LEC55: Apoptosis Flashcards

1
Q

what is necrosis? what happens to the cell?

A

form of cell death in which cells and organelles **swell and rupture **

this leakage induces inflammatory response from the body

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is apoptosis? what happens to the cell?

A

cells shrink and condense

organelles and membranes retain their integrity

remnants are then phagocytosed by neighboring cells or macrophages

degredation is rapid; few dead cells are seen

no inflammatory reponse occurs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what assays measure cellular apoptosis?

A

1) visualize “blebs” of apoptotic cells with DNA dye
2) DNA ladder assay
3) flow cytometry and DNA content
4) TUNEL assay
5) Annexin V assay

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what does DNA dye assay show of apoptotic cells?

A

visualizes DNA in apoptotic cells’ nuclei; shows their distinctive morphology

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what does a DNA ladder assay show about apoptotic cells?

A

reflects the DNA degredation occurring

steps of 180-200 bp in ladder visualize

represents the size of the cuts a nuclease makes in genomic DNA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what does flow cytometry analysis show about apoptotic cells?

A

apoptotic cells have a hypodiploid DNA content that = <2N

see this on flow cytometer: hypodiploid peak is less than 2N (right graph) as compared to the (short) G2 peak on the L graph)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what makes the flow cytometer to be a rigorous assay for apoptosis?

A

flow cytometry only works if the membrane of the cell is intact

apoptotic cells’ membranes are intact

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what does the TUNEL assay take advantage of re: apoptosis? how does it work?

A

endonucleases cutting apoptotic cells’ DNA cut the ends unusually

can label those ends with a flourescent deoxynucleotide label

biotinylated dUTP is used in to rxn, can be detected using a streptavidin that has a flourescent tag

visualize flourescence of the apoptotic cells under a microscope

TUNEL: “Terminal Deoxy Uridine Nucleotide End Labeling”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what is signal for macrophages to engulf an apoptotic cell?

A

phosphatidyl serine flipped localization to the outside of the plasma membrane from the cytoplasmic side where it usually is

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

how does annexin V and phosphatidyl serine flap assay work for apoptotic cells?

A

normally, phosphatidyl serine is on cytoplasmic side of plasma membrane

during phagocytosis, it undergoes a flip, is exposed on the extracellular surface of the membrane

this flip is the signal for a macrophage to engulf the cell, incur phagocytosis

can detect the phosphatidyl serine w/ an Annexin V dye, flourescently labeled dye

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

for an Annexin V assay, do you do anything to the membrane?

A

you should not permealize the membrane because then it would interact w/ the phosphatidyl serine on the inside of the membrane, which isn’t desired

if you do this, can visualize the nucleus, though

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

generally, is apoptosis triggered the same way in all cells?

A

no

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

how is apoptosis activated in T cells?

A

by glucocorticoids and antibody binding to the cell surface

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what are things that could occur in the cell that would trigger apoptosis? aka what are causes for a cell to undergo apoptosis?

A

1) specialized cell surface receptors bind ligands
2) DNA damage: ionizing radiation, UV light, genotoxic drugs
3) oncogene activation
4) growth factor withdrawal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what is a caspase

A

a protease that mediates apoptosis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what is the molecular action of caspases?

hint: think about their name

A

caspases cleave after specific aspartic acids, NOT GLUTAMIC ACID

they have a cysteine in their active site

they are synthesized as an inactive precursor or zymogen

cysteine + aspases = caspases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what is the structure of caspases?

A

heterodimer of a large and small subunit; both come from the same original polypeptide

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

how are caspases activated?

A

each heterodimer has 2 cleavage sites that must be cleaved in to the large and small subunits in order to free the active caspase from its prodomains and activate it

19
Q

what different kinds of caspases are there?

A

1) initiator: caspase-8 and caspase-9
2) executioner: -2, -3, -6, -7

20
Q

what is the function of each kind of caspase? what initiates each kind of caspase?

A

initiators: cleave and activate the executioner caspases. are activated by an extracellular signal or DNA damage

executioners: cleave cellular substrates. are activated by the initiator caspases.

21
Q

what breaks down lamins? result?

A

executioner caspases break down lamins

result: loss of nuclear membrane

22
Q

what are executioner caspase’s substrates?

A

1) DNA degredation proteins: CAD/ICAD
2) DNA repair proteins: PARK:poly ADP ribose polymerase
3) cytoskeletal proteins: gelsolin
4) nuclear structures: lamins

23
Q

what cleaves DNA?

