Molecular Pathology of Tumours

Question 1

What is a property unique to a malignant cell ?

Answer 1

Ability to spread to other parts of the body.

Question 2

State some properties of malignant cells

Answer 2

Disordered:

• Proliferation
• Apoptosis
• Differentiation
• Relationship between proliferating cells and surrounding environment
  (invasion, metastasis, angiogenesis)

Question 3

Describe the multi-step process of tumour formation

Answer 3

Normal
Dysplasia
Carcinoma in situ
Invasion (basement membrane is broken)
Metastases

Question 4

Describe tumour formation - clonality

Answer 4

A mutation gives one cell an advantage

A second mutation increases the advantage.

A third mutation increases the advantage further and makes the cell invasive.

Dangerous cell survival, proliferation and invasion.

Question 5

What sort of genes are altered in mutations ?

Answer 5

Oncogene activation

Tumour supressor gene inactivation

Question 6

What are oncogenes ?

Answer 6

• Drivers of neoplastic behaviour (out of control proliferation)
• Proto-oncogene

Question 7

How are oncogenes formed ?

Answer 7

A single mutation event in a proto-oncogene creates an oncogene.

The activation of the mutation, enables the oncogene to stimulate cell survival and proliferation.

Question 8

What type of mutation occurs for proto-oncogenes ?

Answer 8

DOMINANT mutation
Activating mutation

Gain of function (excessive cell survival and proliferation)

Question 9

Give an example of an oncogene

Answer 9

RAS

Question 10

What mechanisms can result in the activation of an oncogene ?

Answer 10

Mutation in the coding sequence
Gene amplification
Chromosome Re-arrangement

Question 11

Describe a mutation in the coding sequence - RAS

Answer 11

Can happen in an oncogene like RAS.

Found in colon cancer, where the 12th amino acid of RAS is converted from glycine to valine.

RAS protein becomes locked in an ON position, and is able to send signals down the cascade to tell cells to divide.

Question 12

Result of a mutation in the coding sequence

Answer 12

Hyperactive protein made in normal amounts

Question 13

Describe gene amplification : HER2

Answer 13

HER2- epidermal growth factor

Frequently happens in breast cancer.

Amplification of HER2 gene, which over expresses the protein to a high extent.

Question 14

Result of gene amplification

Answer 14

Normal protein greatly overproduced

Question 15

Describe chromosome rearrangement : CML (chronic myeloid leukaemia)

Answer 15

Rearrangement of Philadelphia chromosome, in order to generate a fusion protein.

BCL gene fused to abl gene.

This produces a hyperactive fusion protein.

Question 16

Result of chromosome re-arrangement

Answer 16

Fusion to actively transcribed gene produces hyperactive fusion protein.

OR

Nearby regulatory DNA sequence causes normal protein to be overproduced.

Question 17

Functional consequences of oncogenes

What are there mutations in ?

Answer 17

Mutations in:

• Growth factor
• Growth factor receptor
• Signal transducer
• Transcription factor

Question 18

Growth factor mutations

Answer 18

Sis (over expressed gene), Fibrosarcoma

Question 19

Growth factor receptor mutations

Answer 19

HER2, Breast cancer

Question 20

SIgnal transducer mutations

Answer 20

Ras, Colon cancer

Question 21

Transcription factor mutation

Answer 21

Myc, Burkitt’s lymphoma

Question 22

How do oncogenes work ?

Four ways

Answer 22

4 ways:

Direct stimulation of cell cycle dependent transcription.

Increased/activation of growth factor receptors

Increased growth factor

Interference with intracellular signalling

Question 23

Describe tumour suppressor genes

Answer 23

Recessive mutation
LOSS of function mutation

Excessive cell survival and proliferation

Question 24

Feature of tumour suppressor genes

Answer 24

LOSS of function mutations (2 inactivating mutations) functionally eliminates the tumour suppressor gene, stimulating cell survival and proliferation.

Question 25

Retinoblastoma: Knudson's 2 hit hypothesis

Answer 25

Normally paired RB1 genes Mutational loss of one RB1 gene Mutational loss of the other RB1 gene in the same cell/ its daughter cell. This may lead to 1 eye with retinoblastoma. Other eye with none of these cells - normal. --------------------------------------------------------------------------------- Inherited absence of 1 of the paired RB1 genes. Mutational loss of RB1 in any retinal cell High risk of bilateral retinoblastoma

Question 26

Bilateral retinoblastoma

Answer 26

Inherited retinoblastoma Only need 1 mutation Earlier age of onset

Question 27

Unilateral retinoblastoma

Answer 27

Sporadic retinoblastoma Needs 2 mutations to occur

Question 28

Normal function of RB1

Answer 28

A transcription factor, which sits on top of other transcription factors and prevents the expression of genes, which are required for DNA synthesis.

Question 29

Why does mutating RB drive carcinogenesis ?

Answer 29

Non-proliferating cell. Inactive Rb, in an uncontrolled way (mutated). We can activate transcription and expression of S-phase genes are activated.

