Activation of Phosphoinositide 3-Kinase, Protein Kinase C, and Extracellular Signal-Regulated Kinase Is Required for Oridonin-Enhanced Phagocytosis of Apoptotic Bodies in Human Macrophage-Like U937 Cells

A Cocktail of Natural Compounds Holds Promise for New Immunotherapeutic Potential in Head and Neck Cancer

OBJECTIVE

To obtain detailed understanding on the gene regulation of natural compounds in altering prognosis of head and neck squamous cell carcinomas (HNSC).

METHODS

Gene expression data of HNSC samples and peripheral blood mononuclear cells (PBMCs) of HNSC patients were collected from Gene Expression Omnibus (GEO). Differential gene expression analysis of GEO datasets were achieved by the GEO2R tool. Common differentially expressed gerres (DEGs) were screened by comparing DEGs of HNSC with those of PBMCs. The combination was further analyzed for regulating pathways and biological processes that were affected.

RESULTS

Totally 110 DEGs were retrieved and identified to be involved in biological processes related to tumor regulation. Then 102 natural compounds were screened for a combination such that the expression of all 110 commonly DEGs was altered. A combination of salidroside, ginsenoside Rd, oridonin, britanin, and scutellarein was chosen. A multifaceted, multi-dimensional tumor regression was showed by altering autophagy, apoptosis, inhibiting cell proliferation, angiogenesis, metastasis and inflammatory cytokines production.

CONCLUSIONS

This study has helped develop a unique combination of natural compounds that will markedly reduce the propensity of development of drug resistance in tumors and immune evasion by tumors. The result is crucial to developing a combinatorial natural therapeutic cocktail with accentuated immunotherapeutic potential.

LETMD1 Regulates Phagocytosis and Inflammatory Responses to Lipopolysaccharide via Reactive Oxygen Species Generation and NF-κB Activation in Macrophages

LETM1 domain-containing protein 1 (LETMD1), also known as HCCR-1, is a mitochondrial protein and is known to regulate p53 and STAT3 activities in cancer cells. In this study, we present, for the first time (to our knowledge), data indicating that LETMD1 suppresses multiple immune responses in monocyte/macrophage lineage cells and mouse primary macrophages. Attenuation of LETMD1 expression with specific small interfering RNA and short hairpin RNA constructs enhanced LPS-induced expressions of inflammatory mediators in macrophages. In addition, LETMD1 attenuation caused potentiation of phagocytosis as well as migration in a macrophage-like cell line, U937. These enhancing effects were associated with altered activation of signaling adaptors (such as NF-κB, MAPKs, p53, and JAK-STAT) involved in TLR4 signaling. Especially, LETMD1 selectively regulated TLR4-induced NF-κB activation via MyD88 but not via TIR-domain-containing adapter-inducing IFN-β (TRIF). Attenuation of LETMD1 expression caused mitochondrial hyperpolarization and subsequent decrease in ATP production and increase in mitochondrial/cellular reactive oxygen species (ROS) and intracellular calcium levels. LETMD1 attenuation also enhanced LPS-induced expression of NADPH oxidase (NOX) 2, the main producer of cellular ROS in phagocytes, through augmenting IFN regulatory factor 1. Accordingly, treatment with ROS scavenger, NOX2 suppressing agents, or calcium chelators resulted in suppression of LPS-induced cytokine production as well as NF-κB activation in cells with LETMD1 attenuation. These findings reveal a previously unknown function of LETMD1 and provide evidences showing LETMD1 negatively regulates macrophage functions by modulating mitochondrial function, subsequent ROS generation, and NF-κB activation.

Oridonin induces growth inhibition and apoptosis in human gastric carcinoma cells by enhancement of p53 expression and function

The tumor suppressive role of oridonin, an active compound extracted from Rabdosia rubescens, has been proven in several gastric cancer (GC) cell lines. The present study aimed to evaluate the effect of oridonin on another GC cell line, SNU-216, and explore the potential mechanisms. The viable cell numbers, cell migration, survival fraction, and cell viability were, respectively, evaluated by trypan blue exclusion assay, wound healing assay, clonogenic assay, and CCK-8 assay. Cell apoptosis was determined by flow cytometry assay and western blot. The expression of p53 was inhibited by transient transfection, and the efficiency was verified by western blot. qRT-PCR was performed to measure the mRNA expression of p53. Western blot was used to evaluate the protein expression of apoptosis, DNA damage and p53 function related factors. We found that oridonin significantly inhibited cell proliferation, migration, and survivability, and enhanced cell apoptosis in SNU-216 cells. However, it had no influence on HEK293 cell viability. Oridonin also remarkably enhanced the anti-tumor effect of cisplatin on SNU-216 cells, as it significantly increased apoptotic cells and decreased cell viability. Moreover, the mRNA and protein expression of p53 was significantly up-regulated in oridonin-treated cells, while Mdm2 expression was down-regulated. Furthermore, oridonin enhanced p53 function and induced DNA damage. Knockdown of p53 or employing the caspase inhibitor, Boc-D-FMK, reversed the effect of oridonin on cell viability and apoptosis-related protein expression. The present study demonstrated that oridonin exhibited an anti-tumor effect on GC SNU-216 cells through regulating p53 expression and function.

