Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

L2 Stem Cells > Checkpoint controls > Flashcards

Checkpoint controls Flashcards

1
Q

What processes does the genetic material of the daughter cells depend on? (2)

A
  • Faithful DNA replication in S phase
  • Proper allocation of the replicated DNA to daughter cells in M phase
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are checkpoints? (2)

A
  • Surveillance mechanisms to monitor each step of the cell cycle progression
  • Cell cycle is halted if the previous step hasn’t been completed correctly
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the 5 checkpoints in the cell cycle?

A
  • Restriction (R) point
  • G1/S checkpoint
  • S phase checkpoint
  • G2/M checkpoint
  • Spindle assembly checkpoint
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the G1/S checkpoint? (2)

A
  • DNA damage checkpoint before the cell enters S phase
  • DNA damage = can’t enter S phase
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the S phase checkpoint? (2)

A
  • DNA damage checkpoint during DNA replication
  • DNA damage = DNA replication is paused for repair which extends the time in S phase
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the G2/M checkpoint? (2)

A
  • DNA damage and synthesis checkpoint before the cell enters mitosis
  • Cell can’t enter M phase until the whole genome has been replicated without damage
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the spindle assembly checkpoint? (2)

A
  • Checkpoint during mitosis to make sure that the chromosomes are correctly assembled on the mitotic spindle during metaphase
  • Anaphase blocked if chromosomes not assembled correctly
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What happens to the checkpoints in cancer cells?

A

Inactivated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What regulates the restriction (R) point?

A

pRb (retinoblastoma gene)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the function of pRb? (2)

A
  • Inactive pRb in the hyperphosphorylated form allows cells to go through the R point
  • Active pRb in the hypophosphorylated form blocks cells going through the R point
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

When is pRb active?

A

When it is hypophosphorylated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

When is pRb inactive?

A

When it is hyperphosphorylated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What happens to pRb as a cell moves through the R point? (3)

A
  • pRb is unphosphorylated during early/mid G1
  • Presence of mitogens upregulates cyclin D, cyclin D+cdk4/6 complex starts to phosphorylate pRb = hypophosphorylated, pRb still active
  • Cyclin E is upregulated at the R point, cyclin E+cdk2 complex which hyperphosphorylates pRb = inactive
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How does pRb phosphorylation control progression through the R point? (3)

A
  • Un/hypophosphorylated pRb in early/mid G1 binds to E2Fs
  • Hyperphosphorylated pRb dissociates from E2Fs
  • E2Fs are released and cause transcription of genes which allow entry into S phase
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are E2Fs?

A

Transcription factors that promote transcription of genes which mediate the G1/S transition

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How is the action of E2Fs terminated? (2)

A
  • Cyclin A+cdk2 complex is upregulated during G1/S transition which inhibits E2F transcriptional activity
  • E2Fs are ubiquitinated and degraded when S phase transition is complete
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What positive feedback mechanisms drive rapid advance and irreversibility of the cell cycle through the R point? (3)

A
  • E2Fs promote cyclin E expression = more cyclin E+cdk2 = hyperphosphorylation of pRb which releases more E2Fs
  • E2Fs promote E2F expression
  • Cyclin E+cdk2 phosphorylates p27kip1 (CKI) causing degradation = more cdk2 activity = more hyperphosphorylation of pRb
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are the mechanisms of pRb inactivation? (3)

A
  • RB1 gene mutations causing complete loss of pRb/pRb loss of function
  • De-regulated pRb phosphorylation
  • Interaction with viral proteins
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Why does pRb inactivation cause cancer?

A

Absence of pRb activity means there is nothing to inhibit E2Fs so they drive transcription of G1/S transition genes and cause proliferation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How does deregulation of pRb phosphorylation cause cancer?

