Week 10 (Apoptosis) Flashcards
What is Apoptosis?
Cell death
–in normal physiology (death can be physiological)
–In disease
What is the function of apoptosis?
- Removes damaged, unwanted or diseased cells
* Programmed cell death = Ordered cell deletion
C. elegans
–powerful model system
–191 predictable deaths in development
–highly tractable system
–study regulation, activation and execution of apoptosis
•Model systems have underpinned current knowledge
What is Apoptosis is crucial for?
–development
–maintenance
–control
Cell Population Control
Proliferation+
Differentiation -/+
Cell Death -
There is no net change in number of cells
Examples of diseases caused by Overactive Apoptosis?
More cells dying than proliferating –Neurodegeneration –Immunodeficiency –Stroke –Coronary Heart Disease –Transplant Rejection
Examples of diseases caused by Underactive Apoptosis
More cells proliferating than dying
–Cancer
–Autoimmune & Inflammatory conditions
–(e.g. SLE and rheumatoid arthritis)
The Importance of Apoptosis
Life-death imbalance can be desirable (physiological)
Why can Underactive Apoptosis be desirable?
–Allows cell accumulation (e.g. accumulation of cells during an immune response)
What why can Overactive Apoptosis be desirable?
–Returns cell populations to normal after challenge
–Neutrophil apoptosis during inflammation
–CTL death
What are the characteristics of apoptosis?
Tightly controlleed/ programmed Cell shrinkage •Organelle integrity •Chromatin condensation •Plasma membrane integrity
- Thermodynamics uphill
- Internal control
- Purposeful
What are the characteristics of necrosis?
Not tightly controlled (accidental/random), caysed by external factors •Cell swelling •Organelle disruption •Nuclear swelling •Plasma membrane rupture
- Thermodynamics downhill
- External “control”
- Accidental
Caspases
- Cysteinyl ASPartate-specific proteASES
- Key cysteine in active site QACxG
- Aspartate at P1 of substrate tetrapeptide
- Tetrapeptide defines caspase specificity
Three broad categories of caspases
- Inflammatory caspases
- Initiator caspase
- Effector caspase
Inflammatory caspases
- Maturation of pro-inflammatory cytokines
* e.g. Caspases 1, 4, 5, 11, 12, 14
Initiator caspase
- Kick off the caspase cascade
* e.g. Caspase 8, 9
Effector caspase
- Cleavage of cellular substrates
- Mediate the killing
- e.g. Caspases 3,6, 7
Describe the activation of Caspases
•Caspases are produced as inactive zymogens
•Pro domain 23 - 220aa
–large pro-domain = initiator caspase (contains recruitment domains)
–Small pro-domain = executioner caspase
•Activation requires a minimum of 2 cleavages
Cleavage at the prodomain and formation of a tetramer
Cleavage of caspase substrates during apoptosis: what is the function of caspases?
- Pro-caspase (inactive) → active caspase
- Break down Structural proteins and DNA replication/repair enzymes
- Inactive nuclease → active nuclease
What is CAD?
caspase-activated DN-ase
What is ICAD?
inhibitor of CAD (caspase substrate)
End goal of apoptosis
detach cell from neighbours
Dismantle cell
destroy DNA
alter the cell surface
Cell suicide occurs in response to
cellular insults
Extrinsic Pathway
–Cell are instructed to die from outside
–Receptors (“Death Receptors”) on cell surface induce death when ligated
- Killer lymphocyte have a protein (fas ligand) on their surface
- Fas death receptor on pre apoptotic cell recognises the fas ligand
- Recruitment of FADD (adaptor protein) which has a death domain and a death effector domain
- Death domain joins the intracellular Fas death receptor
- Death effector domain recognised by caspases (8 or 10)
- FADD recruits procasapases which leads to initiation and activation of procaspases via cleavage
- Caspase cascade takes place
- Resulting in an apoptotic cell
Intrinsic pathway
- cytochrome c released into the cytoplasm from damaged cell which binds to Apaf-1 (adapter protein)
- this recruits inactive procaspases
- activates then
- caspase cascade initiated