15-Deoxy-delta 12,14-prostaglandin J2 induces apoptosis via JNK-mediated mitochondrial pathway in osteoblastic cells

Oligodendrocyte-lineage cell exocytosis and L-type prostaglandin D synthase promote oligodendrocyte development and myelination

In the developing central nervous system, oligodendrocyte precursor cells (OPCs) differentiate into oligodendrocytes, which form myelin around axons. Oligodendrocytes and myelin are essential for the function of the central nervous system, as evidenced by the severe neurological symptoms that arise in demyelinating diseases such as multiple sclerosis and leukodystrophy. Although many cell-intrinsic mechanisms that regulate oligodendrocyte development and myelination have been reported, it remains unclear whether interactions among oligodendrocyte-lineage cells (OPCs and oligodendrocytes) affect oligodendrocyte development and myelination. Here, we show that blocking vesicle-associated membrane protein (VAMP) 1/2/3-dependent exocytosis from oligodendrocyte-lineage cells impairs oligodendrocyte development, myelination, and motor behavior in mice. Adding oligodendrocyte-lineage cell-secreted molecules to secretion-deficient OPC cultures partially restores the morphological maturation of oligodendrocytes. Moreover, we identified L-type prostaglandin D synthase as an oligodendrocyte-lineage cell-secreted protein that promotes oligodendrocyte development and myelination in vivo. These findings reveal a novel autocrine/paracrine loop model for the regulation of oligodendrocyte and myelin development.

Induction of Heme Oxygenase-1 by 15d-Prostaglandin J2 Mediated via a ROS-Dependent Sp1 and AP-1 Cascade Suppresses Lipopolysaccharide-Triggered Interleukin-6 Expression in Mouse Brain Microvascular Endothelial Cells

Heme oxygenase-1 (HO-1) has been shown to exert antioxidant, anti-inflammatory, and anti-apoptotic effects in various types of cells. Therefore, the induction of HO-1 is an excellent rationale for the development of protective drugs. 15-Deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) can modulate the expression of antioxidant defense proteins and be beneficial for neuroinflammation. Brain endothelial cells play an important role in the pathophysiology of brain disorders. Whether 15d-PGJ₂ can induce HO-1 expression and protect against the inflammatory responses in mouse brain microvascular endothelial (bEnd.3) cells remains unclear. Here, we reveal that 15d-PGJ₂ stimulated HO-1 protein and mRNA expression in a time- and concentration-dependent manner in bEnd.3 cells, which was attenuated by diphenyleneiodonium chloride (DPI) and MitoTempo. Thus, activation of NADPH oxidase (NOX)- and mitochondria-derived reactive oxygen species (ROS) mediated 15d-PGJ₂-induced HO-1 expression. ROS generation could cause phosphorylation of protein kinase C (PKC)δ, leading to HO-1 expression, which was suppressed by Rottlerin (selective inhibitor PKCδ), DPI, and MitoTempo. We further demonstrated that phosphorylation of c-Jun N-terminal kinase (JNK)1/2 participated in 15d-PGJ₂-upregulated HO-1 expression, which was blocked by SP600125 or Rottlerin. Moreover, 15d-PGJ₂-induced HO-1 expression was mediated through the activation of c-Jun (a subunit of activator protein 1 (AP-1)) and specificity protein 1 (Sp1), leading to their interaction with the HO-1 promoter, revealed by chromatin immunoprecipitation assay, which was attenuated by SP600125, Mithramycin A, or Tanshinone II A. We further verified the anti-inflammatory effect of HO-1 expression. Our results showed that 15d-PGJ₂-induced HO-1 could mitigate the lipopolysaccharide-triggered interleukin-6 expression and secretion, as measured by an ELISA assay kit. These results suggest that 15d-PGJ₂-induced HO-1 expression is mediated through the activation of NOX- and mitochondria-derived ROS-dependent PKCδ/JNK1/2/Sp1 and the AP-1 signaling pathway and protects against inflammatory responses in bEnd.3 cells.

Disease-Dependent Antiapoptotic Effects of Cannabidiol for Keratinocytes Observed upon UV Irradiation

Although apoptosis of keratinocytes has been relatively well studied, there is a lack of information comparing potentially proapoptotic treatments for healthy and diseased skin cells. Psoriasis is a chronic autoimmune-mediated skin disease manifested by patches of hyperproliferative keratinocytes that do not undergo apoptosis. UVB phototherapy is commonly used to treat psoriasis, although this has undesirable side effects, and is often combined with anti-inflammatory compounds. The aim of this study was to analyze if cannabidiol (CBD), a phytocannabinoid that has anti-inflammatory and antioxidant properties, may modify the proapoptotic effects of UVB irradiation in vitro by influencing apoptotic signaling pathways in donor psoriatic and healthy human keratinocytes obtained from the skin of five volunteers in each group. While CBD alone did not have any major effects on keratinocytes, the UVB treatment activated the extrinsic apoptotic pathway, with enhanced caspase 8 expression in both healthy and psoriatic keratinocytes. However, endoplasmic reticulum (ER) stress, characterized by increased expression of caspase 2, was observed in psoriatic cells after UVB irradiation. Furthermore, decreased p-AKT expression combined with increased 15-d-PGJ₂ level and p-p38 expression was observed in psoriatic keratinocytes, which may promote both apoptosis and necrosis. Application of CBD partially attenuated these effects of UVB irradiation both in healthy and psoriatic keratinocytes, reducing the levels of 15-d-PGJ₂, p-p38 and caspase 8 while increasing Bcl2 expression. However, CBD increased p-AKT only in UVB-treated healthy cells. Therefore, the reduction of apoptotic signaling pathways by CBD, observed mainly in healthy keratinocytes, suggests the need for further research into the possible beneficial effects of CBD.

Involvement of Metabolic Lipid Mediators in the Regulation of Apoptosis

Apoptosis is the physiological mechanism of cell death and can be modulated by endogenous and exogenous factors, including stress and metabolic alterations. Reactive oxygen species (ROS), as well as ROS-dependent lipid peroxidation products (including isoprostanes and reactive aldehydes including 4-hydroxynonenal) are proapoptotic factors. These mediators can activate apoptosis via mitochondrial-, receptor-, or ER stress-dependent pathways. Phospholipid metabolism is also an essential regulator of apoptosis, producing the proapoptotic prostaglandins of the PGD and PGJ series, as well as the antiapoptotic prostaglandins of the PGE series, but also 12-HETE and 20-HETE. The effect of endocannabinoids and phytocannabinoids on apoptosis depends on cell type-specific differences. Cells where cannabinoid receptor type 1 (CB1) is the dominant cannabinoid receptor, as well as cells with high cyclooxygenase (COX) activity, undergo apoptosis after the administration of cannabinoids. In contrast, in cells where CB2 receptors dominate, and cells with low COX activity, cannabinoids act in a cytoprotective manner. Therefore, cell type-specific differences in the pro- and antiapoptotic effects of lipids and their (oxidative) products might reveal new options for differential bioanalysis between normal, functional, and degenerating or malignant cells, and better integrative biomedical treatments of major stress-associated diseases.

