2.11: Programmed Cell Death Flashcards
why is programmed cell death an essential part of normal development
cleanly removing excess, old, damaged, abnormal, or malfunctioning cells
(embryonic development, metamorphosis, immune system function)
p__ can activate cell death
p53
differentiate between apoptosis vs necrosis
apoptosis: highly regulated, reproducible programmed cell death; carefully dismantles the cell and signals for its removal by engulfment
necrosis: accidental, uncontrolled cell death and can cause inflammation
explain how inflammation occurs
as apoptosis carefully dismantles the cell and signals for its removal by engulfment. the innards goes out and neighboring cells know this is wrong = inflammation
list the changes that happen during apoptosis:
- cell shape changes and shrinkage
- cytoskeleton disassembly
- decreased cell adhesion
- dna fragmentation
- surface lipid changes
- cell removal by engulfment
state the signal for engulment
surface lipid changes
____________ trigger apoptosis and have specific targets
caspase proteases
caspases are synthesized as __________, signals initiate caspase cleavage to form active ______________
inactive procaspases, caspase dimers
how are caspase cascades created and examples
some caspases can cleave and activate other caspases to create an amplified caspase cascade.
ex: active initiator caspases can cleave and activate executioner caspases = cascade and one initiator can cleave many executioners amplifying the signal = cascade
t/f caspases cleave specific target proteins to trigger apoptosis
true
________ caspases activate _________ caspases
initiator caspases activate executioner caspases
which caspases are initiator and which are executioner
initiator: caspase 8 and 9
executioner: caspase 3, 6, 7
how are initiator caspases formed
they are cleaved and activated in response to apoptotic signals
how are executioner caspases formed
active initiator caspases can cleave and activate executioner caspases creating a caspase cascade
t/f one initiator caspase can cleave many executioners
true
executioner/initiator caspases cleave target proteins in the cell to initiate apoptosis
executioner
caspases mediate key changes during apoptosis, state the caspase targets for the following phenotypic changes during apoptosis:
1. cell shape changes and shrinkage
2. dna fragmentation
3. cytoskeleton disassembly
4. surface lipid changes
- cell shape changes and shrinkage: cell-cell adhesion proteins
- dna fragmentation: breakdown of nuclear lamins, activation of dna endonucleases
- cytoskeleton disassembly: alter actin regulating proteins
- surface lipid changes: lipid distribution proteins: flippase inactivation and scramblase activation
explain how executioner caspases indirectly cause DNA breakdown
inactive CAD is bound to iCAD (i stands for inhibitor) and an active executioner caspase (eg 3) comes and cleaves iCAD = activate cad to cause dna cleavage of dna between nucleosomes
describe how caspase 3 causes cleavage of dna between nucleosome
caspase 3 cleaves off iCAD from CAD to allow CAD to do the cleave
executioner caspases alter cell surface lipid composition, compare and contrast between health cells and when apoptotic cells fail to maintain this balance
Healthy cells:
- Have a specific lipid makeup at the cell surface
- Flippases move lipids from one side to the other (ec to cytosol) to maintain this distribution
Apoptotic cells fail to maintain this balance:
- Caspase cleaves flippase to inactivate it
- Caspase activates scramblase (random flipping) to move more lipids to the outer layer
t/f apoptosis can be triggered by extrinsic or intrinsic pathways
true - Both pathways activate executioner caspases & caspase cascade
describe the extrinsic pathway of apoptosis
Extrinsic pathway: depends on cell surface receptors binding to an extracellular signal molecule to activate executioner caspases
describe how apoptosis can be triggered by intrinsic pathways
Intrinsic pathway: depends on intracellular receptors (depends on cytochrome C release) to activate executioner caspases
provide an example of outside signal triggering intrinsic apoptosis
uv light
Fas ligand functions as a monomer, dimer or trimer
trimer
which caspase has a death effector domain (DED)
*actually has two of them
caspase 8
which protein has both a death effector domain and death domain
FADD adaptor protein
which domains do FADD adaptor proteins have
death effector domain and death domain
Fas death receptor at the plasma membrane has which domain
death domain
death domains can be found where, death effector domains can be found where
death domains: FADD adaptor proteins, Fas death receptor
death effector domain: FADD adaptor protein, caspase 8
killer lymphocytes express cell surface _____ ligands that bind to ?
cell surface fas ligands that bind to fas death receptor on the target cell pm
which apoptosis pathway is activated by cell surface receptors
extrinsic pathway
describe how the extrinsic apoptosis pathway is activated by cell surface receptors
- the fas ligand on the killer lymphocyte plasma membrane comes and binds to the fas death receptor on target cell pm
- fas receptor activation, DISC (death inducing signaling complex) assembly, caspase 8 activation by dimerization
- Fas death receptor with exposed death domains, exposed DEDs on caspase 8 and FADD
- caspase 8 filaments do criss cross (cross cleavage), subunit rearrangement, release of mature activated caspase 8 dimers into cytosol
- on the DISC you can release prodomains and activate new caspases - there is activation by cleavage of executioner caspases 3 & 7 leading to apoptosis of the target cell
- release of killer lymphocyte
what is the active form of caspase 8; mono, dimer, trimer
dimer
______ receptors help healthy cells stay alive
decoy receptors
what do decoy receptors lack
the ic death domain
what is the point of decoy receptors
evade extrinsic apoptosis pathway signals
what happens when Fas ligand binds a decoy receptor
no DISC assembles so apoptosis not triggered
the intrinsic apoptosis pathway depends on ______ and _______
apaf1 and cytochrome C
what are the functions of cyt C and apaf1
cytochrome C binds to Apaf1, this exposes the CARD domain (on apaf1) and oligomerization domain on Apaf1
which protein is the CARD domain apart of
apaf1
explain the intrinsic apoptosis pathway that is activated by cyt c release
- the apoptotic stimulus causes cyt c release from the intermembrane space of the mitochondrion
- the inactive apaf1 protein comes and when cyt c + dATP bind to apaf 1 it activates it
- active apaf1 has bound dATP, exposed oligomerization domain, exposed CARD
- oligomerization of apaf1 causes pinwheel structure
- recruitment of caspase 9 monomers to form apoptosome and caspase 9 activation by dimerization (the inactive caspase 9 has unexposed CARD) == apoptosome’
- apoptosome causes cleavage and activation of executioner caspases by activated caspase 9 dimers
where in the mitochondrion are cyt c usually at
intermembrane space
how are caspase 9s activated
dimerization
What will happen in cells containing a mutant Apaf1 that lacks a CARD
domain?