Cystatin F involvement in adenosine A2A receptor-mediated neuroinflammation in BV2 microglial cells

Our previous studies have shown adenosine A_2A R activation markedly promotes the expression of cystatin F (CF) and exacerbates the white matter lesions induced by hypoxic brain injuries. Thus, we hypothesized that CF was probably involved in neuroinflammation of activated microglia induced by A_2A R activation. We transfected the BV2 cells with a CF shRNA vector and examined the production of pro-inflammatory cytokines in hypoxic-BV2 cells in which A_2A R was activated or inactivated to confirm this hypothesis. Additionally, we also investigated the probable signaling pathways involved in modulation of A_2A R activation on CF expression in hypoxia-activated BV2 cells. Activation of A_2A R promoted CF expression, which was significantly increased after the low glucose and hypoxia treatments in BV2 cells. CF gene knockdown markedly inhibited the increase in the expression of pro-inflammatory cytokines induced by A_2A R activation in hypoxic-BV2 cells. Furthermore, the increased expression of the CF induced by A_2A R activation was remarkably inhibited in hypoxic-BV2 cells administrated with the PKA inhibitor H-89 and the PKC inhibitor staurosporine. Hence, these results indicate that hypoxia BV2 cells highly express CF, which is involved in A_2A R activation-mediated neuroinflammation via the PKA/CREB and PKC/CREB or ERK1/2 signaling pathways.

Therapeutic Potential of Oridonin and Its Analogs: From Anticancer and Antiinflammation to Neuroprotection

Oridonin, a diterpenoid natural product commonly used in East Asian herbal medicine, is garnering increased attention in the biomedical community due to its extensive biological activities that include antitumor, anti-inflammatory, antimicrobial, hepatic fibrosis prevention, and neurological effects. Over the past decade, significant progress has been made in structure activity relationship and mechanism of action studies of oridonin for the treatment of cancer and other diseases. This review provides a brief summary on oridonin and its analogs in cancer drug discovery and antiinflammation and highlights its emerging therapeutic potential in neuroprotection applications.

An Essential Role for TAGLN2 in Phagocytosis of Lipopolysaccharide-activated Macrophages

Activated macrophages have a greater ability of phagocytosis against pathogens that is mediated by large-scale actin rearrangement. However, molecular machineries that conduct this task have not been fully identified. Here, we demonstrate an unanticipated role of TAGLN2, a 22-kDa actin-binding protein, in Toll-like receptor (TLR)-stimulated phagocytosis. TAGLN2 was greatly induced in macrophages in response to lipopolysaccharide (LPS), a ligand for TLR4, partly via the NF-κB pathway. TAGLN2-deficient macrophages (TAGLN2^−/−) showed defective phagocytic functions of IgM- and IgG-coated sheep red blood cells as well as bacteria. Cell signaling pathways involved in actin rearrangement—PI3 kinase/AKT and Ras-ERK—were also down-regulated in LPS-stimulated TAGLN2-deficient macrophages. Moreover, TAGLN2^−/− mice showed higher mortality after bacterial infection than wild-type littermates. Thus, our results revealed a novel function of TAGLN2 as a molecular armament required for host defense.

Molecular Insight in the Multifunctional Effects of Oridonin

Oridonin has attracted considerable attention in the last decade because of its anti-cancer pharmacological properties. This ent-kaurane diterpenoid, isolated from the Chinese herb Rabdosia rubescens and some related species, has demonstrated great potential in the treatment profile of many diseases by exerting anti-tumor, anti-inflammatory, pro-apoptotic, and neurological effects. Unfortunately, the mechanisms via which oridonin exerts these effects remain poorly understood. This review provides an overview of the multifunctional effects of oridonin as well as the reasons for its potential for investigations in the treatment of many diseases other than cancer.

Oridonin inhibits BxPC-3 cell growth through cell apoptosis

Oridonin, an ent-kaurene diterpenoid extracted from the traditional Chinese herb Rabdosia rubescens, has multiple biological and pharmaceutical functions and has been used clinically for many years. While the antitumor function of oridonin has been corroborated by numerous lines of evidence, its anticancer mechanism has not been well documented. In this study, the pancreatic cancer cell line BxPC-3 was used as a model to investigate a possible anticancer mechanism of oridonin through examining its effects on cell viability. The results showed that oridonin affected cell viability in a time- and dose-dependent manner. After exposure to different oridonin concentrations, growth rates and cell cycle arrest of BxPC-3 cells were significantly reduced compared with untreated cells, suggesting its effects on proliferation inhibition. Detailed signaling pathway analysis by western blot analysis revealed that low-dose oridonin treatment inhibited BxPC-3 cell proliferation by up-regulating p53 and down-regulating cyclin-dependent kinase 1 (CDK1), which led to cell cycle arrest in the G2/M phase. A high-dose oridonin not only arrested BxPC-3 cells in the G2/M phase but also induced cell accumulation in the S phase, presumably through γH2AX up-regulation and DNA damage. In addition, our results showed that a cell subpopulation was stained with propidium iodide after oridonin treatment. Protein quantification showed that cleaved poly(ADP-ribose) polymerase (PARP) expression was increased after a high-dose oridonin treatment, especially after long-term exposure. Accompanied by the increased level of deactivated PARP in BxPC-3 cells, the apoptosis initiators caspase-3 and caspase-7 expressions were also significantly increased, suggesting that caspase-mediated apoptosis contributed to cell death.

