Mechanisms of Disease 1 - Cell Growth and Cell Differentiation Flashcards
1
Q
What is cell growth and differentiation and what are they repsonsible for?
A
- Cell growth – a bigger organism more cells
- Differentiation – cells become complex (usually) an end to growth.
- Cell growth precedes differentiation, but with some overlap.
They are the basic mechanisms responsible for turning a zygote into a mature multicellular organism.
2
Q
What 3 groups do diseases related to cell growth and differentiation fall into?
A
- Developmental conditions
- Neoplasia (and metaplasia)
- Others
3
Q
What are developmental conditions and what is example?
A
- Can be related to cell growth or differentiation (or both)
- E.g neural tube defects like spina bifida
4
Q
What are some examples of neoplasia (and metaplasia)
A
E.g Cancer, tumours
5
Q
What is an example of another disorder related with growth/ differentiation?
A
e.g cardiac hypertrophy
6
Q
What are the 2 main forms of cell growth and what are they balanced by?
A
- Hypertrophy (bigger cells)
- Hyperplasia (more cells)
- Cell growth is balanced by cell death
7
Q
What is hypertrophy?
A
- Hypertrophy is simply cells growing bigger
- more proteins, more membranes
8
Q
What drives hypertrophy?
A
- Elevated protein synthesis is a big driver for increased cell size.
- E.g the heart
9
Q
What is Hyperplasia?
A
- More cells is caused by cell division or proliferation
- Cell cycle
10
Q
What is differentiation?
A
- Beginning of exit of cells from the cell cycle – Differentiated cells are ‘post-mitotic’
- A program of cell type-specific gene expression
- Cell morphology and function changes.
11
Q
What are the similarities between growth and differentiation?
A
- The mechanisms governing them
- Cell growth and differentiation are governed by the integration of multiple signals
- Intra- and extracellular signals (checks on cellular physiology, growth and inhibitory factors, cell adhesion etc)
12
Q
How do these signals involved in differentiation/ cell growth work?
A
- Signals converge on the promoters of key genes.
- Promoters act as “co-incidence detectors” – promoters converge the signals
- Right combination of signals received by promoter, it will make a binary decision on if the gene is expressed YES/NO? but also how much is made.
13
Q
What are extracellular signals?
A
- Ligand binds to receptor to cause intracellular cascade which activates transcription factors in the nucleus which drive gene expression creating mRNA
- the mRNA is exported back to the cytoplasm for protein transcription and translation.
14
Q
What are the 3 broad classes of extracellular signals?
A
- Paracrine
- Autocrine
- Endocrine
15
Q
What are paracrine signals?
A
Produced locally to stimulate proliferation of a different cell type that has the appropriate cell surface receptor.
16
Q
What are autocrine signals?
A
Produced by a cell that also expresses the appropriate cell surface receptor. Cell-autonomous
17
Q
What are endocrine signals?
A
Conventional hormones, released systemically for distant effects.
18
Q
What are the extracellular signals in cell growth and differentiation?
A
Proteins that:
- Stimulate proliferation and promote survival
- Mitogens e.g growth factors and interleukins (EGF, FGF, NGF, PDGF, IGF1, IL2, IL4)
- Induce differentiation and inhibit proliferation e.g TGFb
- Can do either e.g Wnt ligands
- Induce apoptosis e.g TNFa and other members of the TNF family.
19
Q
What are the phases of the cell cycle?
A
Mitosis, G1, S phase, G2
20
Q
What are quiescent cells and what phase are they in?
A
Cells that have left the cell cycle- G0
21
Q
Can quiescent cells rejoin the cell cycle?
A
Yes
22
Q
How many chromosomes are there after mitosis?
A
After mitosis, the cell is diploid with 2n (G0 and G1 cells).
