FcεRI-Mediated Induction of TNF-α Gene Expression in the RBL-2H3 Mast Cell Line: Regulation by a Novel NF-κB-Like Nuclear Binding Complex

Abstract

Using rat basophilic leukemia (RBL-2H3) cells as a model, we investigated how aggregation of the high affinity receptor for IgE (FcεRI) regulates TNF-α gene expression. Antigenic stimulation of RBL-2H3 cells led to an increase in newly synthesized TNF-α mRNA that was dependent on continuous receptor aggregation and did not require de novo protein synthesis. Kinetic analysis showed that maximal levels were achieved at 60 min and waned by 180 min of stimulation. Concomitant with the transcriptional activation of the TNF-α gene, the rapid appearance and disappearance of a previously uncharacterized nuclear NF-κB DNA binding activity, comprised of two distinct protein complexes, were observed. These protein complexes bound to NF-κB sites within the TNF-α gene and contained novel proteins (three species of Mr between 90,000–110,000) distinct from the classical proteins in NF-κB complexes. The induced NF-κB binding activity required continuous receptor stimulation and induced NF-κB-dependent reporter gene expression. Consistent with a role for the novel NF-κB nuclear binding activity in TNF-α gene expression, deletion of several 5′ κB elements in the TNF-α promoter abolished all measurable FcεRI-dependent induction of a reporter construct. Pharmacologic agents that inhibited the NF-κB binding activity also inhibited TNF-α mRNA expression. Our results demonstrate that a novel NF-κB-like nuclear binding activity plays an important role in regulation of the rapid and transient transcriptional activation of the TNF-α gene via FcεRI.