Receptor tyrosine kinases Flashcards
EGFR domains (4)
ligand binding domain at N terminus, transmembrane domain, tyrosine kinase domain at C terminus, and ATP binding pocket
Modes of EGFR dimerization
ligand-ligand interaction, receptor-receptor interaction (for proximity or conformational change), 3rd molecule involvement (ie heparin)
Why does dimerization matter in EGFR signaling?
Because dimerization brings kinase domains into proximity, which allows for trans-phosphorylation (ie they phosphorylate each other)
what are some examples of EGFR ligands?
growth factors - EGF, NGF, VEGF
what cellular responses are evokes by receptor tyrosine kinase activation?
growth, proliferation, survival, migration, metabolic changes
4 major pathways through which EGFR can signal?
- JAK/STAT
- Small GTPases (RAS) and MAP Kinase
- PI-3 kinase
- Phospholipase C - gamma
Receptor tyrosine phosphatase function
dephosphorylate targets
what is receptor tyr phosphatase inhibited by?
ligand binding and dimerization (opposite of RTKs)
T/F. Receptor tyrosine phosphatases are specific to their targets
False, they can have many targets in the cell
What defines whether cells proliferate or differentiate within the same ERK signaling pathway?
Either transient stimulation (EGF), which leads to proliferation, or sustained stimulation (NGF), which leads to differentiation
How are RTKs implicated in cancer, and how are they targeted in therapies?
They are often oncogenic, as their constitutive activity can lead to increased cell survival, proliferation and growth signaling. Drugs bind to ATP binding pocket of mutated EGFR
JAK function and activation
JAK has a tyrosine kinase domain and pseudokinase domain that is autoinhibitory.
When RTKs dimerize, JAK is able to bind the RTK, causing conformational change that
moves the autoinhibitory pseudokinase domain and releases the active kinase domain.
Three targets of JAK
- The other JAK (trans-phosphorylation again), making the JAKs fully active.
- The C terminal tail of the RTK (this is an additional site, RTK still trans-P as well).
- STAT
When is STAT recruited
after the RTK is phosphorylated by JAK, its SH2 domain binds the phosphorylated tyrosine (as all SH2 domains do).
What happens when STAT is recruited
JAK can phosphorylate its final target, STATs release. They are now free to dimerize via SH2 domains, then translocate to nucleus and act as a transcription factor
Ras GTPase activity and activation
RAS-GDP is inactive; GEF helps release GDP, then RAS immediately picks up GTP and is
active.
RAS-GTP can go on to activate targets (not by phosphorylation). For example, RAS
activates a MAPKKK, Raf, by binding it with high affinity and activating it. (See Lecture 7)
Does RAS need cofactors to undergo GTP hydrolysis?
RAS has intrinsic ability to undergo GTP hydrolysis to GDP, but a GAP can accelerate the
process.
What role does Grb2 play in EGFR signaling?
EGFR can signal through small GTPases like RAS via Grb2, an adapter protein that binds
RTK and recruits SOS. SOS is a RAS-GEF.
Grb2 has SH2 domain (binds phosphorylated Tyr on RTK) and SH3 domain that binds SOS.
T/F. RTK can signal through the MAP kinase pathway
True. RTK can thus signal through the MAP kinase pathway. It contains a SH2 domain (binds to
phosphorylated tyrosines on RTK) and SH3 domains (bind to RasGEF).
Phospholipase C -gamma machanism of activation
PLCγ also contains two SH2 domains, only one binds phosphorylated Tyr on EGFR.
PLCγ is autoinhibited until it is recruited to RTK; then conformational change and now RTK
can phosphorylate it and fully activate it.
The SH2 domain on PLCγ now recognizes this newly phosphorylated Tyr on itself, now
another conformational change to fully open and active form.
PLC-gamma action
cleaves PIP2 to DAG and IP3, leads to PKC activation