A

If pRb is always in the hyperphosphorylated form it can’t bind to E2Fs and block entry into S phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How does interaction with viral proteins cause inactivation of pRb? (2)

A
  • E7 protein produced by HPV displaces E2F from pRb
  • pRb can’t inhibit E2Fs even when hypophosphorylated which leads to uncontrolled proliferation in cervical cancers
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Which cyclins are often overexpressed in tumours? (2)

A
  • Cyclin D
  • Cyclin E
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Why are cyclins not ideal as drug targets? (2)

A
  • No kinase activity (most of the drugs target kinases)
  • Intracellular localisation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Which cell cycle proteins could be targeted for cancer treatment? (2)

A
  • CDKs (kinases)
  • CDK inhibitor drugs are in clinical trials
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is Palbociclib? (2)

A
  • CDK4/6 inhibitor
  • Inhibits breast cancer cell growth in vitro with no effect on normal cells
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is an example of a CDK inhibitor drug?

A

Palbociclib

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is the problem with using CDK inhibitor drugs?

A

All patients with metastatic disease eventually develop resistance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What are CDK4/6 inhibitors approved to treat?

A

Hormone receptor-positive breast cancers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

How does resistance to CDK4/6 inhibitor drugs develop? (3)

A
  • Activation of upstream regulators of CDK4/6
  • Inactivating mutations in pRb to allow cell cycle progression regardless of cyclin D+CDK4/6 activity
  • Downstream activation of cyclin E+CDK2
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What abnormalities are observed in CDK4/6 inhibitor resistant cells? (2)

A
  • Increased myc expression
  • Increased cyclin E+cdk2
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

How does resistance to CDK4/6 inhibitors happen involving myc? (4)

A
  • Cells increase expression of myc
  • Myc promotes cyclin E expression
  • Increased cyclin E+cdk2 activation
  • Causes resistance
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What is the solution to CDK4/6 inhibitor resistance?

A

CDK2/4/6 inhibitors to inhibit downstream cdk2 as well as 4/6 e.g. PF3600

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What is an example of a CDK2/4/6 inhibitor?

A

PF3600

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What is a PDX? (3)

A
  • Patient-derived xenograft
  • Tumour sample taken from the patient and injected into a mouse
  • Test drugs on the mouse to see what works
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What is the disadvantage of PDX?

A

Animal has to be immunocompromised otherwise will reject the patient sample

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

How are CDK4/6 inhibitors used in combination therapy? (3)

A
  • P to T regime (constant treatment with Palbociclib then 24hr Taxol treatment)
  • T to P regime (24hrs of Taxol then constant Palbociclib)
  • T to P regime inhibits cancer cell growth a lot more than P to T/P or T alone
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What is Taxol?

A

A chemotherapy drug

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

How can resistance to CDK inhibitors be overcome? (2)

A
  • Combination therapy
  • Make inhibitors to additional targets
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

What is the DNA damage response (DDR)? (2)

A
  • Complex network of signalling pathways which monitor DNA integrity and activate cell cycle arrest/DNA repair in the case of DNA damage
  • If repair is successful cells carry on, if unsuccessful cells undergo apoptosis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

What happens to DDR in cancer? (2)

A
  • DDR inactivation is a hallmark of cancer, contributes to increased genomic instability
  • Some DDR has to remain intact to maintain enough genomic stability to allow the cancer cells to grow/survive
41
Q

What are the 2 main regulators of DDR?

A

Kinases ATM and ATR

42
Q

What activates ATM in DDR?

A

DNA double strand breaks (DSB)

43
Q

What is the role of ATM in DDR?

A

Acts in the G1/S checkpoint to prevent cells with damaged DNA entering S phase

44
Q

What activates ATR in DDR?

A

DNA single strand breaks (SSB) at stalled replication forks (replicative stress)

45
Q

What is the role of ATR in DDR?

A

Acts in the S phase and G2/M checkpoints to prevent entry into mitosis before DNA replication is complete/if there is DNA damage

46
Q

What is replicative stress (RS)? (2)

A
  • Stalling/slowing of replication fork progression and/or DNA synthesis during replication
  • Stress response when cells are forced to replicate faster than usual
47
Q

Why do cancer cells need DDR?

A

Cancer cells always under replicative stress which can lead to DNA damage so need DDR to allow them to keep growing

48
Q

How could DDR be targeted to treat cancer?

A

DDR inhibitors e.g. CHK1 inhibitor

49
Q

What is CHK1?

