Cancer Flashcards
Define metaplasia.
- a reversible change in which one adult cell type (usually epithelial) is replaced by another adult cell type -> this process is reversible
Give an example of a pathological metaplasia.
- gastro-oesophageal reflux causes the oesophageal epithelium to change from squamous to columnar -> Barrett’s oesophagus
Give an example of a physiological metaplasia.
- in pregnancy the cervix opens up and the columnar epithelium of the endocervical canal is exposed to the acidic uterine fluids making it become squamous -> when the cervix closes up again, the cell type changes back to normal
Define dysplasia.
- abnormal pattern of growth in which some cellular and architectural features of malignancy are present with an intact basement membrane and without showing an invasion
What are the features of dysplasia?
- INCREASED NUCLEO-CYTOPLASMIC RATIO
- loss of architectural orientation
- loss in uniformity of individual cells (pleomorphism)
- nuclei which have become hyperchromatic and enlarged
- abundant, abnormal, mitosis
In what sites is dyplasia common?
- cervix -> HPV infection
- bronchus -> smoking (pseudostratified columnar -> squamous)
- colon -> UC associated with IBD (UC -> dysplasia -> cancer)
- larynx -> smoking
- stomach -> pernicious anaemia (chronic stomach inflammation)
- oesophagus -> acid reflux (Barrett’s oesophagus)
What is the difference between the grades of dysplasia?
- low grade = unlikely to become cancer
- high grade = likely to become cancer -> further changes -> darker due to higher nucleo-cytoplasmic ratio
Define malignancy.
- an abnormal, autonomous proliferation of cells unresponsive to normal growth control mechanisms
Define neoplasia.
- any new growth, benign or malignant
What are the features of a benign tumour?
- do not invade -> do not metastasise
- encapsulated
- usually well differentiated
- slowly growing
- normal mitoses
When can benign tumours be dangerous?
- in a dangerous place -> a benign tumour in the meninges or pituitary
- secretes something dangerous- > insulinoma
- becomes infected
- causes haemorrhage
- it ruptures -> liver adenoma can cause massive haemoperitoneum
- torsion leads to ischaemic necrosis
What are the features of a malignant tumour?
- invade surrounding tissues
- metastasise
- have no capsule
- poorly differentiated
- rapidly growing
- abnormal mitoses
Define metastasis.
- a discontinuous growing colony of tumour cells, at some distance from the primary cancer
What staging system is used for colon cancer?
o Dukes
o Dukes A = growth limited to wall (nodes negative) -> 90-98% survival
o Dukes B = growth beyond muscularis propria (nodes negative) -> 70&
o Dukes C1 = nodes positive (apical lymph node negative)
o Dukes C2 = apical lymph node is positive -> 30-40% survival
Benign and malignant tumours are distinguished from each other by all of the following except:
- Degree of differentiation
- Speed of growth
- Capsulation
- Invasiveness
- Site
- 5
Well differentiated tumours are characterised by all of the following, except:
- A small numbers of mitoses.
- Lack of nuclear pleomorphism
- A high nuclear-cytoplasmic ratio.
- Relatively uniform nuclei
- Close resemblance to the corresponding normal tissue
What types of benign epithelial tumours are there?
- papiloma -> occur on the surface of epithelium -> skin, bladder
- adenoma -> occur on glandular epithelium -> stomack, thyroid, colon, kidney, pituitary, pancreas
What is a carcinoma?
- a malignant tumour derived from epithelium
What types of carcinomas exist?
- squamous cell (if from skin/oesophagus)
- adenocarcinoma (if from glandular epithelium)
- transitional cell (if from transitional epithelium)
- basal cell carcinoma
What are sarcomas?
- malignant tumours dervied from connective tissue cells (soft tissue)
What are the different types of sarcomas?
- fat - liposarcoma
- bone = osteosarcoma
- cartilage = chondrosarcoma
- striated muscle = rhabdomyosarcoma
- smooth muscle = leiomyosarcoma
- nerve sheath = malignant peripheral nerve sheath tumour
Define leukaemia.
- a malignant tumour of bone marrow derived cells which circulate in blood (seen in blood)
Define lymphoma.
- a malignant tumour of lymphocytes (usually) in lymph nodes (seen in lymph nodes)
Define teratoma.
- a tumour derived from germ cells, which have the potential to develop into tumours of all three germ cell layers
What are the three germ cell layers?
- ectoderm
- mesoderm
- endoderm
What is the difference between gonaldal teratomas in males and females?
- males = almost always malignant
- females = alsmost always benign
What are harartomas?
- most are benign, but there is a risk of malignancy
- localised overgrowth of cells and tissues native to the organ
- cells are mature but architecturally abnormal
- common in children and should stop growing when they stop
- e.g. bile duct hamartomas, bronchial hamartomas
A benign tumour of glandular tissue is:
- an adenoma
- a leiomyoma
- an adenocarcinoma
- a squamous papilloma
- a lymphoma
- 1
A malignant tumour derived from soft tissue is a:
- Carcinoma
- Sarcoma
- Teratoma
- Lymphoma
- Melanoma
- 2
What grading system is used for breast cancer?
- Nottingham scoring system
What grading system is used forprostate cancer?
- Gleason
Define anaplastic.
- cells with poor cellular differentiation, losing the morphological characteristics of mature cells and their orientation with respect to each other and to endothelial cells -> very bad tumours
What is tumour grading?
- the degree of differentiation -> higher grade = poor differentiation
What is tumour staging?
- how far a tumoru has spead -> higher stage = greater spread
Which is more important stage or grade?
- stage
Briefly summarise the cell cycle.
- if a cell is quiescent, it is NOT proliferating – this is the G0 phase
- cells can be STIMULATED to enter the cell cycle: G1 -> S phase -> G2 -> MITOSIS
- there are checkpoints within the cell cycle -> they arrest the cell in the cycle, to check everything is okay
What do proto-oncogenes do?
