Signaling involved in PTTH-stimulated 4E-BP phosphorylation in prothoracic gland cells of Bombyx mori.

Our previous studies showed that adenosine 5'-monophosphate-activated protein kinase (AMPK)/the target of rapamycin (TOR) signaling is involved in prothoracicotropic hormone (PTTH)-stimulated ecdysteroidogenesis in Bombyx mori prothoracic glands (PGs). In the present study, we further investigated the signaling involved in PTTH-stimulated phosphorylation of 4E-BP. We found that 4E-BP phosphorylation stimulated by PTTH was partially reduced in Ca2+-free medium, indicating the involvement of Ca2+. In addition, we found that a potent and specific inhibitor of phospholipase C (PLC), U73122, greatly inhibited 4E-BP phosphorylation. However, PTTH-stimulated 4E-BP phosphorylation was not attenuated by a protein kinase C (PKC) inhibitor (chelerythrine C). These results indicate that PLC, but not PKC, is involved in PTTH-stimulated 4E-BP phosphorylation. When PGs were treated with agents that directly elevate the intracellular Ca2+ concentration (either A23187 or thapsigargin), a great increase in 4E-BP phosphorylation was observed. A23187-stimulated phosphorylation of 4E-BP was blocked by a chemical activator of AMPK (5-aminoimidazole-4-carboxamide-1-ß-d-ribofuranoside, AICAR) and a phosphoinositide 3-kinase (PI3K) inhibitor (LY294002), but not by U0126, indicating involvement of AMPK and PI3K. Determination of AMPK phosphorylation showed that treatment with either A23187 or thapsigargin inhibited AMPK phosphorylation. Moreover, PTTH appeared to inhibit AMPK phosphorylation in a Ca2+-dependent manner. Altogether, these results indicate interconnections among Ca2+ signaling, AMPK, and 4E-BP phosphorylation in PTTH-activated PGs of B. mori.

Stimulation of orphan nuclear receptor HR38 gene expression by PTTH in prothoracic glands of the silkworm, Bombyx mori.

A complex signaling network appears to be involved in prothoracicotropic hormone (PTTH)-stimulated ecdysteroidogenesis in insect prothoracic glands (PGs). Less is known about the genomic action of PTTH signaling. In the present study, we investigated the effect of PTTH on the expression of Bombyx mori HR38, an immediate early gene (IEG) identified in insect systems. Our results showed that treatment of B. mori PGs with PTTH in vitro resulted in a rapid increase in HR38 expression. Injection of PTTH into day-5 last instar larvae also greatly increased HR38 expression, verifying the in vitro effect. Cycloheximide did not affect induction of HR38 expression, suggesting that protein synthesis is not required for PTTH's effect. A mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor (U0126), and a phosphoinositide 3-kinase (PI3K) inhibitor (LY294002), partially inhibited PTTH-stimulated HR38 expression, implying the involvement of both the ERK and PI3K signaling pathways. When PGs were treated with agents that directly elevate the intracellular Ca(2+) concentration (either A23187 or thapsigargin), an increase in HR38 expression was also detected, indicating that Ca(2+) is involved in PTTH-stimulated HR38 gene expression. A Western blot analysis showed that PTTH treatment increased the HR38 protein level, and protein levels showed a dramatic increase during the later stages of the last larval instar. Expression of HR38 transcription in response to PTTH appeared to undergo development-specific changes. Treatment with ecdysone in vitro did not affect HR38 expression. However, 20-hydroxyecdysone treatment decreased HR38 expression. Taken together, these results demonstrate that HR38 is a PTTH-stimulated IEG that is, at least in part, induced through Ca(2+)/ERK and PI3K signaling. The present study proposes a potential cross talk mechanism between PTTH and ecdysone signaling to regulate insect development and lays a foundation for a better understanding of the mechanisms of PTTH's actions.

The cell cycle regulator 14-3-3σ opposes and reverses cancer metabolic reprogramming.

