Apoptosis

Question 1

What is apoptosis characterised by?

Answer 1

A series of dramatic perturbations to cellular architecture

Question 2

What do these dramatic disturbances to cellular architecture contribute to?

Answer 2

Cell death
Preparation of cells for removal by phagocytes
Prevent unwanted immune response

Question 3

Which protein family orchestrate the demolition phase of apoptosis?

Answer 3

Caspase family of cysteine proteases

Question 4

What is a caspase?

Answer 4

Family of proteases with an essential cysteine residue in their active site

Question 5

What are the two types of caspase?

Answer 5

Initiator and Effector

Question 6

When are initiator caspases typically activated?

Answer 6

In response to particular stimuli

Question 7

What are effector caspases important for?

Answer 7

Ordered dismantling of vital cellular structures

Question 8

Why is apoptosis controlled?

Answer 8

To minimise damage and disruption to neighbouring cells.

Question 9

How quickly are cells that undergo apoptosis replaced?

Answer 9

Within a few hours

Question 10

How does the cell undergoing apoptosis initially appear from outside?

Answer 10

Becomes rounded and retracts from neighbouring cells

Question 11

What follows cell rounding and retraction?

Answer 11

Plasma membrane blebbing. Blebs pinch off to form apoptotic bodies.

Question 12

Why is phagocytic engulfment of cells undergoing apoptosis remarkable?

Answer 12

Phagocytes normally recognise and remove foreign/non-self entities. The phagocytes recognise a difference between apoptotic cells and their viable counterparts.

Question 13

What do the many alterations in internal architecture do?

Answer 13

• Minimise activation of the immune system

- Increase the efficiency of disposal process

Question 14

What is the most noticeable feature of apoptosis within the cell?

Answer 14

The condensation and fragmentation of the nucleus

Question 15

What else undergoes fragmentation in apoptosis?

Answer 15

• Golgi apparatus
• ER
• Mitochondrial networks

Question 16

What is released from the inter-membrane space of mitochondria?

Answer 16

Numerous proteins, including Cytochrome C

Question 17

What does Cytochrome C do?

Answer 17

Triggers the assembly of caspase-activating complex (the apoptosome) on release into the cytosol.

Question 18

What is the apoptosome?

Answer 18

A large protein complex that recruits pro-caspase-9 and allosterically activates caspase-9. Consists of cytochrome c and APAF1 (apoptotic protease-activating factor 1)

Question 19

What are most proteolysis and cellular events in apoptosis due to?

Answer 19

Caspase-mediated cleavage of particular substrate proteins.

Question 20

What is necrosis accompanied by?

Answer 20

Rapid loss of membrane integrity and release of cellular contents into the ECF

Question 21

How does the immune system respond to necrotic and apoptotic cells?

Answer 21

Differently

Question 22

How do necrotic cells trigger inflammation?

Answer 22

By releasing DAMPs (danger associated molecular patterns) stimulating receptors on neutrophils, macrophages, and other innate immune system elements.

Question 23

How are caspases normally present (i.e. in a healthy cell)?

Answer 23

As zymogens (inactive precursor enzymes)

Question 24

How many main routes to apoptosis associated caspase activation are there?

Answer 24

3

Question 25

What are the major effector caspases?

Answer 25

Caspase-3, caspase-6, and caspase 7

Question 26

What cytoskeleton components are substrates for caspases in apoptosis?

Answer 26

- Actin - Actin-associated proteins - myosin, spectrins, alpha-actinin, gelsolin, filamin - Tubulins, microtubule-associated proteins

Question 27

What is a consequence of weakening the cytoskeleton?

Answer 27

Blebbing - this requires areas of the plasma membrane to be unsupported so blebs can form in these areas. Also requires some areas of intact filaments.

Question 28

How do surrounding cells fill the gap left by dead cells?

Answer 28

Dying cell signal for the formation of actin cables within it's neighbours. These cables contract and extrude the dying cell.

Question 29

What does BCL-2 stand for?

Answer 29

B-cell lymphoma-2

Question 30

What is the BCL-2 family?

Answer 30

Family of proteins crucial in regulation of apoptosis

Question 31

How do BCL-2 proteins regulate apoptosis?

Answer 31

Regulate mitochondrial cytochrome c release

Question 32

How many BCL-2 subfamilies are there?

Answer 32

3

Question 33

What are the 3 BCL-2 subfamilies?

Answer 33

- Anti-apoptotic subfamily - Pro-apoptotic BAX-like subfamily - BH3-only proteins

Question 34

What do BH3-ony proteins do?

Answer 34

Promote apoptosis when overexpressed

Question 35

How many BH3-only proteins are transcriptionally upregulated byp53?

Answer 35

3 (NOXA, PUMA and BID)

Question 36

What happens to some BH3-only proteins during cytockeleton disruption?

Answer 36

They are released from the cytoskeleton, where they are tethered, to promote apoptosis

Question 37

What do anti-apoptotic BCL-2 family members do?

Answer 37

Block apoptosis by preventing BH3-only proteins from inducing the pro-apoptotic family members.

Question 38

How do caspases act functionally?

Answer 38

As heterotetramers

Question 39

Do all mammalian caspases participate in apoptosis?

Answer 39

No

Question 40

Why does the nucleus fragment in apoptosis?

Answer 40

Dunno, no-one's worked it out yet. Possibly to do with contributing to the irreversiblility of the death process.

Question 41

What can result in delay to the onset of DNA fragmentation?

Answer 41

Mutant forms of lamins in the nuclear lamina that resist caspase-mediated proteolysis

Question 42

How do cells undergoing apoptosis retract from neighbouring cells?

Answer 42

Caspase-dependant dismantling of cell-matrix focal adhesion points, and cell-cell adhesion complexes

Question 43

What is a cadherin?

Answer 43

A transmembrane protein that plays a role in cell adhesion.

Question 44

What do caspases do to cadherin?

Answer 44

Degrade them by proteolysis

Question 45

What else do caspases target?

Answer 45

Proteins that function in transcription and translation, and rRNA.

Question 46

What degrades DNA during apoptosis?

Answer 46

Caspase-activaed DNase (CAD)

Question 47

How is CAD normally found?

Answer 47

In healthy cells, CAD is found with its inhibitor in a complex.

Question 48

What happens to the CAD/ICAD complex in apoptosis?

Answer 48

Caspases cleave the ICAD to liberate CAD

Question 49

What is the last act of the dying cell?

Answer 49

The generation of binding sites for phagocytes and the release of chemoattractant molecules

Question 50

What are BCL-2 antagonists?

Answer 50

Cancer therapy that blocks the action of BCL-2 in cancer to promote apoptosis

Question 51

What have BCL-2 antagonists proved effective in treating?

Answer 51

Chronic lymphocytic leukaemia

Question 52

What are SMAC mimetics?

Answer 52

New targeted drug therapy that induce apoptotic death of cancer cells

Question 53

What is IAP?

Answer 53

Inhibitor of Apoptosis protein - normally inhibit caspases to protect against inadvertent cell death. Expressed in excess in many human cancers.

Question 54

What do SMAC mimetics do?

Answer 54

Induce proteasomal degradation of IAPs