Cancer 8 Flashcards
1
Q
where are most human tumors derived from?
A
- 80-90% of human tumours are derived from epithelial tissues
2
Q
what is the structure of human tumors?
A
- They have tight junctions and are polarised
- They are based on top of a basement membrane
- the basement membrane separates them from stromal cells and other tissue
3
Q
what are the stages of conversion of benign cells to a tumour?
A
- genetic alterations
- hyper proliferation
- de differentiation
- invasion
4
Q
what does genetic alteration to the tumour cell do?
A
- this results in hyper-proliferation
- this results in the cells losing their identity
- this leads to a de-differentiation process
- after this has occurred the tumor will not bare any resemblance to the characteristics of the original tissue
5
Q
what occurs to the cells at hyper-proliferation?
A
- this causes cells to lose their identity
6
Q
what happens to the cells at de-differentiation?
A
- disassembly of cell-cell contacts
- causes loss of polarity
- (polarity is essential for function)
7
Q
what does invasion do to the tumour?
A
- Cells secrete proteases to clip the basement membrane
- Cells make protrusions and invade surrounding tissue by cleaving ECM proteins.
8
Q
at what stage does metastasis take place?
A
- Normally, hyper-proliferation leads to a BULK of cells (solid tumor)
- at this point, the cells are still connected to each other and bound within the tissue
- as soon as the cells de-differentiate, they break away from the basement membrane
- at this point, metastasis can take place
- Once tumor cells exit the venous/lymphatic systems, they can COLONISE and METASTASISE at long distances from the site of origin.
9
Q
what are the two types of tumour cell migration?
A
- individual (single cell migration)
- collective (group of cells)
10
Q
what do both types of tumour cell motility require?
what does collective migration specifically require?
A
- integrins and proteases
- collective migration specifically requires modulation of cell-cell contacts and communication between cells (gap junctions)
11
Q
how do different tumour types prefer to migrate?
what are the 4 subgroups of migration ?
A
- Amoeboid (rapid induvidual) : lymphoma, leukaemia, SCLC
- Mesenchymal (single cells/chains): fibrosarcoma, glioblastoma, anaplastic tumours
- Cluster/cohorts: epithelial cancer, melanoma
- Multicellular strands/sheets): epithelial cancer, vascular tumours
12
Q
where else does collective migration occur?
A
eg. vascular sprouting
- Whenever vessels need to be remodelled, cells must invade the surrounding areas as a STRUCTURE
- they cannot travel induvidually
eg. breast feeding
- When tissue has to grow, cells bud to grow and branch in order to form the mammary glands
- . The whole tissue will invade its surroundings and grow around.
13
Q
what is a scratch wound assay?
A
- If a confluent monolayer is scraped the cells sense spaces between them
- Immediately, they will migrate together to close the gap
- healing works using collective migration
14
Q
how do tumor cells demonstrate migration?
A
- Tumour cells demonstrate collective migration but it is not organised
- cells migrate EVERYWHERE
- this is because Contact inhibition of migration is ineffective in tumour cells.
15
Q
what happened when tumour cells and EGF were injected into a mouse?
A
- Tumour cells were inserted into a mouse
- EGF (a growth factor) was injected into the mouse
- when the proteins of the mouse were collected it was shown many of them were up-regulated cytoskeletal proteins and signaling proteins
16
Q
what are examples of stimuli to make cells move?
A
- Organogenesis and morphogenesis
- Wounding
- Growth factors/chemoattractants
- De-differentiation (tumours)
17
Q
what happens to the cell shape when they move?
A
- they become polarised
- they develop a head which leads the motion
18
Q
how do cells know when to stop moving?
A
CONTACT-INHIBITION MOTILITY
this is achieved when cells interact with surrounding cells which tell them to stop
19
Q
what specialised cell structures help with cell motility?
A
- focal adhesion
- lamellae
- filopodia (slender cytoplasmic projections )
20
Q
how do cells attach to the substratum?
A
- the cells must attach in order to migrate
- Focal adhesions hook onto the ECM matrix, and grab it to provide points where the cells can attach
- the cells then generate traction forces so they an move
21
Q
how is the hooking controlled?
A
- the hooking is controlled by dimer integrin receptors
- They are transmembrane proteins (one transmembrane domain) with a short cytoplasmic tail
- the tail has no enzymic activity
- Integrins just have docking places for cytoskeletal proteins
- they form complexes of proteins
22
Q
what is filapodia?
