Chapter 16 Flashcards
The process of eliminating unwanted cells during embryogenesis, metamorphosis, and tissue turnover
programmed cell death
Programmed cell death is the process of eliminating unwanted cells during what 3 events?
embryogenesis, metamorphosis, and tissue turnover
Paw that has an interdigital web
embryonic mouse paw
Paw that has no interdigital web removed
mature mouse paw
Cell death
apoptosis
What are the cell structure changes that accompany apoptosis?
a. compaction, blebbing of the plasma membrane
b. fragmentation of the nucleus and cell
c. condensing of the chromatin
What happens to DNA during apoptosis?
fragmented into a ladder
Apoptosis does not have what response?
no inflammatory response
Apoptosis can be triggered by (6)
a. DNA damage
b. heat or cold shock
c. targeting by cytotoxic lymphocytes
d. various drugs
e. withdrawal of essential growth factors
f. other stressed
Apoptosis is important for removing what?
tumorigenic cells
What tumor suppressor can trigger apoptosis?
p53
Cells that die via ____ swell, burst open, invoke an inflammatory response, and do not display chromatin condensation?
necrosis
Necrosis is cell death after
injury
apoptosis is what cell death
programmed cell death
3 steps of necrosis
- cell swells
- cell bursts
- inflammatory response
3 steps of apoptosis
- nucleus fragments
- cell fragments
- engulfment of fragments: no inflammatory response
Caspases
cysteine aspartate-specific protease
Caspases are available initially as
symogens
How are zygomens activate?
must be proteolytically cleaved
What are the 3 main types of caspases?
a. executioner
b. initiator
c. inflammatory
2 executioner caspases
caspase-3 and caspase-7
What are responsible for cleaving many proteins to effect apoptosis?
executioner caspases
Executioner caspases are responsible for cleaving many proteins at where?
recognition sites of 4 aa residues with couple of AA residues
3 example substrates for executioner caspases
a. CAD
b. ROCK-1
c. Gelsolin
CAD
caspase-dependent DNase
What is CAD responsible for what during apoptosis?
DNA fragmentation
CAD exists as a complex with what?
an inhibitor iCAD
iCAD is cleaved by
an executioner caspase
When iCAD is cleaved by an executioner caspase, CAD is active and digests ____ resulting in?
DNA between the nucleosomes; ladder of DNA fragments
What is a myosin-light chain kinase?
ROCK-1
How is ROCK-1 activated?
by cleaving with an executioner caspase
How is Gelsolin activated?
cleaved and activated by an executioner caspase
Why is gelsolin named gelsolin?
because it helps regulate actin by turning the gel of cross-linked actin into a sol
Role of gelsolin
role in the formation of these podosomes
What 2 affect changes in the cytoskeleton, initiating the blebbing associated with apoptosis?
ROCK-1 and gelsolin
Zymogen forms of executioner caspases are known as?
procaspases
How are procaspases activated?
by clasave at an Asp
Activation of procaspases brings _____ region into proximity with the _____ region
substrate-binding; catalytic cys-his-dimer
What is one protease that can catalytically activate executioner caspase?
Granzyme B
Granazyme B is in the granules of cytotoxic lymphocytes, both __ and ____.
cytotxic T cell (Tc); natural killer (NK) cells
When is granzyme B released from the granules?
when the cytotoxic cell targets another cell, enters the target cell, and activates executioner caspases to cause apoptosis
What cleaves and activates caspase-6?
caspases-3 and -7
What cleaves and activates the executioner caspases?
initiator caspases
What known initiator caspases in mammals preexist as inactive monomers?
initiator caspases-2, -8, -9, and -10
Mechanism of activation of initiator caspases is known as
induced proximity
What is the mechanism for induced proximity?
initiator caspases are activated upon dimerization and activated dimer cleaves and activates executioner procaspases
Initiator caspases contain large prodomains with protein-protein interaction motifs known as?
death folds
Death folds interact with ____ to ____ them or their partner in a dimer) in what manner?
adaptor proteins; activate; like-like manner
What are 4 examples of death folds?
a. DEDs
b. CARDs
c. DD
d. PYR
DEDs
death effector domains
CARDs
caspase recruitment domains
DD
death domains
PYR
pyrin domains
IAPs
inhibitors of apoptosis proteins
XIAP
X-linked IAP
XIAP inhibits what?
initiator caspase-9
executioner caspases -3 and -7
2 IAP domains
BIR
RING finger domain
BIR
Baculovirus IAP repeats
If an IAP has RING finger domain, it functions as what?
Ub-3-ligase
What is the first caspase identified?
caspase-1
Caspase-1 is required for what?
processing/secretion of cytokine IL-1beta (interleukin-1beta)
Caspase-1 is also known as?
