Download integration from proteins to organs: the physiome project

APOPTOSIS
APOPTOSIS
WHEN DOES APOPTOSIS OCCUR?
Normal development e.g. immune system
WHEN DOES APOPTOSIS OCCUR?
Disease states e.g. Alzheimer’s disease
Amyloid plaques in the brain
TYPES OF CELL DEATH
NECROSIS
APOPTOSIS
TYPES OF CELL DEATH
Morphological
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•
NECROSIS
loss of membrane
integrity
swelling of
cytoplasm &
mitochondria
total cell lysis
no vesicle
formation
disintegration of
organelles
APOPTOSIS
• Membrane blebbing, no loss of
integrity
• Aggregation of chromatin at
nuclear membrane
• Shrinking of cytoplasm &
nuclear condensation
• Fragmentation into smaller
bodies
• Formation of apoptotic bodies
• Mitochondria become leaky
Biochemical
NECROSIS
• Loss of regulation of
ion homeostasis
• No energy
requirement
• Random digestion
of DNA
• Postlytic DNA
fragmentaion
• Tightly regulated
process
APOPTOSIS
• Energy dependent
• Non random DNA
fragmentation
• Prelytic DNA fragmentation
• Activation of caspase cascade
• Release of various factors into
cytoplasm
physiological
NECROSIS
• Affects groups of
cells
• Evoked by non
physiological
disturbances
• Phagocytosis by
adjacent cells
• Significant
inflammatory
response
APOPTOSIS
• Affects individual cells
• Induced by physiological
stimuli
• Phagocytosis by macrophages
• No inflammatory response
Caspases – key executioners of apoptosis
(cysteinyl aspartate specific
proteases)
Highly conserved proteases
14 homolgues
inactive zymogens
Caspases divided into
1) Initiator caspases:
Caspases 2, 8,9,10 or
2) Effector caspases:
caspase 3,6,
Properties of proteases
Irreversible Autocatalytic: triggered by cofactor
binding or inhibitor removal
Proteases can regulate their own
activation
Have protease, will have inhibitor
specificity
Caspase structure
3 domains
1) highly variable
NH2 domain
2) large subunit
(~20kD)
3) small subunit
( ~10kD)
Highly specific
absolute requirement for cleavage after aspartic acid
recognition of at least 4 amino acids NH2 terminals to
the cleavage site
Caspase structure
2 key features:
variable N domain regulates
activation
all domains derived from
proenzyme at cleavage
specific sites
Basic apoptotic machinery
DNA fragmentation,
chromatin condensation,
membrane blebbing,
cell shrinkage &
disassembly into apoptotic bodies
engulfment. 30-60 min
effectors responsible for cellular changes associated with
apoptosis.
Caspases inactivate proteins that protect cells from
apoptosis
How do caspases disassemble a cell?
It slices, it dices
Selective cleavage of specific proteins
eg bcl-2, or CAD/ICAD
e.g. nuclear lamina
eg. Gelsolin
What triggers apoptosis?
• Loss of contact with surroundings
• Irreparable internal damage
• Conflicting signals for cell division
• Specific ‘death ligands’
How are caspases activated?
More than one way to skin a cat
Proteolytic cleavage
activation of downstream, effector caspases
How are caspases activated?
More than one way to skin a cat
Induced proximity
aggregation of multiple procaspase-8 molecules into
close proximity somehow results in cross-activation
How are caspases activated?
More than one way to skin a cat
Holoenzyme formation
Activation of caspase-9 is mediated by means of
conformational change, not proteolysis
The roads to ruin
The nematode C.elegans
The roads to ruin
Mammals
External signals
driven by death receptors (DR)
e.g. CD95 (or Fas/Apo)
Each CD95L trimer binds to 3 CD95
leading to DD clustering.
FADD ( Fas associated death domain/
Mort 1) binds via its own DD
Caspase –8 oligomerisation drives
activation through self cleavage
Caspase –8 then activates downstream
effector caspases like caspase –9 (CED-9
homolog)
Internal signals
BCL-2
apoptosis
TRIGGER
REGULATOR
EXECUTIONER
DNA damage
P53
Apaf-1
Death
Bcl-2 family
Caspases
receptors
Growth factor
withdrawal
Death domain
factor
Cytochrome c
oncogenes