1 - CELLULAR GROWTH REGULATION Flashcards
What are the 3 general considerations for cell growth 3
o Growth of a population of cells
o Growth at the cellular level (the cell cycle)
o Loss of cells by programmed cell death (apoptosis)
3 general considerations for cell growth - Growth of a population of cells 2
– Distinguish between increase in cell numbers (hyperplasia) and increase in cell size (hypertrophy)
– Depends on integration of intra- and extracellular signals (checks on cellular physiology, growth and inhibitory factors, cell adhesion etc.)
3 general considerations for cell growth - Growth at the cellular level (the cell cycle) 3
– Cell growth = increase in size (sometimes growth refers to this only) and cell division
– Cell cycle phases (G1, S, G2, and M) G1 is growth phase 1, S is synthesis (where DNA is replicated), M is for mitosis
– Progression controlled at three key checkpoints (restriction points)
3 general considerations for cell growth - Loss of cells by programmed cell death (apoptosis) 3
– A coordinated program of cell dismantling ending in phagocytosis. Distinct from necrosis
– Occurs during normal development (e.g. separation of the digits, involution, immune and nervous system development)
– And in response to DNA damage and viral infection
What is a broad term used to describe Growth factors, cytokines and interleukins 1
Proteins
3 things that Growth factors, cytokines and interleukins do?
– Stimulate proliferation (called mitogens) and maintain survival
– Stimulate differentiation and inhibit proliferation e.g. TGF Beta (transforming growth factor)
– Induce apoptosis e.g. TNFα and other members of the TNF family (tumour necrosis factor)
3 things that Growth factors, cytokines and interleukins do - an example of stimulating proliferation 2
• Usually named after originally identified target e.g. EGF, FGF, Interleukins (IL2 & IL4), NGF •
But see also PDGF (platelet-derived GF) and IGF1 (Insulin-like GF – the main effector of pituitary growth hormone)
3 things that Growth factors, cytokines and interleukins do - an example of stimulating differentiation and inhibit proliferation 1
e.g. TGF Beta (transforming growth factor)
3 things that Growth factors, cytokines and interleukins do - induce apoptosis 1
e.g. TNFα and other members of the TNF family (tumour necrosis factor)
What are the three broad classes of growth factors, cytokines and interleukins 3
PARACRINE: produced locally to stimulate proliferation of a different cell type that has the appropriate cell surface receptor
AUTOCRINE: produced by a cell that also expresses the appropriate cell surface receptor
ENDOCRINE: like conventional hormones, released systemically for distant effect
Define Paracrine 1
PARACRINE: produced locally to stimulate proliferation of a different cell type that has the appropriate cell surface receptor
Define Autocrine 1
AUTOCRINE: produced by a cell that also expresses the appropriate cell surface receptor
Define Endocrine 1
ENDOCRINE: like conventional hormones, released systemically for distant effects
What happens when you add growth factor to cells? 2
They will respond and enter the cell cycle, start dividing
What is PDGF 1
Platelet-derived growth factor (PDGF) is a mitogen for certain cell types, especially cells of connective tissue and cells of the developing nervous system
What happens when PDGF is no longer available to cells
If the PDGF is no longer available, there is a plateau until they receive more PDGF
What happens if you add TGF Beta to cells 1
If the cells receive TGF Beta, they will stop dividing
What happens if you add TNF Alpha to cells 2
TNF Alpha will lead to the cells committing suicide and the number of cells going down
Name the phases of the cell cycle 5
G0, G1 , G2 , S , M
Cell cycle - sheet
On sheet
Mitosis is the….
separation of the chromosomes and the physical separation of the cell into 2 daughter cells
What happens after the M phase 1
After the M phase, one of the daughter cells undergoes interphase. The cell grows using nutrients to create more cytoskeleton etc.
How do cells grow after the M phase 1
After the M phase, one of the daughter cells undergoes interphase. The cell grows using nutrients to create more cytoskeleton etc.
What happens in the growth phases 1
In the growth phases the cells get ready, so they have everything that is required for mitosis
What are Quiescent Cells 1
Quiescent Cells are cells that are arrested in the G0 phase
Define Quiescence 1
Quiescence is the reversible state of a cell in which it does not divide but retains the ability to re-enter cell proliferation. Some adult stem cells are maintained in a quiescent state and can be rapidly activated when stimulated, for example by injury to the tissue in which they reside.