Blockage of Autophagic Flux and Induction of Mitochondria Fragmentation by Paroxetine Hydrochloride in Lung Cancer Cells Promotes Apoptosis via the ROS-MAPK Pathway

Cancer cells are characterized by malignant proliferation and aberrant metabolism and are thereby liable to the depletion of nutrients and accumulation of metabolic waste. To maintain cellular homeostasis, cancer cells are prone to upregulating the canonical autophagy pathway. Here, we identified paroxetine hydrochloride (Paxil) as a late autophagy inhibitor and investigated its killing effect on lung cancer cells and with a xenograft mouse model in vivo. Upregulated LC3-II and p62 expression indicated that Paxil inhibited autophagy. Acid-sensitive dyes (e.g., LysoTracker and AO staining) indicated reduced lysosomal acidity following Paxil treatment; consequently, the maturation of the pH-dependent hydroxylases (e.g., cathepsin B and D) substantially declined. Paxil also induced the fragmentation of mitochondria and further intensified ROS overproduction. Since the autophagy pathway was blocked, ROS rapidly accumulated, which activated JNK and p38 kinase. Such activity promoted the localization of Bax, which led to increased mitochondrial outer membrane permeability. The release of Cytochrome c with the loss of the membrane potential triggered a caspase cascade, ultimately leading to apoptosis. In contrast, the clearance of ROS by its scavenger, NAC, rescued Paxil-induced apoptosis accompanied by reduced p38 and JNK activation. Thus, Paxil blocked the autophagic flux and induced the mitochondria-dependent apoptosis via the ROS-MAPK pathway.

N-Methylparoxetine Blocked Autophagic Flux and Induced Apoptosis by Activating ROS-MAPK Pathway in Non-Small Cell Lung Cancer Cells

The main mechanistic function of most chemotherapeutic drugs is mediated by inducing mitochondria-dependent apoptosis. Tumor cells usually respond to upregulate autophagy to eliminate impaired mitochondria for survival. Hypothetically, inhibiting autophagy might promote mitochondria-dependent apoptosis, thus enhancing the efficacy of chemotherapeutic therapies. We previously identified N-methylparoxetine (NMP) as an inducer of mitochondrial fragmentation with subsequent apoptosis in non-small cell lung cancer (NSCLC) cells. We discovered that ROS was accumulated in NMP-treated NSCLC cells, followed by c-Jun N-terminal kinase (JNK) and p38 MAP kinase (p38) activation. This was reversed by the application of a reactive oxygen species (ROS) scavenger, N-acetylcysteine (NAC), leading to a reduction in apoptosis. Our data suggested that NMP induced apoptosis in NSCLC cells by activating mitogen-activated protein kinase (MAPK) pathway. We further speculated that the remarkable increase of ROS in NMP-treated NSCLC cells might result from an inhibition of autophagy. Our current data confirmed that NMP blocked autophagy flux at late stage wherein lysosomal acidification was inhibited. Taken together, this study demonstrated that NMP could exert dual apoptotic functions—mitochondria impairment and, concomitantly, autophagy inhibition. NMP-related excessive ROS accumulation induced apoptosis by activating the MAPK pathway in NSCLC cells.

Purpurogallin Protects Keratinocytes from Damage and Apoptosis Induced by Ultraviolet B Radiation and Particulate Matter 2.5

Purpurogallin, a natural phenol obtained from oak nutgalls, has been shown to possess antioxidant, anticancer, and anti-inflammatory effects. Recently, in addition to ultraviolet B (UVB) radiation that induces cell apoptosis via oxidative stress, particulate matter 2.5 (PM_2.5) was shown to trigger excessive production of reactive oxygen species. In this study, we observed that UVB radiation and PM_2.5 severely damaged human HaCaT keratinocytes, disrupting cellular DNA, lipids, and proteins and causing mitochondrial depolarization. Purpurogallin protected HaCaT cells from apoptosis induced by UVB radiation and/or PM_2.5. Furthermore, purpurogallin effectively modulates the pro-apoptotic and anti-apoptotic proteins under UVB irradiation via caspase signaling pathways. Additionally, purpurogallin reduced apoptosis via MAPK signaling pathways, as demonstrated using MAPK-p38, ERK, and JNK inhibitors. These results indicate that purpurogallin possesses antioxidant effects and protects cells from damage and apoptosis induced by UVB radiation and PM_2.5.

Diphlorethohydroxycarmalol Attenuates Fine Particulate Matter-Induced Subcellular Skin Dysfunction

The skin, the largest organ in humans, is exposed to major sources of outdoor air pollution, such as fine particulate matter with a diameter ≤ 2.5 µm (PM_2.5). Diphlorethohydroxycarmalol (DPHC), a marine-based compound, possesses multiple activities including antioxidant effect. In the present study, we evaluated the protective effect of DPHC on PM_2.5-induced skin cell damage and elucidated the underlying mechanisms in vitro and in vivo. The results showed that DPHC blocked PM_2.5-induced reactive oxygen species generation in human keratinocytes. In addition, DPHC protected cells against PM_2.5-induced DNA damage, endoplasmic reticulum stress, and autophagy. HR-1 hairless mice exposed to PM_2.5 showed lipid peroxidation, protein carbonylation, and increased epidermal height, which were inhibited by DPHC. Moreover, PM_2.5 induced apoptosis and mitogen-activated protein kinase (MAPK) protein expression; however, these changes were attenuated by DPHC. MAPK inhibitors were used to elucidate the molecular mechanisms underlying these actions, and the results demonstrated that MAPK signaling pathway may play a key role in PM_2.5-induced skin damage.

[Research progress on protease-activated receptor 2 in pathogenesis of osteoarthritis]

Objective

To review the research progress on protease-activated receptor 2 (PAR-2) in the pathogenesis of osteoarthritis (OA).

Methods

The relevant literature about the mechanism of PAR-2 in the occurrence and development of OA in recent years was extensively reviewed and comprehensively analyzed.

Results

Abnormal activation of PAR-2 plays an important role in responses to occurrence and development of OA. Through regulating production and releasing of a variety of cytokines (such as inflammatory factors, metabolic factors, pain factors, etc.), the PAR-2 can involve in pathophysiological progression of OA articular cartilage, subchondral bone, and synovial membrane, as well as occurrence and transmission of pain.

Conclusion

PAR-2 participation in the development of OA has been confirmed. However, since PAR-2 is complicated and widespread, it is necessary to study the specific role of PAR-2 and the interaction between various signal pathways in the progression of OA, and to elucidate the potential pathophysiological mechanisms of PAR-2 participating in the process of OA, in the hope of exploring the new targets for the effective control of OA.

Hematoporphyrin monomethyl ether combined with He-Ne laser irradiation-induced apoptosis in canine breast cancer cells through the mitochondrial pathway

Hematoporphyrin monomethyl ether (HMME) combined with He-Ne laser irradiation is a novel and promising photodynamic therapy (PDT)-induced apoptosis that can be applied in vitro on canine breast cancer cells. However, the exact pathway responsible for HMME-PDT in canine breast cancer cells remains unknown. CHMm cells morphology and apoptosis were analyzed using optical microscope, terminal deoxynucleotidyl transferase dUTP nick end labeling fluorescein staining and DNA ladder assays. Apoptotic pathway was further confirmed by Real-time-polymerase chain reaction and Western blotting assays. Our results showed that HMME-PDT induced significant changes in cell morphology, such as formation of cytoplasmic vacuoles and the gradual rounding of cells coupled with decreased size and detachment. DNA fragmentation and cell death was shown to occur in a time-dependent manner. Furthermore, HMME-PDT increased the activities of caspase-9 and caspase-3, and released cytochrome c from mitochondria into the cytoplasm. HMME-PDT also significantly increased both mRNA and protein levels of Bax and decreased P53 gene expression in a time-dependent manner, while the mRNA and protein expression of Bcl-2 were repressed. These alterations suggest that HMME-PDT induced CHMm cell apoptosis via the mitochondrial apoptosis pathway and had anti-canine breast cancer effects in vitro.

