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Molecular Biology of the Cell > Section 4 Lecture 2 Cell Death > Flashcards

Section 4 Lecture 2 Cell Death Flashcards

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1
Q

Bak

A

Pro-apoptotic effector Bcl2 family protein always located on the mitochondrial outer membrane.
When activated by apoptotic stimulus, oligomerizes to release cytochrome C.

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2
Q

Bax

A

Pro-apoptotic effector Bcl2 family protein located in the cytosol and translocates to mitochondrial outer membrane due to apoptotic stimulus to release cytochrome C.

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3
Q

What are the 3 Bcl 2 family proteins?

A
  1. Anti-apoptotic Bcl2 family proteins
  2. Pro-apoptotic effector Bcl2 family proteins
  3. Pro-apoptotic BH3 only proteins
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4
Q

Examples of pro-apoptotic effector Bcl2 proteins

A

Bak and Bax

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5
Q

Examples of anti-apoptotic Bcl-2 family proteins

A

Bcl2 and BclXL

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6
Q

Examples of pro-apoptotic BH3 only proteins

A

Bad, Bim, Bid, Puma, and Noxa

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7
Q

Bcl2 family proteins regulate which pathway?

A

Intrinsic pathway - stimulate or inhibit cytochrome C release from mitochondria

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8
Q

What are the 2 types of cell death?

A

Necrosis and Apoptosis

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9
Q

What are the differences between necrosis and apoptosis?

A 
Apoptosis: 
programmed cell death
cell breaks into apoptotic bodies
No inflammation
phagocytosis
Necrosis: 
Accidental cell death
Cellular Swelling
Pro-inflammatory
Enzymatic digestion and leakage of cellular contents
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10
Q

PS

A

Phosphatidylserine - on the surface of apoptotic cells

Interact with microphages to produce phagocytosis

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11
Q

Blebbing

A

hallmark of apoptosis

bulges of the plasma membrane that is filled with cytosol

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12
Q

Markers of Apoptosis

A
  1. Flipping of Phosphatidylserine - PS flips from the inner lining of the plasma membrane to the outer membrane > determined using GFP-Annexin V which recognizes PS on the outside of the cell and can be seen via microscopy which cells are committed to apoptosis.
  2. DNA fragmentation > determined via Agarose Gel
  3. Release of cyt C from mito to cytosol > determined with Cyt C-GFP visualization of where it is located
  4. Cleaved caspases and targets > Caspase 3 and PARP fragments determined by Western Blot
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13
Q

Annexin V

A

recognizes PS on the outside of the cell and binds to it

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14
Q

2 types of Caspases

A
  1. Initiator

2. Executioner

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15
Q

Caspases are…

A

proteases with cysteine at the active site and cleave targets at aspartic acids (C = cysteine; asp= aspartic acid; ases= proteases)

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16
Q

Examples of Initiator caspases

A

Caspases 8 and 9

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17
Q

Examples of Executioner caspases

A

Caspases 3, 6, and 7

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18
Q

What form is an inactive initiator caspase in?

A

Monomer

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19
Q

What form is an inactive executioner caspase in?

A

Dimer

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20
Q

What form is an active executioner caspase in?

A

Tetramer

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21
Q

Caspase Cascade

A

Apoptotic Signal > Adapter proteins assemble > Dimerization, Activation , and Cleavage of initiator procaspases > Rearrangement of protease domain = Active initiator caspase > Activate by Cleaving Executioner caspase from a dimer to a tetramer => Cleavage of multiple substrates => Apoptosis

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22
Q

Targets of caspases

A
  1. Nuclear lamins
  2. iCADs proteins > frees endonucleases > DNA fragmentation
  3. cytoskeleton (microtubules and filaments)
  4. cell-to-cell adhesion proteins
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23
Q

Caspase Cascade Activation Pathways

A
  1. Extrinsic Pathway

2. Intrinsic Pathway

24
Q

Extrinsic Pathway

A

Triggered by cell surface receptors receiving an apoptotic signal

25
Q

Intrinsic Pathway

A

Activated by release of Cytochrome C from mitochondria into cytosol

26
Q

Parts of the Extrinsic Pathway

A
  1. TNF family (i.e. TNF and Fas ligands) extracellular signal are received by cell surface death receptors.
  2. Fas receptor recruits FADD adapter protein through death domain
  3. FADD recruits initiator procaspases through death effector domain
  4. DISC complex formed
  5. Activating the interior caspases through induced proximity
  6. Caspase Cascade activation
  7. Apoptosis
27
Q

DISC

A

Death-inducing signaling complex

28
Q

Inhibitors of extrinsic pathway

A
  1. Decoy receptors that lack death domain > does not induce DISC formation
  2. FLIP proteins that lack cleavage domain
29
Q

FADD

A

Fas-associated death domain

30
Q

Cell surface death receptors are…

A

trimeric

31
Q

3 domains of trimeric death receptors

A
  1. Extracellular ligand- binding domain
  2. Single transmembrane domain
  3. Intracellular death domain
32
Q

