Genes and Cancer Flashcards
What environmental factors that causes damage to DNA
Chemical substances (carcinogens of smoking)
Radiation (therapeutic, nuclear, atomic bomb survivors)
Viruses
-all associated with increased incidence of cancer
Cancer genetics
- Cancers are induced by mutations in cancer causing genes (therefore consider cancer as a genetic disorder)
- Acquired or somatic mutations in majority (cannot be inherited)
- In some cases the mutations may be inherited (familial cancers) - mendelian (familial breast/colorectal cancer) + susceptibility genes
Genes which cause cancer
Abnormal growth of tissue giving those cells a proliferative advantage
-Oncogenes
-Tumour Suppressor Genes
-Genes involved in regulation of apoptosis (cell death)
–>cells may not be reapidly proliferating, but impairment of normal death pathways
-Epigenetic changes
-Abnormalities of DNA repair genes
-Non coding RNA – e.g. microRNA (effect regulation of gene expression)
(mutations/changes in other pathways that contribute to development or progression of cancer)
Normal tissue: Homesostasis
Roads to Neoplasia: Proliferation –Neoplasia–> Death
Ongogenes
Dominant acting genes – transform cells
(requires a mutation of a single allelle in the oncogene only to transform cells to give growth/proliferative advantage)
Initially recognized in viral induced tumours
Normal state = proto–oncogene
-switched on when cells divide and then switched off (carefully regulated)
Activated by mutation to oncogene (able to transform a cell)
Proto-ongogene –Mutation–> Ongogene
Function of Oncogene
Most involved in signal transduction
- Growth factors
- Growth factor receptor (more common) (e.g. point mutation, causing it to be constitutively active in absence on ligand binding)
- Intracellular signal transmission
- Nuclear transcription factors
Hyperactive growth control pathway
Growth factor –> Receptor –> Scanning Enzymes –> Cell Nucleus –> Transcription factors –> DNA –> Excessive Cell Proliferation
Transform normal cells to neoplastic cells
Ongogenes transform Normal cells –> Neoplastic cell
-may grow independently of growth factors
Increased cell proliferation
Block normal cell differentiation/maturation
(malignant cells have increased proliferation but also immature (lack normal differentiation of epithelial cells)
Initiation event
Tumour progression
What are the 2 main features of Malignant cells
Increased Proliferation
Immature (lack normal differentiation of epithelial cells)
Diagram of activation of Oncogenes
Proto-oncogene —> (environmental) Cancer causing (UV light, chemicals etc) –> Oncogene –> Cancerous Phenotype
Activation of Oncogenes (molecular level changes)
- Gene amplification
- Over expression of gene (change promotor to make more mRNA and hence more Protein)
- Point mutations
(change critical base pairing, change a/acid, resulting in sig. change in function of proto-oncogene) - Chromosome Translocations
(swapping of chromosome material, and if involving proto-oncogene, can lead to activation to an oncogene)
Amplification of Onocogenes
- Neuroblastoma (paediatric tumour, will respond to chemo)
- N-myc amplification (nuclear transcriptional regulator of a number of critical genes)
- Unfavourable prognosis (amplification fo N-myc is a prognositc factor that carriers worse prognosis and would alter treatment if present)
- Increased gene copy number
FISH of Amplification of Oncogenes
DNA probe that binds to the neuroblastoma proto-oncogene
labelled with red fluorescent probe
let hybridise onto cells
looked at under fluorescent microscope
Amplification of N-myc proto-oncogene = multiple (more than 2) dots
-gives pathogenesis of tumour
-gives clinical info that alters therapy
HER-2 amplification in breast cancer
Red signal = HER-2 gene (on chromosome 17)
-look for its amplification on FISH study
Green signal = ch 17 centromere
Amplification = more than 2 genes
Clinical significance of HER-2 amplification
HER-2 is a proto-oncogene - it encodes for an epidermal growth factor receptor in mammary cells (ETFr)
The HER-2 protein is over-expressed in 30% of breast cancer patients.
In 90% of cases, this is due to amplification of the HER-2 gene (pathogenesis. not initiating event but important in progression)
HER-2 is a target for the antibody herceptin (targeted antibody therapy)
-important part of therapy with cytotoxic drugs
Where is the HER-2 gene located?
Chromosome 17
Clinical significance of HER-2 amplification Diagram
HER-2 Gene amplification in Breast Cancer (chromosome 17 (normal))
- -> HER-2 gene amplification, 20-30% of breast cancer patients
- -> Increased expression of HER-2 mRNA
- -> Increased expression of HER-2 protein
- -> Signals cels to proliferate, tumours more aggressive –> Breast cancer cell