Extended Data Figure 3. Effect of XBP1 on CD44^high/CD24^low cells.

a, UPR markers are upregulated in CD44^high/CD24^low cells. Quantitative RT-PCR analysis of UPR markers BIP, CHOP, ERDJ4, HERP and MBTPS1 in CD44^low/CD24^high cells and CD44^high/CD24^low cells sorted from two TNBC patients. Data are shown as mean ± SD of technical triplicates. *p<0.05, **p<0.01. b, XBP1s overespression in CD44^low/CD24^high cells generates mammosphere-forming ability. Number of mammospheres per 1,000 cells generated by sorted CD44^low/CD24^high cells transduced with empty vector or XBP1s expressing retrovirus. Experiments were performed in triplicate and data are shown as mean ± SD. c, CD44^low/CD24^high cells overexpressing XBP1s are more resistant to chemotherapy. MTT assay was performed to measure the dose-response curves of CD44^low/CD24^high cells or CD44^low/CD24^high cells expressing XBP1s treated with doxorubicin. Experiments were performed in triplicate and data are shown as mean ± SD. *p<0.05, **p<0.01. d, 1000 or 100 CD44^low/CD24^high cells sorted from transformed MCF10A ER-Src cells or CD44^low/CD24^high cells overexpressing XBP1s were injected into NOD/SCID/IL2Rγ-/-mice and the incidence of tumors was monitored. e, 10 CD44^low/CD24^high cells sorted from two human patients with TNBC or CD44^low/CD24^high cells overexpressing XBP1s were injected into NOD/SCID/IL2Rγ-/-mice and the incidence of tumors was monitored.