Receptor tyrosine kinases

Question 1

EGFR domains (4)

Answer 1

ligand binding domain at N terminus, transmembrane domain, tyrosine kinase domain at C terminus, and ATP binding pocket

Question 2

Modes of EGFR dimerization

Answer 2

ligand-ligand interaction, receptor-receptor interaction (for proximity or conformational change), 3rd molecule involvement (ie heparin)

Question 3

Why does dimerization matter in EGFR signaling?

Answer 3

Because dimerization brings kinase domains into proximity, which allows for trans-phosphorylation (ie they phosphorylate each other)

Question 4

what are some examples of EGFR ligands?

Answer 4

growth factors - EGF, NGF, VEGF

Question 5

what cellular responses are evokes by receptor tyrosine kinase activation?

Answer 5

growth, proliferation, survival, migration, metabolic changes

Question 6

4 major pathways through which EGFR can signal?

Answer 6

1. JAK/STAT
2. Small GTPases (RAS) and MAP Kinase
3. PI-3 kinase
4. Phospholipase C - gamma

Question 7

Receptor tyrosine phosphatase function

Answer 7

dephosphorylate targets

Question 8

what is receptor tyr phosphatase inhibited by?

Answer 8

ligand binding and dimerization (opposite of RTKs)

Question 9

T/F. Receptor tyrosine phosphatases are specific to their targets

Answer 9

False, they can have many targets in the cell

Question 10

What defines whether cells proliferate or differentiate within the same ERK signaling pathway?

Answer 10

Either transient stimulation (EGF), which leads to proliferation, or sustained stimulation (NGF), which leads to differentiation

Question 11

How are RTKs implicated in cancer, and how are they targeted in therapies?

Answer 11

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

Question 12

JAK function and activation

Answer 12

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.

Question 13

Three targets of JAK

Answer 13

1. The other JAK (trans-phosphorylation again), making the JAKs fully active.
2. The C terminal tail of the RTK (this is an additional site, RTK still trans-P as well).
3. STAT

Question 14

When is STAT recruited

Answer 14

after the RTK is phosphorylated by JAK, its SH2 domain binds the phosphorylated tyrosine (as all SH2 domains do).

Question 15

What happens when STAT is recruited

Answer 15

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

Question 16

Ras GTPase activity and activation

Answer 16

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)

Question 17

Does RAS need cofactors to undergo GTP hydrolysis?

Answer 17

RAS has intrinsic ability to undergo GTP hydrolysis to GDP, but a GAP can accelerate the
process.

Question 18

What role does Grb2 play in EGFR signaling?

Answer 18

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.

Question 19

T/F. RTK can signal through the MAP kinase pathway

Answer 19

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).

Question 20

Phospholipase C -gamma machanism of activation

Answer 20

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.

Question 21

PLC-gamma action

Answer 21

cleaves PIP2 to DAG and IP3, leads to PKC activation