Fibulin-5 downregulates Ki-67 and inhibits proliferation and invasion of breast cancer cells

In the present study, we have employed well-known human breast cancer cell models to overexpress Fibulin-5 and to investigate changes in cell phenotype using different cell-based approaches including cell proliferation, migration and invasion assays, as well as mammosphere formation. Overall, our data suggest that Fibulin-5 induces antitumor effects by suppression of β-catenin phosphorylation. Immunohistochemical analysis of tumor samples of breast cancer patients indicated that a high Fibulin-5 expression level is concomitant with a low expression of the proliferative marker Ki-67, which suggest that Fibulin-5 may influence breast cancer cell proliferation.Fibulins not only function as molecular bridges within the cellular microenvironment but also influence cell behavior. Thus, fibulins may contribute to create a permissive microenvironment for tumor growth but can also stimulate different mechanisms that may impede tumor progression. This is the case with Fibulin-5, which has been shown to display both tumor-promoting and tumor-protective functions by mechanisms that are not totally defined. We show new evidence on the tumor-protective functions displayed by Fibulin-5 in MCF-7, T47D and MDA-MB-231 breast cancer cells including the inhibition of invasion and proliferation capacity and hampering the ability to form mammospheres. Reduction in the level of phosphorylation of Ser residues involved in the nuclear translocation of β-catenin may underlie these antitumor effects. We also found that Fibulin-5 reduces the level of expression of Ki-67, a nuclear protein associated with cell proliferation. Moreover, reduction in Fibulin-5 expression corresponds to an increase of Ki-67 detection in breast tissue samples. Overall, our data provide new insights into the influence of Fibulin-5 to modify breast cancer cell behavior and contribute to better understand the connections between fibulins and cancer.Y.M. is supported by a Ficyt (Gobierno del Principado de Asturias, Spain) fellowship and T.F. is supported by the IUOPA. The present study is partially supported by a grant from European Union FEDER funds, Principado de Asturias (Plan de Ciencia, Tecnologia e Innovacion), FICYT (GRUPIN 14-069), to J.A.V., S.C. and A.J.O, and by a grant from the Fondo de Investigaciones Sanitarias, FISS PI11/00371. IUOPA is supported by the Obra Social Cajastur, Asturias, Spain

Clonal fitness inferred from time-series modelling of single-cell cancer genomes

Progress in defining genomic fitness landscapes in cancer, especially those defined by copy number alterations (CNAs), has been impeded by lack of time-series single-cell sampling of polyclonal populations and temporal statistical models1-7. Here we generated 42,000 genomes from multi-year time-series single-cell whole-genome sequencing of breast epithelium and primary triple-negative breast cancer (TNBC) patient-derived xenografts (PDXs), revealing the nature of CNA-defined clonal fitness dynamics induced by TP53 mutation and cisplatin chemotherapy. Using a new Wright-Fisher population genetics model8,9 to infer clonal fitness, we found that TP53 mutation alters the fitness landscape, reproducibly distributing fitness over a larger number of clones associated with distinct CNAs. Furthermore, in TNBC PDX models with mutated TP53, inferred fitness coefficients from CNA-based genotypes accurately forecast experimentally enforced clonal competition dynamics. Drug treatment in three long-term serially passaged TNBC PDXs resulted in cisplatin-resistant clones emerging from low-fitness phylogenetic lineages in the untreated setting. Conversely, high-fitness clones from treatment-naive controls were eradicated, signalling an inversion of the fitness landscape. Finally, upon release of drug, selection pressure dynamics were reversed, indicating a fitness cost of treatment resistance. Together, our findings define clonal fitness linked to both CNA and therapeutic resistance in polyclonal tumours