Kornelia Polyak

The epithelial-mesenchymal transition generates cells with properties of stem cells

The epithelial-mesenchymal transition (EMT) is a key developmental program that is often activated during cancer invasion and metastasis. We here report that the induction of an EMT in immortalized human mammary epithelial cells (HMLEs) results in the acquisition of mesenchymal traits and in the expression of stem-cell markers. Furthermore, we show that those cells have an increased ability to form mammospheres, a property associated with mammary epithelial stem cells. Independent of this, stem cell-like cells isolated from HMLE cultures form mammospheres and express markers similar to those of HMLEs that have undergone an EMT. Moreover, stem-like cells isolated either from mouse or human mammary glands or mammary carcinomas express EMT markers. Finally, transformed human mammary epithelial cells that have undergone an EMT form mammospheres, soft agar colonies, and tumors more efficiently. These findings illustrate a direct link between the EMT and the gain of epithelial stem cell properties.

The genomic landscapes of human breast and colorectal cancers.

Human cancer is caused by the accumulation of mutations in oncogenes and tumor suppressor genes. To catalog the genetic changes that occur during tumorigenesis, we isolated DNA from 11 breast and 11 colorectal tumors and determined the sequences of the genes in the Reference Sequence database in these samples. Based on analysis of exons representing 20,857 transcripts from 18,191 genes, we conclude that the genomic landscapes of breast and colorectal cancers are composed of a handful of commonly mutated gene “mountains” and a much larger number of gene “hills” that are mutated at low frequency. We describe statistical and bioinformatic tools that may help identify mutations with a role in tumorigenesis. These results have implications for understanding the nature and heterogeneity of human cancers and for using personal genomics for tumor diagnosis and therapy.

Mesenchymal stem cells within tumour stroma promote breast cancer metastasis

Mesenchymal stem cells have been recently described to localize to breast carcinomas, where they integrate into the tumour-associated stroma. However, the involvement of mesenchymal stem cells (or their derivatives) in tumour pathophysiology has not been addressed. Here, we demonstrate that bone-marrow-derived human mesenchymal stem cells, when mixed with otherwise weakly metastatic human breast carcinoma cells, cause the cancer cells to increase their metastatic potency greatly when this cell mixture is introduced into a subcutaneous site and allowed to form a tumour xenograft. The breast cancer cells stimulate de novo secretion of the chemokine CCL5 (also called RANTES) from mesenchymal stem cells, which then acts in a paracrine fashion on the cancer cells to enhance their motility, invasion and metastasis. This enhanced metastatic ability is reversible and is dependent on CCL5 signalling through the chemokine receptor CCR5. Collectively, these data demonstrate that the tumour microenvironment facilitates metastatic spread by eliciting reversible changes in the phenotype of cancer cells.

Transitions between epithelial and mesenchymal states: acquisition of malignant and stem cell traits

Transitions between epithelial and mesenchymal states have crucial roles in embryonic development. Emerging data suggest a role for these processes in regulating cellular plasticity in normal adult tissues and in tumours, where they can generate multiple, distinct cellular subpopulations contributing to intratumoural heterogeneity. Some of these subpopulations may exhibit more differentiated features, whereas others have characteristics of stem cells. Owing to the importance of these tumour-associated phenotypes in metastasis and cancer-related mortality, targeting the products of such cellular plasticity is an attractive but challenging approach that is likely to lead to improved clinical management of cancer patients.

Cloning of p27Kip1, a cyclin-dependent kinase inhibitor and a potential mediator of extracellular antimitogenic signals

We cloned p27Kip1, a cyclin-dependent kinase inhibitor implicated in G1 phase arrest by TGF beta and cell-cell contact. p27Kip1 associates with cyclin E-Cdk2 complexes in vivo and in vitro, prevents their activation, and inhibits previously activated complexes, and p27Kip1 overexpression obstructs cell entry into S phase. p27Kip1 potently inhibits Rb phosphorylation by cyclin E-Cdk2, cyclin A-Cdk2, and cyclin D2-Cdk4. p27Kip1 is highly conserved and broadly expressed in human tissues, and its mRNA levels are similar in proliferating and quiescent cells. p27Kip1 has a region of sequence similarity to p21Cip1/WAF1, the Cdk inhibitor whose transcription is stimulated by p53. A p27Kip1 peptide corresponding to this region retains Cdk inhibitory activity. We suggest that cell contact, TGF beta, and p53 all restrain cell proliferation through related Cdk inhibitors.

A Syndrome of Multiorgan Hyperplasia with Features of Gigantism, Tumorigenesis, and Female Sterility in p27Kip1-Deficient Mice

SUMMARY Targeted disruption of the murine p27(Kip1) gene caused a gene dose-dependent increase in animal size without other gross morphologic abnormalities. All tissues were enlarged and contained more cells, although endocrine abnormalities were not evident. Thymic hyperplasia was associated with increased T lymphocyte proliferation, and T cells showed enhanced IL-2 responsiveness in vitro. Thus, p27 deficiency may cause a cell-autonomous defect resulting in enhanced proliferation in response to mitogens. In the spleen, the absence of p27 selectively enhanced proliferation of hematopoietic progenitor cells. p27 deletion, like deletion of the Rb gene, uniquely caused neoplastic growth of the pituitary pars intermedia, suggesting that p27 and Rb function in the same regulatory pathway. The absence of p27 also caused an ovulatory defect and female sterility. Maturation of secondary ovarian follicles into corpora lutea, which express high levels of p27, was markedly impaired.

