APOPTOSIS Flashcards
what is the difference between apoptosis and necrosis
apoptosis = “normal” or programmed cell death that occurs under normally physiological conditions and the cell is an active participant in its own demise
necrosis = uncontrolled or accidental cell death. the cell death occurs when cells are exposed to a serious chemical or physical insult (hypoxia, hyperthermia, ischemia)
what are the types of cell death
Necrosis
Apoptosis
Autophagy
Ferroptosis
Oncosis
Necroptosis
name the differences between apoptosis and necrosis
Apoptosis :
- active
- physiological or pathological
- condensation, cross linking
- phagocytosed
-no inflammation
-internally or externally induced
NECROSIS:
- passive
- pathological
- swelling, lysis
- dissipates
- inflammation
- externally induced
outline the process of apoptosis
- shrinking of cytoplasm, resulting in condensation of nucleus
- fragmentation - cell is broken down into smaller pieces
- phagocytosed
- no inflammation
outline the process of necrosis
- swelling of cytoplasts and mitochondria
- Blebbing - irregular bled in the plasma membrane caused by localised decoupling of the cytoskeleton
- burst /lysis - leakage of cell contents which attracts the body’s immune system
- causes inflammation
why is apoptosis important
it’s needed for normal development of multicellular organism (embryonic development) and homoeostasis of their tissues (Adult)
it is needed to remove cells - especially cells that are damaged, cancer or infected.
give examples of where apoptosis is important to remove cells
- cells infected with viruses
- cells of the immune / neurological system
- cells with DNA damage
- cancer cells
give 2 examples where apoptosis is important for normal development
- the formation of fingers and toes of fetu.s lack of apoptosis can lead to webbed digits (syndactyl)
- formation of proper connections between neurons in the brain
give 2 examples where apoptosis is important for normal development
- the formation of fingers and toes of fetu.s lack of apoptosis can lead to webbed digits (syndactyl)
- formation of proper connections between neurons in the brain
give examples of what happens when there is inadequate apoptosis, and the key word for it
results in 👉hyperplasia = increase in the number of cells in an organ or tissue
- cancer
- autoimmune disorders
- restenosis
- frequent infections
give examples of what happens when there is extreme apoptosis
results in ❤tissue atrophy❤: decrease in the size of a tissue or organ due to cellular shrinkage
- neurodegenerative diseases i.e AD, PD, Epilepsy
- cardiovascular diseases - i.e stroke , MI, HF
- hematologic diseases - i.e aplastic anaemia,
- other disorders - i.e sepsis, inflammation, AIDS
what are the 2 main apoptotic pathways
- intrinsic = cell decides to kill itself
- extrinsic = stimulus tells cell to kill itself.
what is the difference between extrinsic and intrinsic pathway
extrinsic - death receptor mediated events (outside of the cell)
intrinsic - mitochondria mediated events ( inside of the cell)
describe the process of intrinsic pathway
cytochrome c => caspases => cell death
describe the process of extrinsic pathway
death receptors —> caspases —> cell death
what signals are secreted for elimination of apoptotic cells
Secreted ‘find me’ -
Exposed ‘eat-me’ - the engulfment of apoptotic cells
Lacking ‘Don’t eat me’
list the two EAT ME steps and explain them
Step 1 - Tethering - the phosphatidylserine (PtdSer) receptor Tim4 tightly binds PtdSer on the apoptotic cell and recruits it to the macrophage surface.
Step 2 – Tickling - Soluble proteins such as protein S/Gas6 or MFG-E8 bind PtdSer on apoptotic cells and activate their receptors (MerTK or integrin, respectively) on phagocytes, leading to Rac1 activation and actin polymerization.
in the extrinsic pathways, what are death receptors
+ they are members of the tumor necrosis factor (TNF) receptor superfamily
what is death domain of death receptors in the extrinsic pathway and describe their qualities and role
+ death receptors have a cytoplasmic domain of about 80 amino acids called the death domain
+ they transmit the death signal from the cell surface to the intracellular signalling pathways
describe the extrinsic pathway
- every cell, including the infected cell has death receptors TNFR1 which bind to death activators trimetric TNFa .
- this leads to the Recruitment of Fas-associated death domain (FADD) and TRADD to TNFR1
- FADD then associates with procaspase 8 , forming a death inducing signalling complex (DISC)
- caspase-8 is activated (auto catalytic activation of procaspase 8)
- This then activates Apoptosis, which takes place on the inside
what does TNF stand for
Tumour Necrosis factor
what does caspases stand for
Cysteinyl aspartate specific proteases
what are caspases?
A family of intracellular cysteine proteases that play a pivotal role in the initiation and execution of apoptosis.
how many different members of caspases have been identified
14 different members
what are caspases synthesised as?
