7 - Oncogenes and Tumour Suppressor Genes

Question 1

Name 4 Major Functional Changes in Cancer 4

Answer 1

1. Increased growth (loss of growth regulation, stimulation of environment promoting growth e.g. angiogenesis)
2. Failure to undergo programmed cell death (apoptosis) or senescence
3. Loss of differentiation (including alterations in cell migration and adhesion)
4. Failure to repair DNA damage (including chromosomal instability)

Question 2

Define Oncogenes 1

Answer 2

An altered gene whose product can act in a dominant fashion to help make a cell cancerous.

Oncogene is a mutant form of a normal gene (a “proto-oncogene”) involved in the control of cell growth or division.

Many oncogenes are normally components of growth factor signalling pathways that when mutated produce products in higher quantities or whose altered products have increased activity and therefore act in a dominant manner.

Their normal job is to make cells divide, driving cell division forward
In cancer, they pick up mutations that mean they are permanently active.

Oncogene: “Gain of function”

If you activate an oncogene you are speeding up the growth

Question 3

Define Tumour suppressor gene 1

Answer 3

Many tumour suppressor gene products act as a stop signal to uncontrolled growth, may inhibit the cell cycle or trigger apoptosis.

Even if you have a mutation in an oncogene that pushes cell division forward, if your tumour suppressor genes are strong enough, they should still be able to counteract the oncogene

A gene whose normal activity prevents formation of a cancer.

Both genes for the tumour suppressor must be mutated

Loss of this function by mutation enhances the likelihood that a cell can become cancerous (a normal process to maintain control of cell division is lost).

In cancer, pick up mutations that switch the gene off.

Tumour Suppressor gene: “Loss of function”

Tumour suppressor act normally as a counteracted to oncogenes

Question 4

Function of a normal oncogene 3

Answer 4

Oncogene is a mutant form of a normal gene (a “proto-oncogene”) involved in the control of cell growth or division.

Their normal job is to make cells divide, driving cell division forward
In cancer, they pick up mutations that mean they are permanently active.

If you activate an oncogene you are speeding up the growth

Question 5

Function of a mutated oncogene 3

Answer 5

An altered gene whose product can act in a dominant fashion to help make a cell cancerous.

Many oncogenes are normally components of growth factor signalling pathways that when mutated produce products in higher quantities or whose altered products have increased activity and therefore act in a dominant manner.

In cancer, they pick up mutations that mean they are permanently active.

Question 6

Function of a normal TSG 3

Answer 6

Many tumour suppressor gene products act as a stop signal to uncontrolled growth, may inhibit the cell cycle or trigger apoptosis.

Even if you have a mutation in an oncogene that pushes cell division forward, if your tumour suppressor genes are strong enough, they should still be able to counteract the oncogene

A gene whose normal activity prevents formation of a cancer.

Question 7

Function of a mutated TSG 3

Answer 7

Both genes for the tumour suppressor must be mutated

Loss of this function by mutation enhances the likelihood that a cell can become cancerous (a normal process to maintain control of cell division is lost).

In cancer, pick up mutations that switch the gene off.

Tumour Suppressor gene: “Loss of function”

Question 8

What is the Knudson hypothesis? 4

Answer 8

Knudson hypothesis, also known as the two-hit hypothesis.

Is the hypothesis that most tumour suppressor genes require both alleles to be inactivated, either through mutations or through epigenetic silencing, to cause a phenotypic change.

Two separate mutations in each allele are required to knockout the function of a tumour suppressor

A mutation in one of those alleles this behaviour in a dominant manner and gene is activated –> cell proliferation. Loss of function.

First mutation in one allele is not enough to have a functional effect on that protein, two mutations one in each allele is required to change function and make that tumour suppressor inactive.

Question 9

There are many pathways affected by oncogenes and tumour suppressor proteins

Answer 9

There are many pathways affected by oncogenes and tumour suppressor proteins

RAS – part of normal cell growth signalling pathways

Myc – important oncogene

Tumour suppressor gene – Rb and P53 (guardian of the genome)

Question 10

Oncogenes - A Historical Perspective - Landmark experiments

Answer 10

Frances Peyton Rous began his work in 1910 that lead to the discovery of Rous sarcoma virus (RSV).

50 years later he received the Nobel Prize in Medicine in 1986

In 1911 when a farmer brought Rous a prized Plymouth Rock hen that had a large tumour growing in the chest muscle, he used the cell free filtrate from the chicken sarcoma and was able to induce sarcomas in healthy chickens

He was brought a chicken which had a massive tumour in the chest wall (sarcoma) –> chicken sarcoma

Although some human cancers are thought to be transmissible through viruses, most are confined to other animals.

