Investigating Cancer

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Investigating Cancer

• KRAS Activity

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What is cancer?

• All cancers derive from single cells that have
  acquired the characteristics of continually
  dividing in an unrestrained manner and invading
  surrounding tissues.
• Cancer cells behave in this abnormal manner
  because of changes in the DNA sequence of key
  genes, which are known as cancer genes. Therefore
  all cancers are genetic diseases.

Human melanoma cell undergoing cell
division Credit Paul Smith Rachel Errington,
Wellcome Images
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Cancer information

• One in three people in the Western world develop
  cancer and one in five die of the disease
• There are approximately 200 types of cancer, each
  with different causes, symptoms and treatments
• In 2007, 297,991 people were newly diagnosed with
  cancer in the UK
• An individual's risk of developing cancer depends
  on many factors, including age, lifestyle and
  genetic make-up

Cancer Research UK http//info.cancerresearchuk.or
g/cancerstats/incidence/?a5441
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The 20 most common causes of death from cancer,
UK, 2008
Cancer Research UK. Accessed July
2010 http//info.cancerresearchuk.org/cancerstats/
mortality/cancerdeaths /
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Cancer cells have altered genomes
Karyotype illustrating structural abnormalities
in cancer
Credit Mira Grigorova and Paul Edwards,
Department of Pathology, University of Cambridge,
unpublished Source www.path.cam.ac.uk/pawefish/B
reastCellLineDescriptions/HCC38.html
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What is a mutation?

• Germline mutation
• A change in the DNA sequence that can be
  inherited from either parent
• Somatic mutation
• A change in the DNA sequence in cells other than
  sperm or egg
• The mutation is present in the cancer cell and
  its offspring, but not in the patients healthy
  cells

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Mutations cancer genes

• Cancer genes are causally implicated in
  oncogenesis
• Mutations in cancer genes can occur somatically
  or can be inherited.
• Mutations in some cancer genes can be inherited
  from parents, in which case they are present in
  every cell of the body. Such people are at a
  higher risk of developing cancer.
• Somatic mutations can occur in any of the cells
  of the body except the germ cells (sperm and egg)
  and therefore are not passed on to children.

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Importance of somatic DNA changes in human cancer

• Only 5 10 of cancer cases have a clear
  hereditary component,
• e.g. BRCA1 and BRCA2 in breast cancer
• Even in those cases where susceptibility is
  clearly inherited, somatic changes are required
  for cancer to develop

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Cancer genes

• There are two types of cancer genes
• Tumour suppressor genes
• Oncogenes
• To date, we know of approximately 400 somatic
  cancer genes but there are almost certainly
  more to be found
• COSMIC is a catalogue of somatic mutations found
  in cancer genes in human tumours and is available
  at http//www.sanger.ac.uk/genetics/CGP/cosmic/
• (COSMIC v47release. July 2010)

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• Tumour suppressor gene

These genes normally function to PREVENT cell
growth/division
TS
Cancer
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• Oncogene

Genes which normally function to PROMOTE cell
growth/division in a controlled manner
Ras
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Examples of mutations
Sequence
1
Sequence 2
Type
ACTCGTTAGGCA
Substitution
ACTCCTTAGGCA
ACTCGTTAGGCA
ACTCGGCA
Deletion
ACTCGTTAGGCA
Insertion
ACTCGTTATCAGGCA
ACTCGTTAGGCA
Inversion
ACTTTGCAGGCA
ACTCGTTAGGCA
Duplication
ACTCGTTAGTTAGGCA
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• Cancer progression

• Mutations in multiple cancer genes are required
  for the development and progression of a single
  cancer

Benign Tumour
In situ cancer
Invasive cancer
Metastatic cancer
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External causes of cancer ultraviolet radiation
www. flickr.com lastexit
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External causes of cancer tobacco smoke
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Lifestyle factor diet
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Biological factor virus

• HPV is a cause of cervical cancer
• Proteins from the virus activate and deactivate
  cancer genes
• The role of HPV in cervical cancer has led to the
  development of vaccines

HPV in cervical epithelium Credit MRC NIMR,
Wellcome Images
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Activity

• The KRAS gene codes for a signalling molecule
• Mutations in KRAS are present in many cancers,
  including pancreatic cancer
• You have to look for the mutations by comparing
  healthy DNA sequence with tumour DNA sequence
• Not all of you will find a mutation

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Your Worksheets
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If you find a mutation
EXAMPLE ONLY
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How to use the codon wheel
Start from the centre and move outwards
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Mark up your sequence
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Heterozygous mutations
Normal DNA sequence
A double peak indicates a mutation on one
chromosome and not the other i.e. a heterozygous
mutation
A
DNA change in cancer
T ? A
BRAF gene mutation Nature 417, 906-7 (June 2002)
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Results
Amino
Acid
Healthy DNA
Tumour DNA
Healthy Amino
Tumour
Amino
Number
Sequence
Sequence
Acid
Acid
GGT
GTT
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G (glycine)
GGC
GAC
13
D
(aspartic
acid)
30
GAC
GAT
61
CAA
CGA
146
GCA
CCA
A (alanine)
P (proline)
173
GAT
GAC
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Significant mutations
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How common?
Source COSMIC July 2010
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RB1 tumour suppressor gene
Source COSMIC July 2010
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How does this affect the KRAS protein?
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Amino acid 12
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Amino acid 13
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Amino acid 61
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Amino acid 146
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Amino acid 146
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Whats the impact?

• KRAS helps to transmit external growth signals to
  the cell nucleus, driving normal cell growth. It
  is
• Activated when it binds GTP
• Inactivated or switched off when GTP is
  hydrolysed to GDP