- code for proteins involved in maintenance of cell growth, division and differentiation
What can happen with mutation to proto-oncogenes?
- can be converted into oncogenes -> protein products of oncogenes don’t respond to control influences
- oncogenes can be be perversely expressed, over-expressed or perversely active e.g. MYC, RAS, ERB, SIS
Name 4 different mechanism which can lead to oncogene formation.
- mutation in the coding sequence
- gene amplification
- chromosomal translocation -> leading to chiamaeric genes
- insertional mutagenesis -> viral infection
Describe a chromosomal translocation leading to cancer.
- the picture is of a Philadelphia chromosome -> translocation of segements from chromosome 9 and 22
- two key areas that are translocated are: ABL on chromosome 9 and BCR on chromosome 22 -> results in BCR-ABL fusion gene -> development of cancer (CML)
What is the mechanism of RAS?
- upon binding GTP, Ras becomes active -> when bound to GTP, it is active so it interacts with a protein called RAF and signals via phosphorylation
- it activates the kinase cascade leading to the production of gene regulatory proteins
- RAS passes the signal on to other proteins within a signal transduction cascade -> the cell goes into a PROLIFERATIVE PHASE
- dephoshorylation of the GTP to GDP to switch Ras off
o when RAS in on it signals to the kinase cascade -> drives recruitment of effector proteins
What process fails in the presence of mutant RAS?
- mutant Ras will fail to dephosphorylate GTP, meaning that the GTP persists so Ras remains active -> consequently INCREASED SIGNALLING with the RAF protein -> continuous proliferative stimulation
Which one of the following statements is incorrect?
a. mutation can convert a protooncogene to an oncogene
b. gene amplification of a protooncogene can be oncogenic
c. chromosome translocation can lead to inappropriate expression of a protooncogene and to an oncogenic effect
d. a protooncogene can be activated to an oncogene by insertional mutagenesis
e. protooncogenes are not expressed in normal cells
- e
What is the the pathway in which RAS is involved?
- a signal transduction cascade called the Mitogenic-activated Protein Kinase (MAPK) Cascade
- MORE SPECIFICALLY THE EXTRACELLULAR SIGNAL-REGULATED KINASE (ERK) CASCADE -> specfic to growth stimulatory signalling
How many copies of proto-oncogenes have to become mutated for it cause cancer?
- only one, the other copy will be insufficient to stop its effects
What are the function classes of proto-oncogenes?
- growth factors
- growth factor receptors
- intracellular transducers (signalling proteins)
- intracellular receptors
- transcription factors
- cell cycle regulatory proteins
- cell death regulators
What are tumour suppressor genes?
- regulate cell proliferation and maintain cell integrity (essential activities in the cell)
- typical proteins whose function is to regulate cellular proliferation and maintain cell integrity
How many copies of tumour suppressor genes must be mutated for it to cause cancer?
- both = two hit hypothesis
- an exception is p53because the mutated gene become dominant
What are the features of inherited cancer suspectibility?
- family history of related cancers
- unusually early onset – the mutation often only affects ONE COPY -> usually of the a tumour suppressor gene
- bilateral tumours in paired organs
- synchronous or successive tumours
- tumours in different organ systems in same individual
- mutation inherited through the germline
Describe retinoblastoma.
- is a malignant cancer of developing retinal cells
- sporadic disease usually involves one eye
- hereditary causes can be unilateral or bilateral and multifocal
What causes retinoblastoma?
- caused by mutation of the RB1 tumour suppressor gene on chromosome 13
- RB1 encodes a nuclear protein that is involved in regulation of the cell cycle
What is the treatment of retinoblastoma?
- removal of th eye
- if it is inherited the tumour will be present at birth or shortly afterwards -> only eye with tumour is removed even though it is likely the other eye will develop the tumour too
What are the functions of p53?
- metabolic homeostais
- anti-oxidant defence
- DNA repair
- growth arrest
- senescence
- apoptosis in worst case
What activates p53?
- stress or DNA damage causes p53 to be released from Mdm2
What is APC tumour suppressor gene involved in?
- cell adhesion and signalling -> involved in WNT pathway -> binds to beta-catenin and inhibits its drive for proliferation
What will patients suffering from mutation in both APC genes develop?
- hyperproliferative state of colonic cells -> polps of the colon will appear -> THIS IS NOT CANCER
- 90% risk of developing colorectal carcinoma
What is the treatment for people with two mutated APC genes?
- removal of their colons in their 20s
The protein products of tumour suppressor genes are not NOT involved with:
a. regulation of cellular proliferation
b. metabolism of drugs
c. regulation of cell cycle
d. repair of DNA damage
e. control of transcription
- b
What factors influence the rate that cells divides at?
- embryonic cells vs adult cells -> embryonic divide at a much faster rate
- complexity of systems/organism -> a less complex system will divide more rapidly
- necessity for renewal -> in the body, certain cell types must divide more rapidly to replenish lost cells -> intestinal epithelial cells are shed very often so need quick replenishment (20 hours) but hepatocytes don’t need frequent renewal (1 year)
- state of differentiation -> some cells NEVER divide ->neurones and cardiac myocytes
Define contact inhibition of growth.
- anti-cancer mechanism which works by promoting pro-liferation in cells which are not in contact with other cells but stopping growth when they do come into contact with one another
- lost in cancer cells
When are cells most vunerable?
- during mitosis
Why are cells most vunerable during mitosis?
