Inim3004 - Apoptosis

Front 1

What is apoptosis?

Back 1

Programmed cell death involving characteristic morphological and biochemical changes that can readily distinguish it from pathological, necrotic death.

Front 2

Describe some of the key changes in apoptosis. (1)

Back 2

Nucleus and cytoplasm shrink.

Front 3

Describe some key changes in apoptosis. Clue: think mitochondria.

Back 3

Mitochondria undergoes morphological changes and membrane depolarisation.

Release of cytochrome c and other proapoptotic material into cytoplasm.

Activation of caspases and nucleases.

Front 4

Describe some key changes in apoptosis. Clue: think plasma membrane.

Back 4

Blebbing of plasma membrane resulting in recognition of apoptotic cell by phagocytes.

Chemical changes in PM to allow its recognition by for phagocytosis.

Front 5

Describe some key changes in apoptosis. Clue: think DNA.

Back 5

Chromatin condenses and nuclei become distorted and fragmented (due to nucleases cleaving DNA in strands between nucleases).

Front 6

Describe one cause of apoptosis. (1)

Back 6

WIthdrawal of survival factors.

Front 7

Describe one cause of apoptosis. (2)

Back 7

Death ligand e.g binding of Fas ligand to Fas (death receptor) activates cell death programme in cell.

Front 8

Describe one cause of apoptosis. (3)

Back 8

Injury/stress e.g. DNA damage. When chromosomal DNA is damaged, a DNA damage response is activated and the p53 tumour suppressor protein plays a crucial role and activates the transcription of DNA repair genes but also genes that trigger apoptosis

Front 9

Describe one cause of apoptosis. (4)

Back 9

Cytotoxic T cells (CTL) kill their targets by inducing apoptosis. Granzyme B produced by CTLs activates caspases in the target.

Front 10

Describe one cause of apoptosis. (5)

Back 10

Viral infection can trigger apoptosis in infected cell. However, this is not good for virus as it would be unable to replicate and produce progeny. Many viruses encode proteins that inhibit apoptosis

Front 11

Name the protein encoded for by adenoviruses that inhibits apoptosis.

Back 11

E1b 19k.

Front 12

Describe one function of apoptosis. (1)

Back 12

Deleting structures that are vestigial e.g. regression of a tadpole tail.

Front 13

Describe one function of apoptosis. (2)

Back 13

Sculpting e.g. removal of webbing between digits found in paws of mice.

Front 14

Describe one function of apoptosis. (3)

Back 14

Adjusting cell numbers; about 50% of neurons that are formed during neurogenesis die via apoptosis during embryogenesis.

Front 15

Describe one function of apoptosis. (4)

Back 15

Eliminating damage cells; e.g. deletion of cells with damaged DNA that could be potentially tumourogenic by p53.

Front 16

Describe one function of apoptosis. (5)

Back 16

Eliminating potentially harmful cells e.g. negative selection of autoreactive T cells by Tregs within the thymus.

Front 17

Describe one function of apoptosis. (6)

Back 17

Killing of pathogen infected cells by CTLs.

Front 18

What are caspases?

Back 18

Central executioners of the apoptotic pathway. They are proteases with a cysteine active site that cleave after aspartic acid residues.

Cleavage of caspase substrates leads to characteristic morphological changes.

Front 19

How is substrate specificty obtained in caspases?

Back 19

By four residues that lie N-terminal to cleavage site.

This helps divide caspases into subfamilies.

Front 20

Describe the structure of a zymogen caspase-precursor.

Back 20

Three domains: N-terminal pre-domain, p20 and p10.

Front 21

Describe the structure of a mature caspase.

Back 21

Heterotetramer with two active sites.

Front 22

Which caspases are cleaved by upstream caspases?

Back 22

Caspases -3, -6 & -7 aka effector caspases.

They are cleaved by upstream caspases (and also by granzyme B) and will then readily form dimers.

Front 23

How are intiator caspases activated?

Back 23

Caspase-8 & -9 are activated by interaction with adaptor proteins via their prodomains and subsequently dimerise and become activated.

Front 24

How is caspase-8 activated?

Back 24

Proximity-induced dimerization; FasL binding Fas results in recruitment of several procaspase-8 molecules via FADD adaptor protein

Procaspase-8 dimerize, become maturationally cleaved and are activated.

Front 25

How is caspase-9 activated?

Back 25

Release of cytochrome C and ATP dependent oligomizeration of Apaf-1 (adaptor protein) results in recruitment of caspase-9 to apoptosome.

Caspase-9 interacts with Apaf-1 via its CARD domain.

Front 26

What is the apoptosome?

Back 26

A quaternary multi-protein structure formed cytochrome C and caspase-9 proteins arranged around a central Apaf-1 protein.

Front 27

Describe one caspase substrate. (1)

Back 27

ICAD; cleavage of ICAD release active CAD (caspase-activated DNase) that cuts genomic DNA between nucleosome.

