L9: Interleukin signalling I Flashcards
1
Q
Biological functions of interleukins and mode of action:
A
- Ligands
- Regulate maturation and differentiation of blood cells and their progenitors
- Both auto- and paracrine (short range in both cases)
- Tend to work in concert to achieve effects (many members)
- Some redundancy in action
2
Q
HSCs:
A
- Multipotent
- Produce all types of red and white blood cells, as well as platelets
- Require interleukins for differentiation signalling (absence or presence)
- Key: Myeloid pathway (RBCs, platelets, monocytes, nuetrophils)
- Lymphoid pathway (T, B cells, NK cells)
3
Q
Pathway from HSC to MEPs vs GMPs:
A
- SCF, TPO -> HSCs to CMP (common myeloid progenitor)
- IL-3, SCF, TPO (Thrombopoietin) -> CMP to MEP (megakaryocyte erythroid progenitor)
- GM-CSF -> CMP to GMP (Granulocyte monocyte progenitor)
4
Q
Types of interleukins:
A
- Type I (IL-3, 5, 6): short chain helices or long chain (2 long 2 short)
- Type II (IFNs): Same as type 1 with an extra helix and kink in last helix sometimes
- Exist as monomers or dimers
5
Q
IL-3 structure, synthesis and effect:
A
- Type I cytokine made up of short chain 4 alpha helices
- Monomer
- Proliferation signal for granulocytes and macrophages
- Synthesised as pro-IL-3 then processed (activated by proteolytic removal of prodomain)
- Secreted by activated CD4+ T cells (‘signal launchers’)
6
Q
IL-3 receptor:
A
- Type I
- 2 receptor chains, loosely associated in absence of IL (covalent binding)
- IL binding to alpha chain forms stable heterodimers
- Conserved WSXWS sequences involved in IL binding, dimerisation and receptor activation
7
Q
JAKs:
A
- Just another kinase/janus kinase
- 4 members (1, 2, 3, Tyk-2)
- Activated by JAK-2 (in case of IL-3 signalling)
- Regulate activity of adjacent kinases
- 7 common domains
- Key domains: JH1 (kinase activity), FERM (mediates interaction with receptor)
8
Q
IL-3 solo vs in combination:
A
- Combination: Proliferation
- Solo: Differentiation of common myeloid lineages
9
Q
How does ligand (IL-3) binding activate kinase activity?
A
- In presence of ligand, binding results in…
- Conformational change in BOX1 domain (essentially swings into proximity with each other) -> passed on to JAK
- Enhances affinity for ATP
- Association of JAKs
- Transphosphorylation on activation lip -> binding of STAT…
10
Q
How are STAT proteins activated?
A
- Cytosolic STATs bind to P-Tyr in beta-c of JAK (via SH2 domains)
- JAK phosphorylates C-terminal TAD of STAT -> dissociates from receptor and dimerises (homo or hetero)
- Conformational change reveals NLS sequence (allowing importin binding) -> nuclear import
11
Q
Which proteins are involved in the JAK/STAT downstream pathway from IL-3?
A
- IL-3
- gp140 receptors
- JAK2
- STAT5a/5b
12
Q
+ What is a binding assay useful for?
A
- Quantifying number of receptors on a cell surface
- How tightly do they bind the ligand?
- Parameters characterised: B^max (maximal amount of binding) and K^d (dissociation constant)
13
Q
+ How is cytokine signalling different to typical GF signalling?
A
- Instead of receptor tyrosine kinase activity, the cytokine receptor has an associated protein tyrosine kinase (JAK)
- There is a fair overlap in the downstream effectors of these two modes
14
Q
Cytokine structure:
A
- All cytokines have a similar 3D structure of four long, conserved alpha helices folded into conserved 3D structure
15
Q
+ What are interferons and how are they useful in disease?
A
- Type of cytokine
- Secreted by several types of cell following viral infection
- Act on nearby cells to induce enzymes rendering the cell resistant to viral infection