- mitosis is a complex process, it must to occur very quickly due to cell vulnerability
- cells are more easily killed during mitosis (manipulated clinically: irradiation, heat shock, chemicals) -> principal of treating tumours
- DNA damage occurring during mitosis cannot be repaired -> mutation may be carried over in DNA
- gene transcription is silenced
- is a slow down in the metabolism of the cells
What happens in the S-phase of the cell cycle?
o replication for division
- DNA replication
- protein synthesis -> initiation of translational proteins, and elongation is increased
- capacity for translation is also increased
- replication of organelles -> with mitochondria, cells needs to co-ordinate with replication of mitochondrial DNA
Describe the structure of centrosomes.
- consists of two centrioles (barrels of 9 triplet microtubules)
- there are matrix proteins holding the centrioles at 90 degree angles to each other
- is a mother and daughter centriole
State the 2 functions of the centrosome.
- microtubule organising centre (MTOC) -> controls the polymerisation of microtubules
- co-ordinate the mitotic spindle
What are the phases of the mitosis?
- prophase
- prometaphase
- metaphase
- anaphase
- telophase
- cytokinesis
What occurs in prohase?
- condensation of chromatin
Explain the process of chromatin condensation.
- double helices are wrapped around histones to forms ‘beads-on-a-string’ form of chromatin
- compact the chromatin from being 2 nm wide to 11 nm wide
- string is then further wrapped around itself to form 30 nm fibres
- 30 nm fibres are then extended as a scaffold forming a chromosome scaffold of 300 nm
- then further wrapped until you end up with a chromosome
What are kinetochore?
- a complex of proteins that are a key regulator of the processes around chromosomes in the cell cycle
- surround the centromere of chromosomes
What processes are happening in late prophase?
- microtubules are radiating away from the centrosome
- the nuclear envelope is breaking down and by doing so, the chromosomes come out into the cytoplasm and migrate to opposite sides
- begin to organise the spindle
What are the 2 types of microtubules?
- radial microtubule arrays
- polar microtubules
What are radial microtubule arrays?
- fibres formed around each centrosome -> as soon as the nucleus starts to break down, they start to form around the MTOC
- come out of the MTOC at all angles
What are polar microtubules?
- when two radial arrays from two centrosomes meet in the middle they are referred to as polar microtubules
What occurs in early prometaphase?
- breakdown of nuclear membrane is finalised
- spindle formation is largely complete
- attachment of chromosomes to spindle via kinetochores
What occurs in lae prometaphase?
- microtubule from opposite pole is captured by sister kinetochore -> chromosomes attached to each pole congress to the middle via the microtubules
What is CENP-E?
- CENP-E is a centromere protein E (kinetochore tension sensing) -> senses whether the kinetochore is attached to microtubules or not
What is metaphase?
- the point/stage at which chromosomes have aligned at the equator of the spindle fibres
What are the overall actions of anaphase?
- paired chromatids separate to form 2 daughter chromosomes
- can be split into anaphase A and anaphase B
What is cohesin?
- a protein complex that holds the sister chromatids tightly bound together -> acts as a glue
What occurs in anaphase A?
- cohesin is broken down and the microtubules get shorter -> daughter chromatids start moving towards opposite spindle poles
What occurs in anaphase B?
o daughter chromosomes can reach the opposite poles by two motions:
- shortening of the microtubules that form the spindles
- pulling apart of the spindle poles (spindle poles migrate apart)
o once chromosmes have reached the poles of the spindles the cell enters telophase
What happens in telophase?
- daughter chromosomes arrive at the pole
- nuclear envelope reassembles at each pole
- is a condensation of material where the cells are going to split
- assembly of a contractile ring of actin and myosin filaments -> squeezes the cell so that it divides into 2 daughter cells -> the cleavage furrow is where the cells are going to be cleaved
Describe the process of cytokinesis.
- when the cells divide, they usually round up
- once the cells divide, we see the remaining component where the cells were once joined -> this is the mid-body
- with time, a new membrane will be inserted here and the cells will become completely separated from each other
How does kinetochore act as a checkpoint?
- kinetochore has proteins that emit a signal when the kinetochore is not attached to microtubules -> once the kinetochore attaches to microtubules, it stops emitting the signal
- are many proteins involved in this signalling process but two important ones are: CENP-E and BUB Protein Kinase
How does BUB protein kinase function?
- BUBs dissociate from the kinetochore when chromatids are properly attached to the spindle -> when all dissociated, they go on to signal progression to anaphase
What is amphelic attachment?
- normal attachment of kinetochore -> the microtubule array of one centrosome is attached to the kinetochore of one sister chromatid, and the microtubule array of another centrosome is attached to the kinetochore of the other chromatid
What is syntelic attachment?
- both the kinetochores are hooked by two microtubule arrays from the SAME centrosome -> one cell having a duplication, and the other having one chromosome less
What is merotelic attachment?
- more than one microtubule array attached to the same kinetochore -> means that one of the chromatids is being pulled in two different directions -> both sister cells will be missing that chromosome
What is monotelic attachment?
- only one of the kinetochores of one chromatid is attached to a microtubule array, the other kinetochore is unattached -> on esister cell will lose a chromosome
What are the two major routes to aneuploidy?
- mis-attachment of microtubules to kinetochores
- aberrant centrosome
- aberrant DNA duplication
How can aberrant centrosomes lead to aneuploidy?
- if centrosome duplication is defective there may be a situation in which you end up with 4 centrosomes -> can lead to very abnormal attachment of the microtubule arrays to the kinetochores leading to abnormal cytokinesis -> result is 4 daughter cells
How can aberrant DNA duplication lead to aneuploidy
- if DNA is over-replicated (usually doubled) -> end up with aberrant cytokinesis, where there are two normal daughter cells, two cells with a single chromosome, and one cell without ANY chromosome
How does checkpoint kinase work as an anti-cancer drug?
