TRAF5, an activator of NF-κB and putative signal transducer for the lymphotoxin-β receptor

Abstract

Tumor necrosis factor (TNF) receptor-associated factors (TRAFs) are signal transducers for several members of the TNF receptor superfamily. We have identified a novel member of the TRAF family by degenerate oligonucleotide polymerase chain reaction amplification that contains a zinc RING finger and zinc finger motifs, a coiled-coil region, and a C-terminal 'TRAF' homology domain. In vitro translated TRAF5 binds to the cytoplasmic region of the lymphotoxin-β receptor (LT-βR) but not to several other related receptors including CD40, both TNF receptors, Fas, and nerve growth factor receptor. TRAF5 and LT-βR coimmunoprecipitate when overexpressed in COS7 cells. TRAF5 mRNA expression is found in all visceral organs and overlaps with LT-βR. These features distinguish TRAF5 from the other members of the TRAF family. The transcription factor NF-κB is activated in HEK293 cells by overexpression of full-length TRAF5 but not a truncated form lacking the zinc binding region. Furthermore, overexpression of LT-βR in HEK293 cells also results in activation of NF-κB, which is partially inhibited by the truncated TRAF5 mutant. These results show TRAF5 is functionally similar to TRAF2 in that both mediate activation NF-κB and implicate TRAF5 as a signal transducer for LT-βR.