Oncogenes

Question 1

Define proto-oncogene.

Answer 1

A normal regulatory gene encoding proteins involved in signal transduction that can be mutated to become an oncogene.

Question 2

Define oncogene.

Answer 2

A mutated form of the corresponding proto-oncogene that induces abnormal cell proliferation and tumour development.

Question 3

List 4 ways by which a proto-oncogene can gain a function mutation to become an oncogene.

Answer 3

1 - Point mutation.

2 - Amplification of a DNA segment that includes a proto-oncogene.

3 - Chromosome translocation that brings a growth regulatory gene under the control of a different promoter.

4 - Chromosome translocation that joins two genes together, creating a fusion gene.

Question 4

Give an example of a proto-oncogene that gains its function mutation by point mutation.

Answer 4

Ras.

Question 5

List 5 proto-oncogenes that gain their function mutations by amplification.

Answer 5

1 - MYC.

2 - MYCN.

3 - MYCL.

4 - HER.

5 - CCND1.

Question 6

Give an example of a proto-oncogene that gains its function mutation by chromosome translocations that bring a growth regulatory gene under the control of a different prometor.

Answer 6

MYC.

Question 7

List 2 proto-oncogenes that gain their function mutations by chromosome translocations that join two genes together, creating a fusion gene.

Answer 7

1 - BCR and ABL.

2 - PML and RARA.

Question 8

List the 3 members of the RAS oncogene family.

Answer 8

1 - KRAS.

2 - NRAS.

3 - HRAS.

Question 9

In what proportion of cancers are RAS function mutations present?

Answer 9

25%.

Question 10

Give an example of a cancer for which HRAS is the most common oncogene.

Answer 10

Head and neck squamous cell carcinoma.

Question 11

Give an example of a cancer for which NRAS is the most common oncogene.

Answer 11

Melanoma.

Question 12

Give an example of a cancer for which both NRAS and KRAS are the most common oncogene.

Answer 12

Multiple myeloma.

Question 13

List 3 cancers for which KRAS is the most common oncogene.

Answer 13

1 - Pancreatic ductal adenocarcinoma.

2 - Colorectal adenocarcinoma.

3 - Lung adenocarcinoma.

Question 14

Which ras oncogenes are involved in acute myeloid leukaemia?

Answer 14

All 3 members (K, N and HRAS).

Question 15

List the 3 most common sites for point mutations on RAS genes.

Answer 15

1 - G12.

2 - G13.

3 - Q61.

*G = glycine and Q = glutamine.

Question 16

Which site of mutation is most common in KRAS?

Answer 16

G12.

Question 17

Which site of mutation is most common in NRAS?

Answer 17

Q61.

Question 18

Which site of mutation is most common in HRAS?

Answer 18

All 3 of the most common sites are affected to an equal degree.

Question 19

How do G12, G13 and Q61 point mutations produce oncogenic activity in ras?

Answer 19

They make ras unresponsive to GAP activity, which is necessary to deactivate ras by converting the GTP on ras to GDP.

Question 20

In which area of the ras protein are the products of the G12, G13 and Q61 genes?

Answer 20

The nucleotide-binding pocket (where GTP binds).

Question 21

How many chromosomes of a proto-oncogene must be mutated in order to create oncogenic activity of that particular gene?

Answer 21

Only one.

Question 22

Give an example of a cancer caused by amplification of the MYCN gene.

Answer 22

Neuroblastoma.

Question 23

List 4 cancers caused by amplification of the MYC gene.

Answer 23

1 - Breast cancer.

2 - Oesophageal cancer.

3 - Ovarian cancer.

4 - Small cell lung cancer.

Question 24

List 2 cancers caused by amplification of the CCND1 gene.

Answer 24

1 - Breast cancer.

2 - Oesophageal cancer.

Question 25

List 2 cancers caused by amplification of the HER gene.

Answer 25

1 - Breast cancer. 2 - Glioblastoma.

Question 26

What are double minutes? Of which gene are they a common feature?

Answer 26

- Autonomously replicating extrachromosomal fragments of DNA. - They are common with MYCN amplification.

Question 27

What are homogeneously staining regions? Of which gene are they a common feature?

Answer 27

- Autonomously replicating strands of DNA that grow attached to the end of a chromosome. - They are common with MYCN amplification.

Question 28

What is MYC? How does it work?

Answer 28

- A transcription factor that controls: 1 - The cell cycle. 2 - Metabolism. 3 - Differentiation. 4 - Angiogenesis. - When bound to MAX, the MYC-MAX complex acts as a co-activator complex at E-box elements (a type of gene promoter).

Question 29

How does the activity of the MAX transcription factor differ when bound to transcription factors other than MYC?

Answer 29

- When MAX is bound to MAD1, they act as co-repressors. | - MYC-MAX and MAX-MAD1 have antagonistic effects.

Question 30

How does MYC differ from most other transcription factors?

Answer 30

MYC is more non-specific than most other transcription factors, and can increase expression of many genes.

Question 31

What type of translocation occurs between MYC and IgH? Between which chromosomes does the translocation occur? On which chromosomes are MYC and IgH found?

Answer 31

- Reciprocal translocation. | - Between chromosome 8 (MYC) and 14 (IgH).

Question 32

What is the outcome of the MYC / IgH translocation?

