Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Cellular and Molecular Immunology > 11. Lymphocyte signalling 3: Signal transduction > Flashcards

11. Lymphocyte signalling 3: Signal transduction Flashcards

1
Q

What is the basis of signal transduction?

A

interactions between proteins

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

How universal are signalling mechansism?

A

Many signalling intermediates are shared through every cell type.

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

What are the functions of signalling?

A
  1. The main function of ligand engagement leading to transcriptional change.
  2. It can have shorter-term consequences like changes in cell shape or motility.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the 4 main signalling protein interaction domains?

A
  1. SH2 domains
  2. SH3 domains
  3. pleckstrin homology domains
  4. C1 domains
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What do SH2 domains bind?

A

Phosphorylated tyrosine residues

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

What do SH3 domains bind?

A

Proline rich domains usually PXXP

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

What do Pleckstrin homology domains bind?

A

Phosphatidylinositol lipids

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

What do C1 domains bind?

A

Diacylglycerol (DAG)

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

What are phosphatidylinositol lipids?

A
  1. They interact with proteins during signal transduction.
  2. They share the same structure as every lipid.
  3. There are 2 main ones: PIP2 and PIP3
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the structure of phosphatidylinositol lipids?

A
  1. 2 long fatty acid chains
  2. A polar head group
  3. The head group is made of the sugar DAG so it has lots of OH groups.
  4. One OH group is used to connect the fatty acid tails.
  5. The other OH groups can be phosphorylated 3 times each.
  6. This means there is a wide variety of different phosphatidylinositol lipids that can be created.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is PIP2?

A
  1. Phosphatidylinositol 4,5-bisphosphate
  2. It mostly has lipid functions like anchoring in the membrane.
  3. Also has enzymatic activity.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is PIP3?

A

Phosphatidylinositol (3,4,5)-trisphosphate

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

How is PIP2 converted to PIP3?

A
  1. Done by PI 3-kinase which CD28 and ICOS recruit.
  2. Plays a key role in regulation of cellular activation and proliferation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How is PIP3 converted to PIP2?

A
  1. PTEN converts PIP3 back to PIP2
  2. This turns off the proliferative signalling caused by PIP3.
  3. PTEN is a key tumour suppressor gene
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How can a PI3-kinase inhibitor prevent cancer growth?

A
  1. eg Apelisib in metastatic breast cancer
  2. Prevents the formation of PIP3 and the proliferation signals it causes.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Why are there so many different phosphatidylinositol lipids?

A
  1. Lipids form all the membranes in the cell, including vesicles and membrane bound organelles.
  2. PIP2 and PIP3 sit in the plasma membrane.
  3. other phosphatidylinositol lipids are enriched in different vesicles marking their function. eg different lipids in secretory and endosomal vesicles.
  4. For a protein to bind to a vesicle it needs to have a PH domain that binds a lipid like a phosphatidylinositol lipid.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is a key function of lipids?

A

Identifying key subsets of membranes that make up different cellular compartments.

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

What are the constraints of protein domain and ligand interactions?

A
  1. Domains exist in large families that are very similar.
  2. Binding affinity to specific domains are very low.
  3. Concentrations of interacting molecules (ligands) are also low.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How is the specificity of protein protein interactions achieved?

A
  1. Localisation
  2. Having multiple protein interaction domains.
  3. If you have two or more domains with low specificity working in combination, you gain a lot of specificity.
  4. Every signalling intermediate has multiple interaction domains.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What can you work out when you know the 4 key protein interaction domains?

A

What interactions it does and what type of molecules it can bind.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What happens at the TCR before the adaptor molecules are recruited?

A
  1. Lck has phosphorylated the ITAM in the TCR.
  2. This recruits ZAP70.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the substrate for ZAP70?

A

The adaptor protein LAT.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is LAT?

A
  1. An adaptor protein so it has no enzymatic activity.
  2. It is made up of lots of protein protein interaction motifs.
  3. It brings other signal intermediates together.
  4. It is a transmembrane protein so is localised to the plasma membrane.
  5. Has lipid modification to make sure LAT ends up in the right membrane.
  6. As LAT is in the plasma membrane it can be phosphorylated by ZAP70.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What signalling elements does LAT have?

