8. Oncogenes

Question 1

what experiment proved that cancer can possibly be transmissible?

Answer 1

1. a chicken from Rhode island had a lump
2. took his chicken to a scientist
3. the sarcoma was removed and broken up and filter
4. inject this into a young chicken
5. the chicken developed sarcoma

Question 2

what is the lifecycle of a retrovirus?

Answer 2

1. the virus in introduced into the cell
2. use reverse transcriptase to make dsDNA
3. a copy of the viral genome is integrated into the host genome. this is called a provirus
4. transcription of the new viral RNA
5. translation into proteins
6. packaged into new mature virions

Question 3

what is a key way cancer passes through animals (not humans)?

Answer 3

retroviruses

Question 4

what caps the end of retroviral RNA?

Answer 4

Long terminal repeats (LTR) which are strong drivers of transcription

Question 5

what is RSV?

Answer 5

1. Respiratory syncytial virus
2. an acute retrovirus

Question 6

what do acute retroviruses have?

Answer 6

an extra gene called src that can cause fast tumourigenesis

Question 7

what are present in the host cell chromosome?

Answer 7

version of src called c-src
this is an proto-oncogene

Question 8

what do slow retroviruses do?

Answer 8

1. integrate the dsDNA provirus next to the c-src gene
2. both the provirus and the oncogene are transcribed together
3. making a new virus but also activating the oncogene

Question 9

what do proto-oncogenes control?

Answer 9

growth and proliferation
control of cell cycle
apoptosis

Question 10

are oncogenes associated with certain cancers?

Answer 10

yes different driving mutations in different tissue types cause different cancers

Question 11

how can we detect oncogenes?

Answer 11

An in vitro transformation assay
1. use normal cells as a monolayer
2. infect a normal cell with the virus
3. transformation of cell
4. overcome the contact inhibition and grow
5. piling of cells = a tumour
6. can see cells on an EM as there is a big change in morphology to be more mesenchymal

Question 12

what are the properties of transformed cells?

Answer 12

1. Altered morphology
2. loss of contact inhibition
3. Anchorage independent - ability to grow without attachment
4. immortalisation
5. reduced requirement for mitogenic growth factors
6. high saturation density
7. inability to halt proliferation in response to deprivation of growth factors
8. increased transport of glucose to meet higher metabolic requirements

Question 13

how can oncogenic activity be detected?

Answer 13

1. DNA extracted from carcinoma to chemically transformed fibroblasts
2. introduced to normal cells
3. formation of morphologically transformed cells
4. check they are tumourigenic by putting into a mouse
5. we can use this method to identify stretches of DNA with tumourigenic activity

Question 14

How do slow acting retroviruses cause cancer without extra genes?

Answer 14

the provirus integrates next to the cellular oncogenes

Question 15

ALV as an example of a slow retrovirus

Answer 15

1. ALV integrates directly upstream exon 2 of the c-myc gene
2. it faces the direction of transcription
3. uses the long terminal repeats to drive transcription of the proto-oncogene making it an oncogene
4. due to survival advantage it is more likely to integrate at one of these sites

Question 16

How common are cancer-causing retroviruses in humans?

Answer 16

not very many known but they are very common for animals

Question 17

what is the only known human cancer causing retrovirus?

Answer 17

Human T cell leukaemia virus

Question 18

what would be easier if most human cancers were caused by retroviruses?

Answer 18

treatment and vaccination

Question 19

what have we learn from animal retroviral cancers and experiments?

Answer 19

that human cells have cellular oncogenes that are hijacked during the process of transformation
(functions tend to be for growth and proliferation)

Question 20

what is epidermal growth factor receptor?

Answer 20

1. a retroviral oncogene
2. a tyrosine kinase receptor
3. the most frequent amplification event in over 90 tumours
4. Glioblastoma, breast, lung

Question 21

how is EGFR signalling deregulated in cancer?

Answer 21

1. mutations that effect the structure of EGFR can cause ligand independent firing and the signal can get stuck on
2. mutations that cause over expression which also leads to ligand independent firing

Question 22

how does normal EGFR signalling work?

Answer 22

1. a growth factor binds to make the tyrosine kinase a duplex
2. once the domain has dimerised then it will send the signal to trigger phosphorylation

Question 23

what is K-Ras?

