Cytotoxic effects of the cigarette smoke extract of heated tobacco products on human oral squamous cell carcinoma: the role of reactive oxygen species and CaMKK2.

BACKGROUND: The increasing prevalence of heated tobacco products (HTPs) has heightened concerns regarding their potential health risks. Previous studies have demonstrated the toxicity of cigarette smoke extract (CSE) from traditional tobacco's mainstream smoke, even after the removal of nicotine and tar. Our study aimed to investigate the cytotoxicity of CSE derived from HTPs and traditional tobacco, with a particular focus on the role of reactive oxygen species (ROS) and intracellular Ca2+. METHODS: A human oral squamous cell carcinoma (OSCC) cell line, HSC-3 was utilized. To prepare CSE, aerosols from HTPs (IQOS) and traditional tobacco products (1R6F reference cigarette) were collected into cell culture media. A cell viability assay, apoptosis assay, western blotting, and Fluo-4 assay were conducted. Changes in ROS levels were measured using electron spin resonance spectroscopy and the high-sensitivity 2',7'-dichlorofluorescein diacetate assay. We performed a knockdown of calcium/calmodulin-dependent protein kinase kinase 2 (CaMKK2) by shRNA lentivirus in OSCC cells. RESULTS: CSE from both HTPs and traditional tobacco exhibited cytotoxic effects in OSCC cells. Exposure to CSE from both sources led to an increase in intracellular Ca2+ concentration and induced p38 phosphorylation. Additionally, these extracts prompted cell apoptosis and heightened ROS levels. N-acetylcysteine (NAC) mitigated the cytotoxic effects and p38 phosphorylation. Furthermore, the knockdown of CaMKK2 in HSC-3 cells reduced cytotoxicity, ROS production, and p38 phosphorylation in response to CSE. CONCLUSION: Our findings suggest that the CSE from both HTPs and traditional tobacco induce cytotoxicity. This toxicity is mediated by ROS, which are regulated through Ca2+ signaling and CaMKK2 pathways.

Mechanism of cytotoxicity induced by the cigarette smoke extract (CSE) of heated tobacco products in vascular smooth muscle cells: A comparative study of the cytotoxic effects of CSE and the ferroptosis inducer, erastin.

Heated tobacco products (HTPs) are marketed worldwide as less harmful alternatives to combustible cigarettes; however, their cytotoxic mechanisms in vascular smooth muscle cells are poorly understood. Ferroptosis is defined as iron-dependent cell death caused by the accumulation of lipid peroxidation products. In this study, the cytotoxic effects of nicotine- and tar-free cigarette smoke extracts (CSE) derived from three types of HTPs and the ferroptosis inducer, erastin, on vascular smooth muscle A7r5 cells were compared. Cigarette smoke from all HTPs was generated according to the following puffing regime: 55 mL, puff volume; 30 s, puff interval; 2 s, puff duration; bell-shaped, puff profile; and no blocking of the ventilation holes. Erastin and CSE decreased mitochondrial metabolic activity and increased lactate dehydrogenase leakage. The cytotoxic effects of erastin were almost completely inhibited by the radical-trapping antioxidant, UAMC-3203; iron chelator, deferoxamine mesylate (DFO); 12/15-lipoxygenase (12/15-LOX) inhibitor, baicalein; and selective 15-LOX inhibitor, ML351. In contrast, CSE-induced cell damage was partially attenuated by UAMC-3203, baicalein, and ML351 but not by DFO. These results suggest that erastin induces ferroptosis via 15-LOX-mediated iron-dependent lipid peroxidation, whereas CSE causes iron-independent cell damage via 15-LOX-mediated lipid peroxidation-dependent and -independent mechanisms.

Effects of cigarette smoke extract derived from heated tobacco products on the proliferation of lung cancer stem cells.

