L10 - TGFbeta and FGF signalling Flashcards
What are the three common features in signal transduction pathways?
Reception – ligand binds to a cell surface receptor and activates it
Transduction – receptor activation induces transduction of signal from membrane to nucleus via a cascade of secondary messenger activation
Response – a transcription factor is activated and induces transcription of specific target genes
What are the three sub groups of the TGFbeta protein superfamily?
BMP like family
GDNFs family
TGF beta like family
BMP like family examples
BMPs
GDFs
GDNFs family examples
GDNF
Neuturin
TGF beta like family
TGF-beta
Activins
Nodal
TGFbeta signal transduction method
- Ligand binds to type 2 receptor
- This leads to oligomerisation bringing together the type 1 and type 2 receptor
- Formation of dimer results in activation of type 2 receptor
- Kinase activity of type 2 receptor promotes phosphorylation of type 1 receptor
a. Promotes overall activation of receptor - Downstream there are two groups of proteins
a. SMAD 4
b. SMAD 2 and SMAD 3 - SMAD 2 and SMAD 3 recruited and phosphorylated by receptor
a. Further activated by binding of smad 4 - Active SMAD transcription factor complex binds to TGF beta target genes and activate their transcription
Why is BMP signalling tightly regulated?
You only want
- Certain cells to respond to the signals
- Cells to respond at certain times/locations
How is BMP signalling operated through inhibition?
The proteins are already synthesised but their activity is controlled through extracellular inhibitors
Antagonists
- Moderate BMP signalling
- These varying levels of inhibition lead to a variety of different cell fates
Examples of antagonists used in BMP signalling
Noggin
Chordin
BMP3
How many RTK families are there?
20 each with many individual receptors – with their ligand partners
RTK ligand receptor complexes
Some ligands are specific for one receptor and vice versa
Some ligands interact with many receptors and vice versa
How many RTK genes have been identified in human genome?
58
Are RTK mainly monomers or polymers?
Monomers
Except insulin receptor
What are RTK extracellular and intracellular domains like?
Extracellular domains vary greatly – ligand binding activity
Intracellular domains have kinase activity – enzyme linked receptors
How many transmembrane domains do RTKs have?
Single transmembrane domain – 25-38 amino acids
How are RTKs activated?
The ligand has ability to dimerise and it facilitates receptor dimerization or oligomerisation
What does cross phosphorylation of RTK receptors do?
Enhancers kinase activity
Opens up docking sites for the recruitment of secondary messengers
Tools for analysis of RTK signalling exploit?
Dimerization
What tools for analysis of RTK signalling can be made?
Using genetic engineering we can generate DNA that encodes for a normal receptor that is mutated in the kinase domain
Receptor does not have kinase activity but retains ability to bind to ligand – dominant negative form
What does the dominant negative form of a receptor do?
Block subsequent activity of the dimer
Cross phosphorylation of the receptors will not occur
Useful to generate tools for loss of function studies
How does the phosphorylated RTK receptor transduce the signal?
Phosphorylated tyrosine acts as docking sites for downstream signalling proteins
What proteins bind to RTKs?
PI-3 kinase – inositol lipid pathway
GTPase-activating protein – RAS/MAP kinase pathway
PLC-gamma – inositol lipid pathway
What two states does Ras have?
Functions as a switch with two distinct states
- Active – bound to GTP
- Inactive – bound to GDP
How does Ras switch between its to states?
Becomes active with help from guanine nucleotide exchange factor (GEF)
Becomes inactive with help from GTPase activating proteins (GAP)
Ras pathway - how docking leads to signal transduction?
- Activated receptor has many phosphorylated tyrosine’s acting as docking sites
- Binding of GRB2 and Sos (GEF) coupled receptor to inactive Ras
- Sos promotes dissociation of GDP from Ras
- GTP binds Ras and then it dissociates from Sos
How does signal transduction downstream of RTKs occur?
Occurs through rapid activation, by Ras, of a series of proteins
- All activated by phosphorylation
- All contain kinase activity so trigger cascade of protein phosphorylation
Signal transduction downstream of Ras method?
Activation of three different kinases with activates various transcription factors
- Raf kinase– activated by GTP activated Ras
- Mek kinase – activated by MAP kinase kinase kinase
- Map kinase - activated by dual phosphorylation of one serine and one threonine by MAP kinase kinase
- Acts just before transcription of target genes
How many FGF ligand members are there?
22
Either paracrine, intracrine or endocrine
FGF receptors are characterised by?
Immunoglobulin like domains
Ligands bind to D2 and D3
Single transmembrane domain
Kinase receptor split into two domains
How many FGF receptors are there?
4
Responsible for downstream events after the other 22 ligands
What is the role of FGF8?
Plays a vital role during development
Patterns midbrain-hindbrain boundary
What do FGFs form a complex with?
FGFs are unable to act on their own – used to help explain their specificity
FGF and its receptor form a complex with HSPGs
FGFs fist form oligomers on HSPGs
What are heparan sulphate proteoglycans used for?
Important extracellular modifiers of cell-cell signalling
HSPG protein core can be?
Transmembrane – fully extracellular
Tethered to membrane
Secreted
What is HSPGs protein core associated with?
Associated with long chains of sugar - heparan
Each molecule of sugar can be modified – mainly by sulphation
- Modification could result in a code that creates binding site for many specific proteins
FGF signalling pathway examples
GRB2 and SOS –> RAS –> RAF, MAPKK and MAPK –> FOS (oncogene) –> cell proliferation
GRB2 and GAB1 –> PI3K –> cell survival
What are mutations in FGF receptors associated with?
Associated with many human disease
Pfeiffer syndrome – FGFR1
Achondroplasia – FGFR3