A

Cell cycle checkpoint kinase 1

50
Q

Which cancer is associated with myc overexpression?

A

Neuroblastoma

51
Q

How could CHK1 inhibitors be used to treat cancer? (4)

A
  • Neuroblastoma cells with myc overexpression show upregulation of CHK1
  • CHK1 inhibitor reduces tumour volume for a certain time
  • Limited efficacy as a monotherapy, combination is required
  • Toxicity also a problem
52
Q

What are the 3 members of the myc family?

A
  • c-Myc
  • N-Myc
  • L-Myc
53
Q

How can myc overexpression be induced in cancer? (3)

A
  • Gene amplification
  • Chromosomal translocation
  • Pro-virus integration
54
Q

How does myc cause cancer?

A

Mutations cause overexpression of normal myc protein which causes transcription of genes involved in proliferation

55
Q

What is bHLH? (2)

A
  • Basic DNA binding domain followed by amino acid sequences forming α-helix, a loop and a second α-helix
  • Group of transcription factors
56
Q

What family of molecules does myc belong to?

A

bHLH family of transcription factors

57
Q

How do bHLH proteins work? (2)

A
  • Form dimers with eachother and bind to gene promoters in DNA
  • Can promote or inhibit expression
58
Q

What is the function of the myc-max dimer? (2)

A
  • Promotes proliferation
  • Inhibits differentiation
59
Q

What is the function of the mad-max dimer? (2)

A
  • Inhibits proliferation
  • Promotes differentiation
60
Q

What broadly determines whether a cell is differentiating or proliferating?

A

Balance between myc and mad

61
Q

What are the actions of myc on the cell cycle? (3)

A
  • Myc-Max promotes expression of cyclin D2 and CDK4
  • Myc-Miz1 suppresses transcription of CKIs p15, p21, p27
  • Myc promotes degradation of p27
62
Q

Is myc alone sufficient to drive proliferation? (3)

A
  • Myc expressed as a fusion protein with the oestrogen receptor
  • Addition of oestrogen/tamoxifen drives myc translocation into the nucleus
  • Tamoxifen addition induces transition from G0 to G1/S = myc alone is enough to drive proliferation
63
Q

What are the 2 types of myc inhibitors?

A
  • Direct
  • Indirect
64
Q

How do direct myc inhibitors work? (2)

A
  • Prevents formation of the myc-max dimer
    OR
  • Stops the myc-max dimer binding to DNA
65
Q

How do indirect myc inhibitors work? (2)

A
  • Prevents myc transcription
    OR
  • Targets the transactivation function of myc
66
Q

How does the PDAC mouse model using Cre/LoxP and tetracycline work? (5)

A
  • Cre is a DNA recombinase that cleaves DNA at LoxP sites
  • Cre is under the control of Pdx1 promoter (pancreas-specific) and is upstream of tTA
  • In the pancreas, Cre cleaves DNA at LoxP sites preceeding tTA, causes tTA expression
  • tTA drives expression of reporter genes and myc
  • Dox inhibits tTA action
67
Q

What is PDAC?

A

Pancreatic ductal adenocarcinoma

68
Q

What were the results from the PDAC Cre/LoxP mouse model? (2)

A
  • Inhibition of myc expression from doxycycline treatment causes tumour regression
  • Significant decline in proliferation and induction of autophagy
69
Q

What is Mycro3?

A

Direct myc inhibitor (prevents dimerisation of myc-max)

70
Q

What is 18F-FDG? (2)

A
  • Labelled version of glucose that can be imaged by PET/CT scan
  • Used to visualise tumours as they have a higher glucose uptake compared to normal tissues
71
Q

What was the effect of myc inhibitors in mice with human PDAC tumours? (3)

A
  • Inject human PDAC cells into mice
  • One group of orthotopic injection, other heterotopic
  • Myc inhibitor reduced tumour growth in both groups
72
Q

What is orthotopic injection?

A

Injection of cells into the location where they should be (i.e. injecting PDAC cells directly into the pancreas)

73
Q

What is heterotopic injection?

A

Subcutaneous injection

74
Q

Why are pancreatic tumours hard to treat?