DNA damage induced by oridonin involves cell cycle arrest at G2/M phase in human MCF-7 cells

Aim of the study

To study the mechanisms of inhibition of cell growth and induction of DNA damage in oridonin-treated MCF-7 human breast cancer cells.

Material and methods

The cytotoxicity of oridonin-treated MCF-7 cells was measured by MTT assay. Cell cycle phase distribution was analyzed by flow cytometry. P-ATM, P-CHK2, γH2AX and P-P53 protein expressions were detected by Western blot analysis. The expression of r-h2ax and P-ATM was also detected by immunofluorescence staining. The degree of cellular damage of oridonin-induced MCF-7 human breast cancer cells was confirmed by the comet assay analysis of DNA fragmentation.

Results

Oridonin inhibited cell growth in a time- and dose-dependent manner. The IC50 values at 48 and 72 hours were 78.3 and 31.62 µmol/l, respectively. Oridonin induced G2/M phase arrest in MCF-7 cells. MCF-7 cells treated with oridonin showed significant DNA damage as shown by an increase in olive tail moment (OTM). The protein expression levels of P-ATM, P-CHK2, γH2AX and P-P53 were increased significantly in a dose-dependent manner.

Conclusions

DNA damage provokes p53-mediated G2/M cell cycle arrest in oridonin-induced MCF-7 cells through the mechanism of CHK2 activation by activated ATM protein kinase, which is induced by oridonin.

Reactive oxygen species H2O2 and •OH, but not O2•(-) promote oridonin-induced phagocytosis of apoptotic cells by human histocytic lymphoma U937 cells

We reported previously that phagocytosis of apoptotic cells by U937 cells was enhanced by the treatment with oridonin that showed high activity to induce the generation of reactive oxygen species (ROS) in many cells. ROS, important signaling molecules, are involved in the immune defenses, cell repair and proliferation. In this study, oridonin caused modest amount of ROS generation in U937 cells, with hydrogen peroxide (H2O2) and hydroxyl free radical (OH) as the major types. Meanwhile, H2O2 and OH were positive regulators involved in oridonin-enhanced engulfment of apoptotic cells through down-regulating mitochondrial membrane potential (MMP) and inducing autophagy. The ROS-mediated phagocytosis was independent of cellular adenosine triphosphate (ATP) levels. H2O2 and OH generation also activated phosphatidylinositol 3-kinases-Akt (PI3K-Akt) and phospholipase C γ-protein kinase C(PLC γ)-Ras-Raf-ERK signaling pathways, which were essential for oridonin-induced engulfment of apoptotic cells. Phagocytosis, the loss of MMP, autophagy and the activated signaling pathways were all suppressed by ROS scavenger N-acetyl-l-cysteine (NAC), H2O2 scavenger catalase or OH scavenger glutathione (GSH). However, superoxide anion (O2-) and its scavenger superoxide dismutase (SOD) did not significantly affect these oridonin-induced biological processes.

Oridonin: targeting programmed cell death pathways as an anti-tumour agent

Oridonin, an active diterpenoid isolated from traditional Chinese herbal medicine, has drawn rising attention for its remarkable apoptosis- and autophagy-inducing activity and relevant molecular mechanisms in cancer therapy. Apoptosis is a well known type of cell death, whereas autophagy can play either pro-survival or pro-death roles in cancer cells. Accumulating evidence has recently revealed relationships between apoptosis and autophagy induced by oridonin; however, molecular mechanisms behind them remain to be discovered. In this review, we focus on highlighting updated research on oridonin-induced cell death signalling pathways implicated in apoptosis and autophagy, in many types of cancer. In addition, we further discuss cross-talk between apoptosis and autophagy induced by oridonin, in cancer. Taken together, these findings open new perspectives for further exploring oridonin as a potential anti-tumour agent targeting apoptosis and autophagy, in future anti-cancer therapeutics.

