Transcription factor NF-κB is constitutively activated in acute lymphoblastic leukemia cells

The pleiotropic transcription factor NF-κB controls cellular apoptotic and growth processes and increasing evidence suggests a role in tumorigenesis. We describe here that constitutively activated NF-κB complexes are found in the vast majority (39 out of 42 samples) of childhood acute lymphoblastic leukemia (ALL) without any subtype restriction. Electrophoretic shift analysis further demonstrates that these complexes are composed of p50-p50 and p65-p50 dimers. Proteasome inhibition in primary ALL cultures results in a hyperphosphorylated form of IκBα, indicating that activation of upstream kinases, which trigger IκBα degradation, has led to nuclear translocation of NF-κB. Careful inhibition of cellular proteolytic activities is of importance when analyzing extracts from primary ALL cells. Degradation of p65 and other proteins in ALL samples could be specifically suppressed by α-1 antitrypsin. Constitutive NF-κB activation is thus a common characteristic of childhood ALL and strongly suggests a critical role of this factor for leukemia cell survival.