SPP1 and colonic neoplasm: To find out whether individual OPN-SI exerts a similar effect in colon cancer cells, we transfected OPNa, OPNb and OPNc with FLAG tags into HT115 or HCT-8 cells (Additional file 1: Fig. S1a, b), then performed apoptosis and cell viability assays under different concentration of 5-FU with transfected cells.