Cancer Flashcards
What is metaplasia?
A reversible change in which one adult cell type (usually epithelial) is replace by another adult cell type
- Adaptive
What is dysplasia?
- An abnormal pattern of growth in which some of the cellular and architectural features of malignancy are present
How does dysplasia appear?
- Loss of architectural orientation
- Loss in uniformity of individual cells
How do nuclei appear in dysplasia?
Hyperchromatic
Enlarged
How do mitotic figures appear in dysplasia?
Abundant
Abnormal
In places where they are not usually found
Where is dysplasia common?
- Cervix- HPV infection
- Bronchus- Smoking
- Colon- UC
- Larynx- Smoking
- Stomach - Pernicious anaemia
- Oesophagus- acid reflux
What is neoplasia/tumour/malignancy?
An abnormal autonomous proliferation of cells unresponsive to normal growth control mechanisms
How do benign tumours differ from malignant tumours?
1) Do not invade/ do not metastasise
2) Encapsulated
3) Usually well differentiated
4) Slowly growin
5) Normal mitoses
When can benign tumours be fatal?
1) When in a dangerous place e.g. meninges, pituitary
2) Secretes something dangerous: insulinoma
3) Gets infected: bladder
4) Bleeds: stomach
5) Ruptures: liver adenoma
6) Torts (twisted): ovarian cyst
What are the characteristics of a malignant tumour?
1) Invade surrounding tissues
2) Spread to distant sites
3) No capsule
4) Well to poorly differentiated
5) Rapidly growing
6) Abnormal mitoses
What is a metastasis?
A discontinuous growing colony of tumour cells, at some distance from the primary cancer
What does a metastasis depend on?
The lymphatic and vascular drainage of the primary site
What is a benign tumour of the surface epithelium?
Papilloma
e.g. skin, bladder
What is a benign tumour of the glandular epithelium?
Adenoma
e.g. stomach, thyroid, colon, kidney, pituitary, pancreas
What is a carcinoma?
Malignant tumour derived from epithelium
What are the different types of carcinomas?
- Squamous cell
- Adenocarcinoma
- Transitional cell
- Basal cell carcinoma
What is a sarcoma?
A malignant tumour derived from connective tissue (mesenchymal) cells
What are the different types of sarcomas?
Fat= liposarcoma Bone= osteosarcoma Cartilage= chondrosarcoma Muscle striated= rhabdomyosarcoma Muscle smooth= leiomyosarcoma Nerve sheath= malignant peripheral nerve sheath tumour
What are the tumours of white blood cells?
Leukaemia
Lymphoma
What is leukaemia?
A malignant tumour of bone marrow derived cells which circulate in the blood
What is lymphoma?
A malignant tumour of lymphocytes (usually) in lymph nodes
What is teratoma?
A tumour derived from germ cells, which have the potential to develop into tumours of all three germ cell layers
1) ectoderm
2) mesoderm
3) endoderm
How do gonadal teratomas differ in males and females?
Males= all malignant Females= most are benign
What is hamartoma?
- 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 do
- E.g. Bile duct hamartomas, bronchial hamartomas
What is the criteria for assessing differentiation of a malignant tumour?
- Evidence of normal function still present production of keratin, mucin, bile and hormones
- Various grading systems, for Ca breast, prostate colon
- There is no differentiation for anaplastic carcinoma
What does the grade of a tumour describe?
Its degree of differentiation
What does the stage of tumour describe?
How far it has spread
What is more important (stage or grade) when determining prognosis?
Stage is more important.
What does the rate of cell division depend on?
1) Embryonic vs adult cells
2) Complexity of system
3) Necessity of renewal
4) State of differentiation (some cells never divide i.e. neurons)
5) Presence of tumour cells
Why is appropriate regulation cell division important?
- Premature, aberrant mitosis results in cells death
- In addition to mutations in oncogenes and tumour suppressor genes, most solid tumours are aneuploid
- Various cancer cell lines show chromosome instability
- Perturbation of protein levels of cell cycle regulators is found in different tumours
- Contact inhibition of growth
- Attacking the machinery that regulates chromosome segregation is one of the most successful anti-cancer strategies n clinical use
What is the cell cycle?
Orderly sequence of events in which a cell duplicates its contents and divides in two
What is the order of the eukaryotic cell cycle?
