CD40-mediated cell death requires TRAF6 recruitment.

CD40 has an important role in T cell-B cell interaction which rescues B lymphocytes from undergoing apoptosis. However, various studies have demonstrated that CD40 can also play a direct role in the induction of specific cell death and thus in the inhibition of tumour cell proliferation. Our previous studies showed that CD40-mediated cell death was independent of caspases and required no de novo protein synthesis. Knowing that CD40 signaling is mediated by its association with several intracellular effectors, including members of TNFR-associated factors (TRAFs) family, the goal of the present study is to investigate the mechanisms involved in the induction of cell death by CD40. Our data reveals that CD40-mediated cell death required lysosomal membrane permeabilization and the subsequent cathepsin B release. In addition, CD40 homodimer formation, a phenomenon known to be necessary for some CD40-mediated signals, was shown to negatively regulate cell death induced by CD40. Moreover, using HEK293 cells ectopically expressing CD40 deficient in TRAF binding, we showed that CD40-mediated apoptosis occurred in the absence of TRAF2 and TRAF3 association, but was significantly reduced when CD40 was deficient in its TRAF6 binding. Therefore, by outlining the role of lysosomal pathways and intracellular effectors, namely TRAF6 in CD40-mediated cell death, our study identifies new targets for anti-cancer therapy.