Glossogyne tenuifolia (Hsiang-ju) extract suppresses T cell activation by inhibiting activation of c-Jun N-terminal kinase
- Jer-Yiing Houng†1,
- Tzong-Shyuan Tai†2, 3,
- Shu-Ching Hsu4, 5,
- Hsia-Fen Hsu1,
- Tzann-Shun Hwang6,
- Chih-Jiun Lin7 and
- Li-Wen Fang1Email author
© The Author(s) 2017
Received: 7 March 2016
Accepted: 17 March 2017
Published: 11 April 2017
Glossogyne tenuifolia (GT) (Hsiang-ju) is a Chinese herbal medicine previously exhibited an anti-inflammatory activity. This study aimed to investigate the effect of GT ethanol extract (GTE) on T cell-mediated adaptive immunity.
Human peripheral blood mononuclear cells (PBMCs) and Jurkat T cells were activated by phytohemagglutinin in the presence of various doses (3.13–50 μg/mL) of GTE. The effect of GTE on T cell activation was examined by a proliferation assay of activated PBMCs and the level of the activation marker CD69 on the surface of activated Jurkat T cells. Apoptosis was determined by propidium iodide staining in hypotonic solution. Signaling pathway molecules were assessed by western blotting.
Glossogyne tenuifolia ethanol extract was demonstrated to inhibit T cell activation, not only in the proliferation of human PBMCs at the concentrations of 12.5, 25 and 50 μg/mL (P = 0.0118, 0.0030 and 0.0021) but also in the CD69 expression in Jurkat cells, which was not due to the cytotoxicity of GTE. The presence of GTE did not change the activity of nuclear factor kappa-light-chain-enhancer of activated B cells or extracellular signal-regulated kinase upon T cell activation. In addition, GTE significantly reduced activation of c-Jun N-terminal kinase (JNK) (P = 0.0167) and p38 (P = 0.0278). Furthermore, decreased JNK activation mediated the preventive effect of GTE on T cell activation-induced cell death (AICD).
Glossogyne tenuifolia ethanol extract inhibited T cell activation of Jurkat cells and freshly prepared human PBMCs due to suppression of JNK activity. Furthermore, GTE inhibited AICD by blocking prolonged JNK phosphorylation in activated T cells. Taken together, the anti-inflammatory effects exerted by GTE were mediated via suppression of JNK phosphorylation in T cell activation.
Inflammation is a normal host defense mechanism against infection, involving not only innate but also adaptive immunity. However, uncontrolled inflammation may lead to tissue damage and cause autoimmune or autoinflammatory diseases. In autoinflammatory diseases, such as type 2 diabetes and obesity, macrophages in innate immunity become dysfunctional . In contrast, autoimmune diseases, such as rheumatoid arthritis, inflammatory bowel disease, type 1 diabetes, psoriasis, lupus, and multiple sclerosis, are often mediated by lymphocytes of adaptive immunity rather than macrophages . T cells are the dominant dysfunctional cells or initiators during the development of autoimmune diseases .
Anti-inflammatory drugs have several adverse side effects. Glossogyne tenuifolia (GT) (Hsiang-ju) is a perennial herb of Asteraceae that is distributed from south Asia to Australia. GT is a Chinese medicine used in antipyretic, hepatoprotective, and anti-inflammatory remedies [2, 3]. Previous studies have shown that GT extract possesses pharmacological activities of antioxidation [4–6], cytotoxicity against several cancer cell lines [4, 7], protection against endothelial cell injury , and prevention of osteoclast-related diseases such as osteoporosis . In addition, GT exhibited activity in immunomodulation [10–12]. GT extract downregulated the gene expression of inducible nitric oxide synthase and cyclooxygenase-2, as well as the production of proinflammatory cytokines upon stimulation by lipopolysaccharide (LPS) in Raw 264.7 cells  and human peripheral blood mononuclear cells (PBMCs) . However, the effect of GT on adaptive immune cells, such as T cells, remains unclear.