- activation of this kinase holds cells in G” until everything is ready -> inhibition of this means cells rush into mitosis -> will be a lack of chromosomes or organelles so the cell will die
How do texanes and vinca alkaloids work as cancer treatments?
- alter microtubule dynamics -> produce unattached kinetochores -> causes long-term mitotic arrest
What cancers can be treated with texanes and vinca alkaloids?
- breast
- ovarian
What happens to cells if something goes wrong during the cell cycle?
- cell cycle arrest -> usually happens at the checkpoints -> may be due to the detection of DNA damage -> can be temporary/can be resolved by repair
- apoptosis -> if something is very wrong in the cell: DNA damage is too great and cannot be repaired, chromosomal abnormalities or toxic agents
At what point are there cell cycle checkpoints?
- 1st checkpoint is during G1
- 2nd is just before mitosis -> checks for DNA damage before entering mitosis (G2)
- 3rd is a metaphase-anaphase checkpoint
How do tumour cells by pass cell cycle checkpoints?
- exploit the first checkpoint by hyper-activating growth factors -> tumour cells over-express growth factors -> result is induction of cells to overcome this checkpoint
- tumours can also block the DNA damage machinery, inducing cells to enter mitosis when they shouldn’t
- block exit from the cell cycle into G0
What processes occur during the signal cascade?
- response to extracellular factors
- signal amplification
- signal integration
- modulation by other pathways
- regulation of divergent responses
State 2 molecules which activates receptor protein tryosine kinase (RPTK)?
- epidermal growth factor (EGF)
- platelet derived growth factor (PDGF)
Explain the mechanism of activation of receptor protein tryosine kinase?
- when the dimeric ligand binds, it induces dimerization of the monomeric receptors -> this is the SIGNALLING UNIT - dimerization activates the kinase domain
- there is cross-phosphorylation of receptors due to kinase domains being brought close together
- phosphorylated amino acid residues in the kinase domain -> ACTIVATION -> phosphorylation of proteins in the tail of the EGF receptor
Describe the kinase cascade.
- first kinase is activated by phosphorylation (ligand binds to tryosine kinase type receptor which acts via a small GTP-binding protein called Ras) -> further kinases are activated by the activated kinases and so on…
What is c-Myc?
- a transcription factor - controls the expression of other genes
- is a proto-oncogene -> overly expressed in a lot of tumours
What are the 3 key components of the signalling pathway?
- regulation of enzyme activity by protein phosphorylation (kinases)
- adapter proteins
- regulation by GTP-binding proteins
What is herceptin?
- an antibody that inhibits HER2 receptor tryosine kinase
- important in a number of tumours including breast cancer where is it overly expressed
What is the treatment for HER2-positive metastatic breast cancer?
- anti-HER2 antibodies -> blocks the early stages of growth stimulation
Describe adaptor proteins.
- adapter proteins are modular containing many domains -> different domains are mixed and matched to give the protein different properties, and are important in molecular recognition -> some domains are important in molecular recognition
- have no enzymatic function of their own, simply bring other proteins together
What is Grb2?
- an important adaptor molecule in growth factor signalling -> an exchange factor for RAS
- has 2 types of protein-protein interactions:
- > SH2 - binds to the phosphorylated tyrosines of the receptor
- > SH3 (2 copies): bind to the proline-rich regions of other proteins -> always bound to it through Sos
What are the 2 most common oncogenic mutations of Ras?
- V12Ras -> glycine residue in position 12 of Ras protein is changed to valine
- L61Ras -> glutamine in position 61 in converted to leucine
Why is V12Ras oncogenic?
- side chain goes from being a simple hydrogen (glycine) to a hydrophobic side chain (valine)
- prevents GAPs from binding to Ras -> Ras can’t turn off very easily -> constantly stimulating division
Why is L61Ras oncogenic?
- side chain goes from being an amide to a hydrophobic side chain
- inhibits the intrinsic GTPase activity of the Ras protein -> Ras ends up constantly being in the GTP bounds (on) state and therefore giving growth stimulatory signals
What is the first kinase in the kinase cascade, plus name a common oncogenic mutation of the enzyme?
- Raf
- B-Raf is a common mutation in melanomas -> can be be inhibited for a while until the tumour takes over
What is the overall end product of the kinase cascade?
- once phosphorylated, the transcription factors go on to regulate gene expression
- one of the most important genes that is activated by this pathway is the c-Myc gene -> Myc and Ras are key molecules in stimulating growth
What activates cyclin-dependent kinases?
- cyclin -> once they have actived the CDKs they are degraded (higher concentration during mitosis)
- different CDK-cyclin interactions activates/controls different stages of the cell cycle
- regulated further by cyclins and phosphorylation
Describe cyclin-dependent kinases.
- a family of kinases -> are serine-threonine kinases
- are in the cell throughout the cell cycle but they are not activated until they bind to an activating protein called cyclin
- CDKs are present in proliferating cells throughout the cycle, but the levels vary. -> are involved in controlling the process
What does CDK1 do?
- binds to cyclin B to phophorylate substrates at mitosis -> breaks down the nuclear envelope
What does does CDK2 do?
- binds to cyclin E -> active kinase will be phosphorylated at the start of synthesis
- a tumour suppressor that is inactivated in many cancers
What is the overall mechanism which activates CDK1?
- cyclin binds to CDK -> activates phosphorylation by CDK activating kinase
- this is followed by Cdc25 removing the inhibitory function from the kinase Wee1 by removing the phospahe -> Wee1 provides inhibition from entering mitosis to early
- after this you get ACTIVE MPF
Describe the metaphase-anaphase checkpoint.
- when active at the end of metaphase MPF phosphorylates a number of key substrates that are involved in the mitotic process -> puts mitosis on hold when the substrates are phosphorylated
- once the kinetochores are correctly attached to the microtubule spindles, a signal is released that causes cyclin B to be degraded/inactivated -> substrates which were keeping mitosis on hold are dephosphorylated so then mitosis can progress
What CDKs and cyclins control the G1 phase of the cell cycle?
