L13 - Receptor Tyrosine Kinase Flashcards
7 capabilities of tumor cells
- Independence from growth signals
- Insensitivity to anti-growth signals
- Able to evade apoptotic signals
- Become immortal
- Develop own blood supply
- Able to invade and grow in distant sites
- Able to evade the immune system
general structure of kinase linked receptors
one transmembrane domain
intracellular enzyme/kinase domain
- linked to an intracellular domain or linked to a cytoplasmic or non-receptor kinase
basic steps of kinase phosphorylation
- ligand binds
- receptor activation –> phosphorylation
- phosphorylation of intracellular proteins
- activation of signalling pathways
- activation of target functions e.g. metabolism
what is phosphorylation
most common PTM - process of taking the gamma-phosphate from ATP and attaching it to a protein
MAJOR mechanism of protein activity regulation - on/off switch
- 30% of proteins are modified by P
preformed by kinases and is reversed by phosphatases
rapid process of phosphorylation and dephosphorylation
what does phosphorylation regulate
- Division
- Growth
- Metabolism
- Differentiation
- Motility
- organelle trafficking
- membrane transport
- muscle contraction
- Immunity
- learning and memory
which residues do protein kinases phosphorylate
serine, threonine and tyrosine
the kinase domain is highly variable or conserved?
conserved
what are the two main function groups of protein kinases
serine/threonine kinase
tyrosine kinase
protein kinase structure
small, beta sheet n terminal
larger, alpha helices c terminal
highly conserved ATP + substrate binding pocket interlobular cleft
how is the catalytic cleft impacted by the presence of different AA
the depth of the cleft is dependant on which aa is present:
* shallow (S/T)
* deep (Y)
what are the two main kinds of tyrosine kinase receptors
- True receptor tyrosine kinases (RTKs): intrinsic kinase within intracellular domain
- cytokine receptors (interleukins, G-CSF, GM-CSF, erythropoietin, others) have no kinase domain - linked to cytoplasmic tyrosine kinases
TRUE or FALSE: tyrosine phosphorylation is the most common form of phosphorylation
FALSE
less common (~0.05%) than serine phosphorylation (S, ~90%) or threonine phosphorylation (T, ~10%)
what are oncogenes
oncogenes cause cancer when mutated or over-expressed
what are proto-oncogenes
proto-oncogenes, regulate cell growth,
proliferation, survival, migration etc. (i.e. hallmarks of cancer) these give cancer cells their function but are not disease causing until they are mutated
how do tyrosine kinases cause cancer
Deregulation of TKs - on/off switch is
stuck in “on” → constitutive activation
of signals causes uncontrolled proliferation
how are receptor tyrosine kinases classified
by their extracellular domain
Receptor tyrosine kinase structure
- Extracellular domain - ligand binding
- TM domain - single α helix
- Intracellular tyrosine kinase (TK) domain
- Tyrosine (Y) residues - autophosphorylated
- Juxta-membrane and C-ter regulatory regions
what kind of ligands bind to RTKs
growth factors
cytokines
hormones
RTK ligand examples
- Insulin
- EGF (epidermal growth factor)
- VEGF (vascular endothelial growth factor)
- CSF-1 (macrophage colony stimulating factor)
receptor tyrosine kinase activation
- basal activity is very low without bound ligand
- Ligand addition triggers ligand-mediated dimerisation of RTKs
- Close apposition of 2 RTK molecules activates intrinsic kinase domains
- Kinase domains phosphorylate tyrosine residues within the RTK via:
1. Activation loop Y on the partner RTK, i.e. in trans
2. Regulatory Ys are recruited to remove kinase inhibition
3. Signalling Ys are activated to provide docking sites for downstream proteins
receptor CSF-1 tyrosine kinase activation example
- Ligand - CSF-1 (homodimer) binds two CSF-1R (RTK) monomers
- CSF-1R monomers dimerise - brings their kinase domains together
- Kinase domains trans-autophosphorylate Y807 on the other CSF-1R
- Activation loop Y phosphorylation → ↑↑ kinase activity
- Phosphorylation of additional Y residues on RTK - 7 different Ys in CSF-1R
CSF-1 receptor tyrosine kinase downstream signalling
- pY residues on RTK are docking sites for proteins containing pY
binding domains - Docked proteins are then phosphorylated on Y by RTK
- Activation of multiple downstream pathways
CSF-1 receptor tyrosine kinase deactivation
- Phosphatases → remove phosphates & turn signals off
- Ubiquitylation → tags RTKs leading to internalisation & degradation
what are non-receptor tyrosine kinases
TKs that associate with receptors that lack a tyrosine kinase domain
