An accommodating host

75 Pages·2013·6.37 MB·English

RESEARCH HIGHLIGHTS
Nature Reviews Cancer | AOP, published online 31 January 2013; doi:10.1038/nrc3470
MICROENVIRONMENT Y
T
T
E
G
An accommodating host
The survival of chronic lymphocytic in wild-type, but not in Prkcb–/–,
leukaemia (CLL) cells partly depends BMSCs following co-culture with
lack of PKCβ on pro-survival signals that come CLL cells, and the survival of CLL cells
in host mice from the stromal cells. Research pub- in co-culture with EL08-1D2 cells was
lished in Cancer Cell has uncovered a blocked by pharmacological inhibi-
prevented
signalling pathway that controls this tion of NF-κB using an inhibitor
the formation cancer cell–stromal cell crosstalk. of IKKβ (inhibitor of NF-κB (IκB)
of CLL-like Using co-culture of primary kinase-β). To confirm that this effect
human CLL cells and a mouse was specific to the stromal cells, the
malignancies
stromal cell line (EL08-1D2), Ingo authors used BMSCs from mice
Ringshausen and colleagues showed deficient in the IκB complex member
that the presence of stromal cells NEMO (also known as IKKγ).
protects the CLL cells from apoptosis. BMSCs with conditional knockout
These stromal cells share genetic and of Nemo did not protect CLL cells
morphological properties with so- from apoptosis, and although NF-κB
called cancer-associated fibroblasts. activation was blocked PKCβII was
Protein kinase C βII (PKCβII) in CLL still induced, suggesting that PKCβII
cells has been shown to be required acts upstream in this pathway.
for apoptosis resistance, and the Transcriptome analysis of BMSCs
PKCβ inhibitor enzastaurin blocked with and without Nemo knockout
the protective effect of EL08-1D2 following co-culture with CLL cells
cells, indicating the importance pointed to decreased expression of
of this kinase for stroma–CLL cytokines in Nemo-null cells, and the
interactions. Expression of PKCβII authors showed that interleukin-1α
was increased in EL08-1D2 cells (IL-1α) and IL-15 were induced in in areas of bone marrow with CLL
following contact with CLL cells, stromal cells in a NEMO-dependent infiltration but not in areas lacking
and CLL cells were no longer manner. Exogenous administra- CLL cells.
protected from apoptosis when tion of these cytokines to CLL cells Interestingly, the authors also
co-cultured with EL08-1D2 cells in co-cultured with NEMO-deficient observed a similar requirement for
which PKCβII was suppressed by BMSCs could also protect the CLL stromal PKCβII–NF-κB signalling in
small interfering RNA (siRNA) or cells from apoptosis. permitting the survival of primary
when co-cultured with bone mar- Is this pathway relevant in vivo? human acute lymphoblastic leukae-
row stromal cells (BMSCs) from The authors transplanted malignant mia (ALL) and mantle cell lymphoma
Prkcb–/– (which encodes PKCβII) cells from mice bearing a CLL-like (MCL) cells, suggesting that this
mice. Furthermore, ectopic expres- disease into Prkcb–/– or wild-type pathway could be crucial for several
sion of PKCβ in Prkcb–/– BMSCs mice and found that lack of PKCβ in haematological malignancies.
rescued CLL cell survival. Together, host mice prevented the formation Sarah Seton-Rogers
these data indicate that PKCβII is of CLL-like malignancies. In patients
important in the stromal cells. with CLL, PKCβII was expressed in ORIGINAL RESEARCH PAPER Lutzny, G. et al.
Protein kinase C-β-dependent activation of NF-κB
PKCβII is involved in the activa- endothelial cells (these stromal cells in stromal cells is indispensable for the survival of
tion of nuclear factor-κB (NF-κB) sig- were analysed owing to technical dif- chronic lymphocytic leukemia B cells in vivo.
Cancer Cell 23, 77–92 (2013)
nalling; indeed, NF-κB was activated ficulties with analysing other subsets)
NATURE REVIEWS | CANCER VOLUME 13 | MARCH 2013
© 2013 Macmillan Publishers Limited. All rights reserved
RESEARCH HIGHLIGHTS
Nature Reviews Cancer | AOP, published online 31 January 2013; doi:10.1038/nrc3471
MED13 and MED13L and that this
Y
T
ET interaction in the presence of a
G
functional SCFFBXW7 ligase results in
the ubiquitylation and degradation
of these proteins.
What effect does this have
on CDK8–Mediator function?
Co-immunoprecipitation experi-
ments showed that loss of FBXW7
increased the levels of MED13
and MED13L, as well as other
CDK8 module proteins that were
associated with the Mediator core
complex. The authors also found
that SCFFBXW7 can interact with and
ubiquitylate MED13 and MED13L
UBIQUITYLATION when these proteins are associated
with the core Mediator complex.