The idea that cancer was transmissible was already circulating as early as 1840 when an Italian scientist

Domenico Rigoni-Stern observed that nuns in Verona rarely developed cervical cancer. Papilloma virus was not identified until 1983

He took the chicken and removed the sarcoma and broke it into small chunks and then ground them with sand and filtered it

He took the filtrate and injected it into young healthy chickens

Question 11

Why are retroviruses important experimentally 5

Answer 11

Retroviruses were important experimentally:

1. technological advances
2. funding
3. improved tissue culture techniques
4. the discovery of reverse transcriptase, RNA
5. genome, replicates via DNA intermediate and that they are enveloped.

Question 12

c-scr definition 1

Answer 12

c-src, cellular oncogene

C-src is a cellular oncogene that is acquired by the virus.

Question 13

v-src defintion 1

Answer 13

v-src proto-oncogene altered form transduced by retroviruses

V-src is a proto-oncogene, an altered form of c-src transduced by retroviruses.

Following infections, the v-src oncogene was expressed at high level in the host cell, causing uncontrolled cell growth and division and cancer.

Question 14

How did Frances Peyton Rous induce sarcoma in healthy chickens 1

Answer 14

cell free filtrate from the chicken sarcoma and was able to induce sarcomas in healthy chickens

Question 15

Oncogenic transformations by RSV were found to be caused by? 1

Answer 15

Decades later oncogenic transformation by this virus was found to be caused by an extra gene contained in its genome an ‘oncogene’ called v-src

Oncogenic transformations by RSV were found to be caused by? 1

Question 16

Rous’s protocol for inducing sarcoma in chickens

Answer 16

• Bacteria was too small so must’ve been a virus
• Tumours developed weeks later
• Taking the new sarcoma, filtrates produced could also induce tumours in other chickens
• The cycles could be repeated indefinitely. Also the carcinogenic agent was small enough to pass through a filter
• Although the filter used excluded bacteria it was not small enough to exclude viruses
• Rous concluded that a virus must be responsible for the induction of tumour formation
• Discovery that this sarcoma was transmissible through viruses- Rous Sarcoma Virus.

Question 17

Harold Varmus and J. Michael Bishop research on RSV 7

Answer 17

• Upon finding there was a gene homologous sequence to v-src in uninfected chickens, in 1989 Harold Varmus and J. Michael Bishop received the noble prize for laying down the foundation of mutations in carcinogenesis
• Discovered that some genes of cancer-causing viruses were mutated forms of the cellular gene not viral genes
• They concluded that the RSV gene was in fact a host gene that had been ‘kidnapped’ by the virus (and ‘transformed’ into an oncogene)
• An oncogene is any cellular gene that upon activation can transform a cell. Viral SRC was a mutated cellular gene.
• Used hybridisation experiments, and they found that the c-src gene was present in the genome of many species.
• They then showed that the host cell c-src gene was normally involved in the positive regulation of cell growth and cell division.
• Following infection, however, the v-src oncogene was expressed at high levels in the host cell, leading to uncontrolled host cell growth, unrestricted host cell division, and cancer.

Question 18

Harold Varmus and J. Michael Bishop concluded that RSV is? 1

Answer 18

They concluded that the RSV gene was in fact a host gene that had been ‘kidnapped’ by the virus (and ‘transformed’ into an oncogene)

Question 19

What did Harold Varmus and J. Michael Bishop find from their hybridisation experiments? 3

Answer 19

Used hybridisation experiments, and they found that the c-src gene was present in the genome of many species.

They then showed that the host cell c-src gene was normally involved in the positive regulation of cell growth and cell division.

Following infection, however, the v-src oncogene was expressed at high levels in the host cell, leading to uncontrolled host cell growth, unrestricted host cell division, and cancer.

Question 20

When proto-oncogenes are activated what do they become> 1

Answer 20

Proto oncogenes have to be activated to become active oncogenes

Question 21

Function of SRC 1

Answer 21

SRC was usually involved in cell growth but when mutated you lose that function

Question 22

Capture of c-src by retrovirus 6

Answer 22

• During evolution, the virus can acquire fragments of genes from the host at integration sites and this process results in the creation of oncogenes.
• This results in the creation of oncogenes.
• The oncogene product was characterised as a 60kDa intracellular tyrosine kinase
• Can phosphorylate cellular proteins and affect growth
• The provirus is accidentally integrated next to the host cellular SRC sequence –> you get this fusion which then gets packaged into a capsid.
• End up with an RSV with a viral-src.

