The role of mmu-miR-155-5p-NF-κB signaling in the education of bone marrow-derived mesenchymal stem cells by gastric cancer cells.

Bone marrow-derived mesenchymal stem cells (BM-MSCs) are important precursors of tumor stromal cells. Previously, we have demonstrated that miR-155-5p inhibition directly induced transition of BM-MSCs into gastric cancer-associated MSCs. Whether miR-155-5p is involved in the education of BM-MSCs by gastric cancer cells has not been established. Murine BM-MSCs (mMSCs) were isolated and grown in conditioned medium derived from gastric cancer cell line MFC (MFC-CM). The tumor-promoting phenotype and function of mMSCs were detected by immunofluorescence staining, quantitative reverse transcription-polymerase chain reaction (qRT-PCR), cell colony formation assay, transwell migration, and invasion assays. Luciferase reporter assays and western blot analyses were conducted to reveal the relationship between nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) p65 and mmu-miR-155-5p. miRNA mimics, inhibitor, and the NF-κB inhibitor pyrrolidine dithiocarbamic acid (PDTC) were used to evaluate the role of miR-155-5p-NF-κB signaling in the education of mMSCs by MFC-CM. We successfully established the education model of mMSCs by MFC-CM and found that mmu-miR-155-5p expression levels were reduced in mMSCs. Mimicking this deregulation by transfecting miRNA inhibitor into mMSCs produced a similar effect as that of MFC-CM on mMSCs. NF-κB p65 was validated as a target of mmu-miR-155-5p, which also negatively regulated NF-κB activation. Inhibition of NF-κB activation by PDTC abolished the effect of the miRNA inhibitor on mMSCs. mmu-miR-155-5p overexpression partially blocked the effect of MFC-CM in educating mMSCs, while PDTC treatment completely eliminated MFC-CM activity. These results indicate that miR-155-5p is not the sole miRNA mediating the education of BM-MSCs by gastric cancer cells, but downstream NF-κB signaling is indispensable for this process.