Peroxisome proliferator-activated receptor γ is essential for secretion of ANP induced by prostaglandin D2 in the beating rat atrium

Prostaglandin D₂ (PGD₂) may act against myocardial ischemia-reperfusion (I/R) injury and play an anti-inflammatory role in the heart. Although the effect of PGD₂ in regulation of ANP secretion of the atrium was reported, the mechanisms involved are not clearly identified. The aim of the present study was to investigate whether PGD₂ can regulate ANP secretion in the isolated perfused beating rat atrium, and its underlying mechanisms. PGD₂ (0.1 to 10 µM) significantly increased atrial ANP secretion concomitantly with positive inotropy in a dose-dependent manner. Effects of PGD₂ on atrial ANP secretion and mechanical dynamics were abolished by AH-6809 (1.0 µM) and AL-8810 (1.0 µM), PGD₂ and prostaglandin F2α (PGF2α) receptor antagonists, respectively. Moreover, PGD₂ clearly upregulated atrial peroxisome proliferator-activated receptor gamma (PPARγ) and the PGD₂ metabolite 15-deoxy-Δ12,14-PGJ₂ (15d-PGJ₂, 0.1 µM) dramatically increased atrial ANP secretion. Increased ANP secretions induced by PGD₂ and 15d-PGJ₂ were completely blocked by the PPARγ antagonist GW9662 (0.1 µM). PD98059 (10.0 µM) and LY294002 (1.0 µM), antagonists of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) and phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt) signaling, respectively, significantly attenuated the increase of atrial ANP secretion by PGD₂. These results indicated that PGD₂ stimulated atrial ANP secretion and promoted positive inotropy by activating PPARγ in beating rat atria. MAPK/ERK and PI3K/Akt signaling pathways were each partially involved in regulating PGD₂-induced atrial ANP secretion.

Tudor staphylococcal nuclease drives chemoresistance of non-small cell lung carcinoma cells by regulating S100A11

Lung cancer is the leading cause of cancer-related deaths worldwide. Non-small cell lung cancer (NSCLC), the major lung cancer subtype, is characterized by high resistance to chemotherapy. Here we demonstrate that Tudor staphylococcal nuclease (SND1 or TSN) is overexpressed in NSCLC cell lines and tissues, and is important for maintaining NSCLC chemoresistance. Downregulation of TSN by RNAi in NSCLC cells led to strong potentiation of cell death in response to cisplatin. Silencing of TSN was accompanied by a significant decrease in S100A11 expression at both mRNA and protein level. Downregulation of S100A11 by RNAi resulted in enhanced sensitivity of NSCLC cells to cisplatin, oxaliplatin and 5-fluouracil. AACOCF₃, a phospholipase A₂ (PLA₂) inhibitor, strongly abrogated chemosensitization upon silencing of S100A11 suggesting that PLA₂ inhibition by S100A11 governs the chemoresistance of NSCLC. Moreover, silencing of S100A11 stimulated mitochondrial superoxide production, which was decreased by AACOCF₃, as well as N-acetyl-L-cysteine, which also mimicked the effect of PLA₂ inhibitor on NSCLC chemosensitization upon S100A11 silencing. Thus, we present the novel TSN-S100A11-PLA₂ axis regulating superoxide-dependent apoptosis, triggered by platinum-based chemotherapeutic agents in NSCLC that may be targeted by innovative cancer therapies.

Activation of the MAPK/Akt/Nrf2-Egr1/HO-1-GCLc axis protects MG-63 osteosarcoma cells against 15d-PGJ2-mediated cell death

Despite considerable efforts to improve treatment modalities for osteosarcoma (OS), patient survival remains poor mainly due to pro-survival pathways in OS cells. Among others, prostaglandins (PGs) are the potent regulators of bone homoeostasis and OS pathophysiology. Therefore, the present study aimed to elucidate the impact of 15-deoxy-Δ^12,14-PGJ₂ (15d-PGJ₂, a stable PGD₂ degradation product) on cell death/cell survival pathways in p53-deficient MG-63 OS cells. Our findings show that 15d-PGJ₂ induces generation of reactive oxygen species that promote p38 MAPK activation and subsequent Akt phosphorylation. This pathway induced nuclear expression of Nrf2 and Egr1, and increased transcription of haem oxygenase-1 (HO-1) and the catalytic subunit of glutamate cysteine ligase (GCLc), catalysing the first step in GSH synthesis. Silencing of Nrf2, Egr1 and HO-1 significantly elevated 15d-PGJ₂-mediated reduction of cellular metabolic activity. Activation of cell survival genes including HO-1 and GCLc inhibited 15d-PGJ₂-induced cleavage of pro-caspase-3 and PARP. Annexin V/propidium iodide staining showed an increase in early/late apoptotic cells in response to 15d-PGJ₂. The observed 15d-PGJ₂-mediated signalling events are independent of PGD₂ receptors (DP1 and DP2) and PPARγ. In addition, the electrophilic carbon atom C9 is a prerequisite for the observed activity of 15d-PGJ₂. The present data show that the intracellular redox imbalance acted as a node and triggered both death and survival pathways in response to 15d-PGJ₂. Pharmacological or genetic interference of the pro-survival pathway, the p38 MAPK/Akt/Nrf2-Egr1/HO-1-GCLc axis, sensitizes MG-63 cells towards 15d-PGJ₂-mediated apoptosis.

Inhibitive effects of 15-deoxy-Δ(12),(14)-prostaglandin J2 on hepatoma-cell proliferation through reactive oxygen species-mediated apoptosis

OBJECTIVE

15-Deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) induces reactive oxygen species (ROS)-mediated apoptosis in many malignant cells, which has not been studied in hepatoma cells. In this study, we investigated whether 15d-PGJ2 induced apoptosis in hepatocellular carcinoma (HCC) associated with ROS.

MATERIALS AND METHODS

The LM3, SMMC-7721, and Huh-7 HCC cell lines were treated with 15d-PGJ2 (5-40 μM) for 24, 48, and 72 hours. Cholecystokinin 8 was used to detect the cytotoxicity of 15d-PGJ2. Flow cytometry, Hoechst staining, and Western blotting were used to analyze apoptosis. ROS were combined with the fluorescent probe dihydroethidium and then observed by fluorescence microscopy and flow cytometry. Activation of JNK and expression of Akt were detected by Western blotting.

RESULTS

15d-PGJ2 inhibited HCC cell proliferation and induced apoptosis in a dose- and time-dependent manner. Apoptosis was mainly induced via an intrinsic pathway and was ROS-dependent, and was alleviated by ROS scavengers. ROS induced JNK activation and Akt downregulation in HCC cells.

