THE ROLE OF NOTCH IN TUMORIGENESIS: ONCOGENE OR TUMOUR SUPPRESSOR?

THE ROLE OF NOTCH IN TUMORIGENESIS:

ONCOGENE OR TUMOUR SUPPRESSOR?

Notch

Speakers: 葉恭誌 李昭鋐

組員 : 林雅葶 張明俐 羅苑菁 鄭伯忻 曾昭穎

蔡志文 陳美君 江承堯 高家民 呂女秀菱

- In 1917,Thomas Hunt Morgan and colleagues described a strain of Drosophila with notches at the end of their wing blades.

Notch:- Genetics: Haploinsufficiency- Structure: transmembrane receptor

notch

notch

Structure : transmembrane receptor

Lin12 repeats (cysteine-rich)CDC10 repeats

Nuclear-localization signal

Transcription activation domain

•Synthesized as a single precursor protein

•Cleaved in two during its transport to the cell surface.

Drosophila Notch receptor Ligand

(Delta)

(Serrate)

Notch receptor LigandHuman

Slight difference

EGFLNRAMANK

TADPEST

(Ser-like)

Notch signaling

(Notch IC)

Notch absence: transcription repressorNotch present:Transcription activator

Translocate into nucleus and bind to transcription factor CSL

Activation leads to cleavage IC domain

- HES (hairy/enhancer of split) family of transcription factors

- cell-cycle regulator-Waf1

Different modification of Notch and signal crosstalk influence Notch activation.

Different cell type uses different signal.

Notch function

• Maintenance of an undifferentiated state

– Notch signaling can maintain stem cells or precursor populations in an undifferentiated state.

– Gain-of-function studies ： (in the chicken)

• using a dominant active Notch-IC ： Notch signaling prevents progenitors from undergoing neurogenesis.

• blocking the Notch pathway ： excessive neurogenesis and depletion of the progenitor pool.

Notch function

Lewis, J. (1998) Semin. Cell Dev. Biol. 9, 583–589

Henrique, D. (1997) Curr. Biol. 7, 661–670

Participate in Cell-fate decision

Epidermal cell

Neuronal cell

Equitpotent cell

Equitpotent cell

?

Differentiation

receptor

ligand

• During the development of neuronal-precursor cells of the sensory organ in Drosophila.

Inductive cell-fate determination

Notch signal

Cell differentiation

Example : bipotential mouse neural-crest stem cell adopt to glial cell.

Early lymphocyte precursors

T-cell

B-cell

Mouse thymic epithelial cell

– DLL1-induced Notch signaling initiates a terminal-differentiation program in human skin.

– Other possible mechanism (Jagged-mediated) ： activated Notch1 causes keratinocyte growth arrest through increased p21WAF1/Cip

1 expression.

—Rangarajan, A. (2001) EMBO J. 20, 3427–3436

Induction of terminal differentiation

Notch as an oncogene

Notch and T-cell leukaemia

• Translocation of a portion of chromosome 7 to chromosome 9, which contains T-cell receptor- gene.

• Expreesion of truncated NOTCH1 transcripts (similar to NOTCH1-IC) from TCR promoter causes T-cell acute lymphoblastic leukaemia (T-ALL).

Ellisen, L. W. et al. Cell 66, 649-661 (1991).

Hot spots of mutations found in more than 50% of T-ALL patients

HD: heterodimerization domain

P: pest domain.

Weng AP. et al.Science 306:269–271(2004)

Why does the hematopoietic oncogenic potential seem to be restricted to T cell leukemia?

• Mice transplanted with Notch1-IC-expressing bone-marrow-progenitor cells from either Rag2–/– or Slp76 –/– mice failed to develop T-cell leukaemia.

• Introduction of a TCR βtransgene into Rag2–/– mice — to re-activate pre-TCR signalling — restored the oncogenic function of Notch1-IC.

Allman, D. et al. J. Exp. Med. 194, 99–106 (2001).

Notch1-IC-mediated transformation is dependent on a second T-cell-specific signal that is mediated by the pre-TCR.

Notch and viruses

•Proviral integration of the Moloney murine-leukaemia virus (MuLV) into the murine Notch1 locus causes T-ALL in mice.

•Integration of the mouse mammary tumour virus (MMTV) in between the Notch/Lin12 repeats and the transmembrane domain of either the Notch1 (NI) or Notch4 (N4) gene causes mammary tumours in the mouse.

Notch and Epithelial tumours

•Transgenic mice that express this Notch4-IC/int-3 gene developed poorly differentiated mammary and salivary-gland adenocarcinomas within 7 months.

•The mammary epithelial of these mice failed to branch.

Notch-IC

(1) RAM domain : CBF binding site (2) ankyrin repeat domain (ANK) : mediates further protein- protein interactions (3) C-terminal domain : a polyglutamine region (OPA) + proline, glutamic acid, serine and threonine rich region (PEST) (4) NLS : nuclear localization sequence

How can Notch contribute to transformation?

• CBF1 is a sequence specific DNA binding protein that functions to repress transcription of cellular genes

• In some cells, Notch-assisted transformation is dependent on the ankyrin repeats of the Notch protein, not CBF1

MOLECULAR AND CELLULAR BIOLOGY, June 2000, p. 3928–3941

E1A-immortalized baby rat kidney cell line (RKE)

Notch needs to partner another oncoprotein to actually cause cancer

Virology 286, 23±30 (2001)

Transformation can be induced by expressiong Notch-IC with oncoproteins such as adenovirus EIA,HPV E6 and E7…

AcN1: a truncated allele of Notch1

• These oncoproteins all share the common property of being able to override the G1-S checkpoint resistance to apoptosis, anoikis or differentiation

ANOIKIS:Cell death induced as a result of the absence of matrix attachment

• The oncogenic effects of Notch include PI3-K activation and induction of ERBB2 and NF-ĸB2 expression (by NOTCH-IC)

• PI3-K resistance to anoikis

• ERBB2 cell proliferation and growth

• NF-ĸB2 expression of genes which encode anti-apoptotic proteins

Notch1 as tumour suppressor

NOTCH1 signaling increases expression of WAF1, which causes cell-cycle arrest in basal cells, to allow the onset of terminal differentiation

• In Notch1-ablated skin, reactivation of Wnt and Sonic-hedgehog pathways result in the development of basal-cell-carcinoma-like tumours in the mouse.

• The tumour-suppressive activity of NOTCH1 might be mediated by several routes, to induce cell-cycle arrest and differentiation

• Tumour cells might counter-select against expression of Notch receptors or ligands to escape from differentiation and cell-cycle arrest

The two faces of Notch in cervical cancer

• Proteins are increasingly being found to have several and possibly opposing functions

HPV was found in 99% cervical cancers

• The E6 oncoprotein encoded by human papillomavirus types 16 and 18 promotes the degradation of p53

1990 Cell

• Telomerase activation by the E6 gene product of human papillomavirus type 16

1996 Nature

=>E6 and E7 are oncoproteins in cervical cancer cells

=>Notch prevent cellular proliferation in normal epithelia

=>upregulate WAF1

=>cells initiation of differentiation

BUT…..

Conclusion

• The outcome of Notch activation is dependent on cellular context

Thank you