Seongjoon Park

Amelioration of age-related inflammation and oxidative stress by PPARγ activator: Suppression of NF-κB by 2,4-thiazolidinedione

Abstract Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily of transcription factors and are key regulators in various pathophysiological processes related to energy metabolism including lipid and carbohydrate metabolism and inflammation. PPARγ signaling pathways are reported to exert anti-inflammatory effects by inhibition of NF-κB. We previously reported that age-related oxidative stress and inflammatory reactions cause reduced PPARγ during the aging process. In present study, we investigated the action of 2,4-thiazolidinedione (2,4-TZD), a well-known PPARγ activator, on aging process using kidneys from Fischer 344 rats, young (9-month-old), old (22-month-old) and old-2,4-TZD fed (4xa0mg/kg for 10 days). The results showed that the 2,4-TZD treatment brought about several major changes, decrease of: (1) age-related oxidative stress; (2) p65 translocation and NF-κB binding activity; (3) NF-κB-regulated gene expression, inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and inflammatory mediators such as interleukin-1β (IL-1β), IL-6, adhesion molecules, VCAM-1 and P-selectin; and (4) age-related disturbance of the redox-status. Therefore, we concluded that 2,4-TZD exerted significant anti-oxidative and anti-inflammatory effects in aged rats, most likely by its ability to attenuate oxidative stress. We propose that 2,4-TZD or other potent PPARγ activators may be useful in the therapy against age-related inflammation.

Short-term feeding of baicalin inhibits age-associated NF-κB activation

Abstract Baicalin is a flavonoid isolated from Scutellaria baicalensis and is known to affect multiple biological functions, including the inhibition of aldose reductase, HIV infection, and nitric oxide producing activity. Oxidative stress is considered a major cause of aging and various age-related diseases, and among the key cellular components exquisitely sensitive to oxidative stress is the transcription factor, nuclear factor-κB (NF-κB). In the present study, we attempted to elucidate the mechanisms underlying the suppression of age-related NF-κB activation by baicalin in kidney tissue from old rats. Results showed NF-κB activation and the upregulation of NF-κB targeting genes, hemoxygenase-1, inducible nitric oxide synthase (iNOS), and COX-2 with age. In contrast, the increased expression of these NF-κB targeting genes was effectively inhibited by baicalin. Baicalin was shown to inhibit the NF-κB cascade via three signal transduction pathways, NIK/IKK, extracellular signal-regulated kinase (ERK), and p38 mitogen-activated protein kinase (MAPK). Our results clearly indicated the anti-oxidative effects of baicalin on age-related redox imbalance. Thus, the significance of the current study is the new information revealing the anti-oxidative properties of baicalin and the role it plays in the regulation of age-related alterations.

The histone demethylase JMJD1A regulates adrenomedullin-mediated cell proliferation in hepatocellular carcinoma under hypoxia

We studied the roles of JMJD1A and its target gene ADM in the growth of hepatocellular carcinomas (HCCs) and breast cancer cells under hypoxic conditions. Hypoxia stimulated HepG2 and Hep3B cell proliferation but had no effect on MDA-MB-231 cell proliferation. Interestingly, the JMJD1A and ADM expressions were enhanced by hypoxia only in HepG2 and Hep3B cells. Our ChIP results showed that hypoxia-induced HepG2 and Hep3B cell proliferation is mediated by JMJD1A upregulation and subsequent decrease in methylation in the ADM promoter region. Furthermore, JMJD1A gene silencing abrogated the hypoxia-induced ADM expression and inhibited HepG2 and Hep3B cell growth. These data suggest that JMJD1A might function as a proliferation regulator in some cancer cell types.

Low-dose radiation activates Nrf1/2 through reactive species and the Ca2+/ERK1/2 signaling pathway in human skin fibroblast cells

In the current study, we explored the effect of LDR on the activation of Nrfs transcription factor involved in cellular redox events. Experiments were carried out utilizing 0.05 and 0.5 Gy X-ray irradiated normal human skin fibroblast HS27 cells. The results showed LDR induced Nrf1 and Nrf2 activation and expression of antioxidant genes HO-1, Mn-SOD, and NQO1. In particular, 0.05 Gy-irradiation increased only Nrf1 activation, but 0.5 Gy induced both Nrf1 and Nrf2 activation. LDR-mediated Nrf1/2 activation was accompanied by reactive species (RS) generation and Ca2+ flux. This effect was abolished in the presence of N-acetyl-cysteine and BAPTA- AM. Furthermore, Nrf1/2 activation by LDR was suppressed by PD98059, an inhibitor of ERK1/2. In conclusion, LDR induces Nrf1 and Nrf2 activation and expression of Nrf-regulated antioxidant defense genes through RS and Ca2+/ERK1/2 pathways, suggesting new insights into the molecular mechanism underlying the beneficial role of LDR in HS27 cells. [BMB Reports 2013; 46(5): 258-263]

