14th Feb - WNT, NFkB, Hedgehog and notch signalling pathways

Question 1

Where are notch ligands localised?

Answer 1

They are membrane bound

Question 2

What are the notch receptors?

Answer 2

JAG1/JAG2, DLL1/DLL4, DLL3

Question 3

Outline the notch signalling pathway

Answer 3

Notch binds notch ligands
Notch is cleave within its ectodomain
Cleaved notch is free in the cytoplasm
Notch migrates to the nucleus where it displaces Co-R w/ a CoA therefore activating the TF CSL –> gene expression

Question 4

What are the targets of NOTCH signalling?

Answer 4

c-myc
NRARP –> Wnt signalling
HES and HEY genes represses the differentiation process

Question 5

What are the main functions of NOTCH signalling ?

Answer 5

Cell-cell communcation causing lateral inhibition, lateral induction, stem cell maintenance or stem cell differentiation

Question 6

How is the NOTCH ligand regulated?

Answer 6

Neuralized - internalisation and degradation of delta like

Fringe - block/promote the formation of the DSL ligand-Notch receptor pairs. Act in the golgi apparatus to transfer G1cNAc to the extracellular domain of Notch

Deltex1 - a positive regulator of Notch signaling through protein-protein interactions

Question 7

How is the active intracellular domain of NOTCH generated?

Answer 7

ADAM 10, 17 - cleaves the ectodomain

Gamma-secretase - TM domain cleavage

NUMB - antagonizes NOTCH signaling by ubiquitination of membrane bound Notch 1 receptor and its subsequent degradation following receptor activation

Question 8

How is the NOTCH ICD deactivated?

Answer 8

Cyclinc/Cdk8 phosphorylate the NOTCH ICD

Fbw/Sel10 ubiquitinates NOTCH ICD –> disassembly of the activator complex

Question 9

Does the NOTCH signalling pathway promote/suppress oncogenesis?

Answer 9

It can do either depending upon the context

Question 10

Outline the Wnt signalling pathway

Answer 10

Wnt binds to the frizzled receptor, activating dishevelled, which inhibits the GSK3-APC-Axin complex, leading the the release of Beta catenin –> TCF activation –> Myc, CycD and Axin 2 expression

Question 11

Vivian (2012) opposes the current model of Wnt signalling, what do they propose instead?

Answer 11

Wnt signaling suppresses Beta-catenin ubiquitination –> complex saturation by accumulated phospho beta catenin therfore there is more free cytosolic beta catenin

Question 12

What is familial adenomatous polyposis (FAP)?

Answer 12

A familial disorder in which patients develop multiple polyps of the colon, which usually give rise to tumours over time

Question 13

What germline mutation causes FAP?

Answer 13

A mutation in the adenomatous polyposis coli (APC) gene, a known tumour suppressor

Question 14

What are the classical direct mammalian targets of Beta-catenin?

Answer 14

cyclin D1 and c-myc

Question 15

How does Beta-catenin OE affect cell-cell adhesion?

Answer 15

Beta catenin OE –> e-cadherin de-regulation –> increase in cell motility and decrease in cell anchorage

Question 16

Outline the NFkB pathway

Answer 16

Stimuli activate IkB kinase (IKK)
IKK phosphorylates the inhibitor of kB (IKB) which inhibits NFkB
IkB phosphorylation labels it for proteasomal degradation releasing NFkB
NFkB translocates to the nucleus where it acts as a transcriptional activator

Question 17

What are the two most common subunits of NFkB?

Answer 17

p50 and p65

Question 18

Which type of cancer is the NFkB pathway most prominent in?

Answer 18

p50 and p65

Question 19

What are the key physiological responses elicited by the NFkB pathway?

Answer 19

Cell survival
Immune response/inflammation
Adhesion/invasion/metastasis
angiogenesis
proliferation

Question 20

Outline the hedgehog signalling pathway

Answer 20

Hedgehog binds to patched
Patched moves away from smoothened therefore activating it
Smoothened activates Gli1
Gli1 translocates to the nucleus and acts as a transcriptional activator

Question 21

What are the three main mechanisms that hedgehog signalling promotes cancer

Answer 21

Smoothened activation mutation
Patched loss of function mutation
Hedgehog autocrine signalling

Question 22

What drug can be used to target the smoothened receptor?

Answer 22

Cyclopamine