Up-modulation of PLC-β2 reduces the number and malignancy of triple-negative breast tumor cells with a CD133⁺/EpCAM⁺ phenotype: a promising target for preventing progression of TNBC

Background: The malignant potential of triple negative breast cancer (TNBC) is also dependent on a sub-population of cells with a stem-like phenotype. Among the cancer stem cell markers, CD133 and EpCAM strongly correlate with breast tumor aggressiveness, suggesting that simultaneous targeting of the two surface antigens may be beneficial in treatment of TNBC. Since in TNBC-derived cells we demonstrated that PLC-β2 induces the conversion of CD133^high to CD133^low cells, here we explored its possible role in down-modulating the expression of both CD133 and EpCAM and, ultimately, in reducing the number of TNBC cells with a stem-like phenotype.

Methods: A magnetic step-by-step cell isolation with antibodies directed against CD133 and/or EpCAM was performed on the TNBC-derived MDA-MB-231 cell line. In the same cell model, PLC-β2 was over-expressed or down-modulated and cell proliferation and invasion capability were evaluated by Real-time cell assays. The surface expression of CD133, EpCAM and CD44 in the different experimental conditions were measured by multi-color flow cytometry immunophenotyping.

Results: A CD133⁺/EpCAM⁺ sub-population with high proliferation rate and invasion capability is present in the MDA-MB-231 cell line. Over-expression of PLC-β2 in CD133⁺/EpCAM⁺ cells reduced the surface expression of both CD133 and EpCAM, as well as proliferation and invasion capability of this cellular subset. On the other hand, the up-modulation of PLC-β2 in the whole MDA-MB-231 cell population reduced the number of cells with a CD44⁺/CD133⁺/EpCAM⁺ stem-like phenotype.

Conclusions: Since selective targeting of the cells with the highest aggressive potential may have a great clinical importance for TNBC, the up-modulation of PLC-β2, reducing the number of cells with a stem-like phenotype, may be a promising goal for novel therapies aimed to prevent the progression of aggressive breast tumors.