Extended Data Figure 3: Effect of XBP1 on CD44^highCD24^low cells.

a, UPR markers are upregulated in CD44^highCD24^low cells. Quantitative RT–PCR analysis of UPR markers BIP, CHOP, ERDJ4, HERP and MBTPS1 in CD44^lowCD24^high cells and CD44^highCD24^low cells sorted from two TNBC patients. Data are shown as mean ± s.d. of technical triplicates. *P < 0.05, **P < 0.01. b, XBP1s overexpression in CD44^lowCD24^high cells generates mammosphere-forming ability. Number of mammospheres per 1,000 cells generated by sorted CD44^lowCD24^high cells transduced with empty vector or XBP1s expressing retrovirus. Experiments were performed in triplicate and data are shown as mean ± s.d. c, CD44^lowCD24^high cells overexpressing XBP1s are more resistant to chemotherapy. MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay was performed to measure the dose–response curves of CD44^lowCD24^high cells or CD44^lowCD24^high cells expressing XBP1s treated with doxorubicin. Experiments were performed in triplicate and data are shown as mean ± s.d. *P < 0.05, **P < 0.01. d, 1,000 or 100 CD44^lowCD24^high cells sorted from transformed MCF10A ER-Src cells or CD44^lowCD24^high cells overexpressing XBP1s were injected into NOD/SCID/Il2rγ^−/− mice and the incidence of tumours was monitored. e, Ten CD44^lowCD24^high cells sorted from two human patients with TNBC or CD44^lowCD24^high cells overexpressing XBP1s were injected into NOD/SCID/Il2rγ^−/− mice and the incidence of tumours was monitored.