Inhibition of Src activation with cardiotoxin III blocks migration and invasion of MDA-MB-231 cells

Cardiotoxin III (CTX III), a basic polypeptide isolated from Naja naja atra venom, has been demonstrated to display anticancer activity. Breast cancer is a highly malignant carcinoma and most deaths of breast cancer are caused by metastasis. In this study, we show that CTX III blocks migration and invasion of MDA-MB-231 breast cancer cells without affecting apoptosis or cell cycle arrest. CTX III caused significant block of Src kinase activity in MDA-MB-231 cells. Moreover, CTX III treatment was correlated with reduced phosphorylation of FAK at Tyr576, 861 and 925 sites, p130(Cas) at Tyr410, and paxillin at Tyr118. CTX III also suppressed the activation of extracellular signal-regulated kinase1/2 and phosphatidylinositol 3-kinase/Akt. Consistent with inhibition of these signaling pathways and invasion, CTX III inhibited the expression of matrix metalloproteinase-9. In addition, Src specific inhibitor PP2 caused a significant decrease in the phosphorylation of FAK, p130(Cas), paxillin, PI3K/Akt, and ERK1/2. Taken together, CTX III significantly inhibited phosphorylation of Src and downstream molecules as well as cell migration and invasion. Our findings provide evidences that CTX III inhibits Src-mediated signaling pathways involved in controlling MDA-MB-231 cell migration and invasion, suggesting that it has therapeutic potential in breast cancer treatment.

Hydroquinone-induced miR-122 down-regulation elicits ADAM17 up-regulation, leading to increased soluble TNF-α production in human leukemia cells with expressed Bcr/Abl

Studies on HQ-treated human leukemia K562 (Bcr/Abl-positive) cells were conducted to address the hydroquinone (HQ) mechanism that promotes soluble TNF-α (sTNF-α) production. HQ post-translationally down-regulated cell surface TNF-α expression increases the release of sTNF-α into K562 cell culture medium. Meanwhile, HQ increased ADAM17 mRNA stability, leading to ADAM17 up-regulation in HQ-treated cells. Knock-down of ADAM17 abrogated HQ-induced sTNF-α secretion. HQ-evoked miR-122 down-regulation was proven to promote ADAM17 mRNA stability and up-regulate ADAM17 expression. HQ-induced p38 MAPK and JNK activation were responsible for suppression of miR-122 promoter luciferase activity and miR-122 expression. Activation of p38 MAPK and JNK elicited phosphorylation of c-Jun, ATF-2 and c-Fos, and knock-down of c-Jun, ATF-2 and c-Fos restored miR-122 expression in HQ-treated cells. Chromatin immunoprecipitating and DNA affinity purification assay revealed c-Jun, ATF-2 and c-Fos binding to the miR-122 gene promoter region. Moreover, HQ-induced sTNF-α production in Bcr/Abl-positive leukemia cell lines KU812 and MEG-01 was also connected with miR-122 down-regulation and ADAM17 up-regulation, while HQ was unable to affect miR-122 and ADAM-17 expression on Bcr/Abl-negative leukemia U937 cells. Taken together, our data indicate that HQ induces down-regulation of miR-122 expression, leading to ADAM17 up-regulation and ADAM17-mediated TNF-α shedding. Consequently, HQ treatment increases the production of sTNF-α in leukemia cells with expressed Bcr/Abl.

Fusogenicity of Naja naja atra cardiotoxin-like basic protein on sphingomyelin vesicles containing oxidized phosphatidylcholine and cholesterol

This study investigated the effect of oxidized phosphatidylcholine (oxPC) and cholesterol (Chol) on Naja naja atra cardiotoxin-like basic protein (CLBP)-induced fusion and leakage in sphingomyelin (SM) vesicles. Compared with those on PC/SM/Chol vesicles, CLBP showed a lower activity to induce membrane permeability but a higher fusogenicity on oxPC/SM/Chol vesicles. A reduction in inner-leaflet fusion elucidated that CLBP fusogenicity was not in parallel to its membrane-leakage activity on oxPC/SM/Chol vesicles. The lipid domain formed by Chol and SM supported CLBP fusogenicity on oxPC/SM/Chol vesicles, while oxPC altered the interacted mode of CLBP with oxPC/SM/Chol vesicles as evidenced by Fourier transform infrared spectra analyses and colorimetric phospholipid/polydiacetylene membrane assay. Although CLBP showed similar binding affinity with PC/SM/Chol and oxPC/SM/Chol vesicles, the binding capability of CLBP with PC/SM/Chol and oxPC/SM/Chol vesicles was affected differently by NaCl. This emphasized that CLBP adopted different membrane interaction modes upon binding with PC/SM/Chol and oxPC/SM/Chol vesicles. CLBP induced fusion in vesicles containing oxPC bearing the aldehyde group, and aldehyde scavenger methoxyamine abrogated the CLBP ability to induce oxPC/SM/Chol fusion. Taken together, our data indicate that Chol and oxPC bearing aldehyde group alter the CLBP membrane-binding mode, leading to fusogenicity promotion while reducing the membrane-damaging activity of CLBP.

p38 MAPK/PP2Acα/TTP pathway on the connection of TNF-α and caspases activation on hydroquinone-induced apoptosis

