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Cytosolic Pattern Recognition Receptors Flashcards

1
Q

What are the cytoplasmic receptors?

A

NOD1 and NOD2
Inflammasaomes
RIGI, MDA-5
cGAS-STING

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2
Q

What are the NLRs?

A

Inflammasomes
NOD-1 and NOD-2

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3
Q

What is oligomerisation?

A

When you form a cluster of molecules - this is basically oligomerisation

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4
Q

What happens when a macrophage eats an apoptotic neutrophil?

A

Becomes anti-inflammatory - triggers a shift towards resolution

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5
Q

What is the general structure of NLRs?

A

N-terminal region
Intermediate NOD
C-terminal leucine-rich repeat

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6
Q

What do NOD-like receptors recognise?

A

MAMPs/DAMPs in the cytosol

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7
Q

What are the 3 types of structure that the N-terminal region of a NOD-like receptor might have?

A

CARD
PYD
BIR

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8
Q

When are caspases activated?

A

Downstream of inflammasome

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9
Q

What is an anti-inflammatory way of a cell dying?

A

Apoptosis

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10
Q

What is a pro-inflammatory way of a cell dying?

A

Pyroptosis
Necroptosis

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11
Q

What residues do caspases (cysteine proteases) cleave after?

A

Aspartic or glutamic

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12
Q

What are the inflammatory caspases?

A

Caspase 1
Caspase 4
Caspase 5
Caspase 11
Caspase 12

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13
Q

What is mouse caspase 11 the homologue of?

A

Human caspase 4 and caspase 5

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14
Q

What does caspase 1 cleave?

A

Precursors of IL-1beta and IL-18 (pro-IL-1beta and pro-IL-18)

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15
Q

What do all inflammatory caspases (expect caspase 12) cleave?

A

All cleave and activate gasmerdin D

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16
Q

What are the two categories of apoptotic caspases?

A

Initiator caspases
Effector caspases

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17
Q

What are the initiator caspases?

A

Caspase 2
Caspase 8
Caspase 9
Caspase 10

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18
Q

What are the effector caspases?

A

Caspase 3
Caspase 6
Caspase 7

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19
Q

What is the difference between caspase 10 in humans and mice?

A

Rodents do not have a gene encoding caspase 10

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20
Q

What is the extrinsic apoptosis pathway induced by?

A

Death receptors, including FAS, tumour necrosis factor receptor 1 and caspase 8

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21
Q

Which caspase initiates extrinsic pathway apoptosis?

A

Caspase 8

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22
Q

What does intrinsic pathway of apoptosis require induction of?

A

Mitochondrial outer membrane permeabilisation which mediates the release of the pro-apoptotic factor cytochrome c for binding of the cytosolic protein apoptotic protease-activating factor 1

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23
Q

What assembles to make a multi-protein complex known as the apoptosome?

A

APAF1 and caspase 9

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24
Q

What is the role of phosphatidylserine?

A

Recognition of it stimulates the phagocyte to engulf the apoptotic cell and to produce anti-inflammatory mediators which inhibit production of pro-inflammatory chemokines and cytokines

