DNA Repair and Oncogene- Induced Replication Stress Flashcards
What is neoplasia?
Tissue composed of cells with the ability to grow beyond their normal confines
What is genomic instability linked to?
DNA damage
What is gammaH2AX?
A phosphorylated form of histones which is generated when DNA damage occurs
What is ATM?
A DNA damage response kinase which signals in the presence of DNA breaks
What is Chk2?
A DNA damage response kinase which signals in response to DNA damage
What is p53?
A tumour suppressor which activates a DNA damage induced checkpoint, promoting apoptosis and senescence
What is increased DNA damage correlated with?
More 53BP1 foci which is correlated with increased p53 mutations
What are the stages of cancer progression?
Normal -> Hyperplastic -> Dysplastic -> Neoplastic -> Metastatic
What is hyperplasia?
The tissue appears normal but there are too many cells
What is dysplasia?
The cells appear abnormal and the relative number of different cell types are abnormal
Precancerous state
What two factors may be the cause of DNA damage in precancerous cells?
Telomere shortening and defects in the DNA repair proteins
Expression of oncogenes
In precancerous cells, what is the general trend?
The cells responding to DNA damage increase
Apoptosis increases
In cancerous cells, what is the general trend?
Less cells respond to DNA damage than precancerous cells but more than normal cells
Apoptosis decreases
What is the less aggressive nature of precancerous lesions a result of?
Tumourigenesis barrier imposed by the DNA damage checkpoint (p53)
What is responsible for the continuous levels of DNA damage in precancerous cells?
Oncogenes deregulate DNA replication -> leads to collapsed replication forks and DNA breaks which initiate DDR
What is the process of replication stress?
DNA replication -> Replication fork stalling due to anything which block replication e.g. bulky DNA lesions -> Replication fork collapse -> one-ended break
How does transcription-replication collisions occur?
In a codirectional encounter - upregulation of transcription makes the replication fork catch up with the RNA polymerase and causes a collision
Head on encounters - The replication fork and the RNA polymerase hit each other head on
In terms of replication, what do oncogenes cause?
Shortened G1 phase
Replication origins to fire in intragenic regions
What is intragenic origin firing related to?
Increased transcription-replication collisions and formation of DNA breaks
Why can R-loops be harmful?
They block DNA replication
What prevents R loops?
RNA binding proteins
What is SFPQ?
A splicing factor
What happens if the splicing factor is removed?
Increase in single stranded DNA and DNA-RNA hybrid
Increased DNA replication
Increased DNA breaks due to collapse of replication forks
Increase DNA damage signalling
- Increased phosphorylation of H2AX
- Increased phosphorylation of Chk1
What does SFPQ interact with?
DHX9 and RNA Pol II
What is DHX9?
A DNA helicase (unwinds DNA)
What does DHX9 loss cause?
DNA replication rescue
In terms of R-loops, what does DHX9 KO cause?
No effect on R loops
In terms of R-loops, what does DHX9 + SFPQ KO cause?
Reduction in R loops
In terms of R-loops, what does SPFQ KO cause?
Gain in R loops
If RNA pol II is phosphorylated on serine 2, what will it do?
Terminate RNA pol II
If RNA pol II is phosphorylated on serine 5, what will it do?
Initiate RNA pol II
If RNA pol II is phosphorylated on serine 2 and serine 5, what will it do?
Elongate RNA pol II
How are R loops formed?
without splicing factors, DHX9 binds to the phosphorylated serine 2 of RNA pol I and doesn’t leave in the beginning like it is supposed to
Where does DHX9 bind to RNA pol II in normal cells?
Serine 5
What do R loops cause RNA pol II to do?
Be stuck on the DNA
What is the pull down of splicing factors dependent on?
DHX9 and RNA
How does DXH9 cause splicing factors to bid to RNA pol II?
DHX9 binds RNA secondary structures and unwinds the nascent transcript -> RNA binding proteins bind nascent RNA to form ribonuclear protein
What happens if there is no DXH9?
RNA secondary structures persist, preventing the formation of RNA-DNA hybrid
What happens if there is no RNA binding proteins?
Nascent RNA can pair with DNA complement to form RNA-DNA hybrid -> RNA pol II is trapped -> increased transcription-replication conflicts and genomic instability
