ATRA-induced OAS1 is responsible for MM cell death in response to Cfz. (A) Western blot showing the expression of OAS1-3 in Ctrl-KD or OAS1-3-KD ARP-1 and MM.1S cells under ATRA treatment of 14 hours. (B) Summarized results of apoptosis of Ctrl-KD or OAS1-3-KD ARP-1 and MM.1S cells with indicated treatment of 24 hours. (C) Western blot showing the expression of OAS1 in Ctrl-knockin (KI) or OAS1-KI ARP-1 or MM.1S cells. (D) Summarized results showing apoptosis of Ctrl-KI or OAS1-KI ARP-1 or MM.1S cells with indicated treatment for 24 hours. (E) ChIP analysis of IRF1 binding to OAS1 promoter under BMS961 treatment for 12 hours. The consensus IRF1 binding motif is listed as the colored DNA sequence at the top. The predicted IRF1 binding sequence in OAS1 promoter region is in the black box, and the binding positions are indicated at below. (F-G) Histogram showing mRNA expression of IRF1 (F) and OAS1 (G) in Ctrl-KD or RARγ-KD ARP-1 or MM.1S MM cells with ATRA treatment for 12 hours. The housekeeping gene GAPDH was used for normalization of quantitative reverse transcription polymerase chain reaction results. (H) Western blot of IRF1 and OAS1 expression in ATRA-treated Ctrl-KD or RARγ-KD ARP-1 or MM.1S MM cells with indicated treatment of 16 hours. Student t test was used to compare 2 samples. *P < .05; **P < .01; ***P < .001.