Receptor Tyrosine Kinases

Question 1

RTK Structure

Answer 1

Extracellular – ligand-binding
Transmembrane – α-helix
Cytoplasmic – tyrosine kinase activity (phosphorylate tyrosine aa)

• needs adapter proteins
• Ras-GTP —> signals downstream kinases

Question 2

Activate RTKs

Answer 2

• bind ligand
• auto-phosphorylation of cytoplasmic domain
• phosphorylate additional tyrosine residues for SH2 docking

Question 3

Adapter Proteins

Answer 3

• domains that recognize specific sequences

- SH2

Question 4

Discover First Oncogene

Answer 4

• inject cell free extract from chicken tumor into healthy chicken —> developed tumors
• gene in virus encodes tyrosine kinase
• normal = cellular src (inhibitory phosphorylation)
• viral = viral src (missing terminus – always on)

Question 5

Ras-GTP Switch Protein

Answer 5

• lipid anchored protein

Inactive (GDP) –> GEF activates Ras, removes GDP
Active (GTP) –> GAP inactivates Ras, removes GTP

Cancer — can’t bind GAP, no GTP removal = always on

Question 6

FGF-Induced Ras Activation Step 1

Answer 6

• Ras inactive
• FGF binds to FGF receptor
• autophosphorylation of tyrosine residues

Question 7

FGF-Induced Ras Activation Step 2

Answer 7

• GRB2 has SH2 domain – binds to phosphotyrosine

- GRB2 has 2 SH3 domains – bind to proline in SOS (GEF)

Question 8

FGF-Induced Ras Activation Step 3

Answer 8

• Sos remove GDP from Ras
• GTP binds and activates Ras
• Ras activates downstream kinase cascade

Question 9

Ras/Map Kinase Pathway

Answer 9

• Ras activated by GTP –> binds + activate Raf
• GTP hydrolysis = Ras dissociate from Raf
• Raf activates MEK activates MAPK activates TF’s

Question 10

Oncogenic Receptors

Answer 10

• mutation in Her2 receptor = activate w/o ligand

- deletion in EGF receptor = always active cytoplasmic kinase domain w/o ligands

Question 11

Human Epidermal Growth Factor Receptors (EGF)

Answer 11

• 4 RTKs = Her1 –> Her4

- Her2 does not bind ligands (gene amplification + targeted by monoclonal antibodies)

Question 12

Herceptin Mode of Action

Answer 12

Block cleavage of extracellular domain of Her2
- no activation of signal transduction

Inhibit dimerization
- reduce Her2 signalling

Recruit immune cells
- destroy tumor cell

Endocytosis of Her2
- less Her2 available to trigger cell growth

Question 13

Controlled Destruction of Cells

Answer 13

Necrosis = rupture + release (inflammation)

Apoptosis = phagocytosis of apoptotic body

Question 14

Block Apoptosis in C.elegans

Answer 14

• dead cells detected by DIC microscopy
• ced-3 and ced-4 —> (promote apoptosis)
• ced-9 –> (suppress apoptosis)

Question 15

Caspases Function

Answer 15

• Fragment DNA, Nucleus, Golgi

- cytoskeletal disruption

Question 16

Initiator vs Effector Caspases

Answer 16

Initiator

• activated by dimerization
• cleave inanctive effector caspases –> to activate

Effector

• cleave protein substrates within cell
• trigger apoptotic process

Question 17

Apoptosome

Answer 17

• Apaf-1 + Cytochrome C + Caspase-9
• bind cytochrome C = Apaf-1 forms disk heptamer
• recruits Caspase-9
• activates initiator caspase

Question 18

Bcl-2 Family Proteins

Answer 18

• inhibits apoptosis

Pro-survival = Bcl-2 homology + TM domain (Bcl-2)
Pro-apoptotic = lack BH4 domain 

BH3 only proteins = counter effects of Bcl-2

Question 19

Evolutionary Conservation of Apoptosis

Answer 19

• Bax/Bac form pores = release cytochrome C
• inhibited by Bcl-2
• BH3 proteins inhibit Bcl-2 (cytochrome C released)

Question 20

Trophic Factor Withdrawal

Answer 20

Cell Survive

• growth factor or cytokine = phosphorylation of RTKs
• phosphorylation of Bad (interact with 14-3-3 inhibitor)

Cell Death

• no growth factor = less phosphorylation of RTKs + Bad
• inhibition of Bcl-2 = Bak releases cytochrome C
• forms apoptosome to activate effector caspase

Question 21

Death Signal

Answer 21

• death signals from other cells bind to receptor
• activates initiator caspase 8
• cleavage of BID –> t-BID inhibits Bcl-2 –> release cytochrome C = cell death
• activates effectors proteins directly = cell death

Question 22

Unregulated Apoptosis

Answer 22

Too Little = increase cell survival, cancer, weak immunity

Too Much = neurodegenerative disorders, aging, autoimmune diseases