Lecture 9: Interleukins Flashcards
True or false: interleukins only work independently of other signalling molecules?
False: they can function in signalling pathways with other cytokines
What is one of the main functions of interleukins?
Blood cell production (maturation of haematopoietic stem cell to common myeloid progenitor or common lymphoid progenitor depends on presence of different interleukins and cytokines)
Which interleukin is primarily responsible for the development of myeloid lineage blood cells?
IL-3 (in combination with other related cytokines such as SCF (Stem Cell Factor) and TPO (Thrombopoietin))
Which interleukin is primarily responsible for the development of lymphoid lineage blood cells?
IL-7
What is the largest group that Interleukins and related cytokines belong to?
helical cytokines
Describe the structure of the helical cytokines (including interleukins and related cytokines)?
4 alpha helical fold (4 conserved alpha helices)
Type I: either short chain (15aa chains), long chain (25aa) or combination of the two.
Type II: same as type I but has extra alpha helix and sometimes also a kinked helix
True or false: type I helical cytokines can form dimers?
False: type II interleukins can form dimers
Give an example of a type I helical cytokine
IL-3
Give an example of a type II helical cytokine
Interferons
Give the name, a brief description, and an example of the second largest helical cytokine structural group
Name: Jelly roll
Brief Description: beta structure, non-covalent assembly of jelly rolls into a trimer
Example: TNF-alpha
Give the name, a brief description, and an example of the smallest helical cytokine structural group
Name: beta trefoil
Brief description: beta structure rotated about the central strand, rolled and sealed with hydrogen bonds between the first and last beta sheets
Example: IL-1
describe the general common structure of the helical cytokine receptors
Heterodimers of Alpha chain and beta common chain
- alpha chain responsible for ligand binding so varies depending on ligand
- beta common chain relays the signal across the plasma membrane to generate signal
What is the structure of the IL-3 receptor and its activation?
GP140 receptor (beta common chain)
DIMER OF DIMERS (two heterodimers come together to forma dimer)
- alpha and beta common chain loosely associated in absence of IL-3
- IL-3 binding to alpha chain results in disulfide bridges between conserved cysteines that stabilises the dimer
- WSXWS motifs involved in IL-3 ligand coordination, disulfide bond formation and receptor activation.
- BOX1 domain of intracellular beta common chain constitutively associated with JAK2
Describe the structure and activation of IL-3
Type I short chain helical cytokine monomer
synthesised as pro-IL-3 then processed to active form
What is one function of IL-3?
Proliferation signal for granulocytes and macrophages (proliferation and, with other cytokines, differentiation of CML for production of myeloid lineage blood cells)
Give an example of a cell type that secretes IL-3
Activated CD4+ T cells
Describe the structure of the JAK kinases
common 7 domain structure including:
JH1 = tyr kinase activity
JH2 = pseudokinase that negatively regulates JH1
FERM = mediates interaction with the beta common chain
What JAK is activated byIL-3 signalling?
JAK2
How many members of the JAK family are there and what are their names?
4 members
- JAK1
- JAK2
- JAK3
- Tyk-2
How does IL-3 binding result in activation of JAK2?
binding results in conformational change in BOX1 domain of beta common chain causing the JAK2 on adjacent dimers to rotate bringing the active sites in closer proximity and increasing their affinity for ATP
- this results in transautophosphorylation of the activation lips
- now the activated JAK2’s can phosphorylate cytosolic tyrosines of beta common chain
What type of signalling pathway is activated by IL-3 signallig?
JAK/STAT pathway
How does IL-3 binding result in STAT protein activation?
Binding of IL-3 activates JAK2, which phosphorylates tyrosine residues of beta common chain
- Cytosolic STATs bind to pY residues via SH2 domains
- JAK2 phosphorylates tyrosine of C-terminal STAT transactivation domain (TAD)
- phosphorylates STAT dissociates from receptor and dimerises (SH2 domains of one STAT bind pY of TAD of other STAT)
- conformation change reveals NLS, bound by importin to allow nuclear localisation
- the SH1 domains of dimer acts as clamp onto DNA
What is the STAT dimer involved in IL-3 signalling?
STAT 5a/5b
