NF-kappaB inhibits TNF-induced accumulation of ROS that mediate prolonged MAPK activation and necrotic cell death.

NF-kappaB downregulates tumor necrosis factor (TNF)-induced c-Jun N-terminal kinase (JNK) activation that promotes cell death, but the mechanism is not yet fully understood. By using murine embryonic fibroblasts (MEFs) that are deficient in TNF receptor-associated factor (TRAF) 2 and TRAF5 (DKO) or p65 NF-kappaB subunit (p65KO), we demonstrate here that TNF stimulation leads to accumulation of reactive oxygen species (ROS), which is essential for prolonged mitogen-activated protein kinase (MAPK) activation and cell death. Interestingly, dying cells show necrotic as well as apoptotic morphological changes as assessed by electron microscopy and flow cytometry, and necrotic, but not apoptotic, cell death is substantially inhibited by antioxidant.

Phosphorylation of serine 276 is essential for p65 NF-kappaB subunit-dependent cellular responses.

Phosphorylation of several serine residues especially in the transactivation (TA) domain of p65 NF-kappaB subunit has been suggested to be important for its transcriptional activity. However, the responsible phosphorylation site of p65 remains controversial. To investigate the biological significance of phosphorylation and to determine the critical phosphorylation sites of p65, we reconstituted murine embryonic fibroblasts (MEFs) from p65(-/-) mice with various serine to alanine (SA)-substituted mutants of p65.

Identification of a novel transcriptional activator, BSAC, by a functional cloning to inhibit tumor necrosis factor-induced cell death.

Tumor necrosis factor (TNF) is a multifunctional cytokine, which induces proliferation or death in a cell type-dependent manner. We previously showed that murine embryonic fibroblasts (MEFs) from TNF receptor-associated factor 2 (Traf2) and Traf5 double-deficient (double knockout (DKO)) mice were highly susceptible to TNF-induced cell death. By functional cloning to rescue DKO MEFs from TNF-induced cell death, we have identified a novel gene, Bsac.