All are synthesized as inactive proenzymes (zymogens) with 32-56 kDa
how are caspases activated
two inactive procaspases are cleaved at two location then join together at the small subunit sections.
where does intrinsic pathway take place
mitochondria
What are the steps of the intrinsic pathway for apoptosis
- it is activated by cellular stress such as UV radiation cytotoxic drugs
- this activates BAX and BAK which bind to BCL-2 , inhibiting it
- they also induce permeabilisation of mitochondrial membrane ( so it punctures the membrane of the mitochondria).
- Multiple effectors, cytochrome c, SMAC (second mitochondria derived activator of caspases) are released through membrane pores from intermembrane space
- SMAC inhibits inhibitors of apoptosis protein (IAP) activity and Cytochrome C activates caspase 9
- caspase 3 is also activated- this is the executioner
- cleavage of host intracellular proteins
- apoptosis
what is BCL-2
This is a protein that in normal cells, it inhibits apoptosis . However, in a damaged cell, BAX binds to BCL-2 inhibiting it from inhibiting apoptosis
what are the proteins that are associated / bind to BCL-2
- Bcl-2 associated x protein (BAX) ;
- Bcl-2 antagonist killer (BAK);
- BH3 interacting-domain death agonist (BID).
explain how BAX and BAK are activated and how they induce mitochondrial permeabilisation
- BH3 interacting domain death (BID) is an agonist that binds to BAK and BAX receptors
- this causes a conformational change in them, causing them to be activated (oligomerisation)
- this conformational change allows for them to bind to BCL-2 and inhibit it
- this also allows them to form dimers and these dimers puncture the outer mitochondrial membrane and formation of pore complex
- this facilitates the initiation of apoptosis
what prevents the activation of BAK or BAX
low levels of BH3
What happens to BIM level sin apoptosis
They rise, and bind to BCL-2/MCL-2, dimers form, leads to apoptosis
what are some BH3 mimetics
OBX
Venetoclax - ABT-737. it binds to BCL-2 enabling apoptosis to continue
why are BH3 mimetics important
they activate the pathway that BH3 will activate to allow for apoptosis
how does cytochrome c help in apoptosis for intrinsic pathway
> Cytochrome c translocates to cytoplasm and combines with apoptotic protease-activating factor-1 (Apaf-1), forming a
complex called apoptosome
> apoptosome binds procaspase 9 , leading to activation of Caspase 9.
> Activation of Caspase 3
> SMAC/DIABLO and HtrA2/Omi inhibit IAP (Inhibitors of apoptosis protein) activity.
> Pro-apoptotic proteins AIF, Endonuclease G and CAD are also released → chromatin modification and DNA degradation.
how is cytochrome c released?
- Cytochrome c is bound to the IMM by electrostatic and hydrophobic interactions with cardiolipin.
2.l Mitochondrial ROS are stimulated early in apoptosis and cardiolipin is oxidised by peroxidase function of cardiolipin-cyctochrome c complex. - This releases cytochrome c and allows its exit from IMM to cytoplasm through pore induced by BAK/BID and BAX.
what does AIF, CAD and DIABLO mean
AIF = apoptosis inducing facto r
CAD = caspase activated DNAse
DIABLO = direct IAP binding protein with low pI
what is Apoptosis inducing factor
- the final mechanism of apoptosis involves using AIF instead of caspases
- AIF is located in the intermembrane space of the mitochondria.
- when the cell is damaged, AIF is released from the mitochondria, and it travels into the cytoplasm of the cell
-3. AIF eventually finds its way into the nucleus, binds to the DNA and triggers destruction of DNA
what does the body do when cells proliferate and become cancerous
the body secrete factors that initiate the process of apoptosis, however, cancers have a way of preventing this.
how are cancer cells and apoptosis related?
> disrupted balance between cell death and proliferation
there is decreased apoptosis in cancer cells
there is enhanced cancer growth
how do cancerous cells avoid apoptosis
changing the functions of anti- or pro-apoptotic proteins through post-translational modifications, such as phosphorylation
what are some causes of dysregulated apoptosis and cancer
+ impaired receptor signalling pathway : i.e reduced expression of death receptor, reduced expression of “eat me” or death signals , no death domain
+ defects / mutations in p53
+ reduced expression of caspases
+ over expression of antiapoptotic proteins such as BCL-2
+ under expression of apoptotic proteins such as BID, BAX, BAK
+ disrupted balance of Bcl-2 family of proteins
+ increased expressions of IAP
can you have tumour that stem from no apoptosis but no proliferation
yes!
a tumour can form even though there is no proliferation.
what is the bh3 mimetic we need to know
venetoclax
what is the mechanism of venetoclax
- BCL-2 is a pro-survival factor that Inhibits formation of BAX-BAK dimers
- Venetoclax binds to BCL-2
- Induces apoptosis
