Malignancy hallmarks - Robyns Chapter 7 Flashcards
What is MSI and how does it relate to dMMR
Microsatellite instability is a genetic result of deficient mismatch repair. Tandem repeats of nucleotides throughout the genome become variable in length as opposed to being very constant where mismatch repair is normal.
Ie, dMMR can be tested by:
-IHC testing for abnormal levels of key mmr proteins
-molecular testing to detect downstream MSI
Robyns pg 314
Define constitutive activation
Mutation leads for a pathway to be in an activated state without any need for its usual activating factor, and resistant to down regulating signals.
Pg 284
Define tumour suppressor gene
A gene which, when acting normally, provides growth inhibitory/ regulating signals which keep cell growth in check. Mutation causes a loss in function which then allows for growth signal pathways to proceed with less inhibition.
Pg 291
Define proto-oncogene
A gene, which when mutated results in a product which is constitutively activated and free of either need for growth factor activation or free from being inhibited. Ie, a gain of functional activity due to mutation.
Pg 284
What are the hallmarks of cancer
Evasion of immune system
Self sufficiency of growth signals
Invasion and Metastasis
Evading growth suppressors
Replicative immortality
Altered cellular metabolism
Evasion of apoptosis
Sustained angiogenesis
What type of protein is ALK
A receptor tyrosine kinase
What type of protein is HER2, what gene encodes it
A receptor tyrosine kinase, encoded by ERBB2
What type of protein is EGFR, and what gene encodes it?
A tyrosine kinase, encoded by ERBB1
What are the most common types of abnormality of the gene encoding EGFR
Point mutations resulting in constitutive activation
What is the most common type of abnormality of the gene encoding HER2?
Up regulation of gene causing receptor over expression
What is the most common abnormality of the gene encoding ALK
Gene rearrangement resulting in a constitutively activated form
What type of proteins are RAS proteins?
Membrane associated small g-proteins. Bind GTP/GDP (GTP in active form), tranducing growth pathway signals from the receptor tyrosine kinase to intracellular pathways
What are the most common type of mutation of RAS proteins and what is the resulting abnormality
Point mutations. Result in less function of GTPase activity of the RAS protein, so the RAS protein remains in its active state.
Why are RAS protein and receptor tyrosine kinase mutations almost mutually exclusive?
Because if RAS proteins are mutated resulting in constitutional activity there is no need for it to receive signalling from the tyrosine kinase inhibitor
What type of protein does the NF1 gene produce
A GTPase activating protein (GAP). These upregulate the intrinsic GTPase activity of RAS proteins up to 1000 fold. therefore mutation will result in increased activity of associated RAS proteins.
What are the complexes that progress cells through the cell cycle, and what activated them
Cyclin dependent kinases. Activated by cyclin proteins
What cascade are RAF (eg BRAF) proteins part of
The MAPK cascade (a downstream part of growth factor signalling pathways)
What cascade results in the transcription of the MYC gene, and what are the functions of the MYC protein
Part of the RAS-MAPK cascade.
MYC is a transcription factor that upregulates many genes;
Many effects of hallmarks of cancer
-D cyclins
-rRNA genes
-promoting Warburg effect
-upregulates expression of telemorase
-may promote stem cell-like properties
What are examples of epigenetic aberrations sometimes found in malignancy
DNA methylation
Histone acetylation
What is the function of p16
Cyclin dependent kinase inhibitor. Ie inhibits cell cycle progression. Binds to cyclin D/CDK4,6 (stops their phosphorylation of RB) and cyclin E/CDK2 to inhibit them
What is associated with p16 to form its functional unit
INK4a
What is the Warburg effect
Tumour cells changing their metabolic state, switching to aerobic glycolysis
What are the two major downstream signalling arms from RAS
-MAPK cascade
-PI3K/AKT
Why have drugs targeting RAS mutations been unsuccessful
Because they would have to restore the missing enzymatic activity of GTPase
What gene encodes e-cadherin , and what are the two major functions
CDH1
Transmembrane protein that contributes to cohesion of normal epithelial cells
Tumour suppressor
What cancers are associated with inherited heterozygous CDH1 mutation
E-cadherin gene
Lobular carcinoma of breast
Signet ring carcinoma of the stomach
What abnormalities of MYC occur in cancer
A multitude
-chromosomal translocation (eg burketts)
-upregulation of upstream signalling pathways
-RAS-MAPK pathway (many cancers)
-Notch signalling (many cancers)
-Wnt pathway (colon ca)
-hedgehog signalling (medulloblastoma)
-single nucleotide polymorphism in surrounding enhancing elements flanking the MYC gene (prostate, ovarian)
What are the four phases of the cell cycle
G1
S (synthesis)
G2
M (mitosis)
Which cancers have upregulation of the CDK4 gene?
