Unexpected transcriptional induction of monocyte chemoattractant protein 1 by proteasome inhibition: involvement of the c-Jun N-terminal kinase-activator protein 1 pathway

Regulation of TRIB1 abundance in hepatocyte models in response to proteasome inhibition

Tribbles related homolog 1 (TRIB1) contributes to lipid and glucose homeostasis by facilitating the degradation of cognate cargos by the proteasome. In view of the key metabolic role of TRIB1 and the impact of proteasome inhibition on hepatic function, we continue our exploration of TRIB1 regulation in two commonly used human hepatocyte models, transformed cell lines HuH-7 and HepG2. In both models, proteasome inhibitors potently upregulated both endogenous and recombinant TRIB1 mRNA and protein levels. Increased transcript abundance was unaffected by MAPK inhibitors while ER stress was a weaker inducer. Suppressing proteasome function via PSMB3 silencing was sufficient to increase TRIB1 mRNA expression. ATF3 was required to sustain basal TRIB1 expression and support maximal induction. Despite increasing TRIB1 protein abundance and stabilizing bulk ubiquitylation, proteasome inhibition delayed but did not prevent TRIB1 loss upon translation block. Immunoprecipitation experiments indicated that TRIB1 was not ubiquitylated in response to proteasome inhibition. A control bona fide proteasome substrate revealed that high doses of proteasome inhibitors resulted in incomplete proteasome inhibition. Cytoplasm retained TRIB1 was unstable, suggesting that TRIB1 lability is regulated prior to its nuclear import. N-terminal deletion and substitutions were insufficient to stabilize TRIB1. These findings identify transcriptional regulation as a prominent mechanism increasing TRIB1 abundance in transformed hepatocyte cell lines in response to proteasome inhibition and provide evidence of an inhibitor resistant proteasome activity responsible for TRIB1 degradation.

Phytochemical Composition, Anti-Inflammatory and ER Stress-Reducing Potential of Sambucus ebulus L. Fruit Extract

Sambucus ebulus L. (SE) fruits are used for their immunostimulation, hematopoietic and antiviral potential. Recently, we focused on analyzing the mechanism underlying SE fruit aqueous extract's (FAE) immunomodulation and anti-inflammatory activities, with attention to its endoplasmic reticulum (ER) stress-reducing potential. J774A.1 macrophages were treated with SE FAE alone or in conditions of lipopolysaccharides (LPS) stimulation. Using GC-MS and LC-MS/MS, its phytochemical composition was analyzed. To measure transcription and protein levels, we used qPCR and Western blot, respectively. The prevailing phytochemicals in SE FAE were hydroxycinnamic acids, proanthocyanidins and anthocyanins. The content of some amino acids, organic acids, alcohols, fatty acids and esters were newly reported. Extracts exerted an immunostimulation potential by stimulating IL-6, TNFα, Ccl2, COX2 and iNOS transcription, without inducing ER stress. SE FAE suppressed the LPS-induced transcription of inflammation related genes (IL-1β, IL-6, TNFα, Ccl2, Icam-1, Fabp4, COX2, iNOS, Noxo1, IL-1ra, Sirt-1) and reduced the protein levels of iNOS, peIF2α, ATF6α and CHOP. The effects were comparable to that of salicylic acid. SE suppresses LPS-stimulated inflammatory markers on the transcription and translation levels. Targeting ER stress is possibly another mechanism underlying its anti-inflammatory potential. These findings reveal the potential of SE fruits as a beneficial therapeutic of inflammation and ER stress-related pathological conditions.

The ssDNA-binding protein MEIOB acts as a dosage-sensitive regulator of meiotic recombination

Meiotic recombination enables reciprocal exchange of genetic information between parental chromosomes and is essential for fertility. MEIOB, a meiosis-specific ssDNA-binding protein, regulates early meiotic recombination. Here we report that the human infertility-associated missense mutation (N64I) in MEIOB causes protein degradation and reduced crossover formation in mouse testes. Although the MEIOB N64I substitution is associated with human infertility, the point mutant mice are fertile despite meiotic defects. Meiob mutagenesis identifies serine 67 as a critical residue for MEIOB. Biochemically, these two mutations (N64I and S67 deletion) cause self-aggregation of MEIOB and sharply reduced protein half-life. Molecular genetic analyses of both point mutants reveal an important role for MEIOB in crossover formation in late meiotic recombination. Furthermore, we find that the MEIOB protein levels directly correlate with the severity of meiotic defects. Our results demonstrate that MEIOB regulates meiotic recombination in a dosage-dependent manner.

JunB can enhance the transcription of IL-8 in oral squamous cell carcinoma

Proteasome inhibitor MG132 was shown to enhance the secretion of interleukin 8 (IL-8) by various cells. The enhancement is regulated by the transcription factor activator protein-1 (AP-1) at the transcriptional level. AP-1 is a dimer formed by AP-1 family proteins. The purpose of the present study was to explore the combinations of the AP-1 family proteins that contribute to MG132-driven IL-8 secretion. Oral squamous cell carcinoma-derived cell lines, Ca9-22 and HSC3, were used to demonstrate their response to MG132. IL-8 secretion was augmented by MG132 in both cell lines. c-Jun expression was detected in both the cell lines, whereas c-Fos expression was detected only in the HSC3. The influence of MG132 stimulation on c-Jun and c-Fos expression was further examined by western blot analysis. c-Jun expression was increased by MG132 stimulation, whereas c-Fos expression was not detected even after MG132 stimulation. As JunB is reported to inhibit the transcriptional activity of the AP-1 complex, we speculated that the c-Jun homodimer should contribute to IL-8 enhancement. Expression vectors encoding wild type and c-Jun mutants, M17 and M22-23, respectively, were constructed and transfected into the Ca9-22 cells. In contrast to our expectations, MG132-induced IL-8 secretion was significantly reduced in all the transfectants suggesting that other c-Jun members might form homodimers with c-Jun and contribute to IL-8 enhancement. Transfection of the cells with c-Jun or JunB small hairpin RNA (shRNA) reduced IL-8 secretion up to 50% and 65% of the control shRNA transfectant. Furthermore, cotransfection of both shRNA almost completely inhibited the IL-8 secretion. These results indicate that JunB not only inhibits but also enhances the transcription of c-Jun targets in combination with c-Jun.

Proteasome Inhibitors in Cancer Therapy and their Relation to Redox Regulation

Redox homeostasis is important for the maintenance of cell survival. Under physiological conditions, redox system works in a balance and involves activation of many signaling molecules. Regulation of redox balance via signaling molecules is achieved by different pathways and proteasomal system is a key pathway in this process. Importance of proteasomal system on signaling pathways has been investigated for many years. In this direction, many proteasome targeting molecules have been developed. Some of them are already in the clinic for cancer treatment and some are still under investigation to highlight underlying mechanisms. Although there are many studies done, molecular mechanisms of proteasome inhibitors and related signaling pathways need more detailed explanations. This review aims to discuss redox status and proteasomal system related signaling pathways. In addition, cancer therapies targeting proteasomal system and their effects on redox-related pathways have been summarized.

Angiotensin III increases monocyte chemoattractant protein-1 expression in cultured human proximal tubular epithelial cells

BACKGROUND/AIMS

We investigated whether angiotensin III (Ang III) is involved in monocyte recruitment through regulation of the chemokine monocyte chemoattractant protein-1 (MCP-1) in cultured human proximal tubular epithelial cells (HK-2 cells).

METHODS

We measured MCP-1 levels in HK-2 cells that had been treated with various concentrations of Ang III and Ang II type-1 (AT1) receptor antagonists at various time points. The phosphorylation states of p38, c-Jun N-terminal kinases (JNK), and extracellular-signal-regulated kinases were measured in Ang III-treated cells to explore the mitogen-activated protein kinase (MAPK) pathway. MCP-1 levels in HK-2 cell-conditioned media were measured after pre-treatment with the transcription factor inhibitors curcumin or pyrrolidine dithiocarbamate.

RESULTS

Ang III increased MCP-1 protein production in dose- and time-dependent manners in HK-2 cells, which was inhibited by the AT1 receptor blocker losartan. p38 MAPK activity increased significantly in HK-2 cells exposed to Ang III for 30 minutes, and was sustained at higher levels after 60 minutes (p < 0.05). Total phosphorylated JNK protein levels tended to increase 20 minutes after stimulation with Ang III. Pre-treatment with a p38 inhibitor, a JNK inhibitor, or curcumin significantly inhibited Ang III-induced MCP-1 production.

CONCLUSIONS

Ang III increases MCP-1 synthesis via stimulation of intracellular p38 and JNK MAPK signaling activity and subsequent activated protein-1 transcriptional activity in HK-2 cells.