This study investigated tumor necrosis factor-α (TNF-α)-mediated death pathway contribution to hydroquinone (HQ) cytotoxicity in human leukemia U937 cells. HQ-induced apoptosis of human leukemia U937 cells was characterized by the increase in mitochondrial membrane depolarization, procaspase-8 degradation and tBid production. Downregulation of Fas-associated death domain protein (FADD) blocked HQ-induced procaspase-8 degradation and rescued the viability of HQ-treated cells, suggesting the involvement of a death receptor-mediated pathway in HQ-induced cell death. HQ induced increased TNF-α mRNA stability led to TNF-α protein expression upregulation, whereas HQ suppressed TNF-α-mediated NFκB pathway activation. HQ elicited protein phosphatase 2A catalytic subunit α (PP2Acα) upregulation via p38 mitogen-activated protein kinase (MAPK)-mediated CREB/c-Jun/ATF-2 phosphorylation, and PP2Acα upregulation was found to promote tristetraprolin (TTP) degradation. Suppression of p38 MAPK activation and protein phosphatase 2A (PP2A) activity abrogated TNF-α upregulation and procaspase degradation in HQ-treated cells. Overexpression of TTP suppressed HQ-induced TNF-α upregulation and restored the viability of HQ-treated cells. Moreover, TTP overexpression increased TNF-α mRNA decay in HQ-treated cells. Taken together, our data indicate that HQ elicits TNF-α upregulation via p38 MAPK/PP2A-mediated TTP downregulation, and suggest that the TNF-α-mediated death pathway is involved in HQ-induced U937 cell death. The same pathway was also proven to be involved in the HQ-induced death of human leukemia HL-60 and Jurkat cells.

A regularly spaced and self-revealing protein ladder for anti-tag Western blot analysis

We designed a protein ladder (hereafter referred to as "Mega-tag") that contains 14 of the most commonly used epitope tags fused to molecular weight markers. The Mega-tag ladder can be simultaneously visualized when anti-tag antibodies are used to detect epitope-tagged recombinant proteins in Western blots. The logarithm of molecular weights and relative mobility of the Mega-tag protein ladder are highly correlated (R(2)=0.997±0.00232), indicating that the dye-free Mega-tag protein ladder is accurate. It can also serve as a positive control for anti-epitope tag immunoblots. The Mega-tag protein ladder should provide a convenient and precise tool for Western blot analysis.

Suppression of Akt/Foxp3-mediated miR-183 expression blocks Sp1-mediated ADAM17 expression and TNFα-mediated NFκB activation in piceatannol-treated human leukemia U937 cells

To address the mechanism of piceatannol in inhibiting TNFα-mediated pathway, studies on piceatannol-treated human leukemia U937 cells were conducted. Piceatannol treatment reduced TNFα shedding and NFκB activation and decreased the release of soluble TNFα into the culture medium of U937 cells. Moreover, ADAM17 expression was down-regulated in piceatannol-treated cells. Over-expression of ADAM17 abrogated the ability of piceatannol to suppress TNFα-mediated NFκB activation. Piceatannol-evoked β-TrCP up-regulation promoted Sp1 degradation, thus reducing transcriptional level of ADAM17 gene in U937 cells. Piceatannol treatment induced p38 MAPK phosphorylation but inactivation of Akt and ERK. In contrast to p38 MAPK inhibitor or restoration of ERK activation, transfection of constitutive active Akt abolished the effect of piceatannol on β-TrCP, Sp1 and ADAM17 expression. Piceatannol-elicited down-regulation of miR-183 expression was found to cause β-TrCP up-regulation. Inactivation of Akt resulted in Foxp3 down-regulation and reduced miR-183 expression in piceatannol-treated cells. Knock-down of Foxp3 and chromatin immunoprecipitating revealed that Foxp3 genetically regulated transcription of miR-183 gene. Taken together, our data indicate that suppression of Akt/Foxp3-mediated miR-183 expression blocks Sp1-mediated ADAM17 expression in piceatannol-treated U937 cells. Consequently, piceatannol suppresses TNFα shedding, leading to inhibition of TNFα/NFκB pathway.

Furano-1,2-Naphthoquinone Inhibits Src and PI3K/Akt Signaling Pathways in Ca9-22 Human Oral Squamous Carcinoma Cells

Furano-1,2-naphthoquinone (FNQ), a biologically active component ofAvicennia marina, has been demonstrated to display anticancer activity. FNQ exerted cytotoxicity with the G2/M cell cycle arrest and apoptosis in Ca9-22 cells. FNQ-induced G2/M arrest was correlated with a marked decrease in the expression levels of cyclin A and cyclin B, and their activating partner cyclin-dependent kinases (CDK) 1 and 2 with concomitant induction of p27. FNQ-induced apoptosis was accompanied by Bax and Bad upregulation, and the downregulation of Bcl-2, Bcl-XL, Mcl-1, and X-linked inhibitor of apoptosis (XIAP), resulting in cytochrome C release and sequential activation of caspase-9 and caspase-3. Mechanistic studies showed that FNQ suppressed Src phosphorylation, PI3K, and Akt activation in Ca9-22 cells. Moreover, the Src inhibitor PP2 reduced the phosphorylation of Src and activation of PI3K/Akt, which was comparable with FNQ treatment. The combined treatment of FNQ with PP2 enhanced the cell cycle arrest and apoptosis and also led to the downregulation of Bcl-XL, Mcl-1, XIAP, cyclin A, cyclin B, CDK1, and CDK2 and upregulation of p27, Bax, and Bad. These findings suggest that FNQ-mediated cytotoxicity of Ca9-22 cells is related with the G2/M cell cycle arrest and apoptosis via inactivation of Src and PI3K/Akt-mediated signaling pathways.

