Lecture 15

Question 1

What is the difference between accidental cell death and programmed cell death?

Answer 1

Programmed cell death is regulated.

Question 2

When is regulated cell death initiated?

Answer 2

Not directly, but only when adaptation of homeostasis fails does the stress signal become leathal

Question 3

What are the types of regulated cell death?

Answer 3

Caspase depenadant and caspase indipendant

Question 4

What are the types of caspase dependant cell deaths?

Answer 4

Apoptosis and Pyroptosis

Question 5

What are the types of caspase independant cell deaths?

Answer 5

Necroptosis, Ferroptosis, …

Question 6

What is the difference between Apoptosis and all other cell deaths?

Answer 6

Apoptosis does not lead to membrane rupture and inflammation while all other programmed cell deaths do.

Question 7

When is apoptosis especially important?

Answer 7

During development to remove tissue and sculpt organs. Also plays an important role in immunity

Question 8

What is the phenotype of apoptosis?

Answer 8

cell shrinkage
membrane blebbing
DNA fragmentation
formation of apoptotic bodies
engulfment by neigboring cells

Question 9

What are the two components of caspase activation

Answer 9

Initiator caspase and executioner/effector caspase

Question 10

How are executioner/effector caspases activated?

Answer 10

By cleavage

Question 11

How are initiator caspases activated?

Answer 11

BY being in close proximity to executioner/effector caspases

Question 12

What is a caspase cascade?

Answer 12

One molecule of caspase X activates many molecules of caspase Y which in turn activates many more molecules of caspase Z

Question 13

What are two modes of caspase activation

Answer 13

Intrinsic or extrinsic

Question 14

What is the extrinsic pathway of caspase activation?

Answer 14

caspase 8 activation due to extrinsic signal

Question 15

What is the intrinsic pathway of caspase activation?

Answer 15

intracellular signals (DNA damage/ Mitochondrial damage) -> released cytochrome c -> binds to apa1 and build apoptosome -> recruits caspase 9

Question 16

Why is it difficult to develop specific inhibitors for caspases?

Answer 16

Caspases have similar catalytic domains,
Caspases involved in many processes, off-target effects.
inhibiting caspases inappropriately can lead to adverse effects.

Question 17

Why are some caspases classified as pro-inflammatory and some as anti-inflammatory?

Answer 17

Caspases are involved in both inflammatory responses and normal apoptosis without inflammation (regulated cell death)

Question 18

Describe all the mechanisms how pro-survival BCL-2 proteins can block apoptosis.

Answer 18

BCL-2 binds pro-apoptotic molecules (Bax and Bak)
-> blocks cytochrome c release
(Co-immunoprecipitation)
Bcl dissasembles Bax oligomeres
Inhibition of BH3-Only Proteins:
Inhibition of Caspase Activation:

Question 19

Propose experiments that would help you detect each of the mechanisms. (BLC-2 apoptosis block)

Answer 19

Co-immunoprecipitation
Caspase Activation Assay

Question 20

How are Bax oligomeres formed?

Answer 20

Binds to membrane as monomere and forms oligomere

Question 21

apoptosis, pyroptosis and necroptosis. Please order them from the least inflammatory to the most inflammatory and explain why.

Answer 21

1. Apoptosis
   not inflammatory at all
   actively suppresses inflammation
2. Necroptosis
   can lead to DAMP release which can trigger immune response
   Still no inflammatory signaling pathways are activated
3. Pyroptosis
   Associated with Caspase 1
   release of pro-inflammatory cytokines

Question 22

What is DISC (Death-Inducing Signaling
Complex) and how can you inhibit it?

Answer 22

DISC formed upon death receptor recruitment
Procaspase 8 binds to DISC and activates

FLIPs, which compete with caspase 8 for
binding to the DISC