Lecture 7 Flashcards
Ch6 Growth inhibition and tumor suppressor genes
What is PTEN?
A tumor suppressor protein
When is the loss of PTEN not a problem?
When EGF (a growth signal) is gone
What can an EGFR mutation lead to?
To an oncogene, whjch signals without needing EGF binding
What is the Knudson’s two-hit hypothesis?
When you need a mutation in both TSG for it to lead to cancer
Why is familial cancer different then normal cancer?
Familial cancer is more frequent and occurs earlier as there is only one additional mutation needed
What is haploinsufficieny?
Some TSG only need one mutation, eg p53
Which cancers belong to the proteins RB1, p53, APC and BRCA
RB1 = retinoblastoma
p53 = Li-Fraumeni
APC = colorectal cancer
BRCA = breast and ovarian cancer
How can E2F be released from Rb?
Release via phosphorylation
What is E2F needed for?
For transcription
Which factors can lead to no cell cycle regulation (by E2F)?
When pRB is lost, when there is a mutation in the pocket region of pRB, hyperphosphorylation of pRB (common) and binding of an oncogene virus to pRB
What are upstream activators of p53?
There is deregulation: eg DNA damage, oncogene activation and cell stress (are sensors)
What are downstream effects of p53?
There is restauration or suicide: eg cell cycle arrest, DNA repair, apoptosis, inhibit angiogenesis (are effectors)
What does p53 do to work?
It has to form tetrameres
Which four domains can be found in a p53 gene?
Tetramerization domain, DNA binding domain (promoter), transactivation (transcription) and MDM3 (inhibits p53) domain and regulatory domain (cofactor binding)
What is the effect of p53 binding to MDM2?
It drives the export of p53 out of the nucleus, then ubiquitination and degradation of p53, so usually p53 has lower levels
What drives the expression of MDM2?
p53
What is the effect of stress on p53?
It leads to production of more p53, which has a fast and strong effect and eventually there will also be more MDM2
What happens after DNA damage and cell stress?
Kinases are activated, which phosphorylate p53 to dislodge MDM2
What happens after oncogene activation?
This activates molecules that bind to MDM2 with a higher affinity than p53, which frees p53
How does p53 introduce cell cycle arrest?
By binding of p53 to p21, which binds to a cyclin inhibitor, which binds to pRB. This means that pRB cannot be phosphorylated, thus E2F cannot be released
How does p53 introduce intrinsic apoptosis?
It releases cytochrome c from the mitochondria and suppresses anti-apoptotics (eg BCL2)
How does p53 introduce extrinsic apoptosis?
Via FasL
What other molecule does p53 work on?
miRNA
Which p53 factors target gene selectivity?
Amount, modification, co-factor of promoter or p53
How does the difference in promoter binding affinity influence the gene selectivity?
eg p21 has a high affinity for p53, anti-apoptotics have a low affinity
How do cofactors binding to the promoter influence the gene selectivity?
By eg MIZ-I binding to the promoter of p21
How do cofactors binding to p53 influence the gene selectivity?
ASPP binds to p53 and increases the affinity for pro-apoptotic promoters
What is the function of Myc oncogenes (in cancer) do to prevent p53 activation?
It binds to MIZ-I with a higher affinity than p53
In which domain can about 90% of the mutations be found?
In the DNA binding domain
What other way is there to prevent p53 apart from mutations?
By inhibiting other proteins, either endogenous or viral
What is a dominant negative p53 mutation?
This mutated p53 can form a tetramer with the WT, but when one mutated protein is in the tetramer it becomes transcriptionally inactive. There is p53 accumulation, as less MDM2 is produced
What is a gain-of-function mutation in p53?
p53 binds to promoters that contribute to carcinogenesis and it activates them
What does the viral DNA do with Rb and E2F
One protein inhibits RB + release of E2F and a second protein blocks p53, so it cannot go into cell cycle arrest and produce new viral DNA
Which proteins of HPV inhibit what?
E7 inhibits RB, E6 inhibits p53
Which proteins of Adenovirus inhibits what?
E1A inhibits RB, E1B inhibits p53
What is needed for the maintenance of cancer?
The continues inhibition of p53
How can p53 be used for cancer treatment?
Restoring the activity of p53
Which ways are there of using p53 activity as treatment?
Introducing functional p53, restore protein conformation, oncolytic adenovirus introduction, inhibitor of MDM2
What is the problem with the introduction of functional p53?
It is hard to introduce it into all the cancer cells
Which molecules can be used to restore protein conformation?
PRIMA-1 or APR-246
How can oncolytic adenovirus be used to restore p53 activity?
It is introduced without E1B, so it will not kill normal cells, but it will cancer cells
How can an inhibitor be used to restore p53 activity?
MDM2 binds to the inhibitor (eg nutlin) when p53 is still active
