L4 - Regulation of TFs Flashcards
How is activity of TFs commonly regulated and whats an example of it?
Post-translational modifications )(PTMs)
p53 is heavily PTMs
What stimuli can cause TFs to be regulated?
Hypoxia
DNA damage
Telomere erosion
dNTP depletion
How can TFs be modified (7 ways)?
Ubiquitination Methylation Neddylation Sumolation Glycosylation Acetylation Phosphorylation
What is Mdm2 and what is its function?
E3 ligase
Controls p53 level by ubiquitation
What do Mdm2 KO mice do?
Die in utero due to p53-induced apoptosis
What are nutlins?
Anti-cancer Drugs to occupy p-53 binding pocket of Mdm2 to prevent degradation
What is neddylation and sumoylation?
Addition of NEDD8 and SUMO
What do NEDD8 and SUMO do?
Influence p53’s ability to regulate txn depending on accepter site, target gene and cel ltype
What phosphorylates p53 and where?
ATM kinase on Ser15
Why is p53 phosphor?
In response to DNA damage - stabilises p53 by inhibiting interaction with Mdm2 - allows p53 to accumulate to direct apoptosis or cell cycle arrest until damage repaired
What acetylates p53 and why?
HATS eg p300 and CBP
Stimulates ability to activate some genes
What did mutating the eight lys residues that are acetylated in p53 do?
Retained DNA binding activity and ability to activate MDM2 but lost ability to induce p32 exp or cell cycle arrest
What is the use of negative feedback control?
Allows transient response that switches itself off once stimulus removed
What is the negative feedback of p53?
Gene encoding MDM2 is a target for p53 - prevents excessive accum of p53 and return to basal levels once stimuli removed
What happens when p53 is monoubiquitinated?
Exported from the nucleus
What favours polyubiquitination (go for degradation)?
Higher levels of MDM2
What is HSF and where is it found?
Heat shock factor
Sequestered with hsp90 in the cytoplasm
What happens when cells are heat shocked?
Dissociated hsp90 chaperone from HSF so it can enter nucleus to activate txn
What 2 things happen to HSF before it activates txn?
Phosphorylated and also trimerises
What ae steroid receptors
TFs that require steroid ligands for activity
What does steroid binding trigger?
hsp90 chaperone to dissociate and allows receptor to enter nucleus to effect txn
What is NF-kB family involved in?
Immune response
Where and how is IkB found, and how is this changed?
Sequested in cytoplasm with p50 and p65
IkB is phosphorylated and ubiquinated and degraded allowing p50 and p65 to go to nucelus
What is the negative feedback for NF-kB?
Gene encoding IkB is a target for NF-kB (so the gene that p50 and p65 induce has IkB too so it comes and gets them again)
What TF is regulated by dimerization?
MYC is unable to bind DNA without MAX
Why do MYC and MAX have to dimerise?
Both have bHLH/leucine zipper domains that only function after dimerisaiton
HLHZip forms extended alpha-helical dimerization interface
What is the difference between MYC and MAX?
MAX can homodimerise, MYC needs MAX
What does MAD do?
Binds DNA with MAX to repress txn by recruiting HDACs
Expressed in differentiated cells
What does MYC do to DNA?
Activates txn by recruiting HAts, P-TEFb, TBP, TFIIH
Expressed in proliferating cells
What is MyoD and what are its features?
a TF that can induce myogenic differentiation
Has a bHLHZip
Dimerises with E2A for function
What is E2A
bHLH protein essential for lymphocyte development
Also a putative tumour suppressor
What are ID proteins and what are their features?
Respressors of bHLH proteins
Have HLH domain so can dimerise with E2A but lacks DNA binding domain (E2A/ID heterodimers inactive)
What can IDs block other than E2A?
Block MyoD function by sequestering E2A
Where are IDs common and uncommon?
Abundant in stem cells and proliferating cells but rare in differentiated cells
How are ID proteins involved in cancers?
ID overexpression in mice causes fatal malignancies.
Elevated ID predicts poor prognosis
What binds to and suppresses ID proteins and how was this shown?
RB (tumour suppressor)
Mice with 1 RB allele predisposed to pituitary tumours
What decreased tumour incidence in RB- mice and what did this show?
ID2 gene deletion
Inhibition of ID2 is important for tumour suppression by RB
What can ID2 do?
Promote angiogenesis by inducing VEGF
What is HIF and what is its function?
Hypoxia inducible factor
Cells starved of oxygen use it to induce VEGF and other genes
Features of HIF?
Only stable under hypoxic conditions (at normal O it is hydroxylated by prolyl hydroxylases (use o2 as co-substrate) then ubiquitinated)
What is VHL?
E3 ubiquitin ligase that recognises hydroxylated proline residues on HIF and targets it for degradation
What do mutation in VHL cause?
Active HIF under normoxic conditions so inappropriate angiogenesis
Von Hippel-Landau disease
