growth factor signal transduction

Question 1

what is the most common growth factor receptor

Answer 1

RTK, receptor tyrosine kinase

Question 2

describe the structure of RTKs

Answer 2

-all RTKs have similar molecular architecture
-extracellular ligand binding domain, a single transmembrane helix and a cytoplasmic region containing protein kinase domain and C terminal and juxta membrane regulatory regions
-diagram in notes

Question 3

examples of RTKs

Answer 3

epithelial growth factor receptors (EGFR), vascular endothelial GFRs, fibroblast GFRs

Question 4

how do RTKs function

Answer 4

forms homo/heterodimers

Question 5

what does ligand binding in RTKs cause

Answer 5

-causes conformational changes or dimerise or both

Question 6

describe signal transductions from RTKs

Answer 6

-phosphorylated tyrosine residues act as docking sites for recruitment of intracellular adapter proteins to initiate downstream signal transduction
-signal amplification occurs

-activated RTK autophosphorylates and phosphorylate neighbouring proteins on tyrosine

Question 7

targeting RTKs with monoclonal antibody advantages and disadvantages

Answer 7

A-selective, evidence of efficacy

D-long term efficacy issues, stability, side effects (hypertension, proteinuria), expensive

Question 8

targeting RTKs with RTK inhibitors advantages and disadvantages

Answer 8

A-cheaper, evidence of efficacy

D-selectivity issues, therapeutic resistance, side effects

Question 9

what are kinases, where can it occur and how can it be removed

Answer 9

enzymes that transfer a phosphate group from ATP to a target

-can occur at Ser/Thr residues or tyrosine

-phosphorylation can be removed by protein phosphatases

Question 10

2 key pathways in signal transduction from EGF receptor

Answer 10

1. RAS/RAF/MAPK (ERK) signalling pathway-required for activation of MYC oncogene and cell proliferation
2. PI3K/AKT/mTOR signalling pathway-directs cell metabolism towards cell growth and proliferation

Question 11

how can RTK mutations contribute to cancer development

Answer 11

amplification
eg. EGFR in glioblastoma, HER2 overexpressed in most breast cancers

ectodomain mutations
receptor can dimerise/activate without ligand eg. vERBB in glioblastoma

activating point mutations in kinase domain
eg. L858R in EGFR in non small cell lung carcinoma

Question 12

how can EGFR activate RAS

Answer 12

by binding of ligand causing receptor dimerisation, kinase activation an phosphorylation of cytosolic receptor tyrosine resides

Question 13

what leads to growth signalling

Answer 13

PI3K activation

Question 14

growth factors like EGF bind to RTKs and trigger a signalling cascade, what two major pathways are activated and what do the two pathways promote

Answer 14

PI3K-Akt pathway

RAS pathway

promtoes production and activation of cyclin D1 and stimulates cells to enter cell cycle

Question 15

what does cyclin D1 do

Answer 15

pushes cell to next stage in cell cycle (G1 to S phase)

Question 16

what does AKt activation lead to

Answer 16

stops inhibition of kinases that block cyclin D1 translation so more cyclin D1 is made

Question 17

where and what does ERK do

Answer 17

works in nucleus to phosphorylate transcription factors to activate them

the TFs turn on cyclin D1 gene to increase the transcription

Question 18

what are the 4 members of EGF receptor family

Answer 18

EGFR (HER1) - only one that directly binds with EGF

HER2 (ERBB2) - doesnt bind to ligands, acts as partner, forms heterodimers

HER3 (ERBB3) - has impaired kinase activity

HER4 (ERBB4) - binds ligands, signals

Question 19

what EGF is often overexpressed in breast cancer

Answer 19

HER2

Question 20

how does EGFR activation cause signal transduction pathways

Answer 20

autophosphorylation

Question 21

what 2 main signal transduction pathways are activated when EGFR activation causes autophosphorylation