Epidemiological studies have suggested that cigarette smoking can increase a person's risk of developing several types of cancer, including lung cancer. Lung cancer originates from cancer stem cells (CSCs), which constitute a minor cell population in tumors, and contribute to drug resistance and recurrence. Heated tobacco products (HTPs) produce aerosols that contain nicotine and toxic chemicals. Current evidence, however, is insufficient to accurately determine if HTPs are less harmful than burned cigarettes. This study has investigated the effects of cigarette smoke extract (CSE) from HTPs on lung CSCs in lung cancer cell lines. We found that CSEs induced the proliferation of lung CSCs and increased the expression levels of stem cell markers. In addition, CSE induced epithelial-mesenchymal transition (EMT) expression and cytokine production. These results suggest that HTPs can induce lung CSCs in vitro.

Comparison of cytotoxicity of cigarette smoke extract derived from heat-not-burn and combustion cigarettes in human vascular endothelial cells.

The present study compared the properties of mainstream smoke generated from heat-not-burn (HNB) cigarettes and a combustion cigarette (hi-lite™ brand). Three types of cigarette heating devices were used to generate cigarette smoke at different heating temperatures [Ploom S™ (200 °C), glo™ (240 °C), and IQOS™ (300-350 °C)]. Mainstream smoke was generated using the following puffing regimen: volume, 55 mL; duration, 3 s; and interval, 30 s. The rank order of particulate phase (nicotine and tar) amounts trapped on a Cambridge filter was Ploom S < glo < IQOS < hi-lite. Heated cigarette-derived smoke extract (hCSE) from the devices except for Ploom S, and burned CSE (bCSE) decreased mitochondrial metabolic activity (glo < IQOS < hi-lite) in human vascular endothelial cells. Furthermore, the cytotoxicity was reduced by removing the particulate phase from the mainstream smoke. Endothelial nitric oxide synthase activity was reduced by nicotine- and tar-free CSE of IQOS and hi-lite (IQOS < hi-lite), but not Ploom S and glo. These inhibitory effects were diminished by removing the carbonyl compounds from the mainstream smoke. These results indicated that the cytotoxicity of hCSE was lower than that of bCSE in vascular endothelial cells.

Cigarette Smoke Extract and Its Cytotoxic Factor Acrolein Inhibit Nitric Oxide Production in Human Vascular Endothelial Cells.

Acrolein (ACR), a highly reactive α,ß-unsaturated aldehyde, is a major cytotoxic factor in nicotine- and tar-free cigarette smoke extract (CSE). There are conflicting results regarding endothelial functions despite the fact that both CSE and ACR cause cellular damage. Several lines of evidence indicate that CSE impairs endothelium-derived nitric oxide (NO)-dependent vasodilation by reducing the activity and protein expression of endothelial NO synthase (eNOS), whereas ACR elicits endothelium-dependent vasorelaxation by increasing the production of NO and expression of eNOS. To clarify whether CSE and its cytotoxic factor ACR cause endothelial dysfunction, this study examined the effects of CSE and ACR on human vascular endothelial EA.hy926 cells. CSE and ACR reduced the phosphorylation of eNOS at serine (Ser)1177 and total expression of eNOS. The CSE- and ACR-induced decrease in the phosphorylation and expression of eNOS was counteracted by glutathione (reduced form), an antioxidant. Basal NO production was inhibited by CSE, ACR, NG-nitro-L-arginine methyl ester (a competitive eNOS inhibitor), and nominally Ca2+-free solution supplemented with BAPTA-AM (a membrane permeable Ca2+ chelator). These results indicate that CSE and ACR increase oxidative stress, and reduce NO production by reducing the activity and total protein level of eNOS.

Endothelin type B receptor interacts with the 78-kDa glucose-regulated protein.

Endothelin (ET)-1 is involved in the vascular system, cell proliferation and apoptosis. ET receptors consist of ET type A receptor (ETA R) and ET type B receptor (ETB R). ETA R and ETB R generally exhibit opposite responses, although many exceptions exist. In the present study, we attempted to identify ETA R- or ETB R-specific binding proteins to understand the differences in ETA R- and ETB R-mediated responses after ET-1 stimulation. The 78-kDa glucose-regulated protein (GRP78) showed a stronger binding affinity towards ETB R than towards ETA R. Moreover, GRP78 overexpression promoted ETB R-mediated ERK activation and GRP78 silencing suppressed ETB R-mediated ERK activation. Furthermore, ETB R can localize GRP78 to the cell periphery. These results suggest that the interaction of ETB R with GRP78 affects ERK activation and GRP78 localization.