CONCLUSION

15d-PGJ2 induced ROS in HCC cell lines, and inhibition of cell growth and apoptosis were partly ROS-dependent.

Localization of 14-3-3δ/ξ on the neuronal cell surface

14-3-3 proteins are intracellularly expressed as ubiquitous adaptor proteins. Here, we found localization of 14-3-3δ/ξ on the neuronal cell surface. 14-3-3δ/ξ was identified as a membrane target for 15-deoxy-Δ(12,14)-prostaglandin J2 (15d-PGJ2). 15d-PGJ2 is a pathological mediator of neurodegenerative diseases including Alzheimer's disease (AD). A causative peptide for AD, amyloid β, is one of binding partner of 14-3-3δ/ξ. Non-permeabilized neurons were used to avoid the intracellular effects of anti-14-3-3δ/ξ antibody in the present study. The plasmalemmal 14-3-3δ/ξ, but not the cytosolic one, was stimulated by its specific antibody, resulting in neuronal cell death. The neurotoxicity of anti-14-3-3δ/ξ antibody was suppressed by an antioxidant, catalase. Catalase prevented neurons from anti-14-3-3δ/ξ antibody-generating neurotoxic H2O2. The neuroprotective effect of catalase was also detected with the post-treatment of neurons after the application of anti-14-3-3δ/ξ antibody. Activation of mitogen-activated protein kinase signaling cascade is a down-stream consequence of H2O2 exposure. A c-Jun N-terminal kinase inhibitor suppressed anti-14-3-3δ/ξ antibody-induced neuronal cell death. To my knowledge, this is the first report that the antibody-stimulated plasmalemmal 14-3-3δ/ξ induced neuronal cell death. Furthermore, H2O2 and JNK contributed to the neurotoxicity of anti-14-3-3δ/ξ antibody as well as those of amyloid β and 15d-PGJ2.

CDK5RAP1 deficiency induces cell cycle arrest and apoptosis in human breast cancer cell line by the ROS/JNK signaling pathway

Cyclin-dependent kinase 5 regulatory subunit associated protein 1 (CDK5RAP1) is an enzyme which post-synthetically converts the RNA modification N6-iso-pentenyladenosine (i6A) into 2-methylthio-N6-isopentenyladenosine (ms2i6A). However, the interaction between CDK5RAP1 deficiency and cell apoptosis has not been studied. Breast cancer has long been a leading cause of mortality in the world. Therefore, in the present study, CDK5RAP1 deficiency in a human breast cancer cell line was investigated. CDK5RAP1 small interfering RNA (siRNA) and negative control siRNA were transfected into MCF-7 cells, and the cells were further incubated for 48 h. CDK5RAP1 deficiency suppressed tumor growth in MCF-7 cells and arrested the cells at G2/M phase. CDK5RAP1 deficiency also induced cell apoptosis and reactive oxygen species (ROS) generation. Furthermore, western blot analysis showed that the expression of phospho-c-Jun N-terminal kinase (p-JNK), p53, caspase-9 and caspase-3 were upregulated in CDK5RAP1-deficient MCF-7 cells. Pretreatment with N-acetyl-cysteine (NAC), the inhibitor of ROS, or with SP600125, the inhibitor of JNK, prevented the apoptosis and the high expression of p-JNK, p53, caspase-9 and caspase-3 in CDK5RAP1-deficient MCF-7 cells. Taken together, these data indicated that CDK5RAP1 deficiency induced cell cycle arrest and apoptosis in human breast cancer MCF-7 cells by the ROS/JNK signaling pathway. Our findings indicated a novel therapeutic strategy for cancer.

Manganese superoxide dismutase is a promising target for enhancing chemosensitivity of basal-like breast carcinoma

AIMS

Although earlier reports highlighted a tumor suppressor role for manganese superoxide dismutase (MnSOD), recent evidence indicates increased expression in a variety of human cancers including aggressive breast carcinoma. In the present article, we hypothesized that MnSOD expression is significantly amplified in the aggressive breast carcinoma basal subtype, and targeting MnSOD could be an attractive strategy for enhancing chemosensitivity of this highly aggressive breast cancer subtype.

RESULTS

Using MDA-MB-231 and BT549 as a model of basal breast cancer cell lines, we show that knockdown of MnSOD decreased the colony-forming ability and sensitized the cells to drug-induced cell death, while drug resistance was associated with increased MnSOD expression. In an attempt to develop a clinically relevant approach to down-regulate MnSOD expression in patients with basal breast carcinoma, we employed activation of the peroxisome proliferator-activated receptor gamma (PPARγ) to repress MnSOD expression; PPARγ activation significantly reduced MnSOD expression, increased chemosensitivity, and inhibited tumor growth. Moreover, as a proof of concept for the clinical use of PPARγ agonists to decrease MnSOD expression, biopsies derived from breast cancer patients who had received synthetic PPARγ ligands as anti-diabetic therapy had significantly reduced MnSOD expression. Finally, we provide evidence to implicate peroxynitrite as the mechanism involved in the increased sensitivity to chemotherapy induced by MnSOD repression.

INNOVATION AND CONCLUSION

These data provide evidence to link increased MnSOD expression with the aggressive basal breast cancer, and underscore the judicious use of PPARγ ligands for specifically down-regulating MnSOD to increase the chemosensitivity of this subtype of breast carcinoma.

15-Deoxy-Δ12,14-prostaglandin J2 induces PPARγ- and p53-independent apoptosis in rabbit synovial cells

A ligand of peroxisome proliferator-activated receptor γ (PPARγ), 15-deoxy-Δ(12,14)-prostaglandin J2 (15d-PGJ2) induces apoptosis in various cells. However, the mechanism appears to be complex and cell-type specific. We investigated the mechanism of 15d-PGJ2-induced apoptosis of rabbit synovial cells. Exposure to 15d-PGJ2 resulted in DNA fragmentation accompanied by caspase-3 and -9 activations in the cells, suggesting occurrence of mitochondria-mediated apoptosis. Although the exposure also induced remarkable increase in p53 protein, its transcriptional activity was rather reduced, suggesting non-necessity of p53 in 15d-PGJ2-induced apoptosis. Covalent binding of 15d-PGJ2 to cellular proteins including p53 resulted in their insolubilization. N-acetylcysteine inhibited not only the 15d-PGJ2-induced apoptotic events but also the protein insolubilizations via its interaction with 15d-PGJ2. The studies using a PPARγ-agonist and -antagonist showed noninvolvement of PPARγ in 15d-PGJ2-induced apoptosis. The pre-exposure to pro-inflammatory cytokines did not affect the cytotoxicity of 15d-PGJ2 in synovial cells. Taken together, these results show that 15d-PGJ2 induces a mitochondria-mediated apoptotic pathway in p53- and PPARγ-independent manners.

15-deoxy-Δ¹²,¹⁴-PGJ₂ promotes inflammation and apoptosis in cardiomyocytes via the DP2/MAPK/TNFα axis

Background

Prostaglandins (PGs), lipid autacoids derived from arachidonic acid, play a pivotal role during inflammation. PGD₂ synthase is abundantly expressed in heart tissue and PGD₂ has recently been found to induce cardiomyocyte apoptosis. PGD₂ is an unstable prostanoid metabolite; therefore the objective of the present study was to elucidate whether its final dehydration product, 15-deoxy-Δ^12,14-PGJ₂ (15d-PGJ₂, present at high levels in ischemic myocardium) might cause cardiomyocyte damage.

