Lecture 16 - Apoptosis Flashcards
1
Q
Three types of cell death
A
- Necrosis (exploding)
- Programmed cell death (suicide)
- Autophagy (organelle cannibalism)
2
Q
Necrosis is induced by
A
Insults to the cell that cannot be repaired:
Injury, infection, cancer, infarction
3
Q
Steps of necrosis (4)
A
- Cells swell, organelle membranes break down and chromatin is digested
- Cells lyse and spill contents into surrounding area
- Hydrolytic enzymes from lysosomes damage other nearby cells
- Leads to inflammation and self perpetuating gangrene
4
Q
Apoptosis is used
A
In the developing nervous system, developing foetus, tadpole frog development, quality control, t and b cells
5
Q
In the developing nervous system, apoptosis is used
A
To reinforce correct neuron connections
6
Q
In the developing foetus, apoptosis is used
A
To form individual digits (from webbing)
7
Q
In the tadpole, apoptosis is used
A
To form legs - cells in the tail die, governed by thyroid hormone
8
Q
Apoptosis is also used as a
A
Quality control - abnormal, non functional or misplaced cells are removed, balance
9
Q
Apoptosis and the immune system
A
T and B cells are trained to apoptose foreign antigens
10
Q
Apoptosis and balance
A
Surplus cells eliminated
11
Q
Steps of apoptosis ‘falling leaves’ (silent) (8)
A
- Cells shrink
- Cytoskeleton collapses
- Golgi fragments
- NE disassembles
- Chromatin hyper condenses and is digested
- Blebbing of the membrane and apoptotic bodies
- Alteration of the cell membrane so it is recognised by macrophages
- Membrane becomes permeable to small molecules
12
Q
How is apoptosis mediated?
A
Specific class of proteases - Cys residue in active site, cleave at Asp
13
Q
Caspases (C-Asp-ases)
A
Proteases in apoptosis
14
Q
Procaspases (inactive caspases) are activated by
A
Cleavage
15
Q
Procaspase cleavage sites are
A
Asp residues themselves
16
Q
When the Procaspase is cleaved
A
The cleaved units reassociate to form a heterotetrameric Caspase with large and small subunits
17
Q
Procaspases are
A
Hetero dimers
18
Q
Caspases are
A
Hetero tetramers
19
Q
Procaspase cleavage is mediated by
A
Initiator caspases (Upstream)
20
Q
The caspase cascade
A
Amplifies the initial signal
21
Q
The initiator caspase
A
Starts the cascade
22
Q
The executioner caspases
A
Amplify the signal
23
Q
What do caspases cleave? (at asp)
A
- Nuclear lamin
2. Cytosolic protein
24
Q
Caspase activity is highly regulated because
A
Unregulated apoptosis could have catastrophic effects for the organism
25
The caspase cascade is
Irreversible
26
Two ways of activating apoptosis
1. Extrinsic cascade
| 2. Intrinsic cascade
27
The Extrinisic cascade contains certain extracellular signalling proteins
TNF (death signal), Fas (death receptor)
28
The death domain
Transmembrane domain where TNF binds to Fas to signal apoptosis
29
Binding of TNF to Fas causes
Clustering of death domains (multimers) in the PM
| Activates apoptosis
30
Caspases associate with the death domain to
Activate the caspase cascade
31
Clustering of the death domains is known as
Lipid raft fusion
32
The death domains are activated by
Conformational change
33
The death domain recruits the
DISC
| Death inducing signalling complex
34
Proteins in the DISC
FADD, TRADD, Caspase 8/10
35
Example of the Extrinsic cascade (4)
Viral infection
1. viral proteins are cleaved and displayed on the surface of cells
2. T killer cells recognise foreign peptide on Fas receptor
3. Fas ligand on T killer cell binds to the Fas receptor
4. Activates the death domain and caspase cascade
36
The Intrinsic Pathway involves
Mitochondria
37
The intrinsic pathway is triggered by
Injury (DNA damage, hypoxia)
38
Initial activators of the intrinsic pathway
Are not known
39
Activation of the apoptotic pathway leads to activation of
Bcl proteins
40
Bcl proteins are either
Pro apoptotic or anti apoptotic
41
Bcl proteins form
Heterodimers in the cytoplasm
42
In the absence of an intrinsic apoptotic signal, Bcl2 proteins
Bind to and inhibit BH123 proteins (pro apoptotic proteins)
43
BH123
Pro apoptotic protein found on the outer mitochondrial membrane
44
BH3 proteins
Pro apoptotic protein that binds Bcl2
45
In the presence of a signal, BH3
Are activated and bind Bcl2
46
Once the Bcl2 protein is bound by BH3,
BH123 becomes active and aggregates, and the mitochondria release cytochrome c
47
What protein is released by the mitochondria that induces apoptosis?
