Enzyme Linked Receptors

Question 1

RTK Structure

Answer 1

1 TMD
extracellular N (ligand bind)
intracellular C (enzyme activity)
ligand binds –> 2 kinase domains together
EXCEPTION: insulin receptor (pre-dimerized)

Question 2

RTK Ligands

Answer 2

Cell Surface Bound Ligands
Secreted Growth Factors (EGF, PDGF, IGF-1)

Question 3

Cell Surface Bound Ligands

Answer 3

ephrins –> ephrin receptors
bidirectional signalling
- signal sent to target and back to signalling cell
regulate – angiogenesis + axon guidance

Question 4

Secreted Growth Factors

Answer 4

Dimeric Ligand
- PDGF = dimerize 2 adjacent PDGF receptors

Monomeric Ligand
- EGF = conformational change - bump into another receptor and dimerize

Question 5

RTK Activation

Answer 5

Dimerize = cytosolic receptor tail contacts
Transactivation = autophosphorylation
Docking = Grb2 recognize specific phosphorylated tyrosine by SH2 domain, recruits SOS

Question 6

Activation of Ras and SH Domains

Answer 6

RTK has SH1 domain
Active RTK binds Grb2 via SH2 domain (recognize phosphotyrosine)
Grb2 binds Sos via SH3 domain (binds proline rich)
Sos activates Ras - via GEF

Question 7

Family of GTPases and Their Functions

Answer 7

Ras – cell proliferation, differentiation, apoptosis
Rho – cytoskeletal dynamics
Rab – membrane and protein traffic in endocytosis
Arf – vesicular trafficking
Ran – nucelocytoplasmic transport

Question 8

Activation of MAP Kinase Cascade

Answer 8

1) Ras activates MAP 3 Kinase (Raf)
2) Raf phosphorylates MAP 2 Kinase (MEK)
3) MEK phosphorylates MAP Kinase (MAPK)
4) MAPK phosphorylates cytoplasmic proteins or translocate to nucleus and phosphorylates TF

Question 9

Scaffolds and MAPK Signalling

Answer 9

Scaffold proteins hold 2 kinases together in complex
- different combination for different signalling pathways

Question 10

EGFR Signalling

Answer 10

1) MAPK (phosphorylate cytoplasmic proteins or TF)
2) Stat (bind, phosphorylate, dimerize, translocate)
3) PI3K (p85 = SH2 domain, p110 = phosphorylate PIP2)
- PIP3 brings PH domains
- phosphorylation of AKT –> mTOR –> cell survival

Question 11

Proto-oncogene vs Oncogene

Answer 11

normal gene + mutation –> oncogene
potential to cause normal cell to become cancerous

Question 12

EGFR Signalling in Cancer

Answer 12

EGFR over-expressed
- spontaneous kinase activity, hyperactive downstream
EGFR mutations
- trans-phosphorylation with no ligand
- respond hyper-well to EGF ligand

Question 13

EGFR Monoclonal Antibodies

Answer 13

FOLFOX-4 = standard chemotherapy
Cetuximab
- bind to extracellular region of EGFR
- antagonizes ligand bind –> EGFR internalize + degrade

Question 14

Insulin Receptor Signalling

Answer 14

• insulin receptor phosphorylate IRS
• IRS binds PI3K (PIP2 –> PIP3)
• PIP3 recruits PDK1 –phosphorylates –> Akt
• Akt phosphorylates AS160 (GLUT4 to PM)
• Akt inhibitory phosphorylates GSK3
• active GS (glucose –> glycogen)

Question 15

EGF vs Insulin Signalling

Answer 15

EGF
- prolonged signal time
- endosomal pH NOT displace ligand from receptor

Insulin
- short signal time
- endosomal pH displace ligand from receptor (recycled)