ICE (IL-1beta converting enzyme)
ICE
interleukin-1beta converting enzyme
Caspase-1 requires ___ to activate it
caspase-5 + 1 adaptors
What are the 2 apoptotic pathways?
a. death receptor pathway
b. mitochondrial pathway
Which pathway is extrinsic?
death receptor pathway
Which pathways is intrinsic?
mitochondrial pathway
Both death receptor and mitochondrial pathway converge to activate what 2?
a. initiator caspases
b. executioner caspases
Initiator caspases activate via?
induced proximity
There is ____ between death receptor and mitochondrial pathway
cross-talk
TNFR
tumor necrosis factor receptor
TNFR includes
death receptors (DR) which are trimeric
What are 3 examples of death receptors?
a. TNFR 1
b. Fas
c. TRAIL receptor
Death receptors share what?
death domain (DD)
4 Examples of death folds
a. DD
b. CARD
c. DED
d. PYR
Death domain in a death receptor interacts with ____
death domains in adaptor molecules
DR trimers are cross-linked by?
ligand binding
Death domains of Fas and TRAIL receptors bind to ____ via ____.
adaptor protein FADD (Fas-associated DD); DDs
FADD
Fas-associated DD
FADD has
DEDs
DEDs of FADD bind to DEDs in what?
prodomain of caspase-8 monomers
Proaspase-8 monomers form what?
dimers
What causes activation of initiator caspases?
induced proximity
DISC
death-inducing signaling complex
DISC is made of
DR, FADD, and caspase-8 complex
DISC activates what 3 that leads to apoptosis?
executioner caspases-3, -6, and -7
TNFR1 activates a pathway to lead to activation of what?
executioner caspase
TNFR1 can bind to what?
TRAFs (TNF receptor associated factors)
TRAFs
TNF receptor associated factor
TRAFs can activate which transcription factor?
NF-kB (nuclear factor-kB)
NF-kB
nuclear factor-kB
Some proteins expressed by NF-kB prevents what?
DISC formation and caspase-8 activation
Expression of NF-kB leads to _____ instead of _____.
inflammation; apoptosis
Most forms of vertebrate apoptosis are triggered via ____.
mitochondrial pathway
MOMP
mitochondrial outer membrane permeability
What is one of the soluble proteins from the intermembrane space released into the cytosol?
holocytochrome c
Role of holocytochrome c in mitochondria
transfers electrons from complex III to complex IV in ETS
Role of holocytochrome c in the cytosol
helps activate caspases
What domains do Bcl-2 family proteins share?
up to four Bcl-2 homology (BH) domains
BH domain
Bcl-2 homology domain
3 subfamilies of Bcl-2 proteins
a. anti-apoptotic
b. pro-apoptotic ‘multi-domain’
c. pro-apoptotoic BH2-only proteins
Anti-apoptotic subfamily of Bcl-2 proteins possess
BH1-3 and BH-4
Function of Anti-apopototic
prevents MOMP
Examples of Anti-apoptotic subfamily
Bcl-2
Bcl-xL
Pro-apoptotic ‘multi-domain’ subfamily of Bcl-2 proteins possess
BH1-3
Examples of pro-apoptotic ‘multi-domain’
Bax
Bak
Examples of pro-apototic BH3-only proteins
Bid
Bim
Bax and Bak are responsible for?
MOMP
What proteins form the pores through which proteins escape the mitochondrial and enter the cytosol?
Bax and Bak
Bax or Bak are induced to oligomerize in the mitochondrial membrane in the presence of what?
pro-apoptotic BH3-only proteins like Bid
Bax-Bak DKO cells
double-knock-out
lack both of these proteins
What happens to Bax-Bak DKO cells when deprived of growth factors?
do not undergo apoptosis but rather undergo autophagy
What does autophagy mean?
self-eating
Bax-Bak DKO cells sustain themselves by?
catabolizing intracellular components
How do normal cells use Bax-Bak?
to engage the mitochondrial pathway of apoptosis when deprived of growth factors
Anti-apoptotic members of the Bcl-2 family act by binding to ___ to prevent their function
activator proteins or active forms of Bax and Bak
Anti-apoptotic members of the Bcl-2 family binding to activator proteins or active forms of Bax and Bak result in
preventing MOMP and apoptosis
Other members of the BH3-only subfamily promote apoptosis by
blocking the function of antiapoptotic Bcl-2 family members
BH3-only subfamily are what?
stress sensors
BH3-only subfamily act as
de-repressors/sensitizers
BH3-only subfamily regulated at levels of_____, ____, ____, and ____
transcription; protein stabilization; protein-protein interactions; modifications
MOMP leads to release of ____ in cytosol
holocytochrome c
holocytochrome c in cytosol binds to what?
