Cytokines - Signal Transduction Flashcards
What types of cytokine receptors are we going to look at?
Type I and Type II cytokine receptors
What is common about both Type I and type II cytokine receptors?
They both dimerise
They both lack their own intracellular signalling motifs e.g. tyrosine kinase domains
How do type I and II cytokine receptors get around not having their own intracellular signalling motifs?
JAKs associate with the receptor in order to signal
What does JAK stand for, what were they renamed to and why?
JAK originally called Just Another Kinase
When it was learnt they associated with cytokine receptors to bring about a signal they were renamed Janus kinases
Janus was a 2 headed Roman god -> statues in roman homes at the entrance, you saw one face when you entered and the other when you left
JAKs have a kinase a pseudokinase domain at either end of the molecule
What are JAKs, where are they found?
Large tyrosine kinases of 120-139kDa
JAK1 and 2 are ubiquitously expressed while JAK3 is exclusive to T-cells, NK cells and B cells
How do JAKs associate with cytokine receptors?
JAKS have a kinase and a psuedokinase domain which bind to proline-rich Box regions on the heterodimeric cytokine receptors
What happens when JAKs bind to cytokine receptors?
The proximity of two JAKs allows them to phosphorylate each other
i.e. JAKs bind to proline rich regions of receptor -> receptor dimerises -> brings JAKS near each other -> JAKs phosphorylate each other
What happens with the phosphorylation of JAKs?
Phosphorylated JAKs then phosphorylate STATs
What are STATs?
Signal Transducers and Activators of Transcription protein
What are STATs?
Signal Transducers and Activators of Transcription protein
What brings about the dimerisation of cytokine receptors?
The receptors only dimerise when they bind their cytokine
i.e. cytokine binding to receptor induces dimerisation
What hapens with the phosphorylation of STAT?
This induces the dimerisation of STAT
What does dimersed STAT do?
STAT dimer is able to move into the nucleus where it can act on DNA to induce specific gene transcription
What is the JAK and STAT combo for IFN-y?
JAK1 and JAK2 + STAT1
What is the JAK and STAT combo for IL-2?
JAK1 and JAK3 + STAT5
Why do different cytokines have different effects on the same receptor?
This is because each cytokine activates different combination of JAKS and STATs e.g. IFN-y = JAK1 and JAK2 + Stat 1 while IFNa/B = JAK1 and TYk-2 with Stat 2
Why do different cytokines have different effects on the same receptor?
This is because each cytokine activates different combination of JAKS and STATs e.g. IFN-y = JAK1 and JAK2 + Stat 1 while IFNa/B = JAK1 and TYk-2 with Stat 2
How are the JAK and STAT pathways regulated?
Regulated by the SOCS family
What are SOCS?
Suppressors of cytokine secretion
How do SOCS work?
They suppress Type I/II cytokine signals by binding to JAKs via their SH2 domain
SOCS also cause ubiquitination of JAKs which leads to their degradation
They create negative feedback loop
What is the STAT/SOCS negative feedback loop?
This is a negative feedback whereby STATs make SOCS
SOCS ubiquitinates STAT -> STAT brought to proteosome for degradation
Cytokine activity is stopped without STAT
What is a synthetic way of inhibiting cytokine signal transduction?
JAK inhibitors
What are JAK inhibitors?
These are drugs of small molecules designed to treat negative effects of cytokines in chronic inflammatory disorders
Give some examples of JAK inhibitors
Baricitinib for rheumatoid arthritis
Filgotinib for ankylosing spodylitis or psoriatic arthritis
How do JAK inhibitors work?
They work by targeting specific combinations of JAK molecules to prevent the activity of certain cytokines involved in specific diseases
e.g. Baricitinib used to treat RA by inhibiting JAK2 and thus IL6 and IFNy (as well as many other cytokines)
What roles do cytokines play in transplantation?
Pro-inflammatory cytokines play a role in transplant rejection e.g. TNFa, IL1, IL6 and IFNy
Hyperacutre rejection can be mediated by a cytokine storm
Anti-inflammatory cytokines can promote graft tolerance
Drugs supressing cytokines can be used as part of the transplant process
In what two ways can anti-inflammatory cytokines promote graft tolerance?
T-regulatory cell (Treg cells) produce IL-10 and TGF-B which promote graft survival
IL-4 and IL-5 promote T-Helper 2 responses and thus prevent damaging TH1 responses
What two kinds of drugs suppress cytokines to be used in preventing rejection?
TNF inhibitors
IL-6 receptor blockade
Give two examples of cytokine targetted drugs, what do they target
Tocilizumab -> targets IL6
Secukinumab - targets IL17
Talk about Tocilizumab in transplantation
A monoclonal antibody which blocks receptor acitivty both on cells and the soluble version of receptors
It prevents IL6 activity -> prevents IL6 binding to receptor by occupying its receptor
In transplant pateints there was generally increased graft survival and reduced donor antibodies
There is some evidence that these can help graft live longer
What is the role of IL-6 in transplantation, what are the affects of blocking its activity?
IL6 plays a role in memory B cell production, if blocked the recipient wont become sensitised to alloantigens in donor tissue
IL6 helps plasma cells survive, if blocked, reduced plasma cell survival and reduced antibodies produced
IL6 is involved in production of cytotoxic T cells, blocking prevents etc
IL6 is associated with T follicular helper cells which cause antibody class switching
How did patients benefit from Tocilizumab
There was a reduction in the amount of DSA produced after 2 years (3/7 patients experienced this)
Graft and patient survival were excellent with kidney function stabilising in 5/7 patients
Side affects were light to moderate -> infections but this is seen with all kinds of immunosuppressants
TCZ seems promissing for Antibody mediated rejection
How did patients benefit from Tocilizumab
There was a reduction in the amount of DSA produced after 2 years (3/7 patients experienced this)
Graft and patient survival were excellent with kidney function stabilising in 5/7 patients
Side affects were light to moderate -> infections but this is seen with all kinds of immunosuppressants
TCZ seems promissing for Antibody mediated rejection
How do we use G-CSF?
Used to mobilise stem cells from the bone marrow to prepare for autologous or allogenic stem cell collection
Administration of G-CSF helps support the generation of neutrophils and reduces susceptibility to infetion post bone marrow transplant
Give some examples of G-CSF drugs
Filgrastim is what we use:
- additives such as PEG (polyethylene glycol) can be added to increase preservation etc etc
- pegfilgrastim, lenograstim, lipegfilgrastim
How does G-CSF signalling work?
It uses JAK2 and STAT3 combination
It can be supressed by SOCS2
Activation of pSTAT3, pERK1/2, PI3K/pAKT induce cellular proliferation, inhibit apoptosis and cause cellular differation