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25
How does innate system know a cell is dying through apoptosis?
Healthy cells have phosphatidylserine in Wants to go up and keeps getting pulled down This is not in the membrane in a healthy cell When this process stops, PS is released and exposed to plasma membrane
26
What can you measure PS with?
Annexin-5 through flow cytometry to link to apoptotic stage
27
What happens once integrity of plasma membrane is lost following initial apoptosis due to secondary necrosis of late-stage apoptotic cells?
The released cellular contents can engage receptors for DAMPs and contribute to immune responses to self antigens
28
What is pyroptosis?
An inflammatory form of cell death
29
What happens if apoptotic cells are not cleared?
They become necrotic
30
What is pyroptosis triggered by?
Gasmerdin D
31
What is pyroptosis cell rupture mediated by?
Ninjurin-1, a protein that participates in several cell death pathways
32
What happens upon activation of caspase 1?
If you activate caspase 1, you will get cleavage of interleukin 1 beta and interlukein 18 Get cleavage of gasmerdin D also Then get a pore formation and release of interleukin 1 beta and interleukin 18 Then NINJ1 leads to apoptotic cells and pyroptosis
33
What does caspase 1-induced pyroptosis release from infected macrophages for uptake by neutrophils?
Intracellular bacteria
34
How does caspase 1 become active?
It exists as an inactive monomer, you bring together two and they dimerise and then become active
35
What is the trail leading from LPS to pore formation?
LPs-> caspase 4/11and gasmerdin activation -> pore formation
36
How many well established canonical inflammasomes are there in humans and mice?
Seven
37
What do most canonical inflammasomes require?
The ASC inflammasome adaptor protein for signalling to caspase 1
38
What are canonical inflammasomes for?
Signalling platforms that facilitate the dimerisation and activation of caspase-1
39
How many inflammasomes can signal to caspase-1 directly without ASC?
Two
40
What causes NLRP3 inflammasome activation?
Several pathogens Danger signals Muramyl-di-peptide and nucleic acids
41
What is the specific receptor that ATP works through?
P2X7
42
Why is the p2x7 receptor important?
ATP binds to receptor, leads to pore formation, which causes potassium efflux through pores in the membrane, and NLRP3 respons to pore because of the potassium efflux
43
What do caspase 4,5 (human) and caspase 11 (mouse) activate?
The NLRP3 inflammasome in response to gram-negative bacteria and intracellularly delivered LPS. This is due to K+ efflux caused through activation of Gasmerdin D
44
What is the NAIP-NLRC4 inflammasome also known as and what does it stand for?
Ipaf inflammasome Ipaf = ICE-protease activating factor
45
There is only been one NAIP protein in humans that has been characterised, what was it found to bind to?
T3SS needle protein
46
What is important about NLRP6 inflammasome?
It recognises gram positive bacteria (recognises lipoteichoic acid)
47
What happens NLRP6 is activated?
Can recruit caspase 11 and caspase 1 Requires ASC Both formation of pores and processing of interleukin 1 beta and 18
48
What does the pyrin inflammasome do?
Pyrin detects the inactivation of Rho GTPases This activates pyrin inflammasome and again recruits pro caspase 1, will process gasmerdin D and interleukin 1 beta and 18
49
What are the two members of the PYHIN inflammasomes?
AIM2 and IF16
50
What does AIM2 do?
Cytosolic-senses dsDNA of viral, bacterial or self-origin
51
Are PYHIN inflammasomes members of the NLR family?
No
52
Are pyrin inflammasomes members of the NLR family?
No
53
What length of DNA does AIM2 require for optimal inflammasome activation?
At least 80 base pairs
54
What downstream pathway does AIM2 use and not use?
Uses downstream of type I interferon signalling rather than NFkappaB
55
What is the process of AIM2 inflammasome?
Activated by interferon pathway Cytosolic bacteria is released into cytosol, there will be molecules that instruct DNA that lyse it and DNA becomes available to bind Once it is bound to DNA, recruits ASC ASC recruits caspase 1 Then have normal system of gasmerdin D, interleukin 1 beta and interleukin 18
56
What is the role of caspase 8?
Fungal recognition by dectin 1 through SYK induces assembly of a complex containing CARD9 that activates caspase 8 to promote IL-1beta maturation
57
What does ASC do upon inflammasome activation and what does it form?
It redistributes and forms a large perinuclear aggregate in cells
58
When are ASC specks released?
By dying cells, leading to cleavage of extracellular pro-IL-1beta and activating caspase-1 in macrophages internalising the specks
59
What does autophagy do?
Eliminates damaged organelles through autophagosomes to keep the cell healthy
60
What happens in Parkinson’s and Alzheimer’s in relation to inflammasomes?
Some triggers that promote these disease form aggregates which can activate the inflammasome Whenever you have anything that forms an aggregate, it will damage the cells and NLRP is there to sense that
61
What receptor do both NOD1 and NOD2 interact with?
RICK
62
What is the main trigger for NOD receptors?
Peptidoglycan
63
Where is peptidoglycan mainly found?
In gram positive but can be found in gram negatives and mycobacteria
64
What is peptidoglycan?
A polymer composed of amino acids and sugars
65
What is the minimal ligand for NOD2?
Muramyl dipeptide (MDP)
66
What is the minimal ligand for NOD-1?
IE-DAP
67
How does peptidoglycan get recognised by NOD1 and NOD2?
It is part of bacterial cell wall, this is in the cytosol so there must be some transport to make sure peptidoglycan reaches cytosol There are transporters Peptidoglycan must be degraded into fragments Type 3SS can inject peptidoglycan fragments into cells
68
How are NOD1 and NOD2 activated?
They are in an auto-inhibited monomeric state They associate with surface membranes and undergo conformational changes and recruit RICK
69
What happens once RICK is recruited to NOD1 and NOD2?
Recruitment of the TAK1 complex to RICK, furhter recruitment of IKK complex Activation of IKKs by TAK1. Degradation of the NFkappaB inhibitor IkBa and translocation of NFkappaB to the nucleus
70
What do NOD1 and NOD2 induce production of in epithelial cells?
Anti microbial peptides and chemokines
71
What do NOD1 and NOD2 induce production of in macrophages?
Pro inflammatory cytokines
72
What is autophagy?
A process in which the cell maintains its health by getting rid of aggregates or damaged organelles
73
Which receptor has particularly been implicated in induction of autophagy?
NOD2
74
What type of viruses can NOD1 sense and what signalling pathways is this invovled with?
ssRNA viruses, involved with MDA5 and RIGI signalling pathway
75
What does RIGI preferentially bind to?
Short dsRNAs that have blunt ends
76
What does MDA5 preferentially bind to?
Long dsRNA with no end specificity
77
When is the cGAS-STING pathway activated?
In recognition of dsDNA in cytosol
78
How does recognition of cGAS-STING occur?
Enzyme cGAS binds dsDNA and becomes active Then using a substrate, GTP and ATPsyntehsises cGAMP And this is the ligand for STING STING doesn’t directly bind nucleic acids,it binds cGAMP This STING is located in ER, moves to the Golgi, then leads to activation of interferon pathway IRF3 phosphorylation Again get pro inflammatory cytokines
79
Which caspase initiates intrinsic pathway of apoptosis?
Caspase 3 and caspase 9?

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