Lecture 3 & 4

Question 1

Which genes can mutations occur in?

Answer 1

1. Oncogenes - eg., protooncogenes
2. Tumour suppressors - eg., p53
3. DNA repair

Question 2

What were the original “Hallmarks of cancer” by Hanahan and Weinberg?

Answer 2

• self-sufficiency in growth signals
• insensitivity to antigrowth signals
• evades apoptosis
• limitless reproductive potential
• sustained angiogenesis
• tissue invasion and metastases

Question 3

What were the revised Hallmarks of Cancer?

Answer 3

• avoiding immune destruction
• tumour promoting inflammation (lack of resolution)
• genome instability and mutation
• deregulation of cellular energetics

Question 4

What induces growth signals in a cell?

Answer 4

Various growth factors, a change in the metabolism that allows the cell to perform DNA synthesis or an increase in glucose/mitochondrial activity

Question 5

What are the four mechanisms in DNA synthesis?

Answer 5

1. Signalling molecules: cytokines and growth factors (IL-3 or EGF)
2. Signal receptors and intracellular receptors: cytokine receptor/ tyrosine kinases/ intracellular receptors
3. Intracellular transducers
4. Transcription factors and cell cycle regulators

Question 6

What are the five different components in a cell that tells it to enter cell cycle or enter a quiescent state?

Answer 6

• growth factor receptors
• monitors of genome integrity
• TGF-beta receptors
• integrins
• monitors of cell metabolism

Question 7

What are the three stages a cell can enter when planning to divide?

Answer 7

• G0 (G not) or quiescent state
• active cell cycle which leads to G1 -> S -> G2 -> M
• programming of cell cycle phases then into any of the four phases

Question 8

What is one example of monitoring genome integrity?

Answer 8

The length of telomeres is important. A short telomere indicates the age of the cell and is not stable genomically.

Question 9

How do integrins play a role in the cell cycle?

Answer 9

They will recognize if there are cells beside it (contact inhibition) and prevent the cell from entering G1.

Question 10

What is the quiescent stage?

Answer 10

G0 (G zero) stage where a cell is neither dividing nor preparing to divide.

Question 11

What is the G1 entry controlled by?

Answer 11

Cyclin D1

Question 12

How can the control of cyclin D1 be partially explained by the effects of mitogens?

Answer 12

They modulate the transcription of the cyclin D1 gene. Different mitogens diverge at D1.

Question 13

What is a mitogen?

Answer 13

A chemical substance that encourages a cell to commence cell division, triggering mitosis, usually a protein.

Question 14

How do cytokines effect D1 levels?

Answer 14

A cytokine binds to a cytokine receptor which activates Jak, which activates STAT, thus resulting in the activation of cyclin D1.

Question 15

How do growth factors effect D1 levels?

Answer 15

A growth factor binds to a tyrosine kinase receptor (RTKs) -> Grb2 -> Sos -> Ras -> Raf -> Erk -> p90Rsk -> Elk-1/SRF -> Fos -> AP-1 -> D1

Question 16

What are the sources of extracellular signal that induce cyclin D1 and D2 expression?

Answer 16

Estrogen receptor - AP-1 TF -> D1
HER2/Neu receptor - E2F and Sp1 TFs -> D1
Bcr/Abl -> D2

Question 17

How do cancer cells produce growth factors?

Answer 17

They acquire the ability to synthesize growth factors, through mutations, to which they respond (autocrine stimulation)

Question 18

What are two examples of growth factors produced by cancer?

Answer 18

eg 1. Platelet-derived growth factor (PDGF) production by glioblastomas
eg 2. TGFalpha production by sarcomas (dimerization of the receptor)

Question 19

What are four mechanisms that can deregulate the receptor tyrosine kinases on the cancer cell surface?

Answer 19

1. Point mutation
2. Deletions
3. Chromosomal rearrangements
4. Overexpression

Question 20

How would a point mutation effect the deregulation of a receptor tyrosine kinase?

Answer 20

It results in continuous phosphorylation

Question 21

How would a deletion effect the deregulation of a receptor tyrosine kinase?

Answer 21

If, for example, the cytosolic, ligand binding portion of the receptor is deleted then the receptor is constantly dimerized and continuously on.

Question 22

In breast cancer, which growth factors are continuously overexpressed?

Answer 22

ErbB1 and ErbB2 (EGF and Her2)

Question 23

How is Ras activated?

Answer 23

Ras is in an inactive state when bound to GDP. Sos, an adapter protein, binds to Ras and Ras undergoes a conformational change. The conformational change allows it bind GTP and become active. Allowing it to bind and activate Raf.

Question 24

Why is Ras so significant in tumours?

Answer 24

Ras is an oncogene in 25-30% of human tumours. Undergoes intracellular transducers activating mutations.

Question 25

How is Mapkinase activated?

Answer 25

1. Ras is activated by the exchange of GDP for GTP 2. Active Ras recruits, binds and activates Raf 3. GTP hydrolysis leads to dissociation of Ras from Raf 4. Raf activates MEK 5. MEK activates MAPK 6. Dimeric form of active MAP kinase translocates to nucleus; activates many transcription factors

Question 26

What occurs when Raf becomes active?

Answer 26

Raf is inactive in cytosolic space, but when bound to Ras it becomes active and releases 14-3-3 proteins, which plays an important role in apoptosis.

Question 27

What does the activation of Map kinase lead to?

Answer 27

The activation of transcription factors TCF and SRF and the production of Fos.

Question 28

What is the role of Fos/Jun?

Answer 28

They control the expression of genes important for G1 progression and G1/S transition.

Question 29

What does Ras control?

Answer 29

- growth - survival - cell division - migration - motility - the proteins involved with the inhibition of apoptosis (PI3K, PIP3, Akt/PKB and Bad) - the proteins Raf, MEK and Erk1 or 2

Question 30

What occurs to Src activity in cancer?

Answer 30

The activity is frequently deregulated which can lead to changes in adhesion and increase proliferation.

Question 31

What is Src?

Answer 31

A proto-oncogene encoding a tyrosine kinase

Question 32

How can transcription factors act as oncoproteins?

Answer 32

Eg., Fos/jun overepression which leads to myc overexpression. Myc leads to the overexpression of cyclin D and entry into G1.

Question 33

How would cyclin D be inhibited if overepressed?

Answer 33

At a DNA damage checkpoint, p53 amount increases which produces p21CIP which inhibits cyclin D. If there's a mutation in this area, then there's a problem.

Question 34

What is E2F?

Answer 34

An important transcription factor for production of proteins that controls G1 to S transition.

Question 35

What is the role of Rb?

Answer 35

It sequesters E2F and prevents cell cycle progression. When phosphorylated, it is inhibited and cannot bind to E2F.