- GDK2 and cyclin E
What CDKs and cyclins control the S phase of the cell cycle?
- CDK2 and cyclin E
- CDK2 and cyclin A
What CDKs and cyclins control the M phase of the cell cycle?
- CDK1 and cyclin B
How do cyclins affect CDKs?
- cyclins activate CDKs AND alter substrate specificity -> the same CDK is being used in G1/S phase and S phase but they are doing different jobs
What is retinoblastoma?
- a key protein in regualting the cell cycle -> is present throughout the cell cycle
o IS A TUMOUR SUPPRESSOR GENE
What is the mechanims of retinoblastoma?
- in the resting G0 state, retinoblastoma is unphosphorylated -> it binds to and sequesters a family of transcription factors called E2F -> E2F TFs are held in the cytoplasm by unphosphorylated retinoblastoma -> EVRYTHING IS TURNED OFF
- retinoblastoma is a target for CDK4/6-cyclin D kinase -> kinase phosphorylates the retinoblastoma protein -> once phosphorylated, it loses its affinity for E2F so it releases E2F -> E2F TFs can then bind to promoters in the nucleus of genes involved in cell cycle progression
What actives the CDK4/6-cyclin D kinase complex?
- c-Myc induction
Name a target for E2F TFs.
- cyclin E -> next cyclin required for cell cycle progression
How do CDK kinase inhibitors regulate CDKs?
o INK4 family is active in G1 -> inhibit CDK4/6 by displacing cyclin D
o CIP/KIP family is active in S phase -> inhibit ALL the CDK/cyclin complexes by binding to them
Describe the chain of CDK-cyclin complexes reuired throughout the cell cycle.
What can damage DNA?
o CARCINOGENS:
o chemicals -> dietary (40-45% of all human cancer is associated with diet), lifestyle, environmental, occupational, medical, endogenous (e.g. mitochondria produce oxygen radicals which may damage DNA)
o radiation -> ionizing, solar, cosmic
How is DNA damaged by carcinogens?
- base dimers and chemical cross-links
- base hydroxylations
- abasic sites
- single strand breaks
- double strand breaks
- DNA adducts and alkylation
What are base dimers and chemical cross-links?
- where DNA molecules are chemically linked up
What are abasic sites?
- during the repair process, the entire DNA base has been removed so the sugar backbone is maintained but the base from the mutagenic molecule has been removed
What are DNA adducts and alkylations?
- general type of damage caused by chemicals
- some chemicals tend to be metabolically activated into electrophiles -> DNA is very rich in electrons because of all the nitrogens in the bases -> electrophiles covalently bind to the DNA
- binding of a big bulky chemical to the DNA causes problems particularly during replication because the DNA polymerase runs along the strand figuring out which base to put next, but ican’t if it is bound to a big chemical group
What group of molecules does the body often metabolise into carcinogens?
o polycyclic aromatic hydrocarbons
- common environmental pollutants, formed from combustion of fossil feusl and tobacco
How does the body metabolise benzo[a]pyrene?
o two-step epoxidation
- oxidised by CYP450, to produce an epoxide/oxide -> is reactive and unstable (potentially dangerous) -> is an electrophile
- epoxide hydrolase metabolises this molecule, to form a dihydrodiol which is harmless.
- the non-toxic dihydrodiol metabolite is also a substrate for P450 -> converts this non-toxic metabolite into another oxide (DIOL EPOXIDE) -> is INCREDIBLY reactive (even more so than the previous reactive oxide) and NOT STABLE AT ALL
How is benzo[a]pyrene a carcinogen?
- the product of it metabolism (a diol epoxide) is a very unstable electrophile -> BIGGEST SOURCE OF ELECTRONS in the cell is DNA -> DNA is adducted -> starts mutation process
What is aflatoxin B1?
- a very potent human liver carcinogen formed by aspergillus flavus mould
- common on poorly stored grains/peanuts -> especially common in Africa and Far-East
How is aflatoxin a carcinogen?
- aflatoxin B1 is oxidised by P450 -> aflatoxin B1-2,3-epoxide (VERY REACTIVE) -> reacts with the N7-position of guanine to form big, bulky, chemical DNA adducts -> DNA in the cell is now read as damaged
- when the DNA is fixed, it’s fixed inappropriately, and a mutation has been introduced into the DNA
What is 2-naphthylamine?
- a potent bladder carcinogen
- used to be used in dye industry but it is now very uncommon to come into contact with it
How is 2-napthylamine metabolised into a carcinogen?
- 2-naphthylamine is a substrate for CYP450, which converts the amino group to form a hydroxylamine -> hydroxylamines are reactive but are glucuronidated (detoxified) in the liver by glucuronyl transferase
- inactive metabolite is excreted by the liver and it goes into the bladder and mixes with the urine -> urine is ACIDIC, and, under acidic conditions, the glucuronides are hydrolysed -> in the acidic conditions, the molecule rearranges to form a positively charged nitrogen (nitrenium ion)
- nitrenium ion is an electrophile, which then goes and binds to the DNA and forms adducts -> the bladder isn’t as capable of detoxifying the hydroxylamine derivative as the liver so can lead to mutations
How can solar/UV radiation cause (skin) cancer?
o UV radiation can lead to the formation of pyrimidine dimers
- if 2 pyrimidines are next to each other, in the presence of UV radiation, they can covalently link -> cell tries to repair this, but in doing so, a mutation is introduced
How can ionising radiation bring about mutations?
