Lecture 5 Flashcards
Ch.5 The cell cycle
What was Rudolf Virchow the first one to propose?
That all cells arise from pre-existing cells
What phases does the interphase include?
Everything except of the M-phase
What is the order of the phases?
G1, S, G2, M, G0
What happens in the S-phase?
Replication, where cohesin holds the sister chromatids toghether
What happens in the M-phase?
The creation of 2 cells with the mitotic spindle
What is the order of the phases that can be found within the M-phase?
Pro/prometaphase, metaphase (neatly alligned chr.), anaphase (separate chr.), telophase/cytokinesis (pinch off the 2 cells)
What is the function of the G1 phase?
Growing, make nucleotides and prepare for DNA synthesis
What is the function of the G2 phase?
Prepare for mitoses and growing
What is the function of CDK’s and when are they active?
They control the cell cycle and are active when cyclin is bound
Which CDK and cyclin match with the G1 phase?
CDK4/6 and cyclin D
Which CDK and cyclin match with the S phase?
CDK2 and cyclin A and E
What is the function of CDK2?
Phosphorylating factors that are needed for DNA replication
Which CDK and cyclin match with the G2/M phase?
CDK1 and cyclin B
What is the function of CDK1?
To proceed the cell from the G2 to the M phase
What happens with the cyclin levels in the cell?
They fluctuate and set the stage (phase) that the cell is in
How are the cyclin levels controlled?
With the use of transcription and proteolytic degradation (Ubiquitin-mediated)
What happens with Cycling B and how does that happen?
It is high until the metaphase and quickly declines before the anaphase with the use of ubiquitin-mediated proteolysis by APC/C
What is the result of less cyclin B?
There is less CDK1, which then triggers mitotic progression
What is the function of CDKi’s?
These are proteins that inhibit CDK activity (eg p21, p16)
Which molecules are involved in the phosphoregulation of CDK?
Wee1/Myt1 : phosphorylate to inactivate
Cdc25 : dephosphorylate to activate
CAK : phosphorylates to activate
Which two ways are there for CDKi’s to inhibit?
Either by binding to the place of cyclin or inhibit the already assembled complex
What is checked in the G1-S checkpoint?
Whether the conditions are favourable to enter the S phase and whether the DNA is intact enough
What is the function of E2F in the G1-S checkpoint?
It drives a program that is required for the S-phase
What is the result of inhibiting E2F via Rb?
It prevents the S-phase genes from being expressed.
How is the inhibition done of E2F via Rb?
Rb bind to E2F and HDAC is recruited
What is the result of Rb phosphorylation by cyclin D/CDK 4?
HDAC is released and there is transcription of cyclin E
What is the result of Rb phosphorylation by cyclin E/CDK 2?
If this is done after cyclin D/CDK 4 it also gives cyclin E transcription and full E2F activation so the cell can go into the S phase
What is the result of genotoxic stress?
p53 in activated, which activates p21, which inhibits CDK2, so there is no progression into the S-phase
What is the purpose of the G2-M checkpoint?
Mitosis is prevented if the DNA is damaged
What are the key component of the G2-M checkpoint?
ATM and ATR kinases, they inhibit CDK activity via phosphorylation
What is ATM (and CHK2) signaling also required for?
For inducing p53/p21 in G1 phase
What is the purpose of the mitotic checkpoint?
To check whether all chr. are properly attached to the spindle
What are important mediators of the mitotic checkpoint?
Aurora kinases
What is the result if not all the chr. are attached properly?
It is arrested in the metaphase, due to inhibition of cyclin B ubiquitination (thus degradation)
Where can most checkpoint defects be found?
In the G1-S phase
What cancers are a consequence of upregulation of cyclin D1?
It can lead to breast, head and neck and esophagul cancer
What cancers are a consequence of the loss of Rb?
Prostate, bladder, lung, breast cancer, retinoblastoma and osteosarcoma
What cancers are a consequence of ATM kinase mutation?
Neurodegenerative diseases, higher risk of lymphoma and leukemia
What cancers are a consequence of p53 mutation?
Li-Fraumeni syndrome, high risk of sarcoma, leukemia and breast cancer
What cancers are a consequence of aurora kinase mutations?
Amplification, mitotic defect, aneuploidy, high risk of breast, colon and pancreatic cancer
What is the role of aneuploidy in cancer?
It is very common in cancer. But it is uncertain whether it is the driver or a consequence
In which checkpoint are mutations rarely found?
In the mitotic checkpoint
What is the function of DNA damaging agents in cancer treatment?
To activate the DNA integrity checkpoints (eg with the use of radiation, doxorubucin and PARP inhibitor)
Which drug does mitotic checkpoint activation?
Taxol
What does Taxol do?
It takes away the mitotic spindles, thus there is mitotic arrest (cells curl up)
What other type of treatment is used for cancers?
Targeting the cell cycle kinases
What are the master regulators of DNA damage checkpoints?
ATM and ATR, their targeting for treatment is explored
What is the ultimate treatment plan?
Combining ATM/ATR inhibition with radiation or cytostatic treatment
What is the drug Palbociclib used for?
It is a CDK4/6 inhibitor that is used for breast cancer (arrest cells in G1), is not useful in all cancers and some are resistant
What is the reason that not all cells are sensitive to Palbociclib?
There is a mutation in Rb, E2F etc which lowers the sensitivity
What study was done to see whether any genes were involved with this insensitivity or higher sensitivity?
Some cells were treated with palbociclib and it was found that a less of the ARMBRA1 gene leads to more cyclin D1, so enter the G1/S, thus you need less CDK4/6
The inhibition of which gene is detrimental to cells that overexpress cyclin E?
The inhibition of PKMYT1 (which regulates CDK phosphorylation)