A
Finger-like protrusions rich in actin filaments
23
Q
what is the function of filopodia?
A
- filopodia are protrusions that are actin-rich
- Vinculin is an ACTIN-BINDING PROTEIN
- the filopodia sense the surrounding environment to see where the cell should attach
- they are required in coordination of movement
24
Q
what are lamellipodia?
A
- sheet like protrusions that are rich in actin filaments
25
Q
what is the function of lamellipodia?
A
- The cell migrates in a certain direction, and the sheets of membrane project to the front of the cell (in the same direction).
- The sheets then ruffle back, so that the cell can move.
26
Q
why is control required in cell movement?
A
- Within a cell, control is needed to coordinate what is happening in different parts
- Control is needed to regulate adhesion/release of cell-extracellular matrix receptors
- From outside to respond to external influences – sensors and directionality
27
Q
what is hapoptatic motility?
what is chemotactic motility?
A
- HAPOPTATIC MOTILITY: directional motility or outgrowth of cells with no purpose (eg. going for a walk in the park)
- CHEMOTACTIC MOTILITY: movement in response to a chemical stimulus (this is a purposeful response like going to buy bread)
28
Q
how do the focal adhesions and lamellipodia work together to allow the cell to move?
A
- the focal adhesions act like feet
- they allow the cell to attach and protrude
- the lamellipod extends and attach to the ECM
- once the focal adhesion has been made the back of the cell must contract using energy to push the cell forward
- the cell moves one step at a time
- the old adhesions are left behind as the cell moves forward
29
Q
how does actin filament polarity help migration direction?
A
- Actin is a fundamental monomer in cells
- Actin can polymerise in the cells
- Actin monomers are polarised
- when a signal reaches a cell to migrate in a certain direction there is a rapid disassembly of the filaments
- then there is rapid diffusion of monomers of actin to the new head of the cell
- repolarisation of the cell.
30
Q
show a migrating cell:
A
31
Q
what allows the cells to contract during migration?
A
- In the filapodium, actin is in its filamentous form, in a parallel arrangement
- Stress fibres have an anti-parallel organisation of the filaments
- in combination they are able to contract to make movement
32
Q
in what ways can actin molecules remodel?
A
- There are different classes of cytoskeletal proteins that control each of these steps.
- nucleation
- elongation
- capping
- severing
33
Q
explain nucleation :
A
- The nucleation step is the rate-limiting step in the organisation of the cytoskeleton
- it requires a lot of energy
- Arp = actin-related proteins. They have similar structures to actin, but they are NOT actin
- they help the monomers form a trimer
- after this happens the filaments can form
- Arp-2,3 complex is the main protein involved
34
Q
explain elongation:
A
- After trimer formation, elongation must occur
- Different classes of proteins assists the process
- profilin is a protein that binds to G-actin and drags it over to the actin filament
- Thymosin protein binds to actin monomers and acts as a brake to inhibit the polymerisation process
35
Q
explain capping?
A
- Capping proteins regulate the elongation process of the filament.
- The capping protein binds the end of the filament and prevent monomers from being added on.
- Once adding is blocked, there is a disassembly process that results in the shortening of the filament.
36
Q
how are the actin filaments generated into filaments?
A
- once the filament has been broken down into small pieces there is the option to glue the pieces of filament back together again
- This process involved the re-annealing of the filaments.
- Alternatively, short filaments may be used to grow a separate fibre.
37
Q
explain severing:
A
- The filament size can be regulated by severing
- Severing proteins chop the filament up, which counter-intuitively generates more ends so that filaments can grow more rapidly.
- Gelsolin has two functions – it is a capping and severing protein
38
Q
what is crosslinking and bundling?
A
- Filaments can take different shapes. Cross-linking and bundling proteins do this.
- Fascin will bind filaments together at a particular distance
- Fimbrin binds long-distance filaments together
- 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.
39
Q
how does bundling occur?
why are motor proteins useful in bundles ?
A
- From the filament formed, bundling may occur
- depending on the way the proteins bundle motor proteins may come in
- if the filaments are too close together then motor proteins will not be able to come in
- Motor proteins include myosin – this comes in to promote sliding, enabling the cell and filaments to contract.