a) Apaf1 will bind to cytochrome c released from mitochondria, but will not
associate with Caspase-9.
b) Apoptosome formation will be unaffected, and cell death will occur
because of cytochrome c loss.
c) Cytochrome c release from mitochondria will be prevented.
d) Apaf1 will not bind to cytochrome c.
A. the pinwheel won’t form
B is wrong bc apoptosome won’t form. C is wrong be it still happens
how are cyt c able to pass through mitochondrial outer membrane
- Cyt c cannot usually pass through the
mitochondrial outer membrane - Apoptotic stimuli trigger Bak & Bax
proteins to form a channel in the outer
mitochondrial membrane
what channels promote MOMP (mitochondrial outer membrane permeabilization)
Bak and Bax
t/f only cyt c can leave the mitochondrial intermembrane after bak and bax channel formed
false, other proteins can also exit
how can other Bcl2 family proteins inhibit MOMP
- Bcl2 family members Bcl2 & BclxL are similar to Bak & Bax
- These can can bind to Bak/Bax and prevent them from forming channels (ie BclxL blocks oligomerization of activated Bak)
- So, Bcl2 & BclxL block MOMP and are anti-apoptotic proteins
list the antiapoptotic bcl2 family proteins
Bcl2, BclxL, Mcl1
list the pro-apoptotic Bcl2 family effectors
bak, bax
list the pro-apoptotic BH3 only proteins
Bad, Bim, Bid, Puma, Noxa
after an apoptotic stimulus, Bak becomes activated and exposes what domain
BH3 domain
what happens if you have too much antiapoptotic bcl2 family proteins
makes cells hard to kill = cancer
describe how Bcl2 family proteins can promote MOMP
- Bad is another Bcl2 family - binds to Bcl2 & BclxL: liberates the activated Bak that the BclxL prevented the oligomerization of
- Bad promotes MOMP and is an
pro-apoptotic protein
t/f IAPs block apoptosis
true, they stand for inhibitors of apoptosis
IAPs block apoptosis from accidentally occurring, provide an example
XIAP can directly block initiator and executioner caspases (eg caspase 9, caspase 3 and 7) = XIAP is an antiapoptotic protein
anti-iaps are pro/anti apoptotic
pro
describe how MOMP releases anti-IAP proteins
- Anti-IAP proteins are usually in the
mitochondrial intermembrane space - Anti-IAPs are released with Cyt c when
MOPM is triggered - Anti-IAPs inhibit XIAP, allowing the caspase
cascade to trigger apoptosis
many cells will undergo apoptosis if they are not continually supplied with _______________
survival factors
what will happen to cells that leave their correct environment
no longer be protected by survival factors
limited availability of ___________ can regulate cell numbers
survival factors
distinguish between how survival factors can activate anti-apoptotic proteins and how they can inactivate pro-apoptotic proteins
Survival factors can activate anti-apoptotic proteins
- Survival factor initiates a signaling cascade
- Bcl2 transcription increases
- Bcl2/BclxL block Bak/Bax from forming a channel in the mitochondrial outer membrane
- MOMP is blocked, apoptosis does not proceed
Survival factors can inactivate pro-apoptotic proteins
- Survival factor initiates a signaling cascade
- Akt kinase is activated and phosphorylates Bad
- Phosphorylated Bad is inactive so Bad cannot
inhibit Bcl2 & BclxL
- Bcl2/BclxL block MOMP, apoptosis does not proceed
does Bcl2 transcription increase or decrease when survival factors are activating anti-apoptotic proteins
increase
what enzyme is activated when survival factors can inactivate pro-apoptotic proteins
Akt Kinase
what does Akt kinase do
phosphorylates Bad during the inactivation of pro-apoptotic proteins mechanism by survival factors
is phosphorylated Bad active or inactive
inactive
explain how inappropriate cell death can lead to disease
- cancer cells display properties that should mark them for apoptosis, including: changes to cell adhesion, DNA damage, survival outside their usual environment
- To grow and proliferate, cancer cells must escape apoptosis
Which of the following would increase apoptosis?
a) Overexpression of a decoy FAS receptor.
b) Reduced cytosolic concentration of IAPs.
c) Increased Bad phosphorylation.
d) Increased Akt kinase activity.
B.
A the decay helps you live. C it inactivate pro-apoptosis. Akt kinase phosphorylates bad rendering it inactive
