Three-dimensional fibroblast-tumor cell interaction causes downregulation of RACK1 mRNA expression in breast cancer cells in vitro.

Fibroblasts are the most abundant stromal cell type in desmoplastic ductal invasive breast tumors, are a substrate of tumor cell invasion and modify tumor cell behavior. However, the complex interaction between tumor cells and fibroblasts remains incompletely understood. Our aim was to identify candidate genes in tumor cells that are affected by fibroblasts and to reveal new molecules involved in this heterologous interaction. To reflect the in vivo situation, a 3-D multicellular spheroid coculture model of breast tumor cells and fibroblasts was combined with cell separation technology (MACS and FACS) and molecular analyses, including RAP-PCR, semiquantitative RT-PCR and reverse Northern blotting. Three tumor cell lines (BT474, T47D and MCF-7) with different invasive potential were applied in coculture with normal skin and/or breast tumor-derived fibroblasts. With the techniques mentioned, 18 different bands in the tumor cDNA band pattern of mono- as opposed to cocultures were identified. One of the mRNAs is considered worth further analysis: rack1. Rack1 mRNA was reproducibly suppressed in tumor cells following interaction with fibroblasts. Downregulation was recorded in all tumor cell lines and for cocultures with both types of fibroblast. This indicates a general regulatory mechanism between epithelial tumor cells and fibroblasts, which may be an interesting tumor cell differentiation-independent target for therapy.