Cancer as a Disease of Ageing

Question 1

What is above the basal lamina?

Answer 1

Basal cell layer

Question 2

What is above the basal cell layer?

Answer 2

Differentiating cells

Question 3

Describe the process of cancer formation

Answer 3

Basal layer cells over divide - invade differentiating cell layer above - dysplasia
Basal layer cells takeover differentiating cell layer - forms carcinoma
Basal layer cells invade connective tissue under basal lamina - forms malignant carcinoma
Malignant carcinoma invades capillaries - travels in blood - adheres to capillary walls in other tissues - escapes from capillary (extravasation) - proliferates - metastasis

Question 4

Name the 4 DNA repair methods

Answer 4

Base-excision repair
Nucleotide-excision repair
Recombinational repair
Mismatch repair

Question 5

What is base-excision repair?

Answer 5

Replacement of single incorrect base

Question 6

What is nucleotide-excision repair?

Answer 6

Replacement of incorrect nucleotide

Question 7

When is nucleotide-excision repair performed?

Answer 7

When DNA helical structure distorted by damage

Question 8

When is recombinational repair performed?

Answer 8

When double-strand break in DNA

Question 9

What are the consequences of severe DNA damage?

Answer 9

Senescence
Apoptosis - depletes stem cell pool - pro-ageing
Mutations - cancer, ageing

Question 10

Give an example of virus that can cause cancer

Answer 10

Sarcoma virus

Question 11

What is the normal structure of cells in a dish and what is the result of infecting them with sarcoma virus?

Answer 11

Normally form monolayer

After infection - become more rounded - duplicate - form cluster

Question 12

Give an example of a chemical agent that can cause cancer

Answer 12

Coal tar

Question 13

How can oncogenes be identified?

Answer 13

Inject DNA fragments into mouse fibroblasts - grow in dish
Cells containing oncogene form focus of morphologically-transformed cells
Inject focus cells into mice - form tumour

Question 14

Define a proto-oncogene

Answer 14

Non-transforming DNA sequence - with mutation could become oncogene

Question 15

Define an oncogene

Answer 15

Transforming version of same proto-oncogene DNA sequence

Question 16

How can the cancer-forming mutation in an oncogene be identified?

Answer 16

Transfect increasingly smaller fragments of oncogene into fibroblasts
Find region causing transformation
Sequence
Compare to proto-oncogene - identify mutation

Question 17

Which mutation types can cause a proto-oncogene to become an oncogene?

Answer 17

Point mutation
Oncogene amplification (CNV)
Translocations between chromosomes

Question 18

Name an example of a translation between chromosomes that causes a proto-oncogene to become an oncogene

Answer 18

Philadelphia transformation

Question 19

What is the Philadelphia transformation?

Answer 19

In chronic myelogenous leukemia
abl gene translocation from chromosome 9 to 22
BCR promoter now controls abl expression
Overexpression of fusion protein (BCR-abl) - tyrokine kinase
Drives cell division, inhibits DNA repair

Question 20

What are the multiple hits needed for transformed cell formation in colon carcinoma?

Answer 20

1st hit - APC mutation - tumour suppressor gene
2nd hit - RAS mutation
3rd hit - PI3K/TGF-beta mutation

Question 21

What do proto-oncogenes stimulate and what normally counterbalances this?

Answer 21

Growth

Counterbalanced by tumour suppressor genes

Question 22

How is it determined if a cancer allele is dominant/recessive?

Answer 22

Cell fusion experiment - fuse normal cell and cancer cells

2 possible products - hybrid cell tumorigenic (mutation dominant), hybrid cell non-tumorigenic (mutation recessive)

Question 23

What is Knudson’s two hit hypothesis?

Answer 23

Two hits needed for tumour development
In familial retinoblastoma - inherit one mutant allele - only one somatic mutation required - acquiring 2nd mutant allele easier - early onset
In sporadic retinoblastoma - must undergo 2 somatic mutations

Question 24

Is Knudson’s two hit hypothesis correct?

Answer 24

No - number of hits require depends on tumour type and specific mutations acquired

Question 25

What are microRNAs and how can they play a role in cancer?

Answer 25

Bind to 3’ UTR – inhibit mRNA translation | Dysregulated in cancer – downregulate tumour suppressor genes

Question 26

How can epigenetic mechanisms be involved in cancer?

