C-myc Flashcards
1
Q
What is the mutation seen in 90% of Burkitt’s lmyphomas?
A
- myc gene on chromosome 8 is translocated to 14
- places c-myc next to a heavy chain promoter
- associated with EBV infection
2
Q
What is c-myc?
A
- proto-oncogene expressed in proliferative cells
- repressed when these cells withdraw from the cell cycle
- can be continuously expressed in cancer leading to continuous proflieration
3
Q
C-myc is normally only associated with growth factor-induced proliferation. When can this be deregulated? (4)
A
- insertion of viral v-myc that plays a similar role
- viral insertion of promoters or enhancers next to c-myc
- chromosomal translocations
- other mutations leading to gene amplification
4
Q
Explain the earliest stages of cancer. What is required?
A
- many mutations
- one single mutation is not enough to cause cancer and is very common
- need multiple mutations in the same cell to lead to altered expression and transformation
- multistep process
5
Q
What is contact inhibition?
A
- normal cells will stop growing on a plate when they form a single layer as they sense that there is no space left to grow
- cancer cells will not sense this and will continue to grow over one another
6
Q
What is oncogene cooperation?
A
- when c-myc or other oncogenes are added to immortalised fibroblasts it can cause their transformation into cancer cells
- if the oncogene is added to primary fibroblasts its not enough to transform them
- one oncogene is only sufficient to cause cancer if the cells are already on the pathway
- need cooperation
- adds to the multistep hypothesis
7
Q
What is the structure of c-myc?
A
- HLH - DNA binding
- LZ - dimerisation
- NLS - nucleus
- Myc Box 1+2 highly conserved and only in Myc
8
Q
How does c-myc bind to DNA?
A
- dimerises with MAX
- binds to the E box (CACGTG)
- short sequence that occurs fairly frequently by random
9
Q
What is Mad?
A
- dimerises with Max
- can have Myc-max or mad-max
- competes for the same DNA binding sites as myc-max but instead switches proliferation genes off by histone deacetylases
- found in differentiated/differentiating cells
- recruits pTEFB, DSIF, NELF and causes SWI/SNF remodelling
10
Q
What are HATs and HDACs?
A
- histone acetyltransferases that add acetyl gorups to histones, giving them a negative charge that makes them move away from DNA and opens up the chromatin
- histone deacetylases that remove these groups
11
Q
What are the 5 basic steps of transcriptional regulation?
A
- chromatin remodelling by histone modifying enzymes
- ATP-dependent chromatin remodelling
- assembly of the preinitiation complex
- transcriptional initiation
- transcriptional pause release
12
Q
Describe the phosphorylation patterns in transcription elongation
A
- RNA pol II binds to the promoter unphosphorylated
- ser5 of the CTD gets phosphorylated at initiation by TFIIH
- PTEFb phosphorylated ser2 during elongation
- ser5 phosphatase removes ser5 phosphorylation as RNA polymerase moves towards termination
- can use the levels of phosphorylation to measure where in the process RNA pol II is
13
Q
What is ATP dependent chromatin remodelleing?
A
- alternative way of altering transcription
- nucleosome remodelling complexes such as SWI/SNF bind DNA and use ATP energy to slide or transfer nucleosomes to alter the chromatin structure
- allows access of gene activators or moves histones in the way of genes
14
Q
What is chip-seq?
A
- the use of antibodies to show protein-DNA interactions across the genome
15
Q
What does Chip-seq show looking at RNA pol II phosphorylation during transcription?
A
- lots of RNA pol II at the 5’ and 3’ ends of activate genes and only at 5’ of inactive
- ser2P at the 3’ of active genes only as termination doesn’t occur in inactive genes
- ser3P seen at 5’ of active genes but also in inactive genes as initiation occurs and then stops
