Physical and functional interactions between Drosophila TRAF2 and Pelle kinase contribute to Dorsal activation

Signaling through the Toll receptor is required for dorsal/ventral polarity in Drosophila embryos, and also plays an evolutionarily conserved role in the immune response. Upon ligand binding, Toll appears to multimerize and a ctivate the associated kinase, Pelle. However, the immediate downstream tar gets of Pelle have not been identified. Here we show that Drosophila tumor necrosis factor receptor-associated factor 2 (dTRAF2), a homologue of human TRAF6, physically and functionally interacts with Pelle, and is phosphoryl ated by Pelle in vitro. Importantly, dTRAF2 and Pelle cooperate to activate Dorsal synergistically in cotransfected Schneider cells. Deletion of the C -terminal TRAF2 domain of dTRAF2 enhances Dorsal activation, perhaps reflec ting the much stronger interaction of the mutant protein with phosphorylate d, active Pelle. Taken together, our results indicate that Pelle and dTRAF2 physically and functionally interact, and that the TRAF domain acts as a r egulator of this interaction, dTRAF2 thus appears to be a downstream target of Pelle. We discuss these results in the context of Toll signaling in fli es and mammals.