Mediation by degradation Thus, the authors concluded that
FBXW7 functions to regulate the
interaction of the CDK8 module
with Mediator by promoting the
The tumour suppressor protein mutated were analysed in detail. dissociation of these complexes
FBXW7 is the substrate recognition Of the 72 proteins identified, 26 through the degradation of MED13.
SCFFBXW7 component of the SKP–cullin–F-box belonged to the Mediator complex These findings expand the
can interact (SCF) ubiquitin ligase. FBXW7 binds that links transcription factors to potential impact of FBXW7 loss dur-
threonine- or serine-phosphorylated the basal transcription machinery, ing tumorigenesis — in addition to
with and
proteins, including many oncopro- such as RNA polymerase II. Several FBXW7 loss increasing the stability
ubiquitylate teins, in the context of a conserved of the proteins bound by FBXW7 of specific proteins, such as MYC and
MED13 and phosphodegron sequence, resulting in belong to the so-called cyclin- cyclin E, FBXW7 loss might also have
their ubiquitylation and proteasome- dependent protein kinase 8 (CDK8) a broader effect through the altera-
MED13L when
mediated degradation. Bruce Clurman module, a four-subunit protein tion of genome-wide transcriptional
these proteins
and colleagues have found that complex that contains CDK8 and events. Moreover, CDK8 is a known
are associated FBXW7 interacts with components is involved in regulating Mediator oncogene in colorectal cancer, so
with the core of the Mediator complex and so it function. Further analyses revealed further work is needed to understand
might be involved in regulating gene that FBXW7 directly interacts with the effect that FBXW7 has on the
Mediator
transcription. MED13 and MED13L. MED13 is function of this oncogene.
complex
The authors used affinity puri- required to link the CDK8 module Nicola McCarthy
fication and mass spectrometry to to the Mediator core complex,
ORIGINAL RESEARCH PAPER Davis, M. A. et al.
identify new FBXW7 substrates. and MED13L is thought to have
The SCF–Fbw7 ubiquitin ligase degrades MED13
Only proteins that bound wild-type a similar function. The authors and MED13L and regulates CDK8 module
FBXW7 and not FBXW7 in which found that FBXW7 interacts with association with Mediator. Genes Dev 15 Jan 2013
(doi:10.1101/gad.207720.112)
the substrate binding site was a phosphodegron sequence on
NATURE REVIEWS | CANCER VOLUME 13 | MARCH 2013
© 2013 Macmillan Publishers Limited. All rights reserved
RESEARCH HIGHLIGHTS
Trial Watch
MOVING FORWARDS
Joseph Tabernero and colleagues have carried out a ‘first-in-man’ Phase I trial
of two small interfering RNAs (siRNAs) to treat patients with refractory
metastatic disease that involves the liver.
In this trial, Tabernero and colleagues used lipid nanoparticles (LNPs) to
encapsulate two siRNAs that target vascular endothelial growth factor (VEGF)
and kinesin spindle protein (KSP; also known as KIF11). Inhibition of VEGF
targets the tumour vasculature, and inhibition of KSP induces mitotic arrest.
One of the limitations of using RNA interference (RNAi) in the clinic is targeting
it to the desired organ or tumour. When given parenterally in animal models, the
therapeutic, termed ALN-VSP, primarily localized to the liver and spleen owing
to their fenestrated endothelium. It also accumulated in tumours owing to their
leaky vasculature and enhanced permeability and retention effect. ALN-VSP
was given to 41 patients who were enrolled sequentially and assigned one of
seven dose levels (0.1–1.5 mg per kg), given as a 15-minute intravenous infusion
every 2 weeks. Eleven patients whose disease had not progressed (based on
computerized tomography (CT) evaluation) after four cycles (eight doses over
4 months) were allowed to continue in the expansion phase of the trial. Six of
these patients received doses at 1 mg per kg and five patients at 1.25 mg per kg
until disease progression or the completion of the trial.
Of the 37 patients in the dose escalation part of the trial in whom a tumour
response could be assessed, four of 24 patients treated with doses ≥0.7 mg
per kg had stable disease or better, according to response evaluation criteria in
solid tumours (RECIST). One patient who had metastatic endometrial cancer
that included several liver metastases had a complete response and completed
the trial in remission after receiving 50 doses at 0.7 mg per kg over 26 months.
Two patients with metastatic renal cell carcinoma had stable disease for
approximately 8–12 months, and one patient with metastatic pancreatic
neuroendocrine tumour had stable disease for 18 months. One patient enrolled
in the trial experienced liver failure after the second dose of ALN-VSP and died.
This patient had extensive liver metastases and had previously undergone a
splenectomy and a partial hepatectomy. Preclinical animal toxicology studies
had shown liver toxicity in rats and splenic toxicity in monkeys (this was a
potentially on-target effect). On the basis of this and other data the trial was
amended to prohibit the recruitment of any patients who had undergone a
splenectomy or who had >50% of the liver affected by metastases. Additional
dose-limiting toxicity data, including liver function tests, indicated that ALN-VSP
was safe, and the recommended dose for Phase II trials was set at 1 mg per kg.