Autophagy enhanced phagocytosis of apoptotic cells by oridonin-treated human histocytic lymphoma U937 cells

Macrophages rapidly engulf and remove apoptotic cells to limit the release of noxious cellular contents and to restrict autoimmune disease or inflammation. Recent developments reveal an important role in autophagy for clearance of apoptotic corpses. However, the relationship between autophagy and phagocytosis remains unclear. In this study we found that low doses of oridonin, an active diterpenoid, enhanced phagocytosis of apoptotic cells by human macrophage-like U937 cells, meanwhile it also induced autophagy in these U937 cells. Moreover, inhibition of extracellular signal-related kinase (ERK), nuclear factor-κB (NF-κB) and caspase-1 significantly suppressed oridonin-induced phagocytosis and autophagy. In addition, oridonin increased the protein levels of p-ERK, NF-κB, caspase-1 and pro IL-1β. Autophagic inhibitor 3-methyladenine (3-MA) decreased phagocytosis and the expression of ERK whereas increased the expression of NF-κB- and caspase-1-mediated IL-1β release. Beclin-1 (known as autophagic regulator) loss also led to the similar results. Pretreatment with autophagic agonist rapamycin caused opposite results. Autophagy-associated proteins, Beclin-1, LC3 and Atg4B, involved in this phagocytosis process. These results demonstrated that autophagy enhanced oridonin-induced phagocytosis through feedback regulation of ERK, NF-κB- and caspase-1-mediated IL-1β release.

The phosphoinositide phosphatase MTM-1 regulates apoptotic cell corpse clearance through CED-5–CED-12 in C. elegans

Multicellular organisms use programmed cell death to eliminate unwanted or potentially harmful cells. Improper cell corpse removal can lead to autoimmune diseases. The development of interventional therapies that increase engulfment activity could represent an attractive approach to treat such diseases. Here, we describe mtm-1, the Caenorhabditis elegans homolog of human myotubularin 1, as a potential negative regulator of apoptotic cell corpse clearance. Loss of mtm-1 function leads to substantially reduced numbers of persistent cell corpses in engulfment mutants, which is a result of a restoration of engulfment function rather than of impaired or delayed programmed cell death. Epistatic analyses place mtm-1 upstream of the ternary GEF complex, which consists of ced-2, ced-5 and ced-12, and parallel to mig-2. Over-activation of engulfment results in the removal of viable cells that have been brought to the verge of death under limiting caspase activity. In addition, mtm-1 also promotes phagosome maturation in the hermaphrodite gonad, potentially through CED-1 receptor recycling. Finally, we show that the CED-12 PH domain can bind to PtdIns(3,5)P2 (one target of MTM-1 phosphatase activity), suggesting that MTM-1 might regulate CED-12 recruitment to the plasma membrane.

Genomic and in vivo evidence of synergy of a herbal extract compared to its most active ingredient: Rabdosia rubescens vs. oridonin

Rabdosia rubescens is a herbal root extract of traditional Chinese medicine (TCM) used to treat inflammatory diseases and oral cancers. A key principle of TCM is that multiple ingredients in a plant extract are more effective and less toxic than a single purified active ingredient or a purified drug derived from a plant product. Rabdosia rubescens extract (RRE) contains terpenoids and flavonoids, but the most active ingredient within the extract attributed to the inhibition of cancer is the kaurene diterpene, oridonin. In order to research synergy with a complete plant extract, the effects of RRE on the inhibition of prostate cancer cell proliferation were compared to the effects of pure oridonin alone in vitro. Three groups of 8 SCID mice bearing human prostate cancer xenografts (LAPC-4) were administered either RRE containing 0.02 mg/g oridonin, pure oridonin at a dose of 0.02 mg/g, or pure oridonin at a dose of 0.1 mg/g, by gavage for 5 days/week for 4 weeks. RRE and pure oridonin at 0.1 mg/g inhibited tumor growth to a similar extent, while oridonin at a dose of 0.02 mg/g did not. Therefore, in comparison to RRE, five times more pure oridonin was required to obtain equivalent prostate xenograft growth inhibition. Since the nuclear factor-κB signaling pathway and inflammation are implicated in prostate carcinogenesis, gene microarray analysis was conducted and demonstrated activation of genes by RRE that was not evident with oridonin treatment alone. This study demonstrated that genomic methods and xenograft studies are capable of demonstrating the benefits of the synergy of whole plant extracts rather than active ingredients isolated and purified as drugs.

Efficacy of rabdosia rubescens in the treatment of gingivitis

This study evaluated the efficacy of rabdosia rubescens against gingivitis and compared the therapeutic efficacy of different dosage forms of rabdosia rubescens. A multi-center, randomized, double-blind, double-simulation, positive-controlled and parallel trial was conducted. A total of 136 patients exhibiting clinical symptoms of gingivitis were enrolled. The subjects were randomly assigned to two groups: test group (n=67), in which rabdosia rubescens drop pill (960 mg) and 4 tablets of simulation agent of rabdosia rubescen were orally given to the subjects three times a day for 5 days; and control group (n=69), in which the subjects were administered the tablets of rabdosia rubescens (1000 mg) and 24 drop pills of simulation agent of rabdosia rubescens thrice daily for 5 days. The experimental protocols and diagnostic criteria were established by expert panel prior to the experiment. The clinical symptoms were graded according to the severity of the disease and quantified. The total scores and scores for each clinical symptom of gingivitis were assessed at baseline and on the 6th day post-treatment. The therapeutic efficacy was compared between the two groups and in each group itself before and after the treatment. The results showed that in the two groups, the subjects who were given rabdosia rubescens, drop pill or tablet, had a decrease in total scores and scores for each clinical symptom when compared with those before treatment (P<0.01). There was significant difference in the therapeutic efficacy between the test group and the control group with the efficacy rate being 92.54% and 79.71% respectively (P<0.05). It was concluded that rabdosia rubescens showed great promise in treating gingivitis. And rabdosia rubescens drop pill was more efficacious than rabdosia rubescens tablet.