Methods and results

Using specific (ant)agonists we show that 15d-PGJ₂ induced formation of intracellular reactive oxygen species (ROS) and phosphorylation of p38 and p42/44 MAPKs via the PGD₂ receptor DP2 (but not DP1 or PPARγ) in the murine atrial cardiomyocyte HL-1 cell line. Activation of the DP2-ROS-MAPK axis by 15d-PGJ₂ enhanced transcription and translation of TNFα and induced apoptosis in HL-1 cardiomyocytes. Silencing of TNFα significantly attenuated the extrinsic (caspase-8) and intrinsic apoptotic pathways (bax and caspase-9), caspase-3 activation and downstream PARP cleavage and γH2AX activation. The apoptotic machinery was unaffected by intracellular calcium, transcription factor NF-κB and its downstream target p53. Of note, 9,10-dihydro-15d-PGJ₂ (lacking the electrophilic carbon atom in the cyclopentenone ring) did not activate cellular responses. Selected experiments performed in primary murine cardiomyocytes confirmed data obtained in HL-1 cells namely that the intrinsic and extrinsic apoptotic cascades are activated via DP2/MAPK/TNFα signaling.

Conclusions

We conclude that the reactive α,β-unsaturated carbonyl group of 15d-PGJ₂ is responsible for the pronounced upregulation of TNFα promoting cardiomyocyte apoptosis. We propose that inhibition of DP2 receptors could provide a possibility to modulate 15d-PGJ₂-induced myocardial injury.

Cytotoxic effects of 15d-PGJ2 against osteosarcoma through ROS-mediated AKT and cell cycle inhibition

Polo-like kinase 1 (PLK1), a critical cell cycle regulator, has been identified as a potential target in osteosarcoma (OS). 15-deoxy-Δ12, 14-prostaglandin J2 (15d-PGJ2), a prostaglandin derivative, has shown its anti-tumor activity by inducing apoptosis through reactive oxygen species (ROS)-mediated inactivation of v-akt, a murine thymoma viral oncogene homolog, (AKT) in cancer cells. In the study analyzing its effects on arthritis, 15d-PGJ2 mediated shear-induced chondrocyte apoptosis via protein kinase A (PKA)-dependent regulation of PLK1. In this study, the cytotoxic effect and mechanism underlying 15d-PGJ2 effects against OS were explored using OS cell lines. 15d-PGJ2 induced significant G2/M arrest, and exerted time- and dose-dependent cytotoxic effects against all OS cell lines. Western blot analysis showed that both AKT and PKA-PLK1 were down-regulated in OS cell lines after treatment with 15d-PGJ2. In addition, transfection of constitutively active AKT or PLK1 partially rescued cells from 15d-PGJ2-induced apoptosis, suggesting crucial roles for both pathways in the anti-cancer effects of 15d-PGJ2. Moreover, ROS generation was found treatment with 15d-PGJ2, and its cytotoxic effect could be reversed with N-acetyl-l-cysteine. Furthermore, inhibition of JNK partially rescued 15d-PGJ2 cytotoxicity. Thus, ROS-mediated JNK activation may contribute to apoptosis through down-regulation of the p-Akt and PKA-PLK1 pathways. 15d-PGJ2 is a potential therapeutic agent for OS, exerting cytotoxicity mediated through both AKT and PKA-PLK1 inhibition, and these results form the basis for further analysis of its role in animal studies and clinical applications.

Role of mitochondria in programmed cell death mediated by arachidonic acid-derived eicosanoids

Arachidonic acid-derived eicosanoids from cyclooxygenases, lipoxygenases, and cytochrome P450 are important lipid mediators involved in numerous homeostatic and pathophysiological processes. Most eicosanoids act primarily on their respective cell surface G-protein coupled receptors to elicit downstream signaling in an autocrine and paracrine fashion. Emerging evidence indicates that these hormones are also critical in apoptosis in a cell/tissue specific manner. In this review, we summarize the formation of eicosanoids and their roles as mediators in apoptosis, specifically on the roles of mitochondria in mediating these events and the signaling pathways involved. The biological relevance of eicosanoid-mediated apoptosis is also discussed.

The Role of PPARγ in the Transcriptional Control by Agonists and Antagonists

In recent years, peroxisome proliferator-activated receptor gamma (PPARγ) has been reported to be a target for the treatment of type II diabetes. Furthermore, it has received attention for its therapeutic potential in many other human diseases, including atherosclerosis, obesity, and cancers. Recent studies have provided evidence that the endogenously produced PPARγ antagonist, 2,3-cyclic phosphatidic acid (cPA), which is similar in structure to lysophosphatidic acid (LPA), inhibits cancer cell invasion and metastasis in vitro and in vivo. We recently observed that cPA negatively regulates PPARγ function by stabilizing the binding of the corepressor protein, silencing mediator of retinoic acid and thyroid hormone receptor. We also showed that cPA prevents neointima formation, adipocyte differentiation, lipid accumulation, and upregulation of PPARγ target gene transcription. We then analyzed the molecular mechanism of cPA's action on PPARγ. In this paper, we summarize the current knowledge on the mechanism of PPARγ-mediated transcriptional activity and transcriptional repression in response to novel lipid-derived ligands, such as cPA.

Copper compound induces autophagy and apoptosis of glioma cells by reactive oxygen species and JNK activation

BACKGROUND

Glioblastoma multiforme (GBM) is the most aggressive of the primary brain tumors, with a grim prognosis despite intensive treatment. In the past decades, progress in research has not significantly increased overall survival rate.

METHODS

The in vitro antineoplastic effect and mechanism of action of Casiopeina III-ia (Cas III-ia), a copper compound, on rat malignant glioma C6 cells was investigated.

RESULTS

Cas III-ia significantly inhibited cell proliferation, inducing autophagy and apoptosis, which correlated with the formation of autophagic vacuoles, overexpression of LC3, Beclin 1, Atg 7, Bax and Bid proteins. A decrease was detected in the mitochondrial membrane potential and in the activity of caspase 3 and 8, together with the generation of intracellular reactive oxygen species (ROS) and increased activity of c-jun NH(2)-terminal kinase (JNK). The presence of 3-methyladenine (as selective autophagy inhibitor) increased the antineoplastic effect of Cas III-ia, while Z-VAD-FMK only showed partial protection from the antineoplastic effect induced by Cas III-ia, and ROS antioxidants (N-acetylcysteine) decreased apoptosis, autophagy and JNK activity. Moreover, the JNK -specific inhibitor SP600125 prevented Cas III-ia-induced cell death.

CONCLUSIONS

Our data suggest that Cas III-ia induces cell death by autophagy and apoptosis, in part due to the activation of ROS -dependent JNK signaling. These findings support further studies of Cas III-ia as candidate for treatment of human malignant glioma.

