Lecture 10: Interleukins Flashcards
How does STAT activation result in activation of gene transcription?
The STAT dimer NLS is bound by importins that allow nuclear localisation
- STAT dimer binds to GAS motifs in the DNA via SH1 domains
- recruits activators (such as histone acetyl transferases (HATs)) and transcription factors to promote gene expression
How are STATs recycled in IL-3 signalling?
following gene activation:
- STATs dephosphorylated by nuclear phosphatase resulting in dissociation of the STAT dimer
- dissociation reveals exportin binding sequence bound by exportin (E.g. CRM1)
- STATs exported from nucleus
How do STATs confer specificity? (2 main ways)
- SH2 domain binds to specific sequence motifs of the beta common chain containing the pY
- STATs effects are cell specific (different transcription factors, cell-specific epigenetic modifications affect DNA accessibility for STAT binding)
What is special about the GAS DNA sequence bound by SH1 domain of STATs?
It is a palindromic sequence separated by variable number of nucleotides to allow different STAT dimers to bind
What are the short term (2) and long term (1) regulators of the helical cytokine signalling pathways?
Short term: cytoplasm (minutes)
- protein tyrosine phosphatases
- protein inhibitors of activated STATs (PIAS)
Long term: hours/days
- CIS-SOCS family
How do protein tyrosine phosphatases regulate helical cytokine signalling?
- Short term
- bind pY on STAT via SH2 domain
How many members of the protein tyrosine phosphatase family are there that regulate helical cytokine signalling? and what are they?
not a particularly important question
4 members
- SHP-1 (SH2-containing phosphatase 1)
- SHP-2
- TCPTP (T cell protein tyrosine phosphatase)
- PTP1b (Protein tyrosine phosphatase)
What is the structure of SHP-1 protein tyrosine phosphatase and how does it regulate helical cytokine signalling?
Structure:
- 2 SH2 domains and 1 catalytic phosphatase domain
Function in regulation:
Resting: no receptor activation, SH2 domains fold back and occlude the phosphatase domain
Activated receptor: SH2 domains recognise and bind pY of beta common chain , unmasks the phosphatase domain, which dephosphorylates JAK2 to prevent downstream signalling.
How do PIAS proteins regulate helical cytokine signalling pathways?
Short term regulation
Bind to the SH1 domain of STATs and prevent their DNA binding.
Describe the structure of the CIS-SOCS family
8 related intracellular proteins:
- 1 CIS (cytokine-inducible SH2 protein)
- 7 SOCS (Suppressor of cytokine signalling 1-7)
All have SH2 domain to bind pY of receptor and JAKs and SOCS box that recruits E3 ubiquitin ligases
Which members of the CIS-SOCS family have kinase inhibitory mechanisms of action and why?
CIS-SOCS1 and CIS-SOCS3
- they have KIR (Kinase inhibitory region) that blocks JAK activity
Why is CIS-SOCS regulation an example of negative feedback?
CIS and SOCS genes are transcriptional targets of STATs
- when low cytokine concentration = less activation of JAK/STAT pathway = less transcription of CIS-SOCS
- high cytokine concentration = more activation of JAK/STAT pathway = increased transcription of CIS-SOCs = long term inhibition of signalling pathway
What is the mechanism by which all CIS-SOCS family proteins can regulate helical cytokine signalling pathways?
Degradation:
- SH2 domain recognises pY of beta common chain and JAKs
- SOCS box recruits E3 ubiquitin ligase
- ubiquitination and proteasomal degradation of the receptor, JAK, and CIS-SOCS member
Disruption of interleukin signalling has pathological consequences for ___(1)___ and other ___(2)___ cells
(1) Immune
(2) blood
What is an example of a disease resulting from disruption of interleukin signalling?
X-linked SCID
- defects in the IL-2 receptor gamma chain that prevent IL-2 signalling required for full and correct maturation of T and B lymphocytes
