Cytokines and Growth Factors Flashcards
what is EPO produced by ?
Peritubular Interstitial Fibroblasts
what are cytokines?
- small proteins 5-20 kDa
- released by cells
- affect other cells
- especially important for cells of the immune system
how many cytokines do we know of?
> 50
what are the four distinct structural families of cytokines?
- TNF tumor necrosis factor
- interferon
- chemokines
- hematopoeitin
what are some principles for tumour necrosis factor type interactions?
- a trimeric receptor and a trimeric ligand
- ligands are beta strand type ptoteins
what are some priniciples of inteferon (IFNy)?
- alpha helical ligand and binds to beta type receptor in similar way
- dimeric interferon binds to dimeric receptor
what are some principles of chemokines?
- structure includes alpha helices and beta strands
- can be monomeric or dimeric
- found in cosmetics and facial creams and wound healing
what are some priniciples of EPO hematopoetin?
- Erythropoietin
- erythrocytes are red blood cells
- two receptors one EPO
- EPO make RBCs
what does expression of a cognate receptor mean?
Its how a cell asks to be able to recieve signal from the blood
what does cytokine response (specifically EPO) depend on ?
- expression of a cognate receptor
Cell type and development:
- chromatin structure
- constellation of transcription factors
- developmental history
If we have less oxygen we have…
more red blood cells and this decrease in oxygen is what EPO reacts to
what tells the body EPO is needed ?
Hif1a (Hypoxia Inducible Factor)
what do we need to raise the EPO response?
- Hif
- Transcription factor (to start transcription of EPO)
what is the mechanism by which hif1a is taken out of circulation and destroyed?
so in the presence of normal oxygen levels…
- prolyl hydroxylase hydroxylates Hif1a and marks it for ubiquitatylation/ destruction
what is the mechanism in hypoxic conditions using Hif1a?
asparagin hydroxylase hydroxylates Hif1a and its activation results in tagaet gene expression
what does EPO activate?
erythroid progenitor cells
what happens when EPO stimulates a Erythroid progenitor cell (CFU-E)?
it divides to two cells then 4, 8 , 16 etc
3-5 divisions and they slowly differentiate into red blood cells that slowly lose EPO receptors
leading to 30-100 erythroids
how many ligands need to be occupied to get 80% of the physiological response?
50%
what can be said about EPO ligand concentrations?
below the KdS
how many EPO receptors does an EPC have?
1000
what is a simple experiment to look at whether the patient has healthy blood ?
hematocrit experiment
centrifuge the blood and it will disperse into
1) RBCs
2) WBCs and platelets
3) Plasma
With men showing 41-50% RBCs
Women showing 36-44% RBCs
what cancers can cause low hematocrit levels?
- lymphoma (increased B/ T Lymphocyte WBC)
- Hodgkin’s Lymphoma (increased lymphocyte WBC)
- Leukemia (increased immature WBC)
- Multiple Myeloma (increased myeloma cellls - malignant plasma cells in the bone marrow - reduces production of RBCs and other blood cells)
why do cancers cause low hematocrit levels?
cancers use the blood producing stem cells on the expense of RBC production
what diseases require the use of EPO to treat anemia?
- chronic kidney disease
- inflammatory bowel disease (Crohn’s disease and ulcer colitis)
- Myelodysplasia (blood disorder) resulting from:
> exposure to chemicals (benzene)
> treatment of cancer (chemotherapy and radiation)
If JAK is deleted from the gene pool what happens?
failure of development in fetal mammals
describe a simple structure of JAK
- a kinase
- multiple domains (incl. linker, domain able to bind to the tail of the receptor and a lip domain)
- two lobes
Describe the JAK/ STAT pathway
1) cytokine binding and cytokine receptor dimerisation occurs
2) phosphorylation of associated JAK kinase - leads to activation (ATP to ADP)
3) phosphorylation of additional residues
4) recognition by inactive monomeric transcription factor STAT
5) phosphorylation and release of STAT
6) STAT dimerisation allows entry into the nucleus
how does EPO act in three simple steps
- EPO binds to the EPO-receptor
- monomeric EPOr dimerises on EPO binding
- this leads to activation of an associated kinase
resulting in a conversion of extracellular signal to intracellular change
describe structure of STAT
C-terminal phosphorylated by JAK, Phosphate tail of one monomer binds to SH2 domain of the other monomer to create a dimer formation
Explain the cascade of protein-protein interactions in the JAK/ STAT pathway
- EPO binds EPOr
- dimerisation of EPOr occurs
- activates cytosolic JAK-Kinase
- Receptor phosphorylation
- Receptor (P) recognised by SH2
- Activates STAT pathway
- Exposes NLS, pathway continues in the nucleus
What is the short term adaptation to deactivate the EPO system?
removes phosphate from lip domain to inactivate the kinase
- has an SH2 domains
- activated upon binding to the c terminus
phosphotases = SHP1
How does the cell achieve long term adapation (deactiviation) in regards to EPOr ?
using SOCS protein recognises SH2 domain and binds on the SH2 domain
SOCs protein has a SOCs box which attracts the E3 Ubiquitin ligase which then marks the receptor for destruction
Name the two ways to switch off EPO’s activation through JAK/ STAT
1) Short term adaptation
- phosphatase SHP1 dephosphorylates JAK –> OFF
2) Long term adaptation
- SOCS –> block of SH2 binding sites
- SOCS –> targets JAK for degredation via E3
name the four processes that JAK2 and the EPO pathway can activate
a) STATS (Transcriptional activation)
b) GRB2 or Shc (Ras - MAP kinase - transcriptional activation or repression)
c) Phospholipase Cy (Elevation of calcium - Transcriptional activation or repression; modification of other cellular proteins)
d)PI-3 kinase (Protein kinase B - Transcriptional activation or repression; modifications of other cellular proteins)
what do STAT 1- 5 interact with
STAT-1: IFNy
STAT-1 and 2: IFNa/B
STAT-3,-5: growth hormones
STAT-4
STAT-5: EPO
what type of interferons do virus infected cells produce?
Dendritic cells: IFNa
Fibroblasts: IFNb
what two directions can type 1 interferons act after release by virus infected cells?
autocrine: towards the infected cell
paracrine: towards uninfected neighbours
what do INFy do in terms of viral defence via the Jak-STAT pathway?
signal through the Jak-STAT pathway to produce >300 gene products, including cytokines
what type of interferond fo T cells and NK cell produce as part of the viral defence?
type II INFy
How can INFy kill virus infected cells or cancerous cells ?
autocrine: inhibition of virus replication, via apoptosis
paracrine: up-regulation of MHC-I and NK-cell activation
