Dominant Negative Mutants of TRAF3 Reveal an Important Role for the Coiled Coil Domains in Cell Death Signaling by the Lymphotoxin-β Receptor

Ligation of the lymphotoxin-β receptor (LTβR) recruits tumor necrosis factor receptor-associated factor-3 (TRAF3) and initiates cell death in HT29 adenocarcinoma cells. The minimal receptor binding domain (TRAF-C) defined by two hybrid analyses is not sufficient for direct recruitment to the ligated receptor. A series of TRAF3 deletion mutants reveal that a subregion of the coiled coil motif is required for efficient recruitment to the LTβR. Furthermore, the ability of TRAF3 to self-associate maps to an adjacent subregion. A TRAF3 deletion mutant that lacks the N-terminal zinc RING and zinc finger motifs, but retains the coiled coil and TRAF-C motifs, competitively displaces endogenous TRAF3 from the LTβR. A second TRAF3 mutant that lacks the receptor binding domain, yet contains the TRAF3 self-association domain, prevents TRAF3 homodimers from being recruited to the LTβR. Both of these mutants have a dominant negative effect on cell death and demonstrate that the recruitment of TRAF3 oligomers is necessary to initiate signal transduction that activates the cell death pathway.