23
Q
How many chromosomes are there going into mitosis (G2/M)
A
After genome replication there is a 4n genome going into mitosis (G2/M)
24
Q
How many chromosomes are there during S phase of the cell cycle
A
The number of chromosomes during S phase is inbetween the amount before end of mitosis and after genome replication (between 2n and 4n)
25
What is the FACS analysis of cell DNA content?
* Flow cytometry
* If a DNA stain is applied, FACs can measure the DNA content of every cell in a population
* **Strength of staining correlates with the amount of DNA in the cell of a population.**
26
Why does G2 stay the same here?
It is a time limited part of the cell cycle.
27
What ways can you look at the cell cycle?
* Fluorescence microscopy
* Flow Cytometry
28
What are the steps of mitosis?
* Prophase (1)
* Prometaphase
* Metaphase (2)
* Anaphase (3)
* Telophase (4)
* Cytokinesis
29
What happens in prophase?
* Nucleus becomes less definite
* Microtubular spindle apparatus assembles
* Centrioles migrate to poles.
30
What happens in prometaphase?
* Nuclear membrane breaks down
* Kinetochores attach to spindle in nuclear region
31
What happens in metaphase?
Chromosomes align in equatorial plane
32
What happens in Anaphase?
Chromatids separate and migrate to opposite poles
33
What happens in Telophase?
Daughter nuclei form
34
What happens in Cytokinesis?
* Division of cytoplasm
* Chromosomes decondense
35
What are cell cycle checkpoints?
These are the controls (involve specific protein kinases and phosphatases) ensure the strict alternation of mitosis and DNA replication.
36
List the cell cycle checkpoints.
1. **Restriction point**
2. **G2/M phase checkpoint**
3. **Mitosis**
37
What is the restriction check point?
1. **Restriction point –** checks DNA is not damaged, cell size (large enough to divide into 2), metabolite/nutrient stores (enough energy to complete mitosis)
38
What is the **G2/M phase checkpoint?**
1. **G2/M phase checkpoint** – checks if DNA is damaged, and the DNA is completely replicated.
39
What is the Mitosis checkpoint?
**Mitosis** – checks chromosomes are aligned correctly on the spindle to ensure right number of chromosomes go into daughter cells.
40
Where do external signals act?
* In the G1 phase up until the restriction point.
* External signals act on G0 cells as this is the main site of control for cell growth.
41
In humans how many genes code for CDKs and Cyclin?
* In humans there are 10 genes encoding **CDKs** and \>20 genes encoding **Cyclin**.
* Expression of cyclins that is controlled by mitotic signals from growth factors.
42
What does CDK stand for?
Cyclin dependent kinases
43
What does cyclin do?
It is a regulatory subunit
44
What is cyclin expression induced by?
Growth factors
45
What is the role of Cyclin-dependent Kinases (CDK)?
It is a catalytic subunit
46
What is active Cyclin- CDK complex?
Cyclin forms a complex with CDK resulting in → **active Cyclin-CDK complex** which phosphorylates specific substrates.
47
What destroys the cyclin-CDK complex?
Prorteasomes
48
What does post-translational phosphorylation result in?
Activation, inhibition or destruction
49
How is Cycin-CDK activity regulated?
* Cyclin proteins have a high rate of turnover: continually synthesised (gene expression) then destroyed (by proteasome).
* Post translational modification by phosphorylation may result in activation, inhibition or destruction.
* Dephosphorylation
* Binding of **cyclin-dependent kinase inhibitors (CDKIs)**
50
What is the retinoblastoma protein (RB)?
* RB is a key substrate of G1 and G1/S cyclin-dependent kinases.
51
What does E2F usually do?
E2F drives the production of S phase proteins.
52
How do E2F and RB work together in the cell cycle?
* When unphosphorylated RB binds to E2F transcription factor it prevents the stimulation of S-Phase protein expression
* The unphosphorylated RB bound to E2F interacts with **Cyclin D-CDK4** & **Cyclin E-CDK2** then RB becomes phosphorylated and dissociated from E2F.