Proof of on-target effects was difficult to assess in this trial. Fifteen patients
volunteered for biopsies of metastases to be carried out before and after
treatment; however, only one sample contained tumour tissue alone. In two
patients whose biopsy samples contained mostly normal liver tissue, evidence
of VEGF mRNA degradation was found, indicating that the drug was delivered
to the liver and had on-target effects. Degradation of KSP mRNA was not
detected, possibly owing to the reduced expression of this mRNA relative to
VEGF mRNA. Most of the biopsy samples showed drug accumulation, but the
concentrations varied substantially. Reduced blood flow to the tumour
(detected by dynamic contrast enhanced magnetic resonance imaging in
28 patients) was evident in several patients but was not dose dependent.
A reduction in spleen size was evident in 25 evaluable patients and this effect
also did not seem to be dose dependent.
Subsequent Phase II trials will be restricted to patients with one cancer type
who have received fewer prior therapies, and all patients will receive the same
dose in order to more fully assess the efficacy and on-target effects of this agent.
ORIGINAL RESEARCH PAPER Tabernero, J. et al. First-in-man trial of an RNA interference therapeutic targeting
VEGF and KSP in cancer patients with liver involvement. Cancer Disc. 28 Jan 2013 (doi:10.1158/2159-8290)
NATURE REVIEWS | CANCER VOLUME 13 | MARCH 2013
© 2013 Macmillan Publishers Limited. All rights reserved
RESEARCH HIGHLIGHTS
Nature Reviews Cancer | AOP, published online 7 February 2013; doi:10.1038/nrc3472
or stalled replication forks. These are of mitosis. Nevertheless, the authors
DNA DAMAGE
associated with an increase in single- also showed that DNA damage
strand DNA (ssDNA) breaks and at both ERFSs and CFSs can be
In at the beginning
are bound by replication protein A induced by the inhibition of ataxia
(RPA). Replication fork collapse telangiectasia and RAD3-related
can also induce DNA double-strand (ATR) kinase, which is involved in
breaks that are repaired by members DNA repair. Moreover, replication
of the homologous recombina- stress induced by the overexpression
tion DNA repair machinery that of oncogenes, such as MYC, triggers
includes BRCA1 and SMC5. Using genome instability at both ERFSs
an RPA-specific antibody, the and CFSs.
authors carried out a genome-wide Further characterization of ERFSs
chromatin immunoprecipitation showed that they contain genes,
(ChIP)–sequencing (seq) screen for such as Bach2, Gimap, MhcII and
ssDNA bound by RPA in synchro- Foxp1, which are implicated in the
nized proliferating mouse B cells that development of B cell lymphoma.
had been treated with hydroxyurea. Indeed, BACH2 and GIMAP have
There were 12,000 regions that previously been characterized as off
showed early replication (identified targets of activation-induced deami-
by bromodeoxyuridine labelling) nase (AID), which is involved in the
and RPA binding, and additional generation of DNA double-strand
ChIP–seq analyses showed that only breaks that are required for antibody
~20% of these were also bound by diversification and immuno globulin
BRCA1 and SMC5, suggesting that class switching. The authors found
these ERFSs are particularly sensitive that the generation of fragility at
to replication stress. ERFSs is not dependent on AID.
The stimuli that result in DNA However, the authors also showed
damage at ERFSs are partly distinct that AID-induced double-strand
IMAGE SOURCE from those that produce damage at breaks that occur in G1 can join to
CFSs. The authors used bacterial ERFS breaks that are generated in
Not all regions of the genome rep- artificial chromosome (BAC) probes S phase, leading to chromosomal
licate equally well. Regions known that bound the CFS sequences translocations. In addition, as DNA
replication as common fragile sites (CFSs) are FRA8E1 and FRA14A2 to show breaks at ERFSs can occur spontane-
stress induced present in genomic areas that are that in metaphase spreads from ously and as a result of replication
characterized by a closed chromatin B cells treated with hydroxyurea stress, they could contribute to
by the
structure and that replicate late in chromosomal abberations did not genomic instability. A comparison
overexpression
S phase. However, recent research occur at these sites. However, BAC of the ERFSs identified in the mouse
of oncogenes, in mouse B cells indicates that, in probes that bind to the six most B cells with copy number changes in
such as MYC, addition to these late replicating CFSs, common ERFS regions showed that 203 biopsy samples of human diffuse
there are early replicating fragile sites 8–15% of chromosomal alterations large B cell lymphoma showed a
triggers
(ERFSs) that could contribute to the occurred in the vicinity of these substantial overlap, suggesting that
genome genetic translocations and copy num- ERFSs. Conversely, treatment with ERFSs contribute to the mutations
instability at ber alterations that are often seen in aphidocolin, which induces dam- that arise in B cell lymphomas.