Annexin A2 is involved in activation of extracellular signal-regulated kinase upon endothelin-1 stimulation.

The overexpression of endothelin (ET)-1 or ET receptors (ETRs) is related to initiation and progression of tumor. In cancer cells, ET-1 activates various signaling pathways, including mitogen-activated protein kinase, phosphatidylinositol 3-kinase, protein kinase C through ETRs, although the mechanisms by which ET-1 activates these signaling pathways remain uncertain. Here, we found that ETRs interacted with annexin A2, which is overexpressed in various cancers. Annexin A2 bound to ET type A receptor and ET type B receptor. Upon ET-1 stimulation, serine phosphorylation of annexin A2 increased, while there is no change in tyrosine phosphorylation of annexin A2. On the other hand, annexin A2 silencing suppressed activation of ERK upon ET-1 stimulation. These results suggest that interaction of ETRs and annexin A2 may play important roles in activation of extracellular signal-regulated kinase upon ET-1 stimulation.

ARF1 recruits RAC1 to leading edge in neutrophil chemotaxis.

BACKGROUND: The small GTPase ARF1 mediates membrane trafficking mostly from the Golgi, and is essential for the G protein-coupled receptor (GPCR)-mediated chemotaxis of neutrophils. In this process, ARF1 is activated by the guanine nucleotide exchanger GBF1, and is inactivated by the GTPase-activating protein GIT2. Neutrophils generate the Gßγ-PAK1-αPIX-GIT2 linear complex during GPCR-induced chemotaxis, in which αPIX activates RAC1/CDC42, which then employs PAK1. However, it has remained unclear as to why GIT2 is included in this complex. RESULTS: We investigated the association between ARF1 and RAC1/CDC42 during the fMLP-stimulated chemotaxis of HL60 cells. We found that the silencing of GBF1 significantly impaired the recruitment of RAC1 to the leading edges, but not PAK1, αPIX, RAC2, or CDC42. A significant population of RAC1 colocalized with ARF1 at the leading edges in stimulated cells, whereas fMLP activated both ARF1 and ARF5. Consistently, the silencing of ARF1, but not ARF5, impaired the recruitment of RAC1, whereas the silencing of RAC1 did not affect the recruitment of ARF1 to the leading edges. CONCLUSIONS: Our results indicated that the activation of ARF1 triggers the plasma membrane recruitment of RAC1 in GPCR-mediated chemotaxis, which is essential for cortical actin remodeling. Thus, membrane remodeling at the leading edges appears to precede actin remodeling in chemotaxis. Together with the fact that GIT2, which inactivates ARF1, is an integral component of the machinery activating RAC1, we proposed a model in which the ARF1-RAC1 linkage enables the regulation of ARF1 by repetitive on/off cycles during GPCR-mediated neutrophil chemotaxis.

Cigarette Smoke Extract Inhibits Platelet Aggregation by Suppressing Cyclooxygenase Activity.

