Cancer Bio Flashcards
Inhibitors of Angiogenesis
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Prolactin, P53, Thrombospondin 1/2, Endostatin (blocks MAPK & MMPS), Angiostatin (binds anexin II), Top1, Notch
Angiogenic Inducers
GROWTH FACTORS
VEGF, PDGF (plt derived growth factor) hepatocyte derived growth factor, fibroblast growth factor, epidermal growth factor
VEGF Signalling Pathway (diagram)
VEGF A Signalling pathway (words)
1) 1 VEGFA binds to 2 VEGFR - dimerisation and autophosphorylation.
2) Activates Ras-raf-mek-mapk cascade - transcription factor activation & gene expression
3) also activates PI3K - AKT - inhibition of apoptosis (blocks BAD which is pro apoptotic) & stimulation of endothelial NO synthease + vascular permeability via NO production.
VEGF & VEGFR
5 ligands VEGF-A - D.
3 receptors VEGFR 1 -3
VEGF-A & VEGFR key to angiogenesis
VEGF1 regulates amount of VEGFA able to bind to VEGFR by competitively binding and so is inhibitory.
VEFGR3 - involved in lymph system - promotes expansion of lympahtic vessels and increases lymph spread risk.
Angiogenic sprouting
- Tip formation
- Stalk elongation
- Anastomosis
- Canalisation
- highest signal - vegfr2 & Vegfa stimulate formation of tip cell
- once vegf2 activated - tip cell induce expression and release of NOTCH ligand, delta like 4 ligand (DLL4) which bind to Notch R on neighbouring cell.
Notch intracellular domain released and transported to nucleus - acts as transcription factor to repress VEGFr2 and induce VEGFR1
VEGFR1 decreases conc of VEGF available for VEGFR2 therefore growing sprout moves along VEGF gradient.
Hypoxia & Hypoxxia inducible factor
Single strand Breaks
- Direct Repair
- Base excision repair
- Nucleotide excision repair
- Mismatch Repair
Detected by alkaline solution assay
Direct Repair
damage recognised by 06 Alkyl guanine DNA alkyl transferase (AGT) & directly chemically reversed by removing an alkyl group from 06 atom of guanine.
Base Excision Repair
Removal of single damaged base - can repair damage by deaminations, alkylations or oxidations of DNA Base
- DNA glycosydases recognise and remove damaged base
- APE2 cuts DNA back bone leaving SS break
- PARP1 detects SSB + promotes recruitment of SSB proteins to DNA damage site
- DNA polyerase B syntheseses new DNA
- DNA ligase II joins end of the newly synthesised DNA to fill the gap
- XRCC1 acts as a scaffold
Nucleotide excision repair
specific for helix distorting lesions (eg. pyrimidine dimers, bulky DNA adducts)
1. XPC recognition of helix distortion
2. recruitment of a number of proteins
3. Endonucleases remove a sequence of oligonucleotides
4. DNA polymerase fiills the gap
5. DNA ligase seals the nick.
Mismatch Repair
corrects replication errors that have resulted in mismatching bases that have escaped editing by polymerases (esp in microsatelite areas).
1. Recognition - MSH2 & MSH3/6 binding to affected DNA sites & recruiting MLH1 & PMS2
2. Excision - recruitment of endonucleases which excise the damaged strand
3. Substitution by DNA polymerase
4. Religation by DNA ligase
Double Strand Breaks
NHEJ
Homologous recombination repair
Detected by alkaline comet assay
Non Homologous End Joining
predominant DNA DSB repair pathway, DNA directly repaired w/o need for homologous DNA molecule
Error prone, can lose DNA
- DNA ends recognised by KU70/80 proteins (aka XRCC5/6) that recruit DNAPK which activates artemis & holds end together and creates stable scaffold.
- ARTEMIS (endonuclease) processing enzymes that tidies the ends to prepare for ligation
- If DNA ends are compatible they are directly ligated otherwise ends are resected until compatible.
- DNA ligase IV and XRCC4 join the DNA together
Homologous recombination Repair
requires sister chromatide, slower, generally S/G2 phase, 2 copies of intact DNA molecules produced with rarely any errors
- Detection of DSB break by aTM protein & MRN complex - excises DNA to create single strand 3 ends
- RPA protein binds to and stabilises the SSDNA
- BRCA1 & 2 aids nuclear transport of RAD51 onto ss DNA
- RAD52 facilitates RAD51 binding to exposed ends - once bond formed nucleoprotein filament that invades SSDNA to look for a homologous sequence
- Once found this is copied & followed either by DSB repair or synthesis dependent strand annealing
- RAD52 anneals the stands, BCM proteins help migrate the junctions toward each other.
Extrinsic pathway of apoptosis
- Death signals, TNF & Fas activate their death receptors TNF receptor & fas receptor respectively
- Binding causes change in shape & trimerisation of receptors
- Leads to aggregation of procaspase 8 (by adaptor proteins)
- leads to CASPASE 8 ACTIVATION
- initiates caspase cascade, proteolysis & apoptosis.
(protein c-flip can inhibit interation of procaspase 8 with the adaptor proteins)
Intrinsic pathway of apoptosis
- Cell stress triggers the BH3 only protein Bid to transiently bind to and activate Bax
- BAx undergoes conformational change - inserts into the outer mitochondrial membrane & oligomerises (6-8 molecules)
- important regulators are released from the intermembrane space
- cytochrome c joins the adaptor protein, apoptotic protease activating factor (APAF-1) & recruits procaspase 9 to form the APOPTOSOME
- caspase aggregation leads to activation of procaspase 9 & caspase cascade
(smac & diablo released from mitochondria inhibit IAPs that normally act to block caspases).