Currently, the discovery of safe natural products for the treatment of inflammatory disorders focuses on inhibition of macrophage activity . However, cells of the adaptive immune system, such as T and B cells, mediate inflammatory processes of some inflammatory diseases such as rheumatoid arthritis and inflammatory bowel disease. Molecules of the activation pathway of T cells might be a good target for modulation of these inflammatory diseases . Resting T cells are in the G0 phase of the cell cycle. In response to T cell receptor (TCR) ligation, mitogenic stimulation, or a combination of a phorbol ester and calcium ionophore, T cells activate and transduce activation signals, leading to their proliferation. TCRs initiate signaling cascades that lead to activation of downstream mitogen-activated protein kinases (MAPKs) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) . Extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and p38 MAPK are important MAPKs involved in T cell activation. Cell proliferation and differentiation into effector cells as well as the production of interleukin (IL)-2 reflect the degree of T cell activation, and a lack of either MAPK or NF-κB impairs T cell activation-induced proliferation and IL-2 production .
Activated T cells undergo apoptosis upon re-stimulation, which is called activation-induced cell death (AICD). AICD is a critical mechanism to eliminate autoreactive lymphocytes in the immune system and maintain immune tolerance and homeostasis . During cancer progression, the immune system acts as a significant barrier. Immune cells, such as CD8+ cytotoxic T lymphocytes (CTLs), CD4+ helper T cells, and natural killer cells, contribute to immunosurveillance and tumor elimination . In antitumor immunotherapy, AICD of T cells is believed to be the key event leading to the failure of anti-tumor effects [18, 19]. Several studies of cancer immunotherapy using different approaches have highlighted inhibition of AICD to rescue activated T cells, thereby enhancing anti-tumor immune responses [18–21]. In adoptive cancer immunotherapy , tumor antigen-specific T cells are susceptible to AICD upon encountering the tumor antigen, causing the low success rate of cancer immunotherapy. Phosphorylation of JNK is critical for AICD of melanoma antigen-specific primary CTLs, and blocking JNK activation prevents AICD of CTLs [20, 23, 24]. This study aimed to investigate the effect of GT ethanol extract (GTE) on T cell-mediated adaptive immunity.
Preparation of GTE
GT plant materials were purchased from an herb store in Penghu Island, Taiwan, and deposited as the number of ISU-JYH-001 in the Herbarium of I-Shou University (Kaohsiung City, Taiwan). The nucleotide sequences of internal transcribed spacer (ITS) 1, ITS2, and 5.8S rDNA were isolated from this plant, and the species was confirmed by the NCBI DNA database . Dry whole plant materials were ground into powder. GT (5.3 kg) was extracted with 20 L of 95% ethanol at room temperature for 1 day and repeated for three times. The extracted solutions were filtered through medicinal gauze. The GTE was obtained by removing the solvent with a rotary evaporator (VP-60DJ, Panchum Co., Kaohsuing City, Taiwan) and drying in a freeze drier (FD8530, Panchum Co.). The total dry weight of this extract was 777 g, and the extraction yield was 14.7%. The quality of the herb extract was monitored by high performance liquid chromatography (L-7100, Hitachi, Tokyo, Japan) analysis using luteolin and luteolin-7-glucoside (Sigma Chemicals Co., St Louis, MO, USA) as the principle control standards [4, 9]. The dry GTE was dissolved in dimethyl sulfoxide (DMSO) at the concentration 50 mg/mL as the GTE stock. The final GTE concentrations (3.13, 6.3, 12.5, 25 and 50 μg/mL) were made by culture medium dilution. The DMSO was added no more than 0.1% (v/v) and used as a mock control in this study.
Cell culture and human PBMC preparation
Human PBMCs were prepared from the whole blood and human leukemia cell line Jurkat was obtained from American Type Cell Collection (ATCC, Manassas, VA, USA). Human PBMCs and leukemic Jurkat cells were grown in RPMI-1640 medium (GE Healthcare, Piscataway, NJ, USA) with 10% fetal bovine serum (FBS; Thermo Fisher Scientific Inc., Waltham, MA, USA), 1% penicillin/streptomycin (Sigma-Aldrich, St. Louis, MO, USA), and 2 mM l-glutamine (Sigma-Aldrich) at 37 °C in a humidified atmosphere with 5% CO2. Human PBMCs were isolated from whole blood using a Ficoll-Paque plus density gradient . Whole bloods from healthy volunteers were mixed with the same volume of Hank’s balanced salt solution (HBSS; Thermo Fisher, St. Louis, MO, USA). The blood-HBSS mixture was layered over Ficoll-Paque PLUS (GE Healthcare) 1:1 (v/v) and centrifuged (5810R, Eppendorf, Hamburg, Germany) (400×g) for 20 min at 25 °C with the break off. The PBMC layer at the interface was collected and washed with HBSS three times by centrifugation (300×g) for 5 min at 4 °C. The PBMCs were suspended in RPMI-1640 medium. The study protocols were approved by the Institutional Review Board of the Research Ethics Committee of National Health Research Institutes (EC1001101) (Additional file 1).