A
  1. 4 tyrosine residues.
  2. These can be phosphorylated by ZAP70
  3. Then they can be bound by SH-2 domains.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What other adaptor molecules does LAT recruit?

A
  1. Grb2 which is in every cell.
  2. Gads which is T cell specific.
  3. SLP-76, which is T cell-specific.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is Gads?

A
  1. Very widely used adaptor protein
  2. Simple protein containing 1 SH-2 domain and 2 SH-3 domains.
  3. This SH-2 domain binds the phosphorylated tyrosines in LAT. This localises Grb2 to the plasma membrane
  4. The SH-3 domains are free to bind PXXP motifs.
  5. SLP76 contains a PXXP motif, so it binds to the SH-3 domain on Gads.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is the sole function of Gads?

A

To recruit SLP-76 to LAT.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is Grb2?

A
  1. Contains an SH-2 and 2 SH-3 domains.
  2. It recruits Sos and PI 3-kinase.
  3. Sos is a GEF that activates Ras GTPase.
  4. PI 3-kinase makes PIP3.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What methods can active PI 3-kinase signalling?

A
  1. TCR signalling through ZAP70 and adaptors LAT and Grb2.
  2. CD28 signalling.
  3. ICOS signalling.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is SLP-76?

A
  1. A key regulator for physiological processes that are controlled by the TCR signalling complex.
  2. It recruits ITK and PLCy
  3. It controls cytoskeletal regulation.
  4. it controls integrin activation through ADAP.
31
Q

What is the main function of SLP-76?

A
  1. They coordinate a large number of signalling event through localisation.
  2. It just brings proteins together.
  3. It amplifies the signal as it starts with 1 TCR and 1 ITAM and now there are 4 adaptors with lots of different functions.
32
Q

What is SLP-65?

A

It does the same functions as SLP-76 just in B cells.

33
Q

How sensitive are T cells?

A
  1. Very sensitive
  2. They can be activated with very little ligand engagement (5-10 interactions).
  3. This means the adaptor molecules are needed to amplify the signal.
34
Q

What makes up the functional T cell receptor?

A
  1. A large number of molecules.
  2. A unit that takes ligand engagement and generates binding sites for signalling intermediates.
  3. This includes: CD4, Lck, ZAP70, LAT, Grb2, Sos.
35
Q

Why does the TCR complex have so many molecules in it?

A
  1. Due to the sensitivity of the TCR.
  2. It is a difficult way to build a receptor and cause changes in the cell.
  3. This complexity is specific to T cells to compensate for the sensitivity.
  4. All these components are present in every receptor just in fewer or only 1 molecule.
36
Q

What is the main role of PIP2 in most cells?

A
  1. Cytoskeletal regulation
  2. Provides localisation
37
Q

What is the secondary function of PIP2?

A

An enzymatic substrate

38
Q

What is the function of phospholipase C?

A
  1. It converts PIP2 into DAG and IP3. These are signalling intermediates.
  2. It is activated by ITK.
    AKA PLC
39
Q

Is PLC function conserved?

A
  1. Yes
  2. PIP2 cleavage is a widely conserved step in signalling, like in GPCR.
40
Q

How is PLC activated?

A

by ITK

41
Q

What is ITK?

A
  1. A Tec family kinase
  2. It contains a PH domain that binds to PIP3. This brings ITK to the plasma membrane
  3. ITK can also bind SLP-76 through other protein interaction domains.
  4. The kinase domain phosphorylates PLCy to activate it.
42
Q

What domains does ITK have?

A
  1. PH domain
  2. SH-2 domain
  3. SH-3 domain
  4. Kinase domain
43
Q

What is BTK?

A
  1. The B cell version of ITK
  2. Has the same function as it also activates PLCy
44
Q

How are the levels of PIP3 affected by a lack of CD28 co-stimulation?