Sutherlandia frutescens may exacerbate HIV-associated neuroinflammation

Background

Neuroinflammation is central to the aetiology of HIV-associated neurocognitive disorders (HAND) that are prevalent in late stage AIDS. Anti-retroviral (ARV) treatments are rolled out relatively late in the context of neuroinflammatory changes, so that their usefulness in directly preventing HAND is probably limited. It is common practice for HIV+ individuals in developing countries to make use of traditional medicines. One such medicine is Sutherlandia frutescens - commonly consumed as a water infusion. Here its efficacy as an anti-inflammatory modality in this context was investigated in an in vitro co-culture model of the blood–brain barrier (BBB).

Methods

Single cultures of human astrocytes (HA), HUVECs and primary human monocytes, as well as co-cultures (BBB), were stimulated with HIV-1 subtype B & C Tat protein and/or HL2/3 cell secretory proteins after pre-treatment with S.frutescens extract. Effects of this pre-treatment on pro-inflammatory cytokine secretion and monocyte migration across the BBB were assessed.

Results

In accordance with others, B Tat was more pro-inflammatory than C Tat, validating our model. S.frutescens decreased IL-1β secretion significantly (P < 0.0001), but exacerbated both monocyte chemoattractant protein-1 (P < 0001) – a major role player in HIV-associated neuroinflammation – and CD14+ monocyte infiltration across the BBB (P < 0.01).

Conclusions

Current data illustrates that the combined use of HL2/3 cells and the simulated BBB presents an accurate, physiologically relevant in vitro model with which to study neuroinflammation in the context of HIV/AIDS. In addition, our results caution against the use of S.frutescens as anti-inflammatory modality at any stage post-HIV infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12952-015-0031-y) contains supplementary material, which is available to authorized users.

Identification of genes and transcription factors associated with glucocorticoid response in lens epithelial cells

Prolonged glucocorticoids (GCs) treatment may lead to the formation of posterior subcapsular cataracts. The present study aimed to investigate differential gene expression in lens epithelial cells (LECs) in response to GCs using DNA microarray profiling. The gene expression profile of GSE13040 was downloaded from the Gene Expression Omnibus database, which includes 12 human LECs treated with vehicle or dexamethasone (Dex) for 4 or 16 h with six samples at each time period, of which three samples were treated with vehicle (control group) and three samples were treated with Dex (Dex group) at each time point. The differentially expressed genes (DEGs) were identified between the control group and the Dex group at each time period with the thresholds of P<0.05 and |logFC|>1. The DEGs were further analyzed using bioinformatics methods. Firstly, DEGs were subject to a hierarchical cluster analysis. Subsequently, the functional enrichment analysis was performed for the common DEGs between the two time periods. Finally, the transcription factors and binding sites of DEGs associated with response to GC stimulus were analyzed. A total of 696 and 949 DEGs were identified at 4 h and 16 h, respectively. Hierarchical cluster analysis revealed that DEG expression was higher in the Dex group than in the control group (P<0.05). A total of 13 significant functions were enriched for the 72 common DEGs at the two time periods. Chemokine (C-C motif) ligand 2 (CCL2), dual-specificity phosphatase-1 (DUSP1) and FAS were associated with the response to GC stimulus and the transcription factor c-Jun bound to promoter regulation regions of CCL2, DUSP1 and FAS. In conclusion, the transcription factors and binding sites of DEGs associated with the response of LECs to GCs may provide potential gene targets for designing and developing drugs to protect against GC-induced cataract formation.

Curcumin a potent cancer preventive agent: Mechanisms of cancer cell killing

There is no doubt that diet could effectively improve health and halt cancers. Dietary phytochemical compounds and their derivatives represent a cornucopia of effectively anticancer compounds. This review discusses existing data on the anticancer activities of curcumin, and then offers possible explanations for and mechanisms of its cancer-preventive action. This review also offers insights into the molecular mechanism and targets through which curcumin modulates cell cycle, apoptotic signals, anti-apoptotic proteins, miRNAs, Wnt/beta-catenin signaling, protein kinases, nuclear factor-κB, proteasome activation, epigenetic regulation including DNA methylation and histone modification. Finally, this review provides explanations for how curcumin reverses the multi-drug resistance (MDR) of cancer cells.

c-Jun N-Terminal Kinases Mediate a Wide Range of Targets in the Metastatic Cascade

Disseminated cancer cells rely on intricate interactions among diverse cell types in the tumor-associated stroma, vasculature, and immune system for survival and growth. Ubiquitous expression of c-Jun N-terminal kinase (jnk) genes in various cell types permits their control of metastasis. In early stages of metastasis, JNKs affect tumor-associated inflammation and angiogenesis as well as tumor cell migration and intravasation. Within the tumor stroma, JNKs are essential for the release of growth factors that promote epithelial-to-mesenchymal transition (EMT) in tumor cells. JNK3, the least ubiquitous isoform, facilitates angiogenesis by increasing endothelial cell migration. Importantly, JNK expression in tumor cells integrates stromal signals to promote tumor cell invasion. However, JNK isoforms differentially regulate migration toward the endothelial barrier. Once tumor cells enter the bloodstream, JNKs increase circulating tumor cell (CTC) survival and homing to tissues. By promoting fibrosis, JNKs improve CTC attachment to the endothelium. Once anchored, JNKs stimulate EMT to facilitate tumor cell extravasation and enhance the secretion of endothelial barrier disrupters. Tumor cells attract barrier-disrupting macrophages by JNK-dependent transcription of macrophage chemoattractant molecules. In the secondary tissue, JNKs are instrumental in the premetastatic niche and stimulate tumor cell proliferation. JNK expression in cancer cells stimulates tissue-remodeling macrophages to improve tumor colonization. However, in T-cells, JNKs alter cytokine production that increases tumor surveillance and inhibits the recruitment of tissue-remodeling macrophages. Therapeutically targeting JNKs for metastatic disease is attractive considering their promotion of metastasis; however, specific JNK tools are needed to determine their definitive actions within the context of the entire metastatic cascade.

Ginkgo biloba extract individually inhibits JNK activation and induces c-Jun degradation in human chondrocytes: potential therapeutics for osteoarthritis

Osteoarthritis (OA) is a common joint disorder with varying degrees of inflammation. The ideal anti-OA drug should have immunomodulatory effects while at the same time having limited or no toxicity. We examined the anti-inflammatory effects of Ginkgo biloba extract (EGb) in interleukin-1 (IL-1)-stimulated human chondrocytes. Chondrocytes were prepared from cartilage specimens taken from patients with osteoarthritis who had received total hip or total knee replacement. The concentrations of chemokines and the degree of cell migration were determined by ELISA and chemotaxis assays, respectively. The activation of inducible nitric oxide synthase (iNOS), mitogen-activated protein kinases (MAPKs), activator protein-1 (AP-1), and nuclear factor-kappaB (NF-κB) was determined by immunoblotting, immunohistochemistry, and electrophoretic mobility shift assay. We found that EGb inhibited IL-1-induced production of chemokines, which in turn resulted in attenuation of THP-1 cell migration toward EGb-treated cell culture medium. EGb also suppressed IL-1-stimulated iNOS expression and release of nitric oxide (NO). The EGb-mediated suppression of the iNOS-NO pathway correlated with the attenuation of activator protein-1 (AP-1) but not nuclear factor-kappaB (NF-κB) DNA-binding activity. Of the mitogen-activated protein kinases (MAPKs), EGb inhibited only c-Jun N-terminal kinase (JNK). Unexpectedly, EGb selectively caused degradation of c-Jun protein. Further investigation revealed that EGb-mediated c-Jun degradation was preceded by ubiquitination of c-Jun and could be prevented by the proteosome inhibitor MG-132. The results imply that EGb protects against chondrocyte degeneration by inhibiting JNK activation and inducing ubiquitination-dependent c-Jun degradation. Although additional research is needed, our results suggest that EGb is a potential therapeutic agent for the treatment of OA.

Transcriptional Upregulation of Plasminogen Activator Inhibitor-1 in Rat Primary Astrocytes by a Proteasomal Inhibitor MG132

Plasminogen activator inhibitor-1 (PAI-1) is a member of serine protease inhibitor family, which regulates the activity of tissue plasminogen activator (tPA). In CNS, tPA/PAI-1 activity is involved in the regulation of a variety of cellular processes such as neuronal development, synaptic plasticity and cell survival. To gain a more insights into the regulatory mechanism modulating tPA/PAI-1 activity in brain, we investigated the effects of proteasome inhibitors on tPA/PAI-1 expression and activity in rat primary astrocytes, the major cell type expressing both tPA and PAI-1. We found that submicromolar concentration of MG132, a cell permeable peptide-aldehyde inhibitor of ubiquitin proteasome pathway selectively upregulates PAI-1 expression. Upregulation of PAI-1 mRNA as well as increased PAI-1 promoter reporter activity suggested that MG132 transcriptionally increased PAI-1 expression. The induction of PAI-1 downregulated tPA activity in rat primary astrocytes. Another proteasome inhibitor lactacystin similarly increased the expression of PAI-1 in rat primary astrocytes. MG132 activated MAPK pathways as well as PI3K/Akt pathways. Inhibitors of these signaling pathways reduced MG132-mediated upregulation of PAI-1 in varying degrees and most prominent effects were observed with SB203580, a p38 MAPK pathway inhibitor. The regulation of tPA/PAI-1 activity by proteasome inhibitor in rat primary astrocytes may underlie the observed CNS effects of MG132 such as neuroprotection.

