Cancer 6: apoptosis

Question 1

What is the definition of necrosis?

Answer 1

-unregulated cell death associated with trauma, cellular disruption and an inflammatory response

Question 2

What is the definition of apoptosis?

Answer 2

• regulated cell death, controlled disassembly of cellular contents without disruption

NO inflammatory response

Question 3

What are the key features of necrosis?

Answer 3

• plasma membrane becomes permeable
• cell swelling and rupture of cellular membranes
• release of proteases leading to autodigestion and dissolution of the cell
• localised inflammation

Question 4

What are the two phases of apoptosis?

Answer 4

latent phase

execution phase

Question 5

What occurs during the execution phase

Answer 5

• loss of microvilli and intercellular junction
• cell shrinkage
• loss of plasma membrane asymmetry
• chromatin and nuclear condensation
• DNA fragmentation
• formation of membrane blebs
• fragmentation into membrane-enclosed apoptotic bodies

Question 6

What is apoptosis- like PCD?

Answer 6

apoptosis like programmed cell death

• has some but not all the features of apoptosis

Question 7

What is necrosis- like PCD?

Answer 7

variable features of apoptosis before cell lysis

Question 8

Which are the initiator caspases?

Answer 8

2,8,9,10

-they have targeting subunits that direct them to a particular location

CARD - caspase recruitment domain
DED - death effector domain

Question 9

How do caspases become active?

Answer 9

• procaspases undergo proteolytic cleavage to form large and small subunits
• after cleavage you will get folding of 2 large and 2 small chains to form active L2S2 heterotetramer

Question 10

What are the main 3 aims of a caspase cascade

Answer 10

• amplification
• divergent responses
• regulation

Question 11

WHat do the initiator caspases do?

Answer 11

trigger apoptosis by cleavage and activating

Question 12

What do the effector caspases do?

Answer 12

-carry out the apoptotic programme

Question 13

WHat 2 ways do the effector caspases carry out the apoptotic programme?

Answer 13

-cleave and inactivate protein or complexes e.g. nuclear lamins leading to nuclear breakdown

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Question 14

WHat 2 ways do the effector caspases carry out the apoptotic programme?

Answer 14

• cleave and inactivate protein or complexes e.g. nuclear lamins leading to nuclear breakdown
• activate enzymes e.g. CAD by direct cleavage or cleavage of inhibitory molecules

Question 15

What are the mechanisms of caspase activation?

Answer 15

• death by design (receptor mediated pathways)

- death by default (mitochondrial death pathway)

Question 16

What do death receptors in cells consist of?

Answer 16

• extracellular cystine rich domain
• singular transcellular domain
• cytoplasmic tail

the receptors are only activated when they come into contact with death ligands e.g. fas

Question 17

Which two adaptor proteins are very important in the extrinsic pathway?

Answer 17

• FADD - positive regulator and promotes cell death

- FLIP - negative regulator, inhibits the death pathway

Question 18

How does signalling occur through death receptors?

Answer 18

• Fas ligand binds to Fas receptor on the surface of cytotoxic T cells
• this causes trimerization of the death domains which the recruit the positive adapter protein FADD through its DD
• this causes the recruitment and oligomerisation of procaspase 8 through its DED to FADD DED
• This then causes a death inducing signalling complex (DISC)

Question 19

What occurs next?

Answer 19

• procaspases bind via their DED domains to FADD
• this brings 3 initiator procaspases into close proximity, which allows cleavage and release of the active initiator caspase 8 tetramer

Question 20

How many procaspases do you need to form an active tetramer?

Answer 20

at least 2

Question 21

How does FLIP inhibit procaspase 8 activation?

Answer 21

• competes for binding to receptor tails via DED domains

- it incorporates into receptor-procaspase complexes and interferes with trans cleavage

Question 22

Summarise what occurs during the mitochondrial regulation of apoptosis

Answer 22

internal stresses cause a loss of mitochondrial membrane potential

• this results in a release of cytochrome C and other apoptosis-inducing factors
• these stimulate the formation of the apoptosis complex