Epigenetic reprogramming of somatic genomes by electrofusion with embryonic stem cells

Cell-cell fusion as a mechanism of DNA exchange in cancer

Cell-cell fusion describes the process by which two cells combine their plasma membranes and become a single cell, possessing and retaining certain genetic information from each parent cell. Here, using a Cre-loxP-based method initially developed to investigate extracellular vesicle targeting, we found that cancer cells spontaneously and rapidly deliver DNA to non-cancer cells in vitro via a cell-cell fusion event. The resulting hybrid cells were aneuploid and possessed enhanced clonal diversity and chemoresistance compared to non-hybrid cancer cells. We also observed cell-cell fusion to occur in vivo between melanoma cells and non-cancer cells of both hematopoietic and non-hematopoietic lineages. These findings suggest that cell-cell fusion occurs during the natural progression of cancer and show that this mechanism has the potential to cause massive genomic alterations that are observed in cancer. Furthermore, these findings somewhat contradict recent publications suggesting that the Cre-loxP method measures only extracellular vesicle-mediated intercellular communication.

Macrophage traits in cancer cells are induced by macrophage-cancer cell fusion and cannot be explained by cellular interaction

Background

Cell fusion is a natural process in normal development and tissue regeneration. Fusion between cancer cells and macrophages generates metastatic hybrids with genetic and phenotypic characteristics from both maternal cells. However, there are no clinical markers for detecting cell fusion in clinical context. Macrophage-specific antigen CD163 expression in tumor cells is reported in breast and colorectal cancers and proposed being caused by macrophages-cancer cell fusion in tumor stroma. The purpose of this study is to examine the cell fusion process as a biological explanation for macrophage phenotype in breast.

Methods

Monocytes, harvested from male blood donor, were activated to M2 macrophages and co-cultured in ThinCert transwell system with GFP-labeled MCF-7 cancer cells. MCF7/macrophage hybrids were generated by spontaneous cell fusion, isolated by fluorescence-activated cell sorting and confirmed by fluorescence microscopy, short tandem repeats analysis and flow cytometry. CD163 expression was evaluated in breast tumor samples material from 127 women by immunohistochemistry.

Results

MCF-7/macrophage hybrids were generated spontaneously at average rate of 2 % and showed phenotypic and genetic traits from both maternal cells. CD163 expression in MCF-7 cells could not be induced by paracrine interaction with M2-activated macrophages. CD163 positive cancer cells in tumor sections grew in clonal collection and a cutoff point >25 % of positive cancer cells was significantly correlated to disease free and overall survival.

Conclusions

In conclusion, macrophage traits in breast cancer might be caused by cell fusion rather than explained by paracrine cellular interaction. These data provide new insights into the role of cell fusion in breast cancer and contributes to the development of clinical markers to identify cell fusion.

A Cell Electrofusion Chip for Somatic Cells Reprogramming

Cell fusion is a potent approach to explore the mechanisms of somatic cells reprogramming. However, previous fusion methods, such as polyethylene glycol (PEG) mediated cell fusion, are often limited by poor fusion yields. In this study, we developed a simplified cell electrofusion chip, which was based on a micro-cavity/ discrete microelectrode structure to improve the fusion efficiency and to reduce multi-cell electrofusion. Using this chip, we could efficiently fuse NIH3T3 cells and mouse embryonic stem cells (mESCs) to induce somatic cells reprogramming. We also found that fused cells demethylated gradually and 5-hydroxymethylcytosine (5hmC) was involved in the demethylation during the reprogramming. Thus, the cell electrofusion chip would facilitate reprogramming mechanisms research by improving efficiency of cell fusion and reducing workloads.

Alternative sources of pluripotent stem cells: altered nuclear transfer

Altered nuclear transfer (ANT) is one of several methods that have been suggested for obtaining pluripotent stem cells without destroying human embryos. ANT proposes to alter the nucleus of a somatic cell and/or the cytoplasm of an enucleated oocyte such that when the two are combined, they do not produce a zygote, but rather they form a cell capable of producing pluripotent stem cells without being an embryo. The ANT proposal raises the serious question of whether it is possible to know with confidence that this procedure generates a non-embryo, rather than merely an embryo with a deficiency. Here I address the question of how embryos can be distinguished from non-embryos using scientific criteria and apply these criteria to the two forms of ANT proposed thus far: ANT combined with oocyte-assisted reprogramming (ANT-OAR) or with gene deletion (ANT-GD). I propose that the first globally coordinated event in human development, the formation of trophoblast and inner cell mass (ICM) lineages via Cdx2-Oct3/4 mutual cross-repression, is the earliest act of the embryo qua embryo; it is an operation intrinsic to an embryo as such, and entities lacking the power (potentia) for such an act cannot be considered embryos. Thus, I will argue that formation of trophoblast-ICM lineages is a both necessary and sufficient criterion for determining whether ANT produces an embryo or a non-embryonic entity.