Extensive reprogramming of cellular energy metabolism is a hallmark of cancer. Despite its importance, the molecular mechanism controlling this tumour metabolic shift remains not fully understood. Here we show that 14-3-3σ regulates cancer metabolic reprogramming and protects cells from tumorigenic transformation. 14-3-3σ opposes tumour-promoting metabolic programmes by enhancing c-Myc poly-ubiquitination and subsequent degradation. 14-3-3σ demonstrates the suppressive impact on cancer glycolysis, glutaminolysis, mitochondrial biogenesis and other major metabolic processes of tumours. Importantly, 14-3-3σ expression levels predict overall and recurrence-free survival rates, tumour glucose uptake and metabolic gene expression in breast cancer patients. Thus, these results highlight that 14-3-3σ is an important regulator of tumour metabolism, and loss of 14-3-3σ expression is critical for cancer metabolic reprogramming. We anticipate that pharmacologically elevating the function of 14-3-3σ in tumours could be a promising direction for targeted anticancer metabolism therapy development in future.

CSN6 drives carcinogenesis by positively regulating Myc stability.

Cullin-RING ubiquitin ligases (CRLs) are critical in ubiquitinating Myc, while COP9 signalosome (CSN) controls neddylation of Cullin in CRL. The mechanistic link between Cullin neddylation and Myc ubiquitination/degradation is unclear. Here we show that Myc is a target of the CSN subunit 6 (CSN6)-Cullin signalling axis and that CSN6 is a positive regulator of Myc. CSN6 enhanced neddylation of Cullin-1 and facilitated autoubiquitination/degradation of Fbxw7, a component of CRL involved in Myc ubiquitination, thereby stabilizing Myc. Csn6 haplo-insufficiency decreased Cullin-1 neddylation but increased Fbxw7 stability to compromise Myc stability and activity in an Eµ-Myc mouse model, resulting in decelerated lymphomagenesis. We found that CSN6 overexpression, which leads to aberrant expression of Myc target genes, is frequent in human cancers. Together, these results define a mechanism for the regulation of Myc stability through the CSN-Cullin-Fbxw7 axis and provide insights into the correlation of CSN6 overexpression with Myc stabilization/activation during tumorigenesis.

Signaling of reactive oxygen species in PTTH-stimulated ecdysteroidogenesis in prothoracic glands of the silkworm, Bombyx mori.

Our previous study demonstrated that mitochondria-derived reactive oxygen species (ROS) generation is involved in prothoracicotropic hormone (PTTH)-stimulated ecdysteroidogenesis in Bombyx mori prothoracic glands (PGs). In the present study, we further investigated the mechanism of ROS production and the signaling pathway mediated by ROS. PTTH-stimulated ROS production was markedly attenuated in a Ca(2+)-free medium. The phospholipase C (PLC) inhibitor, U73122, greatly inhibited PTTH-stimulated ROS production, indicating the involvement of Ca(2+) and PLC. When the PGs were treated with agents that directly elevate the intracellular Ca(2+) concentration (either A23187, or the protein kinase C (PKC) activator, phorbol 12-myristate acetate (PMA)), a great increase in ROS production was observed. We further investigated the action mechanism of PTTH-stimulated ROS signaling. Results showed that in the presence of either an antioxidant (N-acetylcysteine, NAC), or the mitochondrial oxidative phosphorylation inhibitors (rotenone, antimycin A, the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP), and diphenyleneiodonium (DPI)), PTTH-regulated phosphorylation of ERK, 4E-BP, and AMPK was blocked. Treatment with 1mM of H2O2 alone activated the phosphorylation of ERK and 4E-BP, and inhibited AMPK phosphorylation. From these results, we conclude that PTTH-stimulated ROS signaling is Ca(2+)- and PLC-dependent and that ROS signaling appears to lie upstream of the phosphorylation of ERK, 4E-BP, and AMPK.

Supercritical carbon dioxide extraction of aromatic turmerone from Curcuma longa Linn. induces apoptosis through reactive oxygen species-triggered intrinsic and extrinsic pathways in human hepatocellular carcinoma HepG2 cells.

