SRA

The plasma cell transcription factor XBP1 is critical for terminal differentiation of B cells into plasma cells but has no known role at earlier stages of B-cell development. Here we show that XBP1 is not only important during early B-cell development and for survival of pre-B cells but also protects pre-B ALL cells. Among pre-B ALL subset, XBP1 was hypomethylated and highest expressed in the Ph+ ALL subset. Cre-mediated deletion of XBP1 in a mouse model of Ph+ ALL compromised proliferation and viability and prolonged survival of leukemia-bearing mice. Interestingly, XBP1 expression levels were positively transcriptionally regulated by STAT5 and negatively by BACH2 and BCL6. High XBP1 expression in high risk ALL patients at the time of diagnosis predicted poor outcome in two clinical trials. Clinically, small-molecule inhibition of IRE1-dependent XBP1-activation caused cell death of patient-derived pre-B ALL cells and affected leukemia-initiation in transplant recipient mice. Collectively, these studies identify XBP1 as an important survival factor and as a potential therapeutic target to overcome drug-resistance in pre-B ALL. Overall design: Genome-wide profiling of mRNA levels in p210 transduced murine Xbp1 fl/+ pre-B cells with ERT2 (XE.1,2,3) and Cre- ERT2  (XC.1,2,3).