EPITHELIAL-STROMAL INTERACTIONS IN HUMAN BREAST CANCER: IMPLICATIONS FOR CELL ADHESION, MEMBRANE FLUIDITY AND MIGRATION

The migratory/invasive behaviour of breast cancer cells seems to be strongly influenced by their dialogue with neighbouring stromal cells. To verify if this cross-talk may affect some molecular and functional aspects of the cell biology correlated with the metastasizing vocation of tumor cells (i.e. adhesion, membrane fluidity, migration), we co-cultured estrogen receptor (ER)-positive and poorly invasive (MCF-7) or ER-negative and highly invasive (MDA-MB-231) breast cancer cells with normal fibroblasts (NFs) isolated from breast healthy skin or breast tumor stroma (cancer associated fibroblasts, CAFs) in monolayer or in a three-dimensional system (nodules). We previously reported the ability of NFs and CAFs to affect E-cadherin, expression in MCF-7 cells. In the present study, the expression of the mesenchymal adhesion protein N-cadherin (N-cad) was investigated by confocal immunofluorescence microscopy on frozen nodule sections. An increase in N-cad levels was observed in CAFs as a result of the interaction with both kinds of epithelial cancer cells. CAFs, in turn, promoted an increase in N-cad level of MDA-MB-231 cells and induced its expression in MCF-7 cells. Two-photon microscopy imaging of monolayer cells labeled with Laurdan, a membrane fluorescent probe, showed that tumor cell/fibroblast interaction enhanced fluidity of cancer cell membrane while neoplastic cells generally promoted an increase in fibroblast membrane packing density. Cell tracking by confocal microscopy demonstrated that the epithelial cell/fibroblast cross-talk determined a definite increment in tumor cell migration velocity, even with a marked enhancement of the migration directionality induced by CAFs. Our results demonstrate a reciprocal influence of mammary cancer and stromal cells on various adhesiveness/invasiveness features. In particular, an overall pro-invasive effect of CAFs on both well- and poorly differentiated cancer cells was exteriorized by reduction of cell adhesion, induction of membrane fluidity, and migration velocity and directionality, along with a promotion of epithelial-mesenchymal transition.