B cell lymphomas. age at CFSs, did not seem to have Whether ERFSs contribute to
both ERFSs
André Nussenzweig and col- any effect on the ERFSs tested, genomic instability in other cancer
and CFSs
leagues were interested in finding enabling the authors to infer that types requires additional research.
whether there are distinct genomic fragility at ERFSs arises as a result Nicola McCarthy
regions that are susceptible to of replication fork collapse early in
ORIGINAL RESEARCH PAPER Barlow, J. H. et al.
genomic instability in cells treated DNA replication, whereas fragility
Identification of early replicating fragile sites that
with hydroxyurea, an inhibitor of at CFSs arises as a result of a failure contribute to genome instability. Cell 24 Jan 2013
DNA synthesis that results in paused to complete replication ahead (doi:10.1016/j.cell.2013.01.006)
NATURE REVIEWS | CANCER VOLUME 13 | MARCH 2013
© 2013 Macmillan Publishers Limited. All rights reserved
RESEARCH HIGHLIGHTS
Nature Reviews Cancer | AOP, published online 24 January 2013; doi:10.1038/nrc3469
TUMORIGENESIS
All together now
The development of tumours in mice. Moreover, the immunosuppres-
the intestine is partly mediated by sant and S1PR1 antagonist FTY720
inflammation. Three recently pub- suppressed colitis development and
lished papers have strived to address tumour progression in wild-type and
G
more precisely the inflammatory Sphk2-null mice. Further analyses P
N
pathways that contribute to the initia- showed that FTY720 reduces tumour ok/
o
tion and development of colorectal formation by suppressing the br
d
a
cancer (CRC). S1P–NF-κB–IL-6–STAT3-mediated Br
n
Sarah Spiegel and colleagues were inflammatory response and by reduc- mo
interested in inflammatory bowel ing STAT3 nuclear accumulation in Si
disease and the risk that it conveys tumour epithelial cells where it can
for the development of CRC, and function to increase cell survival. cell population and the expression of
whether the signalling molecule Two papers from Florian Greten TNF, which induced NF-κB activation
sphingosine-1 phosphate (S1P) con- and colleagues further show the in IECs. Inhibition of NF-κB activity
tributes to this. Previously published diverse ways in which NF-κB can delayed tumour formation in these
papers have indicated that the gen- contribute to CRC development. mice, whereas its activation promoted
eration of S1P through sphingosine These authors knocked out Trp53 tumour formation. Various experi-
kinase 1 (SPHK1) can result in the from intestinal epithelial cells (IECs), ments showed that β-catenin can bind
production of tumour necrosis factor which, when combined with AOM RELA (a component of the NF-κB
(TNF) and the activation of canonical treatment, induced tumour develop- transcription factor) and that
nuclear factor-κB (NF-κB) signalling. ment and invasive growth, along NF-κB can influence the binding
Using a mouse model of colitis- with the development of lymph node of β-catenin to gene promoters and
associated cancer (induced through metastases. How does Trp53 loss so influence WNT-mediated gene
the treatment of mice with azoxy- induce this? These authors found expression. Importantly, these authors
methane (AOM) and dextran sodium evidence that p53 loss promotes the also found that constitutive expres-
sulphate (DSS)) these authors survival of IECs with DNA damage sion of β-catenin combined with
examined the contribution of SPHK2. that is induced as a result of treatment activation of NF-κB induced the dedi-
They found that Sphk2–/– mice had an with AOM. Induction of Trp53 loss fferentiation of enterocytes in the gut
increased tumour number, size and after treatment with AOM indicated villi, resulting in their acquisition of
load, and that adenomas in these mice that p53 also contributes to the a crypt-stem-cell-like phenotype and
showed a high grade of dysplasia com- integrity of the intestinal epithelium. tumour formation.
pared with wild-type mice. SPHK1 Loss of intestinal integrity in Trp53- Therefore, activation of NF-κB in
expression is increased in Sphk2-null null mice was associated with an tumour epithelial cells and in stromal
mice, as is the generation of S1P. This increase in inflammatory cells and the cells contributes to intestinal tumori-
resulted in the induction of NF-κB activation of NF-κB-dependent gene genesis that is initiated through a
activation
activity and the expression of the pro- transcription in both invasive tumour variety of different pathways.
of NF-κB inflammatory cytokine interleukin-6 epithelial cells and the surrounding Nicola McCarthy
in tumour (IL-6). IL-6 induced the nuclear stromal cells. Tumour epithelial cells
epithelial localization of signal transducer and were also found to have undergone an ORIGINAL RESEARCH PAPERS Liang, G. et al.