The results of studies that were performed to determine whether cigarette smoking affects platelet function have been controversial, and the effects of nicotine- and tar-free cigarette smoke extract (CSE) on platelet function remain to be determined. The aim of this study was to determine the effect of CSE on platelet aggregation and to clarify the mechanism by which CSE affects platelet function. CSE inhibited murine platelet aggregation induced by 9,11-dideoxy-9α,11α-methanoepoxy-prosta-5Z,13E-dien-1-oic acid (U-46619), a thromboxane (TX) A 2 receptor agonist, and that induced by collagen with respective IC 50 values of 1.05 ± 0.14% and 1.34 ± 0.19%. A similar inhibitory action of CSE was also observed in human platelets. CSE inhibited arachidonic acid-induced TXA 2 production in murine platelets with an IC 50 value of 7.32 ± 2.00%. Accordingly, the inhibitory effect of CSE on collagen-induced aggregation was significantly blunted in platelets lacking the TXA 2 receptor compared with the inhibitory effect in control platelets. In contrast, the antiplatelet effects of CSE in platelets lacking each inhibitory prostanoid receptor, prostaglandin (PG) I 2 receptor and PGE 2 receptor subtypes EP 2 and EP 4 , were not significantly different from the effects in respective control platelets. Among the enzymes responsible for TXA 2 production in platelets, the activity of cyclooxygenase (COX)-1 was inhibited by CSE with an IC 50 value of 1.07 ± 0.15% in an uncompetitive manner. In contrast, the activity of TX synthase was enhanced by CSE. The results indicate that CSE inhibits COX-1 activity and thereby decreases TXA 2 production in platelets, leading to inhibition of platelet aggregation.

A Standardized Method for the Preparation of a Gas Phase Extract of Cigarette Smoke.

The gas phase of cigarette smoke is important from the viewpoint of human health, because it can pass through alveolar epithelium and enter the circulation. There is no standard method for the preparation of a gas phase extract of cigarette smoke (CSE), although CSE is widely used for research instead of whole cigarette smoke. We have established a standard method for the preparation of CSE. One cigarette per trial is continuously combusted under a reduced pressure generated by an aspiration pump with a velocity of 1.050 L/min: the main stream of the smoke is passed through a Cambridge filter to remove tar, and subsequently, bubbled through a glass ball filter (pore size, 20-30 µm) into 15 mL of phosphate-buffered saline (PBS). To express the concentration of CSE, a virtual tar concentration is introduced, which is calculated assuming that tar trapped on the Cambridge filter is dissolved in the PBS. CSEs prepared from smaller numbers of cigarettes (original virtual tar concentration≤15 mg/mL) show similar concentration-response curves for cytotoxicity versus virtual tar concentrations. CSEs prepared from various brands of cigarettes and by different smoking regimes (continuous and puff smoking) show similar cytotoxic potency if the virtual tar concentrations are the same. In conclusion, using the standardized method for CSE preparation in combination with the virtual tar concentration, it becomes possible to simply and rapidly prepare standard CSEs with defined concentrations from any brand of cigarettes, which are toxicologically equivalent to CSE prepared by puff smoking.

Carbonyl Compounds in the Gas Phase of Cigarette Mainstream Smoke and Their Pharmacological Properties.

Cigarette mainstream smoke is composed of gas and tar phases and contains >4000 chemical constituents, including nicotine and tar. The substances in the gas phase but not in the tar phase can pass through the airway epithelial barrier, enter the systemic circulation via the pulmonary circulation, and increase systemic oxidative damage, leading to the development of cigarette smoking-related diseases such as atherosclerosis. Recently, we identified some stable carbonyl compounds, including acrolein (ACR) and methyl vinyl ketone (MVK), as major cytotoxic factors in nicotine- and tar-free cigarette smoke extract (CSE) of the gas phase. CSE, ACR, and MVK induce protein kinase C (PKC)-dependent activation of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) and subsequent generation of reactive oxygen species (ROS) via NOX, causing plasma membrane damage and cell apoptosis. CSE, ACR, and MVK also trigger carbonylation of PKC, which is an irreversible oxidative modification. Cell damage and PKC carbonylation in response to treatment with CSE, ACR, or MVK are abolished by thiol-containing antioxidants such as N-acetyl-L-cysteine and reduced glutathione. Thus pharmacological modulation of PKC and NOX activities and the trapping of ROS are potential strategies for the prevention of diseases related to cigarette smoking.

Endothelin-1 suppresses insulin-stimulated Akt phosphorylation and glucose uptake via GPCR kinase 2 in skeletal muscle cells.