M phase Interphase G0 G1 S G2
What occurs during the M phase?
Mitosis
- Nuclear division
- Cell division (cytokinesis)
What occurs during interphase
Duplication
- DNA
- Organelles
- Protein synthesis
Why is mitosis the most vulnerable period of the cell cycle?
- Cells are more easily killed (irradiation, heat shock, chemicals)
- DNA damage can not be repaired
- Gene transcription is silenced
What occurs during the S phase?
Replication for division
- DNA replication
- Protein synthesis: initiation of translation and elongation increased; capacity is also increased
- Replication of organelles (centrosome, mitochondria, Golgi, etc)
In the case of mitochondria, this needs to coordinate with the replication of mitochondrial DNA
What is the centrosome?
- Consists of two centrioles (barrels of nine triplet microtubules)
- Functions: microtubule organising center (MTOC) and mitotic spindle
What are the six different phases of mitosis?
Prophase Prometaphase Metaphase Anaphase Telophase Cytokinesis
What occurs during prophase?
- Replicated chromosome condense to avoid breaking
- Duplicated centrosomes migrate to opposite sides of the nucleus and organise the assembly of spindle microtubules
- Outside the nucleus, the mitotic spindle assembles between the two centrosomes
What does each condensed chromosome consist of?
2 sister chromatids, each with a kinetochore
How does the mitotic spindle form?
- Radial microtubule arrays (ASTERS) form around each centrosome (microtubule organising centres MTOC)
- Radial arrays meet
- Polar microtubules form
- Microtubules are in a dynamic state
What occurs during early prometaphase?
- Breakdown of the nuclear membrane
- Spindle formation is largely complete
- Attachment of the chromosome to spindle via kinetochores (centromere region of chromosome)
What occurs during late prometaphase?
- Microtubule from opposite pole is captured by sister kinetochore
- Chromosomes attached to each pole congress to the middle
- Chromosome slides rapidly towards centre along microtubules
What occurs during metaphase?
The attached chromosome have undergone active movement and are lined up at the midline of the spindle.
The kinetochores of each sister chromatid are attached to opposite poles of the spindle
What occurs during anaphase?
- Paired chromatids separate to form two daughter chromosomes
- Cohesin holds sister chromatids together
- Consists of Anaphase A and B
What occurs during anaphase A?
- Breakdown cohesin
- Microtubules get shorter
- Daughter chromosome pulled toward opposite spindle poles
What occurs during anaphase B
1) Daughter chromosomes migrate towards poles
2) Spindle poles (centrosomes) migrate apart
What occurs during telophase?
- Daughter chromosome arrive at the spindle
- Nuclear envelope reassembles at each pole
- Assembly of contractile ring
What is cytokinesis?
The stage where the cytoplasm is divided into two daughter cells by the contractile ring of actin and myosin filaments.
Each daughter cell now has its own nucleus
What is the Spindle- assembly checkpoint?
Controls the transition out of metaphase into anaphase by sensing completion of chromosome alignment and spindle assembly.
- Achieved by monitoring kinetochore activity
- Requirements for this include CENP-E and BUB protein kinases
- BUBs dissociate when chromosomes are properly attaches to the spindle
- When all has dissociated, anaphase proceeds
What is aneuploidy?
Abnormal number of chromosomes
What are the different ways in which aneuploidy can be caused?
1) Mis-attachment of spindle to kinetochores
2) Aberrant mitosis
3) Anti-cancer therapy
What are the types of attachment of the spindle to kinetochores?
Amphelic attachment= normal: kinetochores do not produce a checkpoint signal
Merotelic attachment= spindle attachment from the same centrosome to both kinetochores
Monotelic attachment= movement of both pairs of chromatids to the same pole
Synthelic attachment= movement of both pairs of chromatids to the same pole, but in this case they are attached to different spindles
Why does merotelic attachment have negative consequences?
Results in aneuploidy
- Kinetochores won’t produce a checkpoint signal which indicates something is wrong
- There is a loss of a chromosome at cytokinesis
Why can synthelic attachment result in aneuploidy?
Both sister chromatids are at the same pole
- These sister chromatids are likely to break and their kinetochores may or may not produce checkpoint signals
Why does aberrant mitosis result in aneuploidy?