For each sample, 1 × 106 cells were washed with phosphate buffered saline (PBS; pH 7.2) and lysed in freshly prepared cell lysis buffer (20 mM Tris–HCl, pH 7.5, 150 mM NaCl, 1 mM Na2EDTA, 1 mM EGTA, 1% Triton X-100, 2.5 mM sodium pyrophosphate, 1 mM β-glycerophosphate, 1 mM Na3VO4, 1 µg/mL leupeptin, and 1 mM phenylmethanesulfonyl fluoride). The cell lysate was separated from debris by centrifugation at 13,200×g for 10 min at 4 °C. The protein concentration was measured by Bio-Rad Protein Assay Dye Reagent (Bio-Rad Laboratories, Hercules, CA, USA). An aliquot of 20 μg protein was separated on a 10% polyacrylamide gel and transferred onto a polyvinylidene fluoride membrane (EMD Millipore, Billerica, MA, USA). The membranes were subsequently blocked with 5% dry skim milk in Tris-buffered saline (TBS; pH 7.5). The membranes were hybridized with the indicated primary antibody at 4 °C overnight, washed three times with 0.05% TBST solution (50 mM Tris–Cl, pH 7.5, 150 mM NaCl, and 0.05% Tween-20) for 10 min, and then hybridized with a horseradish peroxidase (HRP)-conjugated secondary antibody at room temperature for 1 h. After washing three times with 0.05% TBST for 10 min each, the membrane was incubated with Luminata™ Western HRP Substrates (EMD Millipore). The signals were detected using Image Lab software Version 2.0 (Bio-Rad Laboratories).
T cell proliferation and activation assay
PBMCs (1 × 105) were pretreated with GTE (3.13, 6.3, 12.5, 25 and 50 μg/mL) for 30 min and then activated by 2.5 μg/mL phytohemagglutinin (PHA) in each well of a 96-well plate for 48 h. An aliquot of 0.5 μCi 3H-thymidine was added to each well. After 20 h of incubation, the cells were harvested with a FilterMate 96-well harvester (PerkinElmer Inc, Waltham, MA, USA) for a proliferation assay. The radioactivity (counts per minute, CPM) was measured to quantify cell proliferation with a microplate scintillation and luminescence counter (TopCount NXT, Packard Instrument Co, Meriden, CT, USA). Jurkat cells (1 × 105) were pretreated with GTE (25 μg/mL) for 30 min and then stimulated by 10/80 ng/mL 12-O-tetradodecanoyl-phorbol-13-acetate (PMA)/ionomycin (P/I) in each well of a 96-well plate for 24 h. Cells were then harvested for surface marker staining. To detect NF-κB activation, phosphorylation of nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor (IκB) and p65 proteins were determined by western blotting. Jurkat cells (1 × 106) were pretreated with GTE (25 μg/mL) for 30 min and then stimulated by PHA (2.5 μg/mL) for 0, 1, and 3 h. Cell lysates were then prepared for western blot analysis. To detect MAPK activation (p-ERK, p-p38, and p-JNK), 1 × 106 Jurkat cells were pretreated with GTE (25 μg/mL) for 30 min and then stimulated with 2.5 μg/mL PHA for 0, 10 and 20 min. Cell lysates were then prepared for western blotting. Primary antibodies against p-IκB (#2859, 1:500), p-p65 (#3033, 1:2000), p-ERK (#9101, 1:3000), p-p38 (#4511, 1:1000), and p-JNK (#4671, 1:500) were purchased from Cell Signaling Technology (Beverly, MA, USA). Primary antibodies against α-tubulin (#2871, 1:3000) was purchased from Epitomics Inc. (Burlingame, CA, USA). Primary antibodies against ERK2 (sc-154, 1:5000), p38 (sc-535, 1:3000), and JNK1 (sc-1648, 1:1000), and an HRP-conjugated secondary antibody were purchased from Santa Cruz Biotechnology (Dallas, TX, USA).
