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PROGRAMMED CELL DEATH
Normal white blood cell
Apoptotic white blood cell
During apoptosis (programmed cell death) cells bleb
and eventually break apart without releasing contents.
Why should a cell commit suicide?
!   Apoptosis is needed for proper development
Examples:
–  The resorption of the tadpole tail
–  The formation of the fingers and toes of the fetus
–  The sloughing off of the inner lining of the uterus
–  The formation of the proper connections between neurons in the brain
!   Apoptosis is needed to destroy cells
Examples:
–  Cells infected with viruses
–  Cells of the immune system
–  Cells with DNA damage
–  Cancer cells
Apoptosis is also important in the development of the nervous system
NECROSIS Vs APOPTOSIS
Wilde, 1999
Role of RIP1 and Rip 3
in necroptosis
TRADD
RIP1
RIP1
MAPKs
CYCD
P
RIP1
ACTIVE
P
RIP3
ACTIVE
Caspase
inhibition ROS
Cell CELL
survival
SURVIVAL
NECROPTOSIS
Two lymphocytes
Healthy
Staurosporin-treated HeLa cells
Apoptosis
Apoptosis
Apoptotic
Shrinking of nuclear volume
Fragmentation of DNA
Pyknotic
nuclear
fragments
Apoptotic
cell
Phagocytosis of apoptotic bodies
Fragmentation of Golgi bodies
Phosphorylation of Histone 2B
Apoptosis: Pathways
Extrinsic Pathway
Death
Ligands
Death
Receptors
Intrinsic Pathway
DNA
damage
& p53
Mitochondria/
Cytochrome C
Initiator
Caspase 8
Effector
Caspase 3
Initiator
Caspase 9
PCD
Evolutionary conservation of apoptotic pathways
Apoptosis can be intrinsic (signaled from
within or extrinsic to the cell i.e.
from cell receptors
The intrinsic
apoptotic pathway
The extrinsic
pathway
THE PLAYERS INVOLVED.
BCL-2 family of proteins important in apoptotic pathways
= anti-apoptotic
The structure of many of these proteins has been determined and interactions
between them investigated.
The anti-apoptotic protein, BCL-XL , is inhibited by binding of the pro-apoptotic
BH3 only protein (orange) in the groove between BH1 and BH3
Conformational changes in BCL-2 family members during apoptosis.
BAX undergoes extensive conformational changes during the mitochondrial
translocation process. The protein changes from a soluble cytoplasmic protein in
healthy cells to one that appears to have at least 3 helices inserted in the
mitochondrial membrane in apoptotic cells.
Youle and Strasser (2008) The BCL-2 protein family: opposing activities that mediate cell death. Nature Reviews
Molecular Cell Biology, 9, 47-59
Death receptors
Caspase family, 12-13 members
Two classes:
Initiators
Effectors
All caspases have a similar
domain structure
Not all mammalian caspases
participate in apoptosis.
For example Caspases 1, 4, 5,
and 12 are activated during
innate immune responses and
are involved in the regulation of
the inflammatory reponse
Ligand-induced cell death
The death receptors
FasL
Ligand-induced trimerization
Trail
TNF
Death Domains
Death Effectors
Induced proximity of
Caspase 8
Activation of Caspase
8
3 mechanisms of caspase activation
a. Proteolytic cleavage e.g. procaspase 3
b. Induced proximity, e.g. procaspase 8
c. Oligomerization, e.g. cyt c,
Apaf-1 & caspase 9
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The mitochondrial pathway
DNA
damage
Growth factor
receptors
Fas
Casp8
p53
PI3K
Bid
Bid
Bax
Bid
Bax
Akt
casp3
BAD
Bcl2
casp9
Apaf1ATP
Cyt.C
IAPs
casp3
Smac/
DIABLO
H2O2
AIF
Pollack etal., 2001
Transcriptional
c-Myc
regul.
Ubiquitin ligase
FBW7
Ubiq
MCl1
Release
from MOM
Displace
s NOXA
Mcl-1
NOXA
BIM
PUMA
De-ubiquitinases
Promotes deubiq.
p53
Upregulates
NOXA
USP9X
Mule
Apoptosis: regulation of the levels of the antiapoptotic protein Mcl-1.
GFP = Green Fluorescent protein
Control
UV-treated to induce
apoptosis
Heptamer ( 7 chains)
The blue helices in the
middle bind and activate
procaspase 9 to caspase 9
Caspase 9 activates
procaspases 3, 6 and 7
Weinberg Fig 9.28 The APOPTOSOME is assembled in the cytoplasm when
cytochrome c is released from the mitochondria and binds to Apaf-1
APOPTOSIS
SURVIVAL
P53 & Apoptosis
p53 first arrests cell growth between G1 → S
This allows for DNA repair during delay
If the damage is too extensive then p53
induces gene activation leading to
apoptosis (programmed cell death)
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JNK