XBP1 and breast cancer: When LOXL2 was knocked down in two independent breast cancer cell lines, Eo771 and MDA-MB-231 expressing high endogenous LOXL2 levels16, 59, XBP1 splicing and transactivation of the UPRE and ERSE gene reporters were abrogated or strongly decreased in both cell lines (Fig. 3a,b).