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BMS2.21 Apoptosis (FOTY) > Apoptosis > Flashcards

Apoptosis Flashcards

1
Q

Apoptosis is defined as:

A
  • programmed cell death
    • death by suicide
  • integral to tissue development
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2
Q

Autophagy is defined as:

A
  • a catabolic process involving the degradation of a cell’s own components through the lysosomal machinery
  • death by self-cannibalism
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3
Q

Necrosis is defined as:

A
  • the premature death of cells by external factors
  • death by accident or murder
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4
Q

Four functions of apoptosis:

A
  • Development
    • tissue-sculpting
  • Immune System
    • eliminating used T and B cells after infection
  • Tissue homeostasis
    • balance between cell proliferation and death
  • Cancer prevention
    • eliminating cells that have been damaged by UV, radiation, chemical toxins, or viral infection
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5
Q

Syndactyly:

A
  • a condition wherein two or more digits are fused together.
  • due to apoptosis misregulation
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6
Q

What is the major distinction between necrosis and apoptosis?

A
  • the cell membrane remains intact during apoptosis - leads to NO immune response.
    • it bursts in necrosis, leading to an immune response.
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7
Q

Cell shrinkage and membrane blebbing during apoptosis is due to:

A

actin cytoskeleton degradation

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8
Q

8 Morphological Markers of Apoptosis:

A
  1. Electron-dense nucleus (early phase).
  2. Nuclear fragmentation.
  3. Intact cell membranes.
  4. Disorganized cytoplasmic organelles.
  5. Large, clear vacuoles.
  6. Blebs at the surface.
  7. Loss of cell-cell adhesion.
  8. Apoptotic bodies.
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9
Q

What is this an image of?

A

Apoptosis

Cell shrinkage.

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10
Q

What is this an image of?

A

Apoptosis

Membrane Blebbing

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11
Q

What is this an image of?

A

Apoptosis

Chromatin Condensation

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12
Q

What is this an image of?

A

Apoptosis

Apoptotic Bodies

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13
Q

What are the four biochemical markers of apoptosis?

A
  • phosphatidyl-serine flipping (Annexin V)
  • increase in DNA nicks (TUNEL)
  • DNA laddering (PCR)
  • caspase activation (PCR)
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14
Q

Phosphatidyl-serine (PS) flipping:

A
  • a biochemical marker of apoptosis
  • phosphatidyl-serine is a phospholipid normally on the cytoplasmic side of the membrane, but flips to the extracellular side during apoptosis.
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15
Q

Phosphatidyl-serine (PS) flipping can be visualized through what method?

A
  • annexin V antibody coupled with GTP
  • can use flow cytometry to quantify amount of apoptosis.
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16
Q

Reasoning behind TUNEL:

(Terminal Transferase dUTP Nick-End Labeling)

A
  • DNA in an apoptotic cell has more nicks in it.
  • label the nicks with dUTP with a flourescent protein on it.
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17
Q

TUNEL advantages and disadvantages:

(Terminal Transferase dUTP Nick-End Labeling)

A
  • fast, sensitive, reproducible.
  • Disadvantages:
    • # of breaks necessary for detection unknown.
    • necrotic cells cen generate false +.
    • detergent used may make cells fragile.
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18
Q

DNA Laddering:

A
  • apoptosis marker.
  • distinctive feature of DNA degraded by caspase-activated DNase (CAD).
  • CAD cleaves genomic DNA at internucleosomal linker regions, resulting in DNA fragments that are multiples of 180–185 base-pairs in length.
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19
Q

What band on PCR comes up during apoptosis due to Caspase cleavage/activation?

A
  • Cleaved caspase produces a band at 17kDa on PCR; APOPTOSIS.
  • Uncleaved caspase produces a band at 33kDa on PCR; NORMAL.
  • Lanes 2, 3, and 4 are dying cells.
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20
Q

In order to become active, caspases must be:

A
  • cleaved.
    • this process of cleavage is reversible if the apoptotic-causing agent is removed.
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21
Q

What are the two major apoptotic pathways?