BACKGROUND AND PURPOSE: Endothelin-1 (ET-1) reduces insulin-stimulated glucose uptake in skeletal muscle, inducing insulin resistance. Here, we have determined the molecular mechanisms underlying negative regulation by ET-1 of insulin signalling. EXPERIMENTAL APPROACH: We used the rat L6 skeletal muscle cells fully differentiated into myotubes. Changes in the phosphorylation of Akt was assessed by Western blotting. Effects of ET-1 on insulin-stimulated glucose uptake was assessed with [(3) H]-2-deoxy-d-glucose ([(3) H]2-DG). The C-terminus region of GPCR kinase 2 (GRK2-ct), a dominant negative GRK2, was overexpressed in L6 cells using adenovirus-mediated gene transfer. GRK2 expression was suppressed by transfection of the corresponding short-interfering RNA (siRNA). KEY RESULTS: In L6 myotubes, insulin elicited sustained Akt phosphorylation at Thr(308) and Ser(473) , which was suppressed by ET-1. The inhibitory effects of ET-1 were prevented by treatment with a selective ETA receptor antagonist and a Gq protein inhibitor, overexpression of GRK2-ct and knockdown of GRK2. Insulin increased [(3) H]2-DG uptake rate in a concentration-dependent manner. ET-1 noncompetitively antagonized insulin-stimulated [(3) H]2-DG uptake. Blockade of ETA receptors, overexpression of GRK2-ct and knockdown of GRK2 prevented the ET-1-induced suppression of insulin-stimulated [(3) H]2-DG uptake. In L6 myotubes overexpressing FLAG-tagged GRK2, ET-1 facilitated the interaction of endogenous Akt with FLAG-GRK2. CONCLUSIONS AND IMPLICATIONS: Activation of ETA receptors with ET-1 suppressed insulin-induced Akt phosphorylation at Thr(308) and Ser(473) and [(3) H]2-DG uptake in a GRK2-dependent manner in skeletal muscle cells. These findings suggest that ETA receptors and GRK2 are potential targets for overcoming insulin resistance.

A simple and rapid method for standard preparation of gas phase extract of cigarette smoke.

Cigarette smoke consists of tar and gas phase: the latter is toxicologically important because it can pass through lung alveolar epithelium to enter the circulation. Here we attempt to establish a standard method for preparation of gas phase extract of cigarette smoke (CSE). CSE was prepared by continuously sucking cigarette smoke through a Cambridge filter to remove tar, followed by bubbling it into phosphate-buffered saline (PBS). An increase in dry weight of the filter was defined as tar weight. Characteristically, concentrations of CSEs were represented as virtual tar concentrations, assuming that tar on the filter was dissolved in PBS. CSEs prepared from smaller numbers of cigarettes (original tar concentrations ≤ 15 mg/ml) showed similar concentration-response curves for cytotoxicity versus virtual tar concentrations, but with CSEs from larger numbers (tar ≥ 20 mg/ml), the curves were shifted rightward. Accordingly, the cytotoxic activity was detected in PBS of the second reservoir downstream of the first one with larger numbers of cigarettes. CSEs prepared from various cigarette brands showed comparable concentration-response curves for cytotoxicity. Two types of CSEs prepared by continuous and puff smoking protocols were similar regarding concentration-response curves for cytotoxicity, pharmacology of their cytotoxicity, and concentrations of cytotoxic compounds. These data show that concentrations of CSEs expressed by virtual tar concentrations can be a reference value to normalize their cytotoxicity, irrespective of numbers of combusted cigarettes, cigarette brands and smoking protocols, if original tar concentrations are ≤15 mg/ml.

Endothelin-1 activates extracellular signal-regulated kinases 1/2 via transactivation of platelet-derived growth factor receptor in rat L6 myoblasts.

AIMS: Endothelin (ET) system plays a critical role in the development of insulin resistance and type 2 diabetes. In skeletal muscle, differentiation of myoblasts to myotubes is accompanied by the development of insulin sensitivity. Activation of extracellular signal-regulated kinase (ERK) 1/2 inhibits the differentiation of myoblasts, leading to insulin resistance. Although ET receptor (ETR) stimulation generally activates ERK1/2, the mechanism for ETR-mediated ERK1/2 activation in skeletal muscle is unknown. The purpose of this study was to determine the signal transduction pathway involved in ET-1-stimulated ERK1/2 phosphorylation in L6 myoblasts derived from rat skeletal muscle. MAIN METHODS: Changes in phosphorylation levels of ERK1/2 following stimulation with ET-1 were analyzed by Western blot in L6 myoblasts. To inhibit receptor internalization, dominant-negative dynamin (K44A) was overexpressed in L6 myoblasts using adenovirus-mediated gene transfer. KEY FINDINGS: ET-1 induced phosphorylation of ERK1/2 in L6 myoblasts. The ERK1/2 phosphorylation was abolished by BQ123 (a selective ET type A receptor (ETAR) antagonist), YM-254890 (a Gαq/11 protein inhibitor), and AG370 (a platelet-derived growth factor receptor (PDGFR) kinase inhibitor), while U-73122 (a phospholipase C (PLC) inhibitor) was less potent. The ERK1/2 phosphorylation was inhibited by overexpression of dominant-negative dynamin (K44A). These results suggest that ETAR stimulation induces ERK1/2 phosphorylation in L6 myoblasts through Gq/11 protein-dependent, PLC-independent PDGFR transactivation which requires dynamin-dependent ETAR internalization. SIGNIFICANCE: Because activation of ERK1/2 is considered to inhibit differentiation of myoblasts with the development of insulin sensitivity, the ETAR-mediated PDGFR transactivation and subsequent ERK1/2 activation play an important role in ET-1-induced insulin resistance.

Endothelin receptor signaling: new insight into its regulatory mechanisms.

The endothelin (ET) system consists of two G protein coupled-receptors (GPCRs), ET type A receptor (ETAR) and ET type B receptor (ETBR), and three endogenous ligands, ET-1, ET-2, and ET-3. Stimulation of ETRs with ET-1 induces an increase in intracellular Ca(2+) concentration that is involved in a diverse array of physiological and pathophysiological processes, including vasoconstriction, and cell proliferation. Store-operated Ca(2+) entry and receptor-operated Ca(2+) entry triggered by activation of ETRs are regulated or modulated by endoplasmic reticulum Ca(2+) sensor (stromal interaction molecule 1) and voltage-independent cation channels (transient receptor potential canonical channels and Orai1). The ET-1-induced Ca(2+) mobilization results from activation of heterotrimeric G proteins by ETRs. In contrast, GPCR biology including modulation of receptor function and trafficking is regulated by a variety of GPCR interacting proteins (GIPs) that generally interact with the C-terminal domain of GPCRs. The ETR signaling is also regulated by GIPs such as Jun activation domain-binding protein 1. This review focuses on the regulatory mechanisms of the ETR signaling with special attention to the components involved in Ca(2+) signaling and to GIPs in the signal transduction, modification, and degradation of ETRs.

Identification of stable cytotoxic factors in the gas phase extract of cigarette smoke and pharmacological characterization of their cytotoxicity.

