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

Although TRAF-3 gene products are required for signaling in T-B cell collab oration, full-length TRAF-3 appears to lack signaling function in transient transfection assays that measure NF-kappa B activation. However, the TRAF- 3 gene also encodes at least three mRNA splice-deletion variants that predi ct protein isoforms (Delta 25aa, Delta 52aa and Delta 56aa) with altered zi nc (Zn) finger domains and unknown functional capacities. To determine whet her TRAF-3 splice-deletion variants may transmit activating receptor signal s to the nucleus, cDNAs for five additional splice-variant isoforms (Delta 27aa, Delta 83aa, Delta 103aa, Delta 130aa and Delta 221aa) were cloned fro m 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 va riants, TRAF-3 Delta 130 mRNA is expressed by tonsillar B cells and by each of a panel of B and T cell lines. TRAF-3 Delta 221 protein is expressed by tonsillar B cells and by each of the lymphocytic lines. The functional eff ect of over-expressing each TRAF-3 splice-deletion variant on NF-kappa B ac tivation was studied in 293 T cells. Seven of the TRAF-3 splice-deletion va riants, such as TRAF-3 Delta 130, induce substantial NF-kappa B-driven luci ferase activity (80-500 fold). In contrast, TRAF-3 Delta 221 (in which the complete Zn finger domain is absent) fails to induce NF-kappa B activation. Although full-length TRAF-3 alone is inactive, it augments the functional effects of the seven activating TRAF-3 splice-deletion variants (1.4-5 fold ). These data indicate that alterations of the Zn finger domains render the TRAF-3 splice-deletion variants capable of inducing NF-kappa B activation and that full-length TRAF-3 augments their signaling. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.