Wnt, TGF-B, Hippo

Question 1

What are the other roles of APC?

Answer 1

Has a microtubule domain binding site - deletion of this domain decreases APC's ability to stabilise MTs, 
Cell adhesion (Bcat) - (influence membrane pool of B-cat) 
Differentiation (BCat) - maintains stem cell character
Genetic Stability (MTs) - chromosomal aberrations
Apoptosis (MTs/Bcat)  - decreases

Question 2

What are the B-catenin target genes?

Answer 2

C-myc, Cyclin D1, MMP7, Ephrin receptors, Lgr5 and Rnf43 (stem cell components) Bcl-9.

Question 3

How is APC involved in the mitotic spindle?

Answer 3

APC localises to kinetochores, spindles and centrosomes during mitosis. Mutations in APC gene shown to induce chromosome instability –> clonal expansion and genetic instability.

Question 4

How does TGF-B become involved with the cell cycle?

Answer 4

Smad 2/3 + Smad-4 represses transcription of Ski/SnoN, N-Ras, c-myc, Id1/Id3.
Activates p21 and p15 transcription.
Inhibits G1 to S.

Question 5

What happens in EMT?

Answer 5

E-cadherin down regulated. Cell-cell junctions dissolve, lose apical-basal polarity. Upregulate MMPs. Increased deposition of ECM proteins. Increased mesenchymal markers.

Question 6

What feedback loop can be seen in EMT?

Answer 6

Negative feedback loop. miR-200, 205 and 183 suppress ZEB1 l/2.

ZEB1 represses miR-200.

BMPs induce miR-200 and miR-205.

Question 7

How can TGF-B signalling become altered in cancers?

Answer 7

1) oncogenic driver mutation –> cells now liable to undergo apoptosis if exposed to TGF-b.
2) Acquire additional mutations to disable TS responsiveness of cell. Either (I) lose SMAD signalling.
(II) retain SMAD signalling but lose TS response.

Question 8

How does cell adhesion repress YAP/TAZ activity?

How does cell contact alter YAP and TAZ activity?

Answer 8

Certain proteins at adheres and tight junctions e.g. angiomotin and alpha catenin, sequester YAP/TAZ.

In high cell density YAP/TAZ change from nucleus to cytoplasmic –> growth inhibition. Activated on a stiff matrix and by shear stress.

Question 9

How is the hippo pathway linked to cell senescence?

Answer 9

Knockdown of Lats2 surpasses Rb-induced senescence.

Lats2 overexpression increases Rb mediated silencing of E2F target genes.

Question 10

How is high YAP/TAZ linked to cancer?

Answer 10

Enables cells to escape contact inhibition.
High YAP induces expression of ZEB1/2 - stimulates EMT.
Shows resistance to drugs such as taxol and doxorubicin.