Reactive oxygen species mediate oridonin-induced HepG2 apoptosis through p53, MAPK, and mitochondrial signaling pathways

Oridonin, a diterpenoid isolated from Rabdosia rubescences, could induce apoptosis through the generation of reactive oxygen species (ROS) in human hepatoma HepG2 cells. p53, a specific inhibitor of pifithrin alpha (PFT alpha), markedly inhibited ROS generation and apoptosis, showing that p53 was responsible for the cytotoxity of oridonin through mediation by ROS. Moreover, the ROS activated the p38 kinase, which in turn promoted the activation of p53, as verified by evidence showing that the ROS scavenger N-acetyl-cysteine (NAC) not only blocked the phosphorylation of p38 but also partially inhibited the activation of p53, and the p38 inhibitor SB203580 reduced the activation of p53 as well. Mitochondria were either the sources or the targets of ROS. This study showed that oridonin stimulated mitochondrial transmembrane permeabilization in a ROS-dependent manner because NAC almost thoroughly reversed the drop of mitochondrial transmembrane potential (Deltapsim) and the release of cytochrome c from the mitochondrial inter-membrane space into cytosol. Furthermore, as a result of mitochondrial permeability transition, procaspases-9 and -3 were cleaved into 37- and 17-kDa proteolytic products, respectively, which acted as executors of oridonin-induced apoptosis.

Staurosporine aglycone bilaterally regulates ERK1/2 phosphorylation in rat pulmonary arterial smooth muscle cells

Staurosporine, a protein kinase C (PKC) inhibitor, has been reported to regulate the phosphorylation of ERK1/2 in several cell lines. It is still unknown, however, whether its derivative staurosporine aglycone (SA) has the same effect on ERK1/2 activation. In this study, we investigated the effect of SA on ERK1/2 activity in rat pulmonary arteries and pulmonary arterial smooth muscle cells (PASMCs). The pulmonary arteries and PASMCs were treated with SA at different time points and concentrations, and the activation of ERK1/2 was analyzed by Western blotting. The results showed that SA at nanomolar concentrations suppressed ERK1/2 phosphorylation through the PKC pathway alone, but SA at 30 micromol/L for 2 h enhanced the phosphorylation of ERK1/2. The activation of ERK1/2 was inhibited by the MAPK/ERK kinase inhibitor PD98059 or the protein kinase A (PKA) activator isoproterenol. Together, these results suggest that SA has a strong dual regulating effect on ERK1/2 through the PKC and (or) PKA pathways in rat PASMCs.

Oridonin induces human melanoma A375-S2 cell death partially through inhibiting insulin-like growth factor 1 receptor signaling

Our previous studies indicated that oridonin, a diterpenoid isolated from Rabdosia rubescens, induced human melanoma A375-S2 cell apoptosis. In this study, we investigated whether the proapoptotic effect of oridonin on A375-S2 cells would depend on an interference with function of the insulin-like growth factor 1 (IGF-1) receptor, a plasma membrane receptor critical for the survival or antiapoptotic ability in melanoma cells. We found that IGF-1 receptor (IGF-1R) signaling was a potential survival pathway against a low concentration of 20 micromol/L oridonin-induced apoptosis in A375-S2 cells. The activation of Ras or its downstream effector p38 mitogen-activated protein kinase (p38 MAPK) was shown to be necessary for IGF-1-mediated protection, but the activation of phosphatidylinositol-3-OH kinase (PI3 kinase) or extracellular signal-regulated kinase (ERK) did not correlate with the regulation of survival. However, in the presence of 40 micromol/L (IC50 at 24 h) oridonin, A375-S2 cells could not be protected by IGF-1 from apoptosis, accompanied by a severe impairment of IGF-1R expression. Therefore, we concluded that the proapoptotic activity of oridonin was partially attributed to its repression of IGF-1R signaling. In addition, p53 was supposed to be a pivotal transducer of proapoptotic and survival signaling pathway in this system.

