The atypical PKCs in inflammation: NF-κB and beyond

From the very early days of nuclear factor-κB (NF-κB) research, it was recognized that different protein kinase C (PKC) isoforms might be involved in the activation of NF-κB. Pharmacological tools and pseudosubstrate inhibitors suggested that these kinases play a role in this important inflammatory and survival pathway; however, it was the analysis of several genetic mouse knockout models that revealed the complexity and interrelations between the different components of the PB1 network in several cellular functions, including T-cell biology, bone homeostasis, inflammation associated with the metabolic syndrome, and cancer. These studies unveiled, for example, the critical role of PKCζ as a positive regulator of NF-κB through the regulation of RelA but also its inflammatory suppressor activities through the regulation of the interleukin-4 signaling cascade. This observation is of relevance in T cells, where p62, PKCζ, PKCλ/ι, and NBR1 establish a mesh of interactions that culminate in the regulation of T-cell effector responses through the modulation of T-cell polarity. Many questions remain to be answered, not just from the point of view of the implication for NF-κB activation but also with regard to the in vivo interplay between these pathways in pathophysiological processes like obesity and cancer.     

Nuclear lamina defects cause ATM-dependent NF-κB activation and link accelerated aging to a systemic inflammatory response

Alterations in the architecture and dynamics of the nuclear lamina have a causal role in normal and accelerated aging through both cell-autonomous and systemic mechanisms. However, the precise nature of the molecular cues involved in this process remains incompletely defined. Here we report that the accumulation of prelamin A isoforms at the nuclear lamina triggers an ATM- and NEMO-dependent signaling pathway that leads to NF-κB activation and secretion of high levels of proinflammatory cytokines in two different mouse models of accelerated aging (Zmpste24^−/− and Lmna^G609G/G609G mice). Causal involvement of NF-κB in accelerated aging was demonstrated by the fact that both genetic and pharmacological inhibition of NF-κB signaling prevents age-associated features in these animal models, significantly extending their longevity. Our findings provide in vivo proof of principle for the feasibility of pharmacological modulation of the NF-κB pathway to slow down the progression of physiological and pathological aging.     

Demethyleneberberine alleviates inflammatory bowel disease in mice through regulating NF-κB signaling and T-helper cell homeostasis

Objective

The activation of NF-κB signaling and unbalance of T-helper (Th) cells have been reported to play a key role in the pathogenesis of colitis. Cortex Phellodendri Chinensis (CPC) is commonly used to treat inflammation and diarrhea. Demethyleneberberine (DMB), a component of CPC, was reported to treat alcoholic liver disease as a novel natural mitochondria-targeted antioxidant in our previous study. In this study, we investigated whether DMB could protect against dextran sulfate sodium (DSS)-induced inflammatory colitis in mice by regulation of NF-κB pathway and Th cells homeostatis.

Methods

Inflammatory colitis mice were induced by 3% DSS, and DMB were orally administered on the doses of 150 and 300 mg/kg. In vitro, DMB (10, 20, 40 μM) and N-acetyl cysteine (NAC, 5 mM) were co-cultured with RAW264.7 for 2 h prior to lipopolysaccharide (LPS) stimulation, and splenocytes from the mice were cultured ex vivo for 48 h for immune response test.

Results

In vivo, DMB significantly alleviated the weight loss and diminished myeloperoxidase (MPO) activity, while significantly reduced the production of pro-inflammatory cytokines, such as interleukin (IL)-6 and tumor necrosis factor-α (TNF-α), and inhibited the activation of NF-κB signaling pathway. Furthermore, DMB decreased interferon (IFN)-γ, increased IL-4 concentration in the mice splenocytes and the ratio of IgG1/IgG2a in the serum. In vitro, ROS production and pro-inflammation cytokines were markedly inhibited by DMB in RAW264.7 cell.

Conclusions

Our findings revealed that DMB alleviated mice colitis and inhibited the inflammatory responses by inhibiting NF-κB pathway and regulating the balance of Th cells.

     

Control of NF-κB and inflammation by the unfolded protein response

Under inflammatory situations, endoplasmic reticulum (ER) stress occurs at local sites and modulates inflammatory processes. NF-κB is a key regulator for immune and inflammatory responses, and its activity is influenced by ER stress positively or negatively. Recent investigation suggested that ER stress induces activation of NF-κB in the early phase, whereas in the later phase, consequent unfolded protein response (UPR) inhibits NF-κB. This review summarizes current knowledge on potential mechanisms underlying the biphasic, bidirectional regulation of NF-κB by the UPR and possible roles for ER stress in the regulation of inflammation.     

