Siming Zhao,Murim Choi, John D. Overton, and Alessandro D. Santin
Uterine serous carcinoma (USC) is a biologically aggressive subtype of endometrial cancer. We analyzed the mutational landscape of USC by whole-exome sequencing of 57 cancers, most of which were matched to normal DNA from the same patients. The distribution of the number of protein-altering somatic mutations revealed that 52 USC tumors had fewer than 100 (median 36), whereas 5 had more than 3,000 somatic mutations. The mutations in these latter tumors showed hallmarks of defects in DNA mismatch repair. Among the remainder, we found a significantly increased burden ofmutation in 14 genes. In addition to well-known cancer genes (i.e., TP53, PIK3CA, PPP2R1A, KRAS, FBXW7), there were frequent mutations in CHD4/Mi2b, a member of the NuRD–chromatin-remodeling complex, and TAF1, an element of the core TFIID transcriptional machinery. Additionally, somatic copy-number variation was found to play an important role inUSC, with 13 copy-number gains and 12 copy-number losses that occurred more often than expected by chance. In addition to loss of TP53, we found frequent deletion of a small segment of chromosome 19 containing MBD3, also a member of the NuRD–chromatin-modification complex, and frequent amplification of
chromosome segments containing PIK3CA, ERBB2 (an upstream activator of PIK3CA), and CCNE1 (a target of FBXW7-mediated ubiquitination). These findings identify frequent mutation of DNA damage, chromatin remodeling, cell cycle, and cell proliferation pathways in USC and suggest potential targets for treatment of this lethal variant of endometrial cancer.
Fig. 5. Major altered pathways in USC. The altered percentages shown for genes and pathways come from the 25 matched tumors with CNV information.Genes are colored based on their activity in the pathway diagram. Pink, predicted activated; blue, predicted inactivated; gray, uncertain at this stage; lines with blunt end, inhibiting effect; lines with pointed end, promoting effect; dotted line, uncertain. Mutation and CNV status for each gene across the 25samples are shown at the bottom following the pathway diagram.
Hans Cleversは一貫してLgr5細胞を研究しているが、今回の論文では肝組織におけるLgr5細胞について報告している。CleversのLgr5最初期の報告では、肝組織におけるLgr5陽性細胞はほとんどないというものだった。2007年にCleversの報告を目の前で聞いたときの驚きの一つであったから良く覚えている。今回の報告でも成体マウス肝組織にはLgr5陽性細胞は認められない。ダメージを与えるとどうだろう？ よく使われる急性肝障害モデルである四塩化炭素投与マウスでみるとあまり多いとはいえないが誘導されてくる。ここから単細胞分離してシャーレ上で培養すると、Hepatic
The Wnt target gene Lgr5 (leucine-rich-repeat-containing
G-protein-coupled receptor 5) marks actively dividing stem cells in
Wnt-driven, self-renewing tissues such as small intestine and colon1, stomach2 and hair follicles3. A three-dimensional culture system allows long-term clonal expansion of single Lgr5+
stem cells into transplantable organoids (budding cysts) that retain
many characteristics of the original epithelial architecture2, 4, 5. A crucial component of the culture medium is the Wnt agonist RSPO16, the recently discovered ligand of LGR57, 8. Here we show that Lgr5-lacZ is not expressed in healthy adult liver, however, small Lgr5-LacZ+
cells appear near bile ducts upon damage, coinciding with robust
activation of Wnt signalling. As shown by mouse lineage tracing using a
new Lgr5-IRES-creERT2 knock-in allele, damage-induced Lgr5+ cells generate hepatocytes and bile ducts in vivo. Single Lgr5+
cells from damaged mouse liver can be clonally expanded as organoids in
Rspo1-based culture medium over several months. Such clonal organoids
can be induced to differentiate in vitro and to generate functional hepatocytes upon transplantation into Fah−/− mice. These findings indicate that previous observations concerning Lgr5+
stem cells in actively self-renewing tissues can also be extended to
damage-induced stem cells in a tissue with a low rate of spontaneous
Antonija Kreso, Catherine A. O'Brien et al and Darryl Shibata, John E. Dick
Campbell Family Institute, Ontario Cancer Institute, Princess Margaret Cancer Centre, University Health Network, Toronto Department of Molecular Genetics, University of Toronto, Toronto
Intratumoral heterogeneity arises through the evolution of genetically diverse subclones during tumor progression. However, it remains unknown whether cells within single genetic clones are functionally equivalent. By combining DNA copy number alteration (CNA) profiling, sequencing, and lentiviral lineage tracking, we followed the repopulation dynamics of 150 single lentivirus-marked lineages from 10 human colorectal cancers through serial xenograft passages in mice. CNA and mutational analysis distinguished individual clones and showed that clones remained stable upon serial transplantation. Despite this stability, the proliferation, persistence, and chemotherapy tolerance of lentivirally marked lineages were variable within each clone. Chemotherapy promoted the dominance of previously minor or dormant lineages. Thus, apart from genetic diversity, tumor cells display inherent functional variability in tumor propagation potential, which contributes to both cancer growth and therapy tolerance.