Answer 23

an oncogene where mutation is common in a lot of cancers.
Change of function mutation.

Question 24

what makes K-Ras unique?

Answer 24

Its mutation is very localised.
In a sample of 10,000 tumours 98% had the mutation in codon 12

Question 25

what other genes are in the K-Ras family of oncogenes?

Answer 25

1. H-Ras 2. N-Ras

Question 26

what does K-Ras present?

Answer 26

A major challenge as it is present in a large variety of tumours and it is a focus of developing treatment

Question 27

what is the process of Ras activation and downstream signalling?

Answer 27

1. Inactive Ras is bound to GDP 2. GEF induces the exchange of GDP to GTP 3. Active Ras is bound to GTP 4. downstream phosphorylation events include the MAP-kinase pathway and other cancer driving signalling 5. GAP causes GTP hydrolysis to GDP and inactivate Ras 6. signalling process stops

Question 28

what is GEF?

Answer 28

guanine nucleotide exchange factor

Question 29

what is GAP?

Answer 29

Ras-GTPase activiting protein

Question 30

how is Ras signalling altered in cancer?

Answer 30

1. A mutation in NF1 prevents Ras from returning to the inactive state and keeps signalling active 2. signal epigenetic changes 3. drive proliferation

Question 31

what is NF1?

Answer 31

1. neurofibromatosis 1 2. a common tumour suppressor gene lost in CRC, AML, neuroblastoma 3. GTPase activity of Ras lost

Question 32

how does chromosomal translocation lead to C-myc over-expression in Burkitt's lymphoma?

Answer 32

1. A reciprocal translocation of the IgH heavy chain next to C-myc 2. uses enhancers to drive transcription 3. activating mutation

Question 33

what is Myc?

Answer 33

A major oncogene activated by translocation, amplification, and deregulation

Question 34

what genes are in the myc family and myc interactors?

Answer 34

C-myc: oncogene N-myc: oncogene L-myc: not really an oncogene HLH transcription factor (helix-loop-helix) TAD domain: topologically associating domain, interacts with proteins to control transcription Co-activators or co-repressors: Max and Mad

Question 35

what is the function of the myc protein?

Answer 35

1. Lots of signalling events feed through myc and it regulated a huge number of genes 2. Works with lots of other proteins 3. intracellular and extracellular signals

Question 36

what can mutations in myc lead to?

Answer 36

constant activation and results is many phenotypes including increased proliferation

Question 37

what can trigger myc signalling?

Answer 37

1. growth factors 2. cytokines 3. cell adhesion 4. contact-inhibition 5. TGFß 6. differentiation

Question 38

what can myc signalling cause that drives cancer?

Answer 38

1. growth and proliferation 2. prevent differentiation 3. Immortalisation 4. transformation 5. Angiogenesis 6. migration 7. Apoptosis or senescence 8. genomic instability

Question 39

what can myc acts as?

Answer 39

an activator or repressor depending on what is bound to. It can also interact with epigenetic factors Myc and max = activator Myc, max and Miz = inhibitor

Question 40

Do different oncogenes interact?

Answer 40

Yes and it is critical for tumorigenesis. mostly 1 mutation isn't enough to cause cancer but complementary oncogenic mutations can cause tumours

Question 41

what 2 mutations often occur together?

Answer 41

Ras and myc. Ras signalling can lead to a mutation that can stabilise the myc mutation

Question 42

Why can finding treatment for cancer be difficult?

Answer 42

due to the massive variation in cancer phenotypes

Question 43

what is p53?

Answer 43

A tumour suppressor gene

Question 44

what mutations can complement oncogene mutations?

Answer 44

Mutations in tumour suppressor genes

Question 45

why are oncogenes hard to design targeted treatments for?

Answer 45

1. they mostly encode transcription factors 2. So they do not have active sites so can't easily inhibit them

Question 46

how can you use cancer mutations against it?

Answer 46

1. Mutations accumulate and cells become dependent on 1 proliferation pathway 2. This means once cancer reaches this stage then we can design targeted treatment without having to target the oncogene itself

Question 47

how do oncogenes keep the cells alive?

Answer 47

1. hijack replication pathways and prevent safe guarding mechanisms for doing their function 2. if we can knock out these pathways them we can force apoptosis or senescence