TRAF-3 mRNA splice-deletion variants encode isoforms that induce NF-κB activation

Although TRAF-3 gene products are required for signaling in T-B cell collaboration, full-length TRAF-3 appears to lack signaling function in transient transfection assays that measure NF-κB activation. However, the TRAF-3 gene also encodes at least three mRNA splice-deletion variants that predict protein isoforms (Δ25aa, Δ52aa and Δ56aa) with altered zinc (Zn) finger domains and unknown functional capacities. To determine whether TRAF-3 splice-deletion variants may transmit activating receptor signals to the nucleus, cDNAs for five additional splice-variant isoforms (Δ27aa, Δ83aa, Δ103aa, Δ130aa and Δ221aa) were cloned from a TRAF-3⁺ lymphoma and the expression and function of each of the eight TRAF-3 splice-deletion variants was analyzed. Among the splice-deletion variants, TRAF-3 Δ130 mRNA is expressed by tonsillar B cells and by each of a panel of B and T cell lines. TRAF-3 Δ221 protein is expressed by tonsillar B cells and by each of the lymphocytic lines. The functional effect of over-expressing each TRAF-3 splice-deletion variant on NF-κB activation was studied in 293 T cells. Seven of the TRAF-3 splice-deletion variants, such as TRAF-3 Δ130, induce substantial NF-κB-driven luciferase activity (80-500 fold). In contrast, TRAF-3 Δ221 (in which the complete Zn finger domain is absent) fails to induce NF-κB activation. Although full-length TRAF-3 alone is inactive, it augments the functional effects of the seven activating TRAF-3 splice- deletion variants (1.45 fold). These data indicate that alterations of the Zn finger domains render the TRAF-3 splice-deletion variants capable of inducing NF-κB activation and that full-length TRAF-3 augments their signaling.