Answer 21

ERK and mTOR

Question 22

what happens when EGFR is activated

Answer 22

ligand binds to EGFR causing it to dimerise and becomes autophosphorylated (phosphate added to itself), activates 2 major pathways that tell cell to grow/divide

Question 23

what does the recruitment of an adaptor protein to phosphorylated EGFR induce

Answer 23

exchange of GDP to GTP on RAS G-protein, which activates RAF kinase which activates MEK kinase which phosphorylates and activates ERK MAP kinase which regulates cell cycle

RAS-RAF-MEK-ERK pathway

ERK then enters nucleus and turns on genes like cyclin D1 to push cell through cell cycle

Question 24

describe the PI3K-AKT-mTOR pathway

Answer 24

PI3k activated by phosphorylated EGFR, PI3K makes PIP3 which activates PDK1, PDK1 and mTORC2 activate AKT, AKT activates mTORC1 which promotes cell growth and survival by increasing protein synthesis and metabolism

Question 25

what does RAS-RAF-MEK-ERK pathway do

Answer 25

drive cell division

Question 26

what does PI3K-AKT-mTOR pathway do and how

Answer 26

drive cell growth and survival by increasing protein synthesis and metabolism

Question 27

why are growth factor signals widely targeted in cancer and a problem with them

Answer 27

theyre overactivated in cancer cells resistance arises, severe side effects

Question 28

common mutations in signal transduction components in PI3K pathway:

Answer 28

PTEN=tumour suppressor PIK3CA (catalytic subunit of PI3K)=oncogene PIKR1 (regulatory subunit of PI3K)=oncogene AKT1 and AKT2=oncogene

Question 29

oncogenic mutations in MAP kinase pathway:

Answer 29

EGFR, ERBB2, ERBB3 (EGFR family) FGFR1, FGFR2 (fibroblast gfr) KRAS, NRAS, RAS BRAF

Question 30

drugs ending in -mab are ... drugs ending in -ib are...

Answer 30

-mab=monoclonal antibodies -ib=kinase inhibitors

Question 31

inhibitors of signalling for cancer in clinics

Answer 31

AKT inhibitors, PI3K inhibitors, antibodies that stop activation, KRAS inhibitor, BRAF inhibitor, MEK inhibitors

Question 32

what are melanomas treated with

Answer 32

vemurafenib

Question 33

what gene is commonly mutated in melanomas

Answer 33

BRAF

Question 34

describe RAS and B-RAF mutations in melanomas compared to healthy cells

Answer 34

in healthy cells=GTP bound RAS activates Raf kinase by dimerisation RAS mutation=makes this activation occur independently of receptor stimulation B-Raf mutation=non valine 600 mutation/dimerises even with no RAS, B-raf doesnt need to dimerise to activate

Question 35

why 50% of patients treated with vemurafenib relapse within 6 months?

Answer 35

-vemurafenib activates ERK signalling through promoting dimerisation of B-raf by paradoxically activating c-Raf -design and use of pan-Raf inhibitors may overcome this or use inhibitors that act on B-Raf and dont promote dimerisation

Question 36

what is primary resistance

Answer 36

intrinsic, drug will have no clinical benefit, try to avoid by better patient stratification (eg. look at mutation or which protein expresses it)

Question 37

what is secondary resistance

Answer 37

acquired during treatment, drug delays cancer progress initially but then relapses, often due to additional mutations

Question 38

resistance mech for signal transduction inhibitors either...

Answer 38

-bypass the block -activate growth signalling downstream

Question 39

BRAFV600 mutation tumours treated with vemurafenib, 3 common resistance mechanisms:

Answer 39

1. Upregulation of MEK activity (eg C-Raf expression, B-Raf amplification, Growth Factor receptor over expression, N-Raf activating mutations) 1. Upregulation of the PI3K/AKT/mTOR pathway (eg. PTEN inactivation, PI3K, AKT activation) 1. Activation of CDK4/cyclin D1 complex directly – bypasses both signal transduction pathways