Physiology 3140A Lecture Notes - Lecture 19: Epidermal Growth Factor Receptor, Insulin Receptor, Ephrin
2 May 2018
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Cell Physiology Lecture 19
Receptor Tyrosine Kinases (RTKs)
Tyrosine Phosphorylation
- Growth factor signaling (and oncogenesis)
- Cell adhesion, spreading, migration and shape
- Cell cycle control
- Cell differentiation in development
- Gene regulation and transcription
- Endocytosis and exocytosis
- Stimulation of glucose uptake (Insulin)
o Insulin receptor gets phosphorylated, where GLUT2 goes up to PM
- Angiogenesis (formation of new blood vessels)
- Regulation of ion channels in nerve transmission
How many tyrosine kinases are there?
- The finding that v-Src and c-Src phosphorylate tyrosine residues provided the first evidence for
tyrosine kinase in 1979 (protein phosphorylation discovered in 1906)
o Src = sarcoma
o V-Src = viral sarcoma – they have been translated into the mammalian genome
o c-Src = cellular sarcoma
▪ Found in all of our cells
o Took over 70 years that phosphorylation is not just with threonine and serine
- Src phosphorylates tyrosine resiues
- By the end of 1980 four tyrosine kinases were known (Src, Abl, EGF receptor, Fps/Fes)
o EGF = epidermal growth factor
- By the end of 1990 over 50 tyrosine kinases had been identified in vertebrates and equal numbers of
tyrosine kinases and serine kinases were known, leading to the prediction that there might be
hundreds of tyrosine kinases in a vertebrate genome and a total of over a 1000 protein kinases
- The complete human genome sequence reported in 2001 revealed that there are 90 tyrosine kinases
out of a total of 518 protein kinases
o 30k genes in our genome, 500K-1M proteins that come from these genes
o Proteins are either glycosylated or phosphorylated – the proteins that carry out function in
the cell
- Tyrosine phosphorylation is 0.1% of all cellular phosphorylation, serine + threonine is 99.9%
o Took 70 years to figure out!
o EVEN THOUGH ITS 0.1% IT IS STILL IMPT
Structure:
- 99.9% are monomeric when inactive EXCEPT insulin
- Has transmembrane domain, extracellular domain, intracellular tyrosine kinase domain
Receptor Tyrosine Kinase (RTK) Families
- Transmembrane proteins with extracellular ligand binding domain
find more resources at oneclass.com
find more resources at oneclass.com
- Their carboxyl-terminal domains either have intrinsic enzymatic activity (tyrosine kinase activity) or
are directly associated with cytosolic enzymes (that are usually tyrosine kinase activity
- Each subunit of an RTK has one transmembrane spanning domain
o True for ALL, even the insulin receptors
- Most inactive RTKs are monomers
o Exception: Insulin receptor family where receptors are dimers (have an extra level of
control to maintain them inactive in absence of ligand)
o The reason all of the receptors except insulin is monomer, is because it is their off state
▪ They are alone + do not bind to another receptor = OFF STATE
- Ligand binding causes a conformational change, which brings two internal kinase domains together
to be transphosphorylated
o True for insulin too: insulin binds receptor, two domains can transphosphorylate
- Cell associated OR water soluble growth factor
o Do not cross the membrane!
o Have to bind a receptor at the cell surface to signal
- There is a low concentration ligand floating around in our body (bloodstream)
- Since the concentration is so low (10-9 – 10-12 M), they can only bind a few receptors
o Need signal amplification
▪ Signal = ligand
▪ Reception = receptor
▪ Transduction of the signal is the amplification process
o Ligand binds to receptors causing them to phosphorylate – cause sos to be activated, then
Ras, then MAP-kinase pathway
▪ One MAP-kinase phosphorylates a few downstream cascade members, etc.
find more resources at oneclass.com
find more resources at oneclass.com
RTK Ligands
- Receptor tyrosine kinases (RTKs) are activated by two types of ligands:
o I) Cell Surface Bound Ligands
o Ii) Secreted Growth Factors
<- Secreted Growth Factors
Cell Surface Bound Ligands:
- Ephrins which activate ephrin receptors
o BIGGEST FAMILY!
- Bidirectional signaling: ligand engagement of the receptor can result in
signaling from the target cell to the signaling cell
o Transmembrane ligand binds the receptor on the target cell causing
activation of the tyrosine kinase
o Ephrin associate with tyrosine kinase and sends a signal back
- The signal is not only sent to the target cell but is also sent back to the signaling
cell
- Regulate:
o Angiogenesis
o Axon guidance
o Synaptic plasticity
RTK Ligands Secreted Growth Factors
- Ligand can be dimeric OR monomeric
Dimeric Ligand:
- E.g., PDGF is a covalently linked dimer with two distinct receptor binding domains (sites)
o The ligand itself is a dimer!
- PDGF can dimerize two adjacent PDGF receptors to initiate intracellular signaling
o The kinase activity is stimulated by cross-phosphorylation
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Insulin receptor gets phosphorylated, where glut2 goes up to pm. Regulation of ion channels in nerve transmission. By the end of 1980 four tyrosine kinases were known (src, abl, egf receptor, fps/fes: egf = epidermal growth factor. Tyrosine phosphorylation is 0. 1% of all cellular phosphorylation, serine + threonine is 99. 9% the cell: took 70 years to figure out, even though its 0. 1% it is still impt. Has transmembrane domain, extracellular domain, intracellular tyrosine kinase domain. Their carboxyl-terminal domains either have intrinsic enzymatic activity (tyrosine kinase activity) or are directly associated with cytosolic enzymes (that are usually tyrosine kinase activity. Each subunit of an rtk has one transmembrane spanning domain: true for all, even the insulin receptors. Ligand binding causes a conformational change, which brings two internal kinase domains together to be transphosphorylated: true for insulin too: insulin binds receptor, two domains can transphosphorylate.
