Signalling Mechanisms in Growth and Division

Question 1

What transcription factor is stimulated by growth factor signalling and is vital to starting the cell cycle?

Answer 1

c-Myc

Question 2

Give an example of an anti-cancer drug that targets tyrosine kinase receptors.

Answer 2

Herceptin – inhibits the Her2 tyrosine kinase receptor (important in many tumours e.g. breast)

Question 3

Broadly speaking, how might Ras signalling be different in cancer?

Answer 3

Ras could be permanently switched on (in the GTP bound form), thus it constantly signals cell division

Question 4

What is the family that the ERK cascade belongs to called?

Answer 4

MAPK cascade (Mitogen-activated protein kinase cascade)

Question 5

What are the three kinases involved in the ERK cascade?

Answer 5

Raf
MEK
ERK

Question 6

What important gene is turned on by the kinase cascade?

Answer 6

c-Myc

Question 7

What type of kinase are cyclin-dependent kinases (Cdks)?

Answer 7

Serine-threonine kinases

Question 8

What conditions do Cdks require to become activated?

Answer 8

Binding to cyclin

Phosphorylation (activating phosphorylation and removal of inhibitory phosphorylation)

Question 9

What does the mitosis-promoting factor (MPF) consist of?

Answer 9

Cdk1 + cyclin B

Question 10

What are the requirements, in terms of phosphorylation, for MPF to become active?

Answer 10

Cdk activating kinase (CAK) adds an activating phosphate and Wee1 adds an inhibitory phosphate at the same time
Cdc25 then removes the inhibitory phosphate

Question 11

What activates MPF at the end of interphase?

Answer 11

Removal of the inhibitory phosphorylation by Cdc25

Question 12

Describe the positive feedback loop that is formed by MPF activation.

Answer 12

Removal of the inhibitory phosphorylation by Cdc25 produces active MPF, which then phosphorylates Cdc25 and increases its activity meaning that more MPF can be activated

Question 13

Which Cdk/cyclin is required for G1/S phase?

Answer 13

Cdk2-cyclin E

Question 14

Which Cdk/cyclin is required for S phase?

Answer 14

Cdk2-cyclin A

Question 15

How can the same Cdk be used for two different stages?

Answer 15

Cyclin binding alters the substrate specificity of Cdk

Also, different substrates are available at different stages of the cell cycle

Question 16

What is one of the most important transcription targets of c-Myc?

Answer 16

Cyclin D

Question 17

What is the first Cdk/cyclin complex that is formed when a cell goes from G0 to G1?

Answer 17

Cdk4/6-cyclin D

Question 18

This Cdk/cyclin complex then stimulates the expression of the next cyclin in the cell cycle. What properties does this system give to the cell cycle?

Answer 18

This gives the cell cycle direction and timing (because the Cdk-cyclin complexes must reach a certain concentration before they can trigger the next stage of the cycle)

Question 19

Give an example of a phosphorylation target of MPF that allows the cell cycle to progress.

Answer 19

Phosphorylation of nuclear lamins allows breakdown of the nuclear envelope

Question 20

What is start kinase and what is one of its most important targets?

Answer 20

Start kinase = Cdk2-cyclin E

Retinoblastoma

Question 21

Describe the role of retinoblastoma in the quiescent G0 state.

Answer 21

Retinoblastoma is unphosphorylated and binds to and sequesters a group of transcription factors called E2F

Question 22

Role of Cdk4/6-D

Answer 22

It multiply phosphorylates retinoblastoma – as it becomes phosphorylated it loses its affinity for E2F and releases E2F
This means that the E2F transcription factors can regulate gene expression and promote progression of the cell cycle

Question 23

What is one of the main targets of E2F?

Answer 23

Cyclin E

Question 24

What type of gene is retinoblastoma?

Answer 24

Tumour suppressor gene (it acts a break on the cell cycle)

Question 25

The initial release of E2F allows transcription of cyclin E leading to the formation of Cdk2-cyclin E. What effect does this complex have on retinoblastoma?

Answer 25

Cdk2-cyclin E further phosphorylates retinoblastoma so more E2F is released and the concentration of E2F increases

Question 26

What is the significance of the increasing concentration of E2F?

Answer 26

This means that E2F can now bind to targets with a lower affinity (e.g. cyclin A gene promoter isn’t activated until the E2F concentration is high enough)

Question 27

What are the two families of Cdk inhibitors?

Answer 27

NK4 | CIP/KIP

Question 28

During which phase do each of the NK4 and CIP/KIP act and how do they inhibit Cdk?

Answer 28

INK4 – G1 phase – it displaces cyclin D from the Cdk4/6-cyclin D complex CIP/KIP – S phase – it binds to the Cdk/cyclin complexes and inhibits them NOTE: these inhibitors need to be degraded at various stages for the cell cycle to progress

Question 29

State some common and important oncogenes.

Answer 29

``` EGFR/HER2 Ras Cyclin D1 B-Raf c-Myc ```

Question 30

State some important tumour suppressor genes.

Answer 30

Rb – inactivated in many cancers | p27KIP1–under-expression correlates with poor prognosis in many malignancies

Question 31

When are Cdks present

Answer 31

Present throughout cell cycle in proliferating cells to control the cycle

Question 32

Life of cyclins

Answer 32

Transiently expressed Levels regulated by levels of expression Are quickly synthesised then degraded

Question 33

What happens when growth factor binds to GFR and where does ligand normally come from

Answer 33

Dimerisation with another ligand bound receptor- this allows trans-autophosphorylation of the others tyrosine residue

Question 34

What type of receptor is GFR

Answer 34

Tyrosine kinsae

Question 35

What does phosphorylation of tyrosine residue of GFR allow

Answer 35

Docking of Grb2 protein via its SH2 region

Question 36

Describe structure of Grb2 protein

Answer 36

Two SH3 regions surrounding central SH2

Question 37

What does SH3 region of Grb2 bind to

Answer 37

Proline rich region of SOS

Question 38

What does SOS do

Answer 38

It is an exchange factor- exchanges GDP on RAS for GTP thus activating it

Question 39

RAS is deactivated by what

Answer 39

GTPase activating protein

Question 40

Role of Ras

Answer 40

To phosphorylate Raf

Question 41

Where are Ras and Raf found

Answer 41

They are membrane bound

Question 42

Phopsphorylating chain

Answer 42

Ras Raf MEK ERK

Question 43

What do Raf and Mek use to phosphorylate their next protein

Answer 43

ATP

Question 44

What happens to ERK after it is phosphorylated

Answer 44

Goes to nucleus and phosphorylates C-Myc protein