A
  1. PIP3 can be generated by Grb2 from TCR signalling and from CD28.
  2. CD28 is a co-stimulation molecule, so its role is to make the TCR signalling more effective.
  3. Without the CD28 signalling less PIP3 is generated and this reduces the PLCy activation.
  4. This can have downstream effects like less efficient activation of the T cells.
45
Q

How are BTK inhibitors used in cancer therapy?

A
  1. Ibrutinib is an irreversible Btk inhibitor that can also target tyrosine kinases.
  2. Treats chronic lymphoid leukaemia, small lymphocytic lymphoma, marginal zone lymphoma, and graft-versus-host disease
46
Q

What brings ITK and PLC togther?

A

SLP-76 recruits both ITK and PLC and brings them together. This increases the efficiency of the interactions.

47
Q

What do all the adaptor proteins form?

A

a large protein complex that are hubs to bring together signalling functionality

48
Q

What cells is calcium signalling important for?

A

excitable cells like neurons and T cells

49
Q

How does the calcium concentration vary across a cell?

A
  1. The cytoplasm has very low concentrations of calcium. This is actively maintained by ATP-dependant protein pumps to get rid of the calcium.
  2. The ER and the mitochondria have very high concentrations of calcium. This makes up a large amount of the cell.
  3. There are high concentrations of calcium in the extracellular space.
  4. This creates a massive gradient across the plasma membrane. This gradient drives calcium signalling.
50
Q

How does calcium signalling trigger changes in transcription?

A
  1. Various receptors can cause calcium signalling.
  2. Starts with PLCy producing IP3 and DAG.
  3. IP3 binds the IP3 receptor that is in the ER membrane.
  4. This opens the ion channel part of the IP3 receptor, and this allows calcium to be released into the cytoplasm and causes an increase in calcium concentration in the cytoplasm.
  5. The drop of calcium in the ER is detected by Stim which activates the extracellular domain.
  6. Stim’s extracellular domain binds to a calcium channel in the plasma membrane called Orai1.
  7. This causes a massive influx of calcium into the cytoplasm.
51
Q

What are the 2 steps of calcium signalling?

A
  1. IP3 mediated release of calcium from the ER or mitochondria
  2. Stim mediated influx from the extracellular space.
52
Q

What does calcium signalling do?

A

It causes conformational changes in proteins which can activate them.

53
Q

How does calcium signalling cause the activation of calmodulin?

A
  1. Calcium binds calmodulin and changes its shape.
  2. The change in shape means calmodulin can bind to downstream signalling intermediates like calcineurin.
54
Q

How does calcium signalling activate calcineurin?

A
  1. Calcium binds to the calcineurin subunit B causes a conformational change and partial activation.
  2. The binding of activated calmodulin to calcineurin fully activates calcineurin.
  3. Calmodulin is activated by Ca2+.
55
Q

What is calcineurin?

A
  1. A phosphatase.
  2. Contains an auto inhibitory domain
56
Q

How can calcineurin be a therapeutic target?

A
  1. The drug FK506 can bind the endogenous FK506 binding protein.
  2. This blocks the calcineurin catalytic site.
  3. This creates very effective immunosuppression and is widely used in solid organ transplants.
57
Q

What is the function of calcineurin?

A
  1. It is a phosphatase, so it dephosphorylates things.
  2. It dephosphorylates NFAT which allows it to move to the nucleus and alter transcription.
58
Q

What is NFAT?

A
  1. A transcription factor
  2. When it is phosphorylated it is retained in the cytoplasm.
  3. It is activated by calcineurin.
59
Q

What is the full process from TCR signalling through to transcriptional change with NFAT?

