Transcriptional regulation of heme oxygenase-1 gene expression by MAP kinases of the JNK and p38 pathways in primary cultures of rat hepatocytes

Heme oxygenase-1 (HO-1) gene expression is induced by various oxidative stress stimuli including sodium arsenite. Since mitogen-activated protein kinases (MAPKs) are involved in stress signaling we investigated the role of arsenite and MAPKs for HO-1 gene regulation in primary rat hepatocytes. The Jun N-terminal kinase (JNK) inhibitor SP600125 decreased sodium arsenite-mediated induction of HO-1 mRNA expression. HO-1 protein and luciferase activity of reporter gene constructs with -754 bp of the HO-1 promoter were induced by overexpression of kinases of the JNK pathway and MKK3. By contrast, overexpression of Raf-1 and ERK2 did not affect expression whereas overexpression of p38alpha, beta, and delta decreased and p38gamma increased HO-1 expression. Electrophoretic mobility shift assays (EMSA) revealed that a CRE/AP-1 element (-668/-654) bound c-Jun, a target of the JNK pathway. Deletion or mutation of the CRE/AP-1 obliterated the JNK- and c-Jun-dependent up-regulation of luciferase activity. EMSA also showed that an E-box (-47/-42) was bound by a putative p38 target c-Max. Mutation of the E-box strongly reduced MKK3, p38 isoform-, and c-Max-dependent effects on luciferase activity. Thus, the HO-1 CRE/AP-1 element mediates HO-1 gene induction via activation of JNK/c-Jun whereas p38 isoforms act through a different mechanism via the E-box.     

Role of the JNK/c-Jun/AP-1 signaling pathway in galectin-1-induced T-cell death

Galectin-1 (gal-1), an endogenous β-galactoside-binding protein, triggers T-cell death through several mechanisms including the death receptor and the mitochondrial apoptotic pathway. In this study we first show that gal-1 initiates the activation of c-Jun N-terminal kinase (JNK), mitogen-activated protein kinase kinase 4 (MKK4), and MKK7 as upstream JNK activators in Jurkat T cells. Inhibition of JNK activation with sphingomyelinase inhibitors (20 μM desipramine, 20 μM imipramine), with the protein kinase C-δ (PKCδ) inhibitor rottlerin (10 μM), and with the specific PKCθ pseudosubstrate inhibitor (30 μM) indicates that ceramide and phosphorylation by PKCδ and PKCθ mediate gal-1-induced JNK activation. Downstream of JNK, we observed increased phosphorylation of c-Jun, enhanced activating protein-1 (AP-1) luciferase reporter, and AP-1/DNA-binding in response to gal-1. The pivotal role of the JNK/c-Jun/AP-1 pathway for gal-1-induced apoptosis was documented by reduction of DNA fragmentation after inhibition JNK by SP600125 (20 μM) or inhibition of AP-1 activation by curcumin (2 μM). Gal-1 failed to induce AP-1 activation and DNA fragmentation in CD3-deficient Jurkat 31-13 cells. In Jurkat E6.1 cells gal-1 induced a proapoptotic signal pattern as indicated by decreased antiapoptotic Bcl-2 expression, induction of proapoptotic Bad, and increased Bcl-2 phosphorylation. The results provide evidence that the JNK/c-Jun/AP-1 pathway plays a key role for T-cell death regulation in response to gal-1 stimulation.     

The involvement of p62–Keap1–Nrf2 antioxidative signaling pathway and JNK in the protection of natural flavonoid quercetin against hepatotoxicity

Quercetin, one of the most abundant dietary flavonoids, is reported to have protective function against various hepatotoxicant-induced hepatotoxicity. The present study aims to investigate the critical role of the nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidative signaling pathway in the protection of quercetin against hepatotoxicity. Quercetin prevented the cytotoxicity induced by a variety of hepatotoxicants including clivorine (Cliv), acetaminophen (APAP), ethanol, carbon tetrachloride (CCl₄), and toosendanin (TSN) in human normal liver L-02 cells. Quercetin induced the nuclear translocation of Nrf2, along with the increased expression of the antioxidant responsive element (ARE)-dependent genes like catalytic or modify subunit of glutamate-cysteine ligase (GCLC/GCLM), and heme oxygenase-1 (HO-1). In addition, the HO-1 inhibitor zinc protoporphyrin (ZnPP) and the GCL inhibitor L-buthionine-(S,R)-sulfoximine (BSO) both reduced the hepatoprotection induced by quercetin. Quercetin had no effect on kelch-like ECH-associated protein-1(Keap1) expression, but molecular docking results indicated the potential interaction of quercetin with the Nrf2-binding site in Keap1 protein. Quercetin increased the expression of p62, and p62 siRNA decreased quercetin-induced hepatoprotection. Quercetin induced the activation of c-Jun N-terminal kinase (JNK) in hepatocytes. JNK inhibitor SP600125 and JNK siRNA both reduced quercetin-induced hepatoprotection. SP600125 and JNK siRNA decreased the increased p62 expression induced by quercetin. In addition, SP600125 also decreased the increased mRNA and protein expression of GCLC, GCLM, and HO-1 induced by quercetin. Taken together, our present study demonstrates that quercetin prevents hepatotoxicity by inducing p62 expression, inhibiting the binding of Keap1 to Nrf2, and thus leading to the increased expression of antioxidative genes dependent on Nrf2. Meanwhile, our study indicates that JNK plays some regulation in this process.     

