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Ch 2: Cellular responses to stress etc > Apoptosis and Autophagy > Flashcards

Apoptosis and Autophagy Flashcards

1
Q

The extrinsic pathway of apoptosis is also called the

A

Death receptor initiated pathway

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2
Q

Death receptors are members of the ____ _____ family that contain a cytoplasmic domain called the ________ ________

A

TNF receptor

Death domain

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3
Q

T or F: some TNF receptor family members do not contain cytoplasmic death domains

A

T. Their function is to activate inflammatory cascades.

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4
Q

2 examples of death receptors

A
  1. Type 1 TNF receptor (TFNR1)

2. Fas

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5
Q

The ligand for Fas is called

A

Fas ligand (FasL)

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6
Q

Fas is expressed __ _____ _____ _____.

FasL is expressed on _ _____ that recognise ____ ___________ and on some _________ _ _______.

A

On many cell types
T cells
Self-antigen
Cytotoxic T cells

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7
Q

Describe the pathway initiated by Fas/FasL

A
  1. FasL binds to Fas
  2. 3 or more molecules of Fas are brought together
  3. The Fas cytoplasmic death domains come together to form a binding site for Fas associated death doman (FADD)
  4. FADD binds inactive caspase-8 and caspase-10
  5. Multiple pro-caspase-8 molecules brought into proximity with each other cleave one another to active caspase-8
  6. Subsequent steps same as intrinsic pathway
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8
Q

Fas-mediated apoptosis can be inhibited by?

A

FLIP

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9
Q

Describe the action of FLIP

A

FLIP binds to but cannot activate pro-caspase-8

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10
Q

The intrinsic pathway of apoptosis is also called the?

A

Mitochondrial pathway

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11
Q

T or F: The mitochondrial pathway of apoptosis is the major mechanism of apoptosis in mammalian cells.

A

T

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12
Q

What is the name of the family of proteins responsible for regulation of the mitochondrial pathway of apoptosis?

A

BCL2 family

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13
Q

BCL2 family is divided into 3 groups based on?

A
  1. Pro- or anti-apoptotic action

2. Which BCL2 homology domains (BH domains) they possess

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14
Q

What are the 3 groups of BCL2 proteins?

A
  1. Anti-apoptotic
  2. Pro-apoptotic
  3. Sensors
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15
Q

Name 3 anti-apoptotic BCL2 proteins.

A
  1. BCL-2
  2. BCL-XL
  3. MCL1
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16
Q

What is the action of the anti-apoptotic BCL2 proteins?

A

To keep the outer mitochondrial membrane impermeable.

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17
Q

Name 2 pro-apoptotic BCL2 proteins

A
  1. BAX

2. BAK

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18
Q

Name 5 sensors in the BCL2 family

A
  1. BAD
  2. BIM
  3. BID
  4. Puma
  5. Noxa
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19
Q

Why are the BCL2 sensor proteins also called “BH3” proteins?

A

Because they only contain one of the four BH domains - the third BH domain - whereas the pro- and anti-apoptotic proteins contain all 4 BH domains (BH1-4).

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20
Q

What stimulates production of the anti-apoptotic BCL2 family members?

A

Growth factors and other survival signals.

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21
Q

What activates the sensor/BH3 proteins?

A

Deprivation of survival signals
DNA damage
ER stress from misfolded proteins

22
Q

What activates the pro-apoptotic proteins?

A

Activation of the sensor proteins

23
Q

Upon activation, what do BAX and BAK do?

A

Oligomerize within the outer mitochondrial membrane and promote permeability, possibly by forming a channel in the membrane.

24
Q

At the same time, the production of BCL-2 and BCL-XL _________ because of ______ ____ ________ _________

A

Decline

Deficiency of survival signals

25
Q

Outer mitochondrial membrane permeability allows leakage of ________ __ into the cytosol

A

Cytochrome C

26
Q

Once in the cytosol, Cytochrome C binds?

A

APAF1 - apoptosis activating factor 1

27
Q

Cytochrome C binding to APAF1 forms?

A

A wheel-like hexamer called the apoptosome

28
Q

What is the function of the apoptosome?

A

It activates caspase-9 which goes on to cleave other caspases thereby activating them and creating an autocatalytic caspase cascade that eventually activates executioner caspases eg caspase 3

29
Q

At the same time, other proteins are released from the mitochondria due to outer membrane permeability. What are their names and what is their function?

