Resistance to cell death Flashcards
what affects the net number of cells in the body
balance between cell growth and apoptosis
what enzymes are the key players in apoptosis?
caspases
what does caspaces catalyse?
proteolysis to help breakdown cellular components for disposal
what does defects in apoptosis influence the effectiveness of?
the drugs which exert their effect by inducing apoptosis
external induction of apoptosis
by death factors
internal inducers of apoptosis
physical or chemical insults such as DNA damage or oxidative stress
which two pathways can be activated to cause apoptosis?
extrinsic
intrinsic
caspases work by cleaving where on proteins?
proteolysis at aspartate residues
TF: caspases are central to the intrinsic pathways only
false
central in both
how many mammalian caspases have been identified so far?
13
how are caspases synthesised?
as inactive enzymes called procaspases
how do procaspases get activated
by cleavage at aspartate residues
what are the class of receptors on the cell membrane which are related to apoptosis called?
death receptors
examples of death factors and their ligands
Fas ligand- Fas receptor
tumour necrosis factor ligand - TNF receptor
how is TNF found compared to Fas ligand
TNF is a soluble factor
Fas ligand is bound to the plasma membrane of neighbouring cells
what happens firstly when ligands bind to the death receptor son cells?
the receptor undergoes a conformational change and oligomerize in order to transduce the signal
the conformational change exposes the death domains on the cytoplamsmic tail
this enables intracellular adapter proteins such as FADD and TRADD to bind to their death domains.
where are death domains located on the death receptor?
cytoplasmic tail
when the death domains are exposed which proteins can then bind to these domains?
FADD and TRADD
what does FADD and TRADD stand for
Fas associated death domain protein
TNF Receptor associated death domain protein
what do these FADD and TRADD proteins do when they bind to the death domain on the cytoplasmic tail on the recepot?
transduce the death signal from the receptor to the caspases.
they recruit procaspase 8 which when in close proximity of other procaspase 8 will become activated by self cleavage
how do procaspase 8 become activated once recruited to the death domains by TRADD and FADD?
when they come in close proximity of each other they activate by self cleavage
what is this combination of death ligands, receptor adaptors (FADD and TRADD) and imitator caspases called?
death inducing signalling complex or DISC
once caspase 8 is produced what happens?
they activate other procaspases which are called executioner caspaces
what numbers are the caspases known as executioner caspases?
3,6,7
what does this whole extrinsic pathway result in once caspases 3,6 and 7 are produced by caspase 8 ?
proteolysis of target proteins
target proteins of caspases 3,6 and 7 in the extrinsic pathway?
nuclear lamins cytoskeletal proteins structure kinases enzymes
what do targeting nuclear lamins result in?
nuclear shrinkage
which cytoskeletal proteins get targeted by caspases 3,6 and 7? effect?
actin
allow for cell rearrangement
what triggers the intrinsic pathway?
DNA damage and oxidative stress
which family of proteins are activated in DNA damage and oxidative stress in the intrinsic pathway? where are they located?
bcl-2
outer membrane of the mitochondria
properties of the bcl 2 family? number of members?
25 members
mediates protein protein interactions
forms homodimeric or heterodimeric complexes
anti-apoptotic members of the bcl-2 family share sequence similarity across which domains?
BH1-4
what happens if these antis-apoptotic members of the bcl-2 family (BH1-4) are over expressed
resistance to apoptosis
what family of proteins are Bid, Bim and Bad apart of?
BCL-2
effect of Bid, bim and bad on apoptosis
bid and bim : can induce apoptosis directly
bad: sensitise to activation of apoptotic program when stress signal is present
what does the inter membrane space of mitochondria supply to help apoptosis?
apoptotic mediators
what regulates the release of apoptotic mediators from the mitochondrial inter membrane space? what is this process called?
proapoptotic bcl-2 members
mitochondrial outer membrane permeabilisation
what is mitochondrial outer membrane permeabilisation?
proapoptotic bcl-2 members mediators regulate the release of apoptotic mediators from the mitochondrial inter membrane space
what are the BH3 only proteins in the bcl 2 family??
Bid and Bim and bad
what domains does Bax have?
multi domain
what happens regarding Bid, Bim and Bax once activated by an apoptotic signal?
BH3 only proteins Bid and Bim bind to and activate Bax.
this causes a conformational change in Bax and it translocates from the cytoplasm to the mitochondria and inserts itself into the outer mitochondrial membrane
what happens to Bax when its activated by BH3 only proteins Bid and Bim?
it undergoes conformational change and translocates from the cytoplasm to the mitochondrial outer membrane
what happened once Bax translocates into the outer mitochondrial membrane?
oligomerization of molecules which increases the permeability of the outer membranes by forming chandelles which allows the release of apoptotic mediators
what is XIAP and what does it do in relation to apoptosis?
STOP APOPTOSIS: X chromosome linked inhibitor of apoptotic proteins
binds directly to and inhibits the activity of caspase 3 and 7 (executioner) after they have been processed by binding to their active site.and inhibits caspase 9 by disrupting the active site
besides inhibitors of apoptotic proteins, what else mediates apoptosis? how?
Smac- second mitochondria derived activator
inhibits IAPs
how does p53 effect apoptosis
induces
2 means by which p53 induces apoptosis?
transcription dependent and transcription independent means
how does p53 induce apoptosis by acting as a Transcription factor?
induces expression of genes encoding for death and pro apoptotic members of the bcl-2 family
examples of genes which p53 upregulates when acting as a transcription factor?
Fas receptors Bax and Bak
examples of factors which p53 reduces the expression of when acting as a transcription factor for apoptosis
anti apoptotic factors such as:
bcl-2 and bcl-cl and IAPs
example of how p53 can exert transcription independent regulation of apoptosis
activation of Bax in the cytoplasm and subsequent caspase activation
how can p53 also alter the net functional balance of the bcl-2 family of proteins?
by releasing Bid from sequestration by antiapoptotic proteins such as the Bcl-xL
what is puma and what is it a target of?
p53 unregulated modulator of apoptosis
p53 target essential for apoptosis induced by p53
what does p53 do to puma and what is the results of this (regarding Bcl-xL and Bak)
p53 activates transcription of Puma which then acts to release P53 from bcl-xl in the cytoplasm so that p53 can directly activate Bak
what is essential to the development of cancer regarding apoptosis
inactivation of apoptosis
what can happen to treatment in tumours where apoptosis is not the main mechanism for cell death?
resistance to treatment
how can inactivation of p53 help cancer cells evade cell death?
reduces the overall level of cell death
what happens in cells of epithelial origin which do not primarily undergo apoptosis if p53 is lost?
no change in level of cell death
other pathways induce cell death
2 ways to target caspases for therapy?
- inhibit anti-apoptotic members of the family
3. induce the expression of proapoptotic members of the bcl-2 family
what drug types can be used to target caspases to promote apoptosis ?
IAP inhibitors
Smac peptides
what is a common feature of all IAPs regarding a repeat on amino acids? what can this be targeted by ? what will this achieve
presence of baculovirus IAP repeat on approximately 70 amino acid domains
small molecules to achieve selective activation of caspases
what does ABT737 inhibit?
what is it classed as?
Bcl-2, Bcl-xL and bcl
BH3 mimetic small molecule inhibitors
does ABT737 directly induce apoptosis
no it enhances death signals