Beta-eleostearic acid induce apoptosis in T24 human bladder cancer cells through reactive oxygen species (ROS)-mediated pathway

Beta-eleostearic acid (β-ESA, 9E11E13E-18:3), a linolenic acid isomer with a conjugated triene system, is a natural and biologically active compound. Herein, we investigated effects of β-eleostearic acid on T24 human bladder cancer cells. In this study, results showed that β-eleostearic acid had strong cytotoxicity to induce cell apoptosis, which was mediated by reactive oxygen species (ROS) in T24 cells. The cell viability assay results showed that incubation with β-eleostearic acid concentrations of 10-80μmol/L caused a dose- and time-dependent decrease of T24 cell viability, and the IC(50) value was 21.2μmol/L at 24h and 13.1μmol/L at 48h. Annexin V/PI double staining was used to assess apoptosis with flow cytometry. Treatment with β-eleostearic acid caused massive ROS accumulation and GSH decrease, which lead to activation of caspase-3 and down-regulation of Bcl-2 indicating induction of apoptosis. Subsequently, N-acetyl-l-cysteine (NAC) and PEG-catalase effectively blocked the ROS elevated effect of β-eleostearic acid, which suggested that β-eleostearic acid-induced apoptosis involved ROS generated. Additionally, we found that treating T24 cells with β-eleostearic acid induced activation of PPARγ. A PPARγ-activated protein kinase inhibitor was able to partially abrogate the effects of β-eleostearic acid. These results suggested that β-eleostearic acid can induce T24 cells apoptosis via a ROS-mediated pathway which may be involved PPARγ activation.

15-Deoxy-Δ12,14-prostaglandin J2 induces Cox-2 expression in human osteosarcoma cells through MAPK and EGFR activation involving reactive oxygen species

Prostaglandins (PGs), important modulators in bone biology, may also contribute to tumor formation and progression in human osteosarcoma. 15-Deoxy-Δ(12,14)-PGJ(2) (15d-PGJ(2)), a metabolite of PGD(2) and PPARγ-ligand, exerts a panel of biological activities via receptor-dependent and -independent mechanisms. As inducible cyclooxygenase-2 (Cox-2) is a candidate inflammatory marker in human osteosarcoma and a rate-limiting enzyme in PG biosynthesis, this study aimed at investigating intracellular redox status and signaling cascades leading to Cox-2 induction in human MG-63 osteosarcoma cells. 15d-PGJ(2) induced the accumulation of reactive oxygen species (ROS) that in turn may lead to upregulation of Cox-2 via two different routes in a PPARγ-independent manner. First, phosphorylation of p38 MAPK directly enhances Cox-2 expression by promoting mRNA stability. Second, 15d-PGJ(2) induces activation of epidermal growth factor receptors and downstream activation of Cox-2 via phosphorylation of p42/44 MAPK. Glutathione precursor molecules reversed enhanced ROS levels and Cox-2 expression. Functional activity of Cox-2 expression was tested by measurement of PGE(2) and PGF(2α). The synthetic compound 9,10-dihydro-15d-PGJ(2) lacking the α,β-unsaturated carbonyl group in the cyclopentenone ring did not exhibit the cellular responses observed with 15d-PGJ(2). We conclude that the electrophilic carbon atom of 15d-PGJ(2) is responsible for alterations in intracellular redox status and Cox-2 expression.

Induction of apoptosis by 15d-PGJ2 via ROS formation: an alternative pathway without PPARγ activation in non-small cell lung carcinoma A549 cells

Cyclopentenone prostaglandin 15-deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ(2)), which is generated from the dehydration of PGD(2), is a natural ligand of peroxisome proliferator-activated receptor gamma (PPARγ) and a potential apoptotic mediator. The synthetic PPARγ ligands, troglitazone and ciglitazone, inhibit tumor progression in many cells by PPARγ activation, but the mechanism of 15d-PGJ(2) is still unclear. In this study, GW9662, an antagonist of PPARγ, and quercetin, a natural antioxidant, were used to study the apoptotic mechanism of 15d-PGJ(2) in A549 cells. Results showed that 15d-PGJ(2) induced apoptosis, which was associated with the production of reactive oxygen species (ROS) and the decrease of GSH levels. Furthermore, quercetin reduced the activity of caspases in 15d-PGJ(2)-induced apoptotic processes. These results suggest that 15d-PGJ(2) induces apoptosis in A549 cells mainly through the formation of ROS; it does not depend on PPARγ activation. Moreover, these findings support the use of quercetin and PPARγ agonists in non-small cell lung carcinoma.

Inflammation as death or life signal in diabetic fracture healing

Increased apoptosis of chondrocytes and osteoblasts and prolonged survival of osteoclasts lead to early destruction of callus tissue and impair bone remodeling in fracture healing of diabetic patients. Diabetes is accompanied by an increased inflammatory state, reactive oxygen species (ROS) generation and accumulation of advanced glycation end products (AGEs), a heterogenous group of toxic metabolites that can induce inflammation. Prolonged hyperglycemia and insulin resistance correlate with increased apoptosis rate and, accordingly, the proapoptotic role of several inflammatory mediators, ROS and AGEs has been also documented. In this review we summarize the most recent reports supporting the idea that inflammatory signaling increases chondrocyte and osteoblast death and prolongs osteoclast survival, resulting in impaired bone regeneration in diabetes. Antagonising inflammatory signal pathways and solution of inflammation may deserve greater attention in the management of diabetic fracture healing.

Rosiglitazone inhibits proliferation of renal proximal tubular cells via down-regulation of ERK and Akt

Rosiglitazone has been reported to exert the protective effect against acute renal failure in animal models. However, the underlying mechanisms by which it protects the damaged kidney cells are poorly understood. The present study was therefore undertaken to examine the effect of rosiglitazone on cell proliferation and to determine its molecular mechanism in opossum kidney (OK) cells, an established renal proximal tubular cell line. Rosiglitazone treatment inhibited cell proliferation in a dose- and time-dependent manner, and such effects were not associated with induction of cell death. The anti-proliferative effect of rosiglitazone was accompanied by the cell cycle arrest at the G1 phase. Western blot analysis data showed that rosiglitazone caused down-regulation of extracellular signal-regulated kinase (ERK) and Akt pathway. Transfection of constitutively active forms of MEK (an upstream kinase of ERK) and Akt prevented the proliferation inhibition induced by rosiglitazone. Rosiglitazone facilitated the recovery of cells after cisplatin-mediated injury. Taken together, these data suggest that rosiglitazone induces inhibition of cell proliferation through ERK and Akt-dependent cell cycle arrest at the G1 phase. The cell cycle arrest may play a protective role in kidney cells by preventing injured cells from progressing in the cell cycle.

