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TRAF5, a Novel Tumor Necrosis Factor Receptor-Associated Factor Family Protein, Mediates CD40 Signaling
Takaomi Ishida, Tadashi Tojo, Tsutomu Aoki, Norihiko Kobayashi, Tsukasa Ohishi, Toshiki Watanabe, Tadashi Yamamoto and Jun-Ichiro Inoue
Proceedings of the National Academy of Sciences of the United States of America
Vol. 93, No. 18 (Sep. 3, 1996), pp. 9437-9442
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/39728
Page Count: 6
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Signals emanating from CD40 play crucial roles in B-cell function. To identify molecules that transduce CD40 signalings, we have used the yeast two-hybrid system to clone cDNAs encoding proteins that bind the cytoplasmic tail of CD40. A cDNA encoding a putative signal transducer protein, designated TRAF5, has been molecularly cloned. TRAF5 has a tumor necrosis factor receptor-associated factor (TRAF) domain in its carboxyl terminus and is most homologous to TRAF3, also known as CRAF1, CD40bp, or LAP-1, a previously identified CD40-associated factor. The amino terminus has a RING finger domain, a cluster of zinc fingers and a coiled-coil domain, which are also present in other members of the TRAF family protein except for TRAF1. In vitro binding assays revealed that TRAF5 associates with the cytoplasmic tail of CD40, but not with the cytoplasmic tail of tumor receptor factor receptor type 2, which associates with TRAF2. Based on analysis of the association between TRAF5 and various CD40 mutants, residues 230-269 of CD40 are required for the association with TRAF5. In contrast to TRAF3, overexpression of TRAF5 activates transcription factor nuclear factor κ B. Furthermore, amino-terminally truncated forms of TRAF5 suppress the CD40-mediated induction of CD23 expression, as is the case with TRAF3. These results suggest that TRAF5 and TRAF3 could be involved in both common and distinct signaling pathways emanating from CD40.
Proceedings of the National Academy of Sciences of the United States of America © 1996 National Academy of Sciences