Cell Death Flashcards
(31 cards)
what are the four cell death pathways?
- apoptosis
- necroptosis
- pyroptosis
- ferroptosis
cell death in disease
-too little: abnormal development and cancer where the division > death
-too much: neurodegeneration, HIV/AIDS, and normal aging
discovering cell death
-growth factors required for neurons to live
-lysosomes- LMP- organelle in cell that kills proteins
-BCL-2- B cell lymphoma- first oncogene discovered and keeps cells alive
-caspase- protease responsible for death –> cells that die require caspase
programming/regulated cell death (PCD/RCD)
-developing, normal physiological processes and type of regulated cell death (any kind of gene-dependent death)
-if a cell contributes to its own death –> programmed
what happens generally when a cell decides to die?
cell has to decide to die –> amplify death signal –> death effector
does the dying cell actively contribute to its own death?
-no- accidental and could be instant death or murder
-yes- programmed or regulated cell death that is cell autonomous and cell suicide
“apoptosis” based on cell morphology
-healthy cell then ligation of portal vein –> we see necrotic death then cells destroyed themselves by blebbing together and being engulfed
-apoptosis is non-inflammatory compared to necrosis
classic apoptotic morphology
cell on the right has been blebbed together and nuclei have been broken up
how did we map the apoptosis pathway?
-WT c. elegans
-131 cells die during development and ran screen for worms that didn’t have any death –> turned out to be those that had mutant in caspase
caspase nomenclature
-“c”- cysteine amino acid at the active site
-“asp”- cleaves its substrates after aspartate/asp/D
-“ase”- standard for enzymes
-14 mammalian caspases –> only 3, 8, and 9 are involved in apoptosis
apoptosis pathway
BH3 –| BCL-2 –| BAX –> MOMP produces cytochrome C –> Aparf1 apoptosome –> caspase 3 –> execution (no lysis)
discovery of the first human apoptosis regulator- BCL-2
-go to patients whose tumors had classic chromosomes translocations and clone out genes next to the breakpoint –> you’ll find new oncogenes
-BCL-2- doesn’t behave like a regular oncogene since it’s an inhibitor of cell death
BCL-2 homology motifs (BH)
-BH3- facilitates interaction between pro- and anti-death in BCL-2 family membranes
-“BH3-only” proteins- mostly unrelated to the BCL-2 family
-BH3 is required for cell death activity of BCL-2 homolog BAX and BH3-only proteins
BCL-2 is intact and likely overexpressed by strong enhancer- BCL-2 proteins have deep groove b/c that’s where the BH3 interacts
BH3 memetics occupy the same groove –> led to generation of venetoclax that sits in BCL-2
BCL-2 proteins regulate mammalian apoptosis (intrinsic pathway)
-BCL-2, BCLX, and BCL1- anti-death proteins have homologs that are pro-apoptotic
–> BCL-2 and BAX are opponents
-BH3-only proteins have several stress signals- can activate death proteins and inhibit anti-death proteins –> lynch pins of pathway
-if BAX wins, it goes to the mitochondria and oligomerizes on outer mitochondrial membrane and pokes a hole and releases cytochrome C from IM space
-cytochrome C serves as co-factor to drive assembly of apoptosome (Aparf1 apoptosome) –> recruits caspase 9 then cleaves and activates caspase 3 –> makes key cuts in cells that makes them look morphologically apoptotic
what happens in a mouse without apoptosis?
- mouse took out all three of the BH3-only proteins and those animals have webs between their toes
- KO all three of the pro-death proteins (BAX/bak/bok) and mouse has too many neurons
- make a version of cytochrome C- only works in the ETC
- KO components of the apoptosis path like Apaf-1, caspase 9, and caspase 3 –> brain has a lot of neurons
extrinsic and intrinsic apoptosis pathways converge on caspase 3
-TNFRI binds to its ligand RIPK 1/3 and activates caspase 8, which activates caspase 3
-extrinsic- caspase 8 and intrinsic (mitochondrial)- caspase 9 –> both amplify the death signal, leading to downstram caspase 3
-caspase 3 chops up several substrates in the cell
caspase-3 causes apoptotic morphology and death
-activates other caspases
-inactivates Rb
-cleaves things that make cells recognized by their neighboring cells
how do you detect apoptosis?
-cytochrome C tagged with GFP and phosphatidylserine (eat me) signal flips from inner to outer leaf of PM
-DNA turns blue when the cell membrane becomes permeable (apoptosis –> necrosis)
TUNEL assay labels the ends of DNA tha are cleaved up when they cut by an enzyme that gets activated through caspase pathway into these nucleosomes
-specific for apoptosis? yes if you’re watching cells, they have apoptopic morphology and they expose phosphotidylserine but for necrotic cell since you have fragmented DNA –> yes or no depends on how you read the gel
we don’t have that many proteins that inhibit caspases
- mimic caspase 8
- caspase inhibitor XIAP with loop that sits in the active site of caspase
what would be a possible treatment strategy for leukemia patient with a tumor overexpressing BCL-2?
XIAP inhibitor- inhibit anti-death protein
necroptosis
-you don’t see apoptotic cell death bodies and they eventually rupture
-begins with death receptor from extrinsic apoptosis that leads to caspase 8 then 3 and apoptosis
-TNF-alpha has a pro-survival fnction- activates NFKB and other signaling pathways –> also plays a role in necroptosis
-crosstalk downstream of receptor from apoptotic pathway via caspase 8, which can inhibit necroptosis
-RIPK1 activates RIPK3- when kinase amplifies and makes huge complex, it activates pore-forming protein (MLKL) and goes up to the plasma membrane from inside the cell and pokes a hole
what treatment would cause patients with IBD to get worse?
caspase-8 inhibitor –> now you can’t use caspase 8 to cut up RIPK1
