Chapter Five Flashcards
What is a good definition for the cell cycle?
The stages that a cell goes through between divisions.
What is a mitogen?
Something that induces cell division.
What are the three stages of the cell cycle?
Interphase
Mitosis
Cytokinesis
What is mitosis?
The segregation or division of nucleus
Cyclins are expressed _________.
Cyclically.
When are cdks present?
They are always present, but rely on cyclins.
When G0 is referred to as the quiescent phase, what does this mean?
It means that cells are doing normal functions.
Before the G1 restriction point, mutagens are required for progression into cell division.
What are such examples of mitogens?
PDGF
EGF
How does EGF result in progression into the cell cycle?
MAPK will phosphorylate transcription factors like AP-1 stuff and Myc that will promote expression of genes needed for cell cycle progression.
What are genes that are transcribed in G1?
- Cyclins
- Checkpoint proteins
Cell cycle progression is ___________, ___________, and _____________.
- Unidirectional
- Bistable (on or off)
- Regulated by checkpoints.
What are cyclins?
What do they do to CDK’s?
How does their concentration change during the cell cycle?
They are regulatory subunits (coassign with other proteins) of cyclin-dependent kinases.
They induce a conformational change in the catalytic subunit of the CDK, exposing the active site (kinase domain)
Their concentration changes during the cell cycle.
What are CDK’s?
How does their concentration change during the course of the cell cycle?
They are ser thr kinases that regulate the cell cycle progression, and are activated by cyclins.
They stay the same.
What is the first cyclin to be expressed?
Who expresses it?
Cyclin D
AP-1
What activates the expression of Cyclin E?
Cyclin D
What is the G1 checkpoint?
It occurs before the cell goes into the S phase.
It arrests the cell cycle in response to DNA damage.
What is the G2 checkpoint?
It occurs before the cell goes into mitosis at the end of G2
It arrests the cell cycle in response to damaged or unreplicated DNA
What is the M-phase checkpoint?
it occurs during metaphase of mitosis
it arrests the cell cycle in response to misalignment on the mitotic spindle.
If checkpoints are working correctly, what are the consequences?
There will be genomic and chromosomal instability.
What are some things that cdks are responsible for phosphorylating?
Transcriptional regulators
Cytoskeleton proteins
Nuclear pore proteins
Histones
What is the result of cdks on each of these?
A. Transcriptional regulators
B. Cytoskeleton proteins
C. Nuclear pore proteins
A. Changes in gene expression
B. Chromosomal condensation
C. Nuclear breakdown
What is the cell cycle progression controlled by?
- Protein phosphorylation by kinases
- Protein dephosphorylation by phosphatases
- Ubiquitination - tagging stuff that marks it to be degraded
How can cdk activity be regulated?
- Associate with cyclins - it will work
- Association with cdk inhibitors - it won’t work
- Addition of an inhibitory kinase
- likely by wee kinase
- Addition of an activating phosphate
What about the conformation of the inactive cdk prevents it from working?
- Blocks substrate binding
- Blocks the correct alignment of ATP
What does cyclin binding do to cdk?
it causes a conformational change.
What are the two families of inhibitors of CDKs?
p16 (INK) family - bind cdk 4 and 6 inhibiting the binding of cdks to cyclin D
p21 (Cip/Kip) family - block the ATP binding site of cdk2
cdk still binds to cyclin
What can cyclin dependent kinases do that keeps the cell cycle going?
They prevent p21 family activity, so cdk2 is able to be activated by cyclin E
What about inhibitors are important for progression of the cell cycle?
Inhibitors being inactivated are important for progression.
How does Wee1 kinase inhibit cdks?
It phosphorylates 2 sites on the amino terminal end of the cdk, which interferes with ATP binding.
What are the two steps to activate cdks that have been inhibited via phosphorylation?
- cdc25 phosphatase must take these phosphates off
- Central threonine must be phosphorylated by CAK (CDK activating kinase)
What is the RB protein?
A nuclear, tumor suppressor that regulates E2F activity
It is also a key substrate of cyclin-D to cdk 4/6 complex.
What is E2F?
What is included on the functional heterodimer?