Results in 4 instead of 2 centrosomes being produced
- This leads to a multi-polar spindle with abnormal cytokinesis following. This results in 4 daughter cells
Why can anti-cancer therapy induce aneuploidy?
- Drugs have been developed to induce chromosome mis-segregation with the aim of this to lead to apoptosis of the cancer cell
- This is achieved by either inhibiting attachment-error-correction mechanisms, or inhibiting checkpoint protein kinases
Give examples of anti-cancer therapies that can result in aneuploidy
- Taxanes and vinca alkaloids
- Used in breast and ovarian cancers
- Produces unattached kinetochores
- Causes long-term mitotic arrest
What might happen if something goes wrong during the cell cycle?
1) Cell cycle arrest
- At check points (G1 and spindle check point)
- Can be temporary, allowing time for DNA repair
2) Programmed cell death (apoptosis)
- DNA damage too great and cannot be repaired
- Chromosome abnormalities
- Toxic agents
What is the G1/S checkpoint influenced by?
Growth factors
What is the G2/M checkpoint influenced by?
DNA damage
What is the Metaphase checkpoint influenced by?
Sister chromatid alignment
During the cell cycle, what occurs in the absence of stimulus?
The cells go into G0 (quiescent phase)
- This is how most differentiated cells in the body exist where they are able to perform specific functions without dividing
What does exit from the G0 phase require?
- Is highly regulated
- Requires growth factors and intracellular signalling cascades
- This does not happen in tumour cells
How are signalling cascades activated?
In response to extracellular ligands that bind to cell surface receptors and trigger an intracellular signal
What happens to the intracellular signal that is triggered by a signalling cascade?
- Amplified
- Integrated
- Modified by other pathways before diverging to have effects on metabolism, gene expression and the cytoplasm
Give an example of an intracellular signalling cascade
EGF (epidermal growth factor) and PDGF (platelet-derived growth factor) attach to their respective receptors (receptor protein tyrosine kinase)
- These are found in a monomeric, inactive state
During a signalling cascade, what happens in the presence of a ligand?
- Receptors form dimers
- Are activated by phosphorylation of amino acid residues in the kinase domain
During a signalling cascade, how does phosphorylation to activate receptors occur?
Via the transfer of phosphate from ATP to a hydroxyl group on serine, threonine and tyrosine.
During a signalling cascade when the receptor is activated, how does the added phosphate group alter protein function?
- The phosphate group is negatively charged
- It causes a change in conformation leading to a change in activity (+ve or -ve)
- Creating a docking site for another protein
During a signalling cascade, what does activation of a receptor result in?
- Intracellular kinase cascade mediated by adaptor proteins which bind to the newly created docking site
What do protein kinase cascades result in?
Lead to signal amplification, diversification and opportunity for regulation
Why are their protein kinase cascades?
Frequently the protein regulated by a kinase is another kinase, and so on
How can protein kinase cascades be reversed?
By phosphatases
How long does G1 last?
10 hours
How long does the S phase last?
9 hours
How long does G2 last?
4 hours
Which stages are interphase?
G1
G0
G2
What is c-Myc?
A transcription factor which stimulates the expression of cell cycle genes
- Has an important role in G1
What are they key components of signalling pathways?
1) Regulation of enzyme activity by protein phosphorylation (kinases)
2) Adapter proteins
3) Regulation by GTP-binding proteins
How does growth factor stimulate signalling pathways?
Mitogenic growth factor -> Receptor protein tyrosine kinase -> Small G (GTP-binding) protein (Ras) -> Kinase cascade -> Immediate early genes- control the expression of other genes
What does the first 15 minutes of growth factor stimulation of signalling pathways consist of?
- The mitogenic growth factor binding to the cell surface receptor protein tyrosine kinase
- Phosphorylation of RTPK initiates the kinase cascade which provides additional docking sites and activates Ras
What does the Ras binding stimulate?
Stimulates and mediates early-response gene expression from the MAPK/ERK cascade e.g. c-Myc expression
What does the last hour of growth factor stimulation of signalling pathways involve?
Stimulation of expression of delayed-response genes which leads to the activation of the cell-cycle control system
What happens following phosphorylation of receptor protein tyrosine kinase?
Additional docking sites are formed.
