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
what is the function of lamellipodia?
* 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
why is control required in cell movement?
* 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
what is hapoptatic motility?
what is chemotactic motility?
* 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
how do the focal adhesions and lamellipodia work together to allow the cell to move?
* 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
how does actin filament polarity help migration direction?
* 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
show a migrating cell:
31
what allows the cells to contract during migration?
* 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
in what ways can actin molecules remodel?
* There are different classes of cytoskeletal proteins that control each of these steps.
* nucleation
* elongation
* capping
* severing
33
explain nucleation :
* 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
explain elongation:
* 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
explain capping?
* 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
how are the actin filaments generated into filaments?
* 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
explain severing:
* 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
what is crosslinking and bundling?
* 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
how does bundling occur?
why are motor proteins useful in bundles ?
* 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
how does the branching process take place?
* 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
what is gel sol transition by actin filament severing?
* 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
which of the following diseases is not related to the actin cytoskeleton ?
* 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
summarise the actin activities during cell movement:
* 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
what is lamellae protrusion?
* 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
how does filopodia grow?
* 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
what are the 4 signalling molecules that regulate the actin cytoskeleton?
1. Ion flux changes (i.e. intracellular calcium levels can affect proteins)
2. Phosphoinositide signalling (phospholipid binding)
3. Kinases/phosphatases (phosphorylation cytoskeletal proteins)
4. Signalling cascades via small GTPases – master regulators
47
what does the RHo subfamily of small GTPases belong to?
* 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
what does
CDC42 activation
RAC activation
RHO activation
result in?
CDC42 activation = induces filopodia into the cells
RAC activation = huge expansion and flattening of the cell.
RHO activation = stress fibres
49
how is the actin cytoskeleton controlled by small G proteins?
* 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
how does signaling from small GTPases regulate actin cytoskeleton and motility?
* 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
what is the participation of small GTP-ases on cell migration?
* 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
what happens if RHO is blocked?
* If you block Rho, cells may be ripped apart.
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