Piperine protects cisplatin-induced apoptosis via heme oxygenase-1 induction in auditory cells

Piperine is a major component of black pepper, Piper nigrum Linn, used widely in traditional medicine. In this study, we examined whether piperine could protect House Ear Institute-Organ of Corti 1 (HEI-OC1) cells against cisplatin-induced apoptosis through the induction of heme oxygenase (HO)-1 expression. Piperine (10-100 microM) induced the expression of HO-1 in dose- and time-dependent manners. Piperine also induced antioxidant response element-luciferase and translocated nuclear factor-E2-related factor-2 (Nrf2) to nucleus. Piperine activated the c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase and p38 mitogen-activated protein kinase (MAPK) pathways, and the JNK pathway played an important role in piperine-induced HO-1 expression. Piperine protected the cells against cisplatin-induced apoptosis. The protective effect of piperine was abrogated by zinc protoporphyrin IX, an HO inhibitor, and antisense oligodeoxynucleotides against HO-1 gene. These results demonstrate that the expression of HO-1 by piperine is mediated by both JNK pathway and Nrf2, and the expression inhibits cisplatin-induced apoptosis in HEI-OC1 cells.     

Induction of Heme Oxygenase-1 by Na+-H+ Exchanger 1 Protein Plays a Crucial Role in Imatinib-resistant Chronic Myeloid Leukemia Cells

Resistance toward imatinib (IM) and other BCR/ABL tyrosine kinase inhibitors remains troublesome in the treatment of advanced stage chronic myeloid leukemia (CML). The aim of this study was to estimate the reversal effects of down-regulation of Na⁺/H⁺ exchanger 1 (NHE1) on the chemoresistance of BCR-ABL-positive leukemia patients'' cells and cell lines. After treatment with the specific NHE1 inhibitor cariporide to decrease intracellular pH (pH_i), the heme oxygenase-1 (HO-1) levels of the K562R cell line and cells from IM-insensitive CML patients decreased. HO-1, as a Bcr/Abl-dependent survival molecule in CML cells, is important for the resistance to tyrosine kinase inhibitors in patients with newly diagnosed CML or IM-resistant CML. Silencing PKC-β and Nrf-2 or treatment with inhibitors of p38 pathways obviously blocked NHE1-induced HO-1 expression. Furthermore, treatment with HO-1 or p38 inhibitor plus IM increased the apoptosis of the K562R cell line and IM-insensitive CML patients'' cells. Inhibiting HO-1 enhanced the activation of caspase-3 and poly(ADP-ribose) polymerase-1. Hence, the results support the anti-apoptotic role of HO-1 induced by NHE1 in the K562R cell line and IM-insensitive CML patients and provide a mechanism by which inducing HO-1 expression via the PKC-β/p38-MAPK pathway may promote tumor resistance to oxidative stress.     

Genipin up-regulates heme oxygenase-1 via PI3-kinase-JNK1/2-Nrf2 signaling pathway to enhance the anti-inflammatory capacity in RAW264.7 macrophages

Genipin, an aglycon of geniposide, has been reported to exhibit diverse pharmacological functions such as antitumor and anti-inflammatory effects. This study aimed to elucidate the anti-inflammatory mechanism of genipin, focusing particularly on the role of heme oxygenase-1 (HO-1), a potent anti-inflammatory enzyme. In RAW264.7 cells, genipin increased HO-1 expression and its enzyme activity via a NF-E2-related factor 2 (Nrf2)–antioxidant response element (ARE) pathway. These effects were significantly inhibited by exposure to the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor, LY294002, or by expression of a dominant negative mutant of PI 3-kinase. Additional experiments showed that the activation of c-Jun NH₂-terminal kinase 1/2 (JNK1/2) is required for genipin-induced phosphorylation and nuclear translocation of Nrf2 and antioxidant response element (ARE)-driven induction of HO-1, and acts as a downstream effector of PI 3-kinase. Furthermore, functional significance of HO-1 induction was revealed by genipin-mediated inhibition of lipopolysaccharide-stimulated inducible nitric oxide synthase expression or cyclooxygenase-2 promoter activity, the response was reversed by the blocking of HO-1 protein synthesis or HO-1 enzyme activity. Therefore, identification of PI 3-kinase-JNK1/2-Nrf2-linked signaling cascade in genipin-mediated HO-1 expression defines the signaling event that could participate in genipin-mediated anti-inflammatory response.     

