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J. Exp. Med.,
Volume 187, Number 2, January 19, 1998 237-244
By



* Department of Immunology, National Institute of Infectious Diseases, 1-23-1 Toyama, Shinjuku-ku,
Tokyo 162, Japan; CD40 activates nuclear factor kappa B (NF
Department of Oncology, The Institute of Medical Science, The University of
Tokyo, 4-6-1, Shiroganedai, Minato-ku, Tokyo 108, Japan; § Department of Immunology, School of
Medicine, Juntendo University, 2-1-1, Hongo, Bunkyo-ku, Tokyo 113, Japan;
CREST (Core
Research for Evolutional Science and Technology) of Japan Science and Technology Corporation (JST),
and ¶ Department of Molecular Biology, Biomolecular Engineering Research Institute, 6-2-3 Furuedai,
Suita-shi, Osaka-fu 565, Japan
B) and the mitogen-activated protein kinase
(MAPK) subfamily, including extracellular signal-regulated kinase (ERK). The CD40 cytoplasmic tail interacts with tumor necrosis factor receptor-associated factor (TRAF)2, TRAF3,
TRAF5, and TRAF6. These TRAF proteins, with the exception of TRAF3, are required for
NF
B activation. Here we report that transient expression of TRAF6 stimulated both ERK
and NF
B activity in the 293 cell line. Coexpression of the dominant-negative H-Ras did not
affect TRAF6-mediated ERK activity, suggesting that TRAF6 may activate ERK along a Ras-independent pathway. The deletion mutant of TRAF6 lacking the NH2-terminal domain
acted as a dominant-negative mutant to suppress ERK activation by full-length CD40 and suppress prominently ERK activation by a deletion mutant of CD40 only containing the binding
site for TRAF6 in the cytoplasmic tail (CD40
246). Transient expression of the dominant-negative H-Ras significantly suppressed ERK activation by full-length CD40, but marginally suppressed ERK activation by CD40
246, compatible with the possibility that TRAF6 is a
major transducer of ERK activation by CD40
246, whose activity is mediated by a Ras-independent pathway. These results suggest that CD40 activates ERK by both a Ras-dependent pathway and a Ras-independent pathway in which TRAF6 could be involved.
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