The orphan nuclear receptor ESRRB regulates GC-induced cell death in vitro and in vivo. (A) ESRRB was identified as a mediator of GC resistance in a whole-genome mouse shRNA screen, using the whole-genome TRC shRNA library. (B) ESRRB contains a ligand and DNA binding domain that binds an ERRE site and mediates transcriptional changes via the recruitment of coactivator or corepressor proteins to its AF2 domain. (C) Mouse T-ALL cells (1390) were transduced with lentiviruses expressing NS control or 2 independent shRNAs targeting mouse Esrrb (1, 2) or Nr3c1 and Esrrb and Nr3c1 mRNA expression was analyzed by qRT-PCR. The copy number was normalized to β-actin using the ΔΔCT method. Knockdown of Esrrb in mouse T-ALL cells 1 (1390) and 2 (5059) resulted in resistance to dexamethasone-induced apoptosis. (D,F) Mouse T-ALL cells expressing NS or Esrrb-shRNAs were cultured with dexamethasone (50 nM) for 2 days, and apoptosis was assayed by annexin V-FITC/7-AAD staining followed by flow cytometry. (E,G) ESRRB repression significantly shifted dexamethasone GI50. NS cells or cells deficient in ESRRB or NR3C1 were cultured in increasing concentrations of dexamethasone for 48 hours, and viability was assayed by MTS. Absorbance values were normalized to vehicle control. (H) Experimental approach to examine dexamethasone response in vivo. Esrrb or Nr3c1 knockdown mediated dexamethasone resistance in vivo. Kaplan-Meier survival curves demonstrate that dexamethasone significantly delayed disease in mice receiving transplants of mouse T-ALL cells transduced with NS shRNA (I) but had no effect on mice receiving transplants of Nr3c1- (J) or Esrrb- (K) gene–specific shRNAs (n = 5-7 mice per group; statistics by log-rank test). The results are averages of 3 independent experiments; error bars represent standard error of the mean (SEM). *P < .05; **P < .01; ***P < .001. NS, not significant.