Molecular mechanisms of constitutive NF-κB/Rel activation in Hodgkin/Reed-Sternberg cells

Abstract

A common characteristic of malignant cells derived from patients with Hodgkin's disease (HD) is a high level of constitutive nuclear NF-kB/Rel activity, which stimulates proliferation and confers resistance to apoptosis. We have analysed the mechanisms that account for NF-kB activation in a panel of Hodgkin/Reed-Sternberg (H-RS) cell lines. Whereas two cell lines (L428 and KMH-2) expressed inactive IkBa, no signi®cant changes in NF-kB or IkB expression were seen in other H-RS cells (L591, L1236 and HDLM-2). Constitutive NF-kB was susceptible to inhibition by recombinant IkBa, suggesting that neither mutations in the NF-kB genes nor posttranslational modi®cations of NF-kB were involved. Endogenous IkBa was bound to p65 and displayed a very short half-life. IkBa degradation could be blocked by inhibitors of the NF-kB activating pathway. Proteasomal inhibition caused an accumulation of phosphorylated IkBa and a reduction of NF-kB activity in HDLM-2 and L1236 cells. By in vitro kinase assays we demonstrate constitutive IkB kinase (IKK) activity in H-RS cells, indicating ongoing signal transduction. Furthermore, H-RS cells secrete one or more factor(s) that were able to trigger NF-kB activation. We conclude that aberrant activation of IKK's, and in some cases defective IkBs, lead to constitutive nuclear NF-kB activity, which in turn results in a growth advantage of Hodgkin's disease tumor cells.

Transcriptional regulatory effects of lymphoma-associated NFKB2/lyt10 protooncogenes

“…This latter model would be consistent with the complete loss of p100 NF-kB-2 seen in the HUT78 CTCL cells, as well as with the lymphoid hyperplasia observed in mice in which targeted gene deletions were performed to`knock-out' p100 while retaining p52 gene expression (Ishikawa et al, 1997). A model invoking loss of IkB-like activity would also be consistent with older reports that inhibition of IkBa by antisense approaches resulted in transformation of NIH3T3 cells (Beauparlant et al, 1994), and with reports of IkBa mutations in patients with Hodgkin's disease (Cabannes et al, 1999;Krappmann et al, 1999;Wood et al, 1998). This model is also reminiscent of one reported mechanism by which HTLV-1 Tax leads to increased NF-kB activity (Kanno et al, 1994).…”

Inhibition of RelA phosphorylation sensitizes apoptosis in constitutive NF-kappaB-expressing and chemoresistant cells

“…13 Several mechanisms including increased expression of NF-kB proteins, mutations and/or deletions in IkBa gene, and increased IkBa turnover, and so on, are involved in NF-kB activation in tumor cells. 1,20 In spite of the growing evidence of the important role of NF-kB in tumorigenesis and its resistance to chemotherapy, only few attempts have been made to understand the mechanisms of the constitutive activity of NF-kB in tumor cells and its regulation for successful therapy.…”

Upregulation of cyclooxygenase-2 is accompanied by increased expression of nuclear factor-κB and IκB kinase-α in human colorectal cancer epithelial cells

“…(3) More recently, NF-kB constitutive activity, as observed in Hodgkin's lymphoma cells, has been associated with a mutation in the gene encoding the IkB-inhibitor (Krappmann et al, 1999), which can lead to impaired control of NF-kB activity and hence to enhanced nuclear activity (Bours et al, 2000). The NF-kB transcription factor is activated in response to a broad range of preapoptotic stimuli (Osborn et al, 1989;Brach et al, 1991;Schreck et al, 1991), dissociates from its attached inhibitory protein IkB and translocates to the nucleus to induce the expression of target genes, including several well-known antiapoptotic genes such as TNF-receptor-associated factor 1 (TRAF1), and TRAF2, cIAPs, manganese superoxide dismutase, A20 and IEX-IL (Wang et al, 1998;Wu et al, 1998).…”