The mechanisms underlying the antiproliferative and antitumor activities of aromatic turmerone (ar-turmerone), a volatile turmeric oil isolated from Curcuma longa Linn., have been largely unknown. In this study, 86% pure ar-turmerone was extracted by supercritical carbon dioxide and liquid-solid chromatography and its potential effects and molecular mechanisms on cell proliferation studied in human hepatocellular carcinoma cell lines. Ar-turmerone exhibited significant antiproliferative activity, with 50% inhibitory concentrations of 64.8 ± 7.1, 102.5 ± 11.5, and 122.2 ± 7.6 µg/mL against HepG2, Huh-7, and Hep3B cells, respectively. Ar-turmerone-induced apoptosis, confirmed by increased annexin V binding and DNA fragmentation, was accompanied by reactive oxygen species (ROS) production, mitochondrial membrane potential dissipation, increased Bax and p53 up-regulated modulator of apoptosis (PUMA) levels, Bax mitochondrial translocation, cytochrome c release, Fas and death receptor 4 (DR4) augmentation, and caspase-3, -8, and -9 activation. Exposure to caspase inhibitors, Fas-antagonistic antibody, DR4 antagonist, and furosemide (a blocker of Bax translocation) effectively abolished ar-turmerone-triggered apoptosis. Moreover, ar-turmerone stimulated c-Jun N-terminal kinase (JNK) and extracellular signal-related kinase (ERK) phosphorylation and activation; treatment with JNK and ERK inhibitors markedly reduced PUMA, Bax, Fas, and DR4 levels and reduced apoptosis but not ROS generation. Furthermore, antioxidants attenuated ar-turmerone-mediated ROS production; mitochondrial dysfunction; JNK and ERK activation; PUMA, Bax, Fas, and DR4 expression; and apoptosis. Taken together, these results suggest that ar-turmerone-induced apoptosis in HepG2 cells is through ROS-mediated activation of ERK and JNK kinases and triggers both intrinsic and extrinsic caspase activation, leading to apoptosis. On the basis of these observations, ar-turmerone deserves further investigation as a natural anticancer and cancer-preventive agent.

Antcin B and its ester derivative from Antrodia camphorata induce apoptosis in hepatocellular carcinoma cells involves enhancing oxidative stress coincident with activation of intrinsic and extrinsic apoptotic pathway.

The triterpenoids methylantcinate B (MAB) and antcin B (AB), isolated from the medicinal mushroom Antrodia camphorata , have been identified as strong cytotoxic agents against various type of cancer cells; however, the mechanisms of MAB- and AB-induced cytotoxicity have not been adequately explored. This study investigated the roles of caspase cascades, reactive oxygen species (ROS), DNA damage, mitochondrial disruption, and Bax and Bcl-2 proteins in MAB- and AB-induced apoptosis of hepatocellular carcinoma (HCC) HepG2 cells. Here, we showed that MAB and AB induced apoptosis in HepG2 cells, as characterized by increased DNA fragmentation, cleavage of PARP, sub-G1 population, chromatin condensation, loss of mitochondrial membrane potential, and release of cytochrome c. Increasing the levels of caspase-2, -3, -8, and -9 activities was involved in MAB- and AB-induced apoptosis, and they could be attenuated by inhibitors of specific caspases, indicating that MAB and AB triggered the caspase-dependent apoptotic pathway. Additionally, the enhanced apoptotic effect correlates with high expression of Fas, Fas ligand, as well as Bax and decreased protein levels of Bcl-(XL) and Bcl-2, suggesting that both the extrinsic and intrinsic apoptosis pathways were involved in the apoptotic processes. Incubation of HepG2 cells with antioxidant enzymes superoxide dismutase and catalase and antioxidants N-acetylcysteine and ascorbic acid attenuated the ROS generation and apoptosis induced by MAB and AB, which indicate that ROS plays a pivotal role in cell death. NADPH oxidase activation was observed in MAB- and AB-stimulated HepG2 cells; however, inhibition of such activation by diphenylamine significantly blocked MAB- and AB-induced ROS production and increased cell viability. Taken together, our results provide the first evidence that triterpenoids MAB and AB induced a NADPH oxidase-provoked oxidative stress and extrinsic and intrinsic apoptosis as a critical mechanism of cause cell death in HCC cells.