Adapter proteins such as Grb2 dock to the phosphorylated site
What happens when Grb2 binds to the phosphorylated site?
Recruits inactive Ras protein to the cytosolic surface of the plasma membrane. The inactive Ras protein is associated with a GDP molecule.
How do Ras-activating proteins activate Ras?
Using exchange factor Sos, which exchanges a phosphate from a GTP molecule associate with the Ras-activating protein for the GDP molecule associated with Ras
How is Ras deactivated?
G-proteins act as a molecular switch, turning Ras off.
They do this through GTP hydrolysis using GTPase activating proteins (GAP)
How is Ras oncogenically activated?
Mutations that increase the amount of active GTP-loaded Ras.
The mutations either prevent GAP binding or prevent GTP hydrolysis.
What does Ras activate one it is in its active GTP-loaded form?
Protein kinase cascade.
Specifically= Extracellular signal-regulated kinase (ERK) cascade
Gernerically= Mitogen-activated protein kinase (MAPK) cascades
What are the generic and specific names of the protein kinase cascde
Kinase I- Generic name: MAP-KKK Specific: Raf Kinase 2- Generic name: MAP-KK Specific: MEK Kinase 3- Generic name: MAP-K Specific: ERK
What does ERK go on to stimulate?
Changes in cell protein and gene expression (eg c-Myc) in order to promote cell division
What do mutated Ras and c-Myc act as?
Oncogenes
Lead to uncontrolled cell division and tumour proliferation
What is cell cycle control based on?
Cyclin-dependent kinases (Cdks)
- They are present in proliferating cells throughout the cell cycle
How is the activity of cyclin-dependent kinases (Cdks) regulated?
- Through their interaction with cyclins
- Their phosphorylation
What are cyclins?
- Proteins which activate Cdks
- Transiently expressed at specific points in the cell cycle
- Level of expression if highly regulated
- They are synthesised and then degraded
- Form cyclin-Cdk complexes of which different complexes trigger different events in the cell cycle
What are the different cyclin-Cdk complexes which trigger different events in the cell cycle?
S phase: Cdk2/Cyclin A
Mitosis: Cdk1/Cyclin B
G1 progression: Cdk2/Cyclin E
What types of genes are activated by the Ras-ERK pathway?
c-jun, c-fos, c-myc encoding transcription factors
How does mitotic cyclin B interact with Cdk1?
They form a complex which acts as the mitosis promoting factor (MPF)
How is the mitosis promoting factor (MPF) activated?
Requires activating phosphorylation using CAK (cdk activating kinase)
- As well as removal of the inactivating phosphorylation by inhibitory kinase - Wee1
What determines whether the mitosis promoting factor becomes activated?
The balance between CAK and Wee1
Why is mitosis promoting factor activated at the end of interphase?
WEE1 is removed at the end of interphase using CDC25 phosphatase.
- There is positive feedback
How does mitosis progress?
Cdk1/cycB active- then mitosis is on hold and the key substrates are phosphorylated.
A signal from fully attached kinetochores causes cyclin B to be degraded
- Cdk1 inactivated
- Key substrates dephosphorylated
- Mitosis progresses
How does growth factor stimulation of signalling pathways promote G0 to G1 transition?
c-Myc is an immediate early gene transcription factor.
- c-Myc stimulates transcription of cyclin D which is required for re-entry into the cell cycle from G0
How does Cyclin D stimulate progression from G1 into the S phase?
Cyclin D activate cdk4 and cdk6 which stimulates cyclin E production which is required for the cell cycle to progress
What is the purpose of Cdks
Sequentially activated by cyclins and stimulate the synthesis of genes required for the next phase
e.g. CycD/Cdk4/6 stimulates the expression of CycE
- This gives direction and timing to the cycle
How Cdks work?
They phosphorylate proteins (or Serine or threonine) to drive cell cycle progression
What do MPF target?
Nuclear lamins.
The phosphorylation of which causes the breakdown of the nuclear envelope
What does Cdk4/6- Cyclin D target?
Retinoblastoma protein
The phosphorylation of which inactivates the protein
Releases E2F transcription factor, driving gene transcription of Cyclin E and allowing the progression of the cell cycle from G1 > S phase
How can the Cdk5/6-cyclin D complex have negative effects.
