Lecture 15 - MAPK Pathways Flashcards
What leads to the activation of the MAPK signalling cascade?
Ras dependent pathway
Which part of the MAPK signalling cascade gets dephosphorylated and by what?
MAPK by phosphotases
What are the 3 mammalian MAPK pathways?
ERK, JNK and p38
Some components are shared between JNK and p38
What are the different signals that activates the ERK pathway?
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
What is MAPKKK in the ERK pathway?
Raf
What is MAPKK in the ERK pathway?
MEK
What is MAPK in the ERK pathway?
ERK
Where does ERK become phosphorylated?
ERK becomes phosphorylated on 2 residues, it is phosphorylated in the TEY motif, Threonine Glutamate Tyrosine, it is phosphorylated on the Threonine and Tyrosine
What does ERK target once activated?
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
What can deactivate the ERK
PTP-SL and DUSPs
What is this p38 pathway activated by?
Lots of different proteins upstream
By atleast 2 MAPKK and 4 MAPKKK
What are the different isoforms of p38 and where are they expressed?
Alpha and beta - most tissues
Gamma - skeletal muscle
Delta - pancreas, intestine, adrenal gland, kidney and heart
What are the MAPKKKs in the p38 pathway?
ASK, MEKK1-4, MLK2, DLK4
ASK = Apoptosis Stimulating Kinase
What are the MAPKKS in the p38 pathway?
MEK3/6
Where does p38 get phosphorylated?
Phosphorylation of tyrosine and threonine of TGY motif (threonine, glycine, tyrosine)P
What does phosphorylation of p38 induce?
Induces a conformational change in the protein enabling ATP and the substrate to bind
What deactivates the p38 pathway?
Protein phosphatase 1 and 2a deactivate the p38 pathway
How is duration of phosphorylation crucial in regulating cells fate?
Sustained - frequently associated with induction of apoptosis
Transient - growth factor induced survival (gets switched on and off quickly)
What do scaffold proteins do?
Bind to multiple components of the MAPK pathway and bring them into close proximity
Confer spatial and temporal regulation
What is Hog1?
The homologue of p38
Which two MAPK pathways in yeast are activated by the same upstream protein kinase?
Invasion and Pheromone response - Both use Ste11p
How does the cell differentiate between Invasion and Pheromone response in yeast?
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
What scaffold proteins are used in mammalian cells?
Kinase Suppressor of Ras (KSR)
What does Kinase Suppressor of Ras do?
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
What is MP1 and what does it do?
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
What does MP-1 require to increase its MAPK signalling?
Protein p14, which localises it to the endosomes
What are MP-1 and p14 essential for?
Epidermal Growth Factor dependent activation of ERK
What can we target as an anti fungal drug? and Why?
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
What is Tdh1?
A glyceraldehyde 3-phopshate dehydrogenase
It is activated in response to oxidative stress
What is Txp1?
2-cys peroxiredoxin
Required for Sty1 activation in response to H2O2
What is Sty1?
MAPK homologue of p38 in human cells
Stabilised aft1 mRNA leading to increased expression of antioxidant gene expression
What are Mak1/2/3?
Sensor kinases, they activate phosphotransfer proteins
Deletion of MAk2/3 - sensitive to salt stress
Deletion of Mak1 - resistant to salt stress and hydrogen peroxide
What activates the p38 pathway?
Oxidative stress, UV, Osmotic stress, Cytokines