Question 23

Following infections what oncogene is expressed? 1

What does it cause? 1

Answer 23

Following infections, the v-src oncogene was expressed at high level in the host cell, causing uncontrolled cell growth and division and cancer.

Question 24

Viral Oncogenesis 3

Answer 24

Approximately 15%-20% of all human cancers are caused by oncoviruses

Viral oncogenes can be transmitted by either DNA or RNA viruses.

DNA viruses can cause lytic infection leading to the death of the cellular host or can replicate their DNA along with that of the host and promote neoplastic transformation

Question 25

How many human cancers are caused by oncoviruses 1

Answer 25

Approximately 15%-20% of all human cancers are caused by oncoviruses

Question 26

How can Viral oncogenes be transmitted? 2

Answer 26

Viral oncogenes can be transmitted by either DNA or RNA viruses.

Question 27

How can DNA viruses cause a lytic infection? 1

Answer 27

DNA viruses can cause lytic infection leading to the death of the cellular host or can replicate their DNA along with that of the host and promote neoplastic transformation

Question 28

Viral Oncogenesis - DNA Viruses 1

Answer 28

Encode various proteins along with environmental factors can initiate and maintain tumours

Question 29

Viral Oncogenesis - RNA Viruses

Answer 29

Integrate DNA copies of their genomes into the genome of the host cell and as these contain transforming oncogenes they induce cancerous transformation of the host

Question 30

Examples of human oncogenic viruses - table

Answer 30

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Question 31

Selected oncogenes, their mode of activation and associated human tumours - table

Answer 31

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Question 32

How can you activate an oncogene? 3

Answer 32

1. Mutation 2. Amplification/duplication 3. Translocation Ways to become an active oncogene and can INCREASE synthesis of protein

Question 33

How to become a bad oncogene - diagram

Answer 33

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Question 34

What do protooncogenes do in the growth factor signal transduction pathway 1

Answer 34

Proto-oncogenes encode components of the growth factor signal transduction pathway The majority of oncogene proteins function as elements of the signalling pathways that regulate cell proliferation and survival in response to growth factor stimulation

Question 35

What 4 types of proteins are involved in the transduction of growth signals 4

Answer 35

4 types of proteins are involved in the transduction of growth signals Growth factors Growth factor receptors Intracellular signal transducers Nuclear transcription factors

Question 36

What do oncogene proteins act as 3

Answer 36

Oncogene proteins act as * growth factors (e.g. EGF) * growth factor receptors (e.g. ErbB) * intracellular signalling molecules (Ras and Raf).

Question 37

What are the oncogene pathways that are intracellular signalling molecules 2 What pathway do they activate 1 What does this pathway lead to 1

Answer 37

Ras and Raf activate the ERK MAP kinase pathway leading to the induction of additional genes (e.g. fos) that encode potentially oncogenic transcriptional regulatory proteins

Question 38

What studies was RAS discovered in 2

Answer 38

ras genes were identified from studies of two cancer-causing viruses the 1. HARVEY SARCOMA VIRUS 2. KIRSTEN SARCOMA VIRUS These viruses were discovered originally in rats hence the name **Ra**t **s**arcoma

Question 39

What are RAS proteins 1 What are they normally bound to 1

Answer 39

RAS proteins are small GTPases Normally bound to GDP in a neutral state

Question 40

How is RAS activated 1 What % in oncogenic cancer 1

Answer 40

Activated by point mutations Oncogenic activation of ras is seen in about 30% of human cancer

Question 41

Name 3 most commonly mutated oncogenes 3

Answer 41

Most commonly mutated oncogene Point mutations in codons 12, 13 and 61 Glycine to valine - bladder carcinoma Glycine to cysteine - lung cancer

Question 42

Intracellular Signal Transducers - Activation of Ras - steps 5

Answer 42

1. Binding of extracellular growth factor signal 2. Promotes recruitment of RAS (GTPase) proteins to the receptor complex 3. Recruitment promotes Ras to exchange GDP (inactive Ras) with GTP (active Ras) 4. Activated Ras then initiates the remainder of the signalling cascade (mitogen activated protein kinases) 5. These kinases ultimately phosphorylate targets, such as transcription factor to promote expression of genes important for growth and survival 6. Ras hydrolyses GTP to GDP fairly quickly, turning itself “off” * Consequence of each of these mutations is a loss of GTPase activity of the RAS protein normally required to return active RAS to the inactive RAS GDP

Question 43

What can a mutation in Ras cause 1,2

Answer 43

Mutation in RAS means it’s always switched on, hyperactivation Continually get progression through the cell cycle, they can’t stop and so that leads to tumour genesis, don’t go through checkpoints.