Time-resolved measurements of PM2.5 carbonaceous aerosols at Gosan, Korea

In order to better understand the characteristics of atmospheric carbonaceous aerosol at a background site in Northeast Asia, semicontinuous organic carbon (OC) and elemental carbon (EC), and time-resolved water-soluble organic carbon (WSOC) were measured by a Sunset OC/ EC and a PILS-TOC (particle-into-liquid sampler coupled with an online total organic carbon) analyzer, respectively, at the Gosan supersite on Jeju Island, Korea, in the summer (May 28-June 17) and fall (August 24-September 30) of 2009. Hourly average OC concentration varied in the range of approximately 0.87-28.38 microgC m-3, with a mean of 4.07+/- 2.60 microgC m-3, while the hourly average EC concentration ranged approximately from 0.04 to 8.19 .microgC m-3, with a mean of 1.35 +/- 0.71 microgC m-3, from May 28 to June 17, 2009. During the fall season, OC varied in the approximate range 0.9-9.6 microgC m-3, with a mean of 2.30 +/-0.80 microgC m-3, whereas EC ranged approximately from 0.01 to 5.40 microgC m-3, with a mean of 0.66 +/- 0.38 microgC m-3. Average contributions of EC to TC and WSOC to OC were 26.0% +/- 9.7% and 20.6% +/-7.4%, and 37.6% +/- 23.5% and 57.2% +/- 22.2% during summer and fall seasons, respectively. As expected, clear diurnal variation of WSOC/OC was found in summer, varying from 0.22 during the nighttime up to 0.72 during the daytime, mainly due to the photo-oxidation process. In order to investigate the effect of air mass pathway on the characteristics of carbonaceous aerosol, 5-day back-trajectory analysis was conducted using the HYSPLIT model. The air mass pathways were classified into four types: Continental (CC), Marine (M), East Sea (ES) and Korean Peninsula (KP). The highest OC/EC ratio of 3.63 was observed when air mass originated from the Continental area (CC). The lowest OC/EC ratio of 0.79 was measured when air mass originated from the Marine area (M). A high OC concentration was occasionally observed at Gosan due to local biomass burning activities. The contribution of secondary OC to total OC varied approximately between 8.4% and 32.2% and depended on air mass type.

Antimetastatic potential of cardiotoxin III involves inactivation of PI3K/Akt and p38 MAPK signaling pathways in human breast cancer MDA-MB-231 cells

AIM

The aim of this study is to determine whether cardiotoxin III (CTX III) inhibited the metastasis in MDA-MB-231 cells and to further explain its possible mechanisms.

MAIN METHODS

The MTT assay, wound healing assay, Boyden chamber invasion assay, zymography analysis, reverse transcriptase polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA), inhibitor assay, and Western blot analysis were used to reveal molecular events of CTX III in this study.

KEY FINDINGS

During treatment with non-toxic doses of CTX III, not only cell migration and invasion were markedly suppressed but the expression/activity of matrix metalloproteinase-9 (MMP-9) was also significantly and selectively suppressed in a concentration-dependent manner. In addition, CTX III decreased the nuclear protein level of nuclear factor kappa B (NF-κB), and pretreatment with NF-κB inhibitor (PDTC) or IκB protease inhibitor (TPCK) also reduced MMP-9 expression/activity and cell migration. Our biochemical assays indicated that CTX III potently suppressed the phosphorylation of p38 mitogen-activated protein kinase (MAPK), phosphatidylinositide-3-kinase (PI3K) and Akt. Additionally, the treatment of inhibitors specific for p38 MAPK (SB203580) or PI3K (wortmannin) to cells could result in a reduced expression of NF-κB and MMP-9 expression, concomitantly with an inhibition on cell metastasis.

SIGNIFICANCE

These results demonstrated that CTX III inhibition of MDA-MB-231 cells may occur through inactivation of both PI3K/Akt and p38 MAPK signaling pathways, exerting inhibitory effects on NF-κB transcriptional factor, thereby decreasing the activity of MMP-9 and then posing an anti-metastatic effect in the cells.

Guanidination of notexin promotes its phospholipase A(2) activity-independent fusogenicity on vesicles with lipid-supplied negative curvature

To address the requirement of phospholipase A(2) (PLA(2)) activity in membrane fusion events and membrane perturbation activity of notexin and guanidinated notexin (Gu-notexin), the present study was conducted. Notexin and Gu-notexin did not show PLA(2) activity after the removal of Ca(2+) with EDTA. Metal-free notexin and Gu-notexin were found to induce membrane leakage and fusion of phospholipid vesicles. Fusogenic activity of native and modified notexin correlated positively with their membrane-damaging activity underlying the deprivation of PLA(2) activity. Compared with Ca(2+)-bound Gu-notexin, fusogenicity of metal-free Gu-notexin was notably increased by incorporation of cholesterol, cholesterol sulfate, phosphatidylethanolamine, α-tocopherol and phosphatidic acid that supplied negative curvature into phospholipid bilayer. The ability of Gu-notexin to induce membrane fusion of vesicles with lipid-supplied negative curvature was higher than that of notexin regardless of the absence or presence of Ca(2+). Consistently, metal-free Gu-notexin markedly induced membrane fusion of red blood cells (RBCs) compared with metal-free notexin, and fusion activity of metal-free Gu-notexin on cholesterol-depleted RBCs notably reduced. Compared with notexin, Gu-notexin highly induced uptake of calcein-loaded phosphatidylcholine (PC)/cholesterol and PC/cholesterol sulfate vesicles by K562 cells in the presence of EDTA. Taken together, our data suggest that notexin and Gu-notexin could induce vesicle leakage and fusion via a PLA(2) activity-independent mechanism, and guanidination promotes PLA(2) activity-independent fusogenicity of notexin on vesicles with lipid-supplied negative curvature.