NF-κB与TNF诱导的细胞凋亡

不同类型的细胞对于TNF-α诱导的细胞凋亡的敏感性可以有很大差别,但是多数的细胞在同时给予蛋白质合成抑制剂处理时会对TNF-α变得非常敏感。有学者认为有一个基因或一组基因在TNF受体活化后被诱导而传导细胞凋亡信号。近期的研究表明,一种被TNF激活的NF-κB转录因子在这一过程中起部分的作用。该发现把NF-κB原先只作为免疫和炎症反应调控因子的功能拓宽到了也可参与细胞凋亡的调控。     

Artemisinin inhibits inflammatory response via regulating NF-κB and MAPK signaling pathways

Artemisinin, isolated from the Chinese plant Artemisia annua, has been used for many years to treat different forms of malarial parasites. In this study, we explored the anti-inflammatory activity of artemisinin and the underlying mechanism of this action. We demonstrated that the anti-inflammatory effects of artemisinin in TPA-induced skin inflammation in mice. Then the artemisinin significantly inhibited the expression of NF-κB reporter gene induced by TNF-α in a dose-dependent manner. Artemisinin also inhibited TNF-α induced phosphorylation and degradation of IκBα, p65 nuclear translocation. Artemisinin also has an impact on upstream signaling of IKK through the inhibition of expression of adaptor proteins, TNF receptor-associated factor 2 (TRAF2) and receptor interacting protein 1 (RIP1). Furthermore, pretreatment of cells with artemisinin prevented the TNF-α-induced expression of NF-κB target genes, such as anti-apoptosis (c-IAP1, Bcl-2, and FLIP), proliferation (COX-2, cyclinD1), invasion (MMP-9), angiogenesis (VEGF), and major inflammatory cytokines (TNF-α, iNOS, and MCP1). We also proved that artemisinin potentiated TNF-α-induced apoptosis. Moreover, artemisinin significantly impaired the ROS production and phosphorylation of p38 and ERK, but did not affect the phosphorylation of JNK. Taken together, artemisinin may be a potentially useful therapeutic agent for inflammatory-related diseases.     

AMP-activated protein kinase inhibits NF-κB signaling and inflammation: impact on healthspan and lifespan

Adenosine monophosphate-activated protein kinase (AMPK) is a crucial regulator of energy metabolic homeostasis and thus a major survival factor in a variety of metabolic stresses and also in the aging process. Metabolic syndrome is associated with a low-grade, chronic inflammation, primarily in adipose tissue. A low-level of inflammation is also present in the aging process. There are emerging results indicating that AMPK signaling can inhibit the inflammatory responses induced by the nuclear factor-κB (NF-κB) system. The NF-κB subunits are not direct phosphorylation targets of AMPK, but the inhibition of NF-κB signaling is mediated by several downstream targets of AMPK, e.g., SIRT1, PGC-1α, p53, and Forkhead box O (FoxO) factors. AMPK signaling seems to enhance energy metabolism while it can repress inflammatory responses linked to chronic stress, e.g., in nutritional overload and during the aging process. AMPK can inhibit endoplasmic reticulum and oxidative stresses which are involved in metabolic disorders and the aging process. Interestingly, many target proteins of AMPK are so-called longevity factors, e.g., SIRT1, p53, and FoxOs, which not only can increase the stress resistance and extend the lifespan of many organisms but also inhibit the inflammatory responses. The activation capacity of AMPK declines in metabolic stress and with aging which could augment the metabolic diseases and accelerate the aging process. We will review the AMPK pathways involved in the inhibition of NF-κB signaling and suppression of inflammation. We also emphasize that the capacity of AMPK to repress inflammatory responses can have a significant impact on both healthspan and lifespan.     