Melanoma
Glioblastoma
Sarcomas
Abnormalities in which cyclin and CDK are most important in malignancy, and why
Cyclin D/CDK4 because the are the main ones controlling the G1/S checkpoint. If this checkpoint fails it is much more likely that a mutator phenotype can develop. Also key to dysregulated growth
What is the specific function of CyclinD/CDK4
Phosphorylation RB, releasing RBs breaks on transcription factor E2F, allowing G1/S cell cycle progression
What is E2F
A transcription factor that drives transition through the G1/S checkpoint
What protein complex inhibits MDM2
p14/ARF.
By inhibiting MDM2 it increases p53 levels
What malignancies are associated with somatic mutation/inactivation of p16
Glioblastoma (40-70%)
Oesophageal (50%)
Pancreatic (75%)
ALL (20-70%)
NSCLC (20%)
What tends to happen in cells with intact tumour suppressor pathways that develop a mutant oncogene
They enter cell cycle arrest or apoptosis
What cancers are associated with familial Rb mutation
Retinoblastoma (10000 times increased risk)
Osteosarcoma
Other soft tissue sarcomas
What is the inheritance pattern of familial Rb mutation
Autosomal dominant
-but cancer only develops when the normal allele also gets mutated in a retinoblast (or other cell leading to a sarcoma) leading to both Alleles being mutated
Which cyclin/CDK complexes contribute to phosphorylation of Rb
CyclinD/CDK4
CyclinD/CDK6
CyclinE/CDK2
What are the 4 key regulators of cell cycle progression, with one dysregulated in majority of cancers
CDK4
Cyclin D
Rb
p16/INK4a
How do high risk HPV variants cause dysregulation of the cell cycle
They produce protein E7, which binds to hypophosphorylated Rb, preventing it binding to E2F. Thus it’s transcriptional function becomes uninhibited.
E7 also inhibits p21 and p27 which are CDK inhibitors
Why is p16 raised in HPV associated cancers
Due to feedback loop. P16 levels rise in an attempt to prevent hyperphosphorylation of Rb. This is unsuccessful as Rb has been inactivated by E7 rather than hyperphosphorylation
What is the most mutated gene in human cancers
TP53
What are the functions of p53
Regulation of cell cycle progression
DNA repair
Promotion of cellular senescence
Apoptosis
What syndrome results from TP53 mutation
Li Fraumeni syndrome.
25-fold greater risk than general population of malignancy. Can be of any type
What proportion of sarcomas have upragulated MDM2
33%. Therefore used as a bio marker for sarcomas
What is the effect of E6 protein produced by high risk HPV
Binds to p53 and promotes its degradation
Also upregulates telomerase, thus promoting immortality of cells
How do DNA damage and hypoxia result in p53 upregulation
ATM and ATR sense these changes (both involved in DNA repair pathways)
Both phosphorylate MDM2 and p53, which releases p53 from MDM2 binding and breakdown
How is p53 upregulated by “oncogenic stress” (upregulates cell cycle signalling)
P14/ARF levels rise (via incompletely understood mechanism)
This complex binds MDM2, releasing p53
What gene encodes p14/ARF
CDKN2A
Ie the same gene that encodes p16/INK4a
What is a pathway by which p53 promotes cell cycle arrest
Causes transcription of the CDKN1A gene. This produces p21 which inhibits CDK4/CyclinD (similar to p16)
What are the broad functions of p53
Cell cycle arrest
Enhanced DNA repair
Apoptosis
Senescence
Enhanced catabolic metabolism rather than anabolic
What genes does p53 direct transcription of to promote apoptosis
PUMA
BAX
What is thought to cause p53 to promote a pro-apoptosis pathway
Sustained high levels of p53 due to ongoing cellular stress. Ie, it first promotes cell cycle arrest and DNA repair, then later apoptosis if that has failed
Why do cancers with p53 mutations tend to have worse outcomes
-Due to mutator pho type they are likely to have a wide variety of genetically distinct sub clones that don’t all respond to the same therapy
-because they have a looks of apoptosis promotion they are less likely to respond to chemotherapy and radiation therapy
What cancers is familial NF1 mutation associated with
Neuroblastoma
Juvenile myeloid leukaemia
Peripheral nerve sheath tumours
Neurofibromas
What cancers is familial NF2 mutation associated with
Acoustic scwannoma
Meningioma
What syndrome is APC associated with
Adenomatous polyposis coli
What signalling pathway is APC part of, what is the role of normal APC
Part of the WNT signalling pathway. It normally binds to B-Catenin in the absence of activation of the WNT receptor and causes the breakdown of B-Catenin.
