Mechanisms of Mutagenesis & Carcinogenesis

1. Mechanisms of Mutagenesis & Carcinogenesis Jamil Momand, Ph.D. California State University at Los Angeles

2. Outline (in brief) • Introduction • Carcinogenesis - a definition • Pathways to cancer: overview • Oncogenes • Tumor suppressor genes • Apoptosis • Telomerase • Angiogenesis • Summary

4. 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

5. DNA damage Failure to repair damage Failure to destroy cells with DNA damage Mutation Molecular basis for cancer progression Selection advantage

6. Example of DNA damage From Bertram, Molecular Aspects of Medicine 21, 2001, 161-223

7. Chemical Asbestos Arsenic Chromium Polyaromatic hydocarbons dichlorodiphenyl-trichloroethane (DDT) Physical Gamma radiation UV light Radon X-rays Viruses* List of carcinogens

8. http://www.eur.nl/fgg/ch1/gen_research/dbr-man.html

9. 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

10. From Bertram, Molecular Aspects of Medicine 21, 2001, 161-223

11. 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)

12. http://www.hhmi.org/communic/annrep/research/regulate.htm

13. 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

15. DNA Damage Protection Repair Cell cycle arrest Apoptosis Necrosis Chemotherapy Radiation therapy Progression Mutation Proliferation Immortality Mutator phenotype Angiogenesis Metastasis Normal Cell Initiatied Cell Cancer Cell Proliferation Mutations Adapted from Bertram, Molecular Aspects of Medicine 21, 2001, 161-223

16. Amplification Immortal Oncogene Point mutation Proto-oncogene Transformation Translocation Definitions of terms

17. DNA Amplification

18. c-myc translocation

19. DNA Methylation and Demethylation-ways to control expression of genes

20. Point mutation activation of Ras

21. Oncoprotein pathways http://www.biocarta.com/pathfiles/pdgfPathway.asp

22. 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

24. The Philadelphia Chromosome

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

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

27. 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

28. Design of experiment to clone the first human cellular oncogene (Shi et al., 1979)

29. What we have learned • Human 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 mutation • Overexpression • Proto-oncogenes-The wild-type non-cancerous form of the oncogene

30. 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

31. Tumor suppressor genes • Somatic cell hybrids • Knudsen’s hypothesis • Mutations and mechanisms that • lead to tumor suppressor gene • loss of function • RB • p53

32. Somatic cell hybrids Transformed Cell fusion Normal Harris et al., 1969 Normal

33. Genetics of Retinoblastoma

34. Pedigree of Rb-prone family

35. Alfred Knudson

36. Knudson’s hypothesis

37. 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

39. Genetic mapping of Rb susceptibility gene

40. RB function

42. http://p53.curie.fr/p53%20site%20version%202.0/p53%20in%20cancer/p53_databaseANAL.htmlhttp://p53.curie.fr/p53%20site%20version%202.0/p53%20in%20cancer/p53_databaseANAL.html

43. p53 mutation spectrum

44. p53 structure

45. [MDM2/p53] complex (transient) degradation 1. MDM2 p53 Stabilization p53 Latent DNA Repair Transcription 2. GADD45 3. WAF1/CIP1 Cell cycle arrest 4. DNA damage } 5. Other p53 functions Cell Death synthesis n p53 signal transduction pathway

46. Functional domains of BRCA1 Transcriptional activation Dimerization BRCA1 C-Term. domains NLS Ring finger Proteins that bind BRCA1: BARD1 Rb BRCA2 p300 BAP1 p53 RHA E2F1 Rad51 RNA PolII cMyc Rad50 CREB binding protein

47. 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

48. 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.

49. http://www.biocarta.com/pathfiles/atmPathway.asp