Cancer Biology Flashcards
What is cancer?
Cancer: uncontroled g____ of the p____ of t_____- host cells
Melanoma: M_____ t___ that arises from u_____ p_____ of m______ (pigment producing cells)
What is cancer?
Cancer: uncontroled growth of the progeny of transformed host cells
Melanoma: Malignant tumour that arises from uncontrolled proliferation of melanocytes (pigment producing cells)
Cancer - Cells behaving badly
Normal somatic cells behave in a socialy responsible way to ensure survival of organism
Cancer cells behave selfishly
- accumulate mutations that allow them to
- avoid d______
- divide u______
- move throughout body at expense of ______-
Cancer - Cells behaving badly
Normal somatic cells behave in a socialy responsible way to ensure survival of organism
Cancer cells behave selfishly
- accumulate mutations that allow them to
- avoid death
- divide uncontrollably
- move throughout body at expense of neighbouring cells and whole organism
Benign vs Malignant Tumours
- not all tumours are invasive
Tumour - abnormal growth of tissye
Tumorigenesis - formation of tumours
Benign tumour:
- e.g. freckles and moles
- generally stop g___
- do not i___ other parts of body
- t___ m___ can still cause p____ (less freq) e.g. if impact nerve
- when removed generally d___ g___ b___
- malignant tumours can develop from benign tumours
Malignant tumours
- p____ e____
- i___ healthy tissues
- spread to other parts of the body (m____)
- d____ n____ bodily functions
- induce formation of new b___ v___ (a____) to obtain nutrients and O2 to e___ tumour growth
- can form from benign tumours
Benign tumour:
- e.g. freckles and moles
- generally stop growing
- do not invade other parts of body
- tumour mass can still cause pathology (less freq) e.g. if impact nerve
- when removed generally dont grow back
- malignant tumours can develop from benign tumours
Malignant tumours
- proliferate endlessly
- invade healthy tissues
- spread to other parts of the body (metastasis)
- disrupt normal bodily functions
- induce formation of new blood vessels (angiogenesis) to obtain nutrients and O2 to enhance tumour growth
- can form from benign tumours
Many different types of cancer
Classified based on:
Melanoma: cancer of p____ forming s___ cells (m____)
Many different types of cancer
Classified based on: cells/tissue origin
Melanoma: cancer of pigment forming skin cells (melanocyte)
Cancer - a genetic disease
Cancer is caused by genetic changes that affect gene expression or function
These genetic changes can be caused by:
- m____ e.g. due to ___damage
- c____ a____ e.g. translocation, gene amplification, deletion
- introduction of genes by v___
These genetic changes can be caused by:
- mutations e.g. due to DNA damage
- chromosomal abnormalities e.g. translocation, gene amplification, deletion
- introduction of genes by viruses
Cancer is linked to age
Cancer cells contain many s____ mutations
A single mutation is n__ e___ to change a normal cell into cancer cell
- Cancer cells require several a_____ mutations (takes years)
- number of mutations likely to increase with age
Cancer is linked to age
Cancer cells contain many somatic mutations
A single mutation is not enough to change a normal cell into cancer cell
- Cancer cells require several accumulated mutations (takes years)
- number of mutations likely to increase with age
Age and enhanced exposure to mutagens increases cancer incidence
Why?
- Ageing reduces t____ length, increases chance of f____ and c____ i____
- Ageing reduce ability to r___ ___ d____/e____
- Premature ageing syndromes have underlying genetic DNA repair defects
- Longer exposure to mutagens/risk factors increases risk e.g. smoking/UV light exposure
Age and enhanced exposure to mutagens increases cancer incidence
Why?