What is the normal action of B-Catenin
It binds to a transcription factor in the nucleus, leading to transcription of genes that promote cell cycle progression such as MYC and cyclin D
What is the normal interaction between B-catenin and E-cadherin
B-catenin binds to the cytoplasmic tail of e-cadherin and this regulates b-catenin, reducing its activity in promoting transcription of cell cycle genes. This normal interaction is to promote healing of wounds
What is the the function of the TGF-B pathway
A potent inhibits pathway of proliferation by:
-upregulation of genes such as CDK inhibitors
-downregulation of proliferative genes such as MYC, CDKs, cyclins
What is a key inhibitor of the PIK3/AKT pathway
PTEN
What is the function if HIF1a
Levels increase in hypoxia conditions to promote increased expression of VEGF as thus promote angiogenesis
Also promotes change in cellular metabolism to aerobic glycolysis (Warburg effect)
What is the key function of VHL
In the presence of oxygen it binds of HIF1a and promotes its breakdown. Thus reducing downstream effects promoting angiogenesis.
Also binds to other proteins promoting their breakdown
What malignancies commonly have mutated VHL
Renal cell carcinomas
What does the NF2 gene produce
Merlin, a tumour suppressor
What is the normal role of PD-1
It is used by T and B cells of the immune system to recognise normal host cells (by recognising PD-L1) and avoid attacking these normal cells. Ie, prevent autoimmune disease
What is an immune checkpoint inhibitor target on host immune cells other than PD-1
CTLA 4- Ipilimumab
Describe the changes happening as part of the Warburg effect
Aerobic glycolysis. Cancer cells change to glycolysis metabolism even in the presence of normal oxygen. This promotes increased glucose uptake by cells and conversion of this to lactose (fermentation)
What imaging modality makes use of the Warburg effect
FDG PET
What is the normal type of metabolism of glucose in well oxygenated cells
Oxidative phosphorylation
What is the advantage for a cancer cell in using aerobic glycolysis rather than oxidative phosphorylation
It produces metabolic intermediates the cell can use to synthesise cellular components
Which cell signalling pathways promote aerobic glycolysis
PI3K/AKT
MYC
In general, is autophagy enhanced or suppressed in malignant cells
Suppressed
What metabolic process is IDH part of
The krebs cycle (used by quiescent cells to produce ATP
What does IDH mutation do to its function
Changes its enzymatic activity, with production of abnormal metabolites (2-HG). One effect is to cause abnormal DNA methylation and expression.
What are the two pathways that can induce apoptosis
Intrinsic
Extrinsic (mediated by TNF proteins)
What pro and anti-apoptotic proteins act in balance on the mitochondria, what is the result of increased pro apoptotic signalling
Pro: BAX, BAK
Anti: BCL-2, BCL-XL (neutralised by proteins. Like PUMA)
If pro apoptotic signalling becomes dominant they cause the mitochondrial membrane to become for porous, releasing caspase C.
What is the interaction between p53 and PUMA
p53 upregulates PUMA
What translocation is involved in follicular lymphoma, and what is the key gene involved. Why does it result in a slow growing tumour
14:18 involving the BCL2 gene (an anti apoptotic gene)
It results in slow growing tumours because it results in less cellular death rather than increased cellular proliferation
What anti apoptotic protein has inhibitor medications frequently used in lymphoma/leukaemia treatment
BCL2
What cancers are associated with Cowden syndrome
PTEN mutation (inhibitor of PI3K/AKT pathway)
Breast, thyroid, endometrial carcinoma
What are different examples of small round blue cell tumours
Ewing sarcoma
Neuroblastoma
Medulloblastoma
Small cell lung cancer
Merkel cell cancer
Small cell lymphoma
Mesothelioma
Wilms tumour
What pathways does ALK activate
JAK and STAT pathways
What is a key factor that induces normal tissue inflammation and growth of connective tissue in response to radiation
TGF-B
What is the effect of TNF in response to radiation in normal tissues
Induces proliferation of fibroblasts, inflammatory cells, endothelial cells
What syndrome is associated with familial CDH1 mutation, and what are the two main cancers associated with it
E cadherin gene
Familial diffuse gastric carcinoma syndrome
Lobular breast cancer
Signet ring carcinoma of the stomach
What are microscopic features commonly associated with aggressive tumours. Ie, things to say when you don’t know
High mitotic rate
Necrosis
Pleomorphism/ cytological atypia
Infiltrating growth
Vascular invasion
PNI
What is the most hereditary tumour, and what syndromes is it associated with
Pheochromocytoma
-MEN2 (RET)
-NF1
-SDH (more commonly associated with Mets)
Which genes are associated with SDH deficient tumours, what is tested for
SDHA, SDHB (most common) SDHC, SDHD.
IHC for SDHB LOSS. This will occur for any of the mutations above, not just SDHB
What tumours are associated with SDH mutation
Pheochromocytoma/paraganglioma
GIST
SDH deficient RCC
What is the Carney triad
Tumours associated with non hereditary SDHC promoter hypermethylation
-paraganglioma
-GIST
-pulmonary chondroma
