Apoptosis Flashcards
what is apoptosis?
programmed cell death brought about by external or internal signals
needed for development into adult forms
characteristics of apoptosis
- -cell shrinks
- -loss of CAMS
- -cytoskeleton collapses
cytochrome C
released from mito
marker for apoptosis
DNA cleavage in apoptosis
cleaved at linker DNA between nucleosomes by endonuclease
caspases
proteases that mediate an intracellular proteolytic cascade to cause apoptosis
cysteine in active site
caspases target
target proteins and cleave them where Asp acid residues occur
procaspases
caspases are first synthesized as these = inactive form
activation of procaspases
protease cleaves these
which transforms them into caspases
caspases then also activate procaspases
procaspase cleavage
are cleaved at a specific site to create and small and large subunit
which them form a heterodimer w/ a different cleaved procaspase = active caspase
2 major caspases
initiator caspase
executioner caspase
initiator caspase
–initiates death
–caspase -8 and -10
can self activate
executioner caspase
destroys targets to induce death
caspase -3
cleaves downstream proteins, inactive endonuclease, targeting cytoskeleton and CAMs
caspase cascade
- -irreversible once started
- -some caspases are needed for life and if gone, fetus will die
- -machinery for apoptosis is always present
there are 2 pathways that depend on factors to induce apoptosis
extrinsic path
intrinsic path
mito dependence of the 2 pathways
extrinsic - mito independent
intrinsic - dependent
extrinsic pathway
death receptors
- -survival factors are removed
- -death signals bind
death receptor domains
3 domains
- extracell binding d
- TM d
- intracell death d
receptors are homotrimers - 3 proteins of tumor necrosis family
extrinsic pathway cascade
- -Fas binds to Fas death receptor
- -adaptor proteins recruited
- -death domains come together to form DISC
- -caspase -8 and -10 activated
- -downstream executioner activated
inhibitory proteins can stop the ____ pathway
extrinsic pathway
recruited adaptor proteins - extrinsic pathway
FADD adaptor
procaspase -8 and -10
form trimers
bring death domains together = DISC
DISC
death inducing signal complex
inhibitory proteins
- -are decoy receptors
- -same as death receptors but no death domain so apoptosis is not induced
- -also includes FLIP protein
FLIP
–protein that resembles initiator procaspase but no proteolytic domain
–a competitive inhibitor to oppose procaspase -8 and -10 to prevent apoptosis
both types of inhibitory proteins act like?
sponges to absorb the death signals to prevent the start of apoptosis
intrinsic pathway
internal inducement of apoptosis
due to injury, DNA damage, lack of nutrients
mito dependent
key event of intrinsic path
translocation of cytochrome C from intermediate space to cytosol
release of cytochrome C
- -binds to an adaptor protein Apaf1
- -caspase -9 activated
- -executioner caspase activated
Apaf1
adaptor protein
forms apoptosome which activates caspase -9
which then activates downstream executioner caspase
apoptosome
= Apaf1 + cytochrome C
final step common to both pathways
activation of downstream executioner caspase
caspase -3
Bcl2 protein family
- -controls release of cytochrome C into cytosol
- -3 types of this: pro and anti apoptotic
pro-apoptotic Bcl2
blocks release of cytochrome C
has 3 domains or 1
BH123 or BH3
anti-apoptotic Bcl2
promotes release of cytochrome C
has 4 distinct domains
BH1234 which is also just called Bcl2
BH123 activation
- -pro apoptotic
- -apoptosis is triggered
- -this activates BH123
BH123 function
forms aggregation in mito outer membrane
induces release of cytochrome C
thus inducing intrinsic pathway
BH3
pro-apoptotic
located in cytosol
apoptotic signals activate it which causes it to translocate to mitochondria
BH3 function
inhibits the anti-apoptotic Bcl2 proteins
thus allowing BH123 to do its function
Bcl2
or BH1234
anti-apoptotic
includes Bcl2 & Bcl-XL
located on cytosolic side of outer mito memb.
Bcl2 function
prevent apoptosis by binding to BH123
thus preventing aggregation
IAPs
inhibitors of apoptosis
bind and inhibit caspases
some can add ubiquitin
these are necessary because some caspases are self-activating
Anti-IAPs
when real apoptotic signals are received
–these will stop IAPs from inhibiting caspase activity
they release from mito
excessive Bcl2 production
- -related to lymphoma
- -Bcl2 inhibits apoptosis
- -if in excess cell can never die
relate excessive Bcl2 protein and p53 mutations
in excess Bcl2 – cells will not die
thus cells w/ DNA damage will continue to live and divide
p53 gene stops cell cycles when DNA damage is detected
excessive apoptosis is found in ?
heart attacks and stroke