Answer 32

- MYC comes into the control of the promoters of the IgH gene, leading to overexpression in cells that normally produce immunoglobulin heavy chains in high quantities. - This means that the MYC / IgH translocation commonly affects B cells, so gives rise to Burkitt lymphoma.

Question 33

Give an example of a pair of genes (other than BCR and ABL) that gain their function mutation by translocation to form a fusion gene. Give the full names for each gene.

Answer 33

1 - PML - promyelocytic leukaemia protein. 2 - RARA - retinoic acid receptor alpha.

Question 34

Which cancer is caused by the PML-RARA fusion gene?

Answer 34

Acute promyelocytic leukaemia.

Question 35

What is the function of the protein product of RARA? What must happen in order for it to function?

Answer 35

- It is a transcription factor. | - It only activates transcription when bound to a ligand.

Question 36

What is the protein product of PML? List the functions of PML.

Answer 36

- It is the core component of nuclear structures known as PML nuclear bodies. These bodies are involved in: 1 - Mediating interactions between proteins. 2 - Post-translational modification of proteins. 3 - Cell cycle regulation. 4 - Enhancement of p53 stability, a tumour suppressor gene that promotes apoptosis.

Question 37

How does the PML-RARA fusion gene produce this oncogenic activity in haemopoietic stem cells?

Answer 37

- The PML-RARA fusion gene ceases differentiation at the promyelocyte phase of the myeloid lineage. - It does this by producing a disorganised PML nuclear body in the nucleus mixed with the RARA transcription factor (formation of a dimer). Direct effect: - Disruption of PML nuclear bodies disrupts normal cellular function via loss of regulation (e.g. loss of p53, reducing apoptosis). Indirect effect: - The dimer also attracts corepressors which target repress the target genes for RARA. These genes are important for myeloid differentiation.

Question 38

List 2 treatments for acute promyelocytic leukaemia. How do they work?

Answer 38

1 - Arsenic trioxide, which degrades the PML/RARA dimer. 2 - Retinoic acid, which converts corepressors attracted by the PML/RARA dimer into activators.

Question 39

# Define oncogene addiction. Which type of oncogenes are usually involved in oncogene addiction? List 4 specific oncogenes of this type and give an example of a cancer caused by each gene.

Answer 39

- The phenomenon where a tumor cell, despite the presence of multiple genetic alterations, can exhibit dependence on a single oncogenic pathway or protein for its sustained proliferation and/or survival. - These are usually oncogenes encoding tyrosine kinase domains: 1 - BCR-ABL: chronic myeloid leukaemia. 2 - HER: non-small cell lung cancer (NSCLC). 3 - ALK: non-small cell lung cancer & neuroblastoma. 4 - MET: lung, liver, head & neck cancers.

Question 40

What is the treatment for cancers caused by oncogene addiction?

Answer 40

Tyrosine kinase inhibitors.

Question 41

List 2 mutations that are most common with the HER gene.

Answer 41

1 - Missense substitution. 2 - Inframe deletion.

Question 42

What is the outcome of all mutations to HER genes?

Answer 42

Increased activation of EGFR.

Question 43

Give an example of a cancer that arises from missense mutations in the kinase domain of HER genes.

Answer 43

Non-small cell lung cancer.

Question 44

Give an example of a cancer that arises from small inframe deletions / insertions in the kinase domain of HER genes.

Answer 44

Non-small cell lung cancer.

Question 45

Give an example of a cancer that arises from large deletion mutations in the kinase domain of HER genes.

Answer 45

Glioblastoma.

Question 46

List the cancers that arise from amplification of HER genes.

Answer 46

1 - Non-small cell lung cancer. 2 - Glioblastoma. 3 - Colorectal cancer.

Question 47

Why do patients often relapse with tyrosine kinase inhibitor therapy?

Answer 47

Because secondary mutations arise that affect the target site of the drugs.

Question 48

Which amino acids of the HER genes are most commonly affected by inframe deletions?

Answer 48

Amino acids 747-752.

Question 49

List the 2 most common changes to HER genes that occur with missense mutations. What effect do these changes have on the EGFR protein? What is the clinical outcome?

Answer 49

1 - A change from leucine to arginine. - This increases kinase activity 50-fold, resulting in non-small cell lung cancer. 2 - A change from threonine to methionine. - This changes the ATP binding socket, causing drug resistance.

Question 50

List 4 treatments for EGFR oncogene addiction in non-small cell lung cancer.

Answer 50

- First generation tyrosine kinase inhibitors are reversible (competitive) ATP mimics: 1 - Gefitinib. 2 - Erlotinib. Second generation tyrosine kinase inhibitors are irreversible (non-competitive) ATP mimics: 3 - Afatinib. Third generation tyrosine kinase inhibitors are more avid binders of EGFR mutants compared to the EGFR wild-type: 4 - Osimertinib.

Question 51

What is a problem with second generation tyrosine kinase inhibitors?

Answer 51

They are relatively toxic.

Question 52

Which amino acids of the HER genes are most commonly affected in glioblastomas?

Answer 52

Amino acids 6-73.

Question 53

What is the effect of mutations to the HER gene in glioblastomas?

Answer 53

- Mutation to the HER gene in glioblastomas causes loss of ligand binding and regulatory domains that are necessary for dimerisation of the EGFR. - This enables ligand-independent signalling.