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MBD > Mechanisms Of Oncogenesis > Flashcards

Mechanisms Of Oncogenesis Flashcards

1
Q

What hallmarks define cancer?

A

A group of diseases characterised by:

  • Abnormal cell proliferation
  • Tumour formation
  • Invasion of neighbouring normal tissue
  • Metastasis to form new tumours at distant sites
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2
Q

What are the 3 main types of cancer?

A
  • Carcinomas
  • Sarcomas
  • Adenocarcinomas
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3
Q

Where do carcinomas originate?

A

Epithelial cells

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4
Q

What is a sarcoma?

A

Cancers from mesoderm (bone and muscle) cells

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5
Q

Where do adenosarcomas originate from?

A

Glandular tissue

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6
Q

What are the (many!) hallmarks of cancer?

A
  • Evading growth supressors
  • Avoiding immune destruction
  • Enabling replicative immortality
  • Tumour-promoting inflammation
  • Activating invasion and mutation
  • Resisting cell death
  • Deregulating cellular energetics
  • Sustaining proliferative signalling
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7
Q

Why is cancer more prevelant the older you get?

A

Longer you live the more time there is for DNA to accumulate mutations that may lead to cancer

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8
Q

What is a germline mutation?

A

A mutation in a gamete (egg or sperm cell) means that you can pass on that mutation that may predispose someone to cancer, but majority of mutations are in somatic cells

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9
Q

What do germline carcinogenic mutations cause?

A

An increased risk of developing cancer

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10
Q

Explain why tumorigenesis is initially defined as ‘clonal’

A

As a mutation in a somatic cell will be spread to its daughter cells initially via mitosis, these cells may continue to mutate and become heterogeneous

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11
Q

In what 2 biological processes can mutations lead to tumorigenesis?

A
  • Proliferation pathways
  • Apoptosis pathways
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12
Q

What is cell proliferation caused by?

A
  • Growth factors
  • Cytokines
  • Hormones
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13
Q

What growth factors are cell proliferation caused by?

A
  • EGF
  • PDGF
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14
Q

What cytokines are cell proliferation caused by?

A

Growth hormones, interleukin

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15
Q

What are proto-onco genes?

A

Normal genes that can be activated to become oncogenes

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16
Q

What are oncogenes?

A

Proto-oncogenes that have been mutated in a way that leads to signals that cause uncontrolled growth

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17
Q

What do tumour supressor genes do?

A

Inhibit both growth and tumour formation

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18
Q

When do tumour supressor genes act?

A

In phase G1 of the cell cycle

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19
Q

Describe how carcinogens may lead to tumorigenesis

A

Carcinogens can cause mutations, if mutations are not repaired then there can be an accumulation of irreversible DNA damage

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20
Q

What are the three assumptions that multistage carcinogenesis relies on?

A
  • Malignant transformation of a single cell is sufficient to give rise to a tumour
  • Any cell in a tissue is likely to be transformed as any other of the same type
  • Once a malignant cell is generated the mean time to tumour detection is generally constant
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21
Q

What are the names of the 5 models of carcinogenesis?

A
  • Chemical carcinogens
  • Genome instability
  • Non-genotoxic
  • Darwinian
  • Tissue organisation
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22
Q

What is the chemical carcinogen model of carcinogenesis?

A

Chemicals can alter initiation, promotion and progression to induce their carcinogenic effects

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23
Q

What is knudsons hypothesis for hereditary cancers based on?

A

Two-hit hypothesis

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24
Q

What is the two hit hypothesis?

A

At least two events are necessary for carcinogenesis and the cell with the first event must survive in the tissue long enough to sustain a second event

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25
Q

What are non-genotoxic modulators of risk?

A

Don’t seem to act through a structural change in DNA but rather through functional changes including epigenetic events

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26
Q

What is the mutation and selection model of clonal expansion?

A
  • Sequential accumulation of mutations due to carcinogen exposure
  • Tumour cells selected for ability to grow and invade
  • Selection includes resistance to therapy
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27
Q

What is the somatic mutation theory?

A

Cancer comes from a single somatic cell that has accumulated multiple DNA mutations

28
Q

What is meant by model 5, the ‘tissue organisation’ model?

A

One of our theories (somatic mutation theory) states that there is one catastrophic event (mutation) that causes the cancer.

But we also have the tissue organisation field theory (TOFT) that states that carcinogenesis is a problem of tissue organisation as carcinogenic agents destroy normal tissue architecture so this disrupts cell-cell signaling which can compromise the genomic integrity - so DNA mutations are the effect, not the cause, of tissue-level events

  • so carcinogenesis is a deterioration of tissue organisation microenvironment due to extracellular causes
29
Q

What are the classes of carcinogens?

A
  • Chemical
  • Physical
  • Heritable
  • Viral
30
Q

What are some examples of chemical carcinogens?

A
  • Polycyclic aromatic hydrocarbons
  • Aromatic amines
  • Nitrosamines
  • Alkylating agents
  • Carbamates
  • Halogenated compounds
  • Azo dyes
31
Q

Of the 10 chemical carcinogen groups, 4 groups work in a specific way to cause cancer - how is this?

A

The 4 groups below work by altering the bases of the DNA by adding functional groups to the DNA called DNA adducts.

