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Epstein-Barr virus latent membrane protein 1 (LMP1) activates NF-kappaB and c-Jun N-terminal kinase (JNK), which is essential for LMP1 oncogenic activity. Genetic analysis has revealed that tumor necrosis factor receptor-associated factor 6 (TRAF6) is an indispensable intermediate of LMP1 signaling leading to activation of both NF-kappaB and JNK. However, the mechanism by which LMP1 engages TRAF6 for activation of NF-kappaB and JNK is not well understood. Here we demonstrate that TAK1 mitogen-activated protein kinase kinase kinase and TAK1-binding protein 2 (TAB2), together with TRAF6, are recruited to LMP1 through its N-terminal transmembrane region. The C-terminal cytoplasmic region of LMP1 facilitates the assembly of this complex and enhances activation of JNK. In contrast, IkappaB kinase gamma is recruited through the C-terminal cytoplasmic region and this is essential for activation of NF-kappaB. Furthermore, we found that ablation of TAK1 resulted in the loss of LMP1-induced activation of JNK but not of NF-kappaB. These results suggest that an LMP1-associated complex containing TRAF6, TAB2, and TAK1 plays an essential role in the activation of JNK. However, TAK1 is not an exclusive intermediate for NF-kappaB activation in LMP1 signaling.

The presenilins and nicastrin form high molecular mass, multimeric protein complexes involved in the intramembranous proteolysis of several proteins. Post-translational glycosylation and trafficking of nicastrin is necessary for the activity of these complexes. We report here that although there are differences in the post-translational processing of nicastrin in neurons and glia, both of the presenilins are required for the physiological post-translational modification and for the correct subcellular distribution of nicastrin. Absence of presenilin 1 (PS1) is associated with dramatic reductions in the level of mature glycosylated nicastrin and with redistribution of nicastrin away from the cell surface. In contrast, absence of presenilin 2 (PS2) is associated with only modest reductions in the levels of immature nicastrin. It is notable that these differential effects parallel the differential effects of null mutations in PS1 and PS2 on APP and Notch processing. Our data therefore suggest that the differential interactions of PS1 and PS2 with nicastrin reflect different functions for the PS1 and PS2 complexes.

The present study describes the cloning of two novel serine/threonine kinases termed DRAK1 and DRAK2, whose catalytic domains are related to that of death-associated protein kinase, a serine/threonine kinase involved in apoptosis. Both DRAKs are composed of the N-terminal catalytic domain and the C-terminal domain that is responsible for regulation of kinase activity. DRAK1 and DRAK2 show 59.7% identity and display ubiquitous expression. An in vitro kinase assay revealed that both DRAKs are autophosphorylated and phosphorylate myosin light chain as an exogenous substrate, although the kinase activity of DRAK2 is significantly lower than that of DRAK1. Both DRAKs are exclusively localized to the nucleus. Furthermore, overexpression of both DRAKs induces the morphological changes of apoptosis in NIH 3T3 cells, suggesting the role of DRAKs in apoptotic signaling.