Mechanisms of Mutagenesis &
Carcinogenesis
Jamil Momand, Ph.D.
California State University at Los Angeles
Outline (in brief)
Introduction
Carcinogenesis - a definition
Pathways to cancer: overview
Oncogenes
Tumor suppressor genes
Apoptosis
Telomerase
Angiogenesis
Summary
Maintenance of homeostasis
Adult human maintains ~1015 cells
Stem cells undergo ~1012 divisions per
day
There is a balance between cell birth
and cell death
Random mutations disrupt homeostasis
Molecular basis for cancer
progression
DNA damage
Failure to repair damage
Failure to destroy cells with DNA damage
Mutation
Selection advantage
Example of DNA damage
From Bertram, Molecular Aspects of Medicine 21, 2001, 161-223
List of carcinogens
Chemical
Physical
Asbestos
Gamma radiation
Arsenic
UV light
Chromium
Radon
Polyaromatic
X-rays
hydocarbons
Viruses*
dichlorodiphenyltrichloroethane (DDT)
http://www.eur.nl/fgg/ch1/gen_research/dbr-man.html
Hereditary form of colon
cancer
Case 1:
Beth M.'s father died of colon cancer, as did her grandmother. Now
two of her brothers, both in their 40's, have been diagnosed with colon
cancer. Beth, age 37, feels a curse is hanging over her family and is
worried about her future and that of her children.
Case 2:
Paul C. was 35 when his doctor told him the grim news: he had
advanced colon cancer. As far as he knew, Paul had no family history
of the disease. But after checking, Paul learned that several aunts
and uncles had died of colon cancer at an early age.
Diagnosis:
hereditary nonpolyposis colorectal cancer (HNPCC)
Frequency:
1 in 6 colorectal cancer cases
Cause of the disease: hMLH1 or hMSH2 mutations. Genes responsible for DNA
mismatch repair
From Bertram, Molecular Aspects of Medicine 21, 2001, 161-223
Clonal Nature of Cancer
Cancers are composed of cells that
descended from a single cell.
Evidence 1: X-chromosome inactivation
Evidence 2: Ig genes in lymphomas and leukemias
are identically rearranged.
Multistage theory of cancer development (Armitage
and Doll, 1954)
http://www.hhmi.org/communic/annrep/research/regulate.htm
Viruses and cancer
Viruses account for 15% of all cancers
DNA viruses



Epstein-Barr virus
Human papilloma virus
Hepatitis B virus
RNA viruses



HIV-1
HTLV-1
HTLV-2
Protection
DNA Damage
Progression
Normal
Cell
Repair
Mutation
Cell cycle arrest
Proliferation
Initiatied
Cell
Apoptosis
Immortality
Chemotherapy
Radiation therapy
Mutator phenotype
Cancer
Cell
Angiogenesis
Mutations
Proliferation
Necrosis
Metastasis
Adapted from Bertram, Molecular Aspects of Medicine 21, 2001, 161-223
Definitions of terms
Amplification
Immortal
Oncogene
Point mutation
Proto-oncogene
Transformation
Translocation
DNA Amplification
c-myc translocation
DNA Methylation and
Demethylation-ways to control
expression of genes
Point mutation activation of Ras
Oncoprotein pathways
http://www.biocarta.com/pathfiles/pdgfPathway.asp
Her2/neu/erbB-2
This gene was discovered by three different
groups. That is why it has three different
names.
Its oncogene counterpart is v-erbB-2
Dr. Slamon (UCLA) described the role of
Her2/neu in breast cancer and ovarian cancer.
Overexpression, amplification, rare
translocations
No ligand is known
The Philadelphia Chromosome
BCR-ABL translocation and
expression
http://www.kent.k12.wa.us/staff/vhoward/apbio/oncogenes/brc-ablcartoon.gif
STI-571--an inhibitor of BCRABL function
http://www.blc.arizona.edu/courses/181gh/Lectures_WJG.01/cell_signaling.01/Applications.html
PET scanning to show efficacy of STI-571
on tumor metastasis
http://www.blc.arizona.edu/courses/181gh/Lectures_WJG.01/cell_signaling.01/Applications.html
Design of experiment to clone the first
human cellular oncogene (Shi et al., 1979)
What we have learned
Human cellular oncogenes are dominantacting genes that transform cells and cause
tumors in mice.
Activation-abnormality that results in higher
than normal level of biochemical activity.


Point mutation
Overexpression
Proto-oncogenes-The wild-type noncancerous form of the oncogene
How are oncogenes activated?
Point mutation-Eg. K-ras,
Amplification-Eg. N-myc, MDM2,
Her2/neu/ErbB2
Chromosome translocation-Eg. c-myc,
bcr-abl
Overexpression due to DNA
demethylation
Tumor suppressor genes
•Somatic cell hybrids
•Knudsen’s hypothesis
•Mutations and mechanisms that
lead to tumor suppressor gene
loss of function
•RB
•p53
Somatic cell hybrids
Transformed
Cell fusion
Normal
Harris et al., 1969
Normal
Genetics of Retinoblastoma
Pedigree of Rb-prone family
Alfred Knudson
Knudson’s hypothesis
Mechanisms of tumor
suppressor gene inactivation
Deletion
Point mutation
Mutation followed by duplication
Loss of heterozygosity
DNA methylation
Post-translational mechanism-binding to
DNA viral oncoproteins
Genetic mapping of Rb
susceptibility gene
RB function
http://p53.curie.fr/p53%20site%20version%202.0/p53%20in%20cancer/p53_databaseANAL.html
p53 mutation spectrum
p53 structure
p53 signal
transduction pathway
[MDM2/p53] complex
(transient)
degradation
p53 Latent
p53
Stabilization
1. MDM2
Transcription
DNA damage
Other p53 functions
2. GADD45
3. WAF1/CIP1
4.
5.
}
synthesis
n
DNA Repair
Cell cycle
arrest
Cell Death
Functional domains of BRCA1
Transcriptional
activation
Dimerization
Ring finger
NLS
Proteins that bind BRCA1:
BARD1
Rb
BAP1
p53
E2F1
Rad51
cMyc
Rad50
BRCA1 C-Term. domains
BRCA2
p300
RHA
RNA PolII
CREB binding protein
BRCA1
Mapped to chromosome 17q by Mary Clair King in
1990
Linkage was also found in ovarian cancer families.
More than 90% of women with germline BRCA1
mutations lose the wild-type allele in breast tumor.
The gene encodes a nuclear phosphoprotein of 220
kD (1863 aa’s)
The mRNA is 5711 bases long
24 exons, 22 of which is coding
BRCA1 (cont. 1)
BRCA1-deficient ES cells are hypersensitive to
oxidative reagents
BRCA1-deficient ES cells are defective in
transcription-coupled repair
Expression of BRCA1 leads to p21CIP1/WAF1
upregulation and G1-S cell cycle arrest (is this
through p53?)
BRCA1del11 maintain G1-S cell cycle arrest but not
G2-M arrest.
http://www.biocarta.com/pathfiles/atmPathway.asp
What have we learned about
tumor suppressor proteins?
Both alleles are deleted in the cancer
If one allele is mutated at birth then
patients have increased susceptibility to
cancer at an early age
They often serve as cell cycle
checkpoints or DNA repair activities
Apoptosis-programmed cell
death
BCL-2 is a protooncogene that gets overexpressed in
some B-cell leukemias
Other processes that affect
tumor formation and growth
Telomerase expression
Angiogenesis
The BIG picture-a molecular
analysis of mutations in
colorectal cancers
Correlation of tumor morphology to
specific allelic deletion
(Vogelstein et al., 1988)
Future studies-profiling
cancers with DNA arrays
http://cmgm.stanford.edu/pbrown/
http://www.pnas.org/cgi/content/full/241500798
Dilbert by Scott Adams
San Gabriel Valley Tribune, Sept. 10, 2000
References
Bertram, J.S. (2001) The molecular biology of cancer. Molecular
Aspects of Medicine 21, 167-223.
Gelehrter et al. Principles of Medical Genetics, 2nd ed. pp 245272, Williams & Wilkins, Baltimore, 1998.
Levine and Lane, (2000) Surfing the p53 network. Nature 408,
307-310
Angier, N., Natural Obsessions: Striving to Unlock the Deepest
Secrets of the Cancer Cell, Mariner Books/Houghton Mifflin Co,
1999.
Bazell,R., Her-2: The Making of Herceptin, a Revolutionary
Treatment for Breast Cancer, Crown Publishing Group, 1998.