Angiotensin II induces NF-kappa B activation in HUVEC via the p38MAPK pathway

Angiotensin II (Ang II) is the main active peptide of the renin–angiotensin system (RAS), producing a number of inflammatory mediators that lead to endothelial dysfunction and the progression of atherosclerosis. Ang II-induced NF-κB nuclear translocation plays a pivotal role in this response. This study examines the NF-κB activation mechanism elicited by Ang II in human umbilical vein endothelial cells (HUVEC). Electrophoretic mobility shift assays and Western blotting revealed that Ang II, signaling via AT₁, produces a time-dependent increase in NF-κB DNA binding and IκB degradation. These results also demonstrate that Ang II leads to MAPK phosphorylation and p38MAPK pathway-induced NF-κB activation. Furthermore, AT₁ is required for p38MAPK phosphorylation induced by Ang II. This study provides evidence that Ang II elicits NF-κB activation via the p38MAPK pathway in HUVEC.     

Alteration of subcellular redox equilibrium and the consequent oxidative modification of nuclear factor kappaB are critical for anticancer cytotoxicity by emodin, a reactive oxygen species-producing agent

We previously found that emodin produced reactive oxygen species (ROS) intracellularly. In various tumor cells at low doses it enhances the cytotoxicity of As₂O₃, and at higher doses it renders cytotoxicity independently in vitro and in vivo. The effects involve redox-mediated inhibition of NF-κB activation. In this study, we focus on the mechanisms by which emodin inhibits NF-κB activation. Results in HeLa cells demonstrated that emodin at high doses or in combination with As₂O₃, via generation of ROS especially in the nucleus, altered subcellular redox equilibrium and thus oxidized the redox-sensitive site on NF-κB and prevented its binding to the target DNA. In vivo study showed that tumors exposed to the arsenic/emodin cotreatment had dramatically smaller sizes and weaker antioxidant capacity, compared with arsenic alone. NF-κB binding and transactivation were inhibited in these tumors. These data help in the understanding of the mechanisms by which manipulation of cellular redox and NF-κB activation may enhance chemotherapy.     

NF-κB potentiates caspase independent hydrogen peroxide induced cell death

Background

The pro-survival activity of NF-κB in response to a variety of stimuli has been extensively characterized. Although there have been a few reports addressing the pro-cell death role of NF-κB, the precise mechanism of NF-κB''s pro-cell death function still remains elusive.

Methodology/Principal Findings

In the present study, we investigated the role of NF-κB in cell death induced by chronic insult with hydrogen peroxide (H₂O₂). Here, we show that NF-κB promotes H₂O₂ induced caspase independent but PARP dependent fibroblast cell death. The pro-death activity of NF-κB is due to the DNA binding activity of RelA, which is induced through IKK- mediated IκBα degradation. NF-κB dependent pro-survival genes, Bcl-2 and XIAP, were significantly repressed, while NF-κB dependent pro-death genes, TNFα and Fas Ligand, were induced in response to H₂O₂.

Conclusions/Significance

We discovered an unexpected function of NF-κB, in that it potentiates chronic H₂O₂ exposure induced cell death, and suggest that NF-κB mediates cell death through the repression of pro-survival genes and induction of pro-death genes. Since unremitting exposure of tissues to H₂O₂ and other reactive oxygen species can lead to several degenerative disorders and diseases, our results have important implications for the use of NF-κB inhibitors in therapeutic drug design.     

Angiotensin II induces matrix metalloproteinase-9 expression via a nuclear factor-kappaB-dependent pathway in vascular smooth muscle cells

Angiotensin II (AngII) is widely recognized as a critical regulator of the development of atherosclerosis. Matrix metalloproteinases (MMPs) are thought to participate in plaque destabilization through degradation of the extracellular matrix. In the present study, we investigated the potential mechanism of AngII-induced MMP-9 expression in vascular smooth muscle cells (VSMC). AngII upregulated the expression of MMP-9 significantly in VSMC obtained from rat aorta. RNAi-mediated knockdown of p65 and losartan, an inhibitor of AngII receptors subtype-1 (AT₁), could abolish AngII-induced MMP-9 expression. In addition, AngII induced the NF-κB binding activity via AT₁ and AT₂ receptors in VSMC, and AngII-induced activation of NF-κB is not associated with significant downregulation of IκB. In summary, this study demonstrates that AngII stimulates NF-κB nuclear translocation in VSMC via AT₁ and AT₂. AngII increases the expression of MMP-9 in VSMC, and AT₁ and NF-κB pathways have an important role in this response.     