Bactericidal effect of Naja nigricollis toxin γ is related to its membrane-damaging activity

The aim of the present study is to investigate the causal relationship between membrane-damaging activity and bactericidal activity of Naja nigricollis toxin γ. Toxin γ showed a similar inhibitory activity on the growth of Staphylococcus aureus (Gram-positive bacteria) and Escherichia coli (Gram-negative bacteria). Antibacterial activity of toxin γ correlated positively with increase in membrane permeability of bacterial cells. Morphological examination showed that toxin γ disrupted the integrity of bacterial membrane. Toxin γ showed similar binding capability with lipopolysaccharide (LPS) and lipoteichoic acid (LTA), and destabilization of LPS layer and inhibition of LTA biosynthesis on cell wall increased bactericidal effect of toxin γ on E. coli and S. aureus, respectively. Although the potency of toxin γ on permeabilizing model membrane of E. coli and S. aureus was similar, the mode of interaction between toxin γ and model membrane of E. coli and S. aureus differed. Membrane-damaging activity of toxin γ was inhibited by either LPS or LTA. Nevertheless, LPS and LTA altered differently membrane-bound conformation of toxin γ. Taken together, our data suggest that bactericidal activity of toxin γ depends on its ability to induce membrane permeability, and that LPS and LTA structurally suppresses bactericidal effect of toxin γ.

Membrane-damaging activity of Taiwan cobra cardiotoxin 3 is responsible for its bactericidal activity

This study investigates the causal relationship between membrane-damaging activity and bactericidal activity of Naja naja atra (Taiwan cobra) cardiotoxin 3 (CTX3). CTX3 showed greater inhibitory activity for the growth of Staphylococcus aureus (Gram-positive bacteria) relative to that of Escherichia coli (Gram-negative bacteria). The CTX3 antibacterial activity is positively correlated with the increase in membrane permeability of bacterial cells. Morphological examination showed that CTX3 disrupted bacterial membrane integrity.CTX3 showed similar binding capability with lipopolysaccharide (LPS) and lipoteichoic acid (LTA), and destabilization of LPS layer and inhibition of LTA biosynthesis on cell wall increased the CTX3 bactericidal effect on E. coli. and S. aureus, respectively. Compared with that of E. coli, CTX3 notably permeabilized model membrane of S. aureus. CTX3 membrane-damaging activity was inhibited by LPS and LTA, while increasing the CTX3 concentration counteracted the inhibitory action of LPS and LTA. Oxidation of Met residues on loop II of CTX3 simultaneously reduced the membrane-permeabilizing activity and bactericidal effect of CTX3. Taken together, our data indicate that CTX3 bactericidal activity depends highly on its ability to induce membrane permeability.

Furano-1,2-naphthoquinone inhibits EGFR signaling associated with G2/M cell cycle arrest and apoptosis in A549 cells

Furano-1,2-naphthoquinone (FNQ), prepared from 2-hydroxy-1,4-naphthoquinone and chloroacetaldehyde in an efficient one-pot reaction, exhibits an anti-carcinogenic effect. FNQ exerted anti-proliferative activity with the G(2)/M cell cycle arrest and apoptosis in A549 cells. FNQ-induced G(2)/M arrest was correlated with a marked decrease in the expression levels of cyclin A and cyclin B, and their activating partner cyclin-dependent kinases (Cdk) 1 and 2 with concomitant induction of p53, p21, and p27. FNQ-induced apoptosis was accompanied with Bax up-regulation and the down-regulation of Bcl-2, X-linked inhibitor of apoptosis (XIAP), and survivin, resulting in cytochrome c release and sequential activation of caspase-9 and caspase-3. Western blot analysis revealed that FNQ suppressed EGFR phosphorylation and JAK2, STAT3, and STAT5 activation, but increased in activation of p38 MAPK and c-Jun NH2-terminal kinase (JNK) stress signal. The combined treatment of FNQ with AG1478 (a specific EGFR inhibitor) significantly enhanced the G(2)/M arrest and apoptosis, and also led to up-regulation in Bax, p53, p21, p27, release of mitochondrial cytochrome c, and down-regulation of Bcl-2, XIAP, survivin, cyclin A, cyclin B, Cdk1, and Cdk2 in A549 cells. These findings suggest that FNQ-mediated cytotoxicity of A549 cell related with the G(2)/M cell cycle arrest and apoptosis via inactivation of EGFR-mediated signaling pathway.

Taiwan cobra phospholipase A2 elicits posttranscriptional up-regulation of ADAM17 in human neuroblastoma SK-N-SH cells

Taiwan cobra phospholipase A(2) (PLA(2)) treatment promoted proADAM17 processing into mature ADAM17 in human neuroblastoma SK-N-SH cells. The abolishment of catalytic activity caused a drastic drop in the PLA(2) ability to induce ADAM17 maturation, and lysophosphatidylcholine treatment mimicked the effect of PLA(2). ADAM17 activity measurement, ADAM17 cell surface levels, TNFR2 ectodomain shedding, and ADAM17 mRNA transcription supported that posttranscriptional up-regulation of ADAM17 occurred in PLA(2)-treated SK-N-SH cells. PLA(2) treatment induced p38 MAPK activation and ERK inactivation. p38 MAPK activation suppression by SB202190 (p38 MAPK inhibitor) abolished posttranscriptional up-regulation of ADAM17 in PLA(2)-treated cells, while treatment with U0126 (MEK1 and MEK2 inhibitor) increased ADAM17 maturation in SK-N-SH cells. Constitutively active MEK1 expression abrogated PLA(2)-induced ADAM17 maturation. Taken together, our data indicate that PLA(2)-evoked p38 MAPK activation and ERK inactivation are involved in ADAM17 posttranscriptional up-regulation, and suggest that the action of PLA(2) is catalytic activity-dependent.