CREB1 regulates glucose transport of glioma cell line U87 by targeting GLUT1

Chemical modification of chitosan is a promising method for the improvement of biological activity. In this study, chitosan-caffeic acid (CCA) was prepared and its in vitro hepatoprotective ability against hydrogen peroxide-induced hepatic damage in liver cells was evaluated. Treatment with CCA (50–400 µg/mL) did not show cytotoxicity and also significantly (p < 0.05) recovered cell viability against 650 µM hydrogen peroxide-induced hepatotoxicity. CCA treatment attenuated reactive oxygen species generation and lipid peroxidation in addition to increasing cellular glutathione level in cultured hepatocytes. To validate the underlying mechanism, antioxidant and phase II detoxifying enzyme expressions, which are mediated by NF-E2-related factor 2 (Nrf2) activation, were analyzed and CCA treatment was found to increase the expression of superoxide dismutase-1 (SOD-1), glutathione reductase (GR), heme oxygenase-1 (HO-1), and NAD(P)H:quinine oxidoreductase 1 (NQO1). CCA treatment resulted in increased Nrf2 nuclear translocation. The phosphorylation of extracellular regulated kinase (ERK), c-Jun NH₂-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK) by CCA treatment contributed to Nrf2 activation. Pharmacological blockade of ERK, JNK, and p38 MAPK revealed that SP600125 (JNK inhibitor) and PD98059 (ERK inhibitor) treatment reduced Nrf2 translocation into the nucleus while SB203580 (p38 inhibitor) exhibited weak inhibition. Collectively, CCA protects liver cells against hydrogen peroxide-induced injury and this ability is attributed to the induction of antioxidants and phase II detoxifying enzymes that are mediated by Nrf2 translocation via JNK/ERK signaling.     

Salvianolic acid A protects RPE cells against oxidative stress through activation of Nrf2/HO-1 signaling

Reactive oxygen species (ROS) impair the physiological functions of retinal pigment epithelial (RPE) cells, which is known as one major cause of age-related macular degeneration. Salvianolic acid A (Sal A) is the main effective aqueous extract of Salvia miltiorrhiza. The aim of this study was to test the potential role of Sal A against oxidative stress in cultured RPE cells and to investigate the underlying mechanistic signaling pathways. We observed that Sal A significantly inhibited hydrogen peroxide (H₂O₂)-induced primary and transformed RPE cell death and apoptosis. H₂O₂-stimulated mitogen-activated protein kinase activation, ROS production, and subsequent proapoptotic AMP-activated protein kinase activation were largely inhibited by Sal A. Further, Sal A stimulation resulted in a fast and dramatic activation of Akt/mammalian target of rapamycin complex 1 (mTORC1) signaling, followed by phosphorylation, accumulation, and nuclear translocation of the NF-E2-related factor 2 (Nrf2), along with increased expression of the antioxidant-response element-dependent gene heme oxygenase-1 (HO-1). Both Nrf2 and HO-1 were required for Sal A-mediated cytoprotective effect, as Nrf2/HO-1 inhibition abolished Sal A-induced beneficial effects against H₂O₂. Meanwhile, the PI3K/Akt/mTORC1 chemical inhibitors not only suppressed Sal A-induced Nrf2/HO-1 activation, but also eliminated its cytoprotective effect in RPE cells. These observations suggest that Sal A activates the Nrf2/HO-1 axis in RPE cells and protects against oxidative stress via activation of Akt/mTORC1 signaling.     

Stimulation of GSH synthesis to prevent oxidative stress-induced apoptosis by hydroxytyrosol in human retinal pigment epithelial cells: activation of Nrf2 and JNK-p62/SQSTM1 pathways

The Nrf2-Keap1 pathway is believed to be a critical regulator of the phase II defense system against oxidative stress. By activation of Nrf2, cytoprotective genes such as heme oxygenase-1 (HO-1), NAD(P)H:quinone oxidoreductase (NQO-1) and γ-glutamyl-cysteine ligase (GCL) are induced. GCL-induced glutathione (GSH) production is believed to affect redox signaling, cell proliferation and death. We here report that tert-butyl hydroperoxide (t-BHP)-induced GSH reduction led to mitochondrial membrane potential loss and apoptosis in cultured human retinal pigment epithelial cells from the ARPE-19 cell line. Hydroxytyrosol (HT), a natural phytochemical from olive leaves and oil, was found to induce phase II enzymes and GSH, thus protect t-BHP-induced mitochondrial dysfunction and apoptosis. Depletion of GSH by buthionine-[S,R]-sulfoximine enhanced t-BHP toxicity and abolished HT protection. Overexpression of Nrf2 increased GSH content and efficiently protected t-BHP-induced mitochondrial membrane potential loss. Meanwhile, HT-induced GSH enhancement and induction of Nrf2 target gene (GCLc, GCLm, HO-1, NQO-1) messenger RNA (mRNA) were inhibited by Nrf2 knockdown, suggesting that HT increases GSH through Nrf2 activation. In addition, we found that HT was able to activate the PI3/Akt and mTOR/p70S6-kinase pathways, both of which contribute to survival signaling in stressed cells. However, the effect of HT was not inhibited by the PI3K inhibitor LY294002. Rather, c-Jun N-terminal kinase (JNK) activation was found to induce p62/SQSTM1 expression, which is involved in Nrf2 activation. Our study demonstrates that Nrf2 activation induced by the JNK pathway plays an essential role in the mechanism behind HT's strengthening of the antiapoptotic actions of the endogenous antioxidant system.