Intra-tumour heterogeneity: a looking glass for cancer?

Populations of tumour cells display remarkable variability in almost every discernable phenotypic trait, including clinically important phenotypes such as ability to seed metastases and to survive therapy. This phenotypic diversity results from the integration of both genetic and non-genetic influences. Recent technological advances have improved the molecular understanding of cancers and the identification of targets for therapeutic interventions. However, it has become exceedingly apparent that the utility of profiles based on the analysis of tumours en masse is limited by intra-tumour genetic and epigenetic heterogeneity, as characteristics of the most abundant cell type might not necessarily predict the properties of mixed populations. In this Review, we discuss both genetic and non-genetic causes of phenotypic heterogeneity of tumour cells, with an emphasis on heritable phenotypes that serve as a substrate for clonal selection. We discuss the implications of intra-tumour heterogeneity in diagnostics and the development of therapeutic resistance.

Somatic mutations of the mitochondrial genome in human colorectal tumours.

Alterations of oxidative phosphorylation in tumour cells were originally believed to have a causative role in cancerous growth. More recently, mitochondria have again received attention with regards to neoplasia, largely because of their role in apoptosis and other aspects of tumour biology. The mitochondrial genome is particularly susceptible to mutations because of the high level of reactive oxygen species (ROS) generation in this organelle, coupled with a low level of DNA repair. However, no detailed analysis of mitochondrial DNA in human tumours has yet been reported. In this study, we analysed the complete mtDNA genome of ten human colorectal cancer cell lines by sequencing and found mutations in seven (70%). The majority of mutations were transitions at purines, consistent with an ROS-related derivation. The mutations were somatic, and those evaluated occurred in the primary tumour from which the cell line was derived. Most of the mutations were homoplasmic, indicating that the mutant genome was dominant at the intracellular and intercellular levels. We showed that mitochondria can rapidly become homogeneous in colorectal cancer cells using cell fusions. These findings provide the first examples of homoplasmic mutations in the mtDNA of tumour cells and have potential implications for the abnormal metabolic and apoptotic processes in cancer.

Sequence analysis of mutations and translocations across breast cancer subtypes

Breast carcinoma is the leading cause of cancer-related mortality in women worldwide, with an estimated 1.38 million new cases and 458,000 deaths in 2008 alone. This malignancy represents a heterogeneous group of tumours with characteristic molecular features, prognosis and responses to available therapy. Recurrent somatic alterations in breast cancer have been described, including mutations and copy number alterations, notably ERBB2 amplifications, the first successful therapy target defined by a genomic aberration. Previous DNA sequencing studies of breast cancer genomes have revealed additional candidate mutations and gene rearrangements. Here we report the whole-exome sequences of DNA from 103 human breast cancers of diverse subtypes from patients in Mexico and Vietnam compared to matched-normal DNA, together with whole-genome sequences of 22 breast cancer/normal pairs. Beyond confirming recurrent somatic mutations in PIK3CA, TP53, AKT1, GATA3 and MAP3K1, we discovered recurrent mutations in the CBFB transcription factor gene and deletions of its partner RUNX1. Furthermore, we have identified a recurrent MAGI3–AKT3 fusion enriched in triple-negative breast cancer lacking oestrogen and progesterone receptors and ERBB2 expression. The MAGI3–AKT3 fusion leads to constitutive activation of AKT kinase, which is abolished by treatment with an ATP-competitive AKT small-molecule inhibitor.

Analysis of human transcriptomes

nature genetics • volume 23 • december 1999 387 The term ‘synteny’ (or syntenic) refers to gene loci on the same chromosome regardless of whether or not they are genetically linked by classic linkage analysis1. This term was introduced in 1971 by John H. Renwick, of the London School of Hygiene and Tropical Medicine, at the 4th Internal Congress of Human Genetics in Paris with one of us (E.P.) in attendance. The need for such a term was suggested to J.H. Renwick by E.A. Murphy, of Johns Hopkins University2. It arose as a consequence of the new methods in gene mapping using somatic cell hybrid cells. Human genes located on the same chromosome with a genetic distance that could not be determined by the frequency of recombination lacked a term of reference. ‘Synteny’ means ‘same thread’ (or ribbon), a state of being together in location, as synchrony would be together in time. Although several textbooks3–10 and other reference works11–15 give a correct definition, the term synteny nowadays is often used to refer to gene loci in different organisms located on a chromosomal region of common evolutionary ancestry. This new usage of the term synteny does not correspond to its original definition and correct language derivation. A survey of 11 articles in Nature Genetics since 1992 using the term syntenic or synteny in either the title or the abstract revealed usage incorrect in 8 and ambiguous in 3. We believe molecular biologists ought to respect the original definition of synteny and its etymological derivation, especially as this term is still needed to refer to genes located on the same chromosome. We recognize the need to refer to gene loci of common ancestry. Correct terms exist: ‘paralogous’ for genes that arose from a common ancestor gene within one species and ‘orthologous’ for the same gene in different species. Eberhard Passarge1, Bernhard Horsthemke1 & Rosann A. Farber2 1Institut für Humangenetik, Universitätsklinikum Essen, Essen, Germany. 2Department of Pathology and Laboratory Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA. Correspondence should be addressed to E.P. (e-mail: eberhard.passarge@uni-essen.de).