Caffeine induces matrix metalloproteinase-2 (MMP-2) and MMP-9 down-regulation in human leukemia U937 cells via Ca2+/ROS-mediated suppression of ERK/c-fos pathway and activation of p38 MAPK/c-jun pathway

Caffeine attenuated invasion of human leukemia U937 cells with characteristic of decreased protein expression and mRNA levels of matrix metalloproteinase-2 (MMP-2) and MMP-9. Down-regulation of MMP-2 and MMP-9 in U937 cells was abrogated by abolishment of caffeine-elicited increase in intracellular Ca(2+) concentration and ROS generation. Pretreatment with BAPTA-AM (Ca(2+) chelator) and N-acetylcysteine (ROS scavenger) abolished caffeine-induced ERK inactivation and p38 MPAK activation. Moreover, caffeine treatment led to MAPK phosphatase-1 (MKP-1) down-regulation and protein phosphatase 2A catalytic subunit (PP2Ac) up-regulation, which were involved in cross-talk between p38 MAPK and ERK. Transfection of constitutively active MEK1 or pretreatment with SB202190 (p38 MAPK inhibitor) restored MMP-2 and MMP-9 protein expression in caffeine-treated cells. Caffeine treatment repressed ERK-mediated c-Fos phosphorylation but evoked p38 MAPK-mediated c-Jun phosphorylation. Knock-down of c-Fos and c-Jun by siRNA reflected that c-Fos counteracted the effect of c-Jun on MMP-2/MMP-9 down-regulation. Taken together, our data indicate that MMP-2/MMP-9 down-regulation in caffeine-treated U937 cells is elicited by Ca(2+)/ROS-mediated suppression of ERK/c-Fos pathway and activation of p38 MAPK/c-Jun pathway.

Suppression of ADAM17-mediated Lyn/Akt pathways induces apoptosis of human leukemia U937 cells: Bungarus multicinctus protease inhibitor-like protein-1 uncovers the cytotoxic mechanism

Cell surface proteases have been demonstrated to play an important role in facilitating cell invasion into the extracellular matrix and may contribute significantly to extracellular matrix degradation by metastatic cancer cells. Abundant expression of these enzymes is associated with poor prognosis. Thus, protease inhibitors that repress cell surface proteases may be applicable to cancer therapy. Because soybean Kunitz-type trypsin inhibitor has been found to induce apoptotic death of human leukemia Jurkat cells, anti-leukemia activity of Bungarus multicinctus protease inhibitor-like protein-1 (PILP-1) is thus examined. PILP-1 induced apoptosis of human leukemia U937 cells, characteristic of loss of mitochondrial membrane potential, degradation of procaspase-8, and production of t-Bid. FADD down-regulation neither restored viability of PILP-1-treated cells nor attenuated production of active caspase-8 and t-Bid in PILP-1-treated cells, suggesting that the death receptor-mediated pathway was not involved in the cytotoxicity of PILP-1. It was found that PILP-1-evoked p38 MAPK activation and ERK inactivation led to PILP-1-induced cell death and down-regulation of ADAM17. Knockdown of ADAM17 by siRNA induced death of U937 cells and inactivation of Lyn and Akt. Immunoprecipitation suggested that ADAM17 and Lyn form complexes. Overexpression of ADAM17, LynY507F (gain of function), and constitutively active Akt suppressed the cytotoxic effects of PILP-1. PILP-1-elicited inactivation of Lyn and Akt was abrogated in cells with overexpressed ADAM17 or LynY507F. Taken together, our data indicate that ADAM17-mediated activation of Lyn/Akt maintains the viability of U937 cells and that suppression of the pathway is responsible for PILP-1-induced apoptosis.

Reactive oxygen species and p38 mitogen-activated protein kinase induce apoptotic death of U937 cells in response to Naja nigricollis toxin-gamma

The aim of the present study is to elucidate the signalling components related to Naja nigricollis toxin--induced apoptosis in human leukaemia U937 cells. It was found that toxin--induced apoptotic cell death was attributed mainly to activation of p38 mitogen-activated protein kinase (MAPK), reactive oxygen species (ROS) generation and loss of mitochondrial membrane potential (deltapsim). Subsequent modulation of Bcl-2 family member and cytochrome c release accompanied with activation of caspase-9 and -3 were involved in the death of U937 cells. SB202190 (p38 MAPK inhibitor) and N-acetylcysteine (antioxidant) significantly attenuated toxin--induced cell death and loss of deltapsim, and completely abolished the production of ROS. In contrast to N-acetylcysteine, degradation of Bcl-2/Bcl-XL and mitochondrial localization of Bax were notably decreased by SB202190. Inhibitors of electron transport (rotenone and antimycin A) or inhibitor of mitochondrial permeability transition pore (cyclosporine A) reduced the effect of toxin- on ROS generation, loss of deltapsim and cytochrome c release. Noticeably, pre-treatment with N-acetylcysteine or rotenone eliminated markedly ROS accompanied with reduction in p38 MAPK activation. Taken together, these results suggest that the cytotoxicity of toxin- is initiated by p38-MAPK-mediated mitochondrial dysfunction followed by ROS production and activation of caspases, and that ROS further augments p38 MAPK activation and mitochondrial alteration.