- cause the formation of oxygen free radicals -> very potent electrophiles
- usually either super oxide radicals or hydroxyl radicals
How do oxygen free radicals cause mutations in/on DNA?
o double (DAMAGING) and single strand (not a big deal) breaks -> double stranded breaks have to be re-annealed and rebuilt, which can introduce mutations
o generate apurinic and apyrimidic sites -> base stripped out of the DNA
o introduced are base modifications: -> ring-opened guanine + adenine, thymine + cytosine glycols (2 hydroxy groups on the molecule) or 8-hydroxyadenine + 8-hydroxyguanine (particularly mutagenic)
What enzyme system is most frequently involved in the activation of chemicals to metabolites that can damage DNA?
a. glucuronyl transferase
b. haem oxygenase
c. cytochrome P450
d. xanthine oxidase
e. glutathione transferase
c. cytochrome P450
What is p53 tied up with when unactivated?
- Mdm2
What causes the uncoupling of Mdm2 and p53?
o general stress on the cell, includes:
- oxidative stress, nitric oxide, hypoxia, ribonucleotide depletion, mitotic apparatus dysfunction, oncogene activation, DNA replication stress, double-stranded break, telomere erosion
What is the action of p53?
- a tumour suppressor gene that actiuvates many pathways
- mild physiological stress e.g. DNA repair or growth arrest = p53 orchestrating a transcriptional series of events and activates proteins that help repair the problem
- SEVERE stress = p53 activating an apoptotic pathway by interacting with apoptosis proteins
What are the 4 types of DNA repair?
- direct reversal of DNA damage
- base excision repair
- nucleotide excision repair
- during or post replication repair
Describe the repair mechanism called direct reversal of DNA damage.
- photolyase splits cyclobutane pyrimidine-dimers formed from UV light to recover the pyrimidines
- methyltransferases and alkyltransferases remove alkyl groups from DNA bases
Describe base excision repair.
- DNA glycosylase split/hydrolyses between the sugar and the DNA base
- AP-endonuclease splits the DNA strand so there is a gap in the S-P backbone
- DNA polymerase fills in the missing base (determines correct base using complementary strand)
- DNA Ligase then seals the DNA to form intact DNA
- mainly for apurinic/apyrimidinic damage
Describe nucleotide excision repair.
- endonuclease makes two cuts in the DNA on either side of the site of damage -> patches can be long (100-200 nucleotides) or short (~10-20 nucleotides)
- helicase will then remove this patch, leaving the double stranded DNA with a patch missing
- DNA Polymerase replaces the removed bases using the complementary strand as a template
- DNA Ligase then joins the DNA up again
o process is energy-demanding and requires a lot of proteins
- mainly for bulky DNA adducts
Which of the following is involved in the repair of damaged DNA?
a. mutation
b. epoxidation
c. DNA adduction
d. base excision repair
e. sister chromatid exchange
d. base excision repair
Which base is at most risk to damage?
- guanine and the adenine
- are the most electron-rich molecules -> most susceptible to electrophile damage
Define Cell Bahviour.
- term used to describe the way cells interact with their external environment and their reactions to this, particularly proliferative and motile responses of cells
What external influences do cells detect?
- chemical influences: hormones, growth factors, ion concentrations, ECM (density, composition), molecules on other cells, nutrients and dissolved gas (O2/CO2) concentrations
- physical influences: mechanical stresses, temperature, the topography or “layout” of the ECM and other cells (the organisation of the ECM)
What external factors can influence cell divison?
- growth factors
- cell-cell adhesion
- cell-ECM adhesion
In what situation must cells be in for them to react to growth factors?
- cell require to be bound to an extracellular matrix to be reactive to soluble growth factors and therefore proliferate
What is anchorage dependence?
- attachment to the ECM may be reuired for cell survival
How do cells adhere to the ECM?
- cells have receptors on their cell surface which bind specifically to ECM molecules -> often link at their cytoplasmic domains to the cytoskeleton
- this arrangement means that there is mechanical continuity between ECM and the cell interior
What are integrins?
- one of the groups of cell-ECM adhesion complexes -> MST IMPORTANT ECM RECEPTORS
- are heterodimer complexes of a and b subunits that associate extracellularly by their “head” regions -> each of the “leg” regions spans the plasma membrane
- ligand-binding (attachment to the ECM) occurs at the junction of the head regions
How do integrins bind to the ECM?
- bind specifically to short peptide sequences on ECM proteins
- for example a5b1 fibronectin receptor binds to arg-gly-asp (RGD)
- RDG is found on multiple ECM molecules -> fibronectin, vitronectin, fibrinogne plus others
What does the a5b1 fibronectin receptor bind to?
- binds to arg-gly-asp (RGD)
Which is the only integrin known that doesn’t associate with the actin cytoskeleton?
- a6b4 integrin complex found in epithelial hemidesmosomes are linked to the cytokeratin
How do cell signal to and from the ECM?
- ECM receptors (e.g. integrins) can act to transduce signals -> ECM binding to an integrin complex can stimulate the complex to produce a signal inside the cell
What is “outside-in” integrin signalling?
o a molecule outside the cell stimulates a signal inside the cell -> this is “outside-in” integrin signalling
- the cell binds to the matrix via the integrin -> stimulates an intracellular signal
- the composition of the ECM will determine which integrin complexes bind and which signals it receives -> can alter the phenotype of the cell -> not all cells express the same integrins
How do integrins promote signalling and actin assembly?
- alpha and beta heterodimers don’t have enzymatic activity in themselves -> cannot signal directly -> however, they can recruit other molecules, some of which are signalling molecules and molecules that associate with the actin cytoskeleton
What is “inside-out” signalling?
- a cell can stimulate the cell to generate an internal signal -> a signal generated inside the cell (e.g. as the result of hormone binding to receptor) can act on an integrin complex to alter the affinity of an integrin
Give some example where inside-out integrin signalling occurs.
