
http://www.cellbiol.net/ste/alpobesity4.php
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http://www.cellsignal.com/reference/pathway/AMPK.html
Other targets of AMPK
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Other targets of AMPK
- carbohydrate metabolism
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Other targets of AMPK
- lipid metabolism
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Other targets of AMPK
- cell cycle
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Other triggers of AMPK
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Other triggers of AMPK
- adrenalin
Adrenalin
http://www.cellbiol.net/ste/alpobesity4.php
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Other triggers of AMPK
- adrenalin
http://www.cellbiol.net/ste/alpobesity4.php
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Other triggers of AMPK
- adrenalin
http://www.cellbiol.net/ste/alpobesity4.php
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Other triggers of AMPK
- Insulin
http://stke.sciencemag.org/content/sigtrans/vol2006/issue346/images/large/34
62006re7F1.jpeg
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Amino acids and mTOR
http://www.efdeportes.com/efd131/leucine-stimulates-mtor-01.jpg
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Amino acids and mTOR
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2677387/pdf/nihms103321.pdf
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Autophagy – cell cannibalism
nature cell biology volume 9 | number 10 | O CTOBER
2007
5 NOVEMBER 2004 VOL 306 SCIENCE
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Autophagy – cell cannibalism
Biochem. J. (2005) 391, 191–202
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Autophagy: autophagosome
formation
Phagophore
Nucleation
Phagophore
Elongation
Autophagosome
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Atg2/18
1
Starvation
Vps
34
2
Membrane
transport?
Atg9
PI3P
18
Atg23/27
Vps34
13
LC3-II
mTOR
1
Atg1/ 13
ULK1 Atg13
Atg10
Atg16
Atg7
Atg3
PtdE
LC3-IIGly
Atg4
LC3-I
Atg12 Atg5
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LC3 – a marker of autophagy
http://www.cellsignal.com/products/4108.html
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Autophagy: fusion with lysosome
Autophagosome
Amino
acids
Atg22
Cathepsins
H+
ATP
H+
Autolysosome
ADP
+ Pi
Lysosome
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Autophagy - modulation
Increasing
autophagy
Inhibiting
autophagy
PI3P
p150
Beclin U
9
V
R
A
C
Lipid
transport?
1
Atg9
Vps
34
Chloroquine
H+
ATP
H+
13
mTOR
3-MA
Vps
34
p150
ADP
+ Pi
Lysosome
1
Rapamycin
13
Beclin
Bcl2
U
V
R
A
C
Bcl2
Bafilomycin A
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