Cancer genetics Flashcards
What are cancer cells?
Cancers derived from mutated single cells that have acquired the characteristics of continually dividing in an unrestricted invasive manner into neighboring tissues.
Alterations in the DNA sequence of cancer gene attribute towards the abnormal manner of cancerous cells
All cancers result from changes in the DNA sequence of the genome
Genome within our cells are exposed to mutagens (UV radiation) and accumulates mistakes during replication
What is the probability of DNA polymerase incorrectly inserting bases?
1 in 10,000 bases
How many errors result per generation due to DNA polymerase incorrect base insertion?
2.5 x10^-8 per generation
How does a specific mutation alter the function of a critical gene, subsequently causing cancer?
Provides growth advantage to the cell, over-expression of oncogenes, tumor factor genes and inhibition of tumor suppressor genes, results in increased mitotic rate
How is a tumour formed from an over-proliferating cancer cell?
Increased mitotic rate causes tumor formation, causing it to invade surrounding tissues, leading to metastasis - secondary tumours
What is a benign tumour?
A mass of well-differentiated cells that grows slowly, and is capsulated, lacking the ability to invade neighboring tissue, unable to metastasized.
What is a malignant tumour?
A malignant tumor is not self-limited (evades apoptosis, causes angiogenesis), cells poorly differentiated; the ability to invade adjacent tissues and metastasis. Biopsy analyzed by a pathologist to determine tumor category
How many steps is carcinogenesis divided into?
Initiation
Promotion
Progression
What is the initiation step of carcinogenesis?
Irreversible genetic alteration (Tranversion, transitions or deletions in DNA)
What is the promotion stage of carcinogenesis?
Expression of the genome, mediated through promoter-receptor interactions
What is the progression stage of carcinogenesis?
Molecular targets during the stages of carcinogenesis include protooncogenes, cellular oncogenes, and tumor suppressor genes, alterations in both alleles of the latter found exclusively in the stage of progression.
How does cancer develop?
Begin due to the accumulation of mutation involving oncogenes, tumor suppressor genes, and DNA repair genes.
Which gene in colon cancer is a tumor suppressor?
APC
How does a defect in the tumor suppressor gene, APC lead to cancer?
It enables excessive cell proliferation. Proliferating cells tend to acquire mutations involving DNA repair genes other tumor suppressor genes (p53) or growth-related genes (K-ras)
What is the histology of cancer cells?
Abnormal, non-uniform variations in size and shape. Nucleus has a distorted appearance. Cancer cells have to distinguish histological features visible under the microscope. The nucleus is irregularly large, with cytoplasm abnormalities.
What is melanoma?
Consumption of epidermis, the spread of melanocytes (melanin-forming cells), nests of melanocytes with variable size and shape. Diagnosis of melanoma accurate with biopsy, and analyzed by a pathologist.
What is carcinoma?
Cancer arising from cells that cover the external and internal body surfaces. Lung, breast, and colon (epithelial)
What is a sarcoma?
Cancer arising from cells found in the supporting tissues of the body (bone, cartilage, fat, connective tissue and muscle)
What is lymphoma?
Cancers arising from lymph nodes and tissues associated with the immune system
What is leukemia?
Cancers of immature blood cells that proliferate in the bone marrow, with the tendency to accumulate in large number within the bloodstream
How many mutagens are approximately present within tobacco smoke?
60 mutagens
Which molecules typically cause G-T mutations?
Polycyclic aromatic hydrocarbons (PAH), and nicotine derived nitrosamines
How are heterocyclic amines and PAH formed?
Formed during the Maillard reaction at higher temperatures
Why are PAHs and heterocyclic amines cancerous?
Express DNA-damaging potential upon bioactivation through metabolism. Aryl-hydrocarbon receptor, a transcription factor activated by ligands (PAH), regulates metabolizing enzymes- enzymes cause carcinogenesis by processing the toxicants to reactive mutagen metabolites
What are exogenous factors?
induction events through lysogenic viruses can integrate genes into the host genome, alterations to the gene sequence of the genome can result in the expression of oncogenes
What are the genetic influences of cancer?
Hereditary alterations in genes can result in genetic predisposition to cancer
How many original hallmarks of cancer are there?
6
What are the 6 main hallmarks of cancer?
