5-6, Apoptosis Flashcards
Default pathway ?
Apoptosis (cells require signals for cell survival, e.g. from cell-cell contact)
Why apoptosis is important (4)
- In development (sculpting structures)
- Immune system shaping
- Deleting damaged cells
- Eliminating misplaced cells
Morphological hallmarks of apoptosis (4)
- Blebbing
- Pyknosis
- Nuclear fragmentation
- DNA Fragmentation
Intrinsic apoptosis
- activation of caspases
- due to permeabilisation of mitochondria,
- release of Cyt C (regulated by Bcl-2 fam)
- and formation of apoptosome
Extrinsic apoptosis
- ligand activated death receptors form trimeric complexes,
- = formation of DISC
- = activation of caspase 8
Apoptotic blebbing
side scatter in flow cytometry shows granularity,
blebbing makes cell more granular
Pyknosis
condensing of nucleus
DNA fragmentation
Junctions between nucleosomes chopped off
Bax
Form pores in mitochondria, inducing apoptosis
Lamins
Maintain the structural integrity of the nuclear envelope
- are cleaved by caspases (during caspase-mediated apoptosis)
I/CAD
(caspases cleave I/CAD, releasing activated CAD)
activated by caspases,
CAD causes DNA fragmentation and chromatin condensation
tBID
Type II intrinsic pathway (links extrinsic and intrinsic pathways)
Core (protease) of apoptotic pathways
Caspases
How are caspases activated
proteolytic cleavage of procaspases
(small + large subunits come together = (heterotetramer) ACTIVE caspase)
whats the feedback amplification loop that ensures cell death will occur ?
effector caspases continue cleaving initiator caspases (activating them)
Fas (ligand) binding Fas receptor triggers what complex ?
DISC (death inducing signal complex)
what does DISC do? activates something …
(extrinsic)
= caspase 8 activation
(pro-caspases binding FADD, binding Fas receptor - DISC
pro-caspases are in close proximity in the DISC complex and can cleave each other
–> releasing active caspase
what does the apoptosome do? activates …
(intrinsic)
= caspase 9 activation
(it binds the apoptosome wheel)
Cas 9 -> activates Cas cascade (Cas 3, 6 & 7) – cut substrates + kill cell
Cyt C released from what
(through holes in) Mitochondria
How does Cty C form apoptosome
Cyt C bind APAF-1,
= conformational change
= CARD domain exposed
= CARD domains create wheel structure, that Cas 9 can bind to
the apoptosome is the platform needed for proximity activation in the intrinsic pathway
point of no return in apoptosis
loss of MMP
no. of mitochondria in a cell
100-1000’s
Key event in initiation of apoptosis
release of mitochondrial contents to cytoplasm
- Cytochrome C
- Calcium
Bax induces apoptosis through …
forming holes in the mitochondria
(tubes formed by BH3 proteins)
Fine tuners
BH3 domain-only proteins
too many pro-survival (Bcl-2) signals cause …
cancer
too many pro-apoptotic (Bax) signals cause …
cell death
Bcl-2 family role …
bind to Bax family + restrain them
BID and BIM activate …
BAX and BAK
BCL-2 and BCL-xL sequester (isolate)…
BAX, BAM, BID AND BIM
for activation of mitochondrial membrane permeabilisation what 2 event must occur …
- All Bcl-2 family pro-survival members must be inhibited
- BAX and BAK are activated by activator BH3-only proteins
if no growth signals are received from outside how is apoptosis induced …
Fine tuners bind to Bax and Bak - opening them
exposing their BH3 helix (temporarily)
(if enough Bax/Bak proteins clustering, can form pores in membrane = apoptosis)
deletion of pro-apoptotic genes (Bim)
cancer like results,
lumen full (similar to carcinoma in-situ)
deletion of pro-apoptotic (Bim) and anti-apoptotic (Bcl-2) genes …
cells are rescued (as Bim and Bcl-2 are involved int eh same stress pathway - bind each other)
deletion of anti-apoptotic Bcl-2 genes …
lots of cell death
types of diseases associated with increased (dysregulated) apoptosis (5)
- developmental disorders
- viral infections (AIDs)
- Neurological disorders (parkinsons)
- acute neurological damage
- cardiovascular disease
types of diseases associated with decreased (dysregulated) apoptosis (3)
- developmental disorders
- autoimmunity
- cancer (chronic lymphocytic leukemia)
why we want to treat cancer through cell death by apoptosis ? …
other cell death mechanisms cause inflammation and can make cancer worse
more difficult to control
how cancer cells use plasticity to evade chemo
EMT (epithelial-mesenchymal transition)
alterations of genes in apoptotic pathways that cause cancer (2)
- indirect (reduction of Bax)
- direct (less/no critical caspases)
how are normal cells tipped for survival
more Bcl-2 than Bax
chemotherapeutic agent binds Bcl-2 e.g. …
ABT-199 (mimics BH3)
ABT-199 does what …
replaces Bim and Puma, binding Bcl-2, causes apoptosis
allows free active Bax