Answer 26

CpG methylation of tumour suppressor genes – silence

Question 27

Name the cellular processes typically altered in cancer cells

Answer 27

``` Cell cycle Cellular signalling pathways for growth, differentiation, death – control cell number Cellular metabolism DNA repair Genomic stability Interaction with extracellular matrix and micro-environment Interaction with immune system Ability to metastasise ```

Question 28

How is the cell cycle altered in cancer cells?

Answer 28

Damaged cell continues division – causes cells with genomic instability

Question 29

How is DNA repair altered in cancer cells?

Answer 29

Impaired | Increases mutation rate – predisposes to cancer

Question 30

What is the effect of genomic instability in cancer cells?

Answer 30

Required for cancer cell growth

Question 31

What is the main method of ATP synthesis used by cancer cells and what is the impact of this?

Answer 31

Glycolysis | Use more glucose

Question 32

What are the products of glycolysis in cancer cells?

Answer 32

Less ATP | More cellular building blocks – enables increased cell division

Question 33

What does p53 enable?

Answer 33

Enables G1 arrest, DNA repair, senescence, apoptosis

Question 34

Mutation in which cell cycle regulator is common in cancer?

Answer 34

p53

Question 35

How is inflammation linked to cancer?

Answer 35

Chronic inflammation predisposes to cancer

Question 36

Mutations in which inflammation-related genes are linked to cancer?

Answer 36

Inflammatory cytokine genes

Question 37

What is intratumour heterogeneity and what is the impact on treatment aims?

Answer 37

Within tumour each region slightly different – different mutations Aim to treat common mutations – in all areas of tumour

Question 38

What are the hallmarks of cancer mutation effects?

Answer 38

``` Evade growth suppressors Avoid immune destruction Replicative immortality – by preventing telomere shortening Tumour-promoting inflammation Enable metastasis Induce angiogenesis – supply tumours with nutrients Cause genome mutation and instability Resist cell death Upregulated nutrient sensing Sustain proliferative signalling ```

Question 39

Name the hallmarks of ageing

Answer 39

``` Genomic instability Telomere shortening Epigenetic alterations Loss of proteostasis Deregulated nutrient sensing Mito dysfunction Cellular senescence Stem cell exhaustion ```

Question 40

How can ageing processes increase cancer risk?

Answer 40

Mutation accumulation Tissue microenvironment changes – increase risk of malignant cell growth Increased senescent cells Weaker immune system

Question 41

How do stem cells change with age?

Answer 41

Accumulate DNA damage – genomic instability

Question 42

What are the 2 possible outcomes of DNA damage in stem cells?

Answer 42

Additional mutations – forms cancer | Apoptosis/senescence – depletes stem cell pool – ageing/degenerative disease

Question 43

How could treatments to improve DNA repair help to prevent cancer and ageing?

Answer 43

Prevent stem cell damage accumulation

Question 44

What is the effect of p53 depletion in mice?

Answer 44

Increases cancer incidence | Shortest lifespan

Question 45

What is the effect of p53 truncation (hyperactivity) in mice and what does this suggest?

Answer 45

More cells sent to apoptosis – pro-ageing Intermediate lifespan Lowest cancer incidence Protection from cancer could be pro-ageing

Question 46

What is the effect of WT p53 in mice?

Answer 46

Intermediate cancer incidence | Longest lifespan

Question 47

What are super-p53 mice?

Answer 47

3 copies of p35 | Under endogenous promoter – not always active

Question 48

What are the characteristics of super-p53 mice and what does this suggest?

Answer 48

Normal ageing Protection from cancer Only more p53 when needed decreases cancer – without affecting lifespan – can have cancer and ageing protection

Question 49

What key trait do Daf-2 mutant C. elegans have?

Answer 49

Long-lived

Question 50

What is the effect of crossing Daf-2 mutant with ovarian cancer model C. elegans and what does this suggest?

Answer 50

Offspring protected from ovarian cancer – as Daf-2 sends cancer cells to apoptosis Mutation that increases lifespan also inhibits tumour growth

Question 51

What is the effect of dietary restriction in mice?

Answer 51

Extends lifespan | Prevents cancer

Question 52

Which type of cancer drugs also extends lifespan?

Answer 52

mTOR inhibitors

Question 53

Which drug extends C. elegans lifespan and prevents colon cancer?

Answer 53

Aspirin (anti-inflammatory)

Question 54

Why might aspirin not be a suitable drug to prevent ageing and cancer?

Answer 54

Increases bleeding risk

Question 55

Why does decreasing Myc expression extend mouse lifespan?

Answer 55

Can be increased Myc copies in cancer cells – Myc activates more oncogenes

Question 56

Which type of cancer drugs could also be anti-ageing drugs?

Answer 56

Drugs that inhibit growth pathways