Induction of heat shock protein 70 (Hsp70) prevents neuregulin-induced demyelination by enhancing the proteasomal clearance of c-Jun

Modulating molecular chaperones is emerging as an attractive approach to treat neurodegenerative diseases associated with protein aggregation, DPN (diabetic peripheral neuropathy) and possibly, demyelinating neuropathies. KU-32 [N-(7-((2R,3R,4S,5R)-3,4-dihydroxy-5-methoxy-6,6-dimethyl-tetrahydro-2H-pyran-2-yloxy)-8-methyl-2-oxo-2H-chromen-3-yl)acetamide] is a small molecule inhibitor of Hsp90 (heat shock protein 90) and reverses sensory deficits associated with myelinated fibre dysfunction in DPN. Additionally, KU-32 prevented the loss of myelinated internodes induced by treating myelinated SC (Schwann cell)-DRG (dorsal root ganglia) sensory neuron co-cultures with NRG1 (neuregulin-1 Type 1). Since KU-32 decreased NRG1-induced demyelination in an Hsp70-dependent manner, the goal of the current study was to clarify how Hsp70 may be mechanistically linked to preventing demyelination. The activation of p42/p44 MAPK (mitogen-activated protein kinase) and induction of the transcription factor c-Jun serve as negative regulators of myelination. NRG1 activated MAPK, induced c-Jun expression and promoted a loss of myelin segments in DRG explants isolated from both WT (wild-type) and Hsp70 KO (knockout) mice. Although KU-32 did not block the activation of MAPK, it blocked c-Jun induction and protected against a loss of myelinated segments in WT mice. In contrast, KU-32 did not prevent the NRG1-dependent induction of c-Jun and loss of myelin segments in explants from Hsp70 KO mice. Overexpression of Hsp70 in myelinated DRG explants prepared from WT or Hsp70 KO mice was sufficient to block the induction of c-Jun and the loss of myelin segments induced by NRG1. Lastly, inhibiting the proteasome prevented KU-32 from decreasing c-Jun levels. Collectively, these data support that Hsp70 induction is sufficient to prevent NRG1-induced demyelination by enhancing the proteasomal degradation of c-Jun.

Opioid-induced chemokine expression requires NF-κB activity: the role of PKCζ

Opioid receptor agonists induce broad immunomodulatory activity, which substantially alters host defense and the inflammatory response. Previous studies have shown that the MOR selective agonist DAMGO has the capacity to increase the expression of the proinflammatory chemokines CCL2, CCL5, and CXCL10 in human PBMCs. NF-κB is a transcription factor that plays a pivotal role in innate and adaptive immune responses. We report that NF-κB is a vital player in the DAMGO-induced, MOR-mediated regulation of chemokine expression. Results show that NF-κB inhibitors prevent the induction of CCL2 expression in response to DAMGO administration and that the NF-κB subunit, p65, is phosphorylated at serine residues 311 and 536 in response to MOR activation. Furthermore, we demonstrate that PKCζ is phosphorylated following DAMGO-induced MOR activation, and this kinase is essential for NF-κB activation as well as CCL2 expression and transcriptional activity. Finally, ChIP analysis shows that DAMGO administration induces binding of p65 to the enhancer region of the CCL2 promoter. These data are consistent with the notion that MOR activation promotes a proinflammatory response, which involves NF-κB activation. Our results also suggest a significant and novel role for PKCζ as an essential participant in the MOR-mediated regulation of proinflammatory chemokine expression.

ASK1 negatively regulates the 26 S proteasome

The 26 S proteasome, composed of the 20 S core and 19 S regulatory particle, plays a central role in ubiquitin-dependent proteolysis. Disruption of this process contributes to the pathogenesis of the various diseases; however, the mechanisms underlying the regulation of 26 S proteasome activity remain elusive. Here, cell culture experiments and in vitro assays demonstrated that apoptosis signal-regulating kinase 1 (ASK1), a member of the MAPK kinase kinase family, negatively regulated 26 S proteasome activity. Immunoprecipitation/Western blot analyses revealed that ASK1 did not interact with 20 S catalytic core but did interact with ATPases making up the 19 S particle, which is responsible for recognizing polyubiquitinated proteins, unfolding them, and translocating them into the 20 S catalytic core in an ATP-dependent process. Importantly, ASK1 phosphorylated Rpt5, an AAA ATPase of the 19 S proteasome, and inhibited its ATPase activity, an effect that may underlie the ability of ASK1 to inhibit 26 S proteasome activity. The current findings point to a novel role for ASK1 in the regulation of 26 S proteasome and offer new strategies for treating human diseases caused by proteasome malfunction.

Sphingosine kinase-1 is required for toll mediated beta-defensin 2 induction in human oral keratinocytes

Background

Host defense against invading pathogens is triggered by various receptors including toll-like receptors (TLRs). Activation of TLRs is a pivotal step in the initiation of innate, inflammatory, and antimicrobial defense mechanisms. Human β-defensin 2 (HBD-2) is a cationic antimicrobial peptide secreted upon Gram-negative bacterial perturbation in many cells. Stimulation of various TLRs has been shown to induce HBD-2 in oral keratinocytes, yet the underlying cellular mechanisms of this induction are poorly understood.

Principal Findings

Here we demonstrate that HBD-2 induction is mediated by the Sphingosine kinase-1 (Sphk-1) and augmented by the inhibition of Glycogen Synthase Kinase-3β (GSK-3β) via the Phosphoinositide 3-kinase (PI3K) dependent pathway. HBD-2 secretion was dose dependently inhibited by a pharmacological inhibitor of Sphk-1. Interestingly, inhibition of GSK-3β by SB 216763 or by RNA interference, augmented HBD-2 induction. Overexpression of Sphk-1 with concomitant inhibition of GSK-3β enhanced the induction of β-defensin-2 in oral keratinocytes. Ectopic expression of constitutively active GSK-3β (S9A) abrogated HBD-2 whereas kinase inactive GSK-3β (R85A) induced higher amounts of HBD-2.

Conclusions/Significance

These data implicate Sphk-1 in HBD-2 regulation in oral keratinocytes which also involves the activation of PI3K, AKT, GSK-3β and ERK 1/2. Thus we reveal the intricate relationship and pathways of toll-signaling molecules regulating HBD-2 which may have therapeutic potential.

SP600125, an inhibitor of c-Jun NH2-terminal kinase, blocks expression of angiotensin II-induced monocyte chemoattractant protein-1 in human mesangial cells

BACKGROUND

We investigated the role of c-Jun NH2-terminal kinase (JNK), a member of the mitogen-activated protein kinase family, in the expression of angiotensin II (Ang II)-induced monocyte chemoattractant protein-1 (MCP-1) and transforming growth factor-1 (TGF-1), and in the production of fibronectin (FN), by human mesangial cells (HMCs).

METHODS

JNK activation in cultured human mesangial cells was determined by Western blotting with an antibody against the phosphorylated Ser63 residue of c-Jun. Binding of the activator protein (AP-1) to the MCP-1 AP-1 motif was detected via the electrophoretic mobility shift assay (EMSA). The transient luciferase reporter was used to examine MCP-1 promoter activity; an RNase protection assay and ELISA were used respectively to detect the expression of MCP-1 mRNA and production of MCP-1, TGF-beta and FN.

RESULTS

Anthra (1,9-cd) pyrazol-6(2H)-one (SP600125), a pharmacological inhibitor of JNK, almost completely abolished Ang II-induced Ser63 phosphorylation of c-Jun at concentrations of 5-20 micromol/L: JNK activity was reduced by 75% with 10 micromol/L SP600125, and by 90% with 20 micromol/L. Ang II increased AP-1 binding to the MCP-1 AP-1 motif in a time-dependent manner, as detected by EMSA, while SP600125 effectively blocked this increased AP-1 binding in a concentration-dependent manner. Treatment with 100 nmol/L Ang II led to a steady increase in MCP-1 mRNA expression, and to an enhanced production of MCP-1, TGF-beta and FN. These effects were blocked by SP60025 in a dose-dependent manner. SP600125 also reduced MCP-1 mRNA stability: the halflife of MCP-1 mRNA was approximately 5 hours in cells treated with Ang II only, but was reduced to 2 hours when treated with a combination of Ang II and SP600125.

