Tyrosine kinase receptors Flashcards
3 main types of cell surface receptors
ion-channel linked
GPCR
enzyme-linked
which type of receptor are RTKs?
enzyme-linked
which molecule type signals via RTKs?
example
growth factors
epidermal GF
- stimulate differentiation, survival + proliferation
what can growth factor signalling influence?
‘growth’ (in cell size + no.)
at different levels:
cells, tissues, organs + body
insulin-like growth factors
IGF1 + IGF2 (ligands)
- > IGF1R (receptor)
- > growth
important in foetal development
- promote growth
effects of changes in IGFs
IGF1 knockout
= 60% normal size at birth
IGF1 mutation
= leprechaunism
RTK characteristics
cysteine-rich extracellular domain
single a-helix hydrophobic transmembrane domain
intracellular domain with tyrosine kinase activity + several tyrosine residues
RTK subfamilies
based on structural homology
all have cystine-rich domains on outside of cell
cysteine-rich domains on outside of cell allow…?
disulphide bonding of extracellular portion of receptor
-> to fold into correct shape to recognise signal w/ high specificity
can bind to low [signal] w/ high affinity
experiment to investigate RTK function
EGF introduced to cells
-> no response
.:. cells don’t respond to EGF w/out receptor
introduced plasmids via transfection
experiment to investigate RTK function
- different plasmids + effects
EGFR
-> EGF binding, protein phosphorylation, DNA synthesis + cell division
FGFR + control receptor
-> no response
EGFR + point mutation inactivates kinase
-> EGF binding but not kinase activity
receptor internalisation and degradation via lysosomes
form of adaptation/desensitisation to prolonged signal activation
can occur in absence of a functional TK domain
.:. receptor internalisation not part of signalling process
what is the sequence of responses after EGF is added?
- GF binding
- TK phosphorylation of proteins
- GF/receptor internalised, degraded
- new gene expression
- cell division
how does the signal cross the membrane?
ligand interacts with receptor w/ high affinity + specificity
- > brings together 2 copies of receptor
- > response
activation of PDGF-R
- proteins that form
PDGF
= 2 polypeptides encoded by 2 genes
- dimerise to form 3 proteins
A + A protein
- can homodimerise to form A-A protein
A + B can heterodimerise
= A-B protein
B + B can homodimerise
= B-B protein
activation of PDGF-R
- subunits
alpha receptor
- interacts with PDGF-A + PDGF-B
beta receptor
- interacts only with PDGF-B
activation of PDGF-R
- depletion of alpha-receptors
A-A = a-a
= TK activity
-> DNA synthesis
(internalised + down-regulated)
A-B = beta
b-receptors don’t recognise A protein
-> 2 receptors not brought together
= no response
B-B = b-b
= TK activity
-> DNA synthesis
(internalised + down-regulated)
activation of PDGF-R
- experiment 2
activating mutations
(kinase activity in absence of signal)
- in cancers (various RTKs)
- achondroplasia (FGFR3)
inactivating mutations
- dominant -ve mutations
FGF signalling in anterior-posterior axis patterning
FGF-R over-expression
= suppressed head formation
FGF-R knock down
(point mutation inactive kinase)
= normal head development BUT no tail
TK domain substrates
phospholipase C
Src
PI3-kinase
GAP
TK domain substrates
- contain conserved binding motifs…
SH2 domain
- receptor interaction
SH3 domain
- interactions with other signalling molecules
activation of RTKs
- autophosphorylation
1st phosphorylation involves kinase domain
-> raises kinase activity for subsequent phosphorylation events
RTK activation of SH2/SH3 domain proteins
SH2 domains interact w/ regions of receptor
- where local structure is influenced by presence/absence of P group
-> changes conformation
= allows docking of specific substrates to specific regions of receptors
RTKs as targets for new drugs
deregulation of RTK signalling
- crucial for development of hyper proliferative diseases e.g. cancer
> neutralising Abs bind + block signal
> prevent receptor dimerisation
> kinase inhibitors via binding to kinase domain