Akt2, but not Akt1 or Akt3 mediates pressure-stimulated serum-opsonized latex bead phagocytosis through activating mTOR and p70 S6 kinase

Monocytes and macrophages play critical roles in innate host defense and are sensitive to mechanical stimuli. Tissue pressure is often altered in association with inflammation or infection. Low pressure (20 mmHg), equivalent to normal tissue pressure, increases phagocytosis by primary monocytes and PMA-differentiated THP-1 macrophages, in part by FAK and ERK inhibition and p38 activation. PI-3K is required for macrophage phagocytosis, but whether PI-3K mediates pressure-stimulated phagocytosis is not known. Furthermore, little is known about the role played by the PI-3K downstream Kinases, Akt, and p70 S6 kinase (p70S6K) in modulating macrophage phagocytosis. Thus, we studied the contribution of PI-3K, Akt, and p70S6K to pressure-increased serum-opsonized bead phagocytosis. Pressure-induced p85 PI-3K translocation from cytosolic to membrane fractions and increased Akt activation by 36.1 +/- 12.0% in THP-1 macrophages. LY294002 or Akt inhibitor IV abrogated pressure-stimulated but not basal phagocytosis. Basal Akt activation was inhibited 90% by LY294002 and 70% by Akt inhibitor IV. Each inhibitor prevented Akt activation by pressure. SiRNA targeted to Akt1, Akt2, or Akt3 reduced Akt1, Akt2, and Akt3 expression by 50%, 45%, and 40%, respectively. However, only Akt2SiRNA abrogated the pressure-stimulated phagocytosis without affecting basal. Pressure also activated mTOR and p70S6K. mTORSiRNA and p70S6K inhibition by rapamycin or p70S6KSiRNA blocked pressure-induced, but not basal, phagocytosis. Changes in tissue pressure during inflammation may regulate macrophage phagocytosis by activation of PI-3K, which activates Akt2, mTOR, and p70S6K.

Roles of PI3-K/Akt pathways in nanoparticle realgar powders-induced apoptosis in U937 cells

AIM

To study the mechanism by which nanoparticle realgar powders (NRP) induce human histocytic lymphoma U937 cell apoptosis.

METHODS

After the U937 cells were treated with various doses of NRP, the viability of the NRP-induced U937 cells was detected by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay. Granular apoptotic bodies with membrane blebbing and condensed nuclei were observed by fluorescence microscopy. The apoptotic ratio induced by NRP was measured by lactate dehydrogenase (LDH) activity-based assay. Caspase-3 and the expressions of Akt, p-Akt, a nicotinamide adenine dinucleotide (NAD+)-dependent histone deacetylase (SIRT1), p53, and p-p53 were detected by Western blot analysis.

RESULTS

The growth-inhibitory activity of NRP for U937 cells was in a time- and dose-dependent manner. After treatment with various concentrations of NRP for 24 h, the majority of U937 cells underwent apoptosis as measured by LDH assay. In the presence of NRP, wortmannin, the inhibitor of phosphoinositide 3-kinase (PI3-K), and Akt inhibitor KP372-1 augmented the NRP-induced cell apoptosis. When the U937 cells were treated with NRP for the indicated time periods, procaspase-3 was gradually degraded and the activated caspase-3 was significantly increased. The expressions of anti-apoptotic proteins Akt and p-Akt were downregulated. Importantly, the inhibition of SIRT1 contributed to the activation of p53 and the inactivation of the PI3-K/Akt signaling pathway increased the expression of the p53 protein and downregulated the SIRT1 protein expression.

CONCLUSION

The PI3-K/Akt signaling pathway plays an important role in NRP-induced U937 cell apoptosis. The reduced SIRT1 expression and activated p53 might be partially due to the inhibition of the PI3-K/Akt pathway triggered by the NRP-induced initiation of U937 cell apoptosis.

Foreign body-type multinucleated giant cell formation requires protein kinase C beta, delta, and zeta

Multinucleated giant cells are a classic cellular feature of chronic inflammation, although the mechanism of macrophage fusion leading to their formation is not well understood. Here, we investigate the participation of protein kinase C (PKC) in the interleukin (IL)-4-induced fusion of human monocyte-derived macrophages and foreign body giant cell (FBGC) formation in vitro. The PKC inhibitors H-7 and calphostin C attenuated macrophage fusion, whereas H-8, which is more selective for PKA and PKG, did not. Macrophage fusion was also prevented by the phospholipase C inhibitor, Et-18-OCH(3), the PKC isoform inhibitors GO6983 or rottlerin and by peptide inhibitors for PKC (20-28), PKCbeta, or PKCzeta but not by HBDDE or peptide inhibitors for PKCvarepsilon or PKA. In cultures of fusing macrophages/FBGC, we detected only PKCalpha, beta, delta, and zeta by immunoprecipitation and immunoblotting, and we also observed strong expression of these isoforms by immunocytochemistry. Our collective results suggest that the gamma, epsilon, eta, mu, theta, or iota PKC isoforms are not required in the mechanism of IL-4-induced macrophage fusion; whether PKCalpha is required is unclear. However, new evidence is provided that FBGC formation is supported by PKCbeta, PKCdelta, and PKCzeta in combined diacylglycerol-dependent (PKCbeta and PKCdelta) and -independent (PKCzeta) signaling pathways.