Front 28

Describe one caspase substrate. (2)

Back 28

BID, cleaved by caspase-8, to tBID will induce mitochondrial changes that will lead to cytochrome c release.

Front 29

Describe one caspase substrate. (3)

Back 29

Fodrin and gelsolin are bothe cytoskeletal proteins that when cleaved can lead to a loss of cell shape.

Front 30

What is th Bcl-2 family?

Back 30

A family of proteins that regulate caspase activity by controlling release of cytochrome c (and other proapoptoic material) from mitochondria.

Front 31

Decribe group I of Bcl family.

Back 31

Group I is anti-apoptotic e.g. Bcl-2 and Bcl-xL.

Each has 4 conserved Bcl-homology (BH) domains

Front 32

What is the role of Bcl?

Back 32

Bcl inhibits the release of cytochrome C (and other pro-apoptotic material) from the mitochondria.

Front 33

Decribe group II of Bcl family.

Back 33

Group II is pro-apoptotic e.g. Bax and Bak.

Similar structure to group I (i.e. 4 x -BH domains)

Front 34

What is the function of Bax?

Back 34

Bax undergoes conformational maturation in cytosol allowing it to translocate to outer membrane of mitochondria and form multimer pores to allow cytochrome C release.

Front 35

Decribe group III of Bcl family.

Back 35

Group III is pro-apoptotic e.g. Bim, Bid, Bik, Bad aka BH-3 only proteins.

Front 36

What is function of Bid and Bim?

Back 36

Bid and Bim facilitate conformational changes and translocation of Bax/Bak.

Front 37

What is the function of Bad?

Back 37

To bind and inactivate group I proteins i.e. Bcl-2 and Bcl-xL

Front 38

What are IAPs?

Back 38

Direct inhibitors of caspases.

Front 39

Describe the structure of IAPs?

Back 39

Contain multiple N-terminal BIR domains and a C-terminal RING domain.

Front 40

Which caspases to XIAP inhibit?

Back 40

Effector caspases i.e. -3 & -7 (& -9)

Front 41

What is SMAC?

Back 41

Antagonist of IAP i.e. promote caspase activity and apoptosis.

Front 42

What is another name for Fas receptor?

Back 42

CD95

Front 43

Describe the structure of Fas.

Back 43

Extracellular cysteine-rich domains, transmembrane protein, intracellular region with death domain.

Front 44

What is DISC?

Back 44

Death inducing signalling complex; formed by FasL binding to Fas.

Recruits RADD which has DD and DED.

This recruits procaspase-8 via DED-DED interactions.

Front 45

Survival signalling (1): what is PI3K-Akt pathway?

Back 45

Akt (aka PKB) phosphorylates Bad and is subsequently sequestered.

Pro-apoptotic. Most likely seen in some cancers.

Front 46

Survival signalling (2): what is the Raf-MEK-ERK pathway?

Back 46

ERK 1/2 binds and phosphorylated caspase-9.

ERK also phosphorylates Bim, resulting in its ubiquitination and degradation via the proteasome.

Front 47

How many cells are in a C. elegans and how may die during development?

Back 47

1090 formed, 131 apoptose during development.

Front 48

What gene in C. elegans is the homologue to: caspases?

Back 48

CED-3.

Front 49

What gene in C. elegans is the homologue to: Apaf-1

Back 49

CED-4

Front 50

What gene in C. elegans is the homologue to: Bcl-2

Back 50

CED-9

Front 51

Apoptosis and: retinal degeneration.

Back 51

p35 caspase inhibitor leads to apoptosis of retinal photoreceptor neurons.

Front 52

Apoptosis and: Alzheimer's disease.

Back 52

Beta-amyloid induces apoptosis in cortical neurons.

Front 53

Apoptosis and: Parkinson's disease.

Back 53

Deletion of Bax gene leads to a protective effect against neurodegeneration similar to that observed in Parkinson's.

Front 54

Apoptosis and: cancer. (1)

Back 54

Bcl-2 is upregulated to prevent apoptosis and allow uninterrupted proliferative growth.

Front 55

Apoptosis and: cancer. (2)

Back 55

Deregulation of C-Myc leads to genetic changes that disable apoptotic pathways.

Front 56

Apoptosis and: cancer. (3)

Back 56

p53, guardian of genome, is disactivated in 50% of cancers.

p53 is involved in transcription of pro-apoptotic proteins e.g. PUMA.

Front 57

Apoptosis and: cancer. (4)

Back 57

30% of patients with glioblastomas are homozygous recessive for PTEN.

PTEN inhibits P13K (survival pathway).
-- P13K (aka PKB) phosphorylates, sequesters Bad
-- -- Bad (pro-apoptotic, group III) binds and inactivates Bcl-2

Front 58

Apoptosis and: new chemotherapeutic drugs

Back 58

ABT-737. Small molecule inhbitor that causes cell death in a Bax/Bak dependent manner by neutralising anti-apoptotic (i.e. pro-tumourogenic) Bcl-2 and Bcl-xL