18th Nov - MAPK

Question 1

What is the activation motif of a MAPK?

Answer 1

Thr-X-Tyr which is dually phosphorylated to activate the MAPK

Question 2

Is there signal amplification in the MAPK cascade?

Answer 2

No - believed to be a 1:1:1 stoichiometry

Question 3

Outline ERK1/2 activation from an RTk

Answer 3

RTK pY –> Grb2 –> mSOS (GEF) –> Ras –> Raf1 (MAPKKK) –> MEK1/2 (MAPKK) –> ERK1/2 (MAPK)

Question 4

What are the different targets of Erk?

Answer 4

Cytoplasmic

• cPLA2 (phospholipase)
• P90RSK (ribosomal kinase)
• Ia (A-type K+ channels)

In the Nucleus:
-TFs - cFos, Elk-1, c-Myc

Question 5

What determines the cellular response elicited by ERK?

Answer 5

It’s pattern of activation i.e. magnitude and duration

Question 6

How can GPCRS be linked to MAPK signalling?

Answer 6

Linkage via conventional signalling pathways
Linkage via protein tyrosine phosphorylation dependent mechanisms
Linkage via GF shedding
Coupling through an arrestin signalling scaffold
GPCR regulation of MAPK

Question 7

How can GPCRS be linked to MAPK through conventional signalling pathways?

Answer 7

By involving traditional Galpha/betagamma pathways and their signalling intermediates e.g. Ca2+, PKC, DAG

Question 8

How can GPCRS be linked to MAPK signalling through protein tyrosine phosphorylation dependent mechanisms?

Answer 8

Inhibitors of both receptor tyrosine kinases and non-receptor tyrosine kinases often reduce of even abolish MAPK activation by GPCRs

A number of non-RTKs such as Src family kinases Pyk2 and FAK are intermediates in MAPK activation by some GPCRs

RTKs can be directly involved in transactivation by GPCRs

Question 9

How can GPCRs be linked to MAPK signalling through GF shedding?

Answer 9

GPCR activation can result in proteolytic cleavage of cell surface tethered GFs often via MMPs
The released GF can then act as an autocrine/paracrine RTK activator

Question 10

how can GPCRS regulate MAPK signalling?

Answer 10

There is a family of cAMP/DAG/Ca2+ regulated GEF and GAP proteins that regulate small GTPases which appear to be important in neuronal MAPK signalling

Question 11

What must happen for newly synthesized Ras to become fully active?

Answer 11

Lipidation on a C-terminal cysteine residue

Proteolytically cleaved to remove 3aa beyond the lipidated C-term cysteine

Question 12

What would be the clinical use for Ras inhibitors?

Answer 12

To treat AML

Question 13

What are the two currently used methods for Ras inhibition?

Answer 13

Farnesyl/geranylgeranyl transferase inhibitors e.g. RII5777

Ras-CAAX endoproteases e.g. Rce1

Question 14

What are the potential clinical applications for p38 inhibitors?

Answer 14

Potential to treat COPD and Chron’s

Question 15

What is the potential clinical application for MEK1/2 inhibitors?

Answer 15

Cancer treatment

Question 16

Give an example of a MEK1/2 inhibitor being tested for cancer treatment

Answer 16

PD184352 - showed anti-tumour activity but had serious adverse side effects

Question 17

Name a Raf-1 inhibitor being used clinically and its application

Answer 17

Sorafenib to treat renal cell carcinoma

Question 18

Name a BRAF inhibitor being used clinically and its clinical application

Answer 18

Vemurafenib specifically targets B-RafV600E in melanoma

Question 19

Outline the JNK pathway

Answer 19

Cellular Stress, Cytokinesis and other stimuli –> MEKK1-4, MLKs, ASK1 (MAPKKK) –> MKK 4/7 (MAPKK) –> JNK1/2/3 (MAPK) –> Apoptosis, Inflammation and Differentiation

Question 20

Outline the p38 pathway

Answer 20

Cellular Stress, Cytokineses and other stimuli –> MEKK2/3, MLK3, ASK1 (MAPKKK) –> MKK3/6 (MAPKK)–> p38 alpha, beta, gamma or delta (MAPK)–> Apoptosis, Inflammation and differentiation

Question 21

Which is the most commonly mutated isoform of Ras in cancer?

Answer 21

K-Ras

Question 22

What do oncogenic Ras mutations normally cause?

Answer 22

Stable GTP binding in Ras