- Ageing reduces telomere length, increases chance of fusions and chromosomal instability
- Ageing reduce ability to repair DNA damage/errors
- Premature ageing syndromes have underlying genetic DNA repair defects
- Longer exposure to mutagens/risk factors increases risk e.g. smoking/UV light exposure
Cancer progresses from accumulated mutations (clonal evolution)
The transition of a normal cell to a canrcerous cell involves the accumulation of successive mutations
- First mutation might endow a cell with slight p____ a_____
- Second mutation might g___ e___ p____ and i___ t___ a___
- Third mutation may allow cells to i___ s____ t___ and m____ to distant tissue sites
- Cancer cells are characteristically g____ u____
Cancer progresses from accumulated mutations (clonal evolution)
The transition of a normal cell to a canrcerous cell involves the accumulation of successive mutations
- First mutation might endow a cell with slight proliferative advantage
- Second mutation might greatly enhance proliferation and influence tissue architecture
- Third mutation may allow cells to invade surrounding tissues and metastasise to distant tissue sites
- Cancer cells are characteristically genetically unstable
***cancer cells with 3 mutations have out-proliferated the other cells with fewer mutations and have now become the dominant cell type in the tumour mass
generating the genetic unstability requires the cancer to mutate to overcome the selective pressures of the envronment
Pathways of tumorigenesis
In normal tissues, net birth and death of cells is b____ i.e. at e____
Tumour formation (tumourigenesis) occurs when this balance is disturbed by:
- INCREASED ___
- DECREASED ____
Pathways of tumorigenesis
In normal tissues, net birth and death of cells is balanced i.e. at equilibrium
Tumour formation (tumourigenesis) occurs when this balance is disturbed by:
- INCREASED cell birth
- DECREASED cell death
Hallmarks of Cancer
- a multi-step process
Tumorigenesis
- resisting c___ d___
- sustaining p____ s___
- evading g___ s___
- enabling r___ i____
Metastasis
- Inducing a___
- activating i___and m____
Hallmarks of Cancer
- a multi-step process
Tumorigenesis
- resisting cell death
- sustaining proliferative signaling
- evading growth suppressors
- enabling replicative immortality
Metastasis
- Inducing angiogenesis
- activating invasion and metastasis
Metastasis
- S____ of cancer cells to s___ a__ from the p___ t___
- is what makes cancer such a serious disease
- Responsible for __% cancer-associated deaths
- very common in l___ s___ c___
Metastasis
- Spread of cancer cells to sites away from the primary tumour
- is what makes cancer such a serious disease
- Responsible for 90% cancer-associated deaths
- very common in late stage cancer
Hallmarks of Cancer -an update
Emerging hallmarks
- Deregulating c___ e___
- to feed the high rate of cancer cell p___
- via g___ i___ and m___
- Avoiding i___ d___
- via t___-p____ i____
- “i____e_____” and c___ selection
Hallmarks of Cancer -an update
Emerging hallmarks
- Deregulating cellular energetics
- to feed the high rate of cancer cell proliferation
- via genome instability and mutation
- Avoiding immune destruction
- via tumour-promoting inflammation
- “immunoediting” and clonal selection
Oncogene
- a gene that when mutated or expressed at h___ l___ helps turn a nomal cell into a cancer cell (this process is called t_____)
Proto-oncogene
- the normal form of the gene
- typically invovled in processes that p___ c___ p___ (i.e. d___), cell g___, or cell m____/i___
- well known examples include:
Oncogene
- a gene that when mutated or expressed at high level helps trurn a nomal cell into a cancer cell (this process is called transformation)
Proto-oncogene
- the normal form of the gene
- typically invovled in processes that promote cell proliferation (i.e. division), cell growth, or cell motility/invasivenss
- e.g. Ras, Myc, PI3K, B-Raf
Tumour suppressor gene (TSG)
- gene that acts to p___ a normal cell form turning into a cancer cell (also known as a__-o__)
- TSGs act by l__ c__ p___, promoting a__ (i.e. cell death), and c___ s___ or preventing m___
- Mutations in TSGs may lead to cancer, but one must lose b___ c___ of the gene (Knudson 2-hit theory)
- well known examples include:
Tumour suppressor gene (TSG)
- gene that acts to prevent a normal cell form turning into a cancer cell (also known as anti-oncogenes)