A

Known as very fibrotic (surrounded by ECM) so hard for drugs to penetrate

75
Q

How does TGFβ signalling prevent cell cycle progression? (2)

A
  • Strongly increases levels of p15 which inhibits cyclin D-CDK4/6
  • Weak induction of p21 which inhibits all other cyclin-CDK complexes
76
Q

How does TGFβ counteract myc activity? (2)

A
  • Prevents expression of myc
  • Prevents myc binding to CKI gene promoters = CKIs are expressed, CDK4/6 and CDK2 are inhibited, pRb is not phosphorylated
77
Q

How can TGFβ signalling be inactivated in cancer? (4)

A
  • Smad 4 loss of function
  • Smad 2 loss of function
  • Smad 3 loss of expression
  • TGFβ receptor expression/activity lost
78
Q

What is the problem with targeting TGFβ to treat cancer? (2)

A
  • TGFβ starts as tumour suppressing
  • Becomes tumour promoting as the cancer progresses
79
Q

How is TGFβ tumour promoting? (4)

A
  • Overexpression of myc counteracts the inhibition activity TGFβ
  • Hyperactivation of PI3K/AKT pathway inhibits the cytostatic activity of TGFβ
  • TGFβ signalling causes expression of cytokines and growth factors which increases proliferation in cancer cells
  • TGFβ promotes expression of EMT regulating genes = invasion
80
Q

What is EMT?

A

Epithelial to mesenchymal transition

81
Q

What compounds can be used to target TGFβ signalling? (4)

A
  • Antisense oligonucleotides which prevent expression of TGFβ ligand
  • Neutralising antibodies which block the ligand/receptor interaction
  • Antibodies that sequester ligands
  • TGFβ kinase inhibitors
82
Q

What is the issue with TGFβ inhibitors?

A

They aren’t specific for the pro-oncogenic responses and inhibit all TGFβ induced effects

83
Q

What is p53?

A

Transcription factor that causes expression of genes which prevent cell growth and promote apoptosis

84
Q

What are the most common p53 mutations in cancer?

A

Mutations in the DNA-binding domain so p53 can’t bind to DNA and cause transcription of downstream targets

85
Q

What is the action of p53? (4)

A
  • Rapid increase in p53 levels in response to DNA damage
  • Key element in the cell cycle checkpoints
  • Promotes cell cycle arrest and DNA repair
  • Cell either continues to proliferate or goes into senescence/apoptosis
86
Q

What happens to p53 in the absence of stress?

A

p53 is ubiquitinated by mdm2 and degraded by the proteosome

87
Q

How does p53 respond to DNA damage? (5)

A
  • p53 expression is not regulated at the level of transcription because mRNA levels remain constant
  • ATM and ATR are activated in response to DNA damage
  • ATM and ATR phosphorylate p53 so it can’t bind to mdm2
  • ATM also phosphorylates mdm2 causing inactivation
  • p53 levels accumulate
88
Q

What happens to p53 in the presence of growth factors? (3)

A
  • Growth factors promote mdm2 expression and phosphorylate mdm2 at a different site causing activation
  • Mdm2 binds to p53 promoting ubiquitination and degradation
  • p53 can’t stop the cell cycle
89
Q

How does p53 stop the cell cycle?

A

Upregulates p21 which inhibits most cyclin/CDK complexes

90
Q

True or false: myc activation is necessary and sufficient to drive cell cycle progression

A

True

91
Q

True or false: treatment with myc inhibitors didn’t affect tumour growth in mice

A

False

92
Q

True or false: p53 is regulated at the transcriptional level

A

False

93
Q

True or false: TGFβ signalling is inactivated in some cancers

A

True

94
Q

True or false: E2F transcription factors promote the entry into S phase

A

True

95
Q

True or false: cyclins are easy to target pharmacologically and inhibitors are used in clinical trials

A

False

96
Q

True or false: pRb is activated by phosphorylation at the R point

A

False

97
Q

True or false: pRb can be inactivated in cancer by interaction with viral proteins

A

True

98
Q

What is an indication of the existence of cancer stem cells?

A

Cell heterogeneity

L2 Stem Cells (12 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions