Btk induces its own promoter via NF-κB. (A) NMRI mice were transfected with 1 μg pNF-κB-Luc (NF-κB reporter construct) using the hydrodynamic procedure. At days 4, 5, and 8, mice received a second transfection with 10 μg E41K-Btk and/or were treated with LPS or bortezomib, respectively, as indicated in the figure. In vivo biophotonic imaging was performed using the IVIS imaging system as described in “Methods.” Data are representative of 3 independent experiments. (B) A20 cells were transfected with the 1000-Btk reporter construct with or without a constitutively active form of Btk (E41K-Btk). Luciferase activity was measured and relative levels of luciferase activity are shown. Data are representative of 3 independent experiments. (C) Schematic diagram showing the Btk→NF-κB→Btk signaling module. Following BCR stimulation, Btk together with other components of the BCR signalsome activate the transcription factor NF-κB. NF-κB translocates into the nucleus, binds to the Btk promoter, and induces transcription. The newly synthesized Btk forms a positive feedback loop to activate the Btk→NF-κB→Btk signaling pathway. In addition, NF-κB binds to its own promoter to positively autoregulate its transcription.^15,40