* Thus E2F is no longer repressed and can bind to promoters of its target genes, allowing replication to start.
* E2F binds to promoter of cyclin E which when it becomes partially active it creates a positive feed forward loop.
* More Cyclin E and s-phase proteins created so DNA replication starts.
53
What are some cyclin E and S phase promoters?
DNA polymerase, thymidine kinase, PCNA
54
What are the sequence of events triggered by growth factors?
* Growth factor signalling activates early gene expression (transcription factors - FOS, JUN, MYC)
* Early gene products stimulate delayed gene expression (includes Cyclin D, CDK2/4 and E2F transcription factors.
* E2F sequestered by binding to unphosphorylated retinoblastoma protein (RB).
* G1 cyclin-CDK complexes hypophosphorylate RB and then G1/S cyclin-CDK complexes hyperphosphorylate RB releasing E2F
* E2F stimulates expression of more Cyclin E and S-phase proteins (e.g DNA polymerase, thymidine kinase, proliferating cell nuclear antigen etc)
* S-phase cyclin-CDK and G2/M cyclin-CDK complexes build up in inactive forms. These switches are activated by post-translational modification or removal of inhibitors driving the cell through S-phase and mitosis.
55
After DNA damage is detected at checkpoints, what does this lead to?
* **Stopping the cycle** (e.g CDKIs, CHEK2 etc)
* **Attempt DNA repair** (nucleotide or base excision enzymes, mismatch repair etc)
* If repair impossible, **programmed cell death** (BCL2 family, caspases)
56
What is stopping of the cell cycle driven by?
CDKI genes
57
What things attempt DNA repair?
Nucleotide or base excision enzymes, mismatch repair etc
58
What causes programmed cell death?
BCL2 family or caspases
59
What is the role of TP53?
* Tumour protein 53 – P53 means protein of 53 kDa.
* **TP53 is a tumour suppressor gene.**
*
60
What happens to TP53 if DNA is intact?
* If DNA is intact, TP53 is destroyed continually by the proteasome
61
What happens to TP53 if DNA is damaged?
* If DNA is damaged, important protein kinases are activated which phosphorylate TP53
* TP53 now can no longer be destroyed by proteasome.
* TP53 accumulates and exerts biological effects to that cell.
62
What are the functions of phosphorylated TP53?
* Expression of CKI – Cell cycle arrest
* Activation of DNA repair e.g excision repair
* If repair not possible, P53 activates apoptosis
63
What mutations are the most frequent in cancer?
TP53 loss of function
64
How does TP53 loss of function causes cancer link?
* Prevent cell cycle arrest – faster growth
* Prevent apoptosis – cells do not die
* Prevent DNA repair – more mutations lead to more heterogeneity, more adaptation to environment and cancer progression as a result.
65
What is the aim of chemotherapeutic drugs?
To act on the cell cycle – objective is to stop proliferation and induce apoptosis.
66
What are the 2 S-phase chemotherapeutic drugs and what do they cause?
* **5-fluorouracil**
* **Cisplatin**
67
What do the 2 S-phase chemotherapeutic drugs cause?
DNA damage
68
How does cistplain work?
binds to DNa causing damage and blocking repair
69
How does 5-fluorouracil work?
Prevents synthesis of thymidine
70
What do the M-phase chemotherapeutic drugs do?
Target the mitotic spindle.
71
What are the 2 M-Phase chemo drugs
* **Vinca alkaloids**
* **Paclitaxel (Taxol)**
72
What does paclitaxel do?
* Stabilises microtubules
* Preventing de-polymerisation
* Arrests cells in mitosis
73
What do vinca alkaloids do?
* Stabilise free tubulin
* Prevents microtubule polymerization
* Results in arrest of cells in mitosis
74
What is colchicine used for?
Not just cancer, similar mode of action to vinca alkaloids and is used for immune-suppression.