- TSGs act by limiting cell proliferation, promoting apoptosis (i.e. cell death), and cellular senescence or preventing metastasis
- Mutations in TSGs may lead to cancer, but one must lost both copies of the gene (Knudson 2-hit theory)
- well known examples include: p53, Rb, PTEN, ECadh
Normal cellular functions of Proto-oncogenes and TSGs
Proto-oncogene
Typical Examples
- g__ f___
- r__
- e__ e.g. k____
- t___ f___
Normal cellular roles
- ___ cell p___
- ___cell d___
- ___ a___ or s___
- ___ cell m___
Normal cellular functions of Proto-oncogenes and TSGs
Proto-oncogene
Typical Examples
- growth factors
- receptors
- enzymes e.g. kinases
- transcription factors
Normal cellular roles
- Promote cell proliferation
- inhibit cell differentiation
- inhibit apoptosis or senescence
- promote cell migration
Causative mutations to proto-oncogenes and TSGs
Oncogene
- O_____ mutation (___ of function)
- Promote cell transformation
- only need o___ c___ of proto-oncogene to be mutated in order to have effect on cell
TSG
- U____ mutation (___ of function)
- two i____ mutations
- loss of h___
- functionally e___ the TSG
- promote cell transformation
Causative mutations to proto-oncogenes and TSGs
Oncogene
- Overactivity mutation (gain of function)
- Promote cell transformation
- only need one copy of proto-oncogene to be mutated in order to have effect on cell
- 1 accelerator*
TSG
- Underactivity mutation (loss of function)
- two inactivating mutations
- loss of heterozygosity
- functionally eliminate the TSG
- promote cell transformation
- 2 brakes*
Pathways to oncogene activation
- D___ or p___ m___ in coding sequence
- H__ protein made in n___ amounts
- F__ mutation
- R___ mutation (in p__ region)
- n__ protein g__ o___
- I__ expression
- G__ a___
- N__l protein g__ o__
- I___ expression
- C___ r___
- n___ r__ DNA s___ causes n___ protein to be o___
- I__ expression
- F___ to a__ t___ g___ produces h___ f___ protein
- F___ mutation
- n___ r__ DNA s___ causes n___ protein to be o___
Pathways to oncogene activation
- Deletion or point mutation in coding sequence
- Hyperactive protein made in normal amounts
- Function mutation
- Regulatory mutation (in promoter region)
- normal protein greatly overproduced
- Increased expression
- Gene amplification
- Normal protein greatly overproduced
- Increased expression
- Chromosome rearrangement
- nearby regulatory DNA sequence causes normal protein to be overproduced
- Increased expression
- Fusion to actively transcribed gene produces hyperactive fusion protein
- Function mutation
- nearby regulatory DNA sequence causes normal protein to be overproduced
Pathways to oncogene activation
examples and recap
- Deletion or point mutation in coding sequence
- e.g. mutant G12V H-Ras
- Thyroid/bladder cancer
- e.g. mutant G12V H-Ras
- Regulatory mutation (in promoter region)
- Gene amplification
- ErbB2 amplification
- Breast cancer
- ErbB2 amplification
- Chromosome rearrangement
- Myc over-expression
- Burkitt’s lymphoma
- Bcr-Abl fusion protein
- Chronic myeloid leukaemia
- Myc over-expression
Pathways to oncogene activation
- Deletion or point mutation in coding sequence
- Hyperactive protein made in normal amounts
- Function mutation
- E.g. mutant G12V H-Ras
- Thyroid/bladder cancer
- E.g. mutant G12V H-Ras
- Regulatory mutation (in promoter region)
- normal protein greatly overproduced
- Increased expression
- Gene amplification
- Normal protein greatly overproduced
- Increased expression
- E.g. ErbB2 amplification
- Breast cancer
- E.g. ErbB2 amplification
- Chromosome rearrangement
- nearby regulatory DNA sequence causes normal protein to be overproduced
- Increased expression
- Myc over-expression
- Burkitt’s lymphoma
- Myc over-expression
- Increased expression
- Fusion to actively transcribed gene produces hyperactive fusion protein
- Function mutation
- Bcr-Abl fusion protein
- Chronic myeloid leukaemia
- Bcr-Abl fusion protein
- Function mutation
- nearby regulatory DNA sequence causes normal protein to be overproduced
Key oncogenic pathways in Melanoma
1) NRAS-BRAF-MEK-ERK pathway
- activated (mutated) in 70-80% melanoma PTs
- Downstream of Receptor Tyrosine Kinases (RTKs) e.g. KIT
How?
- BRAFV600E mutation (~80%)
- Results in c___ a____ Ser/Thr k___
- NRAS-i____
- then?
Key oncogenic pathways in Melanoma
NRAS-BRAF-MEK-ERK pathway
- activated (mutated) in 70-80% melanoma PTs
- Downstream of Receptor Tyrosine Kinases (RTKs) e.g. KIT
How?
