IRE1 mRNA levels are downregulated in GCB DLBCL. (A) Two ABC and 2 GCB DLBCL cell lines were treated for 4 or 6 hours with 10 μM proteasome inhibitor MG132. IRE1, XBP1u, and XBP1s protein expression was analyzed by immunoblot. Tubulin (Tbl) is used as loading control. (B) IRE1 mRNA levels in GCB-DLBCL (GCB) compared with ABC-DLBCL (ABC) molecular subtype in 2 independent gene expression–profiled DLBCL data sets GSE10846. Genes were considered differentially expressed between ABC and GCB if bearing a P < .005, q < 0.05, and an absolute log ratio > 0.3 in both cohorts. (C-E) Representative ABC and GCB DLBCL cell lines were analyzed for mRNA expression levels of IRE1 (C), PERK (D), and ATF6 (E) relative to β-actin. Relative IRE1 expression (mean and SD of technical triplicates of 1 representative experiment) for each cell line tested is shown in panel C (left panel). Statistical analyses were done using the unpaired Student t test to compare relative mRNA expression between ABC and GCB cells. ***P ≤ .001 (n.s.); P > .05. n.s., not significant.