Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) activates NF-κB 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-κB and JNK. However, the mechanism by which LMP1 engages TRAF6 for activation of NF-κB and JNK is not well understood. Here we demonstrate that TAK1 MAP 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, IκB kinase γ (IKKγ) is recruited through the C-terminal cytoplasmic region and this is essential for activation of NF-κB. Furthermore, we found that ablation of TAK1 resulted in the loss of LMP1-induced activation of JNK, but not of NF-κB. 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-κB activation in LMP1 signaling.Persistent latent infection with Epstein-Barr virus (EBV), a γ herpes virus that is classified as a human DNA tumor virus, is widespread in the human population, and can cause the development of malignancies such as Hodgkin's lymphoma, Burkitt's lymphoma and nasopharyngel carcinoma. The latent membrane protein 1 (LMP1) is an oncoprotein encoded by EBV and is critically involved in the effective immortalization and proliferation of B-cells latently infected by EBV (1-3).LMP1 is a transmembrane protein of 386 amino acids containing a short N-terminal cytoplasmic domain of 24 amino acids, six transmembrane-spanning domains and a C-terminal cytoplasmic tail of 200 amino acids ( Figure 1A). LMP1 mimics a constitutively activated tumor necrosis factor (TNF) receptor-like molecule, in the absence of ligand binding (4,5). The

Our fieldwork showed more than 1 μM (145.1 μg/L) barium in about 3 μM (210.7 μg/L) arsenic-polluted drinking well water (n = 72) in cancer-prone areas in Bangladesh, while the mean concentrations of nine other elements in the water were less than 3 μg/L. The types of cancer include squamous cell carcinomas (SCC). We hypothesized that barium modulates arsenic-mediated biological effects, and we examined the effect of barium (1 μM) on arsenic (3 μM)-mediated apoptotic cell death of human HSC-5 and A431 SCC cells in vitro. Arsenic promoted SCC apoptosis with increased reactive oxygen species (ROS) production and JNK1/2 and caspase-3 activation (apoptotic pathway). In contrast, arsenic also inhibited SCC apoptosis with increased NF-κB activity and X-linked inhibitor of apoptosis protein (XIAP) expression level and decreased JNK activity (antiapoptotic pathway). These results suggest that arsenic bidirectionally promotes apoptotic and antiapoptotic pathways in SCC cells. Interestingly, barium in the presence of arsenic increased NF-κB activity and XIAP expression and decreased JNK activity without affecting ROS production, resulting in the inhibition of the arsenic-mediated apoptotic pathway. Since the anticancer effect of arsenic is mainly dependent on cancer apoptosis, barium-mediated inhibition of arsenic-induced apoptosis may promote progression of SCC in patients in Bangladesh who keep drinking barium and arsenic-polluted water after the development of cancer. Thus, we newly showed that barium in the presence of arsenic might inhibit arsenic-mediated cancer apoptosis with the modulation of the balance between arsenic-mediated promotive and suppressive apoptotic pathways.

We examined the biochemical effects of arsenic on the activities of RET proto-oncogene (c-RET protein tyrosine kinases) and RET oncogene (RET-MEN2A and RET-PTC1 protein tyrosine kinases) products. Arsenic activated c-RET kinase with promotion of disulfide bond-mediated dimerization of c-RET protein. Arsenic further activated RET-MEN2A kinase, which was already 3- to 10-fold augmented by genetic mutation compared with c-RET kinase activity, with promotion of disulfide bond-mediated dimerization of RET-MEN2A protein (superactivation). Arsenic also increased extracellular domain-deleted RET-PTC1 kinase activity with promotion of disulfide bond-mediated dimerization of RET-PTC1 protein. Arsenic increased RET-PTC1 kinase activity with cysteine 365 (C365) replaced by alanine with promotion of dimer formation but not with cysteine 376 (C376) replaced by alanine. Our results suggest that arsenic-mediated regulation of RET kinase activity is dependent on conformational change of RET protein through modulation of a special cysteine sited at the intracellular domain in RET protein (relevant cysteine of C376 in RET-PTC1 protein). Moreover, arsenic enhanced the activity of immunoprecipitated RET protein with increase in thiol-dependent dimer formation. As arsenic (14.2 microM) was detected in the cells cultured with arsenic (100 microM), direct association between arsenic and RET in the cells might modulate dimer formation. Thus, we demonstrated a novel redox-linked mechanism of activation of arsenic-mediated RET proto-oncogene and oncogene products.

This study focused on the effects of arsenic (As) on fibroblast-derived matrix metalloproteinase (MMP)-2 and -14 levels, as these proteins were reported to be associated with tumor progression. Arsenic was found to promote production of the fibroblast-derived active form of MMP-2. Further, As at 100 or 1000 microM increased MMP-14 expression levels in fibroblasts. In addition, 1000 microM mercury (Hg) but not As increased pro-MMP-2 protein, which is involved in the conversion of the proenzyme into its active form. Since MMP-14 is an activator of pro-MMP-2, data suggest that As promotes production of fibroblast-derived active form of MMP-2 through increased expression of MMP-14. Evidence indicates that As appeared to be less effective than Hg in the conversion of pro-MMP-2 into its active form.