APAF-1
APAF-1
apoptotic protein activating factor-1
How does APAF-1 expose an oligomerization domain?
APAF-1 undergoes a conformation change, binds to dATP, and undergoes a second conformation change
Exposing of oligomerization domain by APAF-1 leads to what complex?
7 APAF-1 complex = apoptosome
Apoptosome has exposed ____ in the center
CARD domains
CARD domains of apoptosome binds to what?
CARD domains of an initiator caspase-9
Active initiator caspase-9 activates what?
executioner caspase-3 and -7
Activation of executioner caspase-3 and -7 leads to what?
apoptosis
What is translated in cytosol and imported into the mitochondrion?
apocytochrome c
What activates APAF-1 and what does not?
holocytochrome c activates APAF-1 but apocytochrome does not activate APAF-1
What interfere with caspase activation?
IAPs
XIAP function (2)
a. inhibits inhibitor caspase-9 on the apoptosome
b. binds and inhibits executioner capsase-3 and -7
Smac is known as
DIABLO
What proteins are released from mitochondria upon MOMP?
smac and omi
Function of smac and omi
antagonize XIAP to allow caspase activation
What is the N-terminus of smac and omi?
AVPI motif
Function of AVPI motif
inhibits XIAP
How is AVPI motif generated?
after removal of the mito-targeting sequence upon translocation of the protein into the mitochondrial membrane space after they were translated in the cytosol
Death receptor pathway activates
initiator caspase-8
Initiator caspase-8 cleave and activate what 3?
executioner caspase-3 and -7, and Bid
Cleaving and activating of Bid by initiator caspase-8 cause what?
MOMP and apoptosis via the mitochondrial pathway
What 2 other protease can cleave and activate Bid?
cathepsins and calpains
What are cathepsins?
lysosomal proteases
What are calpains?
non-lysosomal calcium-dependent proteases
Following cytotoxic lymphocyte granzyme B release, what is a preferred mechanism of apoptosis induction?
Bid-mediated MOMP
What death occurs without chromatin condensation?
Caspase-independent cell death
Caspase-independent cell death involve a slow loss of what function?
mitochondrial function
Caspase-independent cell death may be due to what actions of proteins?
proteins released from mitochondria, other than those that involve caspases
What are 3 proteins to antagonize IAP function?
Reaper, Grim, and Sickle
What does Reaper, Grim, and Sickle carry?
motif related to the AVPI motif of Smac and Omi
Clearance of apoptotic celss occur by what?
phagocytosis
What clears apoptotic cells by phagocytosis?
macrophage or dendritic cells
Apoptotic cells generates signals to _____
solicit its engulfment
What are 3 signals generated by apoptotic cells to solicit its engulfment?
a. find me signals
b. eat me signals
c. discruption of don’t eat me signals
What is an example of don’t eat me signals?
CD31 signal
What is an example of eat me signal?
externalization of phosphatidylserine (PS)
PS normally found on ___ of plasma membrane.
c-face
PS is kept on the c-face of the plasma membrane by what?
by the ATP-dependent flippase type of translocase
Flippase type of translocase function
moves PS from non-c-face to c-face
What activates scramblase type of translocase?
calcium or caspases
Where are scramblases active?
in the SER membrane
Function of scramblase type of translocase
randomly flip-flopps phospholipids to even out the growth of the membrane
PS on the surface can bind to bridges such as _______
MFG-E8
MFG-E8 binds to what?
integrin receptors on phagocytotic cells
Example of a find me signal
lysophosphatidylcholine
lysophosphatidylcholine is produced by what?
by activated phospholipase A
Phospholipase A is activated by what?
executioner caspase
How is executioner activated to activate phospholipase A?
by enzymatic cleavage
Why do many viruses block apoptosis?
to keep their host alive until sufficient virus is produced and the cell is lysed
Some vertebrate viruses prevent what?
apoptosis induced by immune effector cells
What virus produce protease inhibitors, serpins?
Pox viruses
Function of serpins
blocks granzyme B that blocks caspase 8
What is involved with mechanisms of subversion of the mechanisms of the apoptosis?
cancer
Tumor suppressor p53 acts in cancer mechanism by
inducing apoptosis in the transformed cell
Clearance of apoptotic cells can actively inhibit what?
inflammation and immune responses
Function of nitric oxide
signaling molecule for inflammation
When phagocytosed by dendritic cells, apoptotic blebs can result in what?
Ag presentation in a manner that induces a state of immune tolerance
Lupus
autoimmune disease SLE
SLE (lupus) is characterized by what?
auto-AB to intracellular Ag like dsDNA
A characteristic feature of lupus
presence of LE bodies (apoptotic cells) in their circulation - not effectively cleared
