Cancer Flashcards
Oncogene
a gene capable of transforming a normal cell into a tumour cell
Tumour suppressors
factors that reduce the ability of oncogenes turning normal cells into cancerous ones
Major carcinogenic factors
chemical
parasites
radiation
viruses
How are tumours heterogenous?
cells within the same tumour often exhibit differences in terms of differentiation, proliferation, migration and invasion, size, therapeutic resistance and tumorigenicity
Stochastic model
all tumour cells are equipotent and a proportion of them stochastically proliferate to fuel tumour growth
other tumour cells differentiate targets for anti-cancer treatments
Cancer stem cell model
only a small subset of tumour calls have the ability for long term self renewal and these cells give rise to committed progenitors
regulated by same signalling as normal stem cells
Why are cancer stem cells drug resistant?
they have a slow cell cycle and are more dominant, so drugs that target fast proliferating cells don’t work as well
Pathway of how CSCs arise
specialised cell > reprogramming to a CSC like entity or oncogenic transformation of pre-existing stem cells > CSC
In vitro potential of CSCs
establishment of cell lines that can self renew and differentiate
In vivo potential of CSCs
ability to give rise to cancer following transplantation into animals
Leukaemia
blood cancer affecting the myeloid lineage
Glioblastoma
aggressive and invasive form of brain cancer
treatment involves surgical resection, radiation and chemotherapy
recurrant and low survival rate
What are the main approaches to studying cancer?
xenograft models
cancer cell lines
genetically modified animals using oncogene or tumour suppressor mutations
What are the limitations of current cancer studies?
failure to capture the transition from normal to tumorigenic phenotype in a tractable manner and in a human context
lack of mechanism insight
What could cause neuroblastomas?
neural crest cells arise in resopnse to Wnt and BMP
these are marked by Sox10 and overexpressionof this could be the cause
What cells are most commonly connected to cancer? why?
tissues that are continuously replaced and have an active cell population- epithelia and blood
cells are already proliferating and each time the genome is copied there is more of a chance for mistakes to occur
Teratoma
cancers that grow a variety of tissues
cells similar to embryonic cells as can give rise to tissues from all three germ layers
Tumour suppressor genes
Rb
P53
ATP
What are the alternative ways cancer cells are able to proliferate without GFs?
production of GFs by themselves
signals that stimualte surrounding cells to produce GFs
deregulation of GF receptor signalling
constitutive activation of signalling downstream of GFs
disruption of negative feedback mechanisms
When is the discrete window where a cell can consult the extracellular environment?
from the onset of G1 to an hour or 2 before S
What is the restriction point?
the point in the cell cycle when the cell becomes fully committed to the cycle at the G1/S transition
extracellular signals are no longer needed for proliferation
Flow cytometry
cells treated with fluroescent dye that labels DNA quantitatively
as DNA content doubles during S phase the intensity of fluorescence increases in proportion
so cells in G1/0 have half of those in S
Immunofluorescence
staining for proteins that are specifically expressed in different phases of the cell cycle to measure its progression
BrdU
replaces thymidine during DNA synthesis
short pulse identifies cells in S phase
Cyclin B1
marker for G2/M
Histone H3
has a role in mitotic chromosome condensation and is phosphorylated during mitosis
FUCCI
fluorescence ubiquitin cell cycle indicator
allows for in vivo analysis of spatial and temporal patterns of cell cycle dynamics
What are the two components of the replication control system in eurkaryotes?
licensing factor Ctd1
Ctd1 inhibitor geminin
Licensing factor Ctd1
peaks in G1 before the onset of DNA replication and declines abruptly after initiation of S phase
Ctd1 inhibitor geminin
expressed at high levels during S and G2 phase
low levels during mitosis
Colours of cells when sorted by FACS
early G1- no/low red
late G1- high red
G1/S- red and green
S/G2/M- green
What phase of the cell cycle are cells likely to have higher invasive abilities?
G1
cells are able to disrupt the ECM and therefore invade tissues
What viruses are known to induce cancer?
human papilloma virus
hepatitis C virus
Viral genetics
have very simple genomes with very few but potent genes
these perturb the complex regulatory circuitry of the cells they infect
Peyton-Rous
chicken embryo fibrobalsts injected with rous sarcoma showed traits associated with cancer
transformation phenotype was transmitted from an initially infected cell to its descendents
What were the 2 possible explanations for the rous sarcoma experiment?
RSV particle transformed progenitor cells and all descendents but virus must be present to maintain phenotype
RSV particles only needed to transform progenitors that transmit phenotype to inheritants so acts in a hit and run fashion
ts RSV mutant
partially defective proteins but can function at permissive temperatures
What was the eventual conclusion of the rous experiment?
transformed state was lost when cells were kept at non-permissive temps
so the viral transforming protein was required to both initiate and maintain tumour phenotype
What are the 3 genes coding for viral replication?
gag
pol
env
gag
virion nucleoprotein core
pol
reverse transcriptase and integrase
env
glycoprotein spikes of the virion
What additional viral gene is required for transformation?
src
Proto-oncogenes
genomes of normal vertebrates can carry a gene that has the potential under certain circumstances to induce cell transformation and thus cancer
What were other proposed causes of cancer?
activation of endogenous retrovirus
induction by mutagens
Mutagens
physical or chemical agents that induce cancer through their ability to mutate growth and controlling genes such as UV light, x-rays, base analogs and DNA intercalating agents
Oncogene transfection
if a transforming gene is present in the donor DNA, it may become incorperated in the genome of one of the recipient cells and transform the latter → these will form loci
What are proto-oncogenes regulated by?
in normal cells- by their own transcriptional proteins
in cells acquired by viruses- retroviral promoter
How was the difference between a normal gene and oncogene identified?
cleaved by restriction enzymes
recombinant genes made by ligation
transforming activity using transfection locus assay
mutation responsible for activation localised to 350bp fragement and sequence was determined
What are the 3 types of ras genes found to carry point mutations in human tumours?
