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

TOPICS Oncogenesis Epigenetics Hereditary cancer syndromes Viral oncogenesis

Oncogenesis Overview

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

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

“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

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

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

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

CHANGES IN GENOME Chromosomal abnormalities Genetic changes Epigenetic changes

Epigenetics Principles

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

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

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

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

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

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

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

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

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

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

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

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

Hereditary cancer syndromes Related to gynaecology

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

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

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

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% BRCA2 - 50-80%

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

Viral oncogenesis and tumour genetics Related to gynaecology

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

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

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