Histone demethylase JMJD2B-mediated cell proliferation regulated by hypoxia and radiation in gastric cancer cell

Histone modifying factors are functional components of chromatin and play a role in gene regulation. The expression level of JMJD2B, a histone demethylase, is notably up-regulated in cancer tissues. Upregulation of JMJD2B promotes cancer cell proliferation under hypoxic conditions through target gene expression. Here, we describe the patterns of histone methylation and JMJD2B expression under various stressed conditions, such as hypoxia and radiation, in a gastric cancer cell line. JMJD2B expression in AGS cells was actively regulated by hypoxia and radiation. Chromatin immunoprecipitation experiments demonstrated that binding of JMJD2B on the cyclin A1 (CCNA1) promoter resulted in CCNA1 upregulation under hypoxic conditions. Furthermore, we confirmed that AGS cell proliferation was directly affected by JMJD2B and CCNA1 expression by performing experiments with JMJD2B depleted cells. Interestingly, the effects of JMJD2B on cell growth under hypoxia were remarkably repressed after gamma-ray irradiation. These results suggest that JMJD2B may play a central role in gastric cancer cell growth and might constitute a novel therapeutic target to overcome hypoxia-induced radio-resistance, thereby improving the efficiency of radiation therapy.

Growth phase-differential quorum sensing regulation of anthranilate metabolism in Pseudomonas aeruginosa

Pseudomonas quinolone signal (PQS) plays a role in the regulation of virulence genes and it is intertwined in the las/rhl quorum sensing (QS) circuits of Pseudomonas aeruginosa. PQS is synthesized from anthranilate by pqsA-D and pqsH whose expression is influenced by the las/rhl systems. Since anthranilate can be degraded by functions of antABC and catBCA, PQS synthesis might be regulated by the balance between the expression of the pqsA-D/phnAB, pqsH, antABC, and catBCA gene loci. antA and catA are repressed by LasR during log phase and activated by RhlR in late stationary phase, whereas pqsA-E/phnAB is activated by LasR in log phase and repressed by RhlR. QscR represses both but each repression occurs in a different growth phase. This growth phase-differential regulation appears to be accomplished by the antagonistic interplay of LasR, RhlR, and QscR, mediated by two intermediate regulators, AntR and PqsR, and their cofactors, anthranilate and PQS, where the expressions of antR and pqsR and the production of anthranilate and PQS are growth phase-differentially regulated by QS systems. Especially, the anthranilate level increases in an RhlR-dependent manner at late stationary phase. From these results, we suggest that RhlR and LasR regulate the anthranilate metabolism in a mutually antagonistic and growth phase-differential manner by affecting both the expressions and activities of AntR and PqsR, and that QscR also phase-differentially represses both LasR and RhlR functions in this regulation.

Interspecies signaling through QscR, a quorum receptor of Pseudomonas aeruginosa

The QS machinery of Pseudomonas aeruginosa, an opportunistic human pathogen, consists of three acyl-homoserine lactone (acyl-HSL) signaling systems, LasR-I, RhlR-I, and QscR. QscR, known as an orphan receptor and a repressor of other QS systems, operates its own regulon using N-3-oxododecanoyl HSL (3OC12), which is synthesized by LasI, as its signal. In this study, we addressed the role of QscR in interspecies communication. We found that QscR auto-activates its own transcription in the presence of 3OC12. In a single population of P. aeruginosa, where 3OC12 is the sole signal available for QscR, the QscR regulon is activated by 3OC12 produced by the LasI-R system. However, the broad signal specificity of QscR allowed it to respond to a non-P. aeruginosa signal, such as N-decanoyl HSL (C10) and N-3-hydroxydecanoyl HSL (3OHC10), which preferentially activated QscR to LasR. The signal extracts from Pseudomonas fluorescens and Burkholeria vietnamiensis also preferentially activated QscR. These non-P. aeruginosa signals activated QscR more strongly than 3OC12, the authentic P. aeruginosa signal. Since a variety of acyl-HSLs are produced in the multi-species habitat of nature, our study provides a clue for the particular situation that allows QscR to secede from the conventional QS cascade in mixed microbial community.