1) Sustaining proliferative signaling
2) Evading growth suppressors
3) Resisting cell death
4) Enabling replicative immortality
5) Inducing angiogenesis
6) Activating invasion & metastasis
How do cancer cells sustain proliferative signaling?
1) Self-synthesis of growth factor ligands - autocrine proliferative stimulation.
2)Transmit signals that signal normal cells within the supporting tumor-associated stroma, reciprocate by supplying cancer cells with growth factors.
3)Hyperresponseive to growth factors ligand, increased receptor proteins
Cancer cells re-regulate release of growth-promoting signals, signals are conveyed by growth factors that bind cell-surface (intracellular tyrosine kinase domains)
The latter proceeds to emit signals via branched intracellular signaling pathways that regulate progression through the cell cycle, as well as cell, growth
How do cancer cells evade growth suppressors?
1) Deactivation of tumor suppresor genes (Limit cell growth and proliferation)
2) Defects in the RB pathway permits cell proliferation. RB transduces growth-inhibitory signals. TP53 inputs from stress and abnormality sensors; the degree of damage to the genome is excessive. TP53 can halt cell–cycle progression. The sensation of irreparable damage can trigger apoptosis. This is circumvented
How do cancer cells resist cell death?
Loss of TP53 tumour suppressor function eliminates critical damage sensor from apoptosis-inducing circuitry
Tumours may increase expression of antiapoptotic regulators BD-2, BD-X or of survival signals (IGf 1.2)
What is the death ligand?
Fas ligand
What does the FAS ligand activate in terms of apoptosis?
Activates latent protease (capsizes 8 & 9) proceeds to initiate the cascade of proteolysis
What are the antiapoptotic regulators?
bd-2
bd-x
What are the pro-apoptotic factors?
Bax, Bim, Puma
How do cancer cells enable replicative immortality?
Normal cell lineages can only pass through a limited number of successive growth and division cycles.
Telomerase adds telomere repeat segments to ends of telomeric DNA, expressed in immortalized cells. Extension of telomeric DNA counters telomere erosion, resistance to senescence and apoptosis
What is the definition of senescence?
Irreversible non-proliferative state and crisis (cell death). Beyond the stage of the cell crisis cells exhibit unlimited replicative potential
What is the role of telomeres?
Telomeres are involved in the capability for unlimited proliferation.
Telomeres composed of multiple tendon hexanucleotide repeats shorten progressively in non-immortalized cells (losing ability to protect the ends of chromosomal DNAs). Length correlates with the number of successive cells generations
How do cells induce angiogenesis?
Tumours require sustenance in the form of nutrients and oxygen, as well as an ability to evacuate metabolic wastes and carbon dioxide. Tumor-associated neovasculature generated by angiogenesis.
Angiogenic switch activated during tumor progression causing vasculature to sprout new vessels to sustain neoplastic growths.
Angiogenic regulators include signaling proteins that bind to stimulatory cell-surface receptors displayed by vascular endothelial growth factors. These growth factors orchestrate new blood vessel growth.
Which molecule activated cell-cell adhesion? (Begins with E)
E-cadherin
What is the role performed by E-cadherins?
Forms adheren junction with adjacent epithelial cells, maintaining epithelial cell sheets. Increased expression of E-cadherin behaves as an antagonist of invasion and metastasis.
What happens to E-cadherin which causes intravasation of cancer cells?
Reduction of its expression through downregulation and mutations inactivation causes reduction in cell adhesion.
Enables for increased transit of cancer cells and intravasation
What are the four new hallmarks of cancer?
Deregulating cellular energetics
Avoiding immune destruction
Genome instability and mutation
Tumor promoting inflammation
Which antigens are released by tumour cells?
Tumour antigens
How are cancer cells eliminated by T cells?
Tumor antigens bind to antigen-presenting cels, through antigen presentation, naive T cells via TCRs bind to the presented antigen, and are activated. Activated T cells target and eliminate cancer cells
Which proteins downregulate and suppress T cells, promoting self-tolerance?
Programmed cell death protein 1 (PD-1) and C279, proteins on cell surface membrane that has a role in regulation in the immune system’s response to the cells of the human body by downregulating the immune system
What happens during checkpoint pathways in terms of PD-1?
PD-1 is activated, negative signals are transmitted to the T-cell, prevents an attack