A LYMPHOID CELL-SPECIFIC NUCLEAR FACTOR CONTAINING C-REL-LIKE PROTEINS PREFERENTIALLY INTERACTS WITH INTERLEUKIN-6 KAPPA-B-RELATED MOTIFS WHOSE ACTIVITIES ARE REPRESSED IN LYMPHOID-CELLS

The proto-oncoprotein c-Rel is a member of the nuclear factor kappa-B transcription factor family, which includes the p50 and p65 subunits of nuclear factor kappa-B. We show here that c-Rel binds to kappa-B sites as homodimers as well as heterodimers with p50. These homodimers and heterodimers show distinct DNA-binding specificities and affinities for various kappa-B motifs. In particular, the c-Rel homodimer has a high affinity for interleukin-6 (IL-6) and beta interferon kappa-B sites. In spite of its association with p50 in vitro, however, we found a lymphoid cell-specific nuclear factor in vivo that contains c-Rel but not p50 epitopes; this factor, termed IL-6-kappa-B binding factor II, appears to contain the c-Rel homodimer and preferentially recognizes several IL-6-kappa-B-related kappa-B motifs. Although it has been previously shown that the IL-6-kappa-B motif functions as a potent IL-1/tumor necrosis factor-responsive element in nonlymphoid cells, its activity was found to be repressed in lymphoid cells such as a Jurkat T-cell line. We also present evidence that IL-6-kappa-B binding factor II functions as a repressor specific for IL-6-kappa-B-related kappa-B motifs in lymphoid cells.