Decay of female sexual behavior under parthenogenesis

A laboratory strain of Drosophila mercatorum has existed for 20 years without males and therefore without natural selection operating to maintain the genetic basis of female mating behavior. The females of this strain have recently experienced a genetic impairment of mating capacity. This observation exemplifies the mode of evolution of vestigial characters and supports Muller's theory that random mutation will tend to destroy the genetic basis of a character from which selection has been removed.

Piceatannol induces Fas and FasL up-regulation in human leukemia U937 cells via Ca2+/p38alpha MAPK-mediated activation of c-Jun and ATF-2 pathways

To verify whether piceatannol-induced death of leukemia cells was associated with Fas-mediated death pathway, the present study was conducted. Piceatannol-induced apoptotic death of human leukemia U937 cells was characterized by increase in intracellular Ca(2+) concentration ([Ca(2+)]i), ERK inactivation, p38 MPAK activation, degradation of procaspase-8 and production of t-Bid. Piceatannol treatment increased Fas and FasL protein expression, and up-regulated transcription of Fas and FasL mRNA. Down-regulation of FADD blocked piceatannol-induced procaspase-8 degradation and rescued viability of piceatannol-treated cells. Abolition of piceatannol-induced increase in [Ca(2+)]i abrogated p38 MAPK activation and up-regulation of Fas and FasL expression, but restored ERK activation and viability of piceatannol-treated cells. Suppression of p38alpha MAPK or transfection of constitutively active MEK1 abolished piceatannol-induced Fas and FasL up-regulation. Piceatannol treatment repressed ERK-mediated c-Fos phosphorylation but evoked p38alpha MAPK-mediated c-Jun and ATF-2 phosphorylation. Knockdown of c-Fos, c-Jun and ATF-2 by siRNA reflected that c-Fos attenuated the effect of c-Jun and ATF-2 on Fas/FasL up-regulation. Taken together, our data indicate that Fas/FasL up-regulation in piceatannol-treated U937 cells is elicited by Ca(2+)/p38alpha MAPK-mediated activation of c-Jun and ATF-2, and suggest that autocrine Fas-mediated apoptotic mechanism is involved in piceatannol-induced cell death.

Concomitant inactivation of the epidermal growth factor receptor, phosphatidylinositol 3-kinase/Akt and Janus tyrosine kinase 2/signal transducer and activator of transcription 3 signalling pathways in cardiotoxin III-treated A549 cells

1. Cardiotoxin (CTX) III, a basic polypeptide with 60 amino acid residues isolated from Naja naja atra venom, has potential anticancer therapeutic activity. The aim of the present study was to investigate the apoptotic effect (and the underlying mechanism of action) of CTX III in human adenocarcinoma A549 cells. 2. It was found that CTX III induces apoptosis in A549 cells, as indicated by an increase in the sub-G(1) population, phosphatidylserine externalization, loss of mitochondrial membrane potential (Psi(m)) with cytochrome c release and activation of caspases 9 and 3. These actions were correlated with upregulation of Bax and Bad and downregulation of various anti-apoptotic proteins, including Bcl-2, Bcl-X(L), Mcl-1, X-linked inhibitor of apoptosis protein (XIAP) and p-Bad in CTX III-treated cells. 3. The signal transduction pathways involved in the effects of CTX III in A549 cells were evaluated using 5 micromol/L AG1478, an inhibitor of the epidermal growth factor receptor (EGFR), and exposing cells to the drug for 8 h. The results indicated that CTX III suppresses phosphorylation of EGFR and activation of phosphatidylinositol 3-kinase (PI3-K)/Akt and Janus tyrosine kinase (JAK) 2/signal transducer and activator of transcription (STAT) 3, all of which are downstream molecules in the EGFR signalling pathway. 4. Exposure of cells for 8 h to the PI3-K inhibitor wortmannin (10 micromol/L) blocked JAK2 and STAT3 activation, whereas exposure of cells to the JAK2 inhibitor AG490 (5 micromol/L) decreased levels of phosphorylated (p-) JAK2 and p-STAT3 without affecting PI3-K/Akt activation. These observations suggest that PI3-K is an upstream activator of JAK2/STAT3. Furthermore, 5 micromol/L AG490 and 10 micromol/L wortmannin treatment of A549 cells for 8 h resulted in upregulation of Bax and Bad and downregulation of Bcl-2, Bcl-X(L), XIAP and p-Bad. 5. Together, the results of the present study indicate that CTX III induces apoptosis in A549 cells by inactivating the EGFR, PI3-K/Akt and JAK2/STAT3 signalling pathways.