A

Sonic, Diablo. Bind to and neutralise inihbitors of apoptosis (IAP proteins) in the cytosol, which would otherwise block the activation of caspases, including executioners.

30
Q

The intrinsic and extrinsic pathways of apoptosis may be interconnected. Give an example.

A

In hepatocytes and pancreatic beta-cells, the FasL activated caspase 8 (extrinsic pathway) cleaves and activates BID, which is a sensor in the intrinsic pathway

31
Q

Name 2 executioner caspases.

A

Caspase 3 and 6

32
Q

What are some of the functions of executioner caspases?

A
  1. Activate DNAses to degrade cellular DNA
  2. Degrade structural components of the nuclear matrix
  3. Promote nuclear fragmentation
33
Q

What is the process by which plasma membrane structure changes occur, membrane blebs and apoptotic bodies are formed?

A

The process is UNKNOWN.

34
Q

What are the mechanisms by which apoptotic bodies/cells change their membranes to promote phagocytosis by phagocytes?

A
  1. Phosphatidylserine - normally expressed on the cytoplasmic surface of the plasma membrane, where it is recognised by several macrophage receptors
  2. Dying cells secrete soluble factors that recruit phagocytes
  3. Some apoptotic bodies may be covered by thrombospondin, an adhesive glycoprotein recognised by phagocytes
  4. Apoptotic bodies become coated wtih antibodies and complement C1q
  5. Macrophages produce proteins that bind only to dying/dead cells and not living cells.
35
Q

What is the role of p53?

A

Tumour suppressor gene. Arrests cell cycle at G1, but if DNA damage too great, triggers apoptosis.

36
Q

Necroptosis resembles ________ morphologically and __________ mechanistically.

A

Necrosis

Apotosis

37
Q

What are 2 triggers of necroptosis?

A

Ligation of TNF1 receptor

Viral proteins of RNA and DNA viruses

38
Q

T or F: Necroptosis is caspase-dependent.

A

False

39
Q

Necroptosis is dependent on signalling by the ________ and ________ complex.

A

RIP1

RIP3

40
Q

What are the actions of RIP1-RIP3 signalling?

A

Reduction of mitochondrial ATP generation.
Generation of ROS
Permeabilisation of lysosomal membranes

41
Q

In which cells does pyroptosis occur?

A

Cells infected with microbes

42
Q

Pyroptosis involves the activation of which caspase?

A

Caspase-1

43
Q

What is the action of caspase-1?

A

To cleave the precursor of IL-1 to active IL-1 (which then causes fever)

44
Q

In conjunction with caspase-______, caspase-1 also causes death of the infected cell.

A

11

45
Q

List some diseases that autophagy is implicated in.

A
  1. Inflammatory bowel disease
  2. Neurodegenerative disease (Alzheimers, Huntingtons)
  3. Cancer
  4. Infectious diseases (Mycobacteria, Shigella, HSV-1)
46
Q

Macrophage-specific deletion of which autophagy-related protein increases susceptibility to tuberculosis?

A

Atg5

47
Q

Define autophagy

A

A process by which a cell eats its own contents

48
Q

3 types of autophagy

A
  1. Chaperone mediated
  2. Microautophagy
  3. Macroautophagy (or just, “autophagy” - the major form)
49
Q

What are the different steps in the process of autophagy?

A
  1. Initiation: activation of an initiation complex, triggered by starvation or depletion of growth factors
  2. Nucleation: assembly of the nucleation complex, stimulated by the initiation complex
  3. Elongation: the isolation membrane or “phagophore” increases in length and captures its cytosolic cargo
  4. Closure: of the membrane to create an autophagosome
  5. Fusion: of the autophagosome with the endosome and then lysosome to form an autophagolysosome
  6. Degradation: of the inner membrane and contents of the autophagolysosome
50
Q

What is LC3 and describe its role in autophagy

A

One of several ubiquitin-like conjugation systems, called microtubule-associated protein light chain 3. It plays a role in the elongation and closure of the isolation membrane and also in the selective loading of cargo into the autophagosome.

51
Q

What are the functions of autophagy?

A
  1. Survival mechanism - maintains cell integrity, recycles essential metabolites, clears cell debris
  2. Turnover of organelles eg ER, mitochondria, lysosomes
  3. Clearance of intracellular aggregates
  4. Trigger cell death if it is inadequate to cope with the stress imposed on the cell (mechanism unknown)

Ch 2: Cellular responses to stress etc (3 decks)

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