lecture 6 - HIF and p53

Question 1

what protein facilitates the attachment of ubiquitin chains to target protein

Answer 1

E3 ubiquitin ligase

Question 2

what is hypoxia

Answer 2

lowering of the oxygen concentrations compared to the normal levels cells are exposed to

Question 3

anoxia is the

Answer 3

absence of oxygen completely

Question 4

as a tumor grows the core becomes hypoxic the tumor then initiates

Answer 4

the hypoxia response

Question 5

3 cellular responses to hypoxia

Answer 5

restoration of oxygen homeostasis
cell survival
cell death

Question 6

HIF system

Answer 6

hypoxia inducible factor

Question 7

HIF is a heterodimeric transcription factor

Answer 7

HIF-alpha and HIF-1beta

Question 8

3 alpha subunits (1alpha, 2alpha, 3 alpha)

Answer 8

HIF-1alpha: expressed in all tissues

Question 9

HIF structure

Answer 9

helix-loop-helix: mediates DNA binding
C-terminal transactivation domain (CTAD): allows them to activate transcription

Question 10

key thing they have which allows them to repond to oxygen levels is

Answer 10

ODD (oxygen dependent degradation) domain

Question 11

HIG-1beta doesnt have an

Answer 11

ODD domain

Question 12

HIF-1alpha regulation at normal levels of oxygen

Answer 12

PHD (proline hydroxylase) mediate hydroxylation (add OH) of HIF-1a at at proline residues in the ODD domain

Question 13

hydroxylated prolines allow recruitment of

Answer 13

VHL (Von Hippel Lindau protein) which is an E3 ubiquitin ligase which stimulates ubuiqitination of HIF-1a and degrades it

Question 14

HIF-1a is being made continuously by the cell but its also being

Answer 14

continuously degraded

Question 15

if O2 levels drop the PHD and FIH cant function as

Answer 15

they require the oxygen in order to induce the hydroxylated so HIF-1a stabilises and can carry out its functions

Question 16

FIH (factor inhibiting HIF) hydroxylases an asparagine domain in the CTAD this

Answer 16

inhibits transcriptional activity

Question 17

VHL binds to

Answer 17

hydroxylates prolines

Question 18

when HIF-1a is stabilised is dimerizes with HIF-1b

Answer 18

dimer is the active transcription factor

Question 19

CTAD isnt hydroxylated by FIH so it can bind to

Answer 19

p300/CBP do activator proteins to regulate transcription

Question 20

HIF controls many targets

Answer 20

oxygen supply
transcription
cellular metabolism
cell growth/death
HIF control

Question 21

p53 (tumour suppressor and transcription factor) functions as a

Answer 21

tetramer

Question 22

p53 responds to DNA damage

Answer 22

normally its inactive and bound to inhibitor mdm2

Question 23

if the cell recieves a DNA damage stimulus mdm2 becomes

Answer 23

inactivated and p53 becomes active

Question 24

primary response of p53 is to induce

Answer 24

cell cycle arrest:
cell stops proliferating and allows a chance for the DNA repair and the the cell cycle restarts

Question 25

p53 also induces

Answer 25

apoptosis if DNA damage is too severe
eliminate the damages cell

Question 26

p53 prevents the development of

Answer 26

cancer

Question 27

role of mdm2
p53 is being made continuously by the cell but being continuously degraded as mdm2 is also a

Answer 27

E3 ubiquitin ligase, promotes the ubiquitination of p53 leading to its degradation by proteasome
keeps p53 levels low in undamaged cells

Question 28

p53 and mdm2 get phosphorylated by ATM kinases. what does this phosphorylation disrupt

Answer 28

the interactions between p53 and mdm2

Question 29

p53 also regulates the activity of mdm2 this forms

Answer 29

a negative feedback loop that limits the extent of p53 activation

Question 30

p14ARF is induced by increased cellular proliferation. p14ARF binds to

Answer 30

mdm2 and blocks it form binding to p53 and increases levels of p53

Question 31

inactivation of p53 causes most cancer types

Answer 31

can occur through mutation of ARF or ATM kinase
causes amplification of mdm2 so p53 is inactive

Question 32

mutations occur in hotspots which are mainly in the

Answer 32

DNA-binding domain of p53

Question 33

Li-fraumeni sydrome (LFS)

Answer 33

born with mutations in one copy of their p53 gene in DNA binding domain
they have a high percentage of cancer development and early onset
illustrates how efficient these pathways normally are