Taiwan cobra phospholipase A2-elicited JNK activation is responsible for autocrine fas-mediated cell death and modulating Bcl-2 and Bax protein expression in human leukemia K562 cells

Phospholipase A(2) (PLA(2)) from Naja naja atra venom induced apoptotic death of human leukemia K562 cells. Degradation of procaspases, production of tBid, loss of mitochondrial membrane potential, Bcl-2 degradation, mitochondrial translocation of Bax, and cytochrome c release were observed in PLA(2)-treated cells. Moreover, PLA(2) treatment increased Fas and FasL protein expression. Upon exposure to PLA(2), activation of p38 MAPK (mitogen-activated protein kinase) and JNK (c-Jun NH(2)-terminal kinase) was found in K562 cells. SB202190 (p38 MAPK inhibitor) pretreatment enhanced cytotoxic effect of PLA(2) and led to prolonged JNK activation, but failed to affect PLA(2)-induced upregulation of Fas and FasL protein expression. Sustained JNK activation aggravated caspase8/mitochondria-dependent death pathway, downregulated Bcl-2 expression and increased mitochondrial translocation of Bax. SP600125 (JNK inhibitor) abolished the cytotoxic effect of PLA(2) and PLA(2)-induced autocrine Fas death pathway. Transfection ASK1 siRNA and overexpression of dominant negative p38alpha MAPK proved that ASK1 pathway was responsible for PLA(2)-induced p38 MAPK and JNK activation and p38alpha MAPK activation suppressed dynamically persistent JNK activation. Downregulation of FADD abolished PLA(2)-induced procaspase-8 degradation and rescued viability of PLA(2)-treated cells. Taken together, our results indicate that JNK-mediated autocrine Fas/FasL apoptotic mechanism and modulation of Bcl-2 family proteins are involved in PLA(2)-induced death of K562 cells.

Involvement of p38 MAPK- and JNK-modulated expression of Bcl-2 and Bax in Naja nigricollis CMS-9-induced apoptosis of human leukemia K562 cells

CMS-9, a phospholipase A(2) (PLA(2)) isolated from Naja nigricollis venom, induced apoptosis of human leukemia K562 cells, characterized by mitochondrial depolarization, modulation of Bcl-2 family members, cytochrome c release and activation of caspases 9 and 3. Moreover, an increase in intracellular Ca2+ concentration and the production of reactive oxygen species (ROS) was noted. Pretreatment with BAPTA-AM (Ca2+ chelator) and N-acetylcysteine (NAC, ROS scavenger) proved that Ca2+ was an upstream event in inducing ROS generation. Upon exposure to CMS-9, activation of p38 MAPK and JNK was observed in K562 cells. BAPTA-AM or NAC abrogated CMS-9-elicited p38 MAPK and JNK activation, and rescued viability of CMS-9-treated K562 cells. SB202190 (p38 MAPK inhibitor) and SP600125 (JNK inhibitor) suppressed CMS-9-induced dissipation of mitochondrial membrane potential, Bcl-2 down-regulation, Bax up-regulation and increased mitochondrial translocation of Bax. Inactivation of PLA(2) activity reduced drastically the cytotoxicity of CMS-9, and a combination of lysophosphatidylcholine and stearic acid mimicked the cytotoxic effects of CMS-9. Taken together, our data suggest that CMS-9-induced apoptosis of K562 cells is catalytic activity-dependent and is mediated through mitochondria-mediated death pathway triggered by Ca2+/ROS-evoked p38 MAPK and JNK activation.

Surfactin induces apoptosis in human breast cancer MCF-7 cells through a ROS/JNK-mediated mitochondrial/caspase pathway

Surfactin has been known to inhibit proliferation and induce apoptosis in cancer cells. However, the molecular mechanisms involved in surfactin-induced apoptosis remain poorly understood. The present study was undertaken to elucidate the underlying network of signaling events in surfactin-induced apoptosis of human breast cancer MCF-7 cells. In this study, surfactin caused reactive oxygen species (ROS) generation and the surfactin-induced cell death was prevented by antioxidants N-acetylcysteine (NAC) and catalase, suggesting involvement of ROS generation in surfactin-induced cell death. Surfactin induced a sustained activation of the phosphorylation of ERK1/2 and JNK, but not p38. Moreover, surfactin-induced cell death was reversed by PD98059 (an inhibitor of ERK1/2) and SP600125 (an inhibitor of JNK), but not by SB203580 (an inhibitor of p38). However, the phosphorylation of JNK rather than ERK1/2 activation by surfactin was blocked by NAC/catalase. These results suggest that the action of surfactin on MCF-7 cells was via ERK1/2 and JNK, but not via p38, and the ERK1/2 and JNK activation induce apoptosis through two independent signaling mechanisms. Surfactin triggered the mitochondrial/caspase apoptotic pathway indicated by enhanced Bax-to-Bcl-2 expression ratio, loss of mitochondrial membrane potential, cytochrome c release, and caspase cascade reaction. The NAC and SP600125 blocked these events induced by surfactin. Moreover, the general caspase inhibitor z-VAD-FMK inhibited the caspase-6 activity and exerted the protective effect against the surfactin-induced cell death. Taken together, these findings suggest that the surfactin induces apoptosis through a ROS/JNK-mediated mitochondrial/caspase pathway.

15d-PGJ2 induces apoptosis by reactive oxygen species-mediated inactivation of Akt in leukemia and colorectal cancer cells and shows in vivo antitumor activity

PURPOSE

Recent studies have shown that 15-deoxy-Delta(12, 14)-prostaglandin J(2) (15d-PGJ(2)), a natural ligand for peroxisome proliferator-activated receptor-gamma (PPARgamma), inhibits cell proliferation and induces apoptosis. The specific molecular mechanisms underlying this effect remain to be elucidated. We examined whether 15d-PGJ(2) has antitumor activity in vitro and in vivo, and investigated the underlying mechanism.

EXPERIMENTAL DESIGN

We examined 15d-PGJ(2)-induced apoptosis in human leukemia cells in the context of mitochondrial injury, oxidative damage, and signaling pathway disturbances. In addition, we investigated the antitumor effect of 15d-PGJ(2) in a mouse CT-26 s.c. tumor model and HL-60 leukemia xenograft model.

RESULTS

15d-PGJ(2) induced apoptosis in leukemia and colorectal cancer cells in a dose-dependent manner and led to generation of reactive oxygen species (ROS) through mitochondria and NADPH oxidase activation, activation of JNK, and inactivation of Akt, a serine/threonine-specific protein kinase. Constitutive activation of Akt for an engineered myristoylated protein prevented 15d-PGJ(2)-mediated apoptosis but not ROS generation. Collectively, these findings suggest a hierarchical model of apoptosis induced by 15d-PGJ(2) in human leukemia cells: oxidative injury represents a primary event resulting in Akt inactivation, which in turn leads to mitochondrial injury and apoptosis. Moreover, 15d-PGJ(2) markedly reduced growth of mouse CT-26 s.c. tumors and HL-60 xenograft tumors and down-regulated p-Akt and Akt expression in vivo.

CONCLUSIONS

These results suggest that Akt inactivation through ROS production may contribute to 15d-PGJ(2)-induced apoptosis in leukemia and colorectal cancer cell lines and that 15d-PGJ(2) may have therapeutic relevance in the treatment of human leukemia and colorectal cancer.

Proteinase-activated receptor (PAR)-2 activation impacts bone resorptive properties of human osteoarthritic subchondral bone osteoblasts

INTRODUCTION

In osteoarthritis (OA), the subchondral bone undergoes a remodelling process involving several factors synthesized by osteoblasts. In this study, we investigated the expression, production, modulation, and role of PAR-2 in human OA subchondral bone osteoblasts.