Naphthazarin enhances ionizing radiation-induced cell cycle arrest and apoptosis in human breast cancer cells

Naphthazarin (Naph, DHNQ, 5,8-dihydroxy-l,4-naphthoquinone) is one of the naturally available 1,4-naphthoquinone derivatives that are well-known for their anti-inflammatory, antioxidant, antibacterial and antitumor cytotoxic effects in cancer cells. Herein, we investigated whether Naph has effects on cell cycle arrest and apoptosis in MCF-7 human breast cancer cells exposed to ionizing radiation (IR). Naph reduced the MCF-7 cell viability in a dose-dependent manner. We also found that Naph and/or IR increased the p53-dependent p21 (CIP/WAF1) promoter activity. Noteworthy, our ChIP assay results showed that Naph and IR combined treatment activated the p21 promoter via inhibition of binding of multi-domain proteins, DNMT1, UHRF1 and HDAC1. Apoptosis and cell cycle analyses demonstrated that Naph and IR combined treatment induced cell cycle arrest and apoptosis in MCF-7 cells. Herein, we showed that Naph treatment enhances IR-induced cell cycle arrest and death in MCF-7 human breast cancer cells through the p53-dependent p21 activation mechanism. These results suggest that Naph might sensitize breast cancer cells to radiotherapy by enhancing the p53-p21 mechanism activity.

Inhibitory action of salicylideneamino-2-thiophenol on NF-κB signaling cascade and cyclooxygenase-2 in HNE-treated endothelial cells

In the present study, the anti-inflammatory effect of salicylideneamino-2-thiophenol (SAL-2), a derivative of salicylate, on a potent oxidant 4-hydroxynonenal (HNE)-induced oxidative stress was investigated using rat prostate endothelial (YPEN-1) cells. We focused on anti-inflammatory activity of SAL-2 which was determined by its ability to suppress COX-2 and iNOS gene expression through suppression of NF-κB and redox regulation. We found that SAL-2 effectively inhibited HNE-induced reactive species generation, while upregulated GSH/GSSG ratio. Prostagrandin (PG) E2 production stimulated by arachidonic acid was suppressed by SAL-2. SAL-2 also downregulated COX-2 and iNOS expression induced by HNE, but salicylate did not. We found that SAL-2 inhibited HNE-mediated IKK phosphorylation, IκBα degradation and nuclear translocation of p65 which are linked to NF-κB activation. Furthermore, SAL-2 inhibited HNE-induced activation of mitogen-activated protein kinases. Collectively, SAL-2 inhibited COX-2 and iNOS gene expression through suppression of NF-κB leading to the inhibition of PGE2 synthesis. Based on these data, we propose that with its combined effect on strong anti-oxidant and anti-inflammatory action, SAL-2 can be a potent anti-inflammatory agent for treatment of inflammatory-related diseases.

Novel anti-cancer role of naphthazarin in human gastric cancer cells.

Gastric cancer is one of the most common malignant tumors and the second cause of cancer-related deaths worldwide. Naphthoquinones such as juglone and plumbagin are compounds used extensively to overcome resistance to chemotherapeutic agents in cancers due to their cytotoxic role. This study is the first to investigate the anti-cancer effect of naphthazarin (Naph), one of the naphthaquinones, in human gastric cancer AGS cells. We showed that Naph exhibited effective preferential cell growth inhibition via G2/M phase arrest and apoptosis, which was associated with reduced levels of Cdc2 and Cdc25C expression. Naph also increased cleaved caspase-3 and Poly ADR(adenosine diphosphate ribose) Polymerase expression, γ-H2AX expression (an indicator of DNA double strand breaks) and DNA fragmentation. We also found the generation of reactive oxygen species is a critical mediator in Naph-induced cell growth inhibition and apoptosis. The non-protein antioxidant, glutathione significantly abolished Naph-mediated inhibition of cell growth and apoptosis. Taken together, our findings showed that Naph not only inhibited cell growth, but also induced apoptosis of AGS cells, suggesting that Naph may be a potential candidate for cancer therapy against gastric cancers.