Smoking is a major risk factor for atherosclerotic vascular diseases, but the mechanism for its genesis is unknown. We have recently shown that the gas phase of cigarette smoke (nicotine- and tar-free cigarette smoke extract; CSE) likely to reach the systemic circulation contains stable substances which cause cytotoxicity like plasma membrane damage and cell death in cultured cells, and also that the plasma membrane damage is caused through sequential activation of protein kinase C (PKC) and NADPH oxidase (NOX) and the resulting generation of reactive oxygen species (PKC/NOX-dependent mechanism), whereas cell death is caused through PKC/NOX-dependent and -independent mechanisms. To identify these stable substances, the CSE was prepared by passing the main-stream smoke of 10 cigarettes through a Cambridge glass fiber filter, trapping of the smoke in a vessel cooled at -80°C, and subsequent dissolution in 10ml of water. The CSE was fractionated into nine fractions using reversed-phase HPLC, and each fraction was screened for cytotoxicity in cultured cells, using propidium iodide uptake assay for cell membrane damage and MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] reduction assay for cell viability. The cytotoxicity was positive in two of the nine fractions (Fr2 and Fr5). After extraction of the active fractions into dichloromethane, GC/MS analysis identified 2-cyclopenten-1-one (CPO) in Fr5 but none in Fr2. After derivatization of the active fractions with O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydrochloride, GC/MS analysis identified acrolein, acetone and propionaldehyde in Fr2, and methyl vinyl ketone (MVK) in Fr5. After 4-h incubation, authentic acrolein and MVK induced concentration-dependent cytotoxicity with EC50 values of 75.9±8.2 and 47.0±8.0µM (mean±SEM; n=3), respectively, whereas acetone, propionaldehyde and CPO were without effect. However, after 24-h incubation, CPO induced concentration-dependent cytotoxicity with an EC50 value of 264.0±16.9µM (n=3). The concentrations of acrolein, MVK and CPO in the CSE were 3368±334, 2429±123 and 392.9±31.8µM (n=4), respectively, which were higher than the cytotoxic concentrations. The cytotoxicity of acrolein and MVK consisted of plasma membrane damage and decreased cell viability: the plasma membrane damage was totally prevented by treatment with an inhibitor of PKC or NOX, whereas the decreased cell viability was only partially prevented by these inhibitors. The cytotoxicity of CPO consisted only of decreased cell viability, which was totally resistant to these inhibitors. These results show that acrolein and MVK are responsible for the acute cytotoxicity of the CSE through PKC/NOX-dependent and -independent mechanisms, whereas CPO is responsible for the delayed cytotoxicity of the CSE through a PKC/NOX-independent mechanism.

Nicotine- and tar-free cigarette smoke extract induces cell injury via intracellular Ca2+-dependent subtype-specific protein kinase C activation.

Nicotine- and tar-free cigarette smoke extract (CSE) is reported to induce cell damage via activation of protein kinase C (PKC) and NADPH oxidase (NOX) in rat C6 glioma cells. Here we determined PKC isozyme(s) activated by CSE and their activation mechanism. In C6 glioma cells, mRNAs for PKCα, PKCδ, PKCε, and PKCι were expressed. CSE triggered translocation of PKCα and PKCε to plasma membrane. CSE-induced cell damage and PKC translocation were inhibited by chelating intracellular Ca(2+) but not extracellular Ca(2+). These results suggest that CSE induces cell damage through intracellular Ca(2+)-dependent activation of PKCα and PKCε and subsequent NOX activation.

Different binding property of STIM1 and its novel splice variant STIM1L to Orai1, TRPC3, and TRPC6 channels.

Stromal interaction molecule 1 (STIM1) is the endoplasmic reticulum (ER) Ca(2+) sensor to control ER Ca(2+) levels. A recent study has shown that STIM1L, a new splice variant of STIM1, is expressed in various tissues of rodent and in human skeletal muscle, and that the interaction of STIM1L with actin filament allows rapid activation of store-operated Ca(2+) entry (SOCE) mediated through Orai1 channels. Here, we characterize mRNA expression and function of human STIM1 and STIM1L, and compare their binding property to Orai1 functioning as store-operated Ca(2+) channels (SOCCs), and TRPC3 (transient receptor potential canonical 3) and TRPC6 channels functioning as endothelin type A receptor (ET(A)R)-operated Ca(2+) channels (ROCCs). Although mRNA for STIM1 was ubiquitously expressed in human tissues, STIM1L was detected only in skeletal muscle. STIM1L augmented thapsigargin- and endothelin-1-induced SOCE more strongly than STIM1 in human embryonic kidney 293 cells stably expressing ET(A)R, whereas, it tends to suppress ET(A)R-operated Ca(2+) entry (ROCE) via TRPC3 and TRPC6 more strongly than STIM1. Coimmunoprecipitation experiments have revealed that when compared with STIM1, STIM1L binds more abundantly to Orai1 and also to TRPC3 and TRPC6. These results suggest that the higher binding capacity of STIM1L to SOCCs and ROCCs plays an important role in the regulation of Ca(2+) signaling such as the augmentation of SOCE via Orai1 and the inhibition of ROCE via TRPC3 and TRPC6.