  • Aromatic hydrocarbons
  • Aromatic amines
  • Nitrosamines
  • Alkylating agents
32
Q

What are examples of physical carcinogens?

A

Radiation and asbestos

33
Q

What are some viral carcinogens?

A
  • Hepatitis B
  • Epstein Barr
34
Q

How can we test that a chemical is carcinogenic?

A

By doing the Ames test (a test to determine the mutagenic activity of chemicals)

35
Q

What is the ames test?

A

Test to determine the mutagenic activity of chemicals by observing whether they cause mutations in sample bacteria

36
Q

What is the ames test method?

A
  • Add rat liver extract to a salmonella strain that requires histidine
  • Add a possible mutagen and spread over an agar plate that lacks histidine
37
Q

In the ames test, what will happen if a mutagen is present?

A

Lots of colonies that have grown even in the absence of histidine

38
Q

How do physical carcinogens work?

A

Act by imparting energy into biological material and altering bonding of molecules

39
Q

What is the primary physical agent?

A

Radiation

40
Q

What does UV Radiation do to DNA?

A

It causes pyrimidine dimers and DNA breaks which can be repaired but if you have a mutation in DNA repair mechanisms then this results in translocations and mutations.

41
Q

What are heritable carcinogens generally?

A

Monogenic (mutation of a single gene)

42
Q

What does a deficiency in DNA repair cause?

A

More DNA damages to occur → increased risk for cancer

43
Q

What type of genes are mutated in heritable carcinogens?

A

Genes involved in controlling function of the cell cycle or the repair of DNA damage

44
Q

What DNA repair defect syndromes predispose you to cancer?

A
  • Ataxia telangiectasia
  • Blooms syndrome
  • Fanconis anaemia
  • Li-fraumeni syndrome
  • Lynch type II
  • Xeroderma pigmentosum
45
Q

What chromosomal abnormality syndromes predispose you to cancer?

A
  • Downs syndrome
  • Klinefelters syndrome
46
Q

What is the mutated gene (and what does it code for) in ataxia telangiectasia?

A
  • ATM gene
  • Codes for a serine/threonine kinase that is recruited and activated by dsDNA breaks leading to cell cycle arrest, DNA repair and apoptosis
47
Q

What is ataxia telangiectasia?

A

A disorder of neuromotor function and dilation of blood vessels

48
Q

What types of cancer does ataxia telangiectasia predispose you to?

A
  • Lymphoma
  • Leukaemia
  • Breast cancer
49
Q

What does blooms syndrome cause?

A

Short stature and skin rash after sun exposure

50
Q

What gene is mutated in blooms syndrome (and what does it code for)?

A
  • BLM gene
  • Codes for a member of the RecQ helicase family that helps maintain the structure and integrity of DNA
51
Q

What types of cancer does blooms syndrome predispose you to?

A
  • Skin cancer
  • Basal cell carcinoma
  • Squamous cell carcinoma
52
Q

What are the mutations that cause lynch type?

A
  • MLH1
  • MSH2
  • MSH6
  • PMS2
53
Q

What does lynch type predispose you to?

A

Colorectal cancer

54
Q

What are the properties of tumour-genic viruses?

A
  • Stable association with cells
  • Not kill cells
  • Evade immune surveillance of infected cells
55
Q

How can viruses have a stable association with cells?

A

Chromosomal integration and changes in the epigenomes

56
Q

How do viruses not kill cells?

A

Suppress the viral lytic cycle

57
Q

How do viruses evade the immune surveillance of infected cells?

A

Immune supression and viral antigens not being expressed at cell surface

58
Q

What cancer does epstein-barr virus cause?

A

Burkits lymphoma

59
Q

What cancer does papilloma virus cause?

A

Cervical carcinoma

60
Q

What cancer does hepatitis B and C virus cause?

A

Hepatoma

61
Q

What cancer does HTLV-1 virus cause?

A
  • Adult T-cell leukaemia
  • Lymphoma
62
Q

What are the three Es of cancer immunoediting?

A

Elimination, equilibrium and escape

63
Q

Roughly what % of cancer is caused by heritable carcinogens (predisposition)?

A

Only 5%

64
Q

Explain how heritable carcinogens cause cancer

A
  • An inherited germline mutation (from a mutation in one of the gametes that formed you) causes increased risk of causing cancer, but rarely involved in causing cancer immediately.
  • Usually the elevated cancer risk is due to mutation of a single gene which usually has a function in the cell cycle or DNA repair
65
Q

Explain how viruses can cause cancer

A
  • Cancer is most likely to occur in later stages of infection as viruses will show a more restricted pattern of gene expression including oncogenes that the virus has.
  • Virus drives expression of genes that cause transformation of cell.
66
Q

Explain what is meant by the ‘non genotoxic’ (third) model of oncogenesis

A

This is characterised by no structural change to DNA, but functional changes

  • can be due to modulators of cancer risk such as obesity, diet, hormones and insulin resistance

However, there are carcinogens that induce cancer via non genotoxic mechanisms also

67
Q

What is meant by model 4, the ‘Darwinian’ model?

A
  • This is stating that as a tumour progresses, it accumulates more mutations which cause it to become heterogenous.
  • This means that within the tumour, natural selection occurs where more advantageous cell lines outcompete others.
  • Mutations may be positive or deleterious to the tumour

MBD (23 decks)

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