A
  • cell intrinsic pathway
    • works through mitochondria
  • cell extrinsic pathway
    • works through “death receptors” on the cell surface that bind pro-apoptotic ligands
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22
Q

The two major apoptotic pathways of the cell converge on what level?

A

the level of the caspases

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23
Q

Caspases are:

A
  • “molecular hitmen”
  • enzymes that give rise to all of the morphological and biochemical changes arising from apoptosis.
  • Must be cleaved to become active.
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24
Q

What are the two types of apoptotic caspases?

A
  • initiator (apical) caspases (2,8,9, and 10)
  • effector (executioner) caspases (3,6, and 7)
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25
Q

What # caspases are the initiator (apical) caspases?

A

caspases 2, 8, 9, and 10

  • give the order for cell death
26
Q

What # caspases are the effector (executioner) caspases?

A

caspases 3, 6, and 7

27
Q

Caspases are regulated at what level?

A
  • post-translationally
  • caspases are always present in the cell in an inactive state.
    • can become rapidly activated if needed.
28
Q

The caspase cascade:

A
  1. pro-apoptotic stimulus (i.e. p53).
  2. intiator caspases cleaved and activated.
  3. initiator caspases cleave and activate effector caspases.
  4. apoptosis occurs.
29
Q

How many proteolytic cleavages are necessary for initator caspase activation?

A
  • two
30
Q

Steps in how caspase activation results in DNA fragmentation:

A
  • caspase 3 and 7 binds to DFF45/DFF40 dimer.
  • DFF45 cleaved and DFF40 released.
  • DFF40 oligomerizes into an active DNAase and cleaves DNA.
  • leads to DNA ladder on PCR.
31
Q

The BCL2 superfamily of proteins regulates:

A
  • the integrity of the mitochondrial membrane
  • contains pro-apoptotic and anti-apoptotic proteins
32
Q

What occurs when the integrity of the mitochondrial membrane is compromised?

A
  • it leaks out cytochrome C.
  • Cytochrome C interacts with APAF1 to form the apoptosome which will activate the initiator caspases.
    • Effector caspases then activated and apoptosis occurs.
33
Q

Steps in DNA-damage to apoptosis:

A
  1. p53 senses DNA damage.
  2. BH3 sensors BID/BAD/PUMA activated.
  3. BAX and BAK of BCL2 family activated.
  4. BAX and BAK compromise integrity of mitochondrial wall. Cytochrome C leaks out.
  5. Cytochrome C interacts with APAF1 to form the apoptosome.
  6. Apoptosome activates intiator caspase 9.
  7. Initiator caspases activate effector caspases 3, 6, and 7.
  8. Apoptosis occurs.
34
Q

What proteins in the BCL2 superfamily are anti-apoptotic and maintain integrity of the mitochonrial membrane?

A

BCL2, BCL-XL, MCL1

  • bind to mitochondrial membrane
  • no leakage of cytochrome C
35
Q

What proteins in the BCL2 superfamily are pro-apoptotic and compromise integrity of the mitochonrial membrane?

A

BAX and BAK

36
Q

p53 is:

A
  • a transcription factor that regulates the cell cycle and apoptosis
37
Q

p53 mechanisms of anticancer function (3):

A
  • can activate DNA repair proteins when DNA has sustained damage.
  • can arrest growth by holding the cell cycle at the G1/S regulation point.
  • can initiate apoptosis if DNA damage proves to be irreparable.
38
Q

p53 levels in unstressed cells:

A
  • low levels due to continuous degradation
39
Q

How is p53 kept at low levels in unstressed cells?

A
  • Mdm2 acts as ubiquitin ligase and covalently attaches ubiquitin to p53 and thus marks p53 for degradation by the proteasome.
  • Mdm2 also transports p53 from the nucleus to the cytosol.
40
Q

What protein ubiquitinates p53?

A

Mdm2

41
Q

What is the critical event in the activation of p53?

A
  • phosphorylation of the p53 N-terminal domain.
42
Q

What enzymes can activate p53 through phosphorylating its N-terminal domain?