CONCLUSIONS

These results show that the JNK/AP-1 pathway is involved in the expression of MCP-1 and TGF-beta, and in extracellular matrix production. JNK is an important therapeutic target for glomerulonephritis and glomerulosclerosis.

c-Jun NH2-terminal kinase regulates lipopolysaccharide-induced pulmonary mononuclear cell recruitment via CCL2

Subsequent to the initial recruitment of neutrophils, monocytes are recruited to the lung after an injurious insult. Previously the authors have shown that inhibition of either p38 or c-Jun NH(2)-terminal kinase (JNK) decreased pulmonary neutrophil recruitment in mice exposed to lipopolysaccharide (LPS). As the signaling pathways regulating the influx of mononuclear cells to the lung are poorly understood, the authors undertook the present study to examine the roles of p38 and JNK. In a model of LPS-induced lung inflammation, systemic inhibition of JNK, but not p38, decreased the recruitment of mononuclear cells to the lung. Levels of CCL2 (monocyte chemoattractant protein 1 [MCP-1]) were decreased in the setting of JNK inhibition, with LPS-induced pulmonary mononuclear cell recruitment in CCL2-deficient mice similar to that found with JNK inhibition. The decrease in LPS-induced CCL2 levels in the lung seen with JNK inhibition, however, was independent of neutrophil recruitment, as systemic depletion of neutrophils had no effect on pulmonary CCL2 levels after LPS exposure. In sum, these results suggest that JNK, but not p38, regulates LPS-induced mononuclear cell recruitment to the lung, that this occurs through a CCL2-dependent pathway, and that LPS-induced pulmonary CCL2 expression is dependent on JNK but independent of pulmonary neutrophil recruitment.

Proteasomal inhibition upregulates the endogenous MAPK deactivator MKP-1 in human airway smooth muscle: mechanism of action and effect on cytokine secretion

Asthma is a chronic inflammatory condition. Inhibition of the ubiquitin-proteasome system offers promise as a anti-inflammatory strategy, being responsible for the degradation of key proteins involved in crucial cellular functions, including gene expression in inflammation (e.g. inhibitory IkappaB-alpha and the endogenous MAPK deactivator - MKP-1). As MKP-1 inhibits MAPK-mediated pro-remodeling functions in human airway smooth muscle (ASM; a pivotal immunomodulatory cell in asthma) in this study we investigate the effect of the proteasome inhibitor MG-132 on MKP-1 and evaluate the anti-inflammatory effect of MG-132 on cytokine secretion from ASM cells. Examining the time-course of induction of MKP-1 mRNA and protein by MG-132 (10microM) we show that MKP-1 mRNA was first detected at 30min, increased to significant levels by 4h, resulting in a 12.6+/-1.5-fold increase in MKP-1 mRNA expression by 24h (P<0.05). MKP-1 protein levels corroborate the mRNA results. Investigating the effect of MG-132 on secretion of the cytokine IL-6 we show that while short-term pretreatment with MG-132 (30min) partially reduced TNFalpha-induced IL-6 via inhibition of IkappaB-alpha degradation and the NF-kappaB pathway, longer-term proteasome inhibition (up to 24h) robustly upregulated MKP-1 and was temporally correlated with repression of p38-mediated IL-6 secretion from ASM cells. Moreover, utilizing a cytokine array we show that MG-132 represses the secretion of multiple cytokines implicated in asthma. Taken together, our results demonstrate that MG-132 upregulates MKP-1 and represses cytokine secretion from ASM and highlight the potential of the proteasome as a therapeutic target in asthma.

Curcumin inhibits phorbol myristate acetate (PMA)-induced MCP-1 expression by inhibiting ERK and NF-kappaB transcriptional activity

Monocyte chemoattractant protein-1 (MCP-1) is a potent mediator of macrophage migration and therefore, plays an essential role in early events of inflammation. In the present study, we show the protein kinase C activator, phorbol myristate acetate (PMA), potently induced mRNA expression and secretion of the C-C chemokine MCP-1 in U937 cells. We found that curcumin, a natural biologically active compound extracted from rhizomes of Curcuma species, significantly inhibited the PMA-induced increase in MCP-1 expression and secretion. These effects of curcumin are dose dependent and correlate with the suppression of MCP-1 mRNA expression levels. Curcumin inhibited PMA-mediated activation of extracellular signal-regulated kinase (ERK) and NF-kappaB transcriptional activity. Therefore, one possible anti-inflammatory mechanism of curcumin may be to inhibit the secretions of inflammatory MCP-1 chemokine.

Induction of chemokines, MCP-1, and KC in the mutant huntingtin expressing neuronal cells because of proteasomal dysfunction

Huntington's disease is a hereditary neurodegenerative disorder caused by an aberrant polyglutamine expansion in the amino terminus of the huntingtin protein. The resultant mutant huntingtin form aggregates in neurons and causes neuronal dysfunction and degeneration in many ways including transcriptional dysregulation. Here, we report that the expression of mutant huntingtin in the mouse neuroblastoma cell results in massive transcriptional induction of several chemokines including monocyte chemoattractant protein-1 (MCP-1) and murine chemokine (KC). The mutant huntingtin expressing cells also exhibit proteasomal dysfunction and down-regulation of NF-kappaB activity in a time-dependent manner and both these phenomena regulate the expression of MCP-1 and KC. The expression of MCP-1 and KC are increased in the mutant huntingtin expressing cells in response to mild proteasome inhibition. However, the expression of MCP-1 and KC and proteasome activity are not altered and inflammation is rarely observed in the brain of 12-week-old Huntington's disease transgenic mice in comparison with their age-matched controls. Our result suggests that the mutant huntingtin-induced proteasomal dysfunction can up-regulate the expression of MCP-1 and KC in the neuronal cells and therefore might trigger the inflammation process.

Proteasome inhibitor differentially regulates expression of the major immediate early genes of human cytomegalovirus in human central nervous system-derived cell lines

Proteasome inhibitor, which inhibits NF-kappaB activation, has been reported to activate c-Jun N-terminal kinase (JNK)-c-Jun pathway. In this study, we investigated the effects of proteasome inhibitor on the human cytomegalovirus (HCMV) major immediate early (MIE) gene expression in human central nervous system (CNS)-derived cell lines. Treatment of HCMV-infected 118MGC glioma and U373-MG astrocytoma cells with three proteasome inhibitors, MG132, clasto-lactacystin beta-lactone, and epoxomicin, suppressed MIE protein expression. In contrast, in HCMV-infected IMR-32 neuroblastoma cells, the proteasome inhibitors increased MIE protein expression, even in the presence of NF-kappaB inhibitor SN-50. A luciferase reporter assay demonstrated that MG132 markedly elevated the MIE promoter/enhancer (MIEP) activity in IMR-32 cells, but down-regulated it in 118MGC and U373-MG cells. Mutation in five cAMP response elements (CREs) within the MIEP resulted in a loss of the ability to respond to MG132 in IMR-32 cells. Moreover, Western blotting analysis revealed that MG132 induced c-Jun phosphorylation in all three CNS-derived cell lines, whereas a high level of activating transcription factor-2 (ATF-2) phosphorylation was observed only in IMR-32 cells. Finally, MG132-induced MIE protein expression was suppressed by JNK inhibitor that reduced the phosphorylation levels of both c-Jun and ATF-2. Taken together, these results suggest that the proteasome inhibitors activate CRE binding proteins consisting of c-Jun and ATF-2 through activating the JNK-c-Jun pathway, thereby inducing MIE protein synthesis in IMR-32 cells under the condition where NF-kappaB activity is inhibited.

