Transcript Chromosomally unstable mouse tumors have genomic

Chromosomally unstable mouse
tumors have genomic alterations
similar to diverse human cancers
Journal Club
14.09.2007
Introduction
• A hallmark of human cancer is highly
disorganised, unstable genomes driven by
alterations in multiple pathways. Single
gene mouse models of cancer
development have, in general, not
faithfully recapitulated this facet of human
disease leading to restrictions on their
utility in comparative cancer genomics.
Generation of murine lymphoma
model
• Terc, Atm and Trp53 mutant
mice were cross-bread.
Designated TKO
– Terc: stabilize chromosome
– Atm: maintain DNA integrity
– Trp53: tumor suppressor gene
• Trp53+/- and Trp53-/- mice were
more susceptible to develop
lymphomas and at a faster rate
than Trp53+/+
• Trp53+/- derived tumors
showed loss of heterozygosis
Spectral karytype analyses
• Each chromosome is
visualised with
chromosome specific
DNA labelled with a
fluophore
• Used to identify structural
chromosome aberrations
Generation of murine lymphoma
model
• Spectral karytype analyses
– G0 telomere intact (Terc+/+ and Terc+/-)
– G1 – G4 telomere deficient (Terc-/-)
• G1 – G4 are more prone to chromosomal
aberration compared to G0
Translocation
• Non-reciprocal
– Robertsonian translocation
• acrocentric chromosomes in the human genome: 13, 14, 15,
21 and 22.
• Long arm fusion and loss of short arm
– Dicentric chromosome
• Formation of a chromosome with two centromeres
• Reciprocal
– Exchange of material between two non-homologous
chromosomes
Comparative Genomic
Hybridization (CGH)
Copy Number Alteration
• Copy Number Alteration (CNA) detected by
Comparative Genomic Hybridization (CGH) in
TKO lymphomas
• Identification of relevant CNA’s. Notch1 and TCell receptors (Tcr)
Notch1
Notch1
• Re-sequencing of
TKO tumors missing
Notch1 genomic
rearrangement
– Deletion/insertion
– Activation of Notch1
and an up regulation
of its transcriptional
targets
Correlation of TKO lymphoma to human T-Cell
acute lymphoblastic leukemia/lymphoma (T-ALL)
• Minimal Common Region (MCR)
• Comparison of TKO and T-All MCR by synteny mapping
Synteny
• Preserved order of
genes on
chromosomes of
related species, as a
result of descent from
a common ancestor.
FBXW7
• FBXW7 is deleted in
TKO lymphomas and
T-ALL cells
• Fbxw7 is under
expressed in TKO
lymphomas
• FBXW7 was mutated
or deleted in
– 48% cell lines
– 29% clinical samples
FBXW7
• Fbxw7 binds to the PEST
domain in Notch1 and
activates degradation of
Notch1
• When the PEST domain is
mutated there is a less
frequent FBXW7
mutation/deletion compared to
heterodimerization domains
mutation
• Fbxw7 and PEST is part of the
same degradation pathway
PTEN
• PTEN is deleted in TKO
lymphomas and T-ALL cells
• 30.4% cell lines
• 5.2% clinical samples
• Act as a tumor suppressor
by inhibiting the phosphoAKT pathway
PTEN
Correlation to other human tumors
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62% of amplification in 2 or
more tumor types
53% of deletions in 2 or more
tumor types
24 genes from the Cancer
Gene Consus could be found
within the 104 MCR from TKO
tumors (17 oncogenes and 7
tumor suppressors)
Conclusion
• TKO mouse lymphomas resemble the genomic
alterations observed in human tumors
• Syntenic mapping of TKO lymphomas with
human cell lines or patient samples identified
known genes relevant in cancer
– Fbxw7, Notch1, Tcr and Pten
• TKO mouse can be used as a screening model
for identifying genomic alterations relevant in
human cancer
Weakest point
• Have they shown that it is the same
mechanisms that drive human and murine
tumors?
Strongest point
Murine TKO tumor
Identify CNA’s
Notch1 and Tcr
Compare murine MCR
to human MCR in T-ALL
FBXW7 and PTEN
Compare murine MCR
to human MCR in 6
different tumor types
In 102 syntenic MCR’s 24
known genes involved in
cancer could be found
Breakage Fusion Bridge
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G0 Terc+/- Terc+/+ Atm-/- Atm+/+
G1 Terc-/- Atm-/- Atm+/+
G2 Terc-/- Atm-/- Atm+/+
G3 Terc-/- Atm-/- Atm+/+
G4 Terc-/- Atm-/- Atm+/+