Investigating Cancer
KRAS Activity
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
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.org/cancerstats/incidence/?a=5441
The 20 most common causes of
death from cancer, UK, 2008
Cancer Research UK. Accessed July 2010
http://info.cancerresearchuk.org/cancerstats/mortality/cancerdeaths /
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Credit : Mira Grigorova and Paul Edwards, Department of Pathology, University of Cambridge, unpublished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/BreastCellLineDescriptions/HCC38.html
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 patient’s healthy cells
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.
Importance of somatic DNA
changes in human cancer
Both
Inherited
Somatic
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
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)
Tumour suppressor gene
These genes normally function to PREVENT
cell growth/division
TS
Cancer
Oncogene
Genes which normally function to PROMOTE cell
growth/division in a controlled manner
Ras
Cancer
Examples of mutations
Sequence 1
ACTCGTTAGGCA
ACTCGTTAGGCA
Sequence 2
ACTCCTTAGGCA
ACTCGGCA
Type
Substitution
Deletion
ACTCGTTAGGCA
ACTCGTTATCAGGCA
Insertion
ACTCGTTAGGCA
ACTTTGCAGGCA
Inversion
ACTCGTTAGGCA
ACTCGTTAGTTAGGCA
Duplication
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
External causes of cancer:
ultraviolet radiation
www.flickr.com: lastexit
External causes of cancer:
tobacco smoke
Lifestyle factor: diet
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
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
Your Worksheets
If you find a mutation
How to use the codon wheel
Start from the centre
and move outwards
Mark up your sequence
Heterozygous mutations
Normal DNA
sequence
A
DNA change
in cancer
T→ A
BRAF gene mutation Nature 417, 906-7 (June 2002)
A double peak
indicates a mutation
on one chromosome
and not the other i.e.
a heterozygous
mutation
Results
Amino Acid
Number
Healthy DNA
Sequence
Tumour DNA
Sequence
Healthy Amino
Acid
Tumour Amino
Acid
12
GGT
GTT
G (glycine)
V (valine)
13
GGC
GAC
G (glycine)
D (aspartic acid)
30
GAC
GAT
D (aspartic acid) D (aspartic
(Aspartic acid)
acid)
61
CAA
CGA
Q (glutamine)
R (arginine)
146
GCA
CCA
A (alanine)
P (proline)
173
GAT
GAC
D (aspartic
(Aspartic acid)
acid) D (aspartic
(Asparticacid)
acid)
Significant mutations
Amino Acid
Number
Healthy DNA
Sequence
Tumour DNA
Sequence
Healthy Amino
Acid
Tumour Amino
Acid
12
GGT
GTT
G (glycine)
V (valine)
13
GGC
GAC
G (glycine)
D (asparatic
61
CAA
CGA
Q (glutamine)
R (arginine)
146
GCA
CCA
A (alanine)
P (proline)
acid)
How common?
AA 12
13,894
AA 13
2,111
AA 61
212
AA 146
33
Source: COSMIC July 2010
RB1: tumour suppressor gene
Source: COSMIC July 2010
How does this affect the
KRAS protein?
Amino acid 12
Amino acid 13
Amino acid 61
Amino acid 146
Amino acid 146
What’s 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