Methyl antcinate A from Antrodia camphorata induces apoptosis in human liver cancer cells through oxidant-mediated cofilin- and Bax-triggered mitochondrial pathway.

We investigated the effects of antcin A, antcin C, and methyl antcinate A (MAA) isolated from Antrodia camphorata on the proliferation of human liver cancer cell lines Huh7, HepG2, and Hep3B and the normal cell rat hepatocytes. The three compounds selectively inhibit the proliferation of tumor cells rather than normal cells, with IC(50) values ranging from 30.2 to 286.4 microM. The compound MAA was a more potent cytotoxic agent than antcins A and C with IC(50) values of 52.2, 78.0, and 30.2 microM against HepG2, Hep3B, and Huh7 cells, respectively. To elucidate the molecular mechanism, treatment of Huh7 cells with 100 microM MAA induced an apoptotic cell death, which was characterized by the appearance of sub-G1 population, DNA fragmentation, TUNEL positive cells, and caspase activation. MAA triggered the mitochondrial apoptotic pathway, as indicated by an increase in the protein expression of Bax, Bak, and PUMA, as well as a decrease in Bcl-(XL) and Bcl-2 and disruption of mitochondrial membrane potential and promotion of mitochondrial cytochrome c release, as well as activation of caspases-2, -3, and -9. We also found that pretreatment with inhibitors of caspases-2, -3, and -9 noticeably blocked MAA-triggered apoptosis. Furthermore, intracellular reactive oxygen species (ROS) generation and NADPH oxidase activation were observed in MAA-stimulated Huh7 cells. Mechanistic studies showed that MAA induces mitochondrial translocation of cofilin. When Huh7 cells were treated with cyclosporine A and bongkrekic acid, an inhibitor of the mitochondria permeability transition pore, the levels of cell death induced by MAA were significantly attenuated. Additionally, pretreatment of Huh7 cells with antioxidants ascorbic acid and N-acetyl cysteine markedly attenuated the MAA-induced apoptosis by upregulation of Bax, Bak, and PUMA, mitochondrial translocation of cofilin, activation of caspase-3, and cell death. Taken together, our results provide the first evidence of the activation of the ROS-dependent cofilin- and Bax-triggered mitochondrial pathway as a critical mechanism of MAA-induced cell death in liver cancer cells.

Gypenosides induce apoptosis in human hepatoma Huh-7 cells through a calcium/reactive oxygen species-dependent mitochondrial pathway.

We have previously reported that gypenosides induce apoptosis in human hepatocarcinoma Huh-7 cells through a mitochondria-dependent caspase-9 activation cascade. In order to further explore the critical events leading to apoptosis in gypenosides-treated cells, the following effects of gypenosides on components of the mitochondrial apoptotic pathway were examined: generation of reactive oxygen species (ROS), alteration of the mitochondrial membrane potential (MPT), and the subcellular distribution of Bcl-2 and Bax. We show that gypenosides-induced apoptosis was accompanied by the generation of intracellular ROS, disruption of MPT, and inactivation of ERK, as well as an increase in mitochondrial Bax and a decrease of mitochondrial Bcl-2 levels. Ectopic expression of Bcl-2 or treatment with furosemide attenuated gypenosides-triggered apoptosis. Treatment with ATA caused a drastic prevention of apoptosis and the gypenosides-mediated mitochondrial Bcl-2 decrease and Bax increase, but failed to inhibit ROS generation and MPT dysfunction. Incubation with antioxidants significantly inhibited gypenosides-mediated ROS generation, ERK inactivation, MPT and apoptosis. Moreover, an increase of the intracellular calcium ion (Ca(2+)) concentration rapidly occurred in gypenosides-treated Huh-7 cells. Buffering of the intracellular Ca(2+) increase with a Ca(2+) chelator BAMTA/AM blocked the gypenosides-elicited ERK inactivation, ROS generation, Bcl-2/Bax redistribution, mitochondrial dysfunction, and apoptosis. Based on these results, we propose that the rise in intracellular Ca(2+) concentration plays a pivotal role in the initiation of gypenosides-triggered apoptotic death.