40
Q
how does the branching process take place?
A
- in lamellar proteins the branches are at 70 degrees exactly
- The Arp-2 complex is the protein responsible for the branching appearance of the filaments as the cells move forward in the lamellar.
- The Arp-2 complex can nucleate and branch
- this allows the filaments to elongate outwards
41
Q
what is gel sol transition by actin filament severing?
A
- when cells need to move and project the rigid cell cortex must be broken down
- this will allow the cell membrane to move forwards
- This is called gel-sol transition
- gel is a rigid structure of the actin cytoskeleton
- If the membrane pushes through, this gel mesh must be broken down
- severing breaks down the gel
- The actin cross-linking proteins are still present, but the filaments aren’t forming a mesh anymore
- this means the cytoplasm can move to a new area
42
Q
which of the following diseases is not related to the actin cytoskeleton ?
A
- High blood pressure
- Wiskott-Aldrich Syndrome – WAS (immunodeficiency, eczema, autoimmunity) - this means the cell does not know where to migrate to
- Duchenne Muscular Dystrophy (muscle wasting)
- Bullous Pemphigoid (an autoimmune disease)
- Alzheimer’s
43
Q
summarise the actin activities during cell movement:
A
- Proteins can be integrated in the process of directional motility
- When the lamellipodium extension takes place, there is a lot of actin polymerization in the lamellipodium.
- In the focal adhesion formation, there is assembling, nucleation, elongation, capping, severing, branching and bundling
- At the membrane, there is the gel-sol transition on the cortex.
- Finally, cells need to contract at the back; otherwise they will be RIPPED APART
44
Q
what is lamellae protrusion?
A
- When the lamellipod protrudes, the membrane protrudes forwards
- There is an assembly of filaments.
- There is branching and capping.
- At the back of the lamella, there is SEVERING
- so the filament can be released
- This allows the G-monomers to move to the point in the cell (at the front), where they are needed to make new assemblies.
- The net result is new assembly of actin at the leading edge, provided by monomers at the back of the cell
45
Q
how does filopodia grow?
A
- There are tight filaments with bundling proteins
- They form by complexes that stimulate the bundling and polymerisation of the filaments.
- Then they form a bundle, and elongate by adding monomers
- As a result, there is a very fast elongation from the cell.
- When the filopodia senses the removal of the stimulus, it collapses
- This collapsing is done by bring capping proteins, to stop the process
- the membrane is then pushed down
46
Q
what are the 4 signalling molecules that regulate the actin cytoskeleton?
A
- Ion flux changes (i.e. intracellular calcium levels can affect proteins)
- Phosphoinositide signalling (phospholipid binding)
- Kinases/phosphatases (phosphorylation cytoskeletal proteins)
- Signalling cascades via small GTPases – master regulators
47
Q
what does the RHo subfamily of small GTPases belong to?
A
- Rho subfamily of small GTPases belongs to the Ras super-family
- there are 20 family members including Rac, Rho, Cdc42
- When activated, they form the actin cytoskeletal structures
*
48
Q
what does
CDC42 activation
RAC activation
RHO activation
result in?
A
CDC42 activation = induces filopodia into the cells
RAC activation = huge expansion and flattening of the cell.
RHO activation = stress fibres
49
Q
how is the actin cytoskeleton controlled by small G proteins?
A
- activated when GDP -> GTP
- Once activated, small G proteins bind to specific proteins (known as effectors).
- These effectors are the messengers that carry out actions
- . Proteins are inactivated by hydrolysis of GTP à GDP.
50
Q
how does signaling from small GTPases regulate actin cytoskeleton and motility?
A
- Among the effector proteins of the GTPases are many cytoskeletal proteins. Once they are engaged and activated, other proteins are activated.
- For example, Rac protein activates WAVE and Arp-2/3 à so Rac will induce polymerisation.
- By just activating single molecule, there will be branching out to activate many proteins
51
Q
what is the participation of small GTP-ases on cell migration?
A
- The lamellipodia is a classic structure formed by Rac (it is involved in actin branching and polymerisation).
- Focal adhesion assembly is a RAC AND RHO PROCESS
- contraction is a RHO process
- Cdc42 controls the exploratory processes by filopodia, driving polarised motility and actin mobilisation.
52
Q
what happens if RHO is blocked?
A
- If you block Rho, cells may be ripped apart.
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