Proteasome-dependent autoregulation of bruton tyrosine kinase (Btk) promoter via NF-κB

Abstract

Bruton tyrosine kinase (Btk) is critical for B-cell development. Btk regulates a plethora of signaling proteins, among them nuclear factor-[κ]B (NF-κB). Activation of NF-κB is a hallmark of B cells, and NF-κB signaling is severely compromised in Btk deficiency. We here present strong evidence indicating that NF-κB is required for efficient transcription of the Btk gene. First, we found that proteasome blockers and inhibitors of NF-κB signaling suppress Btk transcription and intracellular expression. Similar to Btk, proteasome inhibitors also reduced the expression of other members of this family of kinases, Itk, Bmx, and Tec. Second, 2 functional NF-κB-binding sites were found in the Btk promoter. Moreover, in live mice, by hydrodynamic transfection, we show that bortezomib (a blocker of proteasomes and NF-κB signaling), as well as NF-κB binding sequenceoligonucleotide decoys block Btk transcription. We also demonstrate that Btk induces NF-κB activity in mice. Collectively, we show that Btk uses a positive autoregulatory feedback mechanism to stimulate transcription from its own promoter via NF-κB. © 2008 by The American Society of Hematology.