A
  1. Lck phosphorylates ITAMs that recruits ZAP70.
  2. ZAP70 phosphorylates the adaptor protein LAT.
  3. LAT recruits SLP76 through phos tyrosines and SH2 domain binding.
  4. SLP76 recruits ITK and PLCy
  5. ITK activates PLCy through phosphorylation.
  6. PLCy hydrolyses PIP2 in DAG and IP3.
  7. IP3 binds to the IP3 receptor.
  8. This releases calcium from the ER into the cytoplasm.
  9. The drop in calcium concentration causes the activation of Stim.
  10. Stim binds to Orai1 calcium channel in the plasma membrane.
  11. This allows the entry of massive levels of calcium into the cell.
  12. Calcium binding causes conformational change in calmodulin to activate it and conformational change in calcineurin leading to partial activation.
  13. Calmodulin then binds to calcineurin to fully activate it.
  14. Calcineurin is a phosphatase that dephosphorylates the transcription factor NFAT to activate it.
  15. NFAT can then enter the nucleus and change gene expression.
60
Q

What is the critical principle of transcriptional control?

A
  1. The main way transcription is controlled is by allowing or preventing access of transcription factors to the nucleus.
  2. This is controlled by post-translational modification usually (de)phosphorylation.
  3. There are methods in the nucleus to turn off transcription factors like kinases.
61
Q

What is Ras?

A
  1. A key regulator of proliferation in every cell type.
  2. It is frequently mutated in cancer and drives oncogenic transformation.
  3. It is a small GTPase.
62
Q

How is Ras activity controlled?

A
  1. Ras exists in 2 different conformations.
  2. Inactive Ras has GDP bound.
  3. Active Ras has GTP bound.
  4. The different binding changes conformation.
  5. When Ras is active, it can bind to downstream signalling molecules.
63
Q

How does Ras switch between its 2 conformations?

A
  1. As Ras is a GTPase, it can inactivate itself by stripping a phosphate of the GTP.
  2. GAP is a GTPase activating protein which accelerates the normal inactivation activity of Ras.
  3. GEF is a guanosine exchange factor that exchanges GDP for GTP to activate Ras and other small GTPases.
64
Q

What happens if there is a mutation in Ras?

A
  1. If the mutation is in the GTPase domain Ras is stuck on.
  2. This drives proliferation and oncogenesis.
65
Q

How can Ras inhibitors be used in clinic?

A
  1. Ras is a key stimulator of cell division.
  2. 20% of all cancer patients carry a Ras mutation.
  3. A recent inhibitor has been approved but most patients don’t respond.
  4. There is also intrinsic and acquired resistance.
66
Q

What are small GTPases?

A

A universal signalling system

67
Q

What cellular processes are controlled by small GTPases?

A
  1. Regulation of proliferation by Ras
  2. Regulation of cytoskeleton by Rho.
  3. Regulation of vesicular trafficking by Arf.
  4. Regulation of vesicular identity by Rab
68
Q

How is Ras activated in T cells?

A
  1. Activated to drive proliferation
  2. PIP2 is converted by PLCy into DAG and IP3.
  3. DAG activates the GEFs, Sos and RasGRP.
69
Q

How is Sos recruited in Ras activation in T cells?

A

Through ZAP70 and LAT and Grb2.

70
Q

How is RasGRP recruited in Ras activation in T cells?

A
  1. Recruited and activated through DAG
  2. RasGRP contains a C1 domain that can bind DAG.
  3. It also contains an EF domain that can detect calcium so it can be controlled this way.
71
Q

Why are 2 GEFs needed for Ras activation in T cells?

A
  1. Sos is recruited through LAT and Grb2 so it localises to the membrane.
  2. There are also Ras GAPs at the membrane.
  3. This means you don’t generate much active Ras at the membrane.
  4. RasGRP is activated in the cytoplasm without GAPs around.
  5. This shows the importance of localisation in signalling.
72
Q

Why is most active Ras generated at the Golgi apparatus?

A
  1. DAG is generated at the plasma membrane as PIP2 sits in the membrane.
  2. The DAG is then internalised and the vesicles associate with the Golgi which is where cytoplasmic RasGRP also is.
  3. Most Ras generation happens in the cytoplasm near the Golgi.
73
Q

What are the main principles of signal transduction?

A
  1. Many signalling interactions are mediated by a small number of large domain families.
  2. Adaptors allow the formation of large signalling complexes.
  3. Transcription factors need to ba activated by post-translational modification

Cellular and Molecular Immunology (17 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions