Mechanisms of Mutagenesis & CarcinogenesisJamil Momand, Ph.D.California State University at Los Angeles

Outline (in brief)Introduction Carcinogenesis - a definitionPathways to cancer: overviewOncogenesTumor suppressor genesApoptosisTelomeraseAngiogenesisSummary

Maintenance of homeostasisAdult human maintains ~1015 cellsStem cells undergo ~1012 divisions per dayThere is a balance between cell birth and cell deathRandom mutations disrupt homeostasis

Molecular basis for cancer progressionSelection advantage

Example of DNA damageFrom Bertram, Molecular Aspects of Medicine 21, 2001, 161-223

List of carcinogensChemicalAsbestosArsenicChromiumPolyaromatic hydocarbonsdichlorodiphenyl-trichloroethane (DDT)

PhysicalGamma radiationUV lightRadonX-raysViruses*

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 casesCause 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 cancerViruses account for 15% of all cancersDNA virusesEpstein-Barr virusHuman papilloma virusHepatitis B virusRNA virusesHIV-1HTLV-1HTLV-2

Adapted from Bertram, Molecular Aspects of Medicine 21, 2001, 161-223

Definitions of termsAmplificationImmortalOncogenePoint mutationProto-oncogeneTransformationTranslocation

DNA Amplification

c-myc translocation

DNA Methylation and Demethylation-ways to control expression of genes

Point mutation activation of Ras

http://www.biocarta.com/pathfiles/pdgfPathway.aspOncoprotein pathways

Her2/neu/erbB-2This gene was discovered by three different groups. That is why it has three different names.Its oncogene counterpart is v-erbB-2Dr. Slamon (UCLA) described the role of Her2/neu in breast cancer and ovarian cancer.Overexpression, amplification, rare translocationsNo ligand is known

The Philadelphia Chromosome

BCR-ABL translocation and expressionhttp://www.kent.k12.wa.us/staff/vhoward/apbio/oncogenes/brc-ablcartoon.gif

STI-571--an inhibitor of BCR-ABL functionhttp://www.blc.arizona.edu/courses/181gh/Lectures_WJG.01/cell_signaling.01/Applications.html

PET scanning to show efficacy of STI-571 on tumor metastasishttp://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 learnedHuman cellular oncogenes are dominant-acting genes that transform cells and cause tumors in mice. Activation-abnormality that results in higher than normal level of biochemical activity.Point mutationOverexpressionProto-oncogenes-The wild-type non-cancerous form of the oncogene

How are oncogenes activated?Point mutation-Eg. K-ras, Amplification-Eg. N-myc, MDM2, Her2/neu/ErbB2Chromosome translocation-Eg. c-myc, bcr-ablOverexpression due to DNA demethylation

Tumor suppressor genesSomatic cell hybridsKnudsens hypothesisMutations and mechanisms thatlead to tumor suppressor gene loss of functionRBp53

Somatic cell hybridsHarris et al., 1969TransformedNormalNormalCell fusion

Genetics of Retinoblastoma

Pedigree of Rb-prone family

Alfred Knudson

Knudsons hypothesis

Mechanisms of tumor suppressor gene inactivationDeletionPoint mutationMutation followed by duplicationLoss of heterozygosityDNA methylationPost-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 signaltransduction pathway

Functional domains of BRCA1Ring fingerDimerizationNLSTranscriptionalactivationProteins that bind BRCA1:BARD1RbBRCA2p300BAP1p53RHAE2F1Rad51RNA PolIIcMycRad50CREB binding proteinBRCA1 C-Term. domains

BRCA1Mapped to chromosome 17q by Mary Clair King in 1990Linkage 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 aas)The mRNA is 5711 bases long24 exons, 22 of which is coding

BRCA1 (cont. 1)BRCA1-deficient ES cells are hypersensitive to oxidative reagentsBRCA1-deficient ES cells are defective in transcription-coupled repairExpression 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 cancerIf one allele is mutated at birth then patients have increased susceptibility to cancer at an early ageThey often serve as cell cycle checkpoints or DNA repair activities

Apoptosis-programmed cell death

BCL-2 is a protooncogene that gets overexpressed insome B-cell leukemias

Other processes that affect tumor formation and growthTelomerase expressionAngiogenesis

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 arrayshttp://cmgm.stanford.edu/pbrown/

http://www.pnas.org/cgi/content/full/241500798

Dilbert by Scott AdamsSan Gabriel Valley Tribune, Sept. 10, 2000

ReferencesBertram, 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 245-272, Williams & Wilkins, Baltimore, 1998.Levine and Lane, (2000) Surfing the p53 network. Nature 408, 307-310Angier, 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.

Fig. 2. Squamous, small cell, and large cell lung tumors express a unique set of genes. (A) Hierarchical clustering sorted 918 cDNA clones and 73 lung tissues based on similarity in gene expression. Gene clusters relevant to lung tumor types were extracted from the larger cluster of 918 clones in the regions indicated by the colored bars and expanded on the right to include gene names. A row in the cluster indicates expression of a specific gene across all 73 lung tissues. A column indicates the tissue in which the gene is expressed. Red, green, and black squares indicate that expression of the gene is greater than, less than, or equal to the median level of expression across all 73 lung tissues, respectively. Gray represents missing or poor quality data. (B) (Top) Gene clusters relevant to large cell tumors (blue bar). (Middle) Gene clusters relevant to small cell tumors (yellow bar). (Bottom) Gene clusters relevant to squamous lung tumors (red bar). The scale bar reflects the fold increase (red) or decrease (green) for any given gene relative to the median level of expression across all samples.