H-ras
K-ras
N-ras
Which ras gene is the most frequent driver of tumour development in humans?
K-ras
KRASG12C most prevalent in lung cancer
KRAS inhibitor
AMG 510 forms a covalent bond with GTP-bound KRAS
high specificity for mutant protein
inhibits downstream signalling + cell proliferation in vitro
inhibits tumour growth in mice
What improves efficiency of AMG510?
when in combination with standard chemo or a drug that inhibits MEK which acts as a downstream of Ras
not effective on immunocompromised
What improves efficiency of AMG510 in immunocompromised mice?
when in combination with immunotherapy called anti-PD1
leads to complete tumour regression
What effect does AMG510 have on the immune system?
boosts the expression of pro-inflammatory cytokines in tumour bearing animals
increases infiltration of tumours by T and dendritic cells
What happens when KRAS cancer cells are reintroduced to animals cured by combination therapy?
no tumour formation due to long term T cell response induced by treatment
What are the 3 members of the myc oncogene family?
C-myc
N-myc
L-myc
What are the 3 mechanisms that can cause the myc oncogene to arise?
gene amplification
chromosomal translocation
pro-virus integration
What is the function of myc proteins?
growth promoting TFs in the nucleus
Gene amplification
driven by its normal promoter but the gene is amplified causing increased gene product levels
drives uncontrolled cell proliferation
Chromosomal translocation
region of one chromosome is fused with a region from a second unrelated one
gene comes under control of foreign transcriptional promoter
Pro-virus integration
Avian leukosis virus
viral transciptional promoter disrupts the mechanisms normally controlling the expression of myc
increases expression causing extremely high levels of myc protein
How can deregulation of EGF lead to cancer?
extracellular domain of EGFR is deleted in some lung cancers and glioblastomas
consitutive signalling in the absence of EGF- uncontrolled release of GFs
Cell fusion technique
comparison of 2 alternative alleles and specified phenotypes
when both alleles are forced to co-exist dominant allele wins
What is the fusing agent used in cell fusion technique?
sendai virus or PEG
How did hybrid cells formed by cell fusion prove the existance of tumour suppressors?
hybrid cells were unable to form tumours
genes carried by normal cell were inactivated during development of a tumour
Retinoblasts
population of cells in the developing eye, which normally stop growing during embryogenesis and differentiate
Retinoblastomas
tumour of the retina which arises in the precursor of photoreceptor cells, retinoblasts, which fail to differentiate and divide
What are the 2 forms of retinoblastoma?
sporadic form- children from families with no history of retinoblastoma developing a single tumour in one eye → unilateral retinoblastoma
familial form- genetically predisposed children developing multiple tumours in both eyes → bilateral retinoblastoma + elevated susceptibility to developing other tumours
Alfred Knudson
used maths to determine whether data followed a 1 or 2 hit model of gene mutation
sporadic requires 2 random events
familial requires only 1
Mutations in what gene cause retinoblastomas?
Rb
Mitotic recombination of Rb
chromosomal arm carrying Rb allele might be replaced with one carrying mutant allele
far easier than mutational activation
What are mechanisms to stop cancer development?
- direct suppression of cell proliferation in response to growth inhibitory and differentiation inducing factors
- components of the cellular machinery that inhibits proliferation in response to metabolic imbalance and DNA damage
What were the first tumour suppressor genes to be intensively studied?
P53
Rb
How do TSGs other than P53 and Rb function?
dispatch of gene products to intracellular sites where they suppress cell proliferation
involved in virtually all of the control circuits that govern cell proliferation and survival
Neurofibromatosis
caused by loss of heterozygosity of NF1
familial cancer syndrome causing benign tumours in the PNS called neurofibromas
some progress to malignant neurofibrosarcomas
NF1
neurofibromin
Ras GAP, mutations result in a protein with 1000 fold decreased GTPase stimulating activity
What happens when NF1 is lost?
Ras remains active for longer
cells show overactivation of AKT and mTOR target S6K
tumour formation
What does rapamyacin do?
completely blocks the mTOR target S6K
reverses the ability of NF1 null cells to form colonies in anchorage independent conditions
APC
adenomatous polyposis coli, prone to develop into colon carcinomas
loss of APC gene is first step in colon cancer followed by oncogene mutations of ras and p53
What do mutations in APC lead to?
blocking of the out-migration of cells from gut crypt leads to mutated cells accumulating in the crypt rather than being lost
What is the function of APC?
negatively regulates the levels of b-catenin in the cytosol
as cells move upwards, APC expression is increased
What happens when APC is inactivated?
destruction complex does not form → B-catenin cytosolic accumulation and nuclear translocation → transcription of growth promoting genes including myc
pHVL/ von Hippen-lindau syndrome
hereditary disposition to developing a varitey of tumours
includes clear cell kidney carcinomas, pheochromocytomas, and hemangioblastomas
What causes pVHL tumours?
germ line mutations in the tumour suppressor VHL which codes for the pVHL protein
What is the function of pVHL?
modulates the hypoxic response
destruction of transcription factor HIF-1a
target genes- angiogenesis, erythropoiesis and glycolysis and glucose uptake