A

CAD, an endonuclease

24
Q

describe how DNA cleavage occurs

A

CAD is the endonuclease that cleaves DNA. it is bound to and inhibited by iCAD.

executioner caspases cleave ICAD, freeing CAD

CAD then can actively degrade DNA

25
Q

what are the signaling pathways that initiate apoptosis, activate the initiator caspases?

A

1) extrinsic pathway: extracellular signal, usually binding of a ligand to cell surface receptor
2) intrinsic pathway: something happens internally in cell; commonly for DNA damage; mitochondria-related pathway

26
Q

what are the steps of the extrinsic and intrinsic signaling pathways to apoptosis?

A
27
Q

what is the caspase of each signaling pathway?

A

extrinsic: caspase 8
intrinsic: caspase 9

28
Q

what are the steps of the extrinsic pathway involving cell surface receptors for apoptosis?

A

1) ligand binds to ligand receptor

induces receptor trimerization

2) intracellular receptor-associated proteins are recruited by the clustering of the cytoplasmic ends of the receptors
3) clustering of many procaspase-8 molecules with low levels of proteolytic activity triggers proteolytic cleavage of procaspase-8, initiates execution of the caspases

apoptosis occurs

29
Q

in the extrinsic caspase pathway model, what are examples of the ligand? the receptor?

A

ligand: Fas ligand, Tumor Necrosis Factor, or TRAIL
receptor: Fas **death receptor **or another death receptor

30
Q

what is the “holoenzyme model”?

A

cytochrome C is released from mitochondria’s intermembrane space

cytochrome C interacts with cellular protein Apaf1 and dATP

this forms a holoenzyme that cleaves procaspase-9

causes intracellular pathway of apoptosis

31
Q

what is the apoptosome?

A

combination of cytochrome C from the mitochondria + Apaf-1 from cytoplasm

together recruit and activate procaspase-9

32
Q

what is Bcl-2?

A

anti-apoptotic family of proteins with 4 homology domains (BH1-4)

33
Q

what are the BH123 proteins?

A

pro-apoptotic

Bax, Bak

are related to the pores created in the mitochondrial membrane from which cytochrome c is released

it is not clear if the BH123 cause the pores to be formed, but is clear that an apoptosis signal leads to BH123 proteins’ insertion in mitochondrial membrane

they aggregate at the pores’ site

34
Q

what is the relationship between Bcl-2 and Bax/Bak?

A

Bcl-2 binds to Bax/Bak and inhibits them from forming pores

this inhibition of pore formation prevents apoptosis, keeps cell alive

this inhibition through heterooligimerization

35
Q

would cancer cells tend to have high or low Bcl-2 levels?

A

high

cancer cells w/ high Bcl-2 are resistant to cell death response

36
Q

what are BH3-only proteins?

A

apoptosis activating proteins that come in 2 forms:

1) Bid
2) PUMA and NOXA

37
Q

what is Bid proteins’ action?

A

when Bid is upregulated, it interacts with Bax and Bak, activates them to do pore formation

cytochrome C is release

apoptosis occurs

38
Q

what is PUMA and NOXA proteins’ actions?

A

BH3-onlys that bind to Bcl-2, inhibit it from inhibiting Bax and Bak, and so pores can form and apoptosis occurs

39
Q

how does p53 interact with BH3-onlys?

A

it transcriptionally upregulates PUMA and Noxa, which in turn bind to and inhibit Bcl-2, and BAX and BAK can form the pores

40
Q

what is the phenotype of mice lacking Bax and Bak?

A

this double knockout is lethal

lacking either Bak or Bax is viable

41
Q

if mice lack caspase-8, -9, cytochrome C, or APAF-1, what is result?

A

lethal

shows apoptosis is important in development

42
Q

what roles does apoptosis play during embryonic development?

A

1) sculpts structures
2) does digit formation
3) hollows out solid structures to form lumina
4) deletes unneeded structures - vestigial or 1 sex only

43
Q

what controls cell numbers

A

apoptosis

neurons, oligodendrocytes are over-produced in vertebrates then eliminated to match cells they innervate

44
Q

how is apoptotic response important in cancer?

A

tumor cells suppress apoptosis - cell survival is central to how tumorigenic process occurs

Bax and Bak have been shown to be lost in some tumors