Inactivation of ras and changes of mitochondrial membrane potential contribute to oridonin-induced autophagy in a431 cells

We have previously shown that oridonin isolated from Rabdosia rubescens augmented apoptosis while inhibiting autophagy within 24 h in HeLa cells. However, the mechanisms between apoptosis and autophagy induced by oridonin in A431 cells are largely unknown. Here, it was found that autophagic level is significantly upregulated when A431 cells are pretreated with manumycin A (Ras specific inhibitor) compared with oridonin alone treatment, whereas cells precultured with GW5074 (Raf inhibitor) or PD98059 (ERK inhibitor) did not exhibit such an effect. Ras, but not Raf or ERK, was engaged in the control of oridonin-induced autophagy. At the same time, manumycin A contributes to oridonin-induced downregulation of Ras protein expression. Treatment with the combination of oridonin and manumycin A downregulated phosphorylation of Akt, downstream of phosphatidylinositol 3-OH kinase (PI3-K). Preincubation with the PI3-K inhibitor wortmannin and Akt inhibitor KP372-1 enhanced oridonin-induced apoptosis, whereas it inhibited oridonin-induced autophagy. However, under oridonin treatment, the expression of Beclin-1, which has autophagy-inducing activity, was reduced, suggesting that Beclin-1 did not participate in the oridonin-induced autophagy. Morphologic observations, DNA fragmentation analysis, and LDH activity-based assay showed that 3-methyladenine (3-MA), an inhibitor of autophagy, increased the apoptotic sensitivity of A431 cells to oridonin. In addition, manumycin A contributed to oridonin-induced decrease of mitochondrial membrane potential (Deltapsim), consistent with the upregulation of Bax/Bcl-2 ratio. In conclusion, Ras negatively regulated autophagy in oridonin-treated A431 cells, which might be associated with activation of class I PI3-K. Downregulation of Deltapsim and increasing of the ratio of Bax/Bcl-2 might also be partially responsible for the initiation of the autophagic process.

Autophosphorylation docking site Tyr-867 in Mer receptor tyrosine kinase allows for dissociation of multiple signaling pathways for phagocytosis of apoptotic cells and down-modulation of lipopolysaccharide-inducible NF-kappaB transcriptional activation

Efficient clearance of apoptotic cells is essential for tissue homeostasis, allowing for cellular turnover without inflammatory consequences. The Mer (Nyk and c-Eyk) receptor tyrosine kinase (Mertk) is involved in two aspects of apoptotic cell clearance by acting as a receptor for Gas6, a gamma-carboxylated phosphatidylserine-binding protein that bridges apoptotic and viable cells. First, Mertk acts in a bona fide engulfment pathway in concert with alphavbeta5 integrin by regulating cytoskeletal assemblages, and second, it acts as a negative regulator for inflammation by down-modulating pro-inflammatory signals mediated from bacterial lipopolysaccharide-Toll-like receptor 4 (TLR4) signaling, and hence recapitulating anti-inflammatory immune modulation by apoptotic cells. Here we describe Mertk post-receptor events that govern phagocytosis and cytoskeletal signaling are principally mediated by autophosphorylation site Tyr-867. Using the Mertk Y867F mutant and pharmacological inhibitors, we show that Tyr-867 is required for phosphatidylinositol 3-kinase and phospholipase Cgamma2 activation; their activation in turn elicits protein kinase C-dependent signals that act on the actin cytoskeleton. Although Mertk(Y867F) blocked the tyrosine phosphorylation of FAK on Tyr-861 and p130(cas) and also abrogated the phagocytosis of apoptotic cells, this mutant did not suppress lipopolysaccharide-inducible NF-kappaB transcription, nor was NF-kappaB activation dependent on the protein kinase C inhibitor, calphostin C. Finally, unlike the cytoskeletal events associated with Tyr-867 autophosphorylation, the trans-inhibition of NF-kappaB occurred in a postnuclear-dependent fashion independent of cytosolic IkappaB phosphorylation and p65/RelA sequestration. Taken together, these data suggest that Mertk has distinct and separable effects for phagocytosis and for resolving inflammation, providing a molecular rationale for how immune licensing and inflammation can be dissociated from phagocytosis in a single phagocytic receptor.

Oridonin induces apoptosis via PI3K/Akt pathway in cervical carcinoma HeLa cell line

AIM

To investigate the apoptosis-inducing effect of oridonin, a diterpenoid isolated from Rabdosia rubescens, in the human cervical carcinoma HeLa cell line.

METHODS

A morphological analysis, nuclear condensation, and fragmentation of chromatin were monitored using Hoechst 33342 staining. Cell viability was assessed using the 3-(4, 5-dimethylthiazol-(2)-yl)-2, 5-diphenyl tetrazolium bromide (MTT) assay. Cell apoptosis and the apoptosis-related activation in the HeLa cell line were evaluated by flow cytometry and Western blotting.

