Deregulation of a c-myc-miR34a circuitry in tumorspheres from transformed human fibroblasts

Evidence indicates that a subset of cells endowed with high tumorigenic potential and stemness features (cancer stem cells: CSCs) is responsible for tumor initiation and maintenance in several cancers. In this study, we used a tumor cellular model developed in our laboratory from telomerase immortalized human fibroblasts (named cen3tel) and the tumorsphere assay to possibly isolate and characterize CSCs from in vitro transformed cells. Cen3tel cells were able to form spheres (frequency ~ 2-10%), which showed some stemness features, but were not more tumorigenic than adherent cells in in vivo assays, suggesting an uncoupling between sphere formation capacity and high tumorigenic potential. Moreover, compared to adherent cells, sphere cells showed a reduced expression of genes involved in tumorigenesis and stemness, as c-MYC, GNL3, Notch and ?-Catenin, as well as increased levels of the tumorsuppressor miR-34a. We found that deregulation of these genes was reversible and concerted; in fact, one day after sphere cell seeding in adherent culture conditions, all the genes regained the expression levels of adherent cells, suggesting that they are connected in a circuitry and epigenetic mechanisms likely modulate their expression. Here we show that deregulation of these genes is possibly involved in protecting cells from apoptosis during growth in suspension. This mechanism could play a role as a survival mechanism for cancer cell growing after detachment from the extracellular matrix.