Cell Cycle, Cell Death, Cancer Flashcards
Which 5 steps are included in the M phase (mitosis)
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
What will keep a cell recently made by mitosis in the G0 phase?
If sufficient stimulus, or conditions, are absent, the cell remains in G0 and does not fo on to the growth and division cycle
What is the correct order of cell cycle phases
- Synthesis
- G2
- M
- G0 or G1
SGMO!!!!
Events in S-phase
“Replicatin”
DNA replication
Events in G2 phase
“Waiting”
DNA has finished replication. Waiting to initiate cell division aka waiting to enter the M phase
Events in M phase
“Dividing”
Mitosis (IPMAT)
Events in G0 phase
“Chillin”
Quiescent, non-cycling. Proliferation capacity is intact
Events in G1 phase
“Building”
The cell has finished dividing and it is now building cell mass to begin initiation of DNA replication
When using a flow cytometer to detect the cell cycle phase, within which phase is the most fluorescence seen?
There are more fluorescent cells in G1 because this is when the cells are building mass to initiate DNA replication in the synthesis phase
What kinds of molecules regulate the cell cycle
Cyclins
Cyclin-dependent kinases (CDKs)
Cyclin-dependent kinase inhibitors (CKIs)
Kinase vs. Phosphatase
Kinase: Attaches a phosphate group to a protein
Phosphatase: Removes a phosphate group from a protein
What are positive cell cycle regulators
Cyclins
CDKs
What are negative cell cycle regulators
CKIs
What is happening on a cyclin cycle graph? (Slide 16)
When a cell is transitioning between phases, it is regulated by various cyclins, CKDs, CDIs, etc. These regulators are seen in higher quantities where it is needed for transition.
What is present on a CDK to ensure cyclin binding
PSTAIRE alpha-helix
What must be phosphorylated on a threonine residue by a CDK-activating kinase (CAK) for the catalytic fx of a CDK to become activated?
The activation loop, or T-loop, must get phosphorylated
How do protein kinases and protein phosphatases work in tandem to activate a cyclin-CDK complex?
Protein kinases add the phosphates to inhibitory and activating sites on the CDK. Activating protein phosphatases, such as Cdc25, remove the inhibitory phosphate thereby activating the cyclin-CDK complex
Which cyclins bind to CDK1 (p34 cdc2)
A
B1
B2
Cdk1-cyclin B binds Cdk1 (Cdc kinase subunit)
Which cyclins bind to Cdk2
A, E
Which cyclins bind to Cdk4, Cdk 6
D1-D3
What is the action of CKIs
Block CDK action and ensure control over the cell cycle. CKIs are activated upon cell cycle activation checkpoint.
How do CKIs negatively regulate the cell cycle
Based on the particular regulator, the CKI may:
- Twist the upper lobe of the CDK to block cyclin binding
- Interfere with ATP hydrolysis
- A loop is insinuated in the upper lobe of the CDK to block ATP binding
How does INK4 function
Functions to negatively regulate the cell cycle in 2 ways. If it binds BEFORE the cyclin, it inhibits cyclin binding. If it binds AFTER the cyclin has bound, it interferes with ATP use.
How does p27 function?
Works after the cyclin has bound. A loop is insinuated into the upper lobe of the CDK to block ATP binding.
What gene induces CKI:p21
Induced by p53 tumor suppressor. Makes sense because when we want to SUPPRESS tumors, we want to arrest the cell cycle and this is possible with CKI:p21 (blocks ATP binding)
How is CKI:p27 and INK4:p16 regulated?
They both arrest cells in response to growth suppressors and transforming growth factors like TGF-beta. INK4:p16 action is altered in many cancers…will lead to uncontrollable growth because the CKI is not functioning well.
How so Ras proteins receive their signaling and what is the overall function of Ras signaling?
Ras proteins (aka small G proteins or small GTPases) receive their signals from catalytic receptors that have been activated by a ligand. Overall fx of Ras signaling involves proliferation.
Where is MAPK located?
In the cytoplasm
Where is Myc gene located
In the nucleus
Myc gene alters cyclin D gene, SCF subunit gene, and E2F gene. What is the effect of these?