Up-regulation of Cks1 and Skp2 with TNFα/NF-κB signaling in chronic progressive nephropathy

The cyclin-dependent kinase (CDK) inhibitor p27 level is associated with progression of renal damage. We previously reported that mRNA of Skp2, a component of Skp/Cullin/F-box (SCF)-ubiquitin ligase which targets to p27, was increased in unilateral ureteral obstructive kidneys in mice and that the nephritis was attenuated in Skp2-deficient mice. However, the details have not been fully clarified. Here, we found that not only Skp2 but also cdc kinase subunit 1 (Cks1), an essential cofactor for the SCF-Skp2 ubiquitin ligase in targeting p27, was increased in another chronic progressive model, anti-thymocyte serum (ATS) rat nephropathy. After induction of ATS nephropathy, Skp2(+) /Cks1(+) /Ki67(+) tubular epithelial cell numbers increased, and p27(+) tubular epithelial cells decreased transiently. Moreover, we found that TNFα was involved in expression of both Skp2 and Cks1 in NRK cell line as well as the in ATS nephropathy. Nuclear accumulations of NF-κB subunits RelB and p52 were increased in the tubular epithelial cells of the nephritic kidney. Both Skp2 and Cks1 were colocalized with RelB in these cells. These data suggest that both Skp2 and Cks1 are up-regulated by the TNFα-RelB/p52 pathway in the early stages of renal damage and are collaboratively involved in down-regulation of p27 in proliferative tubular dilation and the progression of chronic nephropathy.     

Effects of Fas,NF-κB and caspases on rat microvascular endothelial cell apoptosis induced by TNFα

Effects of Fas,NF-κB and caspases on rat microvascular endothelial cell apoptosis induced by TNFα     

Collagen gel protects L929 cells from TNFα-induced death by activating NF-κB

Purpose: Type I collagen is one of the most abundant components of extracellular matrix. We previously illustrated that murine fibrosarcoma L929 cells grew well on type I collagen gel and escaped from TNFα-induced cell death. In this study, we investigated the mechanism underlying the protective effect of collagen gel. Material and methods: We used western blot, confocal microscopy, MTT assay and flow cytometry by introducing fluorescence staining to determine the expression levels of nuclear factor kappa B (NF-κB), inhibitory ratio and autophagy. Results: L929 cells on collagen gel showed higher expression of NF-κB in the nucleus. Inhibition of NF-κB with pyrrolidine dithiocarbamate hydrochloride (PDTC) or knockdown by NF-κB-siRNA canceled the protective effect of collagen gel on L929 cells from TNFα-induced death, suggesting for the role of NF-κB in the protection from cell death. We found a new aspect of the effect of PDTC on L929 cells cultured on collagen gel. PDTC alone without TNFα induced apoptosis in the L929 cells cultured on collagen gel but not the cells on plastic dish. The apoptosis induction of the L929 cells cultured on collagen gel with PDTC was repressed by inhibiting autophagy with chloroquine, an autophagy inhibitor, suggesting that autophagy contributes to the death induced by the treatment with PDTC. Possible underlying mechanism of this finding is discussed. Conclusion: NF-κB played an important role in protecting the L929 cells cultured on collagen gel from TNFα-induced death.     

TNFR2 interposes the proliferative and NF-κB-mediated inflammatory response by podocytes to TNF-α

The development of proliferative podocytopathies has been linked to ligation of tumor necrosis factor receptor 2 (TNFR2) expressed on the renal parenchyma; however, the TNFR2-positive cells within the kidney responsible for podocyte injury are unknown. We detected de novo expression of TNFR2 on podocytes before hyperplastic injury in crescentic glomerulonephritis of mice with nephrotoxic nephritis, and in collapsing glomerulopathy of Tg26(HIV/nl) mice, kd/kd mice, and human beings. We further found that serum levels of soluble TNF-α and TNFR2 correlated significantly with renal injury in Tg26(HIV/nl) mice. Thus, we asked whether ligand binding of TNFR2 on podocytes ex vivo precipitates the characteristic proliferative and pro-inflammatory diseased podocyte phenotypes. Soluble TNF-α activated NF-κB and dose-dependently induced podocyte proliferation, marked by the expression of the podocyte G(1) cyclin and NF-κB target gene, cyclin D1. Microarray gene and chemokine protein expression profiling showed a marked pro-inflammatory NF-κB signature, and activated podocytes secreting CCL2- and CCL5-induced macrophage migration in transwell assays. Neutralization of TNFR2 on podocytes with blocking antibodies abrogated NF-κB activation and the induction of cyclin D1 by TNF-α, and identified TNFR2 as the primary receptor that induced IκBα degradation, the initiating event in NF-κB activation. These results suggest that TNFR2 expressed on podocytes and its canonical NF-κB signaling may directly interpose the compound pathogenic responses by podocytes to TNF-α, in the absence of other TNFR2-positive renal cell types in proliferative podocytopathies.