Apoptosis Flashcards
programmed cell death (PCD)
a sequentially ordered death process, three main types: apoptosis, macro-autophagy, necroptosis
apoptosis
type 1 PCD, usually associated with suicide of a cell
caspases
family of cysteinyl aspartate-specific peptidases, that are the effector proteases activated during apoptosis
early identifiers of apoptotic cells
- budding of cytoplasmic membrane
- shrinkage of nuclei
- chromatin condensation
function of apoptosis
balance between loss of positive signals and receipt of negative signals
role of apoptosis
development killing virus removing cytotoxic T-cells aging maintain homeostasis
diseases because apoptosis is INHIBITED
cancers: breast, prostate, ovarian
autoimmune
viral infection
diseased because apoptosis is INCREASED
AIDS alzheimers parkinson's ALS myelodysplastic syndrome heart attack, stroke liver disease via alcohol
steps of apoptotic process
signal to initation to effectos to execution/degradation to corpse disposal
caspase initiators
8, 9, 10
caspase executioners
3, 6, 7
activation of caspases generally involves
cleavage between the carboxyl and middle domains
caspases consist of 3 domains
- amino terminal
- middle large domain
- carboxyl terminal
pro-executionary caspases exist as
dimers
initiator pro-caspases exist as
monomers
caspases differ in lengths of
pro-domains
presence/absence of adapter-recognition
Major Mechanisms for caspase activation: extrinsic pathway
death receptor
Major Mechanisms for caspase activation: intrinsic pathway
mitochondrial
death receptor extrinsic pathway components
- death receptors
- ligands
- adapter proteins
- initiator protease
- executioner proteases
death receptor ligands
structurally related members of the tumor necrosis factor family
span the plasma membrane (have extra and inter cellular tails)
anchored to the cell but can be released by proteolytic cleavage
death receptors
structurally related members of the tumor necrosis factor family
have cysteine-rich extra cellular domains
have cytoplasmic tail that contains a death domain sequence
mitochondrial intrinsic pathway
does not involve death receptors, changes in mitochondrial fucntion preceded caspase activation with many non death receptor inducers of apoptosis
apoptosome
functions as a scaffold for RECRUITMENT and ACTIVATION of pro-caspase 9
intrinsic apoptotic pathway involves
- receipt of apoptotic signal causes release of cytochrome C
- cytochrome C binds to Apaf-1 causing the hydrolysis of ATP and partial relaxing of Apaf-1
- exchange of ATP for bound ADP allows Apaf-1 to fully relax
- the CARD domains in the apoptosome assume a conformation that enables them to recruit pro-caspase 9 molecules
- caspase 9 activates executionary pro-caspases 3 and 7
what activates the mitochondrial apoptotic pathway
anything that will induce the release of cytochrome C
agents that cause mitochondrial dysfunction directly
target the respiratory chain
target the electrochemical gradient of the inner membrane
important concepts regarding mechanism of initiator pro-caspase activation
- involves an adaptor protein
- recruitment of pro-caspase to the adapter protein is mediated by specific “domain-domain” interactions
- adapter protein/pro-caspase complexes aggregate/oligomerize and induces conformational change in pro-caspases facilitating activation
caspase - 3 =
executioinary caspase
caspases are activated by
specific cleavage after an aspartate residue
the whole caspase system is set up into a
self-amplifying loop
caspases generally have a
tetrapeptide recognition sequence
caspase 3 cleaves DFF45/ICAD and when it’s cleaved it releases
DFF40 which facilitates exposure of the nuclear localization signal on DFF40 allowing it to translocate to the nucleus
IAPs
inhibitor of apoptosis - a family of cytoplasmic proteins
3 main ones: cIAP1, cIAP2, XIAP - they all bind to caspases 3,7,9
XIAP is a potent
inhibitor of caspase activity
SMAC/DIABLO
pro-apoptotic
found in mitochondrial membrane space and is released into the cytosol by conditions causing cytochrome c release
FLIPS
inhibitor of apoptosis
really good inhibitor of death receptor apoptosis
p35
a protein produced by a strain of baculovirus that is very potent inhibitor of virtually all caspases, has no effects on any other cysteine protease, forms irreversible covalent complex with caspases
CrmA
a serpine protease inhibtor produced by cow pox virus
excellent inhibitor of caspases 1,8, 9
forms an irreversible complex with caspases
role of caspases in non-apoptotic processes
DNA repair/cell cycle control (caspase2)
differentiation (caspase3, caspase14)
proliferation (caspase 8)
Bcl-2 supergene family role in apoptosis
Bcl-2 could suppress the induction of mitochondrial apoptosis caused by multiple agents
Bcl-2 anti-apoptotic members contain BH
1,2,3 and 4 domains
two pro-apoptotic sub families
1 family contains BH 1,2,3 domains
other family contains BH 3 only domains
Bcl-2 significance of binding partners
many of the Bcl-2 supergene family members can heterodimerize with another family member. this binding reflects the ability of the BH3 domain to bind to a hydrophobic cleft structure composed of BH1,2, and 3 domains
significance of binding for Bcl-2 supergene family
- association of an anti-apoptotic member with a multi-domain pro-apoptotic member neutralizes the PRO-apoptotic member
- association of an anti-apoptotic member with BH3 domain only pro-apoptotic member neutralizes the ANTI-apoptotic
member - association of some BH3 domain only members with Bax or Bak results in Bax or Bak activation
Bax and Bak have been shown to form pores in mitochondria - significance of pores
- facilitate the release of pro-apoptotic molecules like AIF, SMAC and cytochrome c from the mitochondria
- facilitate the release of lysosomal proteases from lysosomes. can cause apoptosis
Bax and Bak are partially redundant in their functions
they are also the principal mediators of the intrinsic apoptotic pathway
activation of cytoplasmic Bax is achieved by its complexing with
“activating BH3 proteins” like PUMA or Bim