Sphingosine-1-phosphate links persistent STAT3
activator of transcription 3 (STAT3) epithelial to mesenchymal transition
cells and in activation, chronic intestinal inflammation, and
in cells of the colonic mucosa, and this that was induced by the protein prod- development of colitis-associated cancer. Cancer
stromal cells resulted in the increased expression of uct of the NF-κB target gene Twist1. In Cell 23, 107–120 (2013) | Schwitalla, S. et al. Loss of
p53 in enterocytes generates an inflammatory
contributes S1P receptor 1 (S1PR1). Bone marrow a separate mouse model of intestinal microenvironment enabling invasion and lymph
transplants were used to show that tumorigenesis, Greten and colleagues node metastasis of carcinogen-induced colorectal
to intestinal
activation of the S1P–NF-κB–IL-6– showed that expression of constitu- tumors. Cancer Cell 23, 93–106 (2013) |
tumorigenesis Schwitalla, S. et al. Intestinal tumorigenesis
STAT3 signalling pathway in haemat- tively active β-catenin to mimic WNT initiated by dedifferentiation and acquisition of
opoietic cells was crucial for the rapid activation in IECs resulted in prolifer- stem-cell-like properties. Cell 27 Dec 2012
(doi:10.1016/j.cell.2012.12.012)
induction of tumours in Sphk2-null ation and expansion of the crypt stem
NATURE REVIEWS | CANCER VOLUME 13 | MARCH 2013
© 2013 Macmillan Publishers Limited. All rights reserved
RESEARCH HIGHLIGHTS
Nature Reviews Cancer | AOP, published online 14 February 2013; doi:10.1038/nrc3475
BREAST CANCER
Circulating and dynamic EMT
Epithelial–mesenchymal transition They used a microfluidic chip to the expected decrease in total CTC
(EMT) is thought to enable the diss­ immuno affinity purify CTCs based counts was accompanied by a skew
CTC emination of tumour cells into the on the expression of epidermal towards epithelial phenotypes, and
surrounding tissue and circulation. growth factor receptor (EGFR), these effects reversed during relapse
characterization
However, characterizing the epithe­ ERBB2 and epithelial cell adhesion in the serially sampled patient.
might be
lial versus mesenchymal phenotypes molecule (EPCAM). Thus, CTC characterization might
a useful of circulating tumour cells (CTCs) CTCs were identified in the blood be a useful biomarker for treatment
biomarker has been challenging because the from 17 of 41 patients with different response. However, the extent to
expression of epithelial markers has stages and subtypes of breast cancer. which this represents dynamic
for treatment
typically been used as the basis for These CTCs were typically enriched switching between epithelial and
response
the isolation and visualization of for mesenchymal cells relative to mesenchymal states, or a differential
CTCs from bulk blood samples. the primary tumours, consistent effect of treatment on existing
A new method to isolate and with a role for EMT in tumour cell epithelial and mesenchymal cancer
characterize both epithelial and dissemination. Interestingly, in three cells, is currently unclear.
mesen chymal CTCs has identified patients, predominantly mesenchy­ Finally, the authors used RNA
intriguing dynamics of EMT in CTCs mal cells were found to form clusters. sequencing of epithelial and mesen­
from patients with breast cancer. Although the relevance is currently chymal CTCs to identify global gene
To distinguish epithelial from unknown, this is contrary to the expression signatures that are associ­
mesenchymal cancer cells, Shyamala usual idea of EMT resulting in highly ated with breast cancer, EMT and
Maheswaran, Daniel Haber and col­ migratory single mesenchymal cells. therapeutic resistance. It will be inter­
leagues devised a method based on The authors also examined CTC esting to fully assess the prognostic
RNA in situ hybridization (RNA­ISH), dynamics during clinical responses and predictive potential of various
in which cells are differentially to various treatments using paired approaches to CTC characterization
stained according to the expression pretreatment and post­treatment in breast cancer and other cancers.
levels of seven epithelial genes versus samples from ten patients, and Darren J. Burgess
three mesenchymal genes. seven serial samples from a further
ORIGINAL RESEARCH PAPER Yu, M. et al.
The authors first demonstrated patient who underwent two rounds Circulating breast tumor cells exhibit dynamic
the discriminating ability of the of treatment response and relapse. changes in epithelial and mesenchymal
composition. Science 339, 580–584 (2013)
method on cell lines of known epi­ When treatment responses occurred,
thelial or mesenchymal phenotypes,
both when cultured in vitro and in
sections of mouse xenografts derived
from these cells. Importantly, they
also found that normal blood cells
— which commonly copurify with
cancer cells in CTC preparations —
were not stained. Furthermore, on
sections of human breast cancer, they
found a subpopulation of cells with
epithelial morphology but which also
had dual staining for epithelial and
mesenchymal markers. These cells
were more abundant in the aggressive ges
a
m
caann icnetre rsmubetdyipaetes satnadte m ofi gEhMt rTe.present etty I
G
The authors then applied their c/
Dis
RNA­ISH technique to CTCs o
ot
in patients with breast cancer. Ph
NATURE REVIEWS | CANCER VOLUME 13 | MARCH 2013
© 2013 Macmillan Publishers Limited. All rights reserved
RESEARCH HIGHLIGHTS
IN BRIEF
TUMOUR SUPPRESSORS
FAT loss lets WNT get active
WNT signalling is activated in some cancers by mutation of
adenomatous polyposis coli (APC) or β-catenin (CTNNB1).
However, the mechanism of WNT pathway activation in
cancers that do not carry these alterations is unclear. Morris
et al. found recurrent somatic inactivating mutations in FAT1,
which encodes a cadherin-like protein, in several cancer types.