- BRAFV600E mutation (~80%)
- Valine-glutamic acid mutation at position 600
- Results in constituently active Ser/Thr kinase
- NRAS-independent
- p-Mek
- p-ERK
- Cell growth and proliferation
Key oncogenic pathways in melanoma (2)
2) A___ NRAS mutations in codon 61 (~90% Q___/Q___ mutations)
- Disrupt ____ activity of NRAS, locking it in a____ c_____
- BRAF-MEK-ERK
- P__>A___>m___ pathways
- Activates both pathways leading to s___ c___ and i___ in gene expression responsible for p___
- BRAF and NRAS mutations and m___ e___ (dont occur in the same melanomas)
- ~70% of all melanomas
- 30% of driver mutations for melanoma not yet described
Key oncogenic pathways in melanoma (2)
2) Activating NRAS mutations in codon 61 (~90% Q61R/Q61K mutations)
- Disrupt GTPase activity of NRAS, locking it in active conformation
- BRAF-MEK-ERK
- PI3K>Atk>mTOR pathways
- Activates both pathways leading to signalling cascade and increase in gene expression responsible for proliferation
- BRAF and NRAS mutations and mutually exclusive (dont occur in the same melanomas)
- ~70% of all melanomas
- 30% of driver mutations for melanoma not yet described
Key oncogenic pathwyas in melanoma
3) KIT - R____ T___ K__ for s___ c__ f___ (SCF)
- Mutated in ~_% skin melanomas
- S__ activates
- Both pathways - recall
- S__ activates
Key oncogenic pathwyas in melanoma
3) KIT - Receptor Tyrosine Kinase for stem cell factor (SCF)
- Mutated in ~2% skin melanomas
- Simultaneously activates
- NRAS-BRAF-MEK-ERK
- PI3K>Atk>mTOR pathways
- Simultaneously activates
Receptor Tyrosine Kinases (RTKs) e.g. KIT
G___ f___ receptors
- activated by l____-i___ d___ and a____
Receptor Tyrosine Kinases (RTKs) e.g. KIT
Growth factor receptors
- activated by ligand-induced dimerization and autophosphorylation
KIT Receptor Tyrosine Kinase
Two major KIT oncogenic activating mechanisms in melanoma
- Point mutation
- L___P (exon 11)
- forces the d___
- K___E (exon 13)
- causes a__
- L___P (exon 11)
- Results in c___ a___ RTK i.e. l__ i__ s____ without s___ from SCF
- Result in g__ a__
KIT Receptor Tyrosine Kinase
Two major KIT oncogenic activating mechanisms in melanoma
- Point mutation
- L576P (exon 11)
- forces the dimerisation
- K642E (exon 13)
- causes autophosphorylation
- L576P (exon 11)
- Results in constitutively active RTK i.e. ligand independent signalling without stimulation from SCF
- Result in gene amplification
KIT/RAS/RAF/ERK Pathway and Therapeutic Targets in Melanoma
Summary slide
Note:
- CCND1>CDK4 are cell-cycle regulators
- MITF is also an oncogene
Note:
- CCND1>CDK4 are cell-cycle regulators
- MITF is also an oncogene
Micropthalmia-associated transcription factor (MITF)
- t____ factor
- p____ by ERK downstream of KIT/NRAS-BRAF-MAPK-ERK pathway
- Required for early melanocyte d___, c__ c___, s___ and m___
- Has different i___ depending on mRNA s___ and a___ p___
- MITF a____ observed in __% melanomas
- ‘_-___’ i___ serves as l___-s____ oncogene in >__% melanomas
Micropthalmia-associated transcription factor (MITF)
- transcription factor
- phosphorylated by ERK downstream of KIT/NRAS-BRAF-MAPK-ERK pathway
- Required for early melanocyte development, cell cycle, survival and metabolism
- Has different isoforms depending on mRNA splicing and alternative promoters
- MITF amplification observed in 20% melanomas
- ‘M-MITF’ isoform serves as lineage-survival oncogene in >80% melanomas
Key TSG pathways in Melanoma
- ___ negatively regulates NRAS
- ___ negatively regulates PI3K
Key TSG pathways in Melanoma
- NF1 (Neurofibromin 1) negatively regulates NRAS
- PTEN (Phosphataseand tensin homologue) negatively regulates PI3K>Atk>mTOR pathway
Neurofibromin 1 (NF1)
- N___ r____ of NRAS
- ‘G___ a___ p___ (GAP)’
- e___ NRAS G___ activity
- P___ c___ from ___ (active) to ___ (inactive)
- NF1 loss of function mutations lead to >NRAS-GTP and >MAPK-ERK activation
- defines ___ most common melanoma subtype after BRAF and NRAS
Neurofibromin 1 (NF1)
- Negative regulator of NRAS
- ‘GTPase activating protein (GAP)’
- enhances NRAS GTPase activity
- Promotes conversion from NRAS-GTP (active) to NRAS-GDP (inactive)
- NF1 loss of function mutations lead to >NRAS-GTP and >MAPK-ERK activation
- defines 3rd most common melanoma subtype after BRAF and NRAS
Phosphatase and tensin homologue (PTEN)
- PI3 Kinase (PI3K) downstream of RTKs p____ PIP2 + ATP > PIP3
- PIP3 required for m____ l____ and a____ of ATK
- PTEN _____ PIP3>PIP2+Pi (p____ s_____ via ___)
- PTEN d___ and i____ mutations found in melanoma, associated with e____ of i___ cells from t___
- Treatment with PI3K i___ e____ i_____
*PIP2 and PIP3 are m___ b___ p____
Phosphatase and tensin homologue (PTEN)
- PI3 Kinase (PI3K) downstream of RTKs promotes PIP2 + ATP > PIP3
- PIP3 required for mebrane localisation and activation of ATK
- PTEN de-phosphorylates PIP3>PIP2+Pi (prevents signalling via ATK)
- PTEN deletions and inactivating mutations found in melanoma associated with exclusion of immune cells from tumour
- Treatment with PI3K inhibitor enhanced immunotherapy
*PIP2 and PIP3 are membrane bound phospholipids
Overcoming Rb and p53 TSG function in Melanoma
Rb and p53 are key TSGs in preventing cancer, but if rarely mutated in melanoma - how are their TSG functions overcome in melanoma?
