The TNF Receptor, CD40 Enters Nucleus through Nuclear Pore Complex and Interacts with c-Rel in Aggressive B Cell Lymphoma.

CD40 is a member of TNF receptor family, which plays important roles in the proliferation, survival and differentiation of lymphocytes. Constitutively active CD40 signaling is one of the hallmarks of aggressive B cell lymphoma development and mediates pivotal functions through its downstream pathways, involving NF-kBs. Recently, our group has reported the nuclear localization of CD40, opening a new paradigm in the functional role of CD40 in non-Hodgkin lymphomas of B cell origin (NHL-B). In this study, we show that CD40 co-localizes and immuno-precipitates with nuclear pore complex (NPC) proteins, which suggests NPC proteins are involved in the classic karyopherin pathway that facilitates the nuclear translocation of CD40 protein. Importantly, our co-immunoprecipitation assays and confocal microscopy have demonstrated that, in NHL-B cells, nuclear localized CD40 interacts with the NF-kB protein-c-Rel, but not p65. Chromotin-IP assay further indicates that CD40 forms complexes with c-Rel on the promoters of several proliferation and survival genes-CD154, Blys/BAFF and Bfl-1/A1 in various NHL-B cell lines. Co-transfection of CD40 and c-Rel in NHL-B cells synergistically enhance Blys promoter-driven luciferase activity while CD40 and p65 do not show such synergy. In normal B cells, transfection of c-Rel has synergistically enhanced the proliferation of B lymphocyte after CD40 ligand stimulation, which results in accumulation of CD40 in the nucleus. Furthermore, co-transfection of c-Rel and wild type CD40 also synergizes the proliferation of NHL-B cells, while co-transfection of c-Rel and nuclear localization signal (NLS) mutated CD40 does not. This study suggests that the nuclear CD40 plays an important role in lymphoma growth and survival mechanisms through its interaction with c-Rel, an oncogene that is amplified in many cases of NHL-B that may contribute to the pathophysiology of the disease process. Modulating the nuclear function of CD40 could provide a new targeted therapeutic approach for lymphoma therapy.