ZAP-70 enhances the constitutive activation of CD19 and SRC. (A,C) Phospho-CD19 (Y531), phospho-SRC (Y416), total CD19, total SRC, ZAP-70, and β-actin immunoblots of primary UM-CLL (in panel A) or M-CLL cells (in panel C), monocultured for 24 hours after nonspecific siRNA or ZAP-70 siRNA transfection. For anti-IgM stimulated samples, CLL cells were treated with bead-bound anti-IgM for 20 minutes. (B,D) Phosphoprotein levels of CD19 and SRC (relative to total CD19 and SRC-protein levels, respectively) 24 hours after siRNA transfection in UM-CLL (in panel B) or M-CLL samples (in panel D). For anti-IgM stimulated samples, CLL cells were treated with bead-bound anti-IgM for 20 minutes. (n = 6 for UM-CLL, n = 5 for M-CLL). Statistical significance between samples was assessed by paired 2-tailed Student t tests. ∗P < 5 × 10−2. LE, long exposure; ns, not significant; SE, short exposure.