A
  • Members of the MAPK family
    • JNK1-3, ERK1-2, p38 MAPK
  • Checkpoint kinases
    • ATR, ATM, CHK1 and CHK2, DNA-PK, CAK, TP53RK
  • Oncogenes, mediated by the protein p14ARF.
43
Q

What pro-apoptotic molecules are normally found in the cytosol, translocate to the mitochondrial membrane, and stimulate the formation of pores allowing cytochrome C to leak out?

A

BAD, BAX, BID

44
Q

BCL-2 protein:

A

anti-apoptotic

  • binds BAX/BAK and prevents mitochondrial pore formation.
45
Q

BID and BAD proteins:

A

promote apoptosis

  • tie up BCL-2 and free BAX/BAK.
  • BID may also interact with BAX/BAK to open mitochondrial pores.
46
Q

BAX and BAK proteins:

A

promote apoptosis

  • promote mitochondrial pore formation and release of cytochrome c when APAF1 initiates apoptosis
47
Q

Follicular lymphoma is due to:

A
  • chromosome translocation that greatly increases the expression of BCL-2.
  • cell do not undergo apoptosis, cancer occurs
48
Q

Conventional anticancer therapies, such as chemotherapy and radiotherapy, activate the intrinsic apoptosis pathway via:

A

p53

49
Q

Steps in the Extrinsic Apoptosis Pathway:

A
  1. Apo2L/TRAIL ligand binds to pro-apoptotic receptors DR4 and DR5.
  2. Activated DR4 and DR5 recruit fas-associated death domain (FADD). Death-inducing signaling complex (DISC) forms.
  3. FADD recruits initiator caspase 8 and/or 10 to the DISC.
  4. DISC undergoes autocatalysis, activating caspase 8 and 10.
  5. Activated caspases 8 and 10 are released into the cytoplasm and activate effector capsizes 3, 6, and 7.
  6. Apoptosis occurs.
50
Q

What ligand binds to the pro-apoptotic receptors DR4 and DR5 in the extrinsic apoptosis pathway?

A

Apo2L/TRAIL

51
Q

Where do the extrinsic and intrinsic apoptosis pathways converge?

A
  • initiator caspases 8 and 10
  • BID
    • BID is activated by initiator caspases 8 and 10.
    • BID ties up BCL-2 and free BAX/BAK, which are all in the intrinsic apoptosis pathway.
52
Q

Autophagy is responsible for:

A
  • degrading cellular proteins and organelles and recycling them.
  • it is a survival pathway.
53
Q

When is autophagy activated?

A
  • response to cellular starvation.
    • when nutrient levels are low, cells self-cannibalize and recycle proteins for metabolism.
  • housekeeping process.
    • long-lived proteins and organelles are recycled.
  • Normal cellular processes.
54
Q

The four stages of autophagy:

A
  • Induction.
  • Autophagosome formation.
  • Autophagosome lysosome fusion.
  • Autophagosome breakdown.
55
Q

What protein regulates autophagy under nutrient-rich and starvation conditions?

A
  • mTOR
    • inhibits autophagy in nutrient-rich conditions
    • in starvation, mTOR is inhibited, which leads to autophagy activation
56
Q

Many of the autophagy genes that are upregulated in response to mTor deactivation participate in what process?

A

Autophagosome Formation

  • formation of a membrane around a targeted portion of the cell.
57
Q

What is autophagosome formation?

A
  • the formation of a membrane around a targeted portion of the cell.
58
Q

Are the effects of necrosis reversible?

A

No.

59
Q

Necrosis is caused by:

A
  • factors external to the cell or tissue, such as infection, toxins, or trauma.
60
Q

Five types of necrosis:

A
  • Coagulation necrosis
    • ischemia
  • Liquefactive necrosis
    • cell destruction leading to escape of hydrolases
  • Enzymatic fat necrosis
    • escape of lipases
  • Caseous necrosis
    • bacterial liquefaction
  • Gangrenous necrosis
    • ischemic + bacterial liquefaction

BMS2.21 Apoptosis (FOTY) (2 decks)

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