Kaposi’s Sarcoma Associated Herpesvirus Encoded Viral FLICE Inhibitory Protein K13 Activates NF-κB Pathway Independent of TRAF6, TAK1 and LUBAC

BACKGROUND: Kaposi's sarcoma associated herpesvirus encoded viral FLICE inhibitory protein (vFLIP) K13 activates the NF-κB pathway by binding to the NEMO/IKKγ subunit of the IκB kinase (IKK) complex. However, it has remained enigmatic how K13-NEMO interaction results in the activation of the IKK complex. Recent studies have implicated TRAF6, TAK1 and linear ubiquitin chains assembled by a linear ubiquitin chain assembly complex (LUBAC) consisting of HOIL-1, HOIP and SHARPIN in IKK activation by proinflammatory cytokines. METHODOLOGY/PRINCIPAL FINDINGS: Here we demonstrate that K13-induced NF-κB DNA binding and transcriptional activities are not impaired in cells derived from mice with targeted disruption of TRAF6, TAK1 and HOIL-1 genes and in cells derived from mice with chronic proliferative dermatitis (cpdm), which have mutation in the Sharpin gene (Sharpin(cpdm/cpdm)). Furthermore, reconstitution of NEMO-deficient murine embryonic fibroblast cells with NEMO mutants that are incapable of binding to linear ubiquitin chains supported K13-induced NF-κB activity. K13-induced NF-κB activity was not blocked by CYLD, a deubiquitylating enzyme that can cleave linear and Lys63-linked ubiquitin chains. On the other hand, NEMO was required for interaction of K13 with IKK1/IKKα and IKK2/IKKβ, which resulted in their activation by "T Loop" phosphorylation. CONCLUSIONS/SIGNIFICANCE: Our results demonstrate that K13 activates the NF-κB pathway by binding to NEMO which results in the recruitment of IKK1/IKKα and IKK2/IKKβ and their subsequent activation by phosphorylation. Thus, K13 activates NF-κB via a mechanism distinct from that utilized by inflammatory cytokines. These results have important implications for the development of therapeutic agents targeting K13-induced NF-κB for the treatment of KSHV-associated malignancies

HOIL-1 is not essential for K13-induced NF-κB activation.

<p><b>A.</b> The expression of FLAG-tagged K13-ER^TAM in wild-type and <i>HOIL-1^−/−</i> MEF was confirmed with Western blotting. The blot was re-probed with a tubulin antibody to show equal protein loading. <b>B.</b> Wild-type and <i>HOIL-1^−/−</i> MEFs stably expressing FLAG-K13-ER^TAM were transfected with NF-κB-Luc and Renilla reporter constructs. Cells were subsequently treated with 4OHT (20 nM) for 48 hours and the luciferase reporter assay was performed essentially as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036601#pone-0036601-g001" target="_blank">Figure 1A</a>. Asterisks (*) indicate significance at levels of p≤0.05 as compared to vehicle-treated cells. <b>C.</b> Wild-type and <i>HOIL-1^−/−</i> MEFs were transfected with NF-κB-Luc and Renilla reporter constructs and 6 hours post-transfection, these cells were treated with mTNF-α (10ng/ml) for 18 hours and the luciferase reporter assay was performed essentially as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036601#pone-0036601-g001" target="_blank">Figure 1A</a>. <b>D.</b> Expression of transduced FLAG-tagged K13 in wild-type and <i>HOIL-1^−/−</i> MEFs was examined by immunoblot analysis; tubulin was used as a loading control. <b>E.</b> Nuclear p65 DNA binding activities in the nuclear extracts of wild-type and <i>HOIL-1^−/−</i> MEFs expressing an empty vector or FLAG-K13. Asterisks (*) indicate significance at levels of p≤0.05 as compared to vector cells. <b>F.</b> Nuclear p65 DNA binding activities in the nuclear extracts of wild-type and <i>HOIL-1^−/−</i> MEFs following treatment with murine TNFα. <b>G.</b> Wild-type and <i>HOIL-1^−/−</i> MEFs expressing FLAG-K13 were examined for NF-κB activation by Western blot analysis using antibodies against phospho-IκBα, Total IκBα, A20 and RelB. The blot was re-probed with FLAG and Tubulin antibodies to check the expression of the transduced K13 and equal protein loading, respectively.</p

Review-Contemporary Progresses in Carbon-Based Electrode Material in Li-S Batteries

Lithium-sulfur batteries are among the rising rechargeable batteries due to their high energy density, theoretical capacity, and low cost. However, their large-scale application is delayed by several challenges, such as degradation due to polysulfide dissolution, low conductivity, and other restricting factors. Li-S batteries have undergone decades of development aimed at improving battery performance by altering the electrode material to overcome these challenges. In the meantime, due to the depletion of fossil fuels and growing energy demand, the need for changes in processes to improve battery performance is now more urgent than ever. Carbon-based materials like conducting polymers, carbon nanotubes, Graphene, and activated Carbon have gained extensive attention due to their low cost, easy availability, good cycling stability, and exceptional electrical, thermal, and mechanical properties. Here, we summarize recent progress in carbon-based electrode material in Li-S batteries, the development of electrolytes, and progress in adopting lithium-sulfur batteries as flexible devices. Furthermore, a comparison of Li-S batteries based on similar parameters with its rechargeable battery competitors is discussed and a comparison with other non-carbon-based electrodes used in the lithium-sulfur battery is also examined. Finally, a general conclusion and future directions are given