Notch1 is associated with the multidrug resistance of hypoxic osteosarcoma by regulating MRP1 gene expression

Hypoxia and Notch signaling pathway are closely related and both participate in cell proliferation and drug resistance of tumors. However, the molecular mechanisms of hypoxia and Notch signaling pathway in cell proliferation and drug resistance of osteosarcoma (OS) remain unclear. In this study, to further evaluate the role of hypoxia and Notch1 on drug resistance of OS, we investigated the influence of inhibiting Notch1 pathway by Notch1 small interference RNA (siRNA) on human MG-63 OS cells in hypoxia. Our data showed that hypoxia promoted OS cell proliferation, induced the GO/G1-S-G2/M phase transition, and increased multidrug resistance of human OS cells. Western blot analysis suggested that hypoxia increased the expression of HIF-1 alpha, Notch1, and multidrug resistance protein-1 (MRP1) in human OS cells. Notch1 siRNA inhibits proliferation and increases apoptosis of hypoxic OS cells. Finally, these hypoxic OS cells can be sensitized to multidrug treatment through inhibition of the Notch protein expression by siRNA. Repression of the Notch protein expression resulted in down-regulation of MRP1 protein. These data support the conclusion that Notch signaling is up-regulated in human OS cells under hypoxia and Notchl may represent a viable target to overcome chemoresistant OS cells in a hypoxic niche by regulating MRP1 gene expression.