Transcript Notch signaling

THE ROLE OF NOTCH IN
TUMORIGENESIS:
ONCOGENE OR TUMOUR SUPPRESSOR?
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
notch
Notch:
- Genetics: Haploinsufficiency
- Structure: transmembrane receptor
Structure : transmembrane receptor
•Synthesized as a single precursor protein
•Cleaved in two during its transport to the cell surface.
Drosophila
Notch receptor
Ligand
Transcription activation domain
CDC10 repeats
Lin12 repeats (cysteine-rich)
(Delta)
(Serrate)
Nuclear-localization signal
Human
ANK RAM
PEST
Ligand
Notch receptor
LN
EGF
TAD
(Ser-like)
Slight difference
Notch signaling


Activation leads to
cleavage IC domain
Translocate into nucleus and bind
to transcription factor CSL
Notch absence:
transcription repressor
Notch present:
Transcription activator
Different modification of Notch and signal
crosstalk influence Notch activation.
Different cell type uses different signal.
(Notch IC)
- HES (hairy/enhancer of split)
family of transcription factors
- cell-cycle regulator-Waf1
Notch function
Notch function
• Maintenance of an undifferentiated state
– Notch signaling can maintain stem cells or
precursor populations in an undifferentiated
Lewis, J. (1998) Semin. Cell Dev. Biol. 9, 583–589
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.
Henrique, D. (1997) Curr. Biol. 7, 661–670
Participate in Cell-fate decision
• During the development of neuronal-precursor
cells of the sensory organ in Drosophila.
receptor
ligand
Equitpotent cell
?
Epidermal cell
Differentiation
Equitpotent cell
Neuronal cell
Inductive cell-fate determination
Notch
signal
Cell
differentiation
Example : bipotential
mouse neural-crest stem
cell adopt to glial cell.
Mouse thymic
epithelial cell
Early
lymphocyte
precursors
T-cell
B-cell
Induction of terminal differentiation
– DLL1-induced Notch signaling
initiates a terminal-differentiation
program in human skin.
– Other possible mechanism (Jaggedmediated)：activated Notch1
causes keratinocyte growth
arrest through increased
p21WAF1/Cip1 expression.
—Rangarajan, A. (2001) EMBO J. 20, 3427–3436
Notch as an oncogene
Notch and T-cell leukaemia
• Translocation of a portion of
chromosome 7 to
chromosome 9, which
contains T-cell receptor-b
gene.
• Expreesion of truncated
NOTCH1 transcripts
(similar to NOTCH1-IC)
from TCRb 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 preTCR 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 Tcell-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 proteinprotein 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
E1A-immortalized
baby rat kidney cell line
(RKE)
MOLECULAR AND CELLULAR BIOLOGY, June 2000, p. 3928–3941
Notch needs to partner another oncoprotein
to actually cause cancer
Virology 286, 23±30 (2001)
AcN1: a truncated allele of Notch1
Transformation can be induced by expressiong Notch-IC with
oncoproteins such as adenovirus EIA,HPV E6 and E7…
• 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 NFĸB2 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 Sonichedgehog pathways result in the
development of basal-cellcarcinoma-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
BUT…..
=>Notch prevent cellular proliferation in normal
epithelia
=>upregulate WAF1
=>cells initiation of differentiation
Conclusion
• The outcome of Notch activation is dependent
on cellular context
Thank you