Lecture 15 - MAPK Pathways

Question 1

What leads to the activation of the MAPK signalling cascade?

Answer 1

Ras dependent pathway

Question 2

Which part of the MAPK signalling cascade gets dephosphorylated and by what?

Answer 2

MAPK by phosphotases

Question 3

What are the 3 mammalian MAPK pathways?

Answer 3

ERK, JNK and p38

Some components are shared between JNK and p38

Question 4

What are the different signals that activates the ERK pathway?

Answer 4

EGF = Epidermal Growth Factor
PGDF = Platelet Derived Growth Factor
NGF = Nerve Growth Factor
Each signal has its own specific receptor
Each signal activates Grb2, SH3 in Grb2 binds to SOS which causes Ras to release GDP and bind GTP which then goes to activate the MAPK pathway

Question 5

What is MAPKKK in the ERK pathway?

Answer 5

Raf

Question 6

What is MAPKK in the ERK pathway?

Answer 6

MEK

Question 7

What is MAPK in the ERK pathway?

Answer 7

ERK

Question 8

Where does ERK become phosphorylated?

Answer 8

ERK becomes phosphorylated on 2 residues, it is phosphorylated in the TEY motif, Threonine Glutamate Tyrosine, it is phosphorylated on the Threonine and Tyrosine

Question 9

What does ERK target once activated?

Answer 9

It has cytoplasmic and nuclear targets
In the cytoplasm it can activate PLA2 which regulates the production of the fatty acid arachidonic acid
In the nucleus it can activate the transcription factors c-Myc and c-Fos

Question 10

What can deactivate the ERK

Answer 10

PTP-SL and DUSPs

Question 11

What is this p38 pathway activated by?

Answer 11

Lots of different proteins upstream

By atleast 2 MAPKK and 4 MAPKKK

Question 12

What are the different isoforms of p38 and where are they expressed?

Answer 12

Alpha and beta - most tissues
Gamma - skeletal muscle
Delta - pancreas, intestine, adrenal gland, kidney and heart

Question 13

What are the MAPKKKs in the p38 pathway?

Answer 13

ASK, MEKK1-4, MLK2, DLK4

ASK = Apoptosis Stimulating Kinase

Question 14

What are the MAPKKS in the p38 pathway?

Answer 14

MEK3/6

Question 15

Where does p38 get phosphorylated?

Answer 15

Phosphorylation of tyrosine and threonine of TGY motif (threonine, glycine, tyrosine)P

Question 16

What does phosphorylation of p38 induce?

Answer 16

Induces a conformational change in the protein enabling ATP and the substrate to bind

Question 17

What deactivates the p38 pathway?

Answer 17

Protein phosphatase 1 and 2a deactivate the p38 pathway

Question 18

How is duration of phosphorylation crucial in regulating cells fate?

Answer 18

Sustained - frequently associated with induction of apoptosis
Transient - growth factor induced survival (gets switched on and off quickly)

Question 19

What do scaffold proteins do?

Answer 19

Bind to multiple components of the MAPK pathway and bring them into close proximity
Confer spatial and temporal regulation

Question 20

What is Hog1?

Answer 20

The homologue of p38

Question 21

Which two MAPK pathways in yeast are activated by the same upstream protein kinase?

Answer 21

Invasion and Pheromone response - Both use Ste11p

Question 22

How does the cell differentiate between Invasion and Pheromone response in yeast?

Answer 22

By using the scaffold protein Ste5
If there is an alpha factor present (pheromone) then Ste5 is present and binds to Fus3, this ensures that the pheromone response is activated instead of the invasion response which use Kss1

Question 23

What scaffold proteins are used in mammalian cells?

Answer 23

Kinase Suppressor of Ras (KSR)

Question 24

What does Kinase Suppressor of Ras do?

Answer 24

Binds to Raf, MEK1/2 and ERK1/2
Also interacts with beta-gamma of G protein and heat shock proteins 70 and 90
MEK is always associated with KSR but ERK associates transiently in response to a stimulus
Maximal levels of KSR are required for a maximal response of ERK

Question 25

What is MP1 and what does it do?

Answer 25

MEK Partner 1
Scaffold protein used in the ERK MAPK pathway
It promotes association of MEK with ERK, enhancing ERK phosphorylation
MP-1 binds MEK all the time, but ERK transiently

Question 26

What does MP-1 require to increase its MAPK signalling?

Answer 26

Protein p14, which localises it to the endosomes

Question 27

What are MP-1 and p14 essential for?

Answer 27

Epidermal Growth Factor dependent activation of ERK

Question 28

What can we target as an anti fungal drug? and Why?

Answer 28

Two component system regulation in MAPKK system in yeast Hog1 which prevent Hog1 expression under stress
Using Histidine protein kinase and phosphotranfer protein, regulation of the system via phosphorylation
Can do this as this isn’t present in p38 in mammalian cells

Question 29

What is Tdh1?

Answer 29

A glyceraldehyde 3-phopshate dehydrogenase

It is activated in response to oxidative stress

Question 30

What is Txp1?

Answer 30

2-cys peroxiredoxin

Required for Sty1 activation in response to H2O2

Question 31

What is Sty1?

Answer 31

MAPK homologue of p38 in human cells

Stabilised aft1 mRNA leading to increased expression of antioxidant gene expression

Question 32

What are Mak1/2/3?

Answer 32

Sensor kinases, they activate phosphotransfer proteins
Deletion of MAk2/3 - sensitive to salt stress
Deletion of Mak1 - resistant to salt stress and hydrogen peroxide

Question 33

What activates the p38 pathway?

Answer 33

Oxidative stress, UV, Osmotic stress, Cytokines