Overexpression of I Kappa B Alpha Without Inhibition of NF-κB Activity and Mutations in the I Kappa B Alpha Gene in Reed-Sternberg Cells

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Abstract
The transcription factor NF kappa B (NF-κB) mediates the expression of numerous genes involved in diverse functions such as inflammation, immune response, apoptosis, and cell proliferation. We recently identified constitutive activation of NF-κB (p50/p65) as a common feature of Hodgkin/Reed-Sternberg (HRS) cells preventing these cells from undergoing apoptosis and triggering proliferation. To examine possible alterations in the NF-κB/IκB system, which might be responsible for constitutive NF-κB activity, we have analyzed the inhibitor I kappa B alpha (IκB) in primary and cultured HRS cells on protein, mRNA, and genomic levels. In lymph node biopsy samples from Hodgkin’s disease patients, IκB mRNA proved to be strongly overexpressed in the HRS cells. In 2 cell lines (L428 and KM-H2), we detected mutations in the IκB gene, resulting in C-terminally truncated proteins, which are presumably not able to inhibit NF-κB–DNA binding activity. Furthermore, an analysis of the IκB gene in single HRS cells micromanipulated from frozen tissue sections showed a monoallelic mutation in 1 of 10 patients coding for a comparable C-terminally truncated IκB protein. We suggest that the observed IκB mutations contribute to constitutive NF-κB activity in cultured and primary HRS cells and are therefore involved in the pathogenesis of these Hodgkin’s disease (HD) patients. The demonstrated constitutive overexpression of IκB in HRS cells evidences a deregulation of the NF-κB/IκB system also in the remaining cases, probably due to defects in other members of the IκB family.