lecture 6

Question 1

define hypoxia

Answer 1

the lowering of oxygen concentrations compared to the normal level cells are exposed to / sea level ±20.9%

Question 2

What happens to cells if the O2 levels are wrong?

Answer 2

they undergo stress as theyre not used to dealing with those conditions

Question 3

What medical conditions are due to hypoxia?

Answer 3

high altitude disease, stroke/ischemia, diabetes, chronic kidney disease, gastrointestinal disease, schizophrenia, neurodegenerative, ageing, rheumatoid arthritis, cance

Question 4

Did COVID cause hypoxia?

Answer 4

80% mild cases
15% severe disease
5% critical disease with respiratory failure

Question 5

what happens in cell as result of hypoxia?

Answer 5

translational block
microRNA
DNA replication block
transcriptional program
chromatin structure changed

Question 6

What is the action of cells to reverse hypoxia?

Answer 6

restoration of oxygen homeostasis
cell survival
cell death

Question 7

what is HIF?

Answer 7

hypoxia inducible factor - a heterodimeric transcription factors: HIF-α, HIF-1α, HIF-2α, HIF-3α and HIF-1β

Question 8

Where is HIF-1α expressed?

Answer 8

ubiquitously expressed in all tissues

Question 9

Which HIF have restricted expression?

Answer 9

HIF-2α and HIF-3α to certain tissues only

Question 10

How is HIF-3α different to the other HIF-α?

Answer 10

lacks C-terminus transactivation domain
functions as a dominant negative inhibitor for HIF-1α and HIF-2α
able to active a different set of genes in hypoxia

Question 11

How do HIF-α differ if structure to HIF-β?

Answer 11

HIF-β doesn’t contain an ODD (oxygen dependent degradation domain)/NTAD

Question 12

Why is HIF continually degraded?

Answer 12

as to turn on the HIF pathway you need to block the degradation step

Question 13

How is HIF-α regulated in normoxia?

Answer 13

proline hydroxylases (PHDs), FIH (factor inhibiting HIF - an asparagine hydroxylases) enzymes use O2 to hydroxylate key residues within the HIF-1α subunit
Hydroxylation of the ODD signals for VHL (Von Hippel Lindau - a ubiquitin E3 ligase) binding and ubiquitination occurs leading to proteasomal degradation

Question 14

How is HIF-1α regulated in hypoxia?

Answer 14

PHDs and FIH are inhibited, and HIF-1α is stabilised and able to dimerize with HIF-1β and activate target gene transcription through recruitment of coactivators

Question 15

What makes up the structure of p53 tumour suppressor?

Answer 15

Transactivation domain,
proline rich domain,
nuclear localisation sequence,
tetramerisation domain

Question 16

What are the positive and negative effects of p53?

Answer 16

:)
tumour suppression, development, stem cell modulation, fertility
:(
ischemia, treacher collins syndrome, neurodegeneration, aging

Question 17

What regulates p53?

Answer 17

its inhibitor MDM2

Question 18

What is the role of p53?

Answer 18

Pushes cell into cycle arrest to promote DNA repair and allow the cell cycle to restart
OR
Trigger apoptosis for death and elimination of damaged cells

Question 19

What is the role of Mdm2?

Answer 19

promotes ubiquitination of p53 leading to its degradation by the proteasome keeping p53 levels low in undamaged cells

Question 20

Describe the action of Mdm2 to activate p53 in response to DNA damage?

Answer 20

In response to DNA damage p53 becomes phosphorylates at serine 15 by the ATM or ATR kinases
Mdm2 is phosphorylated disrupting interaction between p53 and Mdm2 stimulating negative feedback loop with Mdm2 gene expression limiting p53 activation

Question 21

What is the role of ARF?

Answer 21

p14 ARF stops oncogene activation by disrupting interaction between p53 and Mdm2 - tumour suppression
Results in increased levels of transcriptionally active p53

Question 22

How can cancer cells inhibit p53?

Answer 22

Viral infection - interrupting ubiquitin E6
Mutation - stops ARF, ATM, p53
Amplification - Mdm2

Question 23

What is Li-Fraumeni syndrome?

Answer 23

hereditary cancer syndrome
early cancer diagnosis (before 30)

Question 24

what causes Li-fraumeni syndrome?

Answer 24

-hereditory genetic condition
-caused by mutation in TP53
-takes away genes ability to function correctly