Parts of Intrinsic Pathway

A
  1. Apoptotic stimulus from inside of the cell (i.e. DNA damage)
  2. Cytochrome C released from mitochondria
  3. Cyt C binds to Apaf 1
  4. Apaf 1 structural change that exposes CARD
  5. Apoptosome complex forms through exposed CARDs to form wheel-like heptomer
  6. CARD recruits initiator Procaspase 9 to each exposed CARD
  7. Induced proximity induces proteolytic cleavage of Procaspase 9
  8. Activation of executioner caspases
  9. Caspase cascade > Apoptosis
33
Q

Apaf 1

A

Apoptotic protease activating factor 1

34
Q

CARD

A

Caspase Recruitment Domain

35
Q

Apoptosome

A

Heptomer complex that forms in the Intrinsic pathway due to exposed CARD on the Apaf 1 - Cyt C complex
Recruits Procaspase 9

36
Q

Bcl 2 proteins

A

Regulate the intrinsic pathway

Stimulate or inhibit release of cyt C from mito

37
Q

3 types of Bcl 2 proteins

A
  1. Anti-apoptotic Bcl 2
  2. Pro-apoptotic effector Bcl 2
  3. Pro-apoptotic BH3-only protein
38
Q

Bax

A

Pro-apoptotic effector Bcl 2

In cytosol, oligomerizes in the outer mitochondria membrane upon apoptotic stimulus

39
Q

Bcl 2 and BclXL

A

Examples of Anti-apoptotic Bcl 2

40
Q

Largest Bcl 2 subfamily

A

Pro-apoptotic BH3-only proteins

41
Q

Bad

A

Pro-apoptotic BH3-only protein
Binds to anti-apoptotic Bcl 2 survival factor to inhibit it and allow apoptosis to take place.
Akt pathway phosphorylates Bad and deactivates it so that Bcl 2 can prevent apoptosis

42
Q

Bim, Puma, Noxa, Bid, and Bad

A

Pro-apoptotic BH3-only proteins

43
Q

Bid

A

Pro-apoptotic BH3-only protein that links the extrinsic to the intrinsic pathway to amplify the apoptotic signal

  1. Initiator caspase 8 of extrinsic pathway cleaves cytosolic Bid
  2. tBid (truncated Bid) goes to mito and inhibits Bcl 2
  3. Bax and/ or Bak are allowed to oligomerize and release cyt C which will lead to apoptosis
44
Q

Which Bcl 2 BH domain in shared by all?

A

BH3

45
Q

Bac

A

Pro-apoptotic effector Bcl 2
Always bound to the other mitochondrial membrane to oligomerize and allow cytochrome C to exit into the cytosol upon apoptotic signal

46
Q

Pro-apoptotic effector Bcl2 proteins

A

trigger release of cyt. C from mitochondrial intermembrane

i.e Bak and Bax

47
Q

Anti-apoptotic Bcl 2 proteins

A

inhibit oligomerization Bak and Bax effector proteins

located on cytosolic surface of outer mito membrane

48
Q

Pro-apoptotic BH3-only proteins

A

inhibit anti-apoptotic Bcl 2 proteins to allow Bax and Bak to function
Binds to Bcl 2 and neutralizes activity
Produced/ activated from apoptotic signal

49
Q

Apoptotic stimuli to activate BH3-only proteins

A
  1. Deprivation of survival signals > Activate JNK > transcription of Bim
  2. Irreparable DNA damage > activates p53 > transcription of Puma and Noxa
50
Q

IAPs

A

Inhibitors of Apoptosis

Control caspase activity

51
Q

Anti-IAPs

A

inhibit IAPs = Promote apoptosis

released by mitochondria with cyt C to promote intrinsic pathway

52
Q

Extracellular survival factors

A

Inhibit apoptosis
usually cell-to-cell signals in tissue cells
i.e. nervous system
requires continuous signaling to avoid apoptosis
ensures cell survives on when and where needed

53
Q

Nervous system cell survival

A

Nerve cells produced in excess.
Apoptosis regulated by abundance of survival factor that is released by target cells. If there are too many nerve cells they will not receive enough survival factor and undergo apoptosis

54
Q

3 Mechanisms of Action for Survival Factors

A
  1. Increased production of anti-apoptotic Bcl2 family protein through transcription
  2. Inactivation of pro-apoptotic BH3-only protein (Akt -Bad pathway)
  3. Inactivation of anti-IAPs (Hid deactivation through MAP Kinase phosphorylation of Hid > IAPs released to promote survival)
55
Q

Cancer therapies targeting apoptosis

A
  1. Target Bcl 2 > activate intrinsic pathway
  2. Pro-apoptotic receptor peptides = ligands to activate apoptosis (i.e. Fas and TNF)
  3. Target IAPs
56
Q

6 Hallmarks of Cancer

A
  1. Evade apoptosis
  2. Self sufficient growth signals
  3. Insensitivity of antigrowth signals
  4. Sustained angiogenesis
  5. Limitless replicative potential
  6. Tissue invasion and metastasis

Molecular Biology of the Cell (2 decks)

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