- inflammation or blood clotting
- switching on adhesion of circulating leukocytes
Describe the conformation of integrins and how it affects binding?
What is density-dependence of cell division?
- competition for growth factor occurs -> the hihger the density the greater the growth factor -> slower metabolism and division
What signals are required for proliferation of tissue cells?
- growth factor
- ECM -> anchorage dependence
o both activate the same pathways (e.g. MAPK) -> individually they are weak and/or transient but together they strong and sustained
What is contact inhibiton of locomotion?
- most non-epithelial cells “collide”, they do not form stable cell-cell contacts -> actually “repel” one another by paralysing motility at the contact site -> promotes the formation of a motile front at another site, and moving off in the opposite direction -> this is contact inhibition of locomotion
- is responsible for preventing multi-layering of cells in culture and in vivo
What does contact of epithelial cells lead to?
- mutual induction of spreading to create a stable monolayer
- total spread of contacted cells is greater than that of non-contacted
Is beta-catenin the link between cell-cell adhesion and proliferation?
- cadherin is a calcium-dependent, homophilic cell adhesion molecule -> its cytoplasmic tail is associated with BETA-CATENIN which is in turn associated to ALPHA-CATENIN and the actin cytoskeleton
What will neighbouring cells, to a cell undergoing apoptosis, do?
- will form over the top of the dying cell to maintain the constant epithelial barrier
What are the 4 brackets of cell death?
- apoptosis (PCD) -> regulated cell death -> controlled disassembly of cellular contents with no inflammatory response
- apoptosis-like PCD -> some, but not all, features of apoptosis -> may be a display of phagocytic recognition molecules, even before plasma membrane lysis
- necrosis-like PCD -> variable features of apoptosis before cell lysis -> “aborted apoptosis” can occur up to a certain point down the process
- necrosis -> unregulated cell death associated with cellular disruption and an inflammatory response
o NECROSIS AND APOPTOSIS CAN BE INTER-LINKED -> cell death is a SPECTRUM
Describe caspase maturation.
- pro-caspases (zymogens) are single chain polypeptides
- to become activated, they must undergo proteolytic cleavage to form large and small subunits -> initiator caspases must also be cleaved to release the targeting subunit
- these cleavages are done by the caspases themselves
- after the cleavage, you get folding of 2 large and 2 small chains to form an active L2S2 heterotetramer
Describe the structure of death receptors.
- all cells have death receptors on their surface consisting of:
- extracellular cysteine-rich domain
- single transcellular domain
- cytoplasmic tail (with a death domain)
Describe the structure of adaptor proteins in receptor-mediated apoptosis.
Describe death by default mechanism.
- is the intrinsic pathway whereby cellular stresses cause a loss of mitochondrial membrane potential (essential to cell life)
- > results in the release of cytochrome C and other apopotosis-inducing factors
- > stimulate the formation of an apoptosome complex
Describe the structure of the apoptosome (wheel of death).
- consists of an APAF-1 central ring as well as terminals where cytochrome C, ATP and pro-caspase 9 can bind
- APAF-1 is an ATPase protein -> at the C-terminus, it has WD-40 repeats
- 7 APAF-1 monomers form 1 APAF-1 heptamer
Describe the protein called Bid.
- Bid links the receptor-mediated and mitochondrial death pathways -> once one pathway is triggered the other one will be triggered too
- caspase 8 from the receptor-mediated pathway can cleave Bid -> enhances release of mitochondrial proteins, thus engaging the intrinsic pathway -> Bid promotes the release of cytochrome C from the mitochondrion, which triggers the mitochondrial death pathway
What are the steps of tumour progression?
What changes occur in the morphology of a cell when it moves?
- directionality (polarity) of movement that is essential
- become larger in the direction that they are moving
What are the stages of cell motility?
- similar to us rock-climbing
How is actin involved in the movement of a cell?
- signal reaches the cell, and is recognised -> is a rapid disassembly of the filaments -> rapid diffusion of monomers of actin -> reassembly at the side of the cell that is going towards the source -> repolarisation of cell
What are the different structures that cells can form from their actin filament?
Describe cross-linking and bundling of actin.
- fascin will bind filaments together at a particular distance
- fimbrin will also bind filaments together, but between those at a long distance from one another
- alpha-actinin is a dimer, which binds filaments
- spectrin, filamin and dystrophin will cross-link the filaments in particular angles. -> each particular protein will make a specific angle with the filaments
Describe gel-sol transition by actin filament serving.
- when cells needs to move and project, the rigid cell cortex must be broken -> this is called gel-sol transition
- gel is a rigid structure of the actin cytoskeleton -> cross-linking proteins hold the filaments as a mesh
- if the membrane pushes through, this gel mesh must be broken down, severing does this -> actin cross-linking proteins are still present, but the filaments aren’t forming a mesh anymore -> allows a sol that can flow/cytoplasm can move to another area
What happens when 3 members of the Rho family, called Cdc42, Rac and Rho are activated in cells?
- Cdc42= induces filopodia
- Rac = huge expansion and flattening of the cell
- Rho = indcues stress fibres
Describe the cellular organisation of the mammary gland.
- tube is hollow as it has to conduct milk -> ring of 2 layers of epithelial cells lines the lumen -> outermost layer is myoepithelial cells -> are able to contract.
