28th Oct - PI3K

Question 1

What is the most abundant phospholipid in the membrane?

Answer 1

Phosphatidylcholine

Question 2

in the inositol ring in phosphatidylinositol which position is attached to the phosphate group?

Answer 2

1

Question 3

What is the function of PI3Ks?

Answer 3

They phosphorylate the 3’H position of the inositol ring in phophatidylinositol

Question 4

What are the 3 main classes of PI3K?

Answer 4

Classes I, II and III

Question 5

What is the preferred substrate of PI3K 1a?

Answer 5

PIP2

Question 6

Is PI3K class 1a dimeric?

Answer 6

Yes it’s heterodimeric - 1 catalytic subunit and 1 regulatory subunit

Question 7

Outline the basic recruitment of PI3K by a growth factor receptor

Answer 7

GF receptor autophosphorylates reecruiting the p85 regulatory domain of PI3K aswell as Grb2 and SOS which recruit Ras which binds to the p110 catalytic domain of PI3K

Question 8

List 5 downstream effectors of PI3K 1a

Answer 8

Rac and Rho
TEC
ARF6
PLC gamma
PKB
PDK1

Question 9

What is PKB?

Answer 9

A serine/threonine kinase

Question 10

What are the mammalian isoforms of PKB?

Answer 10

alpha, beta and gamma

Question 11

What are the 3 functionallly distinct regions of PKB?

Answer 11

PH domain
Kinase domain
Hydrophobic motif

Question 12

Are most targets inhibited or activated by PKB phosphorylation?

Answer 12

Inhibited

Question 13

How is PKB activated?

Answer 13

1. PIP3 brings PKB to the membrane through its PH domain.
2. PDK1 phosphorylates the catalytic subunit at T308 –> partial activation
3. mTORC1 phosphorylates the regulatory subunit at S473 –> full activation
   
   • -mTORC1 is partially activated in a positive feedback loop by partially activated PKB

Question 14

What are the targets of PKB?

Answer 14

(inhibits) Caspase 9
(inhibits) BAD
(inhibits) GSK3
(inhibits) FKHR-L1
(stimulates) mTORC1

Question 15

What are the two main enzymes involved in PI3K signalling termination?

Answer 15

SHIP and PTEN

Question 16

What is the function of the src-homology 2 containing phosphatases?

Answer 16

They convert PIP3–> PtdIns(3,4)P2 preventing PIP3 dependent proteins from docking to the membrane whilst still allowing PI3k recruitment to the membrane

Question 17

What is the function of the phosphatase and tensin homolog?

Answer 17

PTEN reduced PIP3 by converting it to PIP2, thus inhibiting PI3k

Question 18

What are the two classical PI3K inhibitors?

Answer 18

Wortmannin and LY294002

Question 19

Give an example of a second generation PI3K inhibitor?

Answer 19

Oncothyreon
PWT-458
SF1126
GDC-0941
XL147

Question 20

Why would it be beneficial to inhibit PI3K?

Answer 20

PI3K is often OE in cancer

Question 21

What is Perifosine?

Answer 21

A PKB inhibitor

Question 22

Support the claim that PI3K is linked to cancer

Answer 22

Class 1a PI3K catalytic subunit was isolated as the transforming gene in v-P3K (chicken sarcoma virus)

Amplication of 3q26 occurs in 40% of ovarian cancers

PI3K presence is crucial for v-src cell transformation