Identification of mechanism(s) leading to hyperdiploidy in progenitor tumor cells derived from MCF7 breast cancer cells

Stem cells are a minor population of mostly resting cells defined by their long life, high clonogenicity, self-replicating potential, plasticity, and drug resistance (Finn, 2008). Cells with these properties have been identified in various normal and cancerous human tissues (Wicha, 2006), as well as in several long-term tumor cell lines (Setoguchi, 2004). We have some preliminary data indicating that cells isolated from MCF7 line divide slowly and form spheres, both features of progenitors tumor cells, when grown in ultralow adherent plates and in absence of serum. Furthermore, these features were associated to two distinct populations characterized by different content in terms of number of chromosomes. We hypothesize that there are mechanisms that lead to the formation of hyperdiploid cells starting from progenitors cells with a near-diploid karyotype. We are investigating which genes might be involved in this process and if symmetric or asymmetric division depending by altered mitotic genes expression. Moreover we supposed that cell-cell fusion could be a mechanism that lead to hyperdiploidy. To understand whether changes in ploidy occurring in progenitor cells might be the result of cell fusion, we transfected cells from MCF7-sphere with two vectors encoding H2B-GFP (green) and H2B-RFPruby (red) to stain chromosomes. Cell were cocultured and fusion occurrence was evaluated by fluorescence microscopy detecting nuclei with both types of fluorescence, indicating fusion as possible mechanism to generate hyperdiploid cells.