Down-regulation of EBV-LMP1 radio-sensitizes nasal pharyngeal carcinoma cells via NF-κB regulated ATM expression

Background

The latent membrane protein 1 (LMP1) encoded by EBV is expressed in the majority of EBV-associated human malignancies and has been suggested to be one of the major oncogenic factors in EBV-mediated carcinogenesis. In previous studies we experimentally demonstrated that down-regulation of LMP1 expression by DNAzymes could increase radiosensitivity both in cells and in a xenograft NPC model in mice.

Results

In this study we explored the molecular mechanisms underlying the radiosensitization caused by the down-regulation of LMP1 in nasopharyngeal carcinoma. It was confirmed that LMP1 could up-regulate ATM expression in NPCs. Bioinformatic analysis of the ATM ptomoter region revealed three tentative binding sites for NF-κB. By using a specific inhibitor of NF-κB signaling and the dominant negative mutant of IkappaB, it was shown that the ATM expression in CNE1-LMP1 cells could be efficiently suppressed. Inhibition of LMP1 expression by the DNAzyme led to attenuation of the NF-κB DNA binding activity. We further showed that the silence of ATM expression by ATM-targeted siRNA could enhance the radiosensitivity in LMP1 positive NPC cells.

Conclusions

Together, our results indicate that ATM expression can be regulated by LMP1 via the NF-κB pathways through direct promoter binding, which resulted in the change of radiosensitivity in NPCs.     

Histone Deacetylase Inhibitors Activate NF-��B in Human Leukemia Cells through an ATM/NEMO-related Pathway

Mechanisms underlying histone deacetylase inhibitor (HDACI)-mediated NF-κB activation were investigated in human leukemia cells. Exposure of U937 and other leukemia cells to LBH-589 induced reactive oxygen species (ROS) followed by single strand (XRCC1) and double strand (γ-H2AX) DNA breaks. Notably, LBH-589 lethality was markedly attenuated by small interfering RNA (siRNA) knockdown of the DNA damage-linked histone, H1.2. LBH-589 triggered p65/RelA activation, NF-κB-dependent induction of Mn-SOD2, and ROS elimination. Interference with LBH-589-mediated NF-κB activation (e.g. in IκBα super-repressor transfected cells) diminished HDACI-mediated Mn-SOD2 induction and increased ROS accumulation, DNA damage, and apoptosis. The Mn-SOD2 mimetic TBAP (manganese(III)-tetrakis 4-benzoic acid porphyrin) prevented HDACI-induced ROS and NF-κB activation while dramatically attenuating DNA damage and cell death. In contrast, TRAF2 siRNA knockdown, targeting receptor-mediated NF-κB activation, blocked TNFα- but not HDACI-mediated NF-κB activation and lethality. Consistent with ROS-mediated DNA damage, LBH-589 exposure activated ATM (on serine 1981) and increased its association with NEMO. Significantly, siRNA NEMO or ATM knockdown blocked HDACI-mediated NF-κB activation, resulting in diminished MnSOD2 induction and enhanced oxidative DNA damage and cell death. In accord with the recently described DNA damage/ATM/NEMO pathway, SUMOylation site mutant NEMO (K277A or K309A) cells exposed to LBH-589 displayed diminished ATM/NEMO association, NEMO and p65/RelA nuclear localization/activation, and MnSOD2 up-regulation. These events were accompanied by increased ROS production, γ-H2AX formation, and cell death. Together, these findings indicate that in human leukemia cells, HDACIs activate the cytoprotective NF-κB pathway through an ATM/NEMO/SUMOylation-dependent process involving the induction of ROS and DNA damage and suggest that blocking NF-κB activation via the atypical ATM/NEMO nuclear pathway can enhance HDACI antileukemic activity.