Expression of wild-type FAT1 suppressed tumorigenesis, and
cancer-associated FAT1 mutations enhanced tumour growth in
mice. The authors showed that β-catenin binds FAT1, and that
mutated FAT1 promotes the nuclear localization of β-catenin,
leading to the expression of WNT–β-catenin target genes.
ORIGINAL RESEARCH PAPER Morris, L. G. T. et al. Recurrent somatic mutation of FAT1 in
multiple human cancers leads to aberrant Wnt activation. Nature Genet. 27 Jan 2013
(doi:10.1038/ng.2538)
EPIGENETICS
Methylation in the driver’s seat?
Epigenetic alterations can be heritable and stable, but also
dynamic. This plasticity has raised the question of whether
epigenetic changes can be drivers of tumorigenesis. Aryee et al.
analysed genome-wide methylation profiles in metastatic
prostate cancer using 'cityscape' plots. Although they found
inter-individual heterogeneity among patients, methylation
alterations in the primary tumour and metastases were similar
in each individual. In general, hypermethylated regions were
enriched for cancer-related genes. These results suggest that
DNA methylation might be a selectable driver event.
ORIGINAL RESEARCH PAPER Aryee, M. J. et al. DNA methylation alterations exhibit
intraindividual stability and interindividual heterogeneity in prostate cancer metastases.
Sci. Transl. Med. 5, 169ra10 (2013)
SPLICING
Chimeric expression
Velusamy et al. have identified a reciprocal chimeric fusion
between the transcripts of yippee-like 5 (YPEL5) and the
phosphatase PPP1CB in 97 of 103 (95%) chronic lymphocytic
leukaemia (CLL) samples. No evidence was found for a genomic
fusion between these loci, indicating a role for RNA-splicing
events in forming the chimaeras. YPEL5–PPP1CB produced a
PPP1CB protein with reduced activity, and PPP1CB silencing in
a CLL cell line increased proliferation and colony formation.
The chimaera was not seen in normal cells or in other cancers,
so it may have a specific role in CLL pathogenesis.
ORIGINAL RESEARCH PAPER Velusamy, T. et al. Recurrent reciprocal RNA chimera
involving YPEL5 and PPP1CB in chronic lymphocytic leukemia. Proc. Natl Acad. Sci. USA
4 Feb 2013 (doi:10.1073/pnas.1214326110)
GENETICS
Promoter mutations
Two groups have discovered recurrent mutations in the
promoter of telomerase reverse transcriptase (TERT) in a
large proportion of sporadic melanomas, as well as in a large,
melanoma-prone family. The mutations create binding sites for
ETS transcription factors, leading to increased transcription of
TERT. The high frequency (more frequent than BRAF and NRAS
mutations) and mutually exclusive nature of these mutations
suggest that this may represent a driver mechanism in melanoma.
ORIGINAL RESEARCH PAPERS Horn, S. et al. TERT promoter mutations in familial and
sporadic melanoma. Science 24 Jan 2013 (doi:10.1126/science.1230062) | Huang, F. W. et al.
Highly recurrent TERT promoter mutations in human melanoma. Science 24 Jan 2013
(doi:10.1126/science.1229259)
NATURE REVIEWS | CANCER VOLUME 13 | MARCH 2013
© 2013 Macmillan Publishers Limited. All rights reserved
RESEARCH HIGHLIGHTS
Nature Reviews Cancer | AOP, published online 14 February 2013; doi:10.1038/nrc3473
SENESCENCE To understand this widespread
activation of INK4A, the authors
Improved detection examined whether it was expressed in
the tumour stroma using orthotopic
injection of cells from SV40 TAg-
Monitoring senescence and early cancers in experimentally housed driven mammary tumours (without
tumorigenesis in mouse models, mice. However, they did not analyse the Ink4aLUC allele) into syngeneic
INK4A and understanding how these other age-related phenotypes. Ink4a+/LUC mice. Luciferase activity
activation processes are linked, is challenging. To look more closely at the conn- was observed at the site of injected
Norman Sharpless and colleagues ection between INK4A expression tumour cells but not in mammary
may mark
have developed a knock-in mouse and tumorigenesis, the authors com- glands injected with Matrigel or non-
the majority that expresses luciferase at the locus bined the Ink4aLUC allele with several transformed cells. Similar results were
of, if not all, encoding the senescence promoter mouse tumour models. They first observed with other tumour models,
malignancies and tumour suppressor INK4A (also analysed mammary tumours driven indicating that the tumour cells
known as p16INK4A) that seems to act by SV40 large T-antigen (TAg) and produce local signals that lead to
as a reporter of early tumorigenesis. melanomas driven by activated Hras non-cell-autonomous induction of
To develop the INK4A-luciferase and Cdkn2a loss (these mice lose the senescence in tumour-associated
mouse, the authors ‘knocked in’ remaining Ink4a allele and retain stroma. Furthermore, bone marrow
the firefly luciferase cDNA to the one Arf allele) and observed the transplantations using Ink4a+/LUC
translational start site of INK4A development of intense luminescent donor marrow indicated that some of
(which is encoded, along with ARF, foci in animals as they aged; these the stromal cells expressing luciferase
by Cdkn2a). The resulting mouse, marked the locations where tumours are bone marrow derived.
