Receptor Tyrosine Kinases Flashcards
(42 cards)
Growth factor examples
Discovery
EGFR VEGF PDGF FGF TGF Produced by many tissue types unlike hormones
Nobel prize- Cohen realised EGFR phosphorylates endogenous proteins using isotopic ally labelled ATP
Growth factors for chronic wound repair
GF, target, trial
EGF, epithelium, venous ulcers. Proliferation and migration
FGF, endothelium, diabetic and venous ulcers
TGF-B, fibroblasts, venous ulcers and pressure sores. Fibroblast activity and chemotaxis, stops proliferation (opposite to EGF AND FGF)
Non receptor RTKs
32 in genome
FAK, JAK, SRC
Have kinase, SH2 domains etc.
Growth, proliferation, adhesion. Src and FAK are find at the Integrins complex
4 structural features of RTKs
Kinase
Regulatory
TM domain single
Extra cellular ligand
Activation of GFRs generic
How does FGF enhance ligand binding?
Activation lip blocks kinase activity
Insulin- stops ATP, in FGF prevents substrate
Dimerisation causes phosphorylation of lip
Kinase activity activated by reducing Km for ATP or substrate
Kinase increases transphosphorylation docking sites as well as effect Pi
FGF- 2 ligands simultaneous also to heparan sulphate (ECM) to enhance ligand binding
Crystallisation of EGFR
Space mission STS-47
Microgravity
Mass transport only under gravity
Growth instead occurs by diffusion of molecules
Greater size and reduced defect densities
Structure of VEGF family
Inhibitors of VEGF and disease
Angiogenesis
8 exons by alternative splicing, 5 different sized proteins
The growth factor is disulphide bonded homodimers
Can dimerise the RTKs, as site on each end
Plasmin cleaves the heparin binding domain at either end
Ranibizumab and pegaptanib- used to treat wet type macular degeneration
Structure of the insulin receptor
Heterodimers of alpha beta chains
Constitutive
Extra cellular domain is a covalently linked dimer (dimer of dimers)
Upon ligand binding, the domain still dock
Unfolding and activation of cytoplasmic domains
Insulin in the blood forms inactive hexamer
How insulin engages its binding site
Does not bind first leu repeat
Engages carboxyl tail chain which is remodelled onto the leu repeat
CT displaces the B chain C terminus away from the hormone core
Revels conformational switch
TGFB superfamily
SER/THR NOT TYROSINE
Isoforms 1-3
Actinin and inhibin have opposite effects on FSH release
BMP7- phosphorylates SMAD 1+ 5 promoting osteogenic genes and healing. Promotes messnchymal cells to bone and cartilage
Cell adhesion and cancer crosstalk
Cadherin in cancer
Integrins upregulate EGFR to promote snail which represses markers and starts EMT transition
Kindlin and EGFR link
Beta catenin in Wnt signalling
TGFB is paradoxical
Prevents EM transition
But modulates cell invasion, immunity and microenvironment
Activates tumour suppressors, activates Par6-P and snail and slug
Represses ID1 which blocks transcription factors
Promotes fibroblasts
Inhibits osteoblasts
Formation of mature TGFB
3 proteins, 3 genes
N terminal pro cleaved but still attached
Mature domains bind to form a dimer and latent complex
Proteolysis or conformational change released the disulphide bonded mature domains dimer
In one mature domain, 3 Cys form knot. 4 antiparallel beta sheets
TGFB signalling pathway
TGFB binding to either RIII then RII which recruits RI
RIII increases surface conc
Release of Ri Ser/THR activity
Phosphorylates SMAD3, exposes NLS
The MH2 domain of SMAD3 joins with SMAD4 and another SMAD3
The trimer thing binds importin to the SMAD3 NLS
Ran GTP dissociates importin
TFE3 associates with SMAD complex and binds promoter
Transcription of plasminogen activator inhibitor PAI-1
Dephos by nuclear phosphatases
Mutations in FGFR TM domain
Y373C- thanatophoric dysplasia and bladder cancer
G375C- achondroplasia
Hydrophobic -> polar can lift out of membrane
Dimer stability, membrane segment, extra cellular contacts, catalytic domain
Structure and function of intracellular RTK domain
FGFR- activation loop interfere with peptide binding not ATP
More general autoinhibition mechanism?
Phosphotyrosines
Serve as docking sites for SH2 proteins
Juxtamembrane region of EGFRs
Between the TM and kinase domain
JMA- self interactions, 2 antiparallel helices where Arg face membrane. Interact via a ridges and grooves interaction
Activation lip occludes and inhibits.
JmB forms a clamp between the N lobe of the receiver and the C lobe of the activator- this stabilises the activated form and brings the kinases into close proximity. Point mutations here stop activation
Kinases bind asymmetrically giving activator and receiver
JMA then forms the helical dimer (prevented by c terminal tails in inactive)
The 4 types of EGFRs
HER1-4
HER2 doesn’t bind ligand, forms heterodimers
Enhances signalling, so higher efficacy of ligand binding less ligand needed
HER3 kinase dead
25% cancers have more her2
Herceptin prevents signalling complex and targets dgradarion
20k -> 600K
Regulation and inhibition of EGFR
How does cancer resist this
EGFR is internalised and is then ubiquitinsted
Only one of family
T790M in ATP pocket makes resistant to first generation RTKIs which prevent ATP binding
Change to Met causes resistance because of steric hindrance of the Met and RTKIs
Protein tyrosine phosphatases
Polymorphisms cause type 1 and 2 diabetes
Regulators of liver homeostasis and mediate pancreatic B cell death
PTB1B targets EGFR
107 PTPs compatible with 90 TKs
Regulation of PTP by dimerisation
Ligand binding inhibits the PTPs by dimerisation
Inhibition of catalytic D1 PTP domains
Wedge motif of one D1 occludes active site of other
Essentially opposite of RTKs
PTPs in disease
PTPN1- non insulin dependent diabetes
PTPN2- T cell leukaemia
Tandem kinase domain EGFR
Glioblastoma Elevated basal autophosphorylation Resistant to competitive inhibition Knock outs of either domain show patterns of a constitutively active N site- basal activity C site- ligand responsiveness
EGFR gene in brain tumours
3’ end in glioblastomas
Deletions of 255 bases near cytoplasmic domain
vIVa and vIVb deletion of internal segment distal to the kinase domain. C terminus surface inhibits kinase so the deletion is activating
Exons 2-7 deletions -> TYPE III MUTANT
Activated no ligand
truncated receptor no N terminus