Question 30

State the 2 types of tumour suppressor genes

Answer 30

Gatekeepers Caretakers

Question 31

Gatekeeper - tumour suppressor genes

Answer 31

Inhibit proliferation or promote the death of cells, especially those with DNA damage. Sends negative signals to the cell.

Question 32

Example of a tumour suppressor gene mutation - gatekeeper

Answer 32

Familial adenomatous polyposis coli Retinoblastoma

Question 33

Describe caretaker - tumour supressor genes

Answer 33

Maintain the integrity of the genome by promoting DNA repair. - Nucleotide expansion repair - Mismatch repair - DNA double strand break repair

Question 34

Examples of tumour suppressor gene mutations - caretaker type

Answer 34

Xeroderma Pigmentosa Hereditary non-polyposis colon cancer Breast & Ovarian Cancer

Question 35

State a tumour suppressor genes that is both a caretaker and a gatekeeper

Answer 35

p53 p53 is widely mutated in a wide range of different tumours

Question 36

p53

Answer 36

tumour suppressor gene

Question 37

Li-Fraumeni family

Answer 37

Inherited mutation in p53 Predisposes them to a wide variety of cancers.

Question 38

What is a missense mutation ?

Answer 38

Amino acid substitution

Question 39

Result of a mutation in the p53 gene

Answer 39

Loss of function (normal function is tumour suppressor)

Question 40

Nature of p53 mutations

Answer 40

Sequence specific DNA binding

Question 41

What does p53 do ? | Four things

Answer 41

Stimulates: - Cell cycle arrest - DNA repair - Block of angiogenesis - Apoptosis

Question 42

What activates p53 ?

Answer 42

Cell damage - UV radiation - Lack of nucleotides - Hypoxia - Blockage of transcription

Question 43

Describe homeostatic / normal situations

Answer 43

Normal cell division Normal apoptosis

Question 44

Describe tumour formation situations

Answer 44

IN some either: - Increased cell division / normal apoptosis - Normal cell division / decreased apoptosis

Question 45

BCL2

Answer 45

Anti-apoptotic Inhibits cell death pathway

Question 46

Importance of BCL2

Answer 46

IN some instances, the genetics around BCL2 can be re-arranged as part of chromosome translocation. The wrong promotor can end up in front of BCL2, meaning BCL2 is over expressed. This results in lymphoma. (increased cell survival, decreased cell death)

Question 47

Key feature of tumour

Answer 47

Limitless replicative potential Telomerase can be active is tumours - associated with the worst prognosis

Question 47

Multi-Step model of carcinogenesis

Answer 47

Normal epithelium (tumour supressor gene (APC) lost) Excessive epithelial proliferation (Oncogene (Ras) activated) Small tumour (Another tumour suppressor gene lost) Large tumour (A 3rd tumour supressor gene (p53) lost) Tumour becomes invasive (rapid accumulation of mutations) Metastasis

Question 48

How can DNA be damaged ?

Answer 48

Chemicals Radiation Viruses

Question 49

Describe a chromosome

Answer 49

Ends of the chromosome (telomeric DNA) Body of chromosomal DNA ENDS - repeated many times to protect the ends of the chromosome and make sure it always remains a standard length.

Question 49

Angiogenesis Signalling Cascade

Answer 49

Cancer cell VEGF - vascular endothelial growth factor This factor sends a signal to endothelial cells stimulating growth of new blood vessels.

Question 50

Telomerase function

Answer 50

Recognises the telomeric DNA and maintains it at ideal lengths.

Question 51

When is telomerase expressed ?

Answer 51

Telomerase is highly expressed in dividing cells. In differentiated, somatic cells, telomerase is no longer expressed. So as cells undergo successive divisions, there becomes a crisis point where telomere DNA is so short that the chromosome becomes unstable.

Question 52

Endothelial cell activation

Answer 52

Activated endothelial cells Secretes MMPs that digest surrounding matrix Cell migrates and divides

Question 53

How do tumour cells go from being in a benign state to metastatic state ?

Answer 53

Cells grow as a being tumour in the epithelium. Cells become invasive, break through basement membrane and enter the capillary. They adhere to the blood vessel wall. Escape from the blood vessel to find a new home. Colonise that new home.

Question 54

Changes that occur leading to metastases

Answer 54

Tumour cells detach from each other because of reduced adhesiveness. Cells then attach to the basement membrane via the laminin receptors. Cells secrete proteolytic enzymes, including type IV collegenase and plasminogen activator. Degradation of the basement membrane and tumour cell migration follow.

Question 55

Easy stage of invasion and metastasis

Answer 55

Travel through circulation

Question 56

Difficult stages of invasion and metastases

Answer 56

Escape from parent tissue Colonisation of remote site

Question 57

'7 deadly sins' of tumour cells

Answer 57

Self-sufficiency in growth signals Insensitivity to growth-inhibitory signals Evasion of apoptosis Defects in DNA repair Limitless replicative potential Sustained angiogenesis Ability to invade and metastasise.