Constitutive activation of NF-κB/Stat3 signaling in malignant B cells and plasma cells of MYC- and/or IL-6-transgenic mice. (A) EMSA result indicating high levels of NF-κB DNA-binding activity in BL-like lymphomas and MM-like plasma cell tumors that developed in double-transgenic IL6MYC mice (lanes 2–9) or single-transgenic MYC (lanes 10–14) or IL6 mice (lanes 15–20). Normal B cells (lane 1) were included as control. (B) EMSA result demonstrating high levels of Stat3DNA-binding activity in the same samples used in panel A. (C) EMSA super-shifts indicating both involvement of p50, p65, c-Rel and, to a lesser extent, RelB in NF-κB activation and physical association of NF-κB proteins with Stat3 and p300. Red arrowheads denote shifted bands. In lanes 2–8, NE (10 μg) was incubated with 2 μg of one of the Abs to NF-κB, pStat3 or p300 indicated above the gel image. Antibody to Myc (lane 9) or omission of Ab (lane 1) were used as controls. Red arrowheads denote shifts. (D) EMSA super-shifts suggesting physical association of NF-κB with pStat3 and p300. Red arrowheads, shifted bands; lanes 2–8, Abs to NF-κB, pStat3 or p300; lanes 1 and 9, controls.