JAK-STAT signalling Flashcards
explain the JAK-STAT signalling
- composed of a) transmembrane protein b) JAK at the intracellular domain of the receptor c) STAT ( a transcription factor) and d) Ligand (“tins” EPO, prolactin, thrombopoeitin, leptin , “ters” interferons, interleukins, GM-CSF???
- ligand cause oligomerization of receptor
- When ligand is bound to the receptor, oligomerization induce intracellular activation
- JAK will transautophosphorylate when it is brought in close proximity to one another following oligomerization
- activated JAK will phosphorylate the tyrosine residues on the receptor and also STAT
- STAT will homo/heteroDIMERise trough SH2 domain
- STAT enter the nucleus and bind to GAS element ( Gamma Activated Sequence)
- increase Transcription
how many JAKs and STATs are there?
4 JAKs and 7 STATS
JAK1,2,3, tyk2
stat 1,2,3,4,5A,5B,6
What does JAK-STAT signalling pathway does
- regulate eythropoesis
- signalling mechanism for cytokines and growth factors
*
what are the receptors for these cytokines
a) Erythropoeitin,
b) thrombopoetin, and
c) G-CSF
Erythropoeitin -> EPO - R
Thrombopoeitin -> cMPL (or TPO-R)
G-CSF -> G-CSF R
what are the phenotype of deletion mutation of some cytokine receptos?
- embyronic lethal, failure of definitive eythropoeisis
- cMPL»_space; reduced hematopoeitic stem cells, reduces megakaryocytes and thrombocytopenia
- G-CSF»_space; chronic neutropenia, impaird neutrophil mobility
What is gp130
- GLYCOPROTEIN 130
- a transmembrane domain
- founding member for all cytokine receptor
- activate several pathways
a) JAK-STAT
b) RAS , ERK
describe the activation of gp130
- ligand bound to receptor such as IL6 binds to IL6R or (IL11) or (Mosm-osmrB) or (LIF-LIFR)
- then they will bind to gp130 forming a complex ( consisting fo IL-6R, IL6 and gp130)
- b this complex will dimerize into a hexameric structure and induce downstream signalling
- gp130 does not have an intrinsic kinase activity, thus must be activated by phospharylation on the tyrosine residue by other protein
- phosphorylation recruits and activate JAK and STAT via phosphorylation
5.
can a IL-6Ralpha induce donwstream signalling?
no. IL6Ra is not a signalling receptor, must bound to gp130
Describe the IL-6, IL-6R and gp130 complex
- IL-6 cytokine have 3 binding site for IL-6R(1) and gp130(2)
- following binding, complexes are internalised
describe the intracellular structures of beta receptors
- have box1 and box 2 ( sometimes box3 domains)
* places where JAK binds
Explain hop tuml mutation
- mutation in drosophila
- tuml - tumor lethal
- phenotype : identical to wasp infected larvae
- temperature sensitive
- @ 17c = more blood cells, less lamellocyte
- @ 25c = more lamellocytes, but less total blood count
Explain hop tuml mutation
- mutation in drosophila
- tuml - tumor lethal
- phenotype : identical to wasp infected larvae
- temperature sensitive
- @ 17c = more blood cells, less lamellocyte
- @ 25c = more lamellocytes, but less total blood count
What is the feature of temperature sensitive mutation in HOP tuml?
- @ 17c = more blood cells, less lamellocyte
* @ 25c = more lamellocytes, but less total blood count
gain of function of JAK
increase lamellocytes
What is MPN
myeloproliferative neoplasms
classic examples
MF, ET, PV
MF - scar tissue ET - increased platelet - blood clotting PV - polycythemia vera increased red blood cells enlarged spleen
What is MF
primary myelofibrosis
- chronic blood cancer
- bone marrow impacted by scarring
- enlarged spleen, trying to make up blood making for bone marrow
- can be obtain from progression from pv and et
what is ET
Essential Thrombocythemia
- Blood malignancy with too many platelet
- problem with blood clot
What is PV
polycythemia vera
- increased RED BLOOD CELL
- also increase wbc and platelet
- enlarged spleen
James 2004 in Nature
Jak2 mutation»_space; constitutive signalling»_space; polycythemia vera
difference between the wt and gain of function mutation of jak2
JH1 = kinase domain»_space; switching jakstat signalling pathway on
JH2 = pseudo-kinase domain»_space; looks like a kinase domain but its not!
JH2 negatively regulate JH1
mutation in JH2 , reduced negative regulate, less inhibiting the JH1, so increased activity of JH1
Describe mutation found in MPL
MPL/c mpl / TPO r
ligand = thrombopoeitin
in normal Mpl
- dimerisation of mpl receptor is brought about by binding to TPO
- Dimerisation causes the intracellular domain to be closer together and JAK2 can be phosphorylated ( and the normal downstream signalling)
in mutation
- dimerisation is TPO independent, no need for TPO
- dimerisation of MPL is sufficient to activate the receptor
- this is caused by a mutation that adds cysteine residues, to form disulphide bridges
- -different from domeless–
PML triggers megakaryocytes differentiation and platelet production
What is CALR
a chaperone that lives in the ER
How does CAL R mutation cause MPN?
- frameshift mutation
- +1 frame shift mutation
- causes the whole sequence to be read differently
- producing a completely different peptide sequence
- result in novel protein to be prodcuced
mutation in which gene causes increased in JAK STAT pathway>
- JAK2 > gain of fx in JH2 domain
- MPL > gain of fx in transmembrane domain
- CAL R > frameshift mutation that output novel protein
JAK-STAT drugs
> screen 2000 small molecules
high throughput transcriptional reporter assay
decrease phosphorylation of STAT 5
the mouse with hJAK2 mutation when treated with methotrexate shows a difference compared to control in what aspect?
CELLULAR
control (PBS) shows phos
methotrexate drug shows that the PHOSPHORYLATION of STAT3 and STAT5 are significantly reduced
(mutation causes gain of fx of JAKSTAT signalling pathway, so this drug kind of reduce/ eliminate the pathway?)
using western blot
SPLEEN
spleen is bigger than WT but significantly smaller than control (PBS treated) mutataed animal
why is methotrexate works for rheumatoid arthritis
RA is an autoimmune disease
methotrexate inhibit JAKSTAT pathway
key to progression of inflammatory responses
like IL6, interferon gamma etc
