Mesenchymal Stem Cells Directly Interact with Breast Cancer Cells and Promote Tumor Cell Growth In Vitro and In Vivo

Cellular interactions were investigated between human mesenchymal stem cells (MSC) and human breast cancer cells. Co-culture of the two cell populations was associated with an MSC-mediated growth stimulation of MDA-MB-231 breast cancer cells. A continuous expansion of tumor cell colonies was progressively surrounded by MSCGFP displaying elongated cell bodies. Moreover, some MSCGFP and MDA-MB-231cherry cells spontaneously generated hybrid/chimeric cell populations, demonstrating a dual (green fluorescent protein+cherry) fluorescence. During a co-culture of 5–6 days, MSC also induced expression of the GPI-anchored CD90 molecule in breast cancer cells, which could not be observed in a transwell assay, suggesting the requirement of direct cellular interactions. Indeed, MSC-mediated CD90 induction in the breast cancer cells could be partially blocked by a gap junction inhibitor and by inhibition of the notch signaling pathway, respectively. Similar findings were observed in vivo by which a subcutaneous injecti...