Cytoskeleton and Cancer Flashcards
1
Q
What is the cytoskeleton made up of?
A
Microtubules
Intermediate filaments
Actin microfilaments
2
Q
Metastases are the end products of the invasion-metastasis cascade, true or false?
A
True
3
Q
What is the efficiency of the invasion-metastasis cascade?
A
1 cell out of 5000, i.e. inefficient
4
Q
What is the cytoskeleton?
A
A cellular inner framework that enables cells to move, change shape and much more
5
Q
What is the diameter of microtubules?
A
25nm
6
Q
What is the diameter of intermediate filaments?
A
10nm
7
Q
What is the diameter of microfilaments?
A
8nm
8
Q
Where are microtubules found?
A
They are present in the cytoplasm of all eukaryotic cells
9
Q
What do microtubules exist as?
A
Long, rigid polymeric structures with a length between 200nm and 25um
10
Q
What is the function of the microtubules?
A
To support cell structure and shape
11
Q
What is the role of microtubules in the movement of structures within the cell?
A
Serve as a conveyor belt for moving organelles and secretory vesicles throughout the cytoplasm
12
Q
What is the role of the microtubules in mitosis?
A
They form spindles during mitosis
13
Q
What are microtubules a major component of?
A
Cilia and flagella for specialised surfaced structures, e.g. of epithelial cells of air passage lining
14
Q
At the centrosome-microtubule junction, what are the nucleating sites formed of?
A
Rings of gamma-tubulin
15
Q
What type of filament are microtubules that are growing from the centrosome?
A
Polar filaments (- to +)
16
Q
What is the catastrophe and rescue theory?
A
That microtubules have a reverse switch from growth (polymerisations) to shrinking (depolymerisation) and vice versa
17
Q
Define treadmilling
A
A process of dynamic instability on both + and - ends of the polymer
18
Q
Is treadmilling of microtubules present in vitro or in vivo or both?
A
It is present in vitro and partially in vivo
19
Q
Are all minus ends of the microtubules bound to the centrosome?
A
Not all minus ends
20
Q
What are microtubules stabilised by?
A
Microtubule associated proteins (MAPs)
21
Q
What do MAPs do?
A
Bind mostly at the + end of microtubules and promote growth and disassembly
22
Q
What are neurons stabilised by?
A
Tau, that binds to the sides of filaments and crosslinks adjacent microtubules
23
Q
What MAP stabilises the leading tip of migrating cells (cell polarisation)?
A
‘Plus’ TIP proteins (+TIP), e.g. XMAP214 family, EBs
24
Q
What is the function of kinesin 4/8?
A
Cargo translocation to + end
25
What is the function of kinesin 7/10?
Filament growth
26
What is the function of kinesin 8/13/14?
Promotes catastrophe
27
Post-translational modifications can modulate microtubule dynamics and and functions, true or false?
True
28
What post-translational modifications can control protein-protein interactions and microtubule dynamics?
Detyrosination and tyrosination (C-terminal Tyr)
Acetylation and deacetylation (Lys40)
Polyamination
29
What happens during prometaphase?
Chromosomes are condensed; microtubules interact with chromosomes
30
What happens during early metaphase?
Chromosomes form a metaphase plate
31
What happens during anaphase?
Duplicated chromosomes move to spindle poles
32
What happens during telophase?
Cell division to form two daughter cells
33
How does the drug paclitaxel affect mitosis?
Chromosomes don't congress to the metaphase plate
34
How does the drug vinflunine affect mitosis?
Chromosomes remain at the spindle poles
35
Microtubules cannot be targeted by anticancer drugs, true or false?
False, they can be a target for anticancer drugs
36
Give examples of tubulin polymerisation inhibitors and their mode of action
Vinblastine: blocks + end
Colchicine: interacts with alpha tubulin heterodimer
37
Give an example of a tubulin depolymerisation inhibitor and its mode of action
Paclitaxel: suppresses dynamics
38
Can kinesins be potential targets for cancer drug development?
Yes
39
What is MMP1 and what is its function?