They all lead to increased E2F activity. Cyclin D gene and SCF subunit gene lead to increase E2F activity INDIRECTLY by activating G1-Cdk and G1-S-Cdk cyclins which go on to carry out Rb phosphorylation.
What is a mitogen
a substance that induces or stimulates mitosis.
What are the key molecules involved in the G1/S transition
E2F pRb CDK-2 Cyclin E (hyperphosphorylation)
What are the key molecules involved during the S phase
MCM2-7 Cdt1 Cdc6 ORC1-6 CDK2-Cyclin E CDK2-Cyclin A Cdc7/Dbf4
Key molecules involved in the G2/M transition
CDK1-cyclin B
Cdc25
Ser216
APC (anaphase-promoting complex)
What do the checkpoints do and how are they activated
Checkpoints are biochemical circuits that detect internal/external stimuli sending appropriate signals to the cell-cycle system
Mostly activated by genotoxic stress like DNA damage
Which 2 pathways target the Cyclin/Cdk complexes in G1
Slower: Mdm2 stabilizes p53 which upregulates p21 which inhibits Cyclin/Cdk complexes
Faster: Chk2 is activated and inactivates Cdc-25, this means that inhibitory phosphates CANNOT BE REMOVED.
What is the pathway in the G1 checkpoints that indirectly and directly inhibit CDK2, CDK4,6, and inhibit RB1
The ARP/p16 pathway. DNA damage molecules activate mTOR, DDR, CDKN2A locus, p38, and BRAF.
INDIRECTLY: Depending on the DNA damage molecule, ARF or p53 is activated, leading to upregulation of p21 which inhibits CDK2 (thus inhibiting phosphorylation by Rb1)
DIRECTLY: BRAF directly inhibits CDK4,6 (thus inhibiting phosphorylation by RB1) by upregulating p16.
How does Cdc25 work in the G2 checkpoints
Cdc25 is targeted for nuclear export by Chk1/Chk2. This leads to accumulation of the inactive Cyclin B1/CKDK1 complex. Lack of activated Cyclin B1/CDK1 complex interrupts feedback loops and arrests the cell in G2 so it cannot transition to mitotic phase
Tumor definition
Space occupying lesions that may or may not be neoplasms
Neoplasm definition
Relatively autonomous abnormal growth with abnormal gene regulation. Can be benign or malignant.
Cancer definition
Malignant neoplasm…may produce metastasis
Metastasis definition
Secondary growth of cancer at a different location from primary neoplasm
What is initiation?
A genotoxic event (single gene mutation, translocation, amplification) arising from genotoxic agents (chemicals, radiation, ROS, viruses) to give a change in DNA sequence. May be the result of oncogenes or inactivation of tumor suppressor genes.
What is promotion?
Occurs over a long period of time and is reversible at many stages. This is an epigenetic event and involves changes in gene regulation. The latent phenotype of the initiated cell becomes expressed via cellular selection and CLONAL EXPANSION. May be monoclonal or polyclonal. Cancer is usually monoclonal.
what is progression?
Involves further complex genetic changes (chromosomal translocations, deletions, amplifications) resulting in irreversible changes to gene expression and the evolution of karyotypic instability. Results in malignancy.
What are the hallmarks of cancer
Insensitive to growth-inhibitory signals Evade cell death Promote inflammation Avoid immune destruction etc.
what are oncogenes
Cellular genes whose expression stimulates cell division and/or growth.
What happens when oncogenes are no longer tightly controlled?
They lose regulation of gene expression and this leads to enhanced expression ultimately leading to unregulated cell growth and division.
What are tumor suppressors
Cellular genes that check or inhibit cell division (p16INK4A, p21, p53, Rb, p14ARF, etc)
What happens when tumor suppressors are no longer tightly controlled?
Loss of expression of tumor suppressor genes leads to cell growth or division.
Why are oncogenes “dominant”?
- The result from a “gain of function” mutation that results in their overexpression and resulting unregulated activity
- Only need one of the 2 alleles to be activated for the effects of cell growth to happen.
***Tumor suppressor genes are different because they need the 2nd loss of function mutation on the 2nd allele for abnormal cell growth to occur.