Regulation of human beta-defensin-2 by Mycobacterium bovis bacillus Calmette-Guérin (BCG): involvement of PKC, JNK, and PI3K in human lung epithelial cell line (A549)

Human beta-defensin (HBD)-2 is an inducible antimicrobial peptide that plays an important role in innate immunity. Induction of this peptide by mycobacteria in epithelial cells has been reported. However, the mechanism(s) by which Mycobacterium bovis bacillus Calmette-Guérin (BCG) triggers gene transcription of HBD-2 remains poorly understood. In the present work we found that treatment of human epithelial cells with Ro32-0432 or Gö6976, two selective inhibitors of protein kinase C (PKC), significantly reduced the effect of M. bovis BCG on induced HBD-2 mRNA expression (65 and 80% inhibition by 10microM Ro32-0432, and 1microM Gö6976 as assessed by real-time PCR, respectively). Moreover, there was increased activation of c-Jun N-terminal kinase (JNK) and phosphatidylinositol-3-kinase (PI3K)/Akt in A549 cells infected with M. bovis BCG, and this JNK and PI3K activation was mediated through PKC. Finally, we found that M. bovis BCG-induced HBD-2 mRNA gene expression in A549 cells was dependent on JNK, and PI3K determined by real-time PCR analysis, which was attenuated by inhibitors of JNK (SP600125 and AG126), and PI3K (wortmannin and Ly294002). These studies are the first to show that M. bovis BCG-induced HBD-2 mRNA expression in A549 cells is regulated at least in part through activation of signaling proteins of PKC, JNK and PI3K.

c-Jun controls histone modifications, NF-kappaB recruitment, and RNA polymerase II function to activate the ccl2 gene

Interleukin-1 (IL-1)-induced mRNA expression of ccl2 (also called MCP-1), a prototypic highly regulated inflammatory gene, is severely suppressed in cells lacking c-Jun or Jun N-terminal protein kinase 1 (JNK1)/JNK2 genes and is only partially restored in cells expressing a c-Jun(SS63/73AA) mutant protein. We used chromatin immunoprecipitation to identify three c-Jun-binding sites located in the far 5' region close to the transcriptional start site and in the far 3' region of murine and human ccl2 genes. Mutational analysis revealed that the latter two sites contribute to ccl2 transcription in response to the presence of IL-1 or of ectopically expressed c-Jun-ATF-2 dimers. Further experiments comparing wild-type and c-Jun-deficient cells revealed that c-Jun regulates Ser10 phosphorylation of histone H3, acetylation of histones H3 and H4, and recruitment of histone deacetylase 3 (HDAC3), NF-kappaB subunits, and RNA polymerase II across the ccl2 locus. c-Jun also coimmunoprecipitated with p65 NF-kappaB and HDAC3. Based on DNA microarray analysis, c-Jun was required for full expression of 133 out of 162 IL-1-induced genes. For inflammatory genes, these data support the idea of an activator function of c-Jun that is executed by multiple mechanisms, including phosphorylation-dependent interaction with p65 NF-kappaB and HDAC3 at the level of chromatin.

Divergent effect of proteasome inhibition on interleukin-1beta and tumor necrosis factor alpha signaling in human astroglial cells

Impaired functioning of the proteasome pathway is one of the molecular mechanism underlying neurodegenerative changes in Alzheimer's disease. In this study, we report that dysfunction of the proteasome pathway in astroglial cells leads to decreased survival and dysregulation of chemokines by differential regulation of the nuclear factor kappa B and c-jun N-terminal kinase (JNK) pathways. We further demonstrated that proteasome inhibition augmented interleukin-1 beta- and tumor necrosis factor-alpha-induced activation of the IkappaBalpha kinase and MKK4/JNK/c-Jun pathway along with TAK1 activation. These results suggest that impaired function of the proteasome pathway may potentiate the immuno-pathologic role of secondarily activated astrocytes in the brain.

"Spicing up" of the immune system by curcumin

Curcumin (diferuloylmethane) is an orange-yellow component of turmeric (Curcuma longa), a spice often found in curry powder. Traditionally known for its an antiinflammatory effects, curcumin has been shown in the last two decades to be a potent immunomodulatory agent that can modulate the activation of T cells, B cells, macrophages, neutrophils, natural killer cells, and dendritic cells. Curcumin can also downregulate the expression of various proinflammatory cytokines including TNF, IL-1, IL-2, IL-6, IL-8, IL-12, and chemokines, most likely through inactivation of the transcription factor NF-kappaB. Interestingly, however, curcumin at low doses can also enhance antibody responses. This suggests that curcumin's reported beneficial effects in arthritis, allergy, asthma, atherosclerosis, heart disease, Alzheimer's disease, diabetes, and cancer might be due in part to its ability to modulate the immune system. Together, these findings warrant further consideration of curcumin as a therapy for immune disorders.

"Spicing up" of the immune system by curcumin

Curcumin (diferuloylmethane) is an orange-yellow component of turmeric (Curcuma longa), a spice often found in curry powder. Traditionally known for its an antiinflammatory effects, curcumin has been shown in the last two decades to be a potent immunomodulatory agent that can modulate the activation of T cells, B cells, macrophages, neutrophils, natural killer cells, and dendritic cells. Curcumin can also downregulate the expression of various proinflammatory cytokines including TNF, IL-1, IL-2, IL-6, IL-8, IL-12, and chemokines, most likely through inactivation of the transcription factor NF-kappaB. Interestingly, however, curcumin at low doses can also enhance antibody responses. This suggests that curcumin's reported beneficial effects in arthritis, allergy, asthma, atherosclerosis, heart disease, Alzheimer's disease, diabetes, and cancer might be due in part to its ability to modulate the immune system. Together, these findings warrant further consideration of curcumin as a therapy for immune disorders.

Alpha-Tocopherol counteracts ritonavir-induced proinflammatory cytokines expression in differentiated THP-1 cells

Treatment of HIV-infected individuals with HIV protease inhibitor (HPI) drugs has significantly increased their life span. However, one of the side effects of HPI drugs is the development of premature atherosclerosis, whose molecular pathogenesis remains unclear. Previously we have reported that alpha-tocopherol (alpha-T) normalizes CD36 overexpression induced by ritonavir treatment and reduces oxLDL uptake in THP-1 cells. Since inflammation is a major player in the pathogenesis of atherosclerosis, we hypothesized that HPI drugs, such as ritonavir, increase proinflammatory cytokines synthesis and that alpha-T supplementation counteracts this effect by suppressing proinflammatory cytokines levels. Here, we report that after differentiating THP-1 cells to macrophages, ritonavir treatment (10 microg/mL) significantly increases expression of proinflammatory cytokines, IL-6, MCP-1 and IL-8, at both mRNA and protein levels. This ritonavir-induced effect is significantly suppressed by treatment of THP-1/macrophages with 50 muM alpha-T. We conclude that ritonavir can induce proinflammatory cytokines synthesis in THP-1/macrophages, which might be associated with the development of premature atherosclerosis in ritonavir-treated patients and that this effect is prevented by alpha-T.

Glomerular and tubular induction of the transcription factor c-Jun in human renal disease

The transcription factor c-Jun regulates the expression of genes involved in proliferation and inflammation in many cell types but its role in human renal disease is largely unclear. In the current study we investigated whether c-Jun activation is associated with human renal disease and if c-Jun activation regulates pro-inflammatory and pro-fibrotic genes in renal cells. Activation of c-Jun was quantified by scoring renal expression of phosphorylated c-Jun (pc-Jun) in control human renal tissue and in biopsies from patients with various renal diseases (diabetic nephropathy, focal glomerulosclerosis, hypertension, IgA nephropathy, membranous glomerulopathy, minimal change disease, membranoproliferative glomerulonephritis, systemic lupus erythematosus, acute rejection, and Wegener's granulomatosis); this was correlated with parameters of renal damage. Furthermore, we studied the functional role of c-Jun activation in human tubular epithelial cells (HK-2) stimulated with TGF-beta. Activated c-Jun was present in nuclei of glomerular and tubular cells in all human renal diseases, but only sporadically in controls. Across the diseases, the extent of pc-Jun expression correlated with the degree of focal glomerulosclerosis, interstitial fibrosis, cell proliferation, kidney injury molecule-1 (Kim-1) expression, macrophage accumulation, and impairment of renal function. In HK-2 cells, TGF-beta induced c-Jun activation after 1 h (+40%, p < 0.001) and 24 h (+160%, p < 0.001). The specific c-Jun N-terminal kinase (JNK) inhibitor SP600125 abolished c-Jun phosphorylation at all time points and blunted TGF-beta- or BSA-induced procollagen-1alpha 1 and MCP-1 gene expression in HK-2 cells. We conclude that in human renal disease, the transcription factor c-Jun is activated in glomerular and tubular cells. Activation of c-Jun may be involved in the regulation of inflammation and/or fibrosis in human renal disease.

Opposing action of curcumin and green tea polyphenol in human keratinocytes

Persistent environmental insult can convert a normal cell into a cancer cell. However, various natural chemopreventive agents called antioxidants can retard this progression. We have recently explored the effects of several chemopreventive agents, including green tea polyphenol and curcumin, on normal human keratinocyte function. Our findings suggest that a bioactive polyphenol from green tea, (-)-epigallocatechin-3-gallate (EGCG), acts to increase involucrin gene expression, suggesting that EGCG treatment enhances normal human keratinocyte differentiation. Mechanistic studies indicate that EGCG alters mitogen-activated protein kinase cascade function to activate involucrin gene transcription via a Ras, MEKK1, MEK3, ERK1/2-p38delta cascade that targets AP1 and CAATT enhancer binding protein transcription factors. These findings suggest that EGCG may inhibit disease progression by promoting keratinocyte differentiation. Parallel studies indicate that not all antioxidants produce a similar response. Curcumin, an antioxidant derived from the turmeric, antagonizes the EGCG-dependent response by interfering in this signaling pathway. These studies suggest that different antioxidant may produce antagonistic effects in tissues.

