Cytokines - Signal Transduction

Question 1

What types of cytokine receptors are we going to look at?

Answer 1

Type I and Type II cytokine receptors

Question 2

What is common about both Type I and type II cytokine receptors?

Answer 2

They both dimerise

They both lack their own intracellular signalling motifs e.g. tyrosine kinase domains

Question 3

How do type I and II cytokine receptors get around not having their own intracellular signalling motifs?

Answer 3

JAKs associate with the receptor in order to signal

Question 4

What does JAK stand for, what were they renamed to and why?

Answer 4

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

Question 5

What are JAKs, where are they found?

Answer 5

Large tyrosine kinases of 120-139kDa

JAK1 and 2 are ubiquitously expressed while JAK3 is exclusive to T-cells, NK cells and B cells

Question 6

How do JAKs associate with cytokine receptors?

Answer 6

JAKS have a kinase and a psuedokinase domain which bind to proline-rich Box regions on the heterodimeric cytokine receptors

Question 7

What happens when JAKs bind to cytokine receptors?

Answer 7

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

Question 8

What happens with the phosphorylation of JAKs?

Answer 8

Phosphorylated JAKs then phosphorylate STATs

Question 9

What are STATs?

Answer 9

Signal Transducers and Activators of Transcription protein

Question 10

What are STATs?

Answer 10

Signal Transducers and Activators of Transcription protein

Question 11

What brings about the dimerisation of cytokine receptors?

Answer 11

The receptors only dimerise when they bind their cytokine

i.e. cytokine binding to receptor induces dimerisation

Question 12

What hapens with the phosphorylation of STAT?

Answer 12

This induces the dimerisation of STAT

Question 13

What does dimersed STAT do?

Answer 13

STAT dimer is able to move into the nucleus where it can act on DNA to induce specific gene transcription

Question 14

What is the JAK and STAT combo for IFN-y?

Answer 14

JAK1 and JAK2 + STAT1

Question 15

What is the JAK and STAT combo for IL-2?

Answer 15

JAK1 and JAK3 + STAT5

Question 16

Why do different cytokines have different effects on the same receptor?

Answer 16

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

Question 17

Why do different cytokines have different effects on the same receptor?

Answer 17

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

Question 18

How are the JAK and STAT pathways regulated?

Answer 18

Regulated by the SOCS family

Question 19

What are SOCS?

Answer 19

Suppressors of cytokine secretion

Question 20

How do SOCS work?

Answer 20

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

Question 21

What is the STAT/SOCS negative feedback loop?

Answer 21

This is a negative feedback whereby STATs make SOCS

SOCS ubiquitinates STAT -> STAT brought to proteosome for degradation

Cytokine activity is stopped without STAT

Question 22

What is a synthetic way of inhibiting cytokine signal transduction?

Answer 22

JAK inhibitors

Question 23

What are JAK inhibitors?

Answer 23

These are drugs of small molecules designed to treat negative effects of cytokines in chronic inflammatory disorders

Question 24

Give some examples of JAK inhibitors

Answer 24

Baricitinib for rheumatoid arthritis

Filgotinib for ankylosing spodylitis or psoriatic arthritis

Question 25

How do JAK inhibitors work?

Answer 25

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)

Question 26

What roles do cytokines play in transplantation?

Answer 26

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

Question 27

In what two ways can anti-inflammatory cytokines promote graft tolerance?

Answer 27

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

Question 28

What two kinds of drugs suppress cytokines to be used in preventing rejection?

Answer 28

TNF inhibitors IL-6 receptor blockade

Question 29

Give two examples of cytokine targetted drugs, what do they target

Answer 29

Tocilizumab -> targets IL6 Secukinumab - targets IL17

Question 30

Talk about Tocilizumab in transplantation

Answer 30

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

Question 31

What is the role of IL-6 in transplantation, what are the affects of blocking its activity?

Answer 31

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

Question 32

How did patients benefit from Tocilizumab

Answer 32

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

Question 33

How did patients benefit from Tocilizumab

Answer 33

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

Question 34

How do we use G-CSF?

Answer 34

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

Question 35

Give some examples of G-CSF drugs

Answer 35

Filgrastim is what we use: - additives such as PEG (polyethylene glycol) can be added to increase preservation etc etc - pegfilgrastim, lenograstim, lipegfilgrastim

Question 36

How does G-CSF signalling work?

Answer 36

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