- layer of myoepithelial cells, some of which are slightly vacuolated, make contact with the basement membrane
- myoepithelial cells are important in the development of the tubular structures in the mammary gland
- > tumours can arise from the luminal (inner layer) epithelial cells -> these luminal epithelial cells have receptors required to respond to steroid hormones (particularly oestrogen) -> between 10-20% of luminal cells respond to oestrogen
How does breast cancer progress from normal to malignant?
o can be a local proliferation of cells that are LUMINAL -> proliferate within the tubule, without breaking away from the tube -> is no loss of the myoepithelial cells
- is a benign condition called benign in situ carcinoma -> are locally proliferating cells that may appear as a lump -> easily diagnosed as non-cancer but it is a precursor state for the development of cancer
o lobular carcinoma is where cancer cells try to form tube-like structures, but FAIL -> is some indication that these cells retain the ability to behave like a normal luminal epithelial cell
o medullary carcinoma looks nothing like breast cancer cells or epithelial cells -> packed full of vesicles that are rich in neuro-endocrine peptides and hormones
o vast majority of breast cancers have an intermediate organisation -> involves no specialised structure, and just a growth of cells
Describe the steps that lead to oestrogen reaching the lungs.
Describe hyperplastic polyps.
- very common and BENIGN (NOT dysplastic)
- <0.5 cm
- 90% of all LI polyps
- often multiple occuring in one individual
- no malignant potential -> DON’T CAUSE CANCER
- 15% have k-ras mutation
Describe tubular adenomas.
- columnar cells will have some nuclear enlargement, elongation, multi-layering and loss of polarity
- increased proliferative activity
- reduced differentiation
- complexity/disorganisation of architecture
Describe villous adenomas.
- mucinous cells with nuclear enlargement, elongation, multi-layering and loss of polarity
- exophytic, frond-like extensions
- sometimes have hyper-secretory function and result in excess mucus discharge and hypokalemia
Describe the structure of the epidermis.
- keratinocytes make up the BULK of the cells in the epidermis, but we also have melanocytes, Merkel cells and Langerhans cells (APCs involved in immunity)
- keratinocytes start off at the bottom, and differentiate as they move towards the surface of the skin
- keratinocytes sit on the basement membrane in the layer called the stratum basalae (basal layer of the epidermis) -> where the keratinocytes start of, proliferate, and move on up the skin
- as keratinocytes move towards the surface they change their morphology, becoming keratinocytes within the stratum spinosum (there are spines connecting cells together: desmosomes)
- next layer up is the stratum granulosum: you can see granules in light microscopy
- next layer is the stratum corneum -> where cells are dead and have lost their nuclei
What is this?
- basal cell carcinoma -> usually occur on the face (this is just above the eyebrow
- incidence has increased due to less people wearing hats
Describe the UV spectrum and state which is the most important in causing skin cancer?
- UVC is completely filtered out in the ozone layer
- UVB is partly filtered out
- UVA can penetrate all the way below sea level -> due to deeper penetration is the UV that causes skin ageing
o UBV is considered to be the most significant, but the dose of UVA that penetrates to the surface of the Earth is much higher -> BOTH are significant in causing skin cancer
What are Fitzpatrick phototypes?
I = always burns, never tans -> usually giner
II = usually burns, sometimes tans -> usually blonde
III = sometimes burns, usually tans -> usually have dark brown or black hair
IV = never burns, always tans
V = moderate constitutive pigmentation - south Asian
VI = marked constitutive pigmentation - Afrocaribbean
Describe lentigo maligna.
- lentigo maligna occurs if the atypical melanocytes are restricted to the epidermis -> there is proliferation of malignant melanocytes within the epidermis (in situ) -> is therefore no risk of metastasis
- often occur in elderly patients
- are light and dark brown in colour, have irregular shape, are small (>2cm) and are FLAT -> usually occur on the face
o NOTE -> if there is invasion within a Lentigo maligna, it’s called a Lentigo maligna melanoma
Describe superficial spreading malignant melanomas.
- occurs where atypical melanocytes are in the epidermis, but have invaded the dermis
- is both lateral proliferation of malignant melanocytes, and downwards proliferation -> cells invade through the basement membrane, so there is a risk of metastasis
- sometimes you get regression -> where the melanocytes disappear as a result of immune response
What does a white patch in the middle/around a superficial spreading malignant melanoma mean?
- it is regressing -> immune response against it is effective
- can mean there was a thicker melanoma in that area = worse prognosis
Describe nodular melanomas.
- vertical proliferation of malignant melanocytes (with no previous horizontal/lateral growth) -> means that there is a risk of metastasis
- can ulcerate
Describe nodular melanoma arising within superficial spreading malignant melanoma.
- downward proliferation of malignant melanocytes, following previous horizontal growth
- nodule is developing within an irregular plaque -> prognosis will become WORSE
- tumour may be erythematous or if the tumour can’t make melanin, there will be non-pigmented components
Describe acral lentiginous melanoma.
- occur on the palms of the hand and soles of the foot
- occur more frequently in darker-skinned people than other melanomas
- is a darkly pigmented lesion, which starts of flat. It can develop lumps within it
Describe squamous cell carcinoma of the skin.
- can be either quite rapidly growing, or slow growing
- may occur in scars or scarring processes
- is a risk of metastasis but it is relatively low risk
Describe basal cell carcinoma skin cancer.
- slow growing (a few millimetres a year)
- invades tissue, but does not metastasise -> can go into fat, muscle and bone, but don’t metastasise
Common on the face and even th eyelid
- often described as pearly (their surface glistens, and is often greyish) and flat
Describe mycosis fungoides.
- lymphoma os the skin
- presents with patches of erythematous, scaly skin
- is a patch stage,, plaque stage and tumour stage -> is very slowly progressing -> patients often outlive the disease
- treated with chemo and radiation
Describe Kaposi’s sarcoma.
- tumour is derived from the lymph endothelium
- is related to HIV and aids -> also DRIVEN by HHV8
- clinically, it looks like purple nodules on the skin
Describe epidermodusplasia veruciformis.
- a rare autosomal recessive condition which leads to the predisposition of HPV induced warts and SCCs
- patient will be covered in little warts, which may be flat (right), or thick and keratotic (left)