Nicotine- and tar-free cigarette smoke induces cell damage through reactive oxygen species newly generated by PKC-dependent activation of NADPH oxidase.

We examined cytotoxic effects of nicotine/tar-free cigarette smoke extract (CSE) on C6 glioma cells. The CSE induced plasma membrane damage (determined by lactate dehydrogenase leakage and propidium iodide uptake) and cell apoptosis {determined by MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] reduction activity and DNA fragmentation}. The cytotoxic activity decayed with a half-life of approximately 2 h at 37°C, and it was abolished by N-acetyl-L-cysteine and reduced glutathione. The membrane damage was prevented by catalase and edaravone (a scavenger of (•)OH) but not by superoxide dismutase, indicating involvement of (•)OH. In contrast, the CSE-induced cell apoptosis was resistant to edaravone and induced by authentic H(2)O(2) or O(2)(-) generated by the xanthine/xanthine oxidase system, indicating involvement of H(2)O(2) or O(2)(-) in cell apoptosis. Diphenyleneiodonium [NADPH oxidase (NOX) inhibitor] and bisindolylmaleimide I [BIS I, protein kinase C (PKC) inhibitor] abolished membrane damage, whereas they partially inhibited apoptosis. These results demonstrate that 1) a stable component(s) in the CSE activates PKC, which stimulates NOX to generate reactive oxygen species (ROS), causing membrane damage and apoptosis; 2) different ROS are responsible for membrane damage and apoptosis; and 3) part of the apoptosis is caused by oxidants independently of PKC and NOX.

Adenylate cyclase/cAMP/protein kinase A signaling pathway inhibits endothelin type A receptor-operated Ca²âº entry mediated via transient receptor potential canonical 6 channels.

Receptor-operated Ca²âº entry (ROCE) via transient receptor potential canonical channel 6 (TRPC6) is important machinery for an increase in intracellular Ca²âº concentration triggered by the activation of G(q) protein-coupled receptors. TRPC6 is phosphorylated by various protein kinases including protein kinase A (PKA). However, the regulation of TRPC6 activity by PKA is still controversial. The purpose of this study was to elucidate the role of adenylate cyclase/cAMP/PKA signaling pathway in the regulation of G(q) protein-coupled endothelin type A receptor (ET(A)R)-mediated ROCE via TRPC6. For this purpose, human embryonic kidney 293 (HEK293) cells stably coexpressing human ET(A)R and TRPC6 (wild type) or its mutants possessing a single point mutation of putative phosphorylation sites for PKA were used to analyze ROCE and amino acids responsible for PKA-mediated phosphorylation of TRPC6. Ca²âº measurements with thapsigargin-induced Ca²âº-depletion/Ca²âº-restoration protocol to estimate ROCE showed that the stimulation of ET(A)R induced marked ROCE in HEK293 cells expressing TRPC6 compared with control cells. The ROCE was inhibited by forskolin and papaverine to activate the cAMP/PKA pathway, whereas it was potentiated by Rp-8-bromoadenosine-cAMP sodium salt, a PKA inhibitor. The inhibitory effects of forskolin and papaverine were partially cancelled by replacing Ser28 (TRPC6(S28A)) but not Thr69 (TRPC6(T69A)) of TRPC6 with alanine. In vitro kinase assay with Phos-tag biotin to determine the phosphorylation level of TRPC6 revealed that wild-type and mutant (TRPC6(S28A) and TRPC6(T69A)) TRPC6 proteins were phosphorylated by PKA, but the phosphorylation level of these mutants was lower (approximately 50%) than that of wild type. These results suggest that TRPC6 is negatively regulated by the PKA-mediated phosphorylation of Ser28 but not Thr69.