Block D Lecture 3 - Tyrosine Kinase Linked Receptors Flashcards
What are 5 families of cytokines and what they regulate?
Answers Include:
Interferon - antiviral proteins
Chemokine - Direct cell migration, adhesion and activation
Tumour necrosis factor - Regulate inflammatory and immune responses
Interleukin family - Function depends on interleukin and cell type
Haematopoietins - Promote cell proliferation and differentiation
Transforming growth factor β family - regulation of immune cells
(Slide 3)
Do all cytokines activate the same receptor type?
No, chemokines usually activate GPCRs, TGFβ usually activate serine/threonine kinases… etc
(Slide 3)
What do cytokine receptors often have?
A short intracellular tail
(Slide 5)
What occurs in the Jak/Stat pathway?
- A cytokine or growth factor binds to its receptor
- This induces receptor dimerization or oligomerization
- Janus Kinases (JAKs) which are pre-associated with the receptor’s intracellular domain, are brought into proximity by receptor dimerization
- The JAKs then phosphorylate each other on tyrosine residues (autophosphorylation), becoming activated
- Activated JAKs phosphorylate specific tyrosine residues on the receptor’s intracellular domain
- These phosphorylated residues serve as docking sites for Signal transducer and activator of transcription (STAT) proteins, which bind to the receptor via their SH2 domains
- JAKs phosphorylate the bound STAT proteins on tyrosine residues
- Phosphorylated STATs dissociate from the receptor and dimerize by binding to each other’s phosphorylated tyrosine residues
- STAT dimers translocate into the nucleus, where they bind to specific DNA sequences in the promoter regions of target genes, initiating transcription, resulting in gene expression
(Slide 5)
Do all cytokine receptors use the same combination of JAKS and STATS?
No
(Slide 6)
What pathways do JAKs link the IL-6 receptor to?
ERK and PI3kinase pathways
(Slide 7)
What are 2 drugs which target the JAK/STAT pathway?
IL6 / IL-6R inhibitors and JAK inhibitors
(Slides 8 and 9)
What kind of drugs are IL6 and IL6R inhibitors and how do they work?
Monoclonal antibodies - they either bind directly to IL6 - inhibiting the interaction with the receptor or bind to the IL6 receptor - preventing IL-6 from activating the receptor and subsequent signalling
(Slide 8)
How do JAK inhibitors work?
JAK inhibitors bind to the ATP-binding pocket of JAKs, preventing their phosphorylation and subsequent activation of downstream signalling
(Slide 9)
What are JAK inhibitors used to treat?
Autoimmune inflammatory diseases
Myeloproliferative Disorders
Cancers
COVID-19
(Slide 9)
What is TNF a good model for?
Cytokine signal transduction
(Slide 13)
What are the 2 forms of TNFα and what is the difference between the 2?
Membrane-bound - juxtacrine signalling, meaning it signals to nearby cells
Soluble - generated from the membrane bound form via the action of TNF-α converting enzyme (TACE). Acts in long range signalling (endocrine)
(Slide 14)
What do TNF receptors undergo to become activated?
Trimerization
(Slide 15)
What are the 2 main TNF receptor signalling pathways?
NF-κB Pathway (Cell Survival and Inflammation pathway)
Apoptotic (Cell death pathway)
(Slide 16)
What occurs in the NF-κB Pathway (Cell Survival and Inflammation) pathway in TNF receptor signalling?
- TNF-α binds to TNFR1 or 2, leading to receptor trimerization
- The receptor recruits TRADD (TNFR-associated death domain protein) and RIPK1 (Receptor-Interacting Protein Kinase 1)
- RIPK1 recruits the IKK complex which phosphorylates IκB proteins, which normally inhibit NF-κB dimers
- This allows NF-κB dimers to translocate to the nucleus
- Once in the nucleus, NF-κB activates the transcription of genes involved in inflammation, immune response, cell survival, and proliferation
(Slide 16)
What occurs in the Apoptotic (cell death) pathway in TNF receptor signalling?
- TNF-α binds to TNFR1, leading to receptor trimerization
- The receptor recruits TRADD (TNFR-associated death domain protein) and FADD (Fas-associated death domain protein)
- TRADD and FADD recruit caspase-8 (an initiator caspase), forming the DISC complex
- Caspase-8 is activated within the DISC complex and cleaves and activates caspase-3 an other executioner caspases
- These caspases trigger the apoptotic process by cleaving key cellular substrates, leading to cell death
(Slide 16)
In addition to cell death, what else can result from the apoptotic pathway of TNF receptor signalling?
Inflammation can also be initiated by the release of cellular contents upon cell death contributing to immune responses
(Slide 16)
How did researchers find out that many cytokines (such as TNFα, IL-6 and GMCSF) were at very high levels in samples from arthritis patients?
By using a culture of joint cells (synoviocytes) from patients to get measurements
(Slide 20)
What is a consequence of using an antibody against TNFα
It blocks the synthesis of other cytokines - TNFα is more important than was originally thought
(Slide 20)
What were TNFα antibodies originally developed to treat?
Sepsis, but it was unsuccessful
(Slide 21)
What are 3 examples of diseases which can be treated with anti-TNFα antibodies?
Answers Include:
Uveitis (inflammation of the eye)
Psoriasis
Hidradenitis suppurativa
Spondylitis ankylosans (inflammation of the spine)
Crohn Disease (inflammation of the digestive tract)
Colitis (inflammation of the large intestine)
Rheumatoid arthritis (inflammation of the joints)
Psoriatic Arthritis
(Slide 24)
What are 3 possible side effects of anti-TNFα antibodies?
Neurological sequelae (long term neurological disorder)
Demyelinating disease
Opportunistic infections
Lymphomas malignancies
Tuberculosis reactivation
Paradoxical side effects (development or worsening of conditions that are typically treated with these medications)
Primary / Secondary non-responders (patient shows no improvement / patient shows improvement and then symptoms return)
Anti-drug antibodies
(Slide 24)