M-phase phosphoprotein 1
| Controls cytokinesis
40
What is the function of EG5 kinesin?
Essential for bipolar spindle formation
41
What is CENPE and what is its function?
Centromere-associated protein E
Controls progression from metaphase to anaphase
Depletion initiates chromosomal instability
42
At what stage of clinical trials is the EG5 kinesis targeting drug ARRY-520?
Phase II trials in multiple myeloma
43
At what stage of clinical trials is the EG5 kinesis targeting drug LY2523355?
Phase II trials for 8 different solid tumours
44
What are intermediate filaments important for?
The mechanical stability of cells
45
Intermediate filaments belong to a small protein family encoded by ~20 different genes, true or false?
False, they belong to a large protein family encoded by ~70 different genes
46
How many types of intermediate filaments are there and what are these types based on?
6 types
| Based on the primary sequence and structure
47
Give an example of a type I intermediate filament
Epithelial keratins (acidic)
48
Give an example of a type II intermediate filament
Hair keratins (basic)
49
Give examples of type III intermediate filaments
Vimentin
Desmin (muscle cells)
Peripherin (peripheral neurons)
Glial fibrillary acetic protein (astrocytes)
50
Give examples of type IV intermediate filaments
Internexin
Synemin
Syncolin
Neurofilaments
51
Give an example of a type V intermediate filament
Nuclear lamins
52
Give an example of a type VI intermediate filament
Nestin
53
What is the diameter of intermediate filament polymers?
10nm
54
Are intermediate filaments more or less dynamic than microtubules? Why?
Less dynamic, no turnover of subunits
55
What regulates intermediate filament motility?
Microtubule-associated proteins
56
What does a switch in the pattern of intermediate filaments suggest?
Epithelial to mesenchymal transition
57
What is vimentin a marker for?
Epithelial to mesenchymal transition
58
Are keratins diagnostic or prognostic markers in tumour pathology?
Both
59
Is vimentin a diagnostic or prognostic marker in tumour pathology?
Prognostic
60
What makes up the actin cytoskeleton?
Microfilaments
61
What makes up microfilaments?
Actin filaments
62
How can microfilaments be structured?
```
As 2 strands of F (filamentous)-actin
As G (globular)-actin
```
63
Where can alpha actin be found?
In muscle specific isoforms
64
Where can beta actin be found?
In the cell cortex, in the leading edge of migrating cells
65
Where can gamma actin be found?
In stress fibres
66
What is located in the centre of G-actin?
ATP
67
What is located in the centre of F-actin?
ADP
68
Define actin treadmillg
The rapid turnover of actin filaments
69
Is there the same or different kinetics of subunit binding and dissociation at the opposite ends of F-actin?
Different
70
How does recycling of actin filaments occur?
Severing proteins and cofilins intercalate and cause actin monomer dissociation
71
Do actin filaments treadmill in membrane protrusions?
Yes
72
How does the capping and polymerisation of actin filaments work?
Capping proteins (formin, gelsolin, villin) deliver actin monomers to nucleation centres
73
How does the branching of the Arp2/3 complex in actin filaments work?
Branching protein Arp2/3 intercalates between individual actin filaments
74
What proteins are able to cross-link actin filaments to form thicker bundles or meshwork of higher mechanical strength?
Alpha-actinin
Fascin
Filamin
Tropomyosin
75
How many coiled-coil tropomyosin proteins exist in mammals?
More than 40
76
What do tropomyosin proteins exist as?
Coiled-coil parallel dimers that forma head-to-tail polymer
77
What do tropomyosin proteins regulate?
Interactions of actin filaments with actin-binding proteins
78
What do tropomyosin proteins control?
The stability of the microfilaments
79
The actin cytoskeleton is a potentially vulnerable property of cancer cells, so why aren't current inhibitors successful?
Unacceptable toxicity
80
What is Tm5NM1/2?
An integral component of the specialised actin cytoskeleton of tumour cells
81
What does the anti-tropomyosin compound TR100 disrupt?
The actin cytoskeleton
82
Why has TR100 had such sensational success in clinical trials?