Pathways for Quiescence cells 3
Re-enter the cell cycle and start proliferating
Terminal differentiation
Apoptosis
How can Quiescence cells re-enter the cell cycle 1
These cells can re-enter the cell cycle if we add mitogens and will start proliferating
What cells undergo terminal differentiation 1
Some quiescent cells may start to differentiate. E.g. they could become gut cells. This is called terminal differentiation. Some cells undergo apoptosis and die
How many copies of each chromosome are there after cell division 1
After cell division, the cells have two copies of each chromosome so that is 2N
How many copies of each chromosome are the S phase 1
After the S phase, there is more duplication, so it is 4N
Name one technique where you can find out the DNA content of a cell 1
You can use a fluorescence-activated cell sorter (FACS) to analyse the cell DNA content.
What does this graph show? 1 What difference can you see in the S phase? 1
o This graph shows the difference between a slow and fast rate of proliferation.
o In the high rate of proliferation, there are a lot more cells that are in the S phase
Mitosis stains - diagram
– Stain in blue is for DNA
– Stain in red is for gamma tubulin which is required to form the microtubules that will bind to the centrioles and chromosomes
– Stain in green is for CHEK2 which is a cell cycle checkpoint protein
What are the 3 cell cycle checkpoints 3
– Before the S phase
– Before the cells start Mitosis
– Another checkpoint in mitosis
What happens in the cell cycle checkpoint - Before the S phase
o Checks the cells size, the nutrients, can the cell proceed by expending so much energy?, make sure that the DNA is not damaged
What happens in the cell cycle checkpoint - Before the cells start Mitosis 2
o Is the DNA completely replicated?
o Is the DNA not damaged?
If they are fine, they will proceed to mitosis
What happens in the cell cycle checkpoint - Another checkpoint in mitosis 1
o Are the chromosomes aligned on the spindle?
What do Cyclin-dependent kinase need to be active 1
o To be active, it needs to form a complex with Cyclin.
The retinoblastoma protein and S phase 3
Unphosphorylated RB binds E2F, preventing its stimulation of S-phase protein expression.
When phosphorylated by cyclins, RB releases E2F.
The released E2F stimulates expression of more Cyclin E and S-phase proteins e.g. DNA polymerase, thymidine kinase, PCNA etc. DNA replication starts.
How do growth factors induce cyclin expression - steps 6
- Cells FROM G0 receive GF
- Receptors on cell recognise GF they bind
- Activate signal transducers and in turn intracellular pathways
- Leads to effect in nucleus
- Different waves of transcription factor will be activated
- Regulates expression of P21/Cyclin
Sequential activities in the cycle, triggered by growth factors- steps 8
- 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
- G1 CDKs are activated in response to environmental signals, late CDKs by preceding kinase activities.
- 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.
- Hyperphosphorylated RB is dephosphorylated by protein phosphatase 1. G1 CDKs hypophosphorylate, and late CDKs hyperphosphorylate.
What does DNA damage detected at checkpoints lead to 3
Cell cycle arrest. The cell will stop the cell cycle (with the help of CKIs, CHEK2, etc.).
It will attempt DNA repair (with nucleotides or base excision enzymes, mismatch repair, etc.).
Apoptosis. If repairing is unsuccessful, then the cell is programmed for cell death (via the BCL2 family, capases, etc.).
What does a high expression of TP53 mean 1
High expression = problem with the cell
What happens in response to DNA damage?
o In response to DNA damage, mutagen, kinases atm/atr kinases can detect and then become activates
o Intact DNA molecule has a mutation
o The damage is detected by kinases
o These kinases activate CHEK2 –> TP53 is a substrate for CHEK2
o P53 is expressed in cells however is the protein is not functional as it is quickly degraded by the proteasome.
o In response to DNA damage, kinases phosphorylate P53.
o When it is phosphorylated, it cannot be degraded and it now stabilised and active.
o It will now go and bind the promoters of transcription factors and will help to express genes that are required for DNA repair.
o If a cell cannot be repaired, P53 will trigger apoptosis which gets rids of cells that are deleterious for the whole organism.
