HSP90 inhibition attenuates tonic BCR signaling. (A-B) Scatter plot of log2 SILAC ratios normalized to DMSO for the pYome MS analysis of DG75 (A) and Daudi cells (B) after treatment with AT13387 (x-axis) or STA-9090 (y-axis). Dots are coded according to the number of HSP90 inhibitors that induced pY downregulation by a factor >2. Selected pY sites are labeled. Spearman’s rank correlation coefficients (r) are indicated and marginal distributions of SILAC ratios are shown. (C) Relative change in protein expression levels for the indicated proteins measured by SILAC-based MS after 24 hours of HSP90 inhibition. The average SILAC ratio (avg) across all detected proteins is indicated. (D) Immunoblots of CCL from DG75 and Daudi cells that were treated with DMSO, AT13387, or STA-9090 for 24 and 16 hours, respectively, using antibodies against SYK, BTK, and LYN. Actin was used as loading control. (E) Anti-SYK immunoblots of CCL from bone marrow–derived primary BL cells of 2 patients that were treated in vitro for 16 hours with either DMSO or 250 nM AT13387. Actin was used as loading control.