What are the 3 forms of oncogenes
- Cellular proto-oncogenes that have been captured by retroviruses
- Cellular proto-oncogenes that have been mutated
- Virus-specific genes that behave like cellular proto-oncogenes that have been mutated
Germline inheritance in oncogenes and tumor suppressor genes
Oncogenes: rare
Tumorsuppressor gene: frequent
How do p53 and p21 function differently in response to cell damage
p53: if damage cant be repaired, apoptosis occurs by way of p53
p21: If the damage can be repaired the CDK inhibitor p21 STOPS the cell cycle
basically, p53 kills and p21 stops
On which cells is radiation most effective?
On cells that have:
- Reproductive activity
- Longer dividing future ahead
- Less differentiation
How does radiation work? *2 ways
- Deposit energy directly into DNA via photons to break DNA bonds
- Hydrolysis of water to produce damaging free radicals.
what “kinds” of chemotherapy are there?
- Alkylating agents
- Intercalating agents
- Antimetabolites
- Mitostatic agents
- Platinum derivatives
How do alkylating agents work
Capable of denaturing DNA macromolecules
How do intercalating agents work
Interact w/ DNA and are intercalated between 2 bases inducing a structural change and cleaving agents to break DNA molecules
How do antimetabolites work
Structural analogs of pyrimidines and purines. Block synthesis of corresponding bases or folate analogs.
How do mitostatic agents work
Inhibit tubulin synthesis…act as cell spindle poisons
How do platinum derivatives work
Play a role in DNA binding
What are the 5 mechanisms of cell death
- Apoptosis - programmed cell death
- Autophagy - self-digestion
- Necrosis - explosive disaster
- Mitotic catastrophe
- Senescence - irreversible growth arrest
What molecules are involved in targetting the mitochondria in relation to necrosis
- Receptor-interacting protein 1 (RIP1)
2. Poly [ADP-ribose] polymerase 1 (PARP-1)
What cells are involved in autophagy
Hematopoietic cells and their malignant counterparts (liquid tumors)
What cells are involved in necrosis
All cells
Triggers of apoptosis?
- DNA damage (ATM, p53)
- Death receptors signaling (CD95, TNF receptor, caspase8)
- Cell membrane (sphingomyelinase breaks sphingomyelin into ceramide)
- Mitochondrial damage (ceramide mediated)
How do Bax and Bak affect permeability in apoptosis
They are thought to induce permeability by forming pores upon oligomerization. They do not come together when the anti-apoptotic BCL2-family is inhibiting them from doing so. The pro-apoptotic BH3 family activates Bax/Bak.
How does Bax/Bak get activated by BH3 pro-apoptic family
- Binding of BH3 to the anti-apoptotic Bcl-2 proteins
2. pro-apoptotic BH3 proteins can directly bind to and activate Bax and or Bak.
What happens to Cytochrome C in apoptosis
Once the oligimer Bax/Bak is formed when the Bcl-2 protein is bound by BH3 (or when BH3 binds to Bax and or Bak), the cytochrome C is released.
What are the 5 mechanisms of autophagy?
- Beclin released from Bcl-2 to form the Class III P13K complex
- Two cascades (LC3-II and Atg5-12) elongate nucleation complex to make limiting membrane
- Atg9 delivers more limiting membrane
- Limiting membrane sequesters cargo, seals, and forms the autophagosome
- Autophagosome fuses to the lysosome, degradation happens, nutrients released into the cytosol.
What is a mitotic catastrophe
A type of cell death characterized by aberrant mitosis. Mainly associated w/ cell cycle checkpoint deficiency. Also associated w/ hyperamplification of centrosomes and caspase-2 activation during metaphase
*This and senescence are the only type of cell death with no change to the cell membrane
What cell-cycle checkpoints are messed up in a mitotic catastrophe
- p53- G2 checkpoint
- BUB-related kinase (BUBR) - spindle checkpoint
- increased expression of multiple mitotic checkpoint genes (APC) - spindle assembly
3 fates of cells in a mitotic catastrophe
- Mitotic death
- Delayed cell death
- Senescence
Mechanisms of senescence
- p53-p21 (p53 upregulates p21 which activates senescence and inhibits CDK–>inhibits pRB–>inhibits E2F
- p16-Rb (inhibits CDK–>inhibit pRB (inhibition of pRB leads to activation of senescence)–>inhibit E2F)