- Rb acts downstream of ___ pathway to prevent c__ c___ e___
- p53 is not downstream of ___ but can sense numerous t__-a____ s___ active in melanoma
Overcoming Rb and p53 TSG function in Melanoma
Rb and p53 are key TSGs in preventing cancer, but if rarely mutated in melanoma - how are their TSG functions overcome in melanoma?
- Rb acts downstream of NRAS-BRAF-MEK-ERK pathway to prevent cell cycle entry
- p53 is not downstream of NRAS-BRAF-MAPK-ERK but can sense numerous tumour-associated stresses active in melanoma
Overcoming Rb
1) Role of the cyclin D1-CDK4 oncogenic pathway in Melanoma
- Cyclin D1 binds CDK4 (and CDK6) to ____ Rb (pRb = _____)
- results in c___ c___ e___
- Cyclin D-CDK4-Rb pathway d___ in __% melanomas
- CCND1 (~10%) and CDK4 (~30%) genes a___ in melanoma
- CDK4 a____ m___ - h___ melanoma
Overcoming Rb
1) Role of the cyclin D1-CDK4 oncogenic pathway in Melanoma
- Cyclin D1 binds CDK4 (and CDK6) to phosphorylate Rb (pRb = inactive)
- results in cell cycle entry
- Cyclin D-CDK4-Rb pathway dysregulated in 90% melanomas
- CCND1 (~10%) and CDK4 (~30%) genes amplified in melanoma
- CDK4 activating mutations - heriditary melanoma
Overcoming Rb
2) Role of p16INK4A TSG in melanoma
- CDKN2A gives rise to two m____ encoding p16INK4A and p14ARF respectively
- p16INK4A TSG binds to ___ and d___ its k___ a___
- unable to p___ Rb
- allowing c___ c___ entry
- CDKN2A d___ and p16INK4A i____ m___ in melanoma
Overcoming Rb
2) Role of p16INK4A TSG in melanoma
- CDKN2A gives rise to two mRNAs encoding p16INK4A and p14ARF respectively
- p16INK4A TSG binds to CDK4 and downregulates its kinase activity
- unable to phosphorylate Rb
- allowing cell cycle entry
- CDKN2A deletions and p16INK4A inactivating mutations in melanoma
p53 is a c___ s___ s____
- activated by many tumour-associated stresses
- p53 is not downstream of ___ pathway but can sense numerous t___-a___ s____ active in melanoma
p53 is a cellular stress sensor
- activated by many tumour-associated stresses
- p53 is not downstream of NRAS-BRAF-MAPK-ERK pathway but can sense numerous tumour-associated stresses active in melanoma
Role of p53 and p14ARF TSGs in melanoma
- CDKN2A gives rise to two mRNAs encoding p16INK4A and p14ARF respectively
- MDM2 u___ p53 = marked for d____
- MDM2 important n___ r___ of p53 TSG function
- p14ARF b___/s___ MDM2 = unleashing p53 tumour suppressor function
- CDKN2A d___ and p14ARF i____mutations in melanoma
- CDKN2A i___ mutations = hereditary melanoma
Role of p53 and p14ARF TSGs in melanoma
- CDKN2A gives rise to two mRNAs encoding p16INK4A and p14ARF respectively
- MDM2 ubiquinates p53 = marked for degradation
- MDM2 important negative regulator of p53 TSG function
- p14ARF binds/sequesters MDM2 = unleashing p53 tumour suppressor function
- CDKN2A deletions and p14ARF inactivating mutations in melanoma
- CDKN2A inactivating mutations = hereditary melanoma
Overcoming Rb and p53 TSG pathways in Melanoma
- summary
- CDKN2A gives rise to p16INK4A and p14ARF mRNAs, which regulate Rb and p53 pathways respectively
- CDKN2A deletions and p16INK4A and p14ARF inactivating mutatons in melanoma
- CDKN2A inactivating mutations = hereditary melanoma