Naphtho[1,2-b]furan-4,5-dione induces apoptosis of oral squamous cell carcinoma: involvement of EGF receptor/PI3K/Akt signaling pathway

Naphtho[1,2-b]furan-4,5-dione (NFD), prepared from 2-hydroxy-1,4-naphthoquinone and chloroacetaldehyde in an efficient one-pot reaction, exerts an anti-tumor effect. This study was performed to elucidate whether the epidermal growth factor (EGF) receptor and phosphatidylinositol-3-kinase (PI3K) signaling pathways are involved in NFD-induced apoptosis of oral squamous cell carcinoma (OSCC). Immunoblot showed that NFD suppressed the phosphorylation of EGF receptor and activation of PI3K/Akt, downstream molecules of EGF receptor signaling pathway, in Ca9-22 cells. The levels of downstream targets of Akt, including phospho-glycogen synthase kinase-3beta (p-GSK-3beta), GSK-3beta, forkhead transcription factor (FKHR), and cyclin D1, were also reduced after NFD treatment. Moreover, inactivation of nuclear factor-kappaB (NF kappaB), modulation of I kappa K beta and I kappaB alpha, up-regulation of Bad, and down-regulation of anti-apoptotic proteins including phospho-Bad, Bcl-X(L), myeloid cell leukemia-1(Mcl-1), and XIAP were found in NFD-treated cells. In addition, NFD treatment disrupted mitochondrial membrane potential (Delta Psi m), resulted in release of cytochrome c, and activation of both caspases-9 and caspase-3. Taken together, these results indicate that NFD induces apoptosis in Ca9-22 cells via inactivation of the EGF receptor-mediated survival pathway.

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.

Interaction of Naja naja atra cardiotoxin 3 with H-trisaccharide modulates its hemolytic activity and membrane-damaging activity

To address whether saccharide moieties of blood groups A, B and O antigens modulate hemolytic activity of Naja naja atra cardiotoxins (CTXs), the present study was carried out. Unlike other CTX isotoxins, hemolytic activity of CTX3 toward blood group O cholesterol-depleted red blood cells (RBCs) was notably lower than that of blood groups A and B cholesterol-depleted RBCs. Conversion of blood group B RBCs into blood group O RBCs by alpha-galactosidase treatment attenuated the susceptibility for hemolytic activity of CTX3, suggesting that H-antigen affected hemolytic potency of CTX3. Pre-incubation with H-trisaccharide reduced hemolytic activity and membrane-damaging activity of CTX3. Moreover, CTX3 showed a higher binding capability with H-trisaccharide than other CTXs did. CD spectra showed that the binding with H-trisaccharide induced changes in gross conformation of CTX3. Self-quenching studies revealed that oligomerization of CTX3 was affected in the presence of H-trisaccharide. Taken together, our data suggest that the binding of CTX3 with H-antigen alters its membrane-bound mode, thus reducing its hemolytic activity toward blood group O cholesterol-depleted RBCs.

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.

Suppression of ERK signaling evokes autocrine Fas-mediated death in arachidonic acid-treated human chronic myeloid leukemia K562 cells

Arachidonic acid (AA)-induced apoptotic death of K562 cells (human chronic myeloid leukemic cells) was characteristic of reactive oxygen species (ROS) generation and mitochondrial depolarization. N-Acetylcysteine pretreatment rescued viability of AA-treated cells and abolished mitochondrial depolarization. In contrast to no significant changes in phospho-JNK and phospho-ERK levels, AA evoked notable activation of p38 MAPK. Unlike that of JNK and p38 MAPK, ERK suppression further reduced the viability of AA-treated cells. Increases in Fas/FasL protein expression, caspase-8 activation, the production of tBid and the loss of mitochondrial membrane potential were noted with K562 cells that were treated with a combination of U0126 and AA. Down-regulation of FADD attenuated U0126-evoked degradation of procaspase-8 and Bid. Abolition of p38 MAPK activation abrogated U0126-elicited Fas/FasL up-regulation in AA-treated cells. U0126 pretreatment suppressed c-Fos phosphorylation but increased p38 MAPK-mediated c-Jun phosphorylation. Knock-down of c-Fos and c-Jun protein expression by siRNA suggested that c-Fos counteracted the effect of c-Jun on Fas/FasL up-regulation. Taken together, our data indicate that AA induces the ROS/mitochondria-dependent death pathway and blocks the ERK pathway which enhances the cytotoxicity of AA through additionally evoking an autocrine Fas-mediated apoptotic mechanism in K562 cells.

Naphtho[1,2-b]furan-4,5-dione inactivates EGFR and PI3K/Akt signaling pathways in human lung adenocarcinoma A549 cells

AIMS

Naphtho[1,2-b]furan-4,5-dione (NFD), prepared from 2-hydroxy-1,4-naphthoquinone and chloroacetaldehyde in an efficient one-pot reaction, exhibits an anti-carcinogenic effect. This study was performed to elucidate whether EGFR and PI3K signaling pathways are involved in NFD-induced apoptosis of human lung adenocarcinoma A549 cells.

MAIN METHODS

The effect of NFD on cell viability and apoptosis was measured by the MTT assay and flow cytometry. The phosphorylation levels of EGFR and its regulatory molecules by NFD treatment were studied by immunoblots.

KEY FINDINGS

Immunoblot showed that NFD inhibited EGFR phosphorylation and the activation of PI3K/Akt, downstream molecules of EGFR pathway, in A549 cells. The levels of downstream targets of Akt, including phospho-glycogen synthase kinase-3beta (p-GSK-3beta), GSK-3beta, forkhead transcription factor (FKHR), and cyclin D1, were also reduced after NFD treatment. Moreover, inactivation of nuclear factor-kappaB (NFkappaB), modulation of IkappaKalpha/beta and IkappaBalpha, up-regulation of Bad and Bax, and down-regulation of anti-apoptotic proteins including phospho-Bad, Bcl-2, survivin, and XIAP were also found in NFD-treated cells. In addition, NFD treatment disrupted mitochondrial membrane potential (DeltaPsim) and resulted in release of mitochondrial cytochrome c and activation of both caspases-9 and caspase-3.

