Growth factor signalling Part 2

Question 1

What do SH2 domains do?

Answer 1

• SH2 domains in proteins recognise and bind to phosphotyrosines
• This potentially allows multiple proteins to dock with the activated receptor: allows diversification of pathway and crosstalk

Question 2

How are Phospholipase C gamma (PLCγ) recruited to the receptor?

Answer 2

Via SH2 groups and activated by tyrosine phosphorylation by the receptor

Question 3

PLC gamma has the same downstream intracellular pathway as adrenaline activating alpha1 receptor, but ?

Answer 3

Instead of Galphaq activating PLC beta, PLCγ is recruited to activated receptor directly

Question 4

So what does PLCγ split PIP2 into ?

Answer 4

• DAG and IP3, and the IP3 leads to Ca2+ release from ER
• DAG and Ca2+ activate PKC
• PKC activates the Na+/H+ exchanger in membrane → alkalinisation of cell (stimulates DNA synthesis, cell division)

Question 5

The phosphorylated receptor interacts with the p85 regulatory subunit of?

Answer 5

PI-3-kinase via its SH2 domain leading to activation

Question 6

PI-3-kinase catalytic p110 domain phosphorylates?

Answer 6

PIP2 to PIP3

Question 7

Explain how PI-3-kinase phosphorylates PIP2 to PIP?

Answer 7

• The p110 catalytic domain of PI3K catalyses addition of phosphate to 3’ position on the sugar of PIP2 (already phosphates on 4 and 5 positions) to make PIP3
• Creates lipid docking sites in the membrane that are recognised by proteins with PH domains

Question 8

Explain the activation of Protein Kinase (PKB/Akt) ?

Answer 8

• PIP3 interacts with protein kinase B (PKB)/Akt via its PH domain and causes translocation to the membrane bringing it close to PDK1 which phosphorylates it on the activation loop
• A second phospholipid dependent protein kinase (PDK2) phosphorylates PKB on the C terminus resulting in full activation

Question 9

Explain the downstream effects of PKB (Akt) ?

Answer 9

• PKB phosphorylates GSK-3, inactivating it. GSK-3 phosphorylates glycogen synthase (turning it off) in exercise state, so when PKB is activated, it prevents GSK-3 from doing this. Downstream effects of PKB (Akt)
• PKB also promotes GLUT4 translocation, cAMP breakdown, and fat and protein synthesis
• Phosphorylates and switches on transcription factors and inhibits apoptosis

Question 10

You have made a constitutively active form of protein kinase B in the lab and are testing it in skeletal muscle. Which of the following effects would you expect to see?

Answer 10

1. An increase in glycogen synthesis
2. Decreased activation of protein kinase A (PKA)
3. A decrease in the amount of glycogen phosphorylase a

Question 11

Mutations in RTK pathways cause ?

Answer 11

Many tumours

Question 12

The most common oncogenic Ras mutations lead to ?

Answer 12

Defects in the intrinsic GTPase activation and thereby block Ras protein inactivation

Question 13

Dominant Ras mutations in the GTPase domain lead to?

Answer 13

Chronic stimulation of the MAP kinase signaling pathway, even in the absence of growth factors