The Human Tumor Necrosis Factor (TNF) Receptor-associated Factor 1 Gene (TRAF1) Is Up-regulated by Cytokines of the TNF Ligand Family and Modulates TNF-induced Activation of NF-κB and c-Jun N-terminal Kinase

Abstract

To understand how the TNF receptor-associated factor 1 (TRAF1) is transcriptionally regulated, in vitro DNA binding assays, promoter-reporter gene assays, and RNase protection assays were performed with the human TRAF1 gene. Binding of NF-kappaB to three of five putative binding sites within the human TRAF1 promoter was found in electrophoretic mobility shift assay studies, and analysis of TRAF1 gene promoter luciferase constructs confirmed the functional importance of these elements. Moreover, triggering of TNF-R1, CD40, and the interleukin-1 receptor resulted in transcription of the TRAF1 gene, whereas receptors that are not activators or only poor activators of NF-kappaB in HeLa cells failed to show a significant TRAF1 induction. Because it has been shown that members of the TRAF family are involved in activation of NF-kappaB and the c-Jun N-terminal kinase (JNK) by the interleukin-1 receptor and members of the TNF receptor superfamily, a role of TRAF1 in receptor cross-talk and/or feedback regulation of activated receptor signaling complexes can be suggested. In fact, we found that TNF-induced activation of JNK is prolonged in transfectants overexpressing TRAF1, whereas overexpression of a deletion mutant of TRAF1 in which the N-terminal part had been replaced by the green fluorescent protein interfered with TNF-induced activation of NF-kappaB and JNK.