Notch signalling Flashcards
How was Notch signalling identified
Forward genetics in drosophila - Mutations caused a notched wing phenotype
What are the similarities in Notch and delta structure
Both contain many extracellular EGF repeats, both have a single transmembrane domains
(Notch has intracellular ankyrin repeats)
What are the function of the EGF repeats
Extracellular protein to protein interactions are often mediated by domains containing a repeated amino acid sequence
EGF repeats are made up of 30-40 amino acids with repeated 6 cysteines in regular intervals
The cysteines form sulphide bridges and this pairing adds structure
What enzyme tightly regulates the paring of cysteines
Disulphide isomerase in the endoplasmic reticulum
Give the 5 steps in notch signalling
1) Furin - cleavage in the golgi compartment results in a notch receptor heterodimer
2) TACE - Cuts the extracellular domain after the ligand has bound, this is the ligand dependent step\
3) Presenilin - Cuts within the transmembrane domain creating an intracellular notch fragment
4) Notch(intra) then translocates into the nucleus
5) In the nucleus it interacts with a DNA binding CSL protein causing the CSL protein to become an activator instead of a repressor
What relevance does notch signalling have to Alzheimers
Amyloid precursor protein is also cleaved by presenilin after cleavage by either alpha or beta secretase (similar to the action of Furin/TACE)
Beta secretase products are cut by presenilin in one of two positions in the transmembrane domain producing an extracellular peptide that is either 40-42 amino acids in length
The 42 amino acid product is a major component of the amyloid plaques found in the brains of Alzheimer sufferers.
What mutation causes most cases of early onset Alzheimers
Mutations in human presenilin
What is the role of Su(dx)
The WW domain binds notch, the HECT domain mediates ubiquitination and the C2 domain localizes it to the membrane - acts to reduce Notch
What is the role of Sel-10
Recognizes phosphorylated Notch(intra) in the nucleus. It lacks a ubiquitin ligase domain so it recruits one via its F-box when bound to Notch(intra)
What is the role of Neur/mib
Binds to delta and the RING domain acts as a ligase
however it acts to activate the pathway
By pulling off the ectodomain of notch it facilitates the cleavage of Notch by TACE
What are the 4 domains of Notch(intra)
1) NLS (nuclear localisation signal) brings it to the nucleus
2) RAM domain and ANKYRIN domains are protein-protein interaction domains
4) The activation domain is a transcriptional activator
Where was human notch first cloned from
Patients with T-cell acute lymphoblastic leukemias
(A truncated allele of Notch) As a result of a translocation between two chromosomes - TRC-Beta gene becomes fused to the intracellular domain of Notch1
Why does the fusion of TRC-beta with Notch1 lead to tumours
TRC-beta is strongly expressed in immature T-cells so this results in Notch activation in these cells. Notch is thought to maintain the cells in a proliferative state which could contribute to the tumour which is made up of immature T-cells
DSL proteins (Human ligands delta or jagged) mutations cause what disease
Jagged1 mutation - Alagille syndrome - modelled in drosophila - most genes are haplosufficient however the Notch pathway is an exception - studies indicated that the pathway is very sensitive to gene dosage
What is the link between notch3 and CADSIL
Recurrent strokes leading to progressive dementia - granular material builds up within the smooth muscles of blood vessels.
75% of mutations affect the first 5EGF repeats in Notch3
