Phospholipids

Question 1

What cleaves PIP2, and what are the products?

Answer 1

Phospholipase C cleaves PIP2 into DAG and IP3

Question 2

Give examples of roles for different PLC isoforms

Answer 2

PLC delta activated by calcium 100x more than isoforms beta or gamma.
PLC beta most commonly associated with GPCR signalling and have differential tissue distribution between subtypes. They are GAPs for G alpha q and 11
PLC gamma associated with RTK signalling eg. EGF and NRTK signalling eg src

Question 3

How can PLC activity be monitored?

Answer 3

Can measure downstream responses - changes in Ca.
Can measure accumulation of radiolabelled IP3 against Li block of inositol mono phase activity.
Can use fluorescence studies by tagging IP3 with GFP to have single cell imaging of PLC activity

Question 4

Why is the activity of PLC important?

Answer 4

PLC regulates so much
Alteration of anything it regulates could underlying disease or could provide pharmacological targets to treat the disease.
Drug targets;
-GPCRs most common drug target
-PLC coupled GPCRs extremely prevalent
-Drug mediated regulation of G alpha q coupled receptors central to many disease therapeutics
-Targets mainly PLC beta activation
>Pathophysiological roles of other isoforms less clear, so may prove important drug targets.

Question 5

What are common phospholipids in humans?

Answer 5

Phosphatidylcholine - 50% of membrane lipids
Phosphatidylinositol - 5-10%
Phosphatidylserine - 2-10%
Phosphatidylethanolamine - 15-35%

Question 6

At what positions is PIP2 phosphorylated?

Answer 6

4, 5.

Question 7

At which position is PIP2 bound to its non-polar chain group?

Answer 7

Position 1

Question 8

In what positions can phosphatidylinositol be phosphorylated?

Answer 8

3, 4, 5

Question 9

What do PI3Ks do?

Answer 9

Phosphorylate the 3’ position of the inositol ring of phosphatidylinositol.

Question 10

Which is the preferred substrate of PI3K?

Answer 10

PtdIns(4,5)P2, aka PIP2.

This is phosphorylated to PI(3, 4, 5)P3 aka PIP3

Question 11

Give examples of signalling proteins which PIP3 can act as an anchor for

Answer 11

Pleckstrin homology domains are required in all these proteins. This domain binds to PIP3, and can affect cell growth, survival and movement.
Examples; RAC and Rho GTPases; Tyrosine kinases; PKB aka Akt; many more.

Question 12

What is Akt?

Answer 12

A serine/threonine kinase belonging to the AGB superfamily, conserved across species (so must be really important for life in general)

Question 13

Give some examples of PKB targets and effects

Answer 13

Promotes cell survival by inhibiting apoptosis via caspase 9 inhibition and Bcl-2 and BAD inhibition
Inhibits GSK3, therefore promoting pathways GSK3 normally inhibits such as proliferation and migration

Question 14

How is PI3K signalling terminated?

Answer 14

Degradation of PIP3 by phosphatases eg SHIP (Src-homology 2-containing phosphatases) 1 and 2. 1 only in haemopoietic cells. And PTEN.