Question 44

How can a mutation in Ras lead to hyperactive Ras, what mutation occurs 1

Answer 44

Consequence of each of these mutations is a loss of GTPase activity of the RAS protein normally required to return active RAS to the inactive RAS GDP

Question 45

What is the MYC Oncogene Family 1

Answer 45

Transcription Factors The MYC oncoproteins belong to a family of transcription factors that regulate the transcription of at least 15% of the entire genome

Question 46

Name 3 members of the MYC oncogene family 3 What do they encode for 3

Answer 46

The MYC oncogene family consists of 3 members, 1. C-MYC 2. MYCN 3. MYCL which encode c-Myc, N-Myc, and L-Myc, respectively

Question 47

Where was the MYC oncoproteins originally identified 1

Answer 47

Originally identified in avian myelocytomatosis virus (AMV)

Question 48

Name downstream effects of MYC oncoproteins 4

Answer 48

1. ribosome biogenesis 2. protein translation 3. cell-cycle progression and metabolism 4. orchestrating a broad range of biological functions * cell proliferation, differentiation, survival, and immune surveillance

Question 49

Is the MYC oncoproteins over or underexpressed in the majority of human cancers? 1 What % contributes to human tumours? 1

Answer 49

The MYC oncogene is overexpressed in the majority of human cancers Contributes to the cause of at least 40% of tumours

Question 50

What does the MYC oncogene code for? 1 What does this dimerise with? 1

Answer 50

A helix-loop-helix leucine zipper transcription factor that dimerizes with its partner protein, Max, to transactivate gene expression.

Question 51

What does a helix-loop-helix leucine zipper and its partner protein, Max do? 1

Answer 51

A helix-loop-helix leucine zipper transcription factor that dimerizes with its partner protein, Max, to transactivate gene expression.

Question 52

Activation of MYC oncogenes is a result of what? 1

Answer 52

Such activation is a result of chromosomal translocation This leads to a deregulation of the oncogene that drives relentless proliferation.

Question 53

Activation of MYC oncogenes by chromosomal translocation is a characteristic of what type of tumour? 1 Which you get if you are infected by? 1

Answer 53

Activation via chromosomal translocation very much characteristic of Burkitt lymphoma --\> tumour type that you get if you have been infected with Epstein Barr virus (EBV).

Question 54

What is Burkitt’s lymphoma (BL) 2

Answer 54

BL is a high-grade lymphoma can affect children from the age of 2 to 16 years In central Africa, children with chronic malaria infections have a reduced resistance to the virus. This is known as classical African or endemic BL In Africa it is found in the jawbone.

Question 55

In central Africa why do children have a reduced resistance to the virus? 1 What is this known as? 1 Where is this found? 1

Answer 55

In central Africa, children with chronic malaria infections have a reduced resistance to the virus. This is known as classical African or endemic BL In Africa it is found in the jawbone.

Question 56

The MYC gene is under regulation by what chain? 1 What happens here? 1

Answer 56

MYC gene under the regulation of the Ig heavy chain chromosomal translocations

Question 57

All BL cases carry one of three characteristic chromosomal translocations, what chromosomes do they occur in 3

Answer 57

In BL three distinct, alternative chromosomal translocations involving chromosomes 2, 14 and 22. In all three translocations a region from one of these three chromosomes is fused to a section of chromosome.

Question 58

What happens in the chromosome translocations in BL? 1

Answer 58

In all three translocations a region from one of these three chromosomes is fused to a section of chromosome.