Although it has been hypothesized that some of the somatic mutations found in tumors may occur before tumor initiation, there is little experimental or conceptual data on this topic. To gain insights into this fundamental issue, we formulated a mathematical model for the evolution of somatic mutations in which all relevant phases of a tissue’s history are considered. The model makes the prediction, validated by our empirical findings, that the number of somatic mutations in tumors of self-renewing tissues is positively correlated with the age of the patient at diagnosis. Importantly, our analysis indicates that half or more of the somatic mutations in certain tumors of self-renewing tissues occur before the onset of neoplasia. The model also provides a unique way to estimate the in vivo tissue-specific somatic mutation rates in normal tissues directly from the sequencing data of tumors. Our results have substantial implications for the interpretation of the large number of genome-wide cancer studies now being undertaken.これは面白い論文である。過去5年の研究で癌組織（細胞）の遺伝子変異は20個内外のdriver変異と50〜100個のpassenger変異を認めることが広く知られるようになったが、このうちpassenger変異の多くは、その腫瘍が「がん化する前に」に蓄積されているという主張が本論文の要旨である。このストーリーが成り立つのは、大腸癌、子宮体がん、慢性リンパ性白血病、脳腫瘍（Glioblastome, Mudduloblastoma)などである。ところが膵癌では成り立たず、更に興味深いことに、乳癌でも成り立たないのだそうだ。何故かについては一応論文中に説明がある。
Masahito Kawazu,Toshihide Ueno, et al and Hiroyuki Mano
Members of the RAS superfamily of
small guanosine triphosphatases (GTPases) transition between GDP-bound,
inactive and GTP-bound,
active states and thereby function as
binary switches in the regulation of various cellular activities.
Whereas HRAS, NRAS,
and KRAS frequently acquire transforming
missense mutations in human cancer, little is known of the oncogenic
roles of other
small GTPases, including Ras-related C3
botulinum toxin substrate (RAC) proteins. We show that the human sarcoma
HT1080 harbors both NRAS(Q61K) and
RAC1(N92I) mutant proteins. Whereas both of these mutants were able to
knockdown experiments indicated that
RAC1(N92I) may be the essential growth driver for this cell line.
Screening for RAC1,
RAC2, or RAC3 mutations in cell lines and
public databases identified several missense mutations for RAC1 and
RAC2, with some
of the mutant proteins, including
RAC1(P29S), RAC1(C157Y), RAC2(P29L), and RAC2(P29Q), being found to be
activated and transforming.
P29S, N92I, and C157Y mutants of RAC1 were
shown to exist preferentially in the GTP-bound state as a result of a
from the GDP-bound state, rather than as a
result of a reduced intrinsic GTPase activity. Activating mutations of
were thus found in a wide variety of human
cancers at a low frequency; however, given their marked transforming
mutant proteins are potential targets for
the development of new therapeutic agents.