¹Department of Biology, Boston University, 5 Cummington Street, Boston, Massachusetts, MA 02215, USA

²Metabolism Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, MD 20892, USA

Correspondence to: T D Gilmore, E-mail: gilmore@bu.edu

The human large B-cell lymphoma cell line RC-K8 has a rearranged REL locus that directs the production of a chimeric protein, termed REL-NRG (Non-Rel Gene). In this study, we show that RC-K8 cells have constitutively nuclear heterodimeric and homodimeric DNA-binding complexes that consist of p50, REL, and REL-NRG. In vitro, IB can block the DNA-binding activity of wild-type REL homodimers but not REL-NRG homodimers. In vivo, REL-NRG cannot activate transcription of a B site reporter plasmid, suggesting that it is a transcription repressing or blocking REL protein. By Western blotting, no IB protein can be detected in extracts of RC-K8 cells. The absence of IB protein in RC-K8 cells appears to be due to mutations that cause premature termination of translation in three of the four copies of the IKBA gene in RC-K8 cells. Re-expression of wild-type IB or a super-repressor form of IB in RC-K8 cells is cytotoxic; in contrast, expression of a dominant-negative form of IB kinase does not affect the growth of RC-K8 cells. By cDNA microarray analysis, a number of previously identified Rel/NF-B target genes are overexpressed in RC-K8 cells, consistent with there being transcriptionally active REL complexes. Taken together, our results suggest that the growth of RC-K8 cells is dependent on the activity of nuclear wild-type REL dimers, while the contribution of REL-NRG to the transformed state of RC-K8 cells is less clear. Nevertheless, the RC-K8 cell line is the first tumor cell line identified with mutations in genes encoding multiple proteins in the Rel/NF-B signal transduction pathway.

Oncogene (2002) 21, 8759-8768. doi:10.1038/sj.onc.1206033

RC-K8; c-Rel; Rel; Rel-Nrg; NF-B; IB