Ink4aLUC/LUC, was null for INK4A would later develop and were pre- Overall, these authors have created
but retained expression of ARF. sent well before tumours were pal- a robust and non-invasive system
Heterozygous Ink4a+/LUC mouse pable or visible. Moreover, tumour that allows the early detection of
embryonic fibroblasts produced detection by INK4A-luciferase was tumours in mouse models. It should
nearly identical levels of Ink4a more sensitive and specific than also be useful for monitoring tumour
and luciferase mRNA, and in vivo detection using fluorodeoxyglucose progression and therapeutic efficacy,
luciferase activation mirrored normal positron emission tomography and possibly metastatic spread, in
Ink4a expression under physio logical (FDG-PET). The Ink4aLUC allele these models.
conditions, indicating that the was also able to detect tumours in Sarah Seton-Rogers
luciferase construct faithfully reports 12 other mouse models, and the
ORIGINAL RESEARCH PAPER Burd, C. E. et al.
endogenous Ink4a expression. authors suggest that INK4A activa- Monitoring tumorigenesis and senescence in vivo
The accumulation of senescent tion may mark the majority of, if not with a p16INK4a-luciferase model. Cell 152, 340–351
(2013)
cells that express INK4A has been all, malignancies.
associated with ageing. Indeed,
Ink4a+/LUC mice showed an exponen-
tial increase in total body luciferase
(TBL) activity with age. However,
there was considerable variability in
luciferase expression between indi-
vidual mice; so, given the association
between cellular senescence and age-
related phenotypes, they hypothesized
that higher TBL levels would predict
the development of age-related pheno-
types and mortality. Surprisingly, TBL
was not predictive of mortality,
which was uniformly caused by the
development of spontaneous malig-
nancy. Therefore, expression of the X
D
INK4A marker of senescence is not AN
R
associated with risk of spontaneous B
NATURE REVIEWS | CANCER VOLUME 13 | MARCH 2013
© 2013 Macmillan Publishers Limited. All rights reserved
RESEARCH HIGHLIGHTS
signalling, IFNγ and TNF induce
the expression of the transcription
TUMOUR IMMUNOLOGY
factor JUNB, which in turn induces
the expression of INK4A (a known
Give it a rest
inducer of senescence). The authors
found that INK4A expression was
induced in RIP-Tag2 pancreatic
tumour cells that were treated with
IFNγ and TNF, and in pancreatic
tumour cells that were exposed to
large T antigen-specific T 1 cells in
H
vivo. Knockdown of INK4A expres-
sion in pancreatic tumour cells
prevented the induction of senes-
cence in vitro, and the induction of
a senescence was also shown to be
ali
ustr dependent on TNFR1 expression by
n A the tumour cells in vitro and in vivo.
a
mill The authors also showed that
ac pancreatic tumour cells (which were
M
isolated from RIP-Tag2 tumours
exposed to large T antigen-specific
CD4+ T helper 1 (T 1) cells are Extending these observations, T 1 cells) implanted subcutaneously
H H
associated with antitumour immune Braumüller, Wieder and colleagues into NOD-SCID Il2rg–/– (NSG) mice
T 1 cell- responses that induce growth arrest, showed that tumour cells isolated failed to generate tumours. Finally,
H
derived rather than eradication, of tumour from pancreatic tumours exposed IFNγ and TNF induced the growth
cells. But the mechanism by which to large T antigen-specific T 1 arrest of several types of cancer
cytokines H
tumour growth is arrested remains cells in vivo did not proliferate for cells in vitro, including mammary
IFNγ and TNF unknown. six passages in vitro. In addition, tumour cells from mice expressing
can induce RIP-Tag2 mice develop pan- culturing pancreatic tumour cells polyoma middle T antigen (PyMT),
tumour cell creatic tumours owing to the from the RIP-Tag2 mice with IFNγ primary human melanoma and
expression of SV40 large T antigen and TNF increased the fraction of sarcoma cells, and various cancer
senescence
in pancreatic islet cells. Using this cells in G0 phase and G1 phase, cell lines expressing IFNγ receptor
mouse model it has previously been without increasing the fraction and TNFR1.
shown that large T antigen-specific of apoptotic (sub-G1) cells. This These data indicate that the T 1
H
T 1 cells secreting the cytokines indicates that T 1 cell-derived cell-derived cytokines IFNγ and TNF
H H
interferon-γ (IFNγ) and tumour IFNγ and TNF induce tumour cell can induce tumour cell senescence,
necrosis factor (TNF) attenuate senescence, which is a long-lasting providing a mechanistic explanation
the growth of pancreatic tumours growth arrest. Indeed, IFNγ and for the antitumour effects of these
without inducing tumour cell death, TNF induced markers of senescence cells and a rationale for the continued
which increases the survival of in RIP-Tag2 pancreatic tumour cells development of tumour-specific T 1
H
these mice. This effect on pancreatic in vitro. cells for anticancer therapy.