Cell surface staining
Jurkat cells (1 × 105) were stimulated with P/I (10/80 ng/mL) for 24 h. The cells were then stained with CD69-PE (12-0699, 1:50, eBioscience, San Diego, CA, USA) in staining buffer (PBS with 1% FBS) on ice for 20 min and then washed three times with staining buffer. The CD69-positive population was evaluated by a flow cytometer (FACSCalibur; BD Biosciences). Data were analyzed with FlowJo software (BD Biosciences). The signal obtained for the cells treated without or with GTE alone and stained with mouse IgG1 isotype control-PE (12-4714, 1:50, eBioscience) was used as a control respectively.
Apoptosis was determined by propidium iodide (PI) (Sigma-Aldrich) staining . PBMCs or Jurkat cells (1 × 105) were treated with various concentrations of GTE (3.13, 6.3, 12.5, 25 and 50 μg/mL) in each well of a 96-well plate for 24 h. Harvested cells were suspended in a hypotonic solution (0.1% sodium citrate, 0.1% Triton X-100, and 20 μg/mL PI). The extent of the sub-G0/G1 peak representing apoptotic cells was measured by gating on cells stained in the region below the G0/G1 peak. The apoptotic sub-G0/G1 population was examined by flow cytometry and analyzed with FlowJo software (BD Biosciences).
Healthy female Balb/c mice were obtained from National Laboratory Animal Center (NLAC, Taipei, Taiwan) at 4 weeks of age. The animals were maintained in cages (5 mice/cage) under standard conditions. The mice were euthanized by use of CO2 exposure. CD4+ T cells isolated from the splenocytes of C57BL/6 mice were activated by antibodies against CD3 (16-0031, eBioscience) and CD28 (16-0281, eBioscience) (1 and 2 μg/mL, respectively) in the presence of 100 U/mL IL-2 for 5 days. The activated T cells were washed three times and reactivated by the anti-CD3 (16-0031, eBioscience) antibody (0.5 μg/mL) for 8 h. The cells were then harvested for an apoptosis assay. All animal experiments were performed in accordance with protocols approved by the Institutional Animal Care and Use Committee of I-Shou University (IACUC-ISU-96002) (Additional file 2). The combination of P/I and sodium orthovanadate (Na3VO4) induces significant AICD in Jurkat T cells . Jurkat cells (1 × 105) were pretreated with GTE (25 μg/mL) for 30 min and then activated by P/I (10/80 ng/mL) and 1.5 mM Na3VO4 in each well of a 96-well plate for 24 h. The cells were then harvested for an apoptosis assay.
Each experiment was performed at least three times and measured in triplicates. The data were presented as mean ± standard deviation (SD). Each GTE-treated group was compared to the respective mock-treated (DMSO) control group. Statistical differences were analyzed by Student’s t-test (*P < 0.05, **P < 0.01 and ***P < 0.001). Data were analyzed using GraphPad Prism software (GraphPad Software, La Jolla, CA, USA).
Information of experimental design and resources
Details of our experimental design and statistics and all resources used in this study were included in Additional file 3.
Inhibitory effects of GTE on the activation of T cells and PBMCs
Mitogen stimulation hydrolyzes membrane polyphosphoinositides to inositol trisphosphate (IP3) and diacylglycerol (DAG). Then, IP3 releases Ca2+ into the cytosol, and DAG activates protein kinase C (PKC). These synergistic effects lead to progression of the cell cycle and proliferation of T cells [28, 29]. A combination of phorbol esters, which activates PKC, and a calcium ionophore, which increases the intracellular Ca2+ concentration, mimic the signals triggered by the TCR or mitogen stimulation and can be used as agents for T cell activation. In addition, CD69 is an early activated surface molecule on T cells, and expression of CD69 has been frequently used as an indicator for T cell activation .
Cytotoxic effect of GTE on Jurkat T cells and PBMCs
GTE down-regulated JNK phosphorylation, but not NF-κB activities, in activated human T cells
GTE attenuated prolonged JNK-induced AICD
Several studies have investigated the anti-inflammatory mechanism of GTE, but all of them have focused on GTE effects in activated myeloid lineage macrophages [10, 11]. However, the inflammatory effect of GTE on T cells is still unknown. Cells of the adaptive immune system, especially T cells, mediate the tissue damage of some inflammatory diseases such as rheumatoid arthritis and inflammatory bowel disease . In the present study, we found that GTE suppressed T cell activation in both Jurkat T cells and in human PBMCs (Fig. 1). This suppressive effect was not caused by cytotoxicity of GTE in T cells (Fig. 2).
