Week 1 Flashcards
What is cancer
Uncontrolled growth of abnormal cells in a tissue, invasive and spreading
Origins of cancer- tumours arise from normal tissues
Majority of tumours originate from epithelial tissues
Benign and malignant tumours
Squamous cell carcinomas and adenocarcinomas
Other tumours arise from non-epithelial cells
Sarcomas- from mesenchymal cells
Leukaemias and lymphoid and myeloid tumours- from haematopoietic tissue and cells of immune system
Neuroectodermal tumours- cells from central and peripheral nervous system
Brain tumours- eg gliomas, neuroblastoma
Complexity of disease
“Microevolution” process leading to accumulation of 5-10 critical mutations requires many years
Cancer is a genetic disease:
Mutations causing cancer occur: in germline and in somatic cells
Mutations in different types of genes may initiate cancer
Genes that normally control:
-growth
-passing on of signals from outside the cell
-receptors across the cytoplasm to the nucleus
-programmed cell death (apoptosis)
-the cell cycle
-stemness
-the integrity of the genome- DNA repair
How do mutations arise
Copying errors during DNA replication
Spontaneous depurination
Exposure to different agents
-background ionising radiation
-UV light
-Tobacco products
Cancer is a monoclonal growth
Cancer quickly becomes heterogenous due to genetic instability of cancer cells masking monoclonal origin of this cell population
Cancer a disorder resulting from multiple genetic steps
Gate keeping mutation
Driver mutation
Progressive development of cancer- tumour progression
Tumour suppressor gene (protein)
Normal function- negative regulator of cell growth (prevents cell growth)
Even protein from one of the two alleles is enough to
Need to lose both alleles to lose suppressor effect
Oncogene
Positive regulator of cell growth- makes cells grow
Even when only one allele is mutated
Hallmarks of cancer
Sustaining proliferative signalling
Evading growth suppressors
Avoiding immune destruction
Enabling replicative immortality
Tumor promoting inflammation
Activating invasion and metastasis
Inducing or accessing vasculature
Genome instability and mutation
Resisting cell death
Deregulating cellular metabolism
Hallmark 1- self sufficiency in growth signals, sustaining proliferative signalling
Alterations of :
-extracellular growth signals
-transmembrane transducers of growth signals
-intracellular circuits that translate those signals
Hallmark 2- insensitivity to anti growth signals, evading growth suppression
Disruption of pRb (TSG) pathway- loss of control over progression from G1 into S phase
The central governor of growth and proliferation
Tyrosine kinase receptors, GPCRs, TGF-b receptors, integrins, nutrient status
—cell cycle clock
-enter into G0 quiescent state, enter into active cycle, programming of cell cycle phases
PRB serves as a guardian of the restriction point gate
G1 period during which cells are responsive to mitogenic GFs and to TGF-b
DNA damage checkpoint: entrance into S is blocked if genome is damaged
DNA damage checkpoint: DNA replication halted if genome is damaged
Entrance into M phase blocked if DNA replication not complete
Anaphase blocked if chromatids are not properly assembled on mitotic spindle
Hallmark 3 - evasion of apoptosis, resisting cell death
Loss or mutation of p53 (TSG)- proapoptotic regulator, disruptions in DNA repair
P53 activating signals and P53s downstream effects
Lack of nucleotides, UV radiation, ionising radiation, oncogene signalling, hypoxia, blockage of transcription.
P53
-cell cycle arrest (or senescence, return to proliferation) DNA repair, block of angiogenesis, apoptosis
Anti-apoptotic strategies used by cancer cells
Increase in activity or levels of anti-apoptotic proteins
Decrease in activity or levels of pro apoptotic proteins
Hallmark 4- limitless replicative potential, enabling replicative immortality
Circumvention of senescence and crisis
Increased expression and activity of telomerase
Replicative senescence could be causes by culture conditions
Proliferation of cultured cells is limited by the telomeres of their chromosomes, cancer cells can escape crisis by expressing telomerase
Hallmark 5- sustained angiogenesis, inducing angiogenesis
Angiogenic switch
Control of transcription of pro-angiogenic inducers
Downregulation of angiogenic inhibitors
Vasculature is important for growth and survival of normal and neoplastic cells
Hallmark 6- activating tissue invasion and metastasis
EMT- epithelial to mesenchymal transition
Changes in expression of adhesion receptors: Cadherins, integrins
Activation of extracellular proteases
The metastatic process
Primary tumour-> vascularisation-> detachment-> intravasation -> circulating tumour cell-> adhesion to blood vessel wall-> extravasation-> growth of secondary tumour
Hallmark 7- reprogramming energy metabolism
“Aerobic glycolysis” Warburg effect
Glycolytic switch
Links to activated oncogenes and mutant tumour suppressor genes
Hallmark 8- evading immune destruction
Disabling certain components of the immune system
Recruiting actively immunosuppressive inflammatory cells
Hallmarks of cancer further progress
Unlocking phenotypic plasticity:
-dedifferentiation
-blocked differentiation
-transdifferentiation
Nonmutational epigenetic reprogramming:
-microenvironmental mechanisms of epigenetic reprogramming
-epigenetic regulatory heterogeneity
-epigenetic regulation of the stromal cells in tumour microenvironment
Polymorphic microbiomes:
-modulating tumours in barrier tissues
-impact of intratumoural microbiota
Senescent cells
Environmental factors
Non genetic factors that increase incidence of certain cancers
Eg: diet, lifestyle choices, infectious disease, outdoor/indoor air pollution,water contaminants
Geographic variation in cancer incidence and death rates
Eg skin cancer very high in Australia compared to japan (155% RR)
2 factors contribute to this hereditary and environmental factors
Investigate variations in the incidence in cancers using migratory populations:
Compare incidence common cancers in Japanese populations in Osaka, migratory Japanese population in Hawaii, native Hawaiian Caucasian population
-stomach cancer very high in japan but with one generation of migration to Hawaii the Japanese population have a low incidence of stomach cancer
These examples show that hereditary factors contribute to the incidence of cancer but there are some outside factors that may increase/decrease incidence of cancer- environmental factors
Proportion of cancer deaths attributed to non genetic factors
Tobacco main contributor followed by diet
Alcohol, food additives, reproductive and sexual behaviour, occupation, pollution, medicine and medical procedures, geophysical factors, infection, unknown
Carcinogens- cancer causing agents
IARC carcinogen classifications
Carcinogens are characterised by their ability to cause cancer when they are applied to lab skin of mice
Many are mutagenic (mutagenesis may contribute to cancer and tumour progression)
IARC classification based on probability and possibility of causing cancer in humans
How do we assess harmful nature of certain carcinogens
Risk assessment to determine 3 factors
-potency: potential of a given amount of a substance to cause cancer
-type of exposure required to cause harm: it acute or prolonged exposure required and is it avoidable or unavoidable
-dose response: indicates what happens if some of the carcinogen is either removed or added