MATERIALS AND METHODS

PAR-2 expression and production were determined by real-time PCR and flow cytometry, respectively. PAR-2 modulation was investigated in OA subchondral bone osteoblasts treated with IL-1 beta (100 pg/ml), TNF-alpha (5 ng/ml), TGF-beta1 (10 ng/ml), PGE(2) (500 nM), IL-6 (10 ng/ml) and IL-17 (10 ng/ml). Membranous RANKL protein was assessed by flow cytometry, and OPG, MMP-1, MMP-9, MMP-13, IL-6 and intracellular signalling pathways by specific ELISAs. Bone resorptive activity was measured by using a co-culture model of human PBMC and OA subchondral bone osteoblasts.

RESULTS

PAR-2 expression and production (p<0.05) were markedly increased when human OA subchondral bone osteoblasts were compared to normal. On OA osteoblasts, PAR-2 production was significantly increased by IL-1 beta, TNF-alpha and PGE(2). Activation of PAR-2 with a specific agonist, SLIGKV-NH(2), induced a significant up-regulation of MMP-1, MMP-9, IL-6, and membranous RANKL, but had no effect on MMP-13 or OPG production. Interestingly, bone resorptive activity was also significantly enhanced following PAR-2 activation. The PAR-2 effect was mediated by activation of the MAP kinases Erk1/2 and JNK.

CONCLUSION

This study is the first to demonstrate that PAR-2 activation plays a role in OA subchondral bone resorption via an up-regulation of major bone remodelling factors. These results shed new light on the potential of PAR-2 as a therapeutic target in OA.

Reactive oxygen species: a double-edged sword in oncogenesis

Reactive oxygen species (ROS) are molecules or ions formed by the incomplete one-electron reduction of oxygen. Of interest, it seems that ROS manifest dual roles, cancer promoting or cancer suppressing, in tumorigenesis. ROS participate simultaneously in two signaling pathways that have inverse functions in tumorigenesis, Ras-Raf-MEK1/2-ERK1/2 signaling and the p38 mitogen-activated protein kinases (MAPK) pathway. It is well known that Ras-Raf-MEK1/2-ERK1/2 signaling is related to oncogenesis, while the p38 MAPK pathway contributes to cancer suppression, which involves oncogene-induced senescence, inflammation-induced cellular senescence, replicative senescence, contact inhibition and DNA-damage responses. Thus, ROS may not be an absolute carcinogenic factor or cancer suppressor. The purpose of the present review is to discuss the dual roles of ROS in the pathogenesis of cancer, and the signaling pathway mediating their role in tumorigenesis.

Silibinin inhibits glioma cell proliferation via Ca2+/ROS/MAPK-dependent mechanism in vitro and glioma tumor growth in vivo

Anticancer activity of silibinin, a flavonoid, has been demonstrated in various cancer cell types. However, the underlying mechanism and in vivo efficacy in glioma were not elucidated. The present study was undertaken to determine the effect of silibinin on glioma cell proliferation in vitro and to examine whether silibinin inhibits tumor growth in vivo. Silibinin resulted in inhibition of proliferation in a dose- and time-dependent manner, which was largely attributed to cell death. Silibinin induced a transient increase in intracellular Ca2+ followed by an increase in reactive oxygen species (ROS) generation. The silibinin-induced cell death was prevented by EGTA, calpain inhibitor and antioxidants (N-acetylcysteine and Trolox). Western blot analysis showed that silibinin also induced ROS-dependent activation of extracellular signal-regulated kinase, p38 kinase, and c-Jun N-terminal kinase. Inhibitors of these kinases prevented the silibinin-induced cell death. Silibinin caused caspase activation and the silibinin-induced cell death was prevented by caspase inhibitors. Glioma cell migration was also decreased by silibinin treatment. Oral administration of silibinin in animals with subcutaneous U87MG glioma cells reduced tumor volume. Subsequent tumor tissue analysis showed a decrease in Ki-67 positive cells, an increase in TUNEL-positive cells, and caspase activation. These results indicate that silibinin induces a caspase-dependent cell death via Ca2+/ROS/MAPK-mediated pathway in vitro and inhibits glioma growth in vivo. These data suggest that silibinin may serve as a potential therapeutic agent for malignant human gliomas.

Ciglitazone induces apoptosis via activation of p38 MAPK and AIF nuclear translocation mediated by reactive oxygen species and Ca(2+) in opossum kidney cells

We have previously demonstrated that the synthetic peroxisome proliferator-activated receptor-gamma (PPARgamma) agonist ciglitazone induces apoptosis accompanied by activation of p38 mitogen-activated protein kinase (MAPK) and nuclear translocation of apoptosis inducing factor (AIF) in opossum kidney (OK) renal epithelial cells. However, the precise mechanism by which ciglitazone induces activation of p38 MAPK and the role of AIF in the induction of the apoptosis are not defined. This study was therefore undertaken to determine whether the roles of reactive oxygen species (ROS) generation and intracellular Ca(2+) in the ciglitazone-induced activation of p38 MAPK and whether AIF nuclear translocation is responsible for the ciglitazone-induced apoptosis in OK renal epithelial cells. Ciglitazone caused generation of ROS and an increase in intracellular Ca(2+). Ciglitazone-induced cell death was reduced by the antioxidant Trolox, the Ca(2+) chelator EGTA, and the store-operated Ca(2+) channels (SOCC) blocker lanthanum chloride (La(3+)), indicating involvement of ROS and Ca(2+) in the ciglitazone-induced cell death. Ciglitazone-induced intracellular Ca(2+) increase was decreased by Trolox, while ROS generation was not affected by EGTA and La(3+), suggesting that ROS generation promote the increase of intracellular Ca(2+). Transfection of small interfering RNA (siRNA) of p38 MAPK or vector expressing microRNA (miRNA) of AIF prevented the ciglitazone-induced cell death. Activation of p38 MAPK, mitochondrial membrane depolarization, and AIF nuclear translocation induced by ciglitazone were inhibited by Trolox, EGTA and La(3+). Taken together, these results suggest that ROS-dependent intracellular Ca(2+) increase is responsible for activation of p38 MAPK and nuclear translocation of AIF by ciglitazone.

HL-37, a novel anthracene derivative, induces Ca(2+)-mediated apoptosis in human breast cancer cells

HL-37, a novel anthracene derivative, exhibited potent anticancer activity in many kinds of cancer cells. However, the exact mechanism and signaling pathway involved in HL-37-induced apoptosis have not been fully elucidated. Therefore, we explored the mechanisms of HL-37-mediated apoptosis in MCF-7 and MDA-MB-435 human breast cancer cells. When MCF-7 cells or MDA-MB-435 cells were co-incubated with HL-37, the percentage of apoptotic cell and S phase of cell cycle was markedly increased. In addition, a rise in intracellular calcium levels, ROS production, phosphorylation of JNK and activation of calpain were found in both MCF-7 cells and MDA-MB-435 cells after exposure to HL-37. With the HL-37-mediated reduction of mitochondrial membrane potential, cytochrome c was released from mitochondria to cytosol. Moreover, HL-37 strongly induced cleavage of caspase-4, caspase-9, as well as caspase-3 in MDA-MB-435 cells, whereas, activation of caspase-4, caspase-9 and caspase-7 but not caspase-3 was detected in MCF-7 cells. These results suggested that HL-37 induced MDA-MB-435 and MCF-7 cells apoptosis via oxidative stress and Ca(2+)/calpain/caspase-4 pathway.