1. Prof Greta Dreyer University of Pretoria
TUMOUR GENETICS
Prof Greta Dreyer
University of Pretoria

2. TOPICS
Oncogenesis Epigenetics Hereditary cancer syndromes Viral oncogenesis

3. Oncogenesis
Overview

4. CANCER IS… a cellular genetic disorder resulting from
derangement of physiological cell proliferation control
caused by an accumulation of damaging genetic changes
Development of cancer cells are due to: genome instability mutation and epigenetic changes

5. ONCOGENESIS AS A MULTISTEP PROCESS
Initiation = first genetic changes, neoplastic genotype to escape apoptosis
Promotion = stimulation by external factors to survive as cancer clone 
Progression = further changes to genome & micro-environment to expand and metastasize

6. “HALLMARKS OF CANCER” Sustaining growth signalling
Evading of growth suppression
Resisting cell death
Enabling immortality
Inducing angiogenesis
Activating invasion and metastasis
Acquired over time and accumulated during any of initiation, promotion or progression phases

7. EMERGING CONCEPTS Tumour promoting inflammation Adiponcosis Stem cells
aspirin
Adiponcosis
metformin
Stem cells
‘Tissue stem cells’ = origin of several cancers
‘Stem-ness’ =pluripotent cells
‘Cancer stem cells’ = first clone of tumour cells

8. EMERGING CONCEPTS Aging and cancer (Gerioncosis?)
Linked via sirtuin proteins 1 to 7 (Sirt 1-7)  
Adenoma/carcinoma sequence:
Endometriosis as monoclonal neoplastic benign disease
Pre-invasive intra-epithelial benign neoplastic lesion
Fallopian tube / pelvic peritoneum ? direct carcinogenesis

9. Cellular tumour genetics: sporadic oncogenesis
Viral oncogens
HPV, HHV8
Tumour suppressor genes
p53, DCC, pRB, PTEN, BRCA1/2
Proto-oncogenes & oncogenes
HER-2/neu, Bcl-2, K-ras, C-myc, PKB/Akt, p21
DNA repair genes
hMSH2,hMLH

10. CHANGES IN GENOME Chromosomal abnormalities Genetic changes
Epigenetic changes

11. Epigenetics
Principles

12. EPIGENETICS REFER TO… somatically heritable genetic information
not contained within the DNA base sequence
Epigenetics regulate gene expression in: cancer cells somatic cells and embryonic cells

13. EPIGENETICS CHANGES ARE INVOLVED IN …
gene silencing and aberrant gene expression
carcinogenesis without involving gene mutations
Epigenetic changes are: reversible, thus potential to re-express silenced genes via pharmaceutical agents

14. METHODS OF EPIGENETIC CHANGE
Changes in DNA methylation
Histone modification
Polycomb group
proteins
Post-transcription gene regulation by microRNA

15. DNA METHYLATION Un-methylated gene promotor sections allow
transcription of genes and
expression of protein product
Over- or undermethylation patterns allow
activation of usually silence genes
silencing of important genes

16. DNA METHYLATION
DNA is methylated to change transcription of large parts of genome
May be damaging to cell function
More frequent than mutations in the sequence of genomic DNA

17. HISTONES ARE… Core of eight histone proteins form an octamer
Together with DNA spiralled around it, it forms nucleosomes
These occur at intervals in DNA chain, forming chromatin

18. HISTONE MODIFICATION Modified to favour gene transcription or not
Happens via DNA methylation or hypermethylation
This silences cancer prevention genes and proteins

20. POLYCOMB GROUP PROTEINS ARE…
Group of proteins discovered in fruit flies
Large chromatin modifying complexes similar to histone
Remodel chromatin so that selective gene silencing takes place

21. MicroRNA or miRNA
Very important during embryogenesis and early development
850 mature human miRNA’s described
Fine-tune expression of protein to
influence cellular fate
develop a regulatory framework

22. MicroRNA or miRNA
Interacts by being incorporated into the RNA protein complex
Binds to complementary RNA target sequences
Degrades and/or block mRNA before transcription

23. Epigenetic patterns are reversible
Nuclear targets, thus:
small molecules
hydrophobic
Effect of both inhibitors:
Reactivation of silenced genes
Induced apoptosis
Enzyme classes that can be inhibited
DNA methyltransferases DNMT
Histone deacetylases
H-DACS

24. Implications for gynaecologic cancer treatment
Demethylation agents or DNMT-I are non-specific and can activate deleterious genes by demethylation
Multiple adverse effects seen
Permanent cell damage to normal cells
Long term side effects unknown
HDAC-I currently widely used in clinical trials in solid tumours and haematogenic neoplasias
Pre-clinical phase in EC:
HDAC-I, Valproic acid and TSA

25. Hereditary cancer syndromes
Related to gynaecology

26. Hereditary cancer syndromes - germline mutations
HBOC (Hereditary breast-ovarian cancer)
BRCA1 (17q12-21)
BRCA2 (13q12-13)
SSOC (Site-specific ovarian cancer)
BRCA1 large majority
HNPCC (Hereditary non-polyposis colon cancer)
6% ovarian and 30% endometrium Ca risk
MMR genes
hMSH2,hMLH1,hMLH6,hPMS1,hPMS2

27. Characteristic signs of hereditary breast/ovarian cancer syndrome
Multiple cases of breast and / or ovarian cancer
Early or pre-menopausal breast cancer
Bilateral breast cancer
Any single individual with both diseases
Male breast cancer

28. BRCA1 & 2 - genes, proteins, function
Tumour suppressor genes
BRCA1 on 17p; BRCA2 on 13q
brca1 and brca2 located in nucleus
brca1 and brca2 participate together in a pathway involved in DNA break repair

29. BRCA1 & 2 - involvement in familial br / ov cancer:
Germ-line mutations account for 40-80% of familial cases, 7-15% of all cancer cases
Risk for ovarian cancer at age 70 is mutation specific:
BRCA1 – 20-60%
BRCA2 – 10-40%
Risk for breast cancer at age 70 higher, about:
BRCA1 – 50-80%
BRCA %

30. BRCA1 & 2 – involvement in sporadic br / ov cancer:
Germ-line mutations = all cells
1-5% of sporadic cases
Possibly higher in tubal carcinoma and PSCP?
Higher in populations with high incidence of germ-line mutations
Somatic mutations = in tumour cells
Rare - 3 to 5%
BUT altered gene and protein expression found in vast majority of tumours

31. Viral oncogenesis and tumour genetics
Related to gynaecology

32. Viral oncogenesis: Human Papillomavirus
Tumors & cell lines needs HPV to be integrated into nucleus
Alpha 7: HPV16,31,33,35,39
Alpha 9: HPV18,45
Immortilizes keratinocytes
Causes aneuploid karyotype
E6 & E7 open reading frames code for 20K E7 protein
HPV 16 &18 has splice donor acceptor site in E6
ORF E6 lead to persistence of DNA

33. CONCLUSIONS Tumour genetics: an ever changing very exciting field
finally starting to offer treatment solutions to women with cancer

34. THANK YOU!