Identification of downregulated microRNA in a gastric cancer cell line co-cultured with M1- or M2-polarized macrophage

We showed that co-culture with TAMs triggered Bmi1 expression in gastrointestinal cancer cell lines. miRNAs have been found to target various oncogenes and tumor suppressors. We therefore hypothesized that the regulation of Bmi1 expression in gastrointestinal cancer cells may be mediated by miRNAs using miRNA microarray analysis. THP-1 cells were seeded in the transwell inserts (3540, Corning) for 6-well plates (1 × 106 cells/well). For preparation of M1-polarized THP-1 macrophages, 320 nM phorbol myristate acetate (PMA) was added to THP-1 cells for 6 h, followed by PMA plus 20 ng/ml interferon (IFN)-γ and 100 ng/ml lipopolysaccharide for the following 18 h. For preparation of M2-polarized THP-1 macrophages, 320 nM PMA was added to THP-1 cells for 6 h, followed by PMA plus 20 ng/ml interleukin (IL)-4/IL-13 for the following 18 h. After three washes to remove cytokines, M1- or M2-polarized THP-1 macrophages were co-cultured in upper inserts with AGS cells in 6-well plates (1 × 105 cells/well) without direct contact, in each medium without 10% FBS as described above. After 24 h of co-culture, the upper inserts containing macrophages were discarded. AGS cells were collected and analyzed to identify downregulated microRNA in a gastric cancer cell line co-cultured with M1- or M2-polarized macrophage.