Molecular targets of dietary agents for prevention and therapy of cancer

While fruits and vegetables are recommended for prevention of cancer and other diseases, their active ingredients (at the molecular level) and their mechanisms of action less well understood. Extensive research during the last half century has identified various molecular targets that can potentially be used not only for the prevention of cancer but also for treatment. However, lack of success with targeted monotherapy resulting from bypass mechanisms has forced researchers to employ either combination therapy or agents that interfere with multiple cell-signaling pathways. In this review, we present evidence that numerous agents identified from fruits and vegetables can interfere with several cell-signaling pathways. The agents include curcumin (turmeric), resveratrol (red grapes, peanuts and berries), genistein (soybean), diallyl sulfide (allium), S-allyl cysteine (allium), allicin (garlic), lycopene (tomato), capsaicin (red chilli), diosgenin (fenugreek), 6-gingerol (ginger), ellagic acid (pomegranate), ursolic acid (apple, pears, prunes), silymarin (milk thistle), anethol (anise, camphor, and fennel), catechins (green tea), eugenol (cloves), indole-3-carbinol (cruciferous vegetables), limonene (citrus fruits), beta carotene (carrots), and dietary fiber. For instance, the cell-signaling pathways inhibited by curcumin alone include NF-kappaB, AP-1, STAT3, Akt, Bcl-2, Bcl-X(L), caspases, PARP, IKK, EGFR, HER2, JNK, MAPK, COX2, and 5-LOX. The active principle identified in fruit and vegetables and the molecular targets modulated may be the basis for how these dietary agents not only prevent but also treat cancer and other diseases. This work reaffirms what Hippocrates said 25 centuries ago, let food be thy medicine and medicine be thy food.

Farnesyl and geranylgeranyl transferase inhibitors induce G1 arrest by targeting the proteasome

Isoprenoid inhibitors are being evaluated as agents for the treatment of cancer. Their antitumor activity is attributed to inhibition of post-translational modification of Ras, which is crucial for its translocation and attachment to the plasma membrane, and ultimate involvement in signal transduction. However, whether blocking of Ras is solely responsible for the observed antitumor activity is unresolved. In this report, we propose an alternate mechanism. Using breast tumor models, we show that agents possessing a lactone moiety, including statins (such as lovastatin) and the isoprenoid inhibitors (such as FTI-277 and GGTI-298), mediate their cell cycle inhibitory activities by blocking the chymotrypsin activity of the proteasome in vitro. This results in the accumulation of cyclin-dependent kinase inhibitors p21 and p27 with subsequent G(1) arrest. Cells devoid of p21 were refractory to the growth-inhibitory activity of lovastatin, FTI-277, and GGTI-298. However, in these p21 null cells, isoprenylation of key substrates of farnesyl transferase (such as Ras) and of geranylgeranyl transferase (such as RAP-1) were inhibited by FTI-277 and GGTI-298, respectively, suggesting that although both these isoprenoid inhibitors reached and inhibited their intended targets, inhibition of the isoprenylation of Ras and RAP-1A are not sufficient to mediate G(1) arrest. We also show that the cell cycle effects can be attributed to the functional lactone moiety of the aforementioned agents. Collectively, our data suggest that FTI and GGTI and other agents containing an active lactone moiety mediate G(1) arrest via inhibition of the proteasome and up-regulation of p21, independent of the inhibition of isoprenylation of Ras or RAP-1.

Proteasome blockade exerts an antifibrotic activity by coordinately down-regulating type I collagen and tissue inhibitor of metalloproteinase-1 and up-regulating metalloproteinase-1 production in human dermal fibroblasts

Tissue fibrosis results when dysregulation of extracellular matrix (ECM) turnover favors deposition of collagen and other ECM proteins over degradation. Fibrosis may then lead to organ dysfunction and pathology as observed in systemic sclerosis (SSc). In the present study, we investigated the antifibrotic properties of proteasome blockade. A dose- and time-dependent reduction in type-I collagen and tissue inhibitor of metalloproteinase-1 (TIMP-1) production was observed in normal fibroblasts exposed to proteasome inhibitors (PI). In the same culture conditions, metalloproteinase-1 (MMP-1) protein and the collagenolytic activity on type I collagen was increased. The steady-state mRNA levels of COL1A1, TIMP-1, and MMP-1 paralleled protein levels. These effects were dominant over the profibrotic properties of TGF-beta and were observed with fibroblasts generated from normal and SSc skin. PI decreased type I collagen mRNA levels with kinetics similar to those observed with DRB, a specific RNA polymerase II inhibitor, thus indicating transcriptional inhibition. Of interest, PI induced c-Jun phosphorylation and c-Jun nuclear accumulation. The specific N-terminal Jun-kinase inhibitor SP-600125 selectively abrogated c-Jun phosphorylation and, in a dose-dependent fashion, the up-regulated synthesis of MMP-1 induced by PI. Finally, PI did not affect fibroblast viability. Thus, the coordinated down-regulation of collagen and TIMP-1 and up-regulation of MMP-1 renders proteasome blockade an attractive strategy for treating conditions as SSc, characterized by excessive fibrosis.

Glycogen synthase kinase 3beta functions to specify gene-specific, NF-kappaB-dependent transcription

Loss of glycogen synthase kinase 3beta (GSK-3beta) in mice results in embryonic lethality via hepatocyte apoptosis. Consistent with this result, cells from these mice have diminished nuclear factor kappaB (NF-kappaB) activity, implying a functional role for GSK-3beta in regulating NF-kappaB. Here, we have explored mechanisms by which GSK-3beta may control NF-kappaB function. We show that cytokine-induced IkappaB kinase activity and subsequent phosphorylation of IkappaBalpha, p105, and p65 are not affected by the absence of GSK-3beta activity. Furthermore, nuclear accumulation of p65 following tumor necrosis factor treatment is unaffected by the loss of GSK-3beta. However, NF-kappaB DNA binding activity is reduced in GSK-3beta null cells and in cells treated with a pharmacological inhibitor of GSK-3. Expression of certain NF-kappaB-regulated genes, such as IkappaBalpha and macrophage inflammatory protein 2, is minimally affected by the absence of GSK-3beta. Conversely, we have identified a subset of NF-kappaB-regulated genes, including those for interleukin-6 and monocyte chemoattractant protein 1, that require GSK-3beta for efficient expression. We show that efficient localization of p65 to the promoter regions of the interleukin-6 and monocyte chemoattractant protein 1 genes following tumor necrosis factor alpha treatment requires GSK-3beta. Therefore, GSK-3beta has profound effects on transcription in a gene-specific manner through a mechanism involving control of promoter-specific recruitment of NF-kappaB.

Osmotic Regulation of MG-132-induced MAP-kinase Phosphatase MKP-1 Expression in H4IIE Rat Hepatoma Cells

BACKGROUND/AIMS

Proteasome inhibitors such as MG-132 are considered as potential therapeutical tools in different clinical settings. The dual specificity MAP-kinase phosphatase MKP-1 plays a role in balancing signals mediating cell death or survival. Here the effect of cell hydration on MG-132-induced MKP-1 expression was investigated in H4IIE rat hepatoma cells.

RESULTS

Hyperosmolarity (405mosmol/l) increased MKP-1 expression by MG-132, which was accompanied by an induction of c-Fos, c-Jun, cJun Ser73 phosphorylation, and AP-1 DNA binding. MKP-1 induction by MG-132 plus hyperosmolarity was sensitive to inhibition of p38(MAPK) and c-Jun-N-terminal kinases (JNKs) but not extracellular signal-regulated kinases Erk-1/Erk-2, and was accompanied by a decline of MAP-kinase activities. Although hyperosmolarity increased overall protein ubiquitination in presence of MG-132, ubiquitination of MKP-1 was found under normo-, but not hyperosmotic conditions. Hyperosmolarity also enabled MG-132 to induce poly-ADP-ribose polymerase (PARP) cleavage which was sensitive to inhibition of p38(MAPK) and JNKs but not Erk-1/Erk-2. PARP cleavage and caspase-3 activation in H4IIE cells treated with hyperosmolarity plus MG-132 was further increased by vanadate, consistent with a contribution of MKP-1 to counterbalance proapoptotic MAP-kinase signals.

CONCLUSION

The findings suggest that among other factors cell hydration critically determines the cellular response to proteasome inhibitors.

