Helen Abud

Dr Helen Abud’s current research programs

Intestinal Stem Cells

Cancer Development

Dr Helen Abud’s current research programs • Snail1, Wnt Signaling, Stem Cell Development and Cancer• “Wnt Signaling regulates Snai1 expression and Cellular Localisation in

the Mouse Intestinal Epithelial Stem Cell Niche” – Article

• DNp73 and Stem Cells in Cancer• “Functional studies of the role of DNp73 and stem cells in Cancer” –

Presentation at Conference – Monash Comprehensive Cancer Consortium

Cancer and development

Snai1

Cancer

Wnt Signalling

Intestinal Stem Cells

DNp73

p53/p73

Snai1 and Wnt SignallingWnt signaling – normally stimulate growth by increasing Level of ß catenin

Required for maintenance of epithelium

Wnt signaling does different things: - Promotes cell proliferation, - self-renewal, facilitates migration

Too much Wnt signaling – SELF SUFFICIENCY IN GROWTH SIGNALSPromote CANCER/TUMOUR formation

Dr Abud’s work: to find out relationship between Snai1 and Wnt Signalling in the intestines

Snai1 and Wnt SignalingSnai1 – transcription factor, member of Snail family

Snai1 – high level of expression throughout stem cell populationEvidence – LGR5 marker (stem cells) and Snai1 stain

Snail1 is known to be the factor that keeps cells in the stem-cell stateMaintaining stemness which induces high level of cell proliferation

A crypt base columnar cell (CBC cell)

Snai1 stain LGR5 stain

Wnt signaling found here!

Snai1 and Wnt signaling How it leads to a disease state?

Wnt signaling can be a key factor to tumour formation If it occurs without regulation

Mutation of APC (Tumour supressor) which is found in most tumour polypsINCREASE SNAI1 EXPRESSION Evidence: immunohistochemical stain

Model on Apcmin mice – more Snai1 expression – develop polyps

Apcmin polyp tissue Normal colon tissue

Snai1 and Wnt signaling •The story so far…• Cancer is an acquired development (benign – malignant)• More Wnt signaling, more Snai1 expression, more cell proliferation• Uncontrolled cell proliferation leads to cancer

•Therefore:• Snai1 is the master regulator of stem cell populations

Snai1 and Wnt SignalingConcept of EMT – happens in both NORMAL DEVELOPMENT and TUMOUR GENESIS

Epithelial cells are very polarised in NORMAL DEVELOPMENT but in

TUMOUR GENESIS they start to lose their polarity and become

more migratoryThis is when EPITHELIAL cells become more MESENCHYMAL (EMT)After EMT, they can become enterocytes for example.

Snai1 is involved in EMT (as a regulator)It induces metastasis and maintaining stemness.

Snai1 and Wnt SignalingRelationship between normal tissue development and cancerDevelopment

THE SWITCH IS ALWAYS TURNED ON!Even when Wnt signaling is turned off, Snai1 is still present.

Suggest: There are many other mechanisms that regulate Snai1 and control stem cell population (ongoing research). Knock out of any Protein participants in these pathways can cause dramatic phenotype LOSS OF INTESTINAL STEM CELLS

The threshold of Wnt signals has to be just right!!

Snai1 and Wnt Signaling• The story continues…

Threshold for Wnt: During head-tail embryonic formation, there needs to be a gradient in level of Wnt expression

- Different ways a tissue can respond to Wnt signal; combination of Wnt receptor and inhibitory signals Dickkopf, RNF molecules (inhibit Wnt signals)

Rspondins (enhance Wnt signals)

- Different processes of development require different thresholds (in different organs)

- ANTERIOR – POSTERIOR embryonic patterning: head – low Wnt and tail – high Wnt

DNp73 – mystery uncoveredP73 is a Tumour Suppressor protein – similar p53 in both structure and function

P53 – guardian of the genome – regulates cell cycles – conserves stability of otherproteins and reduce the chances of them undergo mutation

Mutation of p53 has extremely high chances of leading to tumour formation. This can be Discovered in screening of tumourous tissue, DEFINITE MUTATION OF P53

Same screening done on tumourous tissue, hardly any mutations of p73 are found. WHY??

DNp73 – mystery uncovered• DNp73 – dominant negative p73 • A spliced, short, truncated version of p73

• Dominant negative – inhibits actions of other proteins

• DNp73 binds to the full-length versions of p53 and p73

and inhibit their activities

- Cell cycles are not regulated – any of the 6 attributes of

cancer cells can be acquired by cells

• DNp73 can be an oncoprotein – upregulation is shown to

cause intestinal polyp formation on mice