TNF Receptor Family Member BCMA (B Cell Maturation) Associates with TNF Receptor-Associated Factor (TRAF) 1, TRAF2, and TRAF3 and Activates NF-κB, Elk-1, c-Jun N-Terminal Kinase, and p38 Mitogen-Activated Protein Kinase

BCMA (B cell maturation) is a nonglycosylated integral membrane type I protein that is preferentially expressed in mature B lymphocytes. Previously, we reported in a human malignant myeloma cell line that BCMA is not primarily present on the cell surface but lies in a perinuclear structure that partially overlaps the Golgi apparatus. We now show that in transiently or stably transfected cells, BCMA is located on the cell surface, as well as in a perinulear Golgi-like structure. We also show that overexpression of BCMA in 293 cells activates NF-kappa B, Elk-1, the c-Jun N-terminal kinase, and the p38 mitogen-activated protein kinase. Coimmunoprecipitation experiments performed in transfected cells showed that BCMA associates with TNFR-associated factor (TRAF) 1, TRAF2, and TRAF3 adaptor proteins. Analysis of deletion mutants of the intracytoplasmic tail of BCMA showed that the 25-aa protein segment, from position 119 to 143, conserved between mouse and human BCMA, is essential for its association with the TRAFs and the activation of NF-kappa B, Elk-1, and c-Jun N-terminal kinase. BCMA belongs structurally to the TNFR family. Its unique TNFR motif corresponds to a variant motif present in the fourth repeat of the TNFRI molecule. This study confirms that BCMA is a functional member of the TNFR superfamily. Furthermore, as BCMA is lacking a "death domain" and its overexpression activates NF-kappa B and c-Jun N-terminal kinase, we can reasonably hypothesize that upon binding of its corresponding ligand BCMA transduces signals for cell survival and proliferation.