It is a family of transcription factors that regulate expression of cell cycle genes (things like cyclin E, cyclin A, and cdk 2)
It has an EF2 subunit with a DP subunit.
Describe the structure of the whole RB protein.
It is a pocket protein with a A domain and a B domain joined by a linker region.
HDAC and E2F bind to the pocket region
What does RB do for the cell cycle?
It blocks TF’s (E2F)
It holds onto HDACs that take acetyl groups off the DNA making it more condensed
What happens to the RB complex when cyclin D phosphorylates
The first phosphorylation kicks the HDAC it is holding onto on the B domain off, allowing the cyclin E gene to be transcripted.
What happens when RB becomes hyperphosphorylated by cyclin D and E?
RB becomes inactive allowing the cell cycle to move into S phase.
RB being inactivated is what checkpoint?
G1 checkpoint.
What does the G2 checkpoint do?
It blocks the entry into M phase if the DNA is damaged or not replicated properly.
When DNA damage is noticed, what happens?
ATR or ATM kinases are activated.
What do ATR/ATM kinases do?
They will phosphorylate Chk1 (ATR) or Chk2 (ATM)
What do Chk1 and Chk2 do?
They inactivate cdc 25 phosphatase
When this is inactive, CDKs cannot be activated.
What is decatenation?
What happens and what enzymes are involved?
It is part of the G2 checkpoint and aims to detangle the intertwined sister chromatids
Topoisomerase II creates DNA ds breaks that are then fixed by repair.
What does the mitotic checkpoint entail?
It involves checking the spindle assembly - ensuring the correct chromosomal segregation and production of two genetically identical nuclei.
What normally happens in metaphase?
The spindle microtubules attach to the centromere of chromosomes.
If normal activity doesn’t happen correctly, what occurs?
The unattached chromatid pairs will recruit checkpoint proteins that inhibit the APC.
What is APC?
It is Anaphase Promoting Complex.
If correct attachment occurs, what happens?
The APC inhibition is relieved and cohesin is removed.
In simple terms what controls APC?
It is controlled by M phase cyclin-cdk.
What does APC do?
It activates separase, which hydrolyzes cohesin.
What do the Aurora Kinases do?
The regulate chromosome segregation and spindle checkpoint.
What does Aurora A do?
It localizes to the centromeres during interphase and is important for the assembly of the spindle apparatus.
What does Aurora B do?
It is important for bipolar spindle attachment, the spindle checkpoint, and monitoring chromosomal segregation.
What does Aurora C do?
It localizes to the spindle poles late in mitosis.
Growth signal autonomy is one of the hallmarks of cancer. What is this chapter did you learn that causes this?
- There are mutations within the GF signalling pathway
- There are mutations in the genes that code for cell cycle proteins
There is a mutation within cdk 4 that blocks binding to INK 4 inhibitors in some melanomas.
What will this result in?
CDK will never be able to be inactivated.
There is a chromosomal translocation that involves the overexpression of cdk6 seen in some leukemias.
What would be the result?
CDK6 would be more easily activated.
There is overexpression via gene amplification in breast cancer and squamous cell carcinomas.
What is the result?
The cell cycle moves forward much easier.
There is a deletion of the p16 gene is mesothelioma and pancreatic carcinoma.
What is the result?
There is no way to turn off CDKs that are inhibited by the p16 (INK) inhibitors.
What is the most common characteristic of human solid tumors?
Aneuploidy.
What can aneuploidy be caused by?
- Defective centromeres
- Improper cytokinesis
- Changes in the mitotic checkpoint
- weakened if there are individual components are missing
What is mosaic variegated aneuploidy?
What is it caused by?
It is when some cells have the normal amount of chromosomes, but others display varied aneuploidy
It is caused by mutations in genes that code for checkpoint proteins.
CDKs are overexpressed in many cancers.
What is Flavopiridol?
What does it do?
How is Flavopiridol given?
It is the first cdk inhibitor.
It is a competitive inhibitor of cdk activity that targets the ATP binding site.
It will induce cell cycle arrest at G1/S and G2/M
Given via IV
What would chk1 and chk 2 inhibitors do?
They would prevent cell cycle arrest, because normally=
