Studies of the role of actin in tumour progression have highlighted its key contribution in cell softening associated with cell invasion. Here, using a human breast cell line with conditional Src induction, we demonstrate that cells undergo a stiffening state prior to acquiring malignant features. This state is characterized by the transient accumulation of stress fibres and upregulation of Ena/VASP-like (EVL). EVL, in turn, organizes stress fibres leading to transient cell stiffening, ERK-dependent cell proliferation, as well as enhancement of Src activation and progression towards a fully transformed state. Accordingly, EVL accumulates predominantly in premalignant breast lesions and is required for Src-induced epithelial overgrowth in Drosophila. While cell softening allows for cancer cell invasion, our work reveals that stress fibre-mediated cell stiffening could drive tumour growth during premalignant stages. A careful consideration of the mechanical properties of tumour cells could therefore offer new avenues of exploration when designing cancer-targeting therapies.

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Expression profiling is a well established tool for the genome-wide analysis of human cancers. However, the high sensitivity of this approach combined with the well known cellular and molecular heterogeneity of cancer often result in extremely complex expression signatures that are difficult to interpret functionally. The majority of sporadic colorectal cancers are triggered by mutations in the adenomatous polyposis coli (APC) tumor suppressor gene, leading to the constitutive activation of the Wnt/␤-catenin signaling pathway and formation of adenomas. Despite this common genetic basis, colorectal cancers are very heterogeneous in their degree of differentiation, growth rate, and malignancy potential. Here, we applied a cross-species comparison of expression profiles of intestinal polyps derived from hereditary colorectal cancer patients carrying APC germline mutations and from mice carrying a targeted inactivating mutation in the mouse homologue Apc. This comparative approach resulted in the establishment of a conserved signature of 166 genes that were differentially expressed between adenomas and normal intestinal mucosa in both species. Functional analyses of the conserved genes revealed a general increase in cell proliferation and the activation of the Wnt/␤-catenin signaling pathway. Moreover, the conserved signature was able to resolve expression profiles from hereditary polyposis patients carrying APC germline mutations from those with bi-allelic inactivation of the MYH gene, supporting the usefulness of such comparisons to discriminate among patients with distinct genetic defects.

Lopes et al. examine centrosomes in human samples progressing from premalignant to metastatic lesions from patients with Barrett’s esophagus. They find that centrosome amplification can occur before transformation during human tumorigenesis, being repressed by p53, suggesting that centrosome amplification contributes to tumor initiation before p53 mutation.

The vast majority of colorectal cancers display genetic instability, either in the chromosomal instability (CIN) or microsatellite instability (MIN) forms. Although CIN tumors are per definition aneuploid, MIN colorectal cancers, caused by loss of mismatch repair function, are usually near diploid. Recently, biallelic germ line mutations in the MYH gene were found to be responsible for MYH-associated polyposis (MAP), an autosomal recessive predisposition to multiple colorectal polyps, often indistinguishable from the dominant familial adenomatous polyposis (FAP) syndrome caused by inherited APC mutations. Here, we analyzed MYH-and APC-mutant polyps by combining laser capture microdissection, isothermal genomic DNA amplification, and array comparative genomic hybridization. Smoothed quantile regression methods were applied to the MAP and FAP genomic profiles to discriminate chromosomes predominantly affected by gains and losses. Up to 80% and 60% of the MAP and FAP polyps showed aneuploid changes, respectively. Both MAP and FAP adenomas were characterized by frequent losses at chromosome 1p, 17, 19, and 22 and gains affecting chromosomes 7 and 13. The aneuploid changes detected at early stages of MYH-driven tumorigenesis may underlie accelerated tumor progression, increased cancer risk, and poor prognosis in MAP.

Type 2 topoisomerases, in particular the A isoform in human cells, play a key role in cohesion and sister chromatid separation during mitosis. These enzymes are thus vital for cycling cells and are obvious targets in cancer chemotherapy. Evidence obtained in yeast and Xenopus model systems indicates that conjugation of topoisomerase 2 with small ubiquitin-like modifier (SUMO) proteins is required for its mitotic functions.

Comparative genomic hybridization by means of BAC microarrays (array CGH) allows high-resolution profiling of copy-number aberrations in tumor DNA. However, specific genetic lesions associated with small but clinically relevant tumor areas may pass undetected due to intra-tumor heterogeneity and/or the presence of contaminating normal cells. Here, we show that the combination of laser capture microdissection, phi29 DNA polymerase-mediated isothermal genomic DNA amplification, and array CGH allows genomic profiling of very limited numbers of cells. Moreover, by means of simple statistical models, we were able to bypass the exclusion of amplification distortions and variability prone areas, and to detect tumor-specific chromosomal gains and losses. We applied this new combined experimental and analytical approach to the genomic profiling of colorectal adenomatous polyps and demonstrated our ability to accurately detect single copy gains and losses affecting either whole chromosomes or small genomic regions from as little as 2 ng of DNA or 1000 microdissected cells.

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