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Low-expression of TIPE2 is negatively correlated with MDR1 in cis-platin resistant OS cells and tissues.TIPE2 increases cis-platin induced apoptosis and cytotoxicity.Over-expression of TIPE2 enhances cis-platin sensitivity in vivo.TIPE2 suppresses the MDR1 promoter activity via TAK1-NF-κB and -AP-1 pathways.TIPE2 participates in multiple types of cancer development. However, its mechanism underlying chemoresistance in osteosarcoma has not been elucidated. Herein, we observed the expression of TIPE2 and MDR1 in cis-platin-resistant osteosarcoma tissues and cell lines. Compared to their matched sensitive cell lines and tissues, TIPE2 was downregulated while MDR1 expression was increased. Further investigation showed that overexpression of TIPE2 effectively inhibited MDR1 expression and greatly sensitized osteosarcoma cells to cis-platin, both in vivo and in vitro. Mechanistically, TIPE2 inhibited the transcription of the MDR1 promoter by interfering with the TAK1-NF-κB and -AP-1 pathways. Overall, our results elucidated for the first time that TIPE2 sensitizes osteosarcoma cells to cis-platin through downregulation of MDR1 and may be a novel target in osteosarcoma therapy.