Transcriptional regulation of cyclooxygenase-2 in response to proteasome inhibitors involves reactive oxygen species-mediated signaling pathway and recruitment of CCAAT/enhancer-binding protein delta and CREB-binding protein

Inhibition of ubiquitin-proteasome pathway has been shown to be a promising strategy for the treatment of inflammation and cancer. Here, we show that proteasome inhibitors MG132, PSI-1, and lactacystin induce COX-2 expression via enhancing gene transcription rather than preventing protein degradation in the human alveolar NCI-H292 and A549, and gastric AGS epithelial cells. NF-IL6 and CRE, but not NF-kappaB elements on the COX-2 promoter were involved in the gene transcription event. The binding of CCAAT/enhancer binding protein (C/EBP)beta and C/EBPdelta to the CRE and NF-IL6 elements, as well as the recruitment of CBP and the enhancement of histone H3 and H4 acetylation on the COX-2 promoter was enhanced by MG132. However, it did not affect the total protein levels of C/EBPbeta and C/EBPdelta. MG132-induced DNA-binding activity of C/EBPdelta, but not C/EBPbeta was regulated by p38, PI3K, Src, and protein kinase C. Small interfering RNA of C/EBPdelta suppressed COX-2 expression, further strengthening the role of C/EBPdelta in COX-2 gene transcription. In addition, the generation of intracellular reactive oxygen species (ROS) in response to MG132 contributed to the activation of MAPKs and Akt. These findings reveal that the induction of COX-2 transcription induced by proteasome inhibitors requires ROS-dependent protein kinases activation and the subsequent recruitments of C/EBPdelta and CBP.

Up-regulation of astrocyte cyclooxygenase-2, CCAAT/enhancer-binding protein-homology protein, glucose-related protein 78, eukaryotic initiation factor 2 alpha, and c-Jun N-terminal kinase by a neurovirulent murine retrovirus

In susceptible strains of mice, infection with the mutant retrovirus MoMuLV-ts1 causes a neurodegeneration and immunodeficiency syndrome that resembles human human immunodeficiency virus-acquired immunodeficiency syndrome (HIV-AIDS). In this study the authors show increased expression of cyclooxygenase-2 (COX-2) in the brainstem tissues of ts1-infected mice. Up-regulated central nervous system (CNS) levels of this enzyme are associated with HIV-associated dementia and other inflammatory and neurodegenerative diseases such as amyotrophic lateral sclerosis, Alzheimer's disease, and Parkinson's disease. In brainstem sections, the authors find that astrocytes surrounding spongiform lesions contain increased amounts of immunoreactive COX-2. COX-2 is also up-regulated in cultured ts1-infected cells from the C1 astrocytic cell line, and activation of c-Jun N-terminal kinase, or JNK, pathway. Markers of endoplasmic reticulum (ER) stress, specifically the CCAAT/enhancer-binding protein (CHOP), the glucose-related protein 78 (GRP78), and phosphorylated eukaryotic initiation factor 2 alpha (eIF2 alpha), were also up-regulated in ts1-infected C1 astrocytes. Up-regulation of COX-2 and the above ER signaling factors was reversed by treatment of the infected cells with curcumin which specifically inhibits the JNK/c-Jun pathway. These findings indicate that the JNK/c-Jun pathway is most likely responsible for COX-2 expression induced by ts1 in astrocytes, and that ts1 infection in astrocytes may lead to up-regulation of both inflammatory and ER stress pathways in the central nervous system. Because COX-2 inhibitors are now widely used to treat inflammatory conditions in animals and humans, this finding suggests that these drugs may be useful for therapeutic intervention in neurodegenerative syndromes as well.

Tetraspanin CD81 provides a costimulatory signal resulting in increased human immunodeficiency virus type 1 gene expression in primary CD4+ T lymphocytes through NF-kappaB, NFAT, and AP-1 transduction pathways

The tetraspanin superfamily member CD81 has been shown to form microdomains in the plasma membrane and to participate in the recruitment of numerous adhesion molecules, receptors, and signaling proteins in the central zone of the immune synapse. Beside its structural role, CD81 also delivers a cosignal for T cells to trigger cytokine production and cellular proliferation, thus suggesting a key role in some fundamental biological functions. It has been shown that signaling events initiated through the T-cell receptor (TCR)/CD3 complex and the coactivator CD28 positively affect human immunodeficiency virus type 1 (HIV-1) gene expression, but no study had investigated the putative costimulatory activity of CD81 on HIV-1 transcriptional activity. We observed that CD81 engagement potentiates TCR/CD3-mediated signaling, resulting in an enhancement of HIV-1 transcription and de novo virus production in both established Jurkat cells and primary CD4+ T lymphocytes at a magnitude that approximates that with CD28. These observations were made by using transiently transfected plasmids (i.e., nonintegrated viral DNA) and fully competent viruses (i.e., stably integrated provirus). Moreover, the CD81-mediated enhancement of HIV-1 gene expression is linked with increased nuclear translocation of transcription factors known to positively regulate virus transcription, i.e., NF-kappaB, NFAT, and AP-1. These findings suggest that engagement of CD81 decreases the signaling threshold required to initiate TCR/CD3-mediated induction of integrated HIV-1 proviral DNA in primary CD4+ T cells.

Characterization of signaling pathways leading to Fas expression induced by TNF‐α: pivotal role of NF‐κB

TNF-alpha is known to induce a strong up-regulation of Fas expression in mouse Sertoli cell cultures, leading to their apoptosis triggered by effector FasL-bearing cells. These data suggest that increased Fas expression on the cell surface might be a key event in the pathogenesis of autoimmune orchitis, by inducing a leakage of the blood-tubular barrier as a consequence of Sertoli cell apoptosis. In the present paper, we have investigated the signal transduction mechanisms involved in the regulation of Fas expression induced by TNF-alpha in mouse Sertoli cells. We studied the role of the transcription factor NF-kappaB and of MAPKs in regulating Fas expression. By using Sertoli cells transfected with a NF-kappaB Luc reporter gene, we proved that TNF-alpha activates the IkappaB/NF-kappaB system. Moreover, the use of the proteasome inhibitor lactacystin led us to demonstrate that NF-kappaB is required for TNF-alpha mediated Fas expression. By using specific inhibitors for each MAPK, we confirmed the pivotal role of the IkappaB/NF-kappaB system by demonstrating that ERKs, p38, and JNK are not involved in Fas up-regulation by TNF-alpha. The comprehension of these pathways could be relevant to the knowledge of the pathogenesis of autoimmune disorders in immune privileged districts of the body.

Regulation of serum response factor-dependent gene expression by proteasome inhibitors

Serum response factor (SRF) is activated by contractile and hypertrophic agonists, such as endothelin-1 (ET1) to stimulate expression of cytoskeletal proteins in vascular smooth muscle cells (VSMCs). While studying the regulation of smooth muscle alpha-actin (SMA) expression at the level of protein stability, we discovered that inhibition of proteasome-dependent protein degradation by N-benzoyloxycarbonyl (Z)-Leu-Leu-leucinal (MG132) or lactacystin (LC) did not enhance the levels of SMA, but, unexpectedly, attenuated SMA expression in response to ET1, without affecting the viability of VSMCs. Down-regulation of SMA protein by MG132 or LC occurred at the level of SMA transcription and via the inhibition of SRF activity. By contrast, MG132 and LC potentiated the activity of activator protein-1 transcription factor. Regulation of SRF by MG132 was not related to inhibition of nuclear factor-kappaB, an established target of proteasome inhibitors, and was not mediated by protein kinase A, a powerful regulator of SRF activity. Signaling studies indicate that inhibition of ET1-induced SRF activity by MG132 occurs at the level downstream of heterotrimeric G proteins Gq/11 and G13, of small GTPase RhoA, and of actin dynamics but at the level of SRF-DNA binding. MG132 treatment did not result in ubiquitination or accumulation of SRF. By contrast, the levels of c-Jun were rapidly increased upon incubation of cells with MG132, and ectopic overexpression of c-Jun mimicked the effect of MG132 on SRF activity. Together, these data suggest that inhibition of proteasome results in down-regulation of SMA expression via up-regulation of c-Jun and repression of SRF activity at the level of DNA binding.

Antioxidants regulate normal human keratinocyte differentiation

Cancer begins with a normal cell that, due to persistent environmental insult, is transformed, via a series of progressively more insidious steps, into a cancer cell. A major goal of chemopreventive therapy is to alter the normal cell response to the environmental agent with the goal of inhibiting disease progression. (-)-Epigallocatechin-3-gallate (EGCG) is an important bioactive green tea antioxidant that possesses remarkable cancer chemopreventive properties. We have recently explored the hypothesis that EGCG prevents cancer by promoting keratinocyte differentiation. Based on our findings, we argue that EGCG acts to enhance the differentiation of normal keratinocytes. This is a potentially important finding, as it represents a novel mechanism of disease inhibition by EGCG--cancer preventive "differentiation therapy". However, not all antioxidant chemopreventive agents work by this mechanism. Curcumin, for example, inhibits the differentiation-promoting activity of EGCG. This report discusses the mechanism of EGCG and curcumin action in regulating expression of involucrin, a marker of keratinocyte differentiation.

