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

The transcription factor NF kappa B (NF-kappa B) 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-kappa B (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-kappa B/I kappa B system, which might be responsible for constitutive NF-kappa B activity, we have analyzed the inhibitor I kappa B alpha (I kappa B alpha) in primary and cultured HRS cells on protein, mRNA, and genomic levels. In lymph node biopsy samples from Hodgkin's disease patients, I kappa B alpha mRNA proved to be strongly overexpressed in the HRS cells. In 2 cell lines (L428 and KM-H2), we detected mutations in the I kappa B alpha gene, resulting in C-terminally truncated proteins, which are presumably not able to inhibit NF-kappa B-DNA binding activity. Furthermore, an analysis of the I kappa B alpha 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 I kappa B alpha protein. We suggest that the observed I kappa B alpha mutations contribute to constitutive NF-kappa B 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 I kappa B alpha in HRS cells evidences a deregulation of the NF-kappa B/I kappa B system also in the remaining cases, probably due to defects in other members of the I kappa B family. (C) 1999 by The American Society of Hematology.