tumour growth was dependent on Next, the authors sought to Gemma K. Alderton
the infiltration of IFNγ- and TNF- characterize the mechanism of
ORIGINAL RESEARCH PAPER Braumüller, H. et al.
secreting T 1 cells and the expres- senescence induction. Through the T-helper-1-cell cytokines drive cancer into
H
sion of TNF receptor 1 (TNFR1) activation of their respective recep- senescence. Nature 3 Feb 2013 (doi:10.1038/
nature11824)
by the pancreatic tumour cells. tors and subsequent downstream
NATURE REVIEWS | CANCER VOLUME 13 | MARCH 2013
© 2013 Macmillan Publishers Limited. All rights reserved
RESEARCH HIGHLIGHTS
THERAPEUTIC RESISTANCE
ALL-important mutations
Although current treatments for disease evolution. Tzoneva et al.
acute lymphoblastic leukaemia sequenced whole exomes from
(ALL) lead to remission in a large diagnosis, remission and relapse
proportion of cases, those patients samples taken from five patients
who do experience disease recur- with paediatric T-ALL and
rence (approximately 20% of children identified several relapse-specific
and more than 50% of adults) have mutations, including one in
a poor prognosis. To understand the NT5C2. Analysis of 98 additional
molecular mechanisms responsible relapsed T-ALL and 35 relapsed
for chemotherapy resistance and dis- B-ALL samples revealed three dif-
ease relapse in ALL, Meyer et al. and ferent recurrent NT5C2 mutations in
Tzoneva, Perez-Garcia, Carpenter 19 of the T-ALLs (20 of 103, or 19%
et al. sequenced transcriptomes and total) and one of the B-ALLs (3%).
whole exomes, respectively, of diag- These mutations were not present
nosis, remission and relapse samples in 23 T-ALL and 27 B-ALL samples
from patients with ALL. taken at diagnosis.
There are two major subtypes of The NT5C2 nucleotidase can
ALL — B cell ALL (B-ALL) and inactivate the nucleoside analogues
T cell ALL (T-ALL). Meyer et al. 6-mercaptopurine and 6-thioguanine,
looked specifically at paediatric which are chemotherapeutics that
B-ALL, and using transcriptome are commonly used in ALL treat- Y
T
T
sequencing of ten patients found ment. 6-mercaptopurine in particular GE
20 missense mutations that were is important for ALL maintenance
present only in the relapse samples therapy. Both groups tested the
and not in the diagnosis and remis- functional implications of the papers, no resistance to other
sion samples. Many of these were recurrent NT5C2 mutations. Meyer chemo therapeutics was observed
not recurrent, even on analysis et al. found that three of the NT5C2 when the NT5C2 mutants were
of a further 62 B-ALL samples, mutations they identified that led to expressed in cell lines. Both groups
but two different mutations in amino acid substitutions (R238W, also found a significant association of
two patients were observed and R367Q and S445F) increased the NT5C2 mutations with early relapse.
validated at the DNA level in enzymatic activity of the mutant These studies emphasize the
NT5C2 (which encodes the enzyme proteins compared with wild-type importance of looking at relapse-
cytosolic purine 5ʹ-nucleotidase). NT5C2 in vitro, and expression of specific mutations in cancer
Exon sequencing of NT5C2 in each of these in a B-ALL cell line genomic analyses, and could facilitate
an additional 61 relapse samples protected against 6-mercaptopurine- the development of more effective
cell lines
identified five cases with mutations, and 6-thioguanine-induced apop- therapeutic regimens for ALL.
expressing for a total frequency of seven of 71 tosis. Tzoneva et al. found that the Sarah Seton-Rogers
these mutants (10%). They also used ultra-deep K359Q, R367Q and D407A muta- ORIGINAL RESEARCH PAPERS Meyer, J. A. et al.
sequencing to identify two patients tions in NT5C2 increased enzymatic Relapse-specific mutations in NT5C2 in childhood
had increased
in which an NT5C2 mutation activity in vitro, and that T-ALL cell acute lymphoblastic leukemia. Nature Genet. 3 Feb
resistance was present as a rare subclone at lines expressing these mutants had 2013 (doi:10.1038/ng.2558) | Tzoneva, G. et al.
Activating mutations in the NT5C2 nucleotidase
diagnosis, indicating that these increased resistance to 6-mercap- gene drive chemotherapy resistance in relapsed
mutations are selected for during topurine and 6-thioguanine. In both ALL. Nature Med. 3 Feb 2013 (doi:10.1038/nm.3078)
NATURE REVIEWS | CANCER VOLUME 13 | MARCH 2013
© 2013 Macmillan Publishers Limited. All rights reserved