Reactive oxygen species mediate chloroquine-induced expression of chemokines by human astroglial cells

We have previously demonstrated that chloroquine may evoke inflammatory responses in the central nervous system by inducing expression of pro-inflammatory cytokines by astroglial cells. In this study, we further examined the molecular mechanism responsible for chloroquine-induced activation of NF-kappaB and subsequent expression of chemokines by astroglial cells. We observed that (1) chloroquine induced expression of chemokines such as CCL2 and CXCL8 in a dose- and time-dependent manner in human astroglial cells; (2) other lysosomotropic agents such as ammonium chloride and bafilomycin A1 had minimal effects on chemokine expression; (3) inhibition of NF-kappaB by MG-132 and TPCK suppressed chloroquine-induced mRNA expression of chemokines; (4) chloroquine increased the intracellular level of reactive oxygen species (ROS) in a dose- and time-dependent manner by human astroglial cells, but not by monocytic/microglial cells; (5) chloroquine-induced increase of intracellular ROS level was suppressed by pre-incubation with diphenyl iodonium (DPI) and N-acetyl cysteine (NAC); and (6) inhibition of chloroquine-induced ROS production by DPI or NAC suppressed chloroquine-mediated activation of NF-kappaB and subsequent mRNA expression of chemokines in astroglial cells. These results collectively suggest that chloroquine generates ROS, which is responsible for NF-kappaB activation and subsequent expression of pro-inflammatory chemokines in human astroglial cells.

Ectopic expression of nonliganded retinoic acid receptor beta abrogates AP-1 activity by selective degradation of c-Jun in cervical carcinoma cells

Expression of the nuclear retinoic acid receptor beta2 (RARbeta2) gene is often disturbed in cervical carcinoma cells. One important mechanism by which RARbeta2 can exert growth inhibitory function is based on its ability to repress the AP-1 transcription factor in a ligand-dependent manner. Because less is known about the biological effects of RARbeta in the absence of ligand, the corresponding cDNA was stably introduced into HPV18-positive HeLa cervical carcinoma cells. In the present study we describe a novel mechanism by which AP-1 becomes inactivated. Constitutive expression of nonliganded RARbeta abrogated both AP-1 binding affinity and activity by a selective degradation of the c-Jun protein as major dimerization partner, without substitution by other members of the Jun family. Blockage of the proteasomal pathway completely rescued c-Jun and reconstituted the AP-1 function. Moreover, HeLa RARbeta2 clones treated either with tumor necrosis factor-alpha or transfected with a constitutive active upstream mitogen-activated protein kinase (MEKK1Delta) also resulted in c-Jun phosphorylation and restoration of AP-1 affinity and functionality similar to that found in nontransfected parental HeLa cells. These data revealed an important cross-talk between trans-repression of AP-1 and nonliganded RARbeta in human papillomavirus-positive cells. Because AP-1 activity was not irreversibly disturbed, but could be switched on through activation of the Jun N-terminal kinase pathway, a model for the transient activation of AP-1 even in the presence of RARbeta as repressor is suggested.

AP-1-independent sensitization to oxidative stress-induced apoptosis by proteasome inhibitors

Hydrogen peroxide (H(2)O(2)) induces apoptosis of mesangial cells via c-Jun N-terminal kinase (JNK)-activator protein-1 (AP-1) and extracellular signal-regulated kinase (ERK)-AP-1 pathways. We recently found that subtoxic doses of proteasome inhibitors, MG132 and lactacystin, dramatically enhanced H(2)O(2)-induced apoptosis in mesangial cells. In this report, we examined molecular mechanisms involved in this phenomenon, especially focusing on AP-1 pathways. Reporter assays showed that MG132 induced activation of AP-1. However, pharmacological inhibitors of AP-1, retinoic acid, and curcumin, did not suppress the proapoptotic effect of MG132. Suppression of JNK-AP-1 by transfection with either a dominant-negative mutant of JNK or a dominant-negative mutant of c-Jun did not attenuate the apoptosis enhancement by MG132. Similarly, suppression of ERK-AP-1 by PD98059 or dominant-negative mutants of ERK did not affect the apoptosis-promoting effect of MG132. Interestingly, pretreatment with MG132 did not enhance activation of AP-1 by H(2)O(2). These data suggested a novel, AP-1-independent promotion of apoptosis by proteasome inhibitors.

Green tea polyphenol and curcumin inversely regulate human involucrin promoter activity via opposing effects on CCAAT/enhancer-binding protein function

Antioxidants are important candidate agents for the prevention of disease. However, the possibility that different antioxidants may produce opposing effects in tissues has not been adequately explored. We have reported previously that (-)-epigallocatechin-3-gallate (EGCG), a green tea polyphenol antioxidant, stimulates expression of the keratinocyte differentiation marker, involucrin (hINV), via a Ras, MEKK1, MEK3, p38delta signaling cascade (Balasubramanian, S., Efimova, T., and Eckert, R. L. (2002) J. Biol. Chem. 277, 1828-1836). We now show that EGCG activation of this pathway results in increased CCAAT/enhancer-binding protein (C/EBPalpha and C/EBPbeta) factor level and increased complex formation at the hINV promoter C/EBP DNA binding site. This binding is associated with increased promoter activity. Mutation of the hINV promoter C/EBP binding site eliminates the regulation as does expression of GADD153, a dominant-negative C/EBP factor. In contrast, a second antioxidant, curcumin, inhibits the EGCG-dependent promoter activation. This is associated with inhibition of the EGCG-dependent increase in C/EBP factor level and C/EBP factor binding to the hINV promoter. Curcumin also inhibits the EGCG-dependent increase in endogenous hINV levels. The curcumin-dependent suppression of C/EBP factor level is inhibited by treatment with the proteasome inhibitor MG132, suggesting that the proteasome function is required for curcumin action. We conclude that curcumin and EGCG produce opposing effects on involucrin gene expression via regulation of C/EBP factor function. The observation that two antioxidants can produce opposite effects is an important consideration in the context of therapeutic antioxidant use.

Dual regulation of tumor necrosis factor-alpha-induced CCL2/monocyte chemoattractant protein-1 expression in vascular smooth muscle cells by nuclear factor-kappaB and activator protein-1: modulation by type III phosphodiesterase inhibition

Monocyte/macrophage infiltration to the subendothelial space of arterial wall is a critical initial step in atherogenesis, in which CC chemokine ligand 2 (CCL2)/monocyte chemoattractant protein-1 (MCP-1) is thought to play a key role. This study investigated the effectiveness of phosphodiesterase inhibitors, including the nonselective pentoxifylline (PTX) and the selective type III (cilostamide) and type IV (denbufylline) inhibitors, on cytokine-induced CCL2/MCP-1 production in cultured rat vascular smooth muscle cells (VSMCs), and the signal transduction mechanisms whereby they act. Our results showed that tumor necrosis factor (TNF)-alpha induced a marked increase in CCL2/MCP-1 production in dose- and time-dependent manners. 2-(2-Amino-3-methoxyphenyl)-4H-1-benzopyran-4-one (PD98059), 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio) butadiene (U0126) [both inhibitors of p42/44 mitogen-activated protein kinase (MAPK) kinase], and anthra[1hyphen]9-cd]pyrazol-6(2H)-one (SP600125) [an inhibitor of c-Jun NH(2)-terminal kinases (JNKs)] attenuated TNF-alpha-induced CCL2/MCP-1 production, without affecting I-kappaBalpha degradation or p65/nuclear factor-kappaB (NF-kappaB) nuclear translocation. PD98059 abolished TNF-alpha-activated p42/44 MAPK phosphorylation and c-Fos up-regulation, whereas SP600125 inhibited TNF-alpha-activated JNK and c-Jun phosphorylation. The NF-kappaB inhibitor carbobenzoxy-l-leucyl-l-leucyl-l-leucinal (MG132) attenuated TNF-alpha-induced CCL2/MCP-1 production in the presence of increased phospho-JNK and phospho-c-Jun levels. When SP600125 was added simultaneously, MG132 completely inhibited TNF-alpha-induced CCL2/MCP-1 production. Finally, the pretreatment of VSMCs with PTX or cilostamide, but not denbufylline, reduced TNF-alpha-induced CCL2/MCP-1 production, which was preceded by attenuation of p65/NF-kappaB nuclear translocation, p42/44 MAPK, and JNK-c-Jun phosphorylation, and c-Fos up-regulation. These data indicate that TNF-alpha-stimulated CCL2/MCP-1 production in rat VSMCs is dually regulated by activator protein-1 (AP-1) and NF-kappaB pathways, and inhibition of type III phosphodiesterase contributes substantially to the suppressive effect of PTX on CCL2/MCP-1 production via down-regulation of AP-1 and NF-kappaB signals.