Previous studies [4, 7] have reported that GTE possessed an anti-cancer activity. GTE showed cytotoxicity in breast cancer cell lines (MDA-MB-231 and MCF-7) and hepatoma cell lines (HepG2 and Hep3B) . The IC50 doses of GTE in these susceptible cell lines are 20–30 μg/mL . Our data suggest that PBMCs and Jurkat T cells were resistant to GTE-induced cytotoxicity (Fig. 2).
Ha et al.  reported that GTE at a high dose, but not a low dose, inhibited NF-κB activation. In our study, no NF-κB defect in T cell activation was observed with co-treatment at a low concentration of GTE (Fig. 3), although we did find strong inhibition of JNK activity and slight suppression of p38 activity (Fig. 4). LPS treatment induced activation of NF-κB and JNK/p38 , it was possible that a low concentration of GTE might also inhibited JNK activity upon LPS treatment in macrophages.
The mechanism by which GTE regulated JNK activity was unclear. One possible mechanism is through the production of reactive oxygen species (ROS) that induce JNK activation to initiate a downstream signal that amplifies ROS production upon stimulation . Previous studies have shown that GTE has an antioxidant activity [4, 5], and the ability of GTE to modulated JNK might be mediated through its activity as a ROS scavenger by blocking the JNK–ROS activation loop.
In adoptive immunotherapy of cancer treatment, AICD of adoptively transferred T cells represents one of the major hurdles to devise an effective immune intervention therapy. Rescuing T cells from AICD might promote anti-tumor immunity [19, 36]. Previous studies have demonstrated that the modulation effect of JNK prevents AICD of adoptively transferred T cells [20, 23]. Our study demonstrated that GTE inhibited JNK activity upon T cell activation and AICD (Figs. 4, 5b). The mechanism of AICD inhibition by GTE might be mediated through modulation of prolonged JNK phosphorylation in activated T cells. In addition to its roles in cell activation and AICD in the immune system, JNK has been shown to be involved in other stress signaling pathways such as those in response to ultraviolet and γ irradiation . Hence, our findings of the effects of GTE on JNK modulation indicate that GTE may have regulatory effects on other cellular responses.
GTE inhibited T cell activation of Jurkat cells and freshly prepared human PBMCs due to suppression of JNK activity. Furthermore, GTE inhibited AICD by blocking prolonged JNK phosphorylation in activated T cells. Taken together, the anti-inflammatory effects exerted by GTE were mediated via suppression of JNK phosphorylation in T cell activation.
activation-induced cell death
counts per minute
cytotoxic T lymphocytes
extracellular signal-regulated kinase
fetal bovine serum
Glossogyne tenuifolia ethanol extract
Hank’s balanced salt solution
nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor
internal transcribed spacer
c-Jun N-terminal kinases
mitogen-activated protein kinases
mean fluorescence intensity
- Na3VO4 :
nuclear factor kappa-light-chain-enhancer of activated B cells
peripheral blood mononuclear cells
phosphate buffered saline
protein kinase C
T cell receptor
LWF, JYH and TST conceived and designed the study. TST performed the flow cytometry experiments. LWF and TST performed the biological experiments. LWF, TST and SCH interpreted the results. TSH, HFH and CJL performed the statistical analysis. LWF, JYH and TST wrote the manuscript. All authors read and approved the final manuscript.
This work was supported by the National Science Council, Taiwan (NSC 97-2313-B-214-001-MY3-002), and I-Shou University, Taiwan (ISU101-04-06 and ISU-103-01-E-01).
The authors declare that they have no competing interests.
Ethics approval and consent to participate
The study was approved by the Institutional Review Board of the Research Ethics Committee of National Health Research Institutes. All blood donors signed the consent to participate.
This work was funded by the National Science Council, Taiwan (NSC 97-2313-B-214-001-MY3-002), and I-Shou University, Taiwan (ISU101-04-06 and ISU-103-01-E-01).
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