A genome-wide microRNA screen identifies regulators of tetraploid cell proliferation.

Tetraploid cells, which are most commonly generated by errors in cell division, are genomically unstable and have been shown to promote tumorigenesis. Recent genomic studies have estimated that ∼40% of all solid tumors have undergone a genome-doubling event during their evolution, suggesting a significant role for tetraploidy in driving the development of human cancers. To safeguard against the deleterious effects of tetraploidy, nontransformed cells that fail mitosis and become tetraploid activate both the Hippo and p53 tumor suppressor pathways to restrain further proliferation. Tetraploid cells must therefore overcome these antiproliferative barriers to ultimately drive tumor development. However, the genetic routes through which spontaneously arising tetraploid cells adapt to regain proliferative capacity remain poorly characterized. Here, we conducted a comprehensive gain-of-function genome-wide screen to identify microRNAs (miRNAs) that are sufficient to promote the proliferation of tetraploid cells. Our screen identified 23 miRNAs whose overexpression significantly promotes tetraploid proliferation. The vast majority of these miRNAs facilitate tetraploid growth by enhancing mitogenic signaling pathways (e.g., miR-191-3p); however, we also identified several miRNAs that impair the p53/p21 pathway (e.g., miR-523-3p), and a single miRNA (miR-24-3p) that potently inactivates the Hippo pathway via down-regulation of the tumor suppressor gene NF2. Collectively, our data reveal several avenues through which tetraploid cells may regain the proliferative capacity necessary to drive tumorigenesis.

Generation and Purification of Tetraploid Cells.

Tetraploid cells are genetically unstable and have the capacity to promote the development and/or progression of human malignancies. It is now estimated that ~40 % of all solid tumors have passed through a tetraploid intermediate stage at some point during their development. Understanding the biological characteristics of tetraploid cells that impart oncogenic properties is therefore a highly relevant and fundamentally important aspect of cancer biology. Here, we describe strategies to efficiently generate and purify tetraploid cells for use in cell biological studies.

A simple engineered platform reveals different modes of tumor-microenvironmental cell interaction.

How metastatic cancer lesions survive and grow in secondary locations is not fully understood. There is a growing appreciation for the importance of tumor components, i.e. microenvironmental cells, in this process. Here, we used a simple microfabricated dual cell culture platform with a 500 µm gap to assess interactions between two different metastatic melanoma cell lines (1205Lu isolated from a lung lesion established through a mouse xenograft; and WM852 derived from a stage III metastatic lesion of skin) and microenvironmental cells derived from either skin (fibroblasts), lung (epithelial cells) or liver (hepatocytes). We observed differential bi-directional migration between microenvironmental cells and melanoma, depending on the melanoma cell line. Lung epithelial cells and skin fibroblasts, but not hepatocytes, stimulated higher 1205Lu migration than without microenvironmental cells; in the opposite direction, 1205Lu cells induced hepatocytes to migrate, but had no effect on skin fibroblasts and slightly inhibited lung epithelial cells. In contrast, none of the microenvironments had a significant effect on WM852; in this case, skin fibroblasts and hepatocytes--but not lung epithelial cells--exhibited directed migration toward WM852. These observations reveal significant effects a given microenvironmental cell line has on the two different melanoma lines, as well as how melanoma effects different microenvironmental cell lines. Our simple platform thus has potential to provide complex insights into different strategies used by cancerous cells to survive in and colonize metastatic sites.