SIGNIFICANCE

These findings indicate that EGFR and PI3K/Akt signaling pathways play important roles in NFD-induced apoptosis of A549 cells.

Notexin upregulates Fas and FasL protein expression of human neuroblastoma SK-N-SH cells through p38 MAPK/ATF-2 and JNK/c-Jun pathways

Notechis scutatus scutatus notexin induced an increase in Fas and FasL protein expression of human neuroblastoma SK-N-SH cells in a dose- and time-dependent manner. Moreover, notexin treatment upregulated transcription of Fas/FasL mRNA. Downregulation of FADD blocked notexin-induced procaspase-8 degradation and cleavage of Bid and rescued viability of notexin-treated cells. Upon exposure to notexin, activation of JNK and p38 MAPK was observed in SK-N-SH cells. Notexin-induced upregulation of Fas and FasL was suppressed by SB202190 (p38 MAPK inhibitor) and S600125 (JNK inhibitor). Downregulation of p38alpha MAPK and JNK1 by siRNA proved that upregulation of Fas/FasL was related to p38alpha MAPK and JNK1 activation. Notexin treatment evoked p38alpha MAPK-mediated ATF-2 phosphorylation and JNK1-mediated c-Jun phosphorylation. Knockdown of c-Jun and ATF-2 by siRNA or overexpression of dominant-negative c-Jun and ATF-2 revealed that both c-Jun and ATF-2 were crucial for Fas/FasL upregulation. Taken together, our data indicate that notexin-induced upregulation of Fas and FasL is triggered by p38 MAPK/ATF-2 and JNK/c-Jun signaling pathways in SK-N-SH cells.

Calcium-stimulated mitogen-activated protein kinase activation elicits Bcl-xL downregulation and Bak upregulation in notexin-treated human neuroblastoma SK-N-SH cells

Notechis scutatus scutatus notexin induced apoptotic death of SK-N-SH cells accompanied with downregulation of Bcl-xL, upregulation of Bak, mitochondrial depolarization, and ROS generation. Upon exposure to notexin, Ca(2+)-mediated JNK and p38 MAPK activation were observed in SK-N-SH cells. Production of ROS was a downstream event followed by Ca(2+)-mediated mitochondrial alteration. Notexin-induced cell death, mitochondrial depolarization, and ROS generation were suppressed by SB202190 (p38 MAPK inhibitor) and SP600125 (JNK inhibitor). Moreover, phospho-p38 MAPK and phospho-JNK were proved to be involved in Bcl-xL degradation, and overexpression of Bcl-xL attenuated the cytotoxic effect of notexin. Bak upregulation was elicited by p38 MAPK-mediated ATF-2 activation and JNK-mediated c-Jun activation. Suppression of Bak upregulation by ATF-2 siRNA or c-Jun siRNA attenuated notexin-evoked mitochondrial depolarization and rescued viability of notexin-treated cells. Taken together, our data indicate that notexin-induced apoptotic death of SK-N-SH cells is mediated through mitochondrial alteration triggering by Ca(2+)-evoked p38 MAPK/ATF-2 and JNK/c-Jun signaling pathways.

Functional role of EF-hands 3 and 4 in membrane-binding of KChIP1

The aim of the present study is to explore whether membrane targeting of K+ channel-interacting protein 1 (KChIP1) is associated with its EF-hand motifs and varies with specific phospholipids. Truncated KChIP1, in which the EFhands 3 and 4 were deleted, retained the alpha-helix structure, indicating that the N-terminal half of KChIP1 could fold appropriately. Compared with wild-type KChIP1, truncated KChIP1 exhibited lower lipid-binding capability. Compared with wild-type KChIP1, increasing membrane permeability by the use of digitonin caused a marked loss of truncated KChIP1, suggesting that intact EF-hands 3 and 4 were crucial for the anchorage of KChIP1 on membrane. KChIP1 showed a higher binding capability with phosphatidylserine (PS) than truncated KChIP1. Unlike that of truncated KChIP1, the binding of wild-type KChIP1 with membrane was enhanced by increasing the PS content. Moreover, the binding of KChIP1 with phospholipid vesicles induced a change in the structure of KChIP1 in the presence of PS. Taken together, our data suggest that EF-hands 3 and 4 of KChIP1 are functionally involved in a specific association with PS on the membrane.

Inactivation of epidermal growth factor receptor and downstream pathways in oral squamous cell carcinoma Ca9-22 cells by cardiotoxin III from Naja naja atra

Cardiotoxin III (1), a basic polypeptide with 60 amino acid residues isolated from Naja naja atra venom, has potential therapeutic activity in cancer. Treatment with 1 reduced phosphorylation of EGFR and Akt, as well as ERK in Ca9-22 cells. Moreover, 1-treatment inhibited constitutive activation of STAT3 and STAT5 in a time-dependent manner. Up-regulation of Bax and down-regulation of anti-apoptotic proteins including Bcl-2, Bcl-X(L), and myeloid cell leukemia-1(Mcl-1) were also found in cells treated with 1. In addition, 1-treatment disrupted mitochondrial membrane potential (DeltaPsim) and resulted in release of mitochondrial cytochrome c and activation of both caspases-9 and -3. AG1478, a specific pharmacological inhibitor of EGFR activation, mimics the cytotoxic effects of 1. Taken together, these results showed that 1 causes significant induction of apoptosis in Ca9-22 cells via abolition of the EGFR-mediated survival pathway of these cells. Thus, cardiotoxin III appears to be a potential therapeutic agent for killing oral squamous carcinoma Ca9-22 cells.