Interferonα enhances etoposide-induced apoptosis in human osteosarcoma U2OS cells by a p53-dependent pathway

Interferonα (IFNα) induces cell cycle arrest and triggers apoptosis and chemosensitivity. But the mechanism of IFNα in regulating chemosensitivity has not been fully understood. To study whether IFNα affected chemosensitivity of osteosarcoma cells, we treated p53-wild U2OS cells and p53-mutant MG63 cells with IFNα and etoposide, alone or in combination, and then examined growth inhibition, cell cycle arrest and apoptosis. IFNα enhanced etoposide-induced growth inhibition and apoptosis in p53-wild U2OS cells but not p53-mutant MG63 cells in a dose- and time-dependent manner. Etoposide-induced G2/M phase arrest was also enhanced by IFNα. The enhanced apoptosis was associated with the accumulation of transcriptionally active p53 accompanied with increased Bax and Mdm2, as well as decreased Bcl-2. IFNα also activated caspases-3, -8 and -9 protein kinases and PARP cleavage in response to etoposide in U2OS cells. Moreover, the combination-induced cytotoxicity and PARP cleavage were significantly reduced by caspase pan inhibitor and p53 siRNA. Thus we conclude that IFNα enhances etoposide-induced apoptosis in human osteosarcoma U2OS cells by a p53-dependent and caspase-activation pathway. The proper combination of IFNα and conventional chemotherapeutic agents may be a rational strategy for the treatment of human osteosarcoma with functional p53.