Development of model systems for analysis of effects of cell‐cell and cell‐microenvironment interactions on pH regulatory proteins in breast cancer

Abstract

When studying cancer development it is essential to employ models that recapitulate the tumor microenvironment (TME). We recently showed that truncated ErbB2 (ΔNErbB2) increases acid extrusion via the Na+/H+ exchanger NHE1 and the Na+,HCO3− cotransporter NBCn1 and increases NBCn1 expression in MCF‐7 breast cancer cells. Further, NHE1 inhibition strongly sensitized ΔNErbB2‐expressing MCF‐7 cells to chemotherapy‐induced death. Here, we explore the impact of specific aspects of the TME on pH‐regulatory and survival/motility signaling. Employing MCF‐7 cells +/− inducible ΔNErbB2 expression we show that: (i) TME simulation (pHe 6.5, 1% O2, 7.5 mM lactate) strongly increases Akt‐ and ERK1/2 phosphorylation/activity; TME mimicking conditions has no additional effect on NBCn1 expression but further increases ERK1/2 activity in ΔNErbB2+ cells (ii) in 2D coculture with primary human breast fibroblasts, MCF‐7 cells upregulate the lactate‐H+ cotransporter MCT1 and the epithelial‐mesenchymal transition (EMT) marker α‐smooth muscle actin; (iii) in MCF‐7 spheroids NHE1 expression and ERM‐ and Akt (S473) phosphorylation are greatly reduced compared to 2D monoculture, and pERM and apparently also NBCn1 localize to the spheroid periphery. In conclusion, the TME profoundly impacts on pH regulatory ion transporters and survival/motility signaling in MCF‐7 breast cancer cell models.Funding: Danish Cancer Society, Danish Research Council