Lecture 9

Question 1

P53

Answer 1

Tetrameric

Transcriptional Activator

Question 2

P53 Null Cell line experiment

Answer 2

• unable to induce tumour supressor genes
• -Used Dexamethazone small molecule inducer
  to induce expression of wt p53
  -Isolate and compare mRNa
  -Convert it into DNA – hybridise the Combined DNa and carry out subtractive hybridisation to find nucleic acids not expressed in the first codniton but in the second
• Main gene identified was in responses to Dexamethazone WAF1

Question 3

What does WAF1 do ?

Answer 3

• sequenced and compared to a database
• P21 Cip 1
• Cyclin dependent kinase inhibitors
• inhibits the cdks involved in continuation of the cell cycel

Question 4

Up regulation of P21 causes what

Answer 4

Cell cycle arrest

Question 5

What happens in response to Gentoxic stresses in P53 mutants ?

Answer 5

Mutants cannot correct malfunction

- dont actually stop cell cycle&raquo_space; amplify the mistakes in proliferating cells

Question 6

Levels of P53

Answer 6

induce distinctive genes depending on the error

- distinct program pathway

Question 7

What processes does P53 induce when an error occurs ??

Answer 7

• cell cycle arrest or Senescence/ return to proliferation
• DNA repair
• Block of angiogenesis
• apoptosis

Question 8

When do cells die?

Answer 8

When the amount of genomic damage is high and irreparable

Question 9

What hallmark of cancer does P53 relate to?

Answer 9

• very short half life

- Rate of synthesis of P53 and degradation is normally high

Question 10

In a particular subset of mouse sarcomas what was found when addressing the question; What keeps P53 low ??

Answer 10

small set of gene products responsible for a particular phenotype in those sarcomas – double minute chromosomes (fish probes show one or two chromosome fragments when should be one)
- Gene identified as MDM which gives rise to this particular phenotype

Question 11

MDM2

Answer 11

• Directly involved in regulating P53 levels by binding directly
• ubiquitin ligase catalyses ligation reaction and targets P53 for destruction in cytoplasmic proteasomes

Question 12

MDM

Answer 12

itself a target of P53 and regulated

- causes continuous turnover/degradation of P53

Question 13

P53 regulation

Answer 13

P53 has its own mechanism to regulate its levels

Question 14

What keeps P53 levels up ?

Answer 14

• ARf tumour suppressor
  Largely made only in S phase
  Exerts a regulatory control on the system above by binding /mdm2 so it cant access P53 and MDM2 is sequestered in the nucleus

Question 15

Describe the diagram of the tumour suppression pathway before cell cycle arrest or apoptosis ?

Answer 15

E1A/ C-Myc/ Ras 
            I
         E2F
            I 
         ARF
          _I_
       MDM2 
          _I_ 
       P53 >>
Cell cycle arrest or Apoptosis

Question 16

Genotoxic stress

Answer 16

increases P53 levels
-ATM/ATR are activated during genotoxic stress
And phosphorylate P53 > Cell cycle arrest/DNA repair/ Apoptosis

Question 17

ATM

Answer 17

-Monogenetic disease
-kids prone to getting cancer
-No cellular response to ionising radiation
Tissue necrosis

Question 18

ATM

Answer 18

gets turned on in response to double DNA stranded DNA breaks

Question 19

ATR

Answer 19

switched on when DNA replication is arrested

Question 20

Kinase part of ATM/ATR looks like

Answer 20

PI3K

Question 21

Inactive forms of p53 enable

Answer 21

• Oncogene activation without apoptosis
• Higher tolerance of anoxia
• Sloppy oversight of chromosome integrity

Question 22

P53 Re-activation provides potential new cancer treatment

Answer 22

• Interact with P53 and change its shape
• Move mutant version back to wt
• PRIMA1 molecule
• Cells start accumulating more freq in G2 spending more time in G2
• Promote apoptosis with a molecule that binds to P53 and induces functionality

Question 23

The study of what led to the discovery of P53

Answer 23

of how oncogenic viruses subvert host cell control of DNA replication

Question 24

Wild-type p53

Answer 24

Is an unusual type of tumour suppressor gene

Question 25

P53 summary

Answer 25

is mutated in a large proportion of human cancers, with a predominance
of missense mutations

Question 26

P53 null mice

Answer 26

develop normally but die prematurely of cancer

Question 27

P53 is a shortlived protein

Answer 27

whose steady state level is controlled by regulated proteolysis

Question 28

Genotoxic stresses

Answer 28

block p53 destruction and enable it to act as a transcription factor

Question 29

P53 induces what ??

Answer 29

P53 induces the transcription of genes that arrest the cell cycle and induce DNA repair

Question 30

Prolonged expression of p53 induces what ??

Answer 30

Prolonged expression of p53 induces apoptosis

Question 31

Cancer cells

Answer 31

Cancer cells acquire selective advantages by acquiring mutant forms of p53

Question 32

Future..

Answer 32

Future progress in cancer treatment might be obtained by novel drugs that can
“reactivate” mutant, transcriptionally inactive forms of p53