Retinoplastoma protein (pRB) is a tumour supressor which acts as a break on the cell cycle until it receives the signal from the Cdk4/6-Cyclin D complex - Is the tumor suppressor is lost, uncontrolled cell division may occur
How Cdk inhibitors (CKIs) regulate Cdks
Inhibit them to prevent progression through the cell cycle, which is important in ensuring the integrity of the cell cycle is maintained
What are the two familiess of CDk inhibitors (CKIs)
INK4
CIP/KIP
How does the INK4 family inhibit Cdks
Inhibits Cdk4/6 by displacing cyc D
- Arrest G1 at the restriction checkpoint
How does the CIP/KIp family inhibt Cdks
Inhibits all Cdks especially in the S phase
- Does this by binding to the Cdk/cyc complex
What codes for INK4?
p16
What codes for CIP/KIP?
p27
How can problems with Cdk inhibitors result in cancers?
- Loss of INK4 inhibition
- Over-production of cdk4/cyclin D
- Loss of retinoblastoma protein (highly prevalent in lung cancer)
How can cell cycle regulatory proteins lead to cancer and act as oncogenes?
- EGFR/HER2= mutationally activated or over-expressed in many breast cancers
- Ras= mutationally activated in many cancers
- Cyclin D1
- B-Raf
- c-Myc
Why may Ras lead to cancer?
When mutationally activated.
They are inhibitors of membrane attachment
Which tumour suppressors and cell cycle regulatory proteins are inactivated in cancer?
Rb
p27KIP1
What are the types of genetic mutations that cause cancer?
- Chromosome translocation
- Gene translocation
- Gene amplification (copy number variation)
- Point mutations within promotor or enhancer regions of genes
- Deletions or insertions
- Epigenetic alterations to gene expression
- Can be inherited
What are the components of cytotoxic chemotherapy?
1) Alkylating agents
2) Antimetabolites
3) Anthracyclines
4) Vinca alkaloids and taxanes
5) Topoisomerase inhibitors
How is cytotoxic chemotherapy administered?
- Given intravenously or by mouth
- Works systemically
- Non ‘targeted’ affects all rapidly dividing cells in the body
- Given post-operatively: adjuvant
Pre-operatively: neoadjuvant
As monotherapy or in combination
With curative or palliative intent
How do alkylating agents act in cytotoxic chemotherapy?
- Add alkyl groups to guanine residues in DNA
- Cross-link DNA strands and prevent DNA from uncoiling at replication
- Trigger apoptosis (at checkpoint pathway
- Encourage miss-pairing- oncogenic
What are pseudo-alkylating agents?
- Add platinum to guanine residues in DNA
- Same mechanism of cell death as alkylating agents
E.G. Carboplatin, cisplatin, oxaliplatin
Give examples of alkylating agents
Chlorambucil
Cycophosphamide
Dacarbazine
Temozolomide
What are the side effects of alkylating and pseudoalkylating agents?
- Cause hair loss ( not carboplatin)
- Nephrotoxicity
- Neurotoxicity
- Ototoxicity (platinums)
- Nausea
- Vomiting
- Diarrhoea
- Immunosuppression
- Tiredness
How do anti-metabolites act in cytotoxic chemotherapy?
Masquerade as purine or pyrimidine residues leading to inhibition of DNA synthesis, DNA double strand breaks and apoptosis
- Block DNA replication and transcription
- Can be purine (adenine and guanine), pyrimidine or folate antagonists
- Examples= methrorextate (folate), 6-mercaptopurine, carbazine and fludarabine
What are the side effects of anti-metabolites?
- Hair loss (alopecia): not 5FU or capecitabine
- Bone marrow suppression causing anaemia, neutropenia and thrombocytopenia
- Increased risk or neutropenic sepsis (and death) or bleeding
- Nausea and vomiting (dehydration)
- Mucositis and diarrhoea
- Palamar-plantar erthrodysethesia (PPE)
- Fatigue
How do anthracyclines work in cytotoxic chemotherapy?
- Inhibit transcription and replication by intercalating (i.e. inserting between) nucleotides within the DNA/RNA strand
- Also block DNA repair- mutagenic
- They create DNA and cell membrane damaging free oxygen radicals
- E.g. doxorubicin, epirubicin
What are the side effects of anthracyclines?
- Cardiac toxicity (arrhythmias, heart failure)
- Alopecia
- Neutropenia
- Nausea and vomiting
- Fatigue
- Skin changes
- Red urine
How do vinca alkaloids and taxanes work in cytotoxic chemotherapy?
Inhibit assembly (vinca alkaloids or disassembly (taxanes) of mitotic microtubules causing dividing cells to undergo mitotic arrest
What are the side effects of microtubule targeting drugs?
- Nerve damage: peripheral neuropathy, autonomic neuropathy
- Hair loss
- Nausea
- Vomiting
- Bone marrow suppression (neutropenia, anaemia etc)
- Arthralgia
- Allergy
How do topoisomerase inhibitors work in cytotoxic chemotherapy?
- Topoisomerases are required to prevent DNA torsional strain during DNA replication and transcription
- Induce temporary single strand (topo1) or double strand (topo2) breaks in the phosphodiester backbone of DNA
- They protect the free ends of DNA from aberrant recombination events
- Drugs such as anthacyclines have anti-toposomerase effects through their action on DNA
- Specific topoisomerase inhibitors include Tpotecan and irinotecan (topo I) and etoposide (topo II) alter binding of the complex to DNA and allow permanent DNA breaks)
What are the side effects of topoisomerase inhibitors?
- Irinotecan- Acute cholinergic type syndrome- diarrhoea, abdominal cramps and diaphoresis (sweating). - Therefore given with atropine
- Hair loss
- Nausea, vomiting
- Fatigue
- Bone marrow suppression
How can a resistant cell survive?
- Drug effluxed from the cell by ATP-binding cassette (ABC) transporters
- DNA adducts replaced by Base Excision repair (using PARP)
- DNA repair mechanisms are up-regulated and DNA damage is repaired so the DNA double strand does not break
What are the ten hallmarks of a cancer cell?
1) Self-sufficient
2) Insensitive to anti-growth signals
3) Anti-apoptoctic
4) Pro-invasive and metastatic
5) Pro-angiogenic
6) Non-senscent
7) Dysregulated metabolism
8) Evades the immune system
9) Unstable DNA
10) Inflammation
What receptors are over-expressed in cancers?
HER2: amplified and over-expressed in 25% breast cancer
EGFR: over-expressed in breast cancer and colorectal cancer
PDGFR: glioma (brain cancer
What ligands are over-expressed in cancers?
VEGF: prostate cancer, kidney cancer, breast cancer
What are the different monoclonal antibodies?
- momab ( derived from mouse antibodies)
- ximab (chimeric) e.g. cetumixab
- zumab (humanised) e.g. bevacizumab, trastuzumab
- mumab (fully human) e.g. panitumumab
What do monoclonal antibodies target?
The extracellular component of the receptor
- They neutralise the ligand
- Prevent receptor dimerisation
- Cause internalisation of receptor
- mAbs also activate Fcy-receptor-dependent phagocytosis or cytolysis induced complement-dependent cytotoxicity (CDC) or antibody-dependent cellular cytotoxicity (ADCC)
Which monoclonal antibodies are used in oncology?
- Bevacizumab binds and neutralises VEGF. Improves survival colorectal cancer
- Cetuximab targets EGFR
What is the mechanism of small molecule inhibitors (SMIs)?
Bind to the kinase domain of the tyrosine kinase within the cytoplasm and block autophosphorylation and downstream signalling
- Also act on intracellular kinases therefore can affect cell signalling pathways
What is Glivec?
A small molecule inhibitor that targets the ATP binding region within the kinase domain
Give examples of SMIs inhibiting receptors
Erlotinib (EGFR)
Gefitinib (EGFR)
Lapatinib (EGFR/HER2)
Sorafinib (VEGFR)
Give examples of SMIs inhibiting intracellular kinases
Sorafinib (Raf kinase)
Dasatinib (Src kinase)
Torcinib (mTOR inhibitors)
What are the advantages of SMIs
- Can target TKs without an extracellular domain or which are constitutively activated (ligand independent)
- Pleiotropic tagets (useful in heterogenic tumours/cross talk)
- Oral administration
- Good tissue penetration
- Cheap
What is a disadvantage of SMIs and monoclonal antibodies?
Resistance
What are the different resistance mechanisms to targeted therapies?
- Mutations in ATP-binding domain (e.g. BCR-Abl fusion genes and ALK gene, targeted by Glivec and crizotinib respectively)
- Intrinsic resistance (herceptin effective in 85% HER2 & breast cancers, suggesting other driving pathways)
- Intragenic mutations
- Upregulation of downstream or parallel pathways
What are anti-sense oligonucleotides?
- Single stranded, chemically modified DNA like molecule. 17-22 nucleotides in length
- Complementary nucleic acid hybridisation to target gene hindering translation of specific mRNA
- Recruits RNASe H to cleave target mRNA
- Good for ‘undruggable’ targets
What is cell behaviour?
The 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 are detected by cells?
- Chemical: hormones, growth factors, ion concentrations, ECM, molecules on other cells, nutrients and dissolve gas (O2/CO2) cells
- Physical: mechanical stresses, temperature, the topography or layout of the ECM and other cells
What is cell-spreading dependent on?
Gravity dependent
Energy is required to modulate cell adhesion and the cytoskeleton during spreading
What is the importance of cell- ECM adhesion?
- In suspension, cells do not significantly synthesise protein or DNA
- Cells require to be attached to ECM (and a degree of spreading is required) to begin protein synthesis and proliferation (DNA synthesis)
- Attachment to ECM may be required for survival (e.g. epithelia, endothelia)
- i.e. anchorage dependence
What are cell-ECM adhesion molecules?
- Cells have receptors on their cell surface which bind specifically to ECM molecules
- These molecules are often linked at their cytoplasmic domains, to the cytoskeleton
- This arrangement means that there is mechanical continuity between ECM and the cell interior
What are integrins?
Heterodimer complexes of alpha and beta subunits that associate extracellularly by their ‘head’ regions. Each of the ‘tail’ regions spans the plasma membrane.
- Recognise short, specific, peptide sequences
- More than 20 combinations of alpha/beta known
- Each combination specifically binds a particular peptide sequence
- Such peptide sequences found in more than one ECM molecule e.g. RGD found in fibronectin, virtonectin, fibrinogen plus others
- Linked via actin binding proteins to the actin cytoskeleton
What do integrin complexes cluster to form?
Focal adhesions
Hemidesmosome (alpha6Beta4- linked to the cytokeratin network)
- These clusters are involved in signal transduction
- Integrins also bind to specific adhesion molecules to some cells
How can ECM receptors (e.g. integrins) act to transduce signals?
- ECM binding to an integrin complex can stimulate the complex to produce a signals inside the cell i.e. ‘outside-in’ integrin signalling
- A signal generated inside the cell can act on an integrin complex to alter the affinity of an integrin i.e. inside out integrin signalling (e.g. in inflammation or blood-clotting, switching on adhesion of circulating leukocytes
What is outside- in signalling
- A cell can receive information about its surroundings from its adhesion to ECM
- E.g. the composition of the ECM will determine which integrin complexes bind and which signals it receives
- This can alter the phenotype of the cell
Describe the density-dependence of cell division
- When cells in culture form a confluent monolayer, they cease proliferating and slow down many other metabolic activities.
This used to be known as contact inhibition of cell division - Another set of experiments have now suggested that it is competition for external growth factors and not cell-cell contact responsible. This is known as the density dependence of cell division.
What is the ERK MAP kinase Cascade?
- The pathway by which growth factors induce gene expression and cell proliferation is known as the ERK MAP kinase cascade
- The signal starts when a growth factor binds to the receptor on the cell surface and ends when the DNA in the nucleus expresses a protein and produces some change in the cell, such as cell division.
- The proteins included are MAPK which communicate by adding phosphate groups to a neighbouring protein- acts as an on or off switch
- The extracellular growth factor binds to the membrane ligand. This allows Ras to swap its GDP for a GTP. It can now activate MAP3K, which activates MAP2K which activates MAPK. MAPK can now activate a transcription factor, such as myc
What is proliferation dependent on?
Density (e.g. growth factor)
Anchorage (e.g. ECM)
What is the mechanism of anchorage dependence?
- Growth factor receptors and integrin signalling complexes can each activate identical signalling pathways (e.g. MAPK)
- Individually, this activation is weak and/or transient
- Together, activation is strong and sustained
- The separate signalling pathways act synergistically
