Cancer 6: Apoptosis Flashcards
Why do you need programmed cell death?
Harmful cells-viral/dna damage
Development defective cells (self reacting T/B cells)
Excess/Uncessary cells
Obsolete cells (mammary epithelium after lactation)
Exploitation-chemotherapeutic
What is the difference bewteen necrosis and apoptosis?
Necrosis-unregulated cell death with trauma-cellular distuption + inflammatory response
Apoptosis-regulation-controlled dissassembly of cellular content and no inflammatory response
but more on a sprectrum
What is necrosis?
Plasma membrane becomes permeable-cell swelling and rupture of cellular membranes (organelles+cell-lysis_-release of proteases leading of autogidestion of the remnants
macrophages also help clearing up and neighbouring cells proliferate
But the proteins escaped are seen as AG-pro-inflammation
What is apoptosis?
Latent phase– early-death pathway activated but morphologically no difference
Execution phase-
Loss of microvilli and intercellular junction
SHRINK (no swell)
If asymetrical cell (like GI endothelium)-loss of asymetry via lipid appearing at weird placed
Chromatin and nucelar condensation
DNA fragmentation - nucleus condense first then DNA breaks
Formation of membrane bleps
Frragmentation into membrane enclosed apoptotic bodies
PLASMA membrane intact-no inflammation
Macrophage finish it up by eating the apoptotic body
Why is apoptosis and necrosis considered to be a spectruym?
Newly discovered-apoptosis-like programmed cell death (PCD)-some features-display phagocytic recognition before membrane lysis
Necrosis like PCD-variable features of apoptosis-like failred apoptosis-
(and about 10 other types)
graded response-
What is the role of caspases ? What are the different classes? How are they activated? what do they cleave?
Caspases-proteases – executioner of apoptosis
form as zymogens-Activated via proteolysis
Cascade-like activation
2 classes-initiatory and effector caspases
Initiatory–CARD-initiatory- caspace recruitment domain (casp 2/9)
DED-death effector domain-in caspasce 10/8-changes localisation of capase
Form homodimers
Effector caspace-3/6/7 –
DED and CARD domains are part of the zymogen-cut off to form effector caspases Also another (SS (short) domain) cleaved-but still bind to large (LS) chain-form tetramer (L2S2)
Caspases have cascade like activation
Caspace 8/9 (initiators)-> activate 3/7. 3 can then activate 6/2/1 (effectors)
Effector caspases-cleave and inactivate proteins in the cell (like nuclear laminins), -can destroy protein, complexes, activate other zymogens, or release sterical inhbitions
-> like capsace activated DNAse-
By what 2 mechanisms are caspases activated in the first place
Either death by design-receptor mediated extrinsic pathway
Death by default-mitochondrial (intrinsic pathway
How does the receptor mediated extrinsic pathway lead to apoptosis?
Death receptor-transmembrane-when active, become trimeric (eg: FAS)
Intracellular death domain (DD)-uses adaptor proteins to bring other proteins (FADD and FLIP)
FADD-DED +DD domain, FLIP (DEDx2)-
FADD-activate apoptosis, FLIP inhbitory
Adaptor domain bind to similar domains in other proteins-(DED)-so brings caspases (with DED domain) to receptor (via DD domain) -procaspase recruited -this forms death inducing signalling complex (DISC)
As 3 procaspase domain can get recruited to the trimer-cleave each other-form the tetramer formed by the fragments
(the proximity and oligomerisation allows the cleavage-low intrisic activity) –need at least 2 procaspases
How does the receptor mediated extrinsic pathway that lead to apoptosis can be inhibited
via FLIP inhbitory domains-2xDED domains
FLIP has short and long form (same DED domains)
Their DED domains can bind others but have no proteolytic activity-compete for caspase binding sites
one bound to receptor, FLIP forms a sterical block
How does the intrinsic pathway lead to apoptosis?
Regulated by the mitochondria-
Cellular stresses (weird GF, DNA damage via p52, ROS)-cause mito to lose memrbane potential
Release of many OxPhos proteins (like cyt C)-release to apoptosis inducing factors (apoptosome)
apoptosome-large complex made from Apoptotic activating factor 1 (Apaf1), ATP, Cytc and caspace9
Apaf1-card domain and WD40 domains
Oligemerise as a heptamer in a wheel like shape-CARD domains at the center and WD40 like rays from center-cytC binds WD40
The center (card domains)-attract 2 caspases 9 -form dimers which can activate each other
needs energy to happen-but mito not working–maybe the ATP levels determines if cell apoptoses (high ATP demains) or necrosis (low ATP)
How is the intrinsic and extrinsic apoptosis pathway regulated and linked?
Both lead to formation of Caspase 3 (either with caspase 9 or 8)
Bid protein links them-caspase 8 from extrinsic will enhance the mito apoptosome formation–so will lead to both pathways active
Modulators-Bcl2 - 3 groups
Bcl2-group I-BH1/2/3/4 + Transmembrane domain
Grioup II- no BH4
Group III-BH3 only and sometimes no TM
How does Bcl2 familty regulate apoptosis
2 anti-apoptotic
Bcl 2 and BCL xl –mitochondria
pro-apoptotic-bid bad, bax (mito and cytosol)
Their release in via PI3K (via growth factor actiavtion)-PI3K activated AKT/PKB-survival/proliferation pathway
(can also activate via RAS the MAPK pathway-growth)
Akt phosphorylates and incativate Bad, Caspase 9
Inactivates FOXO TF-FOXO promote apoptosis
And stimulated ribosome production and protein synthesis
How does PI3K activates and what does it do (in apoptosis)?
RTKL- adaptor brings PI3K (P85 and P110) to receptor and activated it
Phosphorylates PIP2 to PIP3
PIP3-docking site for (via PH domain)-activated AKt/PKB-has anti-apoptotic signals + mitogenic signal
Inactivated by PTEN- (lipid phosphatase)-make PIP3 back to PIP2-inactivated
How does Bcl2 family activate apoptosis when things are bad?
Bad can be in cytosol
Bax binds Bcl2 normally on mitomembrane-inhbitors them-cant be active
But if AKT/PKB not active-Bad from cytosol released from 14-3-3 inhbitors-moves Bax from Bcl2 binding-free bax forms oligomer which pierces the mitochondrial membrane and release cyt C in cytosol-apoptosome
happens when PTEN deactivates PIP2 pathway
What are the 4 cytoprotectivr pwathawys?
Intrinsic-BCl2, BCL-XL
Flip, IAP (binds themonomers and stpops them from being active)
also general signalling downregulation/inhbitors