Because it does not compromise cardiac function
83
What are myosins?
A superfamily of actin-based motor proteins
84
How do myosins work?
They convert chemical energy in the form of ATP to mechanical energy
85
What domains do myosins have?
A highly conserved globular head domain containing the actin-binding and ATPase domain
A neck domain to which light chains bind
A variety of functionally specialised C-terminal tail regions
86
Outline the 'power stroke' mechanism for myosin movement along actin filaments
1. Rigor state position
2. ATP binding releases the actin filament
3. ATP hydrolysis causes a shift in the 'lever arm' position
4. Release of Pi
5. Power stroke
6. ADP is released
87
During each power stroke cycle, how many molecules of ATP are hydrolysed?
One
88
During each power stroke cycle, how far does myosin move?
5-25nm
89
Describe the structure of myosin II
It is a hexameric protein consisting of three pairs of pepetides: two heavy chains, two essential light chains, and two regulatory chains
90
What is the function of the coiled-coil domain in myosin II?
It is involved in the assembly of myosin II molecules into filaments
91
Where is myosin II found?
In skeletal muscle, smooth muscle, and there can be non-muscle myosin
92
What does myosin II have fundamental roles in?
Processes requiring reshaping and movement, e.g. cell adhesion, cell migration and cell division
93
What is myosin II's function dependent on?
Its ability to form bipolar filaments
94
Myosin II filaments bind to actin through what?
Their head domains
95
What does myosin II use in order to form filaments to regulate the cytoskeleton?
Its actin cross-linking and contractile functions
96
How does the light chain of myosin II regulate its assembly?
It exists in a folded, assembly-incompetent form (10S)
| Phosphorylation of the regulatory light chain on Ser19/Thr18 leads to an unfolded, assembly-competent form (6S)
97
What does S100A4 do?
It binds to the C-terminus of myosin IIA and has been shown to inhibit the formation of myosin into filaments
98
What are the two phosphorylation sites on myosin IIA that may play a role in S100A4 binding and/or filament formation?
S1916-PKC and S1943-CKII
99
What does knockdown of S100A4 promote?
The formation of myosin IIA filaments
100
What is actomyosin contractility controlled by?
Rho GTPase
101
What is RhoGTPase?
A molecular switch that cycles between GDP and GTP bound states
It activates and interacts with downstream effectors
102
Give some examples of Rho GTPases and where they can be found
Rac in lamellipodia
Cdc42 in filopodia
Rho in stress fibres
In focal adhesions
103
How does a new focal adhesion form?
1. Formation of focal complex
2. Formation of stress fibres
3. Growth of stress fibres
104
What is cell migration needed for in the body?
Embryonic development
Wound healing in epithelial cells
To get white blood cells to the sites of infection
In fibroblasts to maintain the extracellular matrix
To allow the migratio of cancer cells to new sites in the body (cancer spreading/metastasis)
105
What are the four stages of mesenchymal migration (in order)?
Protrusion, adhesion, translocation, retraction
106
What happens to the migration of a amoeboid cell with no intrinsic polarity?
It will extend towards chemical and haptotactic stimuli
107
Define chemotaxis
The directional cell movement towards an increasing concentration of a soluble factor (chemokines), contact with extracellular matrix ligands, or physical contact with other cells
108
What is amoeboid migration based on?
The membrane blebbing along the cell surface, which is under control of actin polymerisation
109
What are cortical actin dynamics controlled by?
Small GTPases
110
What is the squeezing of round cells in the extracellular matrix (independent of extracellular matrix cleavage) a characteristic of?
Non-neoplastic cells (lymphocytes and neutrophils), or of tumour lymphoma and small-cell lung carcinoma cells
111
What do short-lived and relatively weak interactions of the cell with the substrate (integrin-independent migration) mimic features of?
The single cell behaviour of the amoeba Dictyostelium discoideum
112
What do carcinoma cells move along?
Extracellular matrix fibres and do not seem to be constrained by the matrix networks
113
What are the three transitions in the mode of cancer cell migration?
EMT, MAT, CAT