Cytochrome C
48
What protein does Cytochrome c bind to?
Apaf1
| Apoptotic protease activating factor
49
When Cyt c binds to Apaf1
A domain on Apaf is exposed which allows oligomerisation of Apaf into the Apoptosome
50
The Apoptosome structure
Oligomer of 7 Apaf1 proteins with bound Cyt c
| Plus a central procaspase9
51
The procaspase9 in the apoptosome is the
Initiator caspase (activates the executioner caspases)
52
IAPs
Inhibitors of apoptosis
53
IAPs were originally discovered in
```
Insect viruses (baculoviruses)
Also present in most animal cells
```
54
IAPs have a
BIR domain
55
The BIR domain in IAPs binds
Caspases
56
Anti IAPs
Block the IAPs
| Located in the mitochondria
57
To avoid apoptosis, most animal cells require
Continuous signalling from neighbouring cells
58
Survival factors bind
To cell surface receptors
59
How do survival factors suppress apoptosis (3)
1. Stimulating transcription of Bcl2 proteins (anti apop)
2. Phosphorylation (by Akt) of apoptotic proteins
3. Phosphorylation (MAPK pathway) of anti IAPs
60
If a cell is deprived of growth signals, what protein is activated
Jnk
| Stress activated MAP kinase
61
Jnk leads to the transcription of
BIM
| Activates the intrinsic pathway
62
Anoikis is the
State of being without a home
| Cell adhesion dependent apoptosis
63
If cells detach from the ECM
They must be destroyed
64
Why do cells die if they detach from the tissue and the ECM?
Survival signals are mediated through cell-cell contacts (integrins)
Without these intrinsic apoptosis is triggered
65
How is the survive signal mediated?
Directly - FAK and ILK (non receptor Tyr Kinases) maintain intracellular pathways
Indirectly - Integrins cause clustering of cell survival receptors in the PM
66
Akt phosphorylates and inactivates
Bad and caspase9
67
PI3K phosphorylates and inactivates
Bim, leads to its degradation
68
If a cell loses interaction of integrins and ECM
Akt and PI3K pathways are deactivated
| Apoptosis triggered
69
When the Akt and PI3K pathways are deactivated
Caspase9 and BH3 proteins are activated
| Apoptosis triggered
70
The apoptotic extrinsic and intrinsic pathways are
Linked
71
In some cells the intrinsic pathway is recruited by the extrinsic pathway to
Amplify the signalling cascade
72
Caspase8 cleaves
BH3 protein BID into tBID
| tBID binds and inhibits Bcl2
73
tBID inhibits
Bcl2
74
Bid, Bim and Puma
All inihibit Bcl2
Potent activators of apoptosis
Link between cell stimuli and apoptosis
75
Apoptotic blebbing of membrane requires assembly of
Conical actin ring that undergoes MyosinII dependent contraction
76
ROCK is a
Rho kinase that forms the conical actin ring for blebbing
| when cleaved by caspase
77
IF and MTs are cleaved by
Caspases
78
Dismantling and remodelling by caspases allows
Packaging of material into apoptotic bodies
79
The apoptotic bodies are engulfed by
Phagocytes
80
Apoptosis also triggers
Ca2+ release which increases apop events
81
The ER loses it's tubulo-reticular shape and forms
Cortical sheets and vesicles
82
The Golgi fragments when
Caspases cleave Golgins
| Cleaved Golgins further trigger apoptosis
83
Cleaved Golgins
Translocate to mitochondria (GRASP65) or nucleus (GM130)
84
Apoptotic cells fail to maintain
The polarity of phosphatidylserine
| exposes inside to outside
85
Cleavage of Lamin B by caspases allows
Larger than normal proteins into the nucleus to fragment DNA
86
DFF
DNA fragmentation factor
Cleaves DNA between nucleosomes
Inactive heterodimer except during apoptosis
87
DFF is activated by
Caspase3
88
During autophagy, what sequesters cytosol and proteins?
Phagophores containing TM Atg proteins
89
Phagophores fuse to form
Autophagosomes
90
What protein allows the autophagosome to fuse with the lysosome?
LC3 protein
91
Acid proteases are contained in the
Lysosome
92
Excessive and insufficient apoptosis can both
Cause disease
93
Neurodegeneration and Alzheimers disease is an example of
Excessive apoptosis (accumulation of aggregated insoluble protein fibres)
94
Cancer is an example of
Insufficient apoptosis and autophagy
95
An accumulation of faulty proteins (through a lack of autophagy) may trigger
Cancer
96
Bcl2 protein is a common
Lymphocyte cancer in humans
| Over production of Bcl2 inhibits apoptosis
97
Tumour suppressor P53 normally promotes
Apoptosis of DNA damaged cells
98
Loss of P53 causes
Loss of apoptosis and cancer cell multiplication