RESULTS

Oridonin suppressed the proliferation of the HeLa cell line in a dose- and time-dependent fashion. Oridonin treatment downregulated the activation of protein kinase B (Akt), the expression of forkhead box class O (FOXO) transcription factor, and glycogen synthase kinase 3 (GSK3). Oridonin also induced the release of cytochrome c accompanied by the activation of caspase-3 and poly-adenosine diphosphate- ribose polymerase cleavage. In addition, Z-D(OMe)-E(OMe)-V-D(OMe)- FMK (z-DEVD-fmk), an inhibitor of caspases, prevented caspase-3 activation and abrogated oridonin-induced cell death. Finally, oridonin treatment of the HeLa cell line downregulated the expression of the inhibitor of the apoptosis protein.

CONCLUSION

Our results showed that oridonin-induced apoptosis involved several molecular pathways. Oridonin may suppress constitutively activated targets of phosphatidylinositol 3-kinase (Akt, FOXO, and GSK3) in the HeLa cell line, inhibiting the proliferation and induction of caspase-dependent apoptosis.

Augmentation of oridonin-induced apoptosis observed with reduced autophagy

Our previous studies showed that oridonin could induce apoptosis in HeLa cells; and in this study, we further investigated autophagy induced by oridonin in HeLa cells and the relationship between apoptosis and autophagy. HeLa cells were exposed with oridonin after 3-methyladenine (3-MA) pre-culture, and we evaluated the growth inhibitory ratio, morphologic changes, DNA fragmentation, proteins expression as well as autophagic and apoptotic levels. Oridonin inhibited the proliferation of HeLa cells in vitro and induced autophagy. Oligonucleosomal fragementation of DNA as well as increased activities of Bax proteins were induced by oridonin, but the expression of p-Bcl-2 protein was reduced. In the condition of oridonin-treatment, when the inhibitor of phosphoinositide 3-kinase (PI3K), wortmannin, was applied, the autophagic level was significantly decreased, while the apoptotic level was increased, indicating that PI3K is a key regulator of both autophagy and apoptosis. Akt, down-stream factor of PI3K, was activated in autophagic process but suppressed in apoptosis in this study. In addition, when autophagy was blocked by 3-MA, the expression of SIRT-1 was decreased, indicating SIRT-1 contributed to autophagy. Taken together, oridonin simultaneously induced HeLa cell both apoptosis and autophagy in HeLa cells, and inhibition of autophagy contributes to upregulation of apoptosis.

Involvement of phosphatidylinositol-3-kinase and ERK pathways in the production of TGF-beta1 by macrophages treated with liposomes composed of phosphatidylserine

We explored the involvement of phosphatidylinositol 3-kinase (PI3K) and ERK pathways in the production of TGF-beta1 by macrophages treated with liposomes composed of phosphatidylserine (PS-liposomes). PS-liposomes activated Akt, downstream of the PI3K signal cascade, and ERK which led to the expression of TGF-beta1. PI3K inhibitors, LY294002 and wortmannin, inhibited the activation of Akt and ERK following the treatment with PS-liposomes. These inhibitors also suppressed the production of TGF-beta1. Furthermore, PS-liposomes activated macrophages to induce TGF-beta1 expression through PS-specific receptors. These findings suggested that a PI3K-ERK signaling pathway via the PS-receptor is intimately involved in the production of TGF-beta1 which regulates macrophage functions.

Differential control of growth, cell cycle progression, and expression of NF-κB in human breast cancer cells MCF-7, MCF-10A, and MDA-MB-231 by ponicidin and oridonin, diterpenoids from the chinese herb Rabdosia rubescens

Ponicidin and oridonin are novel diterpenoids isolated from Rabdosia rubescens. We tested their effects in MCF-7 and MDA-MB-231 cells, as representing low and high invasive breast carcinoma, with normal MCF-10A cells. Clonogenicity and proliferation in MCF-7 cells were inhibited more significantly by ponicidin than oridonin, while the reverse was observed in MCF-10A cells. Ponicidin and oridonin induced S/G2M arrest and G1/S block in MCF-7 cells. In MCF-10A cells treated with either diterpenoid, induction of apoptosis was observed. Moreover, oridonin almost completely blocked MCF-10A progression from S to G2/M phase; in contrast, ponicidin-treated MCF-10A cells showed no discernable changes in cell cycle phase distribution. Neither diterpenoid affected growth of MDA-MB-231 cells, at the dose range effective for MCF-7 or MCF-10A cells. Ponicidin-treated MCF-7 cells expressed reduced levels of cyclin B1, cdc2, transcription factor E2F, and Rb including phosphorylation at S780. Less pronounced effects were found in cells treated with oridonin. Neither compound altered cyclin D1 and cdk4 in MCF-7 cells. In MCF-10A cells, oridonin was more active than ponicidin in inhibiting the expression of cyclin B1, cdc2, S780-phosphorylated Rb, and E2F. To further investigate induction of apoptosis in MCF-10A cells, we measured changes in NF-kappaB. Decreases in p65 or p50 forms of NF-kappaB and its upstream regulator I-kappaB were found in oridonin-treated MCF-10A and not MCF-7 cells. Taken together, these results provide a mechanistic framework for the cellular effects of ponicidin and oridonin in different stage breast cancer cells.