T&H5 Genomic instability and DNA repair Flashcards
In MMR, ________ binds to affected site leading to a conformational change and binding of ______. This complex translocates along DNA until it reaches _______ associated with the replication factor complex (RFC) at the site of the replication fork. The nuclease EXO1 resects the fork backward past the lesion. Excision of the damaged strand triggers DNA looping and brings two sites together. The gap is filled by ________ and ______ seals the nick if necessary. What syndrome is associated with a germline mutation in MMR genes?
- MutS
- MutL
- PCNA
- DNA polymerases d and e
- Ligase I
- Hereditary non-polyposis colorectal cancer / Lynch syndrome
In BER, enzymatic removal of damaged base is done by _________. This leaves site similar to single-strand breaks. _____ activity is needed as intermediate step before DNA regions are recognized. If this activity is inhibited, _____ rescues the day and prevents DSBs.
- DNA glycosylases
- PARP
- Homologous recombination
In NER, recognition of bulky DNA damage is done by ____. This recruits ____ and _____ which opens up DNA. ____ recognizes ssDNA, which leads to excision of an oligonucleotide by dual incision on each side of damaged ends by two endonucleases, ____ and _____/ Fillip of the gap by _____ and ligation of nick then occurs.
- XPC
- XPA and TFIIH
- RPA
- XPG and ERCC1
- DNA polymerase
Homologous recombination requires sister chromatid (ie, homology) as template, which restricts repair to what cell cycle phases?
S and G2
In HR, DSBs are recognized by ____ complex (______________), which is a substrate of ______. This leads to grouping of __________ (exonuclease), _____ (endonuclease), and ______ (helicases). Proteins grouped together are coated with _____. D-loop formation occurs by removal of ______ and addition of _______________________. The extending loop is extended by ______ and D-loop resolves. What are examples of germline mutations of key proteins in this pathway?
- MRN complex (MRE11 + RAD50 + NBS1)
- ATM kinase
- MRN + CtIP + EXO1 (exonuclease)
- DNA2 (endonuclease)
- BLM/WRM (helicases)
- RPA2
- RPA2
- RAD51, RAD52, XRCC2/3, BRCA1/2, and RAD54B
- DNA synthesis
- Ataxia telangiectasia: inherited mutation in ATM kinase, which leads to sensitivity to x-rays and increased risk of LSA
- BRCA1/2 germline mutations which can lead to ovarian and breast cancer
In NHEJ, recognition is by binding of heterodimer ________ to DNA ends, which leads to conformational change that recruits ________. This autophosphorylates, which is essential for NHEJ, and forms active _______. _______ then joins ends together in the “fast pathway.” If DSB ends are unligatable, processing is required. Repair of ends depends on _______ and is processed by nucleases ________ or ______, kinases or phosphatases like ______, or filled by _______.
- KU70/80
- DNA-PKcs
- DNA-PK complex
- ligase IV / XRCC4
- ATM kinase
- MRE11 or Artemis
- PNKP
- Poly mu / lambda
What is the defective repair pathway, defective protein, genomic defect, and cancer predisposition in Li-Fraumeni syndrome?
- DNA DSB response
- p53
- cell cycle checkpoints
- many sarcomas
What cancers in dogs/cats have exhibited telomerase activity?
OSA
Canine/feline LSA
Canine mammary carcinoma
Mutations in NHEJ pathway result in sensitivity to what carcinogen?
ionizing radiation
During what cell cycle phases does NHEJ occur?
all phases but most effective in G1
The ____________ pathway is a specialized pathway for the repair of interstrand crosslinks that can occur during S-phase.
Fanconi anemia pathway
What mutation can cause feline injection site sarcomas?
ATM
What mode of inheritance is Li-Fraumeni syndrome?
highly penetrant autosomal dominant
In people with Li-Fraumeni syndrome, ___% will develop cancer before the age of 40, and ___% will develop cancer before the age of 60.
50%
90%
The majority of the mutations in the TP53 gene in Li-Fraumeni syndrome are ______ mutations.
missense mutations
Xeroderma pigmentosum is an inherited disease in which there is a deficiency in what repair pathway?
NER
What are the defective proteins in XP?
XP and CS
What is the genomic defect seen in patients with xeroderma pigmentosum?
point mutations, typically heterozygous
What 3 disorders exhibit cellular UV sensitivity as a result of NER deficiency?
- Human XP
- Cockayne syndrome
- Trichothiodystrophy (TTD)
XP patients are cancer-prone with _____ fold increase in the incidence of UV-induced cancer.
1000
______ is a TCR defect secondary to mutations in CSB and CSA genes. It leads to neurodegeneration and premature aging due to inappropriate apoptosis.
Cockayne syndrome
_________ is similar to Cockayne syndrome but also causes brittle hair, nails, and scaly skin, secondary to reduced expression of epidermal matrix proteins.
Trichothiodystrophy
Xeroderma pigmentosum patients are very sensitive to ________ radiation and less sensitive to ______ radiation.
UV
Ionizing
NER is used to repair ________.
cyclobutane pyrimidime dimers
What complexes recognize base mismatches and insertion deletion loops (helical distortions) in MMR?
- Base mismatch: MSH2/MSH6 (MutSa) + MLH1/PMS2 (MutLa)
- insertion/deletion loops: MSH2/MSH3 (MutSb) + MLH1/MLH3 (MutLb)
What are the defective proteins in HPCC/Lynch syndrome? What genomic defect does it cause? What cancers does it lead to?
- MSH2 and MLH1
- Microsatellite instability
- colorectal cancer; endometrial, small bowel and renal cancer
More than 300 different predisposing MMR genetic mutations have been documented in human cancers, mainly affecting ______ (___%), ______ (___%), and ______ (____%).
- MLH1 (50%)
- MSH2 (40%)
- MSH6 (10%
________ is likely a common mechanism for MMR inactivation in tumor cells, particularly those that are free of any mutations in MLH1.
Hypermethylation