Question 59

What effect do the chromosomal locations in BL have on Myc gene? 2

Answer 59

* Lose control of Myc so you get lots of proliferation * Mutation of Myc gene so now under control of immunoglobin heavy chain. So from chromosome 2,14,22 to chromosome 8 and Myc is switched on all the time

Question 60

Name another disease caused by the activation of oncogenes due to chromosomal translocation 1

Answer 60

Chronic myelogenous leukaemia (CML) accounts for 15-20% of all leukaemia's

Question 61

What % of leukaemia does CML account for 1

Answer 61

Chronic myelogenous leukaemia (CML) accounts for 15-20% of all leukaemia's

Question 62

What number of CML patients carry a different type of chromosome? 1 What is this chromosome called? 1

Answer 62

95% of CML patients carry the Philadelphia chromosome, that is the product of the chromosomal translocation t(9;22)(q34;q11) generating the BCR-ABL fusion protein

Question 63

The Philadelphia chromosome is a product of what chromosomal translocation 1 What does this generate 1

Answer 63

Philadelphia chromosome, that is the product of the chromosomal translocation t(9;22)(q34;q11) generating the BCR-ABL fusion protein

Question 64

What is the result chromosomal translocation done by the Philadelphia chromosome? 1

Answer 64

95% of CML patients carry the Philadelphia chromosome, that is the product of the chromosomal translocation t(9;22)(q34;q11) generating the BCR-ABL fusion protein As a result of this translocation the tyrosine kinase activity of the oncogene ABL is constitutive leading to abnormal proliferation

Question 65

Name a therapeutic strategies for CML? 1 What is its function? 1

Answer 65

Therapeutic strategies for CML include Imatinib (Gleevac) a tyrosine kinase inhibitor-96% remission in early-stage patients

Question 66

The Logic of Tumour Suppressor Genes

Answer 66

The Logic of Tumour Suppressor Genes Like other well-designed control systems biological systems follow a similar logic-component promoting a process must be counterbalanced by others that oppose the process-tumour suppressor genes.

Question 67

What do tumour suppressor gene products act as 3

Answer 67

Tumour suppressor gene products act as stop signs to uncontrolled growth, promote differentiation or trigger apoptosis

Question 68

What are tumour suppressor genes regulators of 3

Answer 68

Therefore they are usually regulators of 1. cell cycle checkpoints (e.g. RB1) 2. differentiation (e.g. APC) 3. DNA repair (e.g. BRCA1)

Question 69

How can a loss of tumour suppressor gene come about 1 What is it a result of 2

Answer 69

Loss of tumour suppressor gene function requires inactivation of both alleles of the gene Inactivation can be a result of mutation or deletion

Question 70

What type of genes are tumour suppressor genes 2

Answer 70

Tumour suppressor genes are defined as recessive genes Sometimes referred to as ‘anti-oncogenes’

Question 71

Name 3 functions of Tumour suppressor genes and examples 3,3

Answer 71

regulators of cell cycle checkpoints (e.g. RB1), differentiation (e.g. APC) DNA repair (e.g. BRCA1)

Question 72

Tumour suppressor and cancer - table

Answer 72

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Question 73

How does Retinoblastoma develop 1

Answer 73

Develops when immature retinoblasts continue to grow very fast and do not turn into mature retinal cells. Retinoblastoma is a rare childhood cancer (1 in 20,000)

Question 74

If an eye contains a tumour what colour light will reflect back 1 What is the technical term for this 1

Answer 74

An eye that contains a tumour will reflect light back in a white colour. Often called a “cat’s eye appearance,” the technical term for this is leukocoria.

Question 75

What are the 2 forms of the Retinoblastoma disease 2

Answer 75

Two forms of the disease 1. familial (40%) 2. sporadic (60%)

Question 76

Where is the mutation found for retinoblastoma 1

Answer 76

The hereditary mutation is on chromosome 13 (13q14), the retinoblastoma 1 (Rb1) gene

Question 77

What is 'Loss of heterozygosity' 1

Answer 77

"Loss of heterozygosity“ often used to describe the process that leads to the inactivation of the second copy of a tumour suppressor gene a heterozygous cell receives a second hit in its remaining functional copy of the tumour suppressor gene, thereby becoming homozygous for the mutated gene.

Question 78

Mutations that inactivate tumour suppressor genes can also be called 1 What are these caused by 2

Answer 78

Mutations that inactivate tumour suppressor genes, called loss-of-function mutations Often point mutations or small deletions that disrupt the function of the protein that is encoded by the gene.

Question 79

Hereditary tumours vs Sporadic tumours 2

Answer 79

One set of patients which had the inherited form of the disease, and in these patients the first mutations in one of the alleles was inherited, and then second is acquired. Sporadic people developed tumour much later on, not inheritance, patient had to acquire two separate hits/mutations, and patients presented at a much later age.

Question 80

How many members are in the Rb gene family 3 Name them 3 What are they collectively known as 1

Answer 80

The Rb